Voltage regulator for a soldering iron using a triac. To help the home handyman: temperature controller diagram for a soldering iron

The author of this article, L. ELIZAROV, from the city of Makeevka, Donetsk region, offers something that can be repeated by radio amateurs device for maintaining optimal soldering iron tip temperature by measuring the resistance of its heater during periodic short-term disconnections from the network.

Various soldering iron tip temperature control devices have been repeatedly published on the pages of radio engineering magazines, using the soldering iron heater as a temperature sensor and maintaining it at a given level. Upon closer examination, it turns out that all these regulators are just stabilizers of the heater’s thermal power. They, of course, give a certain effect: the tip burns out less and the soldering iron does not overheat as much while it is lying on the stand. But this is still a long way from controlling the temperature of the tip.

Let us briefly consider the dynamics of thermal processes in a soldering iron. In Fig. 1 shows graphs of changes in the temperature of the heater and soldering iron tip from the moment the heater is turned off

The graphs show that in the first fractions of a second the temperature difference is so large and unstable that the temperature of the heater at this moment cannot be used to accurately determine the temperature of the tip, and this is exactly how all previously published regulators work, in which the heater is used as a temperature sensor. From Fig. 1 it can be seen that the curves of the dependence of the temperature of the tip and the heater on the time of its switching off only after two and even more so three or four seconds are sufficiently close in order to interpret the temperature of the heater as the temperature of the tip with sufficient accuracy. In addition, the temperature difference becomes not only small, but also almost constant. According to the author, it is the regulator that measures the temperature of the heater a certain time after it is turned off that is able to more accurately control the temperature of the tip.

It is interesting to compare the advantages of such a regulator with a soldering station that uses a temperature sensor built into the soldering iron tip. In a soldering station, a change in the temperature of the soldering iron tip immediately causes a reaction from the control device, and the increase in the temperature of the heater is proportional to the change in the temperature of the tip. The wave of temperature change reaches the soldering iron tip in 5...7 s. When the temperature of the tip of a conventional soldering iron changes, the wave of temperature change goes from the tip to the heater (with close thermodynamic parameters - 5...7 s). Its control unit will operate in 1...7 s (this depends on the set temperature threshold for switching on) and will raise the temperature of the heater. The reverse wave of the temperature change will reach the soldering iron tip in the same 5...7 s. It follows that the response time of a conventional soldering iron using a heater as a temperature sensor is 2...3 times longer than that of a soldering iron soldering station with a temperature sensor built into the tip.

Obviously, a soldering station has two main advantages over a soldering iron that uses a heater as a temperature sensor. The first (minor) is a digital temperature indicator. The second is a temperature sensor built into the tip. The digital indicator is at first simply interesting, but then regulation still follows the principle of “a little more, a little less.”

A soldering iron that uses a heater as a temperature sensor has the following advantages over a soldering station:
- the control unit does not clutter up the space on the table, since it can be built into a small-sized case in the form of a network adapter;
- lower cost;
- the control unit can be used with almost any household soldering iron;
- ease of repetition, feasible even for a beginning radio amateur.

Let's consider the design features of soldering irons of different designs and power. The table shows the resistance values ​​of the heaters of various soldering irons, where Pw is the power of the soldering iron, W; Rx - resistance of the cold soldering iron heater, Ohm; Rr - resistance of hot after warming up for three minutes, Ohm.

PW,W	R X ,Ohm	R G, Ohm	R Г -R X, Ohm
18	860	1800	940
25	700	1700	1000
30	1667	1767	100
40	1730	1770	40
80	547	565	18
100	604	624	20

The difference between these temperatures shows that the TCS of heaters can differ by 50 times. Soldering irons with a large TCS have ceramic heaters, although there are exceptions. Soldering irons with small TKS are of an outdated design with nichrome heaters. It is necessary to separately note that some soldering irons may have a built-in diode - a temperature sensor, and I came across one soldering iron that was quite interesting: in one polarity of the TKS connection it was positive, and in the other - negative. In this regard, the resistance of the soldering iron must first be measured in cold and hot states in order to connect it to the regulator in the correct polarity.

Soldering iron temperature stabilizer circuit

The regulator diagram is shown in Fig. 2. The duration of the heater's on state is fixed and is 4...6 s. The duration of the off state depends on the temperature of the heater, the design features of the soldering iron and is adjustable in the range of 0...30 s. There may be an assumption that the temperature of the soldering iron tip is constantly “swinging” up and down. Measurements have shown that the change in tip temperature under the influence of control pulses does not exceed one degree, and this is explained by the significant thermal inertia of the soldering iron design.

