Boost voltage converter for 1 watt LED. Several simple LED power circuits. Which stabilizer to use in a car

CONVERTER FOR LED

Incandescent lamps have been replaced by LEDs, which in many cases successfully replace them. But due to the nonlinear current-voltage characteristic, various voltage converters are used to power lighting LEDs from a battery. As you know, an LED is powered by a voltage of at least 2 V, and depending on the type, up to 3.5 V. In addition, at least a simple current stabilizer is needed, because as the battery capacity decreases, the brightness of the LED also decreases. Therefore, a simple power resistor, from a battery with an increased voltage, will work worse than a converter. Below are diagrams of simple converters that can be assembled even by beginners.

The circuit is powered by one AA battery and is a blocking generator. Increased voltage pulses appear on the collector, are rectified by a Schottky diode and charge the capacitor. Transformer T1 is wound manually on a ring core. To do this, take a ferrite ring K10x6x4 and wind two windings of 20 turns with PEL 0.3 wire. In general, the number of turns can be 6:10, 10:10, or 10:15. For the best efficiency and brightness, they must be selected experimentally. Everything that is available is used for the frame.

The circuit uses a low-dropout transistor to achieve maximum efficiency. The output current can be adjusted by resistor R1.

Next we see a somewhat complicated scheme with more stable generation. Current consumption 15 mA. The voltage converter is also made according to the circuit of a single-cycle generator with inductive feedback on a transistor and transformer. The winding data is the same.

The next modernization of this converter was a circuit from Chinese LED flashlight:

Here and in other circuits, a Schottky diode with a low voltage drop is used as a diode (after all, every half a volt counts). The diodes used are IN5817, 1GWJ43, 1SS319, or, as a last resort, the Soviet D311. These diodes can be taken from the power controller board of a non-working lithium-ion battery from a mobile phone.The following converter circuits are made on two transistors and are characterized by an increased output current - up to 25 mA. A correctly assembled converter does not need adjustment unless the transformer windings are reversed; otherwise, swap them.

The transformer used is similar, but the number of turns in the windings is 40. The transistors cost C2458 and C3279. Thanks to feedback on transistor C2458, simple stabilization of the current and, accordingly, the brightness of the LED is obtained.

Another version of the converter with two transistors:

There is no need to wind the transformer here, since a ready-made inductor of 300 - 1000 μH is used.

The last converter circuit was also copied from a Chinese LED lamp and works great when assembled.

The first turn on of a correctly assembled device must be carried out in test mode, in which power from the battery is supplied through a 10 Ohm resistor, so that the transistors do not burn out if the transformer terminals are connected incorrectly. If the LED does not light, it is necessary to swap the terminals of the primary or secondary winding of the transformer. If this does not help, check the serviceability of all elements and installation.

From personal experience I can note that in all the above circuits, domestic transistors KT315 - KT3102 are often successfully launched. The number of transformer windings should be selected for maximum brightness and efficiency. Ready-made “everything that came to hand” from various equipment was used as chokes. It is not recommended to install the cheapest (0.1 W) 5 mm LEDs. It’s better to pay extra and buy a 10 mm LED for 0.5 euros. The brightness will increase significantly. Even better results will be achieved after installing special

Without a doubt, LEDs are by far the most economical and durable light sources. Appeared in last years new devices of this class have made a kind of revolution in the field of lighting and illumination. LED lamps have become widespread in everyday life, coming along with compact fluorescent lamps (CFLs) to replace uneconomical and short-lived incandescent lamps, and today they are increasingly replacing CFLs.

Driver for LEDs

Unfortunately, despite manufacturers’ assurances of durability, estimated at many tens of thousands of hours, LED lamps sometimes fail, much more ahead of schedule. And the reason is often not the quality of the LEDs, but, most likely, the stinginess of manufacturers: in order to save on the cost of lamps, the LEDs in them are forced to work in extreme conditions, at current values close to the maximum permissible, which has a noticeable effect on the rate of degradation of the crystal and phosphors, as well as on the reliability of the lamp. And if you consider that due to the small dimensions of the lamps, unsatisfactory cooling conditions for LEDs are added to the above, it is not surprising that sometimes such lamps fail after just a few hours of operation.

Analysis of faults of burnt-out lamps shows that in 90% of cases one of the LEDs fails, while the driver, as a rule, remains operational. Repairing such lamps is simple, but without taking measures to reduce the current through the remaining LEDs it is often useless: after some time the lamp fails again. Consider the possibility of restoring a 7 W Elektrostandard lamp. Her appearance and a view of the driver board from the side of the printed conductors are shown on the Radiochipi website. First, you should find the burnt-out LED in any way and close it with a jumper. Next, you need to reduce the current through the LEDs. To control the current, a sensor is used, consisting of two SMD resistors connected in parallel (circled in red in Fig. 1).

To reduce the current, you need to unsolder them and solder a new one with a resistance of 2 Ohms in place of any of them. After such repairs, the power and luminous output of the lamp will decrease somewhat, but it will still be able to work long time. The above is fully applicable to similar 15 W lamps (Fig. 2). On their board, to reduce the current through the LEDs, you need to unsolder one of the 5.6 Ohm resistors (also circled in red). But sometimes it is impossible to restore the lamp due to a controller failure. In this case, the LEDs can be powered from another source.

Below we consider the option of connecting a board of LED lamps with a power of 5 or 7 W to a twelve-volt source (for example, car battery). Depending on the rated power, these lamps have 12 or 16 LEDs installed, respectively. Such a lamp can be useful for an emergency or car lamp. Since the LEDs are connected in series on the board, and I didn’t want to change the connection diagram by cutting printed conductors and installing wire jumpers, it was decided to make a converter that increases the battery voltage to the level necessary for the LEDs to glow with normal brightness (in this case, up to 35 or 48 V, respectively) ).

The diagram of a simple converter assembled from widely available and inexpensive parts is shown in Fig. 3 Using a Schmitt trigger DD 1.1, a master oscillator operating at a frequency of about 25 kHz is built according to a standard circuit. Elements DD1.2-DD1.6 connected in parallel invert the generator signal and increase its load capacity, providing fast charging and discharging of the capacitance of field-effect transistor VT2. The microcircuit is powered from the lamp power supply through a linear voltage regulator 0A1, connected according to a standard circuit. The current sensor is resistor R5.
The stabilization circuit works as follows.

If the current through the LEDs becomes more than required. transistor VT1 opens, shunting the input of the Schmitt trigger DD1.1 with resistor R1. In this case, the duration of the control pulses supplied to the gate of the field-effect transistor VT2. decreases, and the duration of pauses between them, on the contrary, increases. 8 As a result, the current through the LEDs decreases. Current stabilization is carried out in the range of input voltage values from 9 to 15 V, which is quite enough for a battery and car lamp. Resistor R3 serves to discharge capacitor C4 after turning off the converter (without it, the LEDs would glow faintly for a long time after turning off the power).

All parts of the device are placed on a printed circuit board (Fig. 4), made of fiberglass foil on one side. Transistor VT2 does not need a heat sink, but if its body heats up noticeably during operation, you can, in addition to the contact pad on the board used as a heat sink, to which its drain pin is soldered, provide it with a small U-shaped heat sink made from a flattened piece of copper wires with a cross section of 2.5 mm2 and a length of 20 mm. You can solder it either to the indicated area on the board (next to the transistor) or to the heat-sinking flange of the transistor itself.

The appearance of the finished unit is shown in Fig. 5. The additional heat sink for the LED panel is made of aluminum alloy sheet, its appearance is also shown in this picture. A few words about the details. In addition to what is indicated in the diagram, any low-power transistor can be used as VT1 structures p-p-p for surface mounting. Field-effect transistor (VT2) - any with a drain current of at least 2 A and a drain-source voltage of at least 80 V, designed to control logical levels. Possible replacement 74NST14 (DD1) microcircuits - from the 74NS14 or 74AC14 series. Instead of the RGP10J (VD1) diode, you can use a 1N4007, but it will heat up noticeably and the efficiency will decrease. Diodes of the KD226 series operate practically without heating. Throttle L1 is industrially manufactured in a cylindrical body, its type is unknown, and its appearance is shown in Fig. 5 (black cylinder in the lower left corner of the board).

If you cannot find a 5 V SMD integrated stabilizer, 8 power supply circuit of the DD1 microcircuit can be built in a parametric stabilizer on a zener diode. You can place it and a ballast resistor with a resistance of 1 kOhm on the microcircuit seat.
A device assembled from serviceable parts requires virtually no adjustment. When you first turn on the converter, it is advisable to power it from a laboratory unit with an adjustable output voltage, gradually increasing it, starting from 5 V. If the LEDs do not light, you should check the polarity of their connection and the serviceability of the parts.

When using replacement microcircuits instead of those indicated in the diagram (DD1), it may be necessary to select capacitor C1 or inductor L1 for maximum efficiency. It may be necessary to select resistor R5 to obtain a current through the LEDs equal to 100 mA. If you don’t find the required resistor among those available, you can install R5 of obviously slightly higher resistance and select an additional resistor R5 connected in parallel to it (shown in the diagram with dashed lines), a place is provided for it on the board.

Next, you should check the interval of input voltage signs at which the current is stabilized through the LEDs. You can try to increase the efficiency of the converter by selecting the inductance of inductor L1. When setting up, you should remember that an open LED circuit can lead to breakdown of the field-effect transistor, so you need to be very careful. Finally, the converter board should be coated with two layers of XB-784 varnish, this will protect it from moisture. When operating such a lamp, remember that when connecting it to a power source, the polarity must be observed.

Flashlight on the power source

Flashlight on a current source, with automatic equalization of current in LEDs, so that LEDs can have any range of parameters (LED VD2 sets the current, which is repeated by transistors VT2, VT3, so the currents in the branches will be the same)
The transistors, of course, should also be the same, but the spread of their parameters is not so critical, so you can take either discrete transistors, or if you can find three integrated transistors in one package, their parameters are as identical as possible. Play around with the placement of the LEDs, you need to choose an LED-transistor pair so that the output voltage is minimal, this will increase the efficiency.
The introduction of transistors leveled the brightness, however, they have resistance and the voltage drops across them, which forces the converter to increase the output level to 4V. To reduce the voltage drop across the transistors, you can propose the circuit in Fig. 4, this is a modified current mirror, instead reference voltage Ube = 0.7V in the circuit in Fig. 3, you can use the 0.22V source built into the converter, and maintain it in the VT1 collector using an op-amp, also built into the converter.

Rice. 4.Flashlight on a current source, with automatic current equalization in LEDs, and with improved efficiency

Because The op-amp output is of the “open collector” type; it must be “pulled up” to the power supply, which is done by resistor R2. Resistances R3, R4 act as a voltage divider at point V2 by 2, so the opamp will maintain a voltage of 0.22*2 = 0.44V at point V2, which is 0.3V less than in the previous case. It is not possible to take an even smaller divider in order to lower the voltage at point V2. a bipolar transistor has a resistance Rke and during operation the voltage Uke will drop on it, in order for the transistor to work correctly V2-V1 must be greater than Uke, for our case 0.22V is quite enough. However, bipolar transistors can be replaced by field-effect transistors, in which the drain-source resistance is much lower, this will make it possible to reduce the divider, so as to make the difference V2-V1 very insignificant.

Throttle.The throttle must be taken with minimal resistance, Special attention The maximum permissible current should be taken into account; it should be about 400 -1000 mA.
The rating doesn't matter as much as the maximum current, so Analog Devices recommends something between 33 and 180 µH. In this case, theoretically, if you do not pay attention to the dimensions, then the greater the inductance, the better in all respects. However, in practice this is not entirely true, because we do not have an ideal coil, it has active resistance and is not linear, in addition, the key transistor at low voltages will no longer produce 1.5A. Therefore, it is better to try several coils of different types, designs and different ratings in order to choose the coil with the highest efficiency and the lowest minimum input voltage, i.e. a coil with which the flashlight will glow for as long as possible.

Capacitors.C1 can be anything. It is better to take C2 with tantalum because It has low resistance, which increases efficiency.

Schottky diode.Any for current up to 1A, preferably with minimal resistance and minimal voltage drop.

Transistors.Any with a collector current of up to 30 mA, coefficient. current amplification of about 80 with a frequency of up to 100 MHz, KT318 is suitable.

LEDs.You can use white NSPW500BS with a glow of 8000 mcd from Power Light Systems.

Voltage transformerADP1110, or its replacement ADP1073, to use it, the circuit in Fig. 3 will need to be changed, take a 760 µH inductor, and R1 = 0.212/60mA = 3.5 Ohm.

Flashlight on ADP3000-ADJ

Options:
Power supply 2.8 - 10 V, efficiency approx. 75%, two brightness modes - full and half.
The current through the diodes is 27 mA, in half-brightness mode - 13 mA.
In order to obtain high efficiency, it is advisable to use chip components in the circuit.
A correctly assembled circuit does not need adjustment.
The disadvantage of the circuit is the high (1.25V) voltage at the FB input (pin 8).
Currently, DC/DC converters with an FB voltage of about 0.3V are produced, in particular from Maxim, on which it is possible to achieve an efficiency above 85%.

Flashlight diagram for Kr1446PN1.

Resistors R1 and R2 are a current sensor. Operational amplifier U2B - amplifies the voltage taken from the current sensor. Gain = R4 / R3 + 1 and is approximately 19. The gain required is such that when the current through resistors R1 and R2 is 60 mA, the output voltage turns on transistor Q1. By changing these resistors, you can set other stabilization current values.
In principle, there is no need to install an operational amplifier. Simply, instead of R1 and R2, one 10 Ohm resistor is placed, from it the signal through a 1 kOhm resistor is supplied to the base of the transistor and that’s it. But. This will lead to a decrease in efficiency. On a 10 Ohm resistor at a current of 60 mA, 0.6 Volt - 36 mW - is dissipated in vain. If an operational amplifier is used, the losses will be:
on a 0.5 Ohm resistor at a current of 60 mA = 1.8 mW + