Blocking generator Chinese lamp LED ball. Low voltage voltage converters for LEDs

I came across an interesting circuit on the Internet for a very simple micro-power driver on a junk field chip from a motherboard, and it turned out to be quite working. A simpler version of the circuit, with a bipolar transistor -. Here’s the diagram I’ve slightly corrected for a more detailed understanding for beginners of what goes where and how to solder:

I found a bunch of these APM2014 field-effect transistors from old motherboards and quickly soldered them for a test, instead of a dumbbell I took ferrite from the inductor, when powered by a dead 1.1 V battery, the 1 W LED shines quite brightly, at 1.4 V it still shines brighter, but already warming up. Later I’ll check with different chokes, but I’ll probably stick with a dumbbell, since they are more convenient to place in the housings. During a test attempt to connect a 0.5 W 60 mA LED, it quickly burned out.

The LED is rated at 1 W, its light is quite enough for illumination in the dark, since this is a decorative flashlight and does not require too much light. Instead of a reflector, a collimator was used; I just had to sharpen it a little around the edge.

During operation, the LED heats up noticeably only from a fresh battery with the choke with the data indicated in the circuit; in this case I used a CD75 choke and rewound it. Since there is little space here, only 14 turns of 0.43 wire fit into it, but the heating of the LED from the fresh element decreased, although the brightness decreased slightly.

The second side of the printed circuit board serves as an LED mount and as cooling; the contacts are indicated in red on the signet; they can be sharpened with any available tool. I placed a couple of pieces of textolite on the field-effect transistor to align the substrate under the positive contact disk, to prevent distortion.

The resulting flashlight shines with a decrease in the luminous flux to an element voltage of 0.5 V, and if it starts to blink, it means the battery is now completely dead, although the same salt batteries can be restored with saline solution and continue to be used in the flashlight. Author of the material - Igoran.

Discuss the article SIMPLE FLASHLIGHT WITH ONE AA BATTERY

LEDs, as sources of optical radiation, have undeniable advantages: small dimensions, high brightness with minimal (units of mA) current, and efficiency.

But due to technological features, they cannot glow at a voltage below 1.6... 1.8 V. This circumstance sharply limits the possibility of using LED emitters in a wide class of devices that have low-voltage power supply, usually from a single galvanic cell.

Despite the obvious relevance of the problem of low-voltage power supply of LED optical radiation sources, a very limited number of circuit solutions are known in which the authors tried to solve this problem.

In this regard, below is an overview of LED power supply circuits from a low (0.25...1.6 V) voltage source. The variety of circuits presented in this chapter can be reduced to two main types of low-to-high voltage conversion. These are circuits with capacitive and inductive energy storage devices [Rk 5/00-23].

Voltage doubler

Figure 1 shows the LED power supply circuit using the principle of doubling the supply voltage. The low-frequency pulse generator is made using transistors of different structures: KT361 and KT315.

The pulse repetition rate is determined by the time constant R1C1, and the duration of the pulses is determined by the time constant R2C1. From the output of the generator, short pulses through resistor R4 are supplied to the base of transistor VT3, the collector circuit of which includes a red LED HL1 (AL307KM) and a germanium diode VD1 of type D9.

A large-capacity electrolytic capacitor C2 is connected between the output of the pulse generator and the connection point between the LED and the germanium diode.

During a long pause between pulses (transistor VT2 is closed and does not conduct current), this capacitor is charged through diode VD1 and resistor R3 to the voltage of the power source. When generating a short pulse, transistor VT2

opens. The negatively charged plate of capacitor C2 is connected to the positive power bus. Diode VD1 is turned off. The charged capacitor C2 is connected in series with the power source.

The total voltage is applied to the LED circuit - the emitter - collector junction of transistor VT3. Since transistor VT3 is unlocked by the same pulse, its emitter-collector resistance becomes small.

Thus, almost double the supply voltage (excluding minor losses) is briefly applied to the LED: a bright flash follows. After this, the process of charging and discharging capacitor C2 is periodically repeated.

Rice. 1. Schematic diagram of a voltage doubler for powering an LED.

Since LEDs can operate at short-term pulse currents tens of times higher than the rated values, the LED does not become damaged.

If it is necessary to increase the reliability of LED emitters with low-voltage power supply and expand the supply voltage range upward, a current-limiting resistor with a resistance of tens or hundreds of Ohms should be connected in series with the LED.

When using an LED of the AL307KM type with a voltage of the beginning of a barely noticeable glow of 1.35... 1.4 V and a voltage at which, without limiting resistance, the current through the LED is 20 mA, 1.6... 1.7 V, the operating voltage of the generator , presented in Figure 1, is 0.8... 1.6 V.

The range limits are determined experimentally in the same way: the lower one indicates the voltage at which the LED begins to glow, the upper one indicates the voltage at which the current consumed by the entire device is approximately 20 mA, i.e. under the most unfavorable operating conditions does not exceed the maximum current through the LED and, at the same time, the converter itself.

As noted earlier, the generator (Figure 1) operates in a pulsed mode, which is, on the one hand, a disadvantage of the circuit, but on the other hand, an advantage, since it allows you to generate bright flashes of light that attract attention.

The generator is quite economical, since the average current consumed by the device is small. At the same time, the circuit must use a low-voltage, but rather bulky, high-capacity electrolytic capacitor (C2).

Simplified version of the voltage converter

Figure 2 shows a simplified version of the generator, which operates similarly to the one described above. The generator, using a small-sized electrolytic capacitor, operates at a supply voltage of 0.9 to 1.6 V.

The average current consumed by the device does not exceed 3 mA at a pulse repetition rate of about 2 Hz. The brightness of the generated flashes of light is slightly lower than in the previous scheme.

Rice. 2. Circuit of a simple low-voltage voltage converter using two transistors from 0.9V to 2V.

Generator using a telephone capsule

The generator shown in Fig. 9.3, uses the TK-67 telephone capsule as a load. This makes it possible to increase the amplitude of the generated pulses and thereby lower the lower limit of the start of generator operation by 200 mV.

By switching to a higher generation frequency, it is possible to continuously “pump” (convert) energy and significantly reduce the capacitance of capacitors.

Rice. 3. Circuit diagram of a low-voltage voltage converter generator using a telephone coil.

Generator with output voltage doubling

Figure 4 shows a generator with an output stage that doubles the output voltage. When transistor VT3 is closed, only a small supply voltage is applied to the LED.

The electrical resistance of the LED is high due to the pronounced nonlinearity of the current-voltage characteristic and is much higher than the resistance of resistor R6. Therefore, capacitor C2 is connected to the power source through resistors R5 and R6.

Rice. 4. Circuit of a low-voltage converter with doubling the output voltage.

Although resistor R6 is used instead of a germanium diode, the principle of operation of the voltage doubler remains the same: charging capacitor C2 with transistor VT3 closed through resistors R5 and R6, followed by connecting the charged capacitor in series with the power source.

When a voltage doubled in this way is applied, the dynamic resistance of the LED at a steeper section of the current-voltage characteristic becomes about 100 Ohms or less for the duration of the capacitor discharge, which is much lower than the resistance of the resistor R6 shunting the capacitor.

The use of resistor R6 instead of a germanium diode allows you to expand the operating range of supply voltages (from 0.8 to 6 V). If there were a germanium diode in the circuit, the device supply voltage would be limited to 1.6...1.8 V.

If the supply voltage were further increased, the current through the LED and germanium diode would increase to an unacceptably high value and irreversible damage would occur.

Converter based on AF generator

In the generator presented in Figure 5, simultaneously with light pulses, ringing pulses of sound frequency are generated. The frequency of sound signals is determined by the parameters of the oscillatory circuit formed by the winding of the telephone capsule and capacitor C2.

Rice. 5. Schematic diagram of a voltage converter for an LED based on an AF generator.

Voltage converters based on multivibrators

LED power supplies based on multivibrators are shown in Figures 6 and 7. The first circuit is based on an asymmetric multivibrator, which, like the devices (Figures 1 - 5), produces short pulses with a long interpulse pause.

Rice. 6. Low-voltage voltage converter based on an asymmetric multivibrator.

Energy storage - electrolytic capacitor SZ is periodically charged from the power source and discharged to the LED, summing its voltage with the supply voltage.

Unlike the previous circuit, the generator (Fig. 7) ensures that the LED glows continuously. The device is based on a symmetrical multivibrator and operates at higher frequencies.

Rice. 7. Converter for powering the LED from a low-voltage source of 0.8 - 1.6V.

In this regard, the capacitance of the capacitors in this circuit is 3...4 orders of magnitude lower. At the same time, the brightness of the glow is noticeably reduced, and the average current consumed by the generator at a power source voltage of 1.5 6 does not exceed 3 mA.

Voltage converters with series connection of transistors

Rice. 8. Voltage converter with series connection of transistors of different conductivity types.

In the generators shown below in Figures 8 - 13, a somewhat unusual series connection of transistors of different conductivity types, moreover, covered by positive feedback, is used as an active element.

Rice. 9. Two-transistor voltage converter for an LED using a coil from a telephone.

The positive feedback capacitor (Figure 8) simultaneously acts as an energy storage device to obtain a voltage sufficient to power the LED.

A germanium diode (or a resistance replacing it, Fig. 12) is connected parallel to the base-collector transition of transistor VT2 (type KT361).

In a generator with an RC circuit (Fig. 8), due to significant voltage losses on semiconductor junctions, the operating voltage of the device is 1.1... 1.6 V.

It became possible to significantly lower the lower limit of the supply voltage by switching to the LC version of the generator circuit using inductive energy storage devices (Fig. 9 - 13).

Rice. 10. Circuit of a simple low-voltage voltage converter 0.75V -1.5V to 2V based on an LC oscillator.

A telephone capsule is used as an inductive energy storage device in the first circuit (Fig. 9). Simultaneously with the light flashes, the generator produces acoustic signals.

When the capacitor capacity increases to 200 µF, the generator switches to a pulsed economical operating mode, producing intermittent light and sound signals.

The transition to higher operating frequencies is possible through the use of a small-sized inductor with a high quality factor. In this regard, it becomes possible to significantly reduce the volume of the device and lower the lower limit of the supply voltage (Fig. 10 - 13).

The coil of the intermediate frequency circuit from the VEF radio receiver with an inductance of 260 μH was used as inductance. In Fig. 11, 12 show the types of such generators.

Rice. 11. Circuit of a low-voltage voltage converter for an LED with a coil from the IF circuit of the receiver.

Rice. 12. Circuit of a simple voltage converter for an LED with a coil from the IF circuit of the receiver.

Finally, Figure 13 shows the most simplified version of the device, in which an LED is used instead of an oscillating circuit capacitor.

Capacitor-type voltage converters (with voltage doubling) used to power LED emitters can theoretically reduce the operating supply voltage only to 60% (the maximum, ideal value is 50%).

Rice. 13. A very simple low voltage voltage converter with an LED on instead of a capacitor.

The use of multistage voltage multipliers for these purposes is unpromising due to progressively increasing losses and a decrease in the efficiency of the converter.

Converters with inductive energy storage are more promising with a further reduction in the operating voltage of the generators that provide operation of the LEDs. At the same time, the high efficiency and simplicity of the converter circuit are maintained.

Voltage converters of inductive and inductive-capacitive type

Figures 14 - 18 show converters for powering LEDs of inductive and inductive-capacitive type, made on the basis of generators using analogues of an injection field-effect transistor as an active element [Rk 5/00-23].

Rice. 14. Circuit diagram of a low-voltage voltage converter 1-6V to 2V of inductive-capacitive type.

The converter shown in Figure 14 is an inductive-capacitive type device. The pulse generator is made on an analogue of an injection field-effect transistor (transistors VT1 and VT2).

The elements that determine the operating frequency of generation in the audio frequency range are the telephone capsule BF1 (type TK-67), capacitor C1 and resistor R1. Short pulses generated by the generator arrive at the base of transistor VT3, opening it.

At the same time, the charge/discharge of the capacitive energy storage unit (capacitor C2) occurs. When a pulse arrives, the positively charged plate of capacitor C2 is connected to the common bus through transistor VT2, which is open for the duration of the pulse. Diode VD1 closes, transistor VT3 opens.

Thus, a power source and a charged capacitor C2 are connected in series to the load circuit (LED HL1), resulting in a bright flash of the LED.

Transistor VT3 allows you to expand the range of operating voltages of the converter. The device is operational at voltages from 1.0 to 6.0 V. Let us recall that the lower limit corresponds to a barely noticeable glow of the LED, and the upper limit corresponds to the device’s current consumption of 20 mA.

In the region of low voltages (up to 1.45 V), sound generation is not audible, although as the supply voltage subsequently increases, the device begins to produce sound signals, the frequency of which decreases quite quickly.

The transition to higher operating frequencies (Fig. 15) through the use of a high-frequency coil makes it possible to reduce the capacitance of the capacitor that “pumps” energy (capacitor C1).

Rice. 15. Schematic diagram of a low-voltage voltage converter with an HF generator.

A field-effect transistor VT3 (KP103G) is used as a key element that connects the LED to the “positive” power bus for the pulse repetition period. As a result, the operating voltage range of this converter has been expanded to 0.7... 10 V.

Noticeably simplified devices, but operating within a limited range of supply voltages, are shown in Figures 16 and 17. They provide LED illumination in the range of 0.7...1.5 V (at R1=680 Ohm) and 0.69...1, 2 V (at R1=0 Ohm), as well as from 0.68 to 0.82 V (Fig. 17).

Rice. 16. Schematic diagram of a simplified low-voltage voltage converter with an HF generator.

Rice. 17. Simplified low-voltage voltage converter with an RF generator and a telephone capsule as a coil.

The simplest generator is based on an analogue of an injection field-effect transistor (Fig. 18), where the LED simultaneously acts as a capacitor and is the load of the generator. The device operates in a rather narrow range of supply voltages, but the brightness of the LED is quite high, since the converter (Fig. 18) is purely inductive and has high efficiency.

Rice. 18. Low-voltage voltage converter with a generator based on an analogue of an injection field-effect transistor.

The next type of converter is quite well known and is more traditional. These are transformer and autotransformer type converters.

In Fig. Figure 19 shows a transformer-type generator for powering LEDs with low voltage voltage. The generator contains only three elements, one of which is a light-emitting diode.

Without an LED, the device is a simple blocking generator, and a fairly high voltage can be obtained at the output of the transformer. If you use an LED as a generator load, it begins to glow brightly even at a low supply voltage (0.6...0.75 V).

Rice. 19. Circuit of a transformer type converter for powering LEDs with low voltage voltage.

In this circuit (Fig. 19), the transformer windings have 20 turns of PEV 0.23 wire. A ferrite ring M1000 (1000NM) K 10x6x2.5 was used as the transformer core. In the absence of generation, the conclusions of one of the transformer windings are as follows! swap.

The converter shown in Figure 20 has the lowest supply voltage of all the devices considered. A significant reduction in the lower limit of the operating voltage was achieved by optimizing the choice of the number (ratio) of winding turns and the method of their inclusion. When using high-frequency germanium transistors such as 1T311, 1T313 (GT311, GT313), such converters begin to operate at a supply voltage above 125 mV.

Rice. 20. Low voltage voltage converter from 0.25V - 0.6V to 2V.

Rice. 21. Experimentally measured characteristics of the generator.

As in the previous circuit, a ferrite ring M1000 (1000NM) K10x6x2.5 was used as the transformer core. The primary winding is made of PEV 0.23 mm wire, the secondary winding is made of PEV 0.33. A fairly bright glow of the LED is observed already at a voltage of 0.3 V.

Figure 21 shows the experimentally measured characteristics of the generator (Fig. 20) when varying the number of turns of the windings. From the analysis of the obtained dependencies it follows that there is an area of optimal ratio between the number of turns of the primary and secondary windings, and with an increase in the number of turns of the primary winding, the minimum operating voltage of the converter gradually decreases, and at the same time the range of operating voltages of the converter narrows.

To solve the inverse problem - expanding the operating voltage range of the converter - an RC circuit can be connected in series with it (Fig. 22).

Rice. 22. Circuit of a low-voltage voltage converter using an RC circuit.

Converter circuits of the inductive or capacitive three-point type

Another type of converter is shown in Figures 23 - 29. Their feature is the use of inductive energy storage devices and circuits made of the “inductive” or “capacitive three-point” type with a barrier mode for turning on the transistor.

The generator (Fig. 23) is operational in the voltage range from 0.66 to 1.55 V. To optimize the operating mode, it is necessary to select the value of resistor R1. As an inductor, as in many previous circuits. an IF filter circuit coil with an inductance of 260 μH was used.

Rice. 23. Voltage converter for LED on one transistor KT315.

Thus, with the number of turns of the primary winding n(1) equal to 50...60 and the number of turns of the secondary winding l(II) - 12, the device is operational in the supply voltage range of 260...440 mV (ratio of the number of turns 50 to 12), and with a ratio of the number of turns of 60 to 12 - 260...415 mV.

When using a ferrite core of a different type or size, this ratio may be disrupted and be different. It is useful to carry out such a study yourself, and present the results in the form of a graph for clarity.

It seems very interesting to use a tunnel diode in the generators under consideration (similar to the one shown in Fig. 20), connected instead of the emitter-base transition of transistor VT1.

The generator (Fig. 24) is slightly different from the previous one (Fig. 23). Its interesting feature is that the brightness of the LED changes with increasing supply voltage (Fig. 25).

Rice. 24. Voltage converter with variable LED brightness.

Rice. 25. Graph of the dependence of the brightness of the LED on the voltage supplying the generator (for Figure 24).

Moreover, the maximum brightness is achieved at 940 mV. The converter shown in Figure 26 can be classified as a three-point generator, with the LED acting as one of the capacitors.

The transformer of the device is made on a ferrite ring (1000HM) K10x6x2.5, and its windings contain approximately 15...20 turns of PELSHO 0.18 wire.

Rice. 26. Low-voltage voltage converter with a three-point generator.

The converter (Fig. 27) differs from the previous one in the LED connection point. The dependence of the brightness of the LED on the supply voltage is shown in Figure 28: as the supply voltage increases, the brightness first increases, then sharply decreases, and then increases again.

Rice. 27. A simple voltage converter for low-voltage power supply of the AL307 LED.

Rice. 28. Dependence of LED brightness on supply voltage.

The simplest circuit for converters of this type is the circuit shown in Figure 29. Setting the operating point is achieved by selecting resistor R1.

The LED, as in a number of previous circuits, simultaneously plays the role of a capacitor. As an experiment, it is recommended to connect a capacitor in parallel with the LED and select its capacitance.

Rice. 29. A very simple circuit of a low-voltage voltage converter using one transistor.

Finally

As a general note on setting up the circuits presented above, it should be noted that the supply voltage of all the devices considered, in order to avoid damage to the LEDs, should not (with rare exceptions) exceed 1.6...1.7 V.

Literature: Shustov M.A. Practical circuit design (Book 1).

Modified August 2018

This craft may become the first self-made generator from which an interest in free energy may develop. For physics lessons, this video will be an excellent tool for schoolchildren.

Best explanation with assembly of working model of current generator

In this lesson I talked about electromagnetic induction and will show you how to make a simple alternating current generator.

Comments

Bliss. Good generator. It’s quite enough for charging gadgets or even for LED lighting if you find something to twist it with. By the way, since you are such a wise inventor, you have an idea - create a vibration generator. Our roads allow electricity to be generated from shaking).

Yuriru05
8 months ago
Everything is very competent. The only thing is that I would not use magnets from hard drives for generators. The fact is that it has 2 poles on a plane, and not on different sides, so the tension is maximum at the edges of the magnet, and zero in the middle. Preferably neodymium magnets - tablets - there will be a significant increase in current and EMF parameters. But for demonstrating the operation of the generator, this is normal.

The simplest efficient generator with magnets

To create a simple current generator for LEDs, you need to take neodymium magnets, copper wire, and LED light bulbs. You can purchase a neodymium magnet in the online store.

However, you can also buy a ready-made electric generator from a Chinese online store.

Glue a CD onto the square block. On another disk we attach four neodymium magnets with glue. Next, we will make 5 coils and connect each of them to LEDs. To do this, we wind a coil of insulated copper wire. We clean the ends of the coil with a knife. We connect the ends of the coil to the LED. We will glue all 5 coils with LEDs attached to them to the CD.

Place a sewing machine spool in the center of the device. Glue a stopper from a tube of toothpaste to the back of the disk with magnets. Glue a washer on the other side. Now let’s install the disk on the axle, which already has a disk with spools on it (with a spool from the sewing machine glued to it). The distance between magnets and coils should be kept to a minimum.

The LED electricity generator is ready to go. All that remains is to run it in a dark room to see the light effect.

Translation of instructions from the authors of the homemade product. For this multiple generator you will need 5 strong neodymium magnets, 5 insulated thin coils of 1000 rpm copper wire and 5 LEDs. Place 5 modules with each coil attached to one LED on a wooden base. There is a vertical rod in the center. A CD with 5 strong magnets can spin on this rod. The gap between the magnets and coils is about 2-3 mm. When you spin a CD, the moving magnetic field creates EMF and all the LEDs glow brightly!

A word of caution: White LEDs are comparatively expensive, so I suggest including a small resistor (1 to 10 ohms) in series with the LED cathode to limit and measure the peak current. While testing the circuit, you can measure the voltage drop across this resistor using either an oscilloscope or a peak detector to see if the peak current is greater than the value recommended by the LED manufacturer. Based on these recommendations, for greater reliability, we will try to obtain a peak current no higher than half of the maximum.

Review

A compact switching converter that can provide enough voltage to power white LEDs consists of a minimum number of parts. The lamp we will receive is much more efficient in terms of lumen hours per pound of battery weight than an incandescent lamp. In addition, the color of the glow is determined by the emission of the LED phosphor, so the color of the glow practically does not change, even when the battery is completely discharged. As a result, the battery lasts a long time. This one is cheap and suitable for use in flashlights, emergency lighting and other applications that require white LEDs to be powered from one or two primary batteries.

Scheme

There couldn't be a simpler scheme than this. The blocking oscillator consists of a transistor, a 1 kOhm resistor and an inductor. When the power button is pressed, the transistor is turned on by current flowing through the 1 kΩ resistor. The voltage that appears across the inductance section from the midpoint to the collector of the transistor induces a voltage across the 1 kΩ resistor, which can be even higher than the battery voltage, thereby providing positive feedback. If there is voltage between the coil tap and the collector of the transistor, the collector current constantly increases. Due to positive feedback, the transistor remains in saturation until something happens to its base current.

At some point, the voltage drop across the inductance section from its midpoint to the transistor's collector approaches the value of the battery voltage (in fact, the battery voltage minus the transistor's collector-emitter saturation voltage). From this point on, the voltage is no longer induced in the coil from the tap to the 1 kΩ resistor, and the voltage at the base begins to decrease and becomes negative, thus accelerating the turn-off of the transistor. Although the transistor is now turned off, the inductor remains a source of current and the collector voltage rises.

The collector voltage quickly becomes high enough to generate current in the LED, and it flows until the inductance is discharged. The collector voltage then begins to “ring”, swinging from ground to power, turning on the transistor and starting another cycle.

Inductance

If you are designing this circuit for a non-commercial application, you have a wide range of inductor design options. The size of the core, its permeability and saturation characteristic (physical dimensions, µ and Bs) determine how many ampere-turns it can provide before saturation. If the core saturates faster than the voltage drop across the inductance section from the tap to the collector of the transistor reaches the battery voltage, the circuit will switch immediately anyway, because the saturation of the core makes the coil like a resistor and there is an inductive coupling between the collector and base (the side with the 1 kΩ resistor) the halves of the coil fall very strongly. This has the same effect as bringing the voltage drop across the coil closer to the battery voltage. The wire gauge determines how many amps the circuit produces before switching due to increasing voltage drop. The parameters of the inductor core (mainly physical dimensions and magnetic permeability) determine how many microseconds the coil is charged by the collector current, which will increase until the transistor turns off. These parameters also determine how long current will flow through the LED while the transistor is turned off. Almost all characteristics of the inductor affect the operation of this circuit.

I made this circuit using ferrite rings a few millimeters in diameter and toroidal cores with a cross-section up to a few centimeters (note the inductance on a rusty nail described below).

Here is, in general, the relationship between core sizes and inductor characteristics:

Large core: easy to wind, low switching frequency, increased power.
Small core: difficult to wind, higher switching frequency, lower power.

How to start. Take a coil core, preferably ferrite, and wind 20 turns on it. Make a tap in the form of a short loop of wire, then continue winding another 20 turns. An increase in the number of turns leads to a decrease in the operating frequency, a decrease leads to an increase in frequency. I wound only 10 turns with a tap from the middle (5+5) and this coil operated at a frequency of 200 kHz. Look at the circuit described below, assembled in the base of a light bulb, operating at a frequency of about 200 kHz.

Improved circuit

This scheme is attractive because it contains a minimum number of elements. The LED is powered by pulsed current. The pulse begins when the voltage across the LED reaches its forward operating voltage, which is higher than the battery voltage, which does not affect the switching of the transistor. The disadvantage is that the ratio of peak current to average LED current is quite high, it can be 3:1 or 5:1, depending on the circuit parameters (mainly coil inductance and battery voltage). If you want the LED to be brighter for a given peak current, you can add the diode and capacitor shown in the diagram below.

One critic suggested a good idea: if there is space available, add a decoupling capacitor between the negative terminal of the battery and the midpoint of the inductor. Some batteries have high output impedance, and this capacitor can increase the circuit's output current. A 10 uF capacitor should be sufficient, but if you are using a very high inductance inductor, it is better to increase the capacitance.

Where will you place the power source?

Since this circuit contains few elements, I made all of them, including an inductor, a 1K resistor, a 2N4401 transistor (in a TO-92 package, by the way), a rectifier diode, a chip capacitor and a Nichia NSPW315BS LED along with a small drop of glue place at the base of the pen lamp.

Using an LED instead of a light bulb allows you to develop a compact flashlight. It provides enough light to walk down the street on a moonless night. I estimated the operating time of the flashlight, which consumes a current of about 35 mA from a 1.5 V battery. It turned out that it would work continuously for at least 30 hours. It's quite long. Specifications for several Duracell alkaline batteries can be found.

The color of the glow remains consistently bluish-white, even when the battery voltage drops. If such a device is treated well, it will last a very long time. I had one of these flashlights, assembled according to the last diagram shown, for 18 months, and I used it every night. I only replaced the battery twice. If the contacts on the battery hadn't deteriorated due to corrosion, I wouldn't have known it was time to replace it, because the flashlight worked great.

Night light of a rusty nail

These blocking oscillator circuits work better with ferrite cores, but they can sometimes be hard to find. Some readers have expressed concern about the manufacture of inductors, which is understandable since inductors have an aura of mystery to many.

I undertake to prove that there is nothing complicated about inductors, and that they are very important. One day, waiting for a tow truck due to a car breakdown, I noticed a rusty nail near the road. It was 6.5 cm long and I decided to use it for the inductor core.

I pulled a twisted pair of ø0.5mm solid copper wire from a long CAT-5 (Ethernet) cable. This wire is similar to that used to install telephone lines inside buildings. I wound 60 turns of twisted pair in about three layers on a nail, then connected the beginning of one conductor to the end of another conductor, making a 120-turn inductor tapped from the middle.

I connected a 2N2222 transistor, a 1 kOhm resistor, a 1.5 V AA battery and a white LED to it. Nothing happened. Then I applied a 0.0027 uF capacitor to a 1 kOhm resistor (it was on the desktop) and the LED came to life. You may need a capacitor of about 0.001uF. The LED glows beautifully and the circuit draws 20mA of current from the AA battery. The signal on the oscilloscope screen looks terrible, but the main thing is that the circuit excited even on this rusty nail, and increased the initial 1.5 V of the AA element to more than 3 V, sufficient to glow the LED.

Those familiar with some aspects of coil core selection will immediately notice that eddy currents will be enormous, since iron has low resistance compared to ferrite, or air for example, and that there will probably be other losses. And the point is not that you should run out and buy nails to make an LED lamp, but that this circuit turned out to be very workable. If a rusty nail and some telephone wire is enough to light up a white LED, then the inductor is not a problem. So, take a break, go and buy a ferrite core and start working on the project.

Where to get ferrite cores

Wolfgang Driehaus from Germany wrote that ferrite cores are used in compact fluorescent lamps, and that he has successfully used them in LED power circuits. The next day I looked up and saw that some of the lights needed replacing.

Some of the CFLs in my house have burned out. After buying new lamps and replacing the burned out ones, I went to the garage to disassemble one of the lamps. The first problem was getting to the electronics in the lamp base. In a subsequent letter, Wolfgang told me that the lamp bulb can be opened and the circuit board removed without damaging the glass. Be careful not to break the glass tubes of the lamp, as they contain toxic mercury.

I wanted to make sure that these cores would be useful to me and removed the windings from the dumbbell and toroidal coil. During the process of disassembling the coil on the EE core, the ferrite cracked in several places, so I was not able to test it in my circuit.

I wound 50 turns of ø0.2 mm enameled wire onto the dumbbell core, made a central tap, and then wound another 50 turns. I assembled a device from this coil, a 2N4401 transistor, a 330 Ohm resistor connected to the base of the transistor, and a white LED in accordance with the diagram given at the beginning of the article. When I connected the 1.5V power supply, the LED flashed brightly. This confirmed that a coil with such a core can be used in this circuit.

I wound 10 turns of ø0.4 mm wire onto the toroidal core, made a tap and wound another 10 turns. Having connected the coil to the same circuit (2N4401, 330 Ohm, white LED) with a 1.5-volt power supply, I saw that the LED was lit, although not as brightly as with the previous coil, but after all, only 20 turns were wound on the toroid.

So now we know where to get ferrite cores. Compact fluorescent light bulbs are very affordable and will eventually break down and require replacement.

Another reader noted that another source of ferrite cores is computer peripheral cables. Monitor cables, keyboard cables, and some USB cables have plastic thickenings that actually contain ferrite cores. If you're going to throw your old keyboard in the trash, why not cut off the ferrite first?

Read the ending

Lyrical introduction

This article will discuss the modernization of a flashlight using the example of a device from the well-known Philips company. So, what disadvantages might it have? Like all pocket flashlights, this device was observed to have a significant decrease in the brightness of the incandescent lamp when the batteries were drained. And naturally, low efficiency and service life. Nevertheless, there is a solution to these eternal problems.

LEDs! But will it be enough to replace only the light source? No. Most flashlights use the now classic circuit, in which two 1.5-volt batteries are connected in series. But a voltage of 3 volts is not enough for the LED to glow brightly, therefore, it is worth including a converter in the circuit. The converter has a more stable output current when the input can be 0.5 V or less. What happens to a flashlight if its batteries are discharged to such a limit? That's right, it doesn't work. Therefore, the converter is the most successful move in solving this problem.

A new problem arises: where to place it? After all, there is often no space in the flashlight body. If you have open-frame components, you can mark them directly in the lamp base, but what if not? My article will help you figure this out.

Circuit design

As I said, there is a solution. Quite an original solution, I think.

Consider the converter circuit:

The diagram shows a blocking generator. Excitation is achieved by transformer coupling on transformer T1. The voltage pulses arising in the right (according to the circuit) winding are added to the voltage of the power source and are supplied to the LED VD1. Of course, it would be possible to eliminate the capacitor and resistor in the base circuit of the transistor, but then failure of VT1 and VD1 is possible when using branded batteries with low internal resistance. The resistor sets the operating mode of the transistor, and the capacitor passes the RF component.

The circuit used a KT315 transistor (as the cheapest) and a super-bright LED (as the brightest). Let's talk about the transformer separately. To make it, you will need a ferrite ring (approximate size 10x6x3 and permeability of about 1000 HH). Wire diameter is about 0.2 mm. Two coils of 20 turns each are wound on the ring. If you don’t have a ring, you can use a cylinder of similar volume and material. You just have to wind 60-100 turns for each of the coils. An important point: you need to wind the coils in different directions. At worst, you can use a nail, but a large nail, and about 150 turns are required for one coil. In addition, the efficiency of a nail is much lower than that of ferrite.

Let's move on to practice now.

Practice

Consider a photo of a flashlight. This is necessary to understand the meaning of my research. There is nothing futuristic here, I will only note that the switch is located in the “fountain pen” button, and the gray cylinder is metal and conducts current.

So, step one. We create the “body” of the device.

We make a cylinder according to the standard size of the battery. For example, the size of the batteries in my flashlight is AAA. It can be made from paper (like I did), or you can use a piece of any rigid tube. For gluing we use “rubber” glue, as it is a good dielectric.

We make holes along the edges of the cylinder, wrap it with tinned conductor, and pass the ends of the wire into the holes. We fix both ends, but leave a piece of conductor at one end so that we can connect the converter to the spiral. (The nut shown in the figure is not needed yet)

Now let's start assembling the converter itself. I didn’t have a ferrite ring (and it wouldn’t fit into the flashlight), so I used a cylinder made of a similar material.

The cylinder was removed from an inductor from an old TV. The first coil is carefully wound onto it. The coils are held together with glue. I got about 60 turns. Then the second one swings in the opposite direction. I got 60 or so again; I definitely didn’t count it - I couldn’t wind it neatly. Secure the edges with glue. Let's dry it. The coil can be slightly warmed up during the drying process. I placed it on a piece of paper on the shade of the table lamp. Let it dry. And we move on.

We assemble the converter according to the diagram:

Everything is located as in the figure: transistor, capacitor, resistor, etc. Passive and active elements have been assembled, we solder the spiral on the cylinder, the coil. The current in the coil windings must go in different directions! That is, if you wound all the windings in one direction, then swap the leads of one of them, otherwise generation will not occur.

We are happy because we got the following:

We insert everything inside, and use nuts as side plugs and contacts.

We solder the coil leads to one of the nuts, and the VT1 emitter to the other. Glue it. We mark the conclusions: where we have the output from the coils we put “-”, where the output from the transistor with the coil we put “+” (so that everything is like in a battery).

All. You get something similar to what is shown in the previous figure.

Now you need to make a “lampodiode”. We take a regular base from a used light bulb, and...

One point: there must be a minus LED on the base. Otherwise nothing will work.

There was another solution to the problem. Of course, you can directly create a converter module with an LED in one package. In this case, as you have probably already noticed, you only need two contacts. You can do it this way. But in this solution, the LEDs cannot be easily changed. Why change? It’s very simple, because you can use an ultraviolet LED to check the authenticity of banknotes and much more. In addition, I believe that my way of solving the problem is more ergonomic and interesting.

Assembly technique

As is clear from the figure, the converter is a “substitute” for the second battery. But unlike it, it has three points of contact: with the plus of the battery, with the plus of the LED, and the common body (through the spiral). However, its location in the battery compartment is specific: it must be in contact with the positive of the LED. To put it simply, the assembly sequence in the picture cannot be changed. Otherwise, as you may have guessed, the device will not work.

Upgraded flashlight in action:

This flashlight is more economical, ergonomic and, due to the absence of a second battery, lightweight. And the main advantage! All parts can be found in the trash!