Let's consider the operation of the regulator. According to the well-known circuit, a power supply for the control unit is assembled on the rectifier bridge VD6, quenching capacitors C4, C5, zener diodes VD2, VD3 and smoothing capacitor C2. The node itself is assembled on two op-amps connected by comparators. The non-inverting input (pin 3) of op-amp DA1.2 is supplied with a reference voltage from the resistive divider R1R2. Its inverting input (pin 2) is supplied with voltage from a divider, the upper arm of which consists of a resistive circuit R3-R5, and the lower arm of a heater connected to the input of the op-amp through a diode VD5. At the moment the power is turned on, the resistance of the heater is reduced and the voltage at the inverting input of op-amp DA1.2 is less than the voltage at the non-inverting one. The output (pin 1) of DA1.2 will have the maximum positive voltage. The output of DA1.2 is loaded in a series circuit consisting of a limiting resistor R8, an LED HL1 and a emitting diode built into the optocoupler U1. The LED signals that the heater is turned on, and the emitting diode of the optocoupler opens the built-in photosimistor. The 220 V mains voltage rectified by the VD7 bridge is supplied to the heater. Diode VD5 will be closed with this voltage. The high voltage level from the output of DA1.2 through the capacitor SZ affects the inverting input (pin 6) of the op-amp DA1.1. At its output (pin 7) a low voltage level appears, which, through diode VD1 and resistor R6, will reduce the voltage at the inverting input of op-amp DA1.2 below the standard one. This will ensure that a high voltage level is maintained at the output of this op-amp. This state remains stable for the time specified by the differentiating circuit C3R7. As the capacitor SZ is charged, the voltage on the resistor R7 of the circuit drops, and when it becomes lower than the exemplary value, the low signal level at the output of the op-amp DA1.1 will change to a high one. A high signal level will close the diode VD1, and the voltage at the inverting input DA1.2 will become higher than the standard one, which will lead to a change in the high signal level at the output of the op-amp DA1.2 to a low one and turning off the HL1 LED and the U1 optocoupler. The closed phototriac will disconnect the VD7 bridge and the soldering iron heater from the network, and the open VD5 diode will connect it to the inverting input of the op-amp DA1.2. The extinguished LED HL1 signals that the heater is turned off. At output DA1.2, the low voltage level will remain until, as a result of cooling of the soldering iron heater, its resistance drops to the switching point DA1.2, specified, as mentioned above, by the reference voltage from the divider R1R2. By that time, the SZ capacitor will have time to discharge through the VD4 diode. Next, after switching DA1.2, optocoupler U1 will turn on again and the whole process will repeat. The cooling time of the soldering iron heater will be longer, the higher the temperature of the entire soldering iron and the lower the heat consumption for the soldering process. Capacitor C1 reduces pickup and high-frequency interference from the network.

The printed circuit board measures 42x37 mm and is made of single-sided foil-coated fiberglass. Its drawing and arrangement of elements are shown in Fig. 3.
PCB drawing in lay format - attached

LED HL1, diodes VD1, VD4 - any low-power ones. VD5 diode - any type for a voltage of at least 400 V. KS456A1 zener diodes are replaceable with KS456A or one 12 V zener diode with a maximum permissible current of more than 100 mA. The SZ oxide capacitor must be checked for leaks. When checking a capacitor with an ohmmeter, its resistance should be greater than 2 megohms. Capacitors C4, C5 are imported film capacitors for an alternating voltage of 250 V or domestic K73-17 for a voltage of 400 V. The LM358P microcircuit is replaceable with an LM393R. In this case, the right terminal of the resistor R8 according to the diagram must be connected to the positive power line of the control unit, and the anode of the LED HL1 - directly to output DA1.2 (pin 1). In this case, the VD1 diode does not need to be installed. The resistance of resistor R6 should be selected based on the existing heater. It should be less than the resistance of the heater in a cold state by about 10%. The resistance of the tuning resistor R5 is selected so that the temperature adjustment interval does not exceed 100 °C. To do this, calculate the difference in resistance of a cold and well-heated soldering iron and multiply it by 3.5. The resulting value will be the resistance of resistor R5 in ohms. Resistor type - any multi-turn.

The assembled unit needs to be adjusted. The circuit of resistors R3-R5 is temporarily replaced by two variables connected in series or adjusted resistances of 2.2 kOhm and 200...300 Ohm. Next, the block with the connected soldering iron is connected to the network. Having achieved the required tip temperature with the temporary resistor engines, the device is disconnected from the network. The resistors are soldered off and the total resistance of the inserted parts is measured. Half of the previously calculated resistance R5 is subtracted from the obtained value. This will be the total resistance of constant resistors R3, R4, which are selected from those available according to the value closest to the total value. A switch can be placed in the gap of this resistive circuit. When it is turned off, the soldering iron will switch to continuous heating. For those who need a soldering iron for several soldering modes, I suggest installing a switch and several resistive circuits for different modes. For example, for soft solder and for normal solder. If the circuit breaks, the mode is forced. The power of the soldering iron used is limited by the maximum current of the rectifier bridge KTs407A (0.5 A) and optocoupler MOS3063 (1 A). Therefore, for soldering irons with a power of more than 100 W, it is necessary to install a more powerful rectifier bridge, and replace the optron with an optoelectronic relay of the required power.

A comparison of the operation of different soldering irons together with the described device showed that soldering irons with a ceramic heater with a large TCR are most suitable. The appearance of one of the variants of the assembled block with the cover removed is shown in Fig. 4.

Many people's work involves using a soldering iron. For some it's just a hobby. Soldering irons are different. They can be simple but reliable, they can be modern soldering stations, including infrared ones. To obtain high-quality soldering, you need to have a soldering iron of the required power and heat it to a certain temperature.

Figure 1. Temperature controller circuit assembled on the KU 101B thyristor.

To help in this matter, various temperature regulators for the soldering iron are designed. They are sold in stores, but skilled hands can independently assemble such a device, taking into account their requirements.

Advantages of temperature controllers

Most home craftsmen use a 40 W soldering iron from a young age. Previously, it was difficult to buy something with other parameters. The soldering iron itself is convenient; you can use it to solder many objects. But it is inconvenient to use it when installing radio-electronic circuits. This is where the help of a temperature controller for a soldering iron comes in handy:

Figure 2. Diagram of a simple temperature controller.

• the soldering iron tip warms up to the optimal temperature;
• the service life of the tip is extended;
• radio components will never overheat;
• there will be no delamination of current-carrying elements on the printed circuit board;
• If there is a forced break in work, the soldering iron does not need to be turned off from the network.

An excessively heated soldering iron does not hold solder on the tip; it drips from an overheated soldering iron, making the soldering area very fragile. The sting is covered with a layer of scale, which can only be cleaned off with sandpaper and files. As a result, craters appear, which also need to be removed, reducing the length of the tip. If you use a temperature regulator, this will not happen; the tip will always be ready for use. During a break in work, it is enough to reduce its heating without unplugging it from the network. After the break, the hot tool will quickly reach the desired temperature.

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Simple temperature controller circuits

As a regulator, you can use a LATR (laboratory transformer), a dimmer for a table lamp, a KEF-8 power supply, or a modern soldering station.

Figure 3. Switch diagram for the regulator.

Modern soldering stations are able to regulate the temperature of the soldering iron tip in different modes - manually, fully automatically. But for a home craftsman, their cost is quite significant. From practice it is clear that automatic adjustment is practically not needed, since the voltage in the network is usually stable, and the temperature in the room where soldering is carried out also does not change. Therefore, for assembly a simple temperature controller circuit assembled on a KU 101B thyristor can be used (Fig. 1). This regulator is successfully used to work with soldering irons and lamps with power up to 60 W.

This regulator is very simple, but allows you to change the voltage within 150-210 V. The duration of the thyristor in the open state depends on the position of the variable resistor R3. This resistor regulates the voltage at the output of the device. The adjustment limits are set by resistors R1 and R4. By selecting R1, the minimum voltage is set, R4 - the maximum. The D226B diode can be replaced with any one with a reverse voltage of more than 300 V. The thyristor is suitable for KU101G, KU101E. For a soldering iron with a power of over 30 W, you need to take a D245A diode and a KU201D-KU201L thyristor. The board after assembly may look something like the one shown in Fig. 2.

To indicate the operation of the device, the regulator can be equipped with an LED, which will glow when there is voltage at its input. A separate switch will not be superfluous (Fig. 3).

Figure 4. Diagram of a temperature controller with a triac.

The following regulator circuit has proven itself to be good (Fig. 4). The product turns out to be very reliable and simple. Minimum details required. The main one is the KU208G triac. Of the LEDs, it is enough to leave HL1, which will signal the presence of voltage at the input and the operation of the regulator. The housing for the assembled circuit can be a suitable sized box. For this purpose, you can use the housing of an electrical outlet or switch with an installed power cord and plug. The axis of the variable resistor must be brought out and a plastic handle placed on it. You can put divisions nearby. Such a simple device is able to regulate the heating of the soldering iron within the range of approximately 50-100%. In this case, the load power is recommended within 50 W. In practice, the circuit worked with a load of 100 W without consequences for an hour.

To solder radio circuits and other parts, you need different tools. The main one is the soldering iron. For more beautiful and high-quality soldering, it is recommended to equip it with a temperature regulator. Instead, you can use various devices that are sold in stores.

You can easily assemble a device from several parts with your own hands.

It will cost very little, but it is of greater interest.

In order for soldering to be beautiful and of high quality, it is necessary to correctly select the power of the soldering iron and ensure the temperature of the tip. This all depends on the brand of solder. For your choice, I provide several circuits of thyristor regulators for regulating the temperature of a soldering iron, which can be made at home. They are simple and can easily replace industrial analogues; moreover, the price and complexity will differ.

Carefully! Touching the elements of the thyristor circuit can lead to life-threatening injury!

To regulate the temperature of the soldering iron tip, soldering stations are used, which maintain the set temperature in automatic and manual modes. The availability of a soldering station is limited by the size of your wallet. I solved this problem by making a manual temperature controller that has smooth adjustment. The circuit can be easily modified to automatically maintain a given temperature mode. But I concluded that manual adjustment is sufficient, since the room temperature and network current are stable.

Classic thyristor regulator circuit

The classic regulator circuit was bad in that it had radiating interference emitted into the air and the network. For radio amateurs, this interference interferes with their work. If you modify the circuit to include a filter, the size of the structure will increase significantly. But this circuit can also be used in other cases, for example, if it is necessary to adjust the brightness of incandescent lamps or heating devices whose power is 20-60 W. Therefore I present this diagram.

To understand how this works, consider the operating principle of a thyristor. A thyristor is a semiconductor device of a closed or open type. To open it, a voltage of 2-5 V is applied to the control electrode. It depends on the selected thyristor, relative to the cathode (letter k in the diagram). The thyristor opened, and a voltage equal to zero formed between the cathode and anode. It cannot be closed through the electrode. It will remain open until the cathode (k) and anode (a) voltage values ​​are close to zero. This is the principle. The circuit works as follows: through the load (soldering iron winding or incandescent lamp), voltage is supplied to the rectifier diode bridge, made of diodes VD1-VD4. It serves to convert alternating current into direct current, which varies according to a sinusoidal law (1 diagram). In the extreme left position, the resistance of the middle terminal of the resistor is 0. As the voltage increases, capacitor C1 is charged. When the voltage of C1 is 2-5 V, current will flow to VS1 through R2. In this case, the thyristor will open, the diode bridge will short-circuit, and the maximum current will pass through the load (diagram above). If you turn the knob of resistor R1, the resistance will increase, and capacitor C1 will take longer to charge. Therefore, the opening of the resistor will not occur immediately. The more powerful R1, the longer it will take to charge C1. By rotating the knob to the right or left, you can adjust the heating temperature of the soldering iron tip.

The photo above shows a regulator circuit assembled on a KU202N thyristor. To control this thyristor (the data sheet indicates a current of 100 mA, in reality it is 20 mA), it is necessary to reduce the values ​​of resistors R1, R2, R3, eliminate the capacitor, and increase the capacitance. Capacitance C1 must be increased to 20 μF.

The simplest thyristor regulator circuit

Here is another version of the diagram, only simplified, with a minimum of details. 4 diodes are replaced by one VD1. The difference between this scheme is that the adjustment occurs when the network period is positive. The negative period, passing through the VD1 diode, remains unchanged, the power can be adjusted from 50% to 100%. If we exclude VD1 from the circuit, the power can be adjusted in the range from 0% to 50%.

If you use a KN102A dinistor in the gap between R1 and R2, you will have to replace C1 with a capacitor with a capacity of 0.1 μF. The following thyristor ratings are suitable for this circuit: KU201L (K), KU202K (N, M, L), KU103V, with a voltage of more than 300 V. Any diodes whose reverse voltage is not less than 300 V.

The above mentioned circuits are successfully suitable for adjusting incandescent lamps in lamps. It will not be possible to regulate LED and energy-saving lamps, as they have electronic control circuits. This will cause the lamp to flicker or run at full power, which will eventually damage it.

If you want to use regulators to operate on a 24.36 V network, you will have to reduce the resistor values ​​and replace the thyristor with an appropriate one. If the power of the soldering iron is 40 W, the mains voltage is 36 V, it will consume 1.1 A.

Thyristor circuit of the regulator does not emit interference

This circuit differs from the previous one in the complete absence of studied radio interference, since the processes take place at the moment when the mains voltage is equal to 0. When starting to create the regulator, I proceeded from the following considerations: the components should have a low price, high reliability, small dimensions, the circuit itself should be simple, easily repeatable, efficiency should be close to 100%, and there should be no interference. The circuit must be upgradeable.

The operating principle of the circuit is as follows. VD1-VD4 rectify the mains voltage. The resulting DC voltage varies in amplitude equal to half a sinusoid with a frequency of 100 Hz (1 diagram). The current passing through R1 to VD6 - a zener diode, 9V (diagram 2) has a different shape. Through VD5, pulses charge C1, creating 9 V voltage for microcircuits DD1, DD2. R2 is used for protection. It serves to limit the voltage supplied to VD5, VD6 to 22 V and generates a clock pulse for the operation of the circuit. R1 transmits the signal to the 5, 6 pins of element 2 or a non-logical digital microcircuit DD1.1, which in turn inverts the signal and converts it into a short rectangular pulse (diagram 3). The pulse comes from the 4th pin of DD1 and comes to pin D No. 8 of the DD2.1 trigger, which operates in RS mode. The operating principle of DD2.1 is the same as DD1.1 (4 diagram). Having examined diagrams No. 2 and 4, we can conclude that there is practically no difference. It turns out that from R1 you can send a signal to pin No. 5 of DD2.1. But this is not true, R1 has a lot of interference. You will have to install a filter, which is not advisable. Without double circuit formation there will be no stable operation.

The controller control circuit is based on a DD2.2 trigger; it works according to the following principle. From pin No. 13 of the DD2.1 trigger, pulses are sent to pin 3 of DD2.2, the level of which is rewritten at pin No. 1 of DD2.2, which at this stage are located at the D input of the microcircuit (pin 5). The opposite signal level is on pin 2. I propose to consider the operating principle of DD2.2. Let's assume that at pin 2 there is a logical one. C2 is charged to the required voltage through R4, R5. When the first pulse appears with a positive drop on pin 2, 0 is formed, C2 is discharged through VD7. The subsequent drop on pin 3 will set a logical one on pin 2, C2 will begin to accumulate capacitance through R4, R5. Charging time depends on R5. The larger it is, the longer it will take to charge C2. Until capacitor C2 accumulates 1/2 capacitance, pin 5 will be 0. The pulse drop at input 3 will not affect the change in the logic level at pin 2. When the capacitor is fully charged, the process will repeat. The number of pulses specified by resistor R5 will be sent to DD2.2. The pulse drop will occur only at those moments when the mains voltage passes through 0. That is why there is no interference on this regulator. Pulses are sent from pin 1 of DD2.2 to DD1.2. DD1.2 eliminates the influence of VS1 (thyristor) on DD2.2. R6 is set to limit the control current of VS1. Voltage is supplied to the soldering iron by opening the thyristor. This occurs due to the fact that the thyristor receives a positive potential from the control electrode VS1. This regulator allows you to adjust the power in the range of 50-99%. Although resistor R5 is variable, due to the included DD2.2, the soldering iron is adjusted in a stepwise manner. When R5 = 0, 50% power is supplied (diagram 5), if turned to a certain angle, it will be 66% (diagram 6), then 75% (diagram 7). The closer to the calculated power of the soldering iron, the smoother the operation of the regulator. Let's say you have a 40 W soldering iron, its power can be adjusted in the region of 20-40 W.

Temperature controller design and details

The regulator parts are located on a fiberglass printed circuit board. The board is placed in a plastic case from a former adapter with an electrical plug. A plastic handle is placed on the axis of resistor R5. On the regulator body there are marks with numbers that allow you to understand which temperature mode is selected.

The soldering iron cord is soldered to the board. The connection of the soldering iron to the regulator can be made detachable to be able to connect other objects. The circuit consumes a current not exceeding 2mA. This is even less than the consumption of the LED in the switch illumination. Special measures to ensure the operating mode of the device are not required.

At a voltage of 300 V and a current of 0.5 A, DD1, DD2 and 176 or 561 series microcircuits are used; any diodes VD1-VD4. VD5, VD7 - pulse, any; VD6 is a low-power zener diode with a voltage of 9 V. Any capacitors, a resistor too. The power of R1 should be 0.5 W. No additional adjustment of the controller is required. If the parts are in good condition and no errors occurred during connection, it will work immediately.

The scheme was developed a long time ago, when there were no laser printers and computers. For this reason, the printed circuit board was manufactured using the old-fashioned method, using chart paper with a grid pitch of 2.5 mm. Next, the drawing was glued with “Moment” onto the paper more tightly, and the paper itself onto foil fiberglass. Why the holes were drilled, the traces of conductors and contact pads were drawn manually.

I still have a drawing of the regulator. Shown in the photo. Initially, a diode bridge with a rating of KTs407 (VD1-VD4) was used. They were torn a couple of times and had to be replaced with 4 KD209 type diodes.

How to reduce the level of interference from thyristor power regulators

To reduce the interference emitted by the thyristor regulator, ferrite filters are used. They are a ferrite ring with a winding. These filters are found in switching power supplies for TVs, computers and other products. Any thyristor regulator can be equipped with a filter that will effectively suppress interference. To do this, you need to pass a network wire through the ferrite ring.

The ferrite filter should be installed near sources that emit interference, directly at the location where the thyristor is installed. The filter can be located both outside the housing and inside. The greater the number of turns, the better the filter will suppress interference, but it is enough to thread the wire going to the outlet through the ring.

The ring can be removed from the interface wires of computer peripherals, printers, monitors, scanners. If you look at the wire that connects the monitor or printer to the system unit, you will notice a cylindrical thickening on it. It is in this place that a ferrite filter is located, which serves to protect against high-frequency interference.

We take a knife, cut the insulation and remove the ferrite ring. Surely your friends or you have an old interface cable for a CRT monitor or inkjet printer lying around.

In order to obtain high-quality and beautiful soldering, it is necessary to correctly select the power of the soldering iron and ensure a certain temperature of its tip, depending on the brand of solder used. I offer several circuits of homemade thyristor temperature controllers for soldering iron heating, which will successfully replace many industrial ones that are incomparable in price and complexity.

Attention, the following thyristor circuits of temperature controllers are not galvanically isolated from the electrical network and touching the current-carrying elements of the circuit is dangerous to life!

To adjust the temperature of the soldering iron tip, soldering stations are used, in which the optimal temperature of the soldering iron tip is maintained in manual or automatic mode. The availability of a soldering station for a home craftsman is limited by its high price. For myself, I solved the issue of temperature regulation by developing and manufacturing a regulator with manual, stepless temperature control. The circuit can be modified to automatically maintain the temperature, but I don’t see the point in this, and practice has shown that manual adjustment is quite sufficient, since the voltage in the network is stable and the temperature in the room is also stable.

Classic thyristor regulator circuit

The classic thyristor circuit of the soldering iron power regulator did not meet one of my main requirements, the absence of radiating interference into the power supply network and the airwaves. But for a radio amateur, such interference makes it impossible to fully engage in what he loves. If the circuit is supplemented with a filter, the design will turn out to be bulky. But for many use cases, such a thyristor regulator circuit can be successfully used, for example, to adjust the brightness of incandescent lamps and heating devices with a power of 20-60 W. That's why I decided to present this diagram.

In order to understand how the circuit works, I will dwell in more detail on the principle of operation of the thyristor. A thyristor is a semiconductor device that is either open or closed. to open it, you need to apply a positive voltage of 2-5 V to the control electrode, depending on the type of thyristor, relative to the cathode (indicated by k in the diagram). After the thyristor has opened (the resistance between the anode and cathode becomes 0), it is not possible to close it through the control electrode. The thyristor will be open until the voltage between its anode and cathode (indicated a and k in the diagram) becomes close to zero. It's that simple.

The classical regulator circuit works as follows. AC mains voltage is supplied through the load (incandescent light bulb or soldering iron winding) to a rectifier bridge circuit made using diodes VD1-VD4. The diode bridge converts alternating voltage into direct voltage, varying according to a sinusoidal law (diagram 1). When the middle terminal of resistor R1 is in the extreme left position, its resistance is 0 and when the voltage in the network begins to increase, capacitor C1 begins to charge. When C1 is charged to a voltage of 2-5 V, current will flow through R2 to the control electrode VS1. The thyristor will open, short-circuit the diode bridge and the maximum current will flow through the load (top diagram).

When you turn the knob of the variable resistor R1, its resistance will increase, the charging current of capacitor C1 will decrease and it will take more time for the voltage on it to reach 2-5 V, so the thyristor will not open immediately, but after some time. The greater the value of R1, the longer the charging time of C1 will be, the thyristor will open later and the power received by the load will be proportionally less. Thus, by rotating the variable resistor knob, you control the heating temperature of the soldering iron or the brightness of the incandescent light bulb.

Above is a classic circuit of a thyristor regulator made on a KU202N thyristor. Since controlling this thyristor requires a larger current (according to the passport 100 mA, the real one is about 20 mA), the values ​​of resistors R1 and R2 are reduced, R3 is eliminated, and the size of the electrolytic capacitor is increased. When repeating the circuit, it may be necessary to increase the value of capacitor C1 to 20 μF.

The simplest thyristor regulator circuit

Here is another very simple circuit of a thyristor power regulator, a simplified version of the classic regulator. The number of parts is kept to a minimum. Instead of four diodes VD1-VD4, one VD1 is used. Its operating principle is the same as the classical circuit. The circuits differ only in that the adjustment in this temperature controller circuit occurs only over the positive period of the network, and the negative period passes through VD1 without changes, so the power can only be adjusted in the range from 50 to 100%. To adjust the heating temperature of the soldering iron tip, no more is required. If diode VD1 is excluded, the power adjustment range will be from 0 to 50%.

If you add a dinistor, for example KN102A, to the open circuit from R1 and R2, then the electrolytic capacitor C1 can be replaced with an ordinary one with a capacity of 0.1 mF. Thyristors for the above circuits are suitable, KU103V, KU201K (L), KU202K (L, M, N), designed for a forward voltage of more than 300 V. Diodes are also almost any, designed for a reverse voltage of at least 300 V.

The above circuits of thyristor power regulators can be successfully used to regulate the brightness of lamps in which incandescent light bulbs are installed. It will not be possible to adjust the brightness of lamps that have energy-saving or LED bulbs installed, since such bulbs have electronic circuits built in, and the regulator will simply disrupt their normal operation. The light bulbs will shine at full power or flicker and this may even lead to their premature failure.

The circuits can be used for adjustment with a supply voltage of 36 V or 24 V AC. You only need to reduce the resistor values ​​by an order of magnitude and use a thyristor that matches the load. So a soldering iron with a power of 40 W at a voltage of 36 V will consume a current of 1.1 A.

Thyristor circuit of the regulator does not emit interference

The main difference between the circuit of the presented soldering iron power regulator and those presented above is the complete absence of radio interference into the electrical network, since all transient processes occur at a time when the voltage in the supply network is zero.

When starting to develop a temperature controller for a soldering iron, I proceeded from the following considerations. The circuit must be simple, easily repeatable, components must be cheap and available, high reliability, minimal dimensions, efficiency close to 100%, no radiated interference, and the possibility of upgrading.

The temperature controller circuit works as follows. The AC voltage from the supply network is rectified by the diode bridge VD1-VD4. From a sinusoidal signal, a constant voltage is obtained, varying in amplitude as half a sinusoid with a frequency of 100 Hz (diagram 1). Next, the current passes through the limiting resistor R1 to the zener diode VD6, where the voltage is limited in amplitude to 9 V, and has a different shape (diagram 2). The resulting pulses charge the electrolytic capacitor C1 through diode VD5, creating a supply voltage of about 9 V for microcircuits DD1 and DD2. R2 performs a protective function, limiting the maximum possible voltage on VD5 and VD6 to 22 V, and ensures the formation of a clock pulse for the operation of the circuit. From R1, the generated signal is supplied to the 5th and 6th pins of the 2OR-NOT element of the logical digital microcircuit DD1.1, which inverts the incoming signal and converts it into short rectangular pulses (diagram 3). From pin 4 of DD1, pulses are sent to pin 8 of D trigger DD2.1, operating in RS trigger mode. DD2.1, like DD1.1, performs the function of inverting and signal generation (Diagram 4).

Please note that the signals in diagram 2 and 4 are almost the same, and it seemed that the signal from R1 could be applied directly to pin 5 of DD2.1. But studies have shown that the signal after R1 contains a lot of interference coming from the supply network, and without double shaping the circuit did not work stably. And installing additional LC filters when there are free logic elements is not advisable.

The DD2.2 trigger is used to assemble a control circuit for the soldering iron temperature controller and it works as follows. Pin 3 of DD2.2 receives rectangular pulses from pin 13 of DD2.1, which with a positive edge overwrite at pin 1 of DD2.2 the level that is currently present at the D input of the microcircuit (pin 5). At pin 2 there is a signal of the opposite level. Let's consider the operation of DD2.2 in detail. Let's say at pin 2, logical one. Through resistors R4, R5, capacitor C2 will be charged to the supply voltage. When the first pulse with a positive drop arrives, 0 will appear at pin 2 and capacitor C2 will quickly discharge through the diode VD7. The next positive drop at pin 3 will set a logical one at pin 2 and through resistors R4, R5, capacitor C2 will begin to charge.

The charging time is determined by the time constant R5 and C2. The greater the value of R5, the longer it will take for C2 to charge. Until C2 is charged to half the supply voltage, there will be a logical zero at pin 5 and positive pulse drops at input 3 will not change the logical level at pin 2. As soon as the capacitor is charged, the process will repeat.

Thus, only the number of pulses specified by resistor R5 from the supply network will pass to the outputs of DD2.2, and most importantly, changes in these pulses will occur during the voltage transition in the supply network through zero. Hence the absence of interference from the operation of the temperature controller.

From pin 1 of the DD2.2 microcircuit, pulses are supplied to the DD1.2 inverter, which serves to eliminate the influence of the thyristor VS1 on the operation of DD2.2. Resistor R6 limits the control current of thyristor VS1. When a positive potential is applied to the control electrode VS1, the thyristor opens and voltage is applied to the soldering iron. The regulator allows you to adjust the power of the soldering iron from 50 to 99%. Although resistor R5 is variable, adjustment due to the operation of DD2.2 heating the soldering iron is carried out in steps. When R5 is equal to zero, 50% of the power is supplied (diagram 5), when turning at a certain angle it is already 66% (diagram 6), then 75% (diagram 7). Thus, the closer to the design power of the soldering iron, the smoother the adjustment works, which makes it easy to adjust the temperature of the soldering iron tip. For example, a 40 W soldering iron can be configured to run from 20 to 40 W.

Temperature controller design and details

All parts of the thyristor temperature controller are placed on a printed circuit board made of fiberglass. Since the circuit does not have galvanic isolation from the electrical network, the board is placed in a small plastic case of a former adapter with an electrical plug. A plastic handle is attached to the axis of the variable resistor R5. Around the handle on the regulator body, for the convenience of regulating the degree of heating of the soldering iron, there is a scale with conventional numbers.

The cord coming from the soldering iron is soldered directly to the printed circuit board. You can make the connection of the soldering iron detachable, then it will be possible to connect other soldering irons to the temperature controller. Surprisingly, the current consumed by the temperature controller control circuit does not exceed 2 mA. This is less than what the LED in the lighting circuit of the light switches consumes. Therefore, no special measures are required to ensure the temperature conditions of the device.

Microcircuits DD1 and DD2 are any 176 or 561 series. The Soviet thyristor KU103V can be replaced, for example, with a modern thyristor MCR100-6 or MCR100-8, designed for a switching current of up to 0.8 A. In this case, it will be possible to control the heating of a soldering iron with a power of up to 150 W. Diodes VD1-VD4 are any, designed for a reverse voltage of at least 300 V and a current of at least 0.5 A. IN4007 (Uob = 1000 V, I = 1 A) is perfect. Any pulse diodes VD5 and VD7. Any low-power zener diode VD6 with a stabilization voltage of about 9 V. Capacitors of any type. Any resistors, R1 with a power of 0.5 W.

The power regulator does not need to be adjusted. If the parts are in good condition and there are no installation errors, it will work immediately.

The circuit was developed many years ago, when computers and especially laser printers did not exist in nature, and therefore I made a drawing of the printed circuit board using old-fashioned technology on chart paper with a grid pitch of 2.5 mm. Then the drawing was glued with Moment glue onto thick paper, and the paper itself was glued to foil fiberglass. Next, holes were drilled on a homemade drilling machine and the paths of future conductors and contact pads for soldering parts were drawn by hand.

The drawing of the thyristor temperature controller has been preserved. Here is his photo. Initially, the rectifier diode bridge VD1-VD4 was made on a KTs407 microassembly, but after the microassembly was torn twice, it was replaced with four KD209 diodes.

How to reduce the level of interference from thyristor regulators

To reduce the interference emitted by thyristor power regulators into the electrical network, ferrite filters are used, which are a ferrite ring with wound turns of wire. Such ferrite filters can be found in all switching power supplies for computers, televisions and other products. An effective, noise-suppressing ferrite filter can be retrofitted to any thyristor regulator. It is enough to pass the wire connecting to the electrical network through the ferrite ring.

The ferrite filter must be installed as close as possible to the source of interference, that is, to the installation site of the thyristor. The ferrite filter can be placed both inside the device body and on its outside. The more turns, the better the ferrite filter will suppress interference, but simply threading the power cable through the ring is sufficient.

The ferrite ring can be taken from the interface wires of computer equipment, monitors, printers, scanners. If you pay attention to the wire connecting the computer system unit to the monitor or printer, you will notice a cylindrical thickening of insulation on the wire. In this place there is a ferrite filter for high-frequency interference.

It is enough to cut the plastic insulation with a knife and remove the ferrite ring. Surely you or someone you know has an unnecessary interface cable from an inkjet printer or an old CRT monitor.

Many soldering irons are sold without a power regulator. When turned on, the temperature rises to maximum and remains in this state. To adjust it, you need to disconnect the device from the power source. In such soldering irons, the flux instantly evaporates, oxides are formed and the tip is in a constantly contaminated state. It has to be cleaned frequently. Soldering large components requires high temperatures, but small parts can be burned. To avoid such problems, power regulators are made.

How to make a reliable power regulator for a soldering iron with your own hands

Power controls help control the heat level of the soldering iron.

Connecting a ready-made heating power controller

If you do not have the opportunity or desire to tinker with the manufacture of the board and electronic components, then you can buy a ready-made power regulator at a radio store or order it online. The regulator is also called a dimmer. Depending on the power, the device costs 100–200 rubles. You may need to modify it a little after purchase. Dimmers up to 1000 W are usually sold without a cooling radiator.

Power regulator without radiator

And devices from 1000 to 2000 W with a small radiator.

Power regulator with small heatsink

And only the more powerful ones are sold with large radiators. But in fact, a dimmer from 500 W should have a small cooling radiator, and from 1500 W large aluminum plates are already installed.

Chinese power regulator with large radiator

Please take this into account when connecting the device. If necessary, install a powerful cooling radiator.

Modified power regulator

To correctly connect the device to the circuit, look at the back of the circuit board. The IN and OUT terminals are indicated there. The input is connected to a power outlet, and the output to a soldering iron.

Designation of input and output terminals on the board

The regulator is installed in different ways. To implement them, you do not need special knowledge, and the only tools you need are a knife, a drill and a screwdriver. For example, you can include a dimmer in the power cord of a soldering iron. This is the easiest option.

1. Cut the soldering iron cable into two parts.
2. Connect both wires to the board terminals. Screw the section with the fork to the entrance.
3. Select a plastic case of suitable size, make two holes in it and install the regulator there.

Another simple way: you can install the regulator and socket on a wooden stand.

You can connect not only a soldering iron to such a regulator. Now let's look at a more complex, but compact option.

1. Take a large plug from an unnecessary power supply.
2. Remove the existing board with electronic components from it.
3. Drill holes for the dimmer handle and two terminals for the input plug. The terminals are sold at a radio store.
4. If your regulator has indicator lights, make holes for them too.
5. Install the dimmer and terminals into the plug body.
6. Take a portable socket and plug it in. Insert the plug with the regulator into it.

This device, like the previous one, allows you to connect different devices.

Homemade two-stage temperature controller

The simplest power regulator is a two-stage one. It allows you to switch between two values: maximum and half of maximum.

Two-stage power regulator

When the circuit is open, current flows through diode VD1. The output voltage is 110 V. When the circuit is closed with switch S1, the current bypasses the diode, since it is connected in parallel and the output voltage is 220 V. Select the diode in accordance with the power of your soldering iron. The output power of the regulator is calculated by the formula: P = I * 220, where I is the diode current. For example, for a diode with a current of 0.3 A, the power is calculated as follows: 0.3 * 220 = 66 W.

Since our block consists of only two elements, it can be placed in the body of the soldering iron using hinged mounting.

1. Solder parallel parts of the microcircuit to each other directly using the legs of the elements themselves and the wires.
2. Connect to the chain.
3. Fill everything with epoxy resin, which serves as an insulator and protection against movement.
4. Make a hole in the handle for the button.

If the housing is very small, use a light switch. Mount it into the soldering iron cord and insert a diode parallel to the switch.

Switch for lamp

On a triac (with indicator)

Let's look at a simple triac regulator circuit and make a printed circuit board for it.

Triac power regulator

PCB manufacturing

Since the circuit is very simple, there is no point in installing a computer program for processing electrical circuits just because of it. Moreover, special paper is needed for printing. And not everyone has a laser printer. Therefore, we will take the simplest route of manufacturing a printed circuit board.

1. Take a piece of PCB. Cut to the size required for the chip. Sand the surface and degrease.
2. Take a laser disc marker and draw a diagram on the PCB. To avoid mistakes, draw with a pencil first.
3. Next, we start etching. You can buy ferric chloride, but the sink is difficult to clean after it. If you accidentally drop it on your clothes, it will leave stains that cannot be completely removed. Therefore, we will use a safe and cheap method. Prepare a plastic container for the solution. Pour in 100 ml hydrogen peroxide. Add half a tablespoon of salt and a packet of citric acid up to 50 g. The solution is made without water. You can experiment with proportions. And always make a fresh solution. All copper should be removed. This takes about an hour.
4. Rinse the board under running water. Dry. Drill the holes.
5. Wipe the board with alcohol-rosin flux or a regular solution of rosin in isopropyl alcohol. Take some solder and tin the tracks.

To apply the diagram on PCB, you can make it even easier. Draw a diagram on paper. Glue it with tape to the cut out PCB and drill holes. And only after that draw the circuit with a marker on the board and etch it.

Installation

Prepare all necessary components for installation:

• solder spool;
• pins into the board;
• triac bta16;
• 100 nF capacitor;
• 2 kOhm fixed resistor;
• dinistor db3;
• variable resistor with a linear dependence of 500 kOhm.

Proceed to install the board.

1. Cut off four pins and solder them onto the board.
2. Install the dinistor and all other parts except the variable resistor. Solder the triac last.
3. Take a needle and brush. Clean the gaps between the tracks to remove any possible shorts.
4. Take an aluminum radiator to cool the triac. Drill a hole in it. The triac with its free end with a hole will be attached to an aluminum radiator for cooling.
5. Use fine sandpaper to clean the area where the element is attached. Take heat-conducting paste of the KPT-8 brand and apply a small amount of paste to the radiator.
6. Secure the triac with a screw and nut.
7. Carefully bend the board so that the triac takes a vertical position in relation to it. To make the design compact.
8. Since all parts of our device are under mains voltage, we will use a handle made of insulating material for adjustment. It is very important. Using metal holders here is dangerous to life. Place the plastic handle on the variable resistor.
9. Use a piece of wire to connect the outer and middle terminals of the resistor.
10. Now solder two wires to the outer terminals. Connect the opposite ends of the wires to the corresponding pins on the board.
11. Take the socket. Remove the top cover. Connect the two wires.
12. Solder one wire from the socket to the board.
13. And connect the second one to the wire of a two-core network cable with a plug. The power cord has one free core left. Solder it to the corresponding contact on the printed circuit board.

In fact, it turns out that the regulator is connected in series to the load power circuit.

Connection diagram of the regulator to the circuit

If you want to install an LED indicator in the power regulator, then use a different circuit.

Power regulator circuit with LED indicator

Diodes added here:

• VD 1 - diode 1N4148;
• VD 2 - LED (operation indication).

The triac circuit is too bulky to be included in a soldering iron handle, as is the case with a two-stage regulator, so it must be connected externally.

Installation of the structure in a separate housing

All elements of this device are under mains voltage, so a metal case cannot be used.

1. Take a plastic box. Outline how the board with the radiator will be placed in it and which side to connect the power cord from. Drill three holes. The two extreme ones are needed to attach the socket, and the middle one is for the radiator. The head of the screw to which the radiator will be attached must be hidden under the socket for electrical safety reasons. The radiator has contact with the circuit, and it has direct contact with the network.
2. Make another hole on the side of the case for the network cable.
3. Install the radiator mounting screw. Place the washer on the back side. Screw on the radiator.
4. Drill a hole of the appropriate size for the potentiometer, that is, for the handle of the variable resistor. Insert the part into the body and secure with a standard nut.
5. Place the socket on the body and drill two holes for the wires.
6. Secure the socket with two M3 nuts. Insert the wires into the holes and tighten the cover with a screw.
7. Route the wires inside the housing. Solder one of them to the board.
8. The other is for the core of the network cable, which you first insert into the plastic housing of the regulator.
9. Insulate the joint with electrical tape.
10. Connect the free wire of the cord to the board.
11. Close the housing with the lid and tighten it with screws.

The power regulator is plugged into the network, and the soldering iron is plugged into the regulator socket.

Video: installation of the regulator circuit on a triac and assembly in the housing

On a thyristor

The power regulator can be made using a bt169d thyristor.

Thyristor power regulator

Circuit components:

• VS1 - thyristor BT169D;
• VD1 - diode 1N4007;
• R1 - 220k resistor;
• R3 - 1k resistor;
• R4 - 30k resistor;
• R5 - resistor 470E;
• C1 - capacitor 0.1mkF.

Resistors R4 and R5 are voltage dividers. They reduce the signal, since the bt169d thyristor is low-power and very sensitive. The circuit is assembled similarly to a regulator on a triac. Since the thyristor is weak, it will not overheat. Therefore, a cooling radiator is not needed. Such a circuit can be mounted in a small box without a socket and connected in series with the soldering iron wire.

Power regulator in a small housing

Circuit based on a powerful thyristor

If in the previous circuit you replace the thyristor bt169d with a more powerful ku202n and remove resistor R5, then the output power of the regulator will increase. Such a regulator is assembled with a thyristor-based radiator.

Circuit based on a powerful thyristor

On a microcontroller with indication

A simple power regulator with light indication can be made on a microcontroller.

Regulator circuit on the ATmega851 microcontroller

Prepare the following components to assemble it:

Using buttons S3 and S4, the power and brightness of the LED will change. The circuit is assembled similarly to the previous ones.

If you want the meter to show the percentage of power output instead of a simple LED, then use a different circuit and appropriate components, including a numeric indicator.

Regulator circuit on microcontroller PIC16F1823

The circuit can be mounted into a socket.

Regulator on a microcontroller in a socket

Checking and adjusting the thermostat block circuit

Test the unit before connecting it to the instrument.

1. Take the assembled circuit.
2. Connect it to the network cable.
3. Connect a 220 lamp to the board and a triac or thyristor. Depending on your scheme.
4. Plug the power cord into the socket.
5. Rotate the variable resistor knob. The lamp must change the degree of incandescence.

The circuit with a microcontroller is checked in the same way. Only the digital indicator will still display the percentage of output power.

To adjust the circuit, change resistors. The greater the resistance, the less power.

It is often necessary to repair or modify various devices using a soldering iron. The performance of these devices depends on the quality of soldering. If you purchased a soldering iron without a power regulator, be sure to install it. With constant overheating, not only electronic components will suffer, but also your soldering iron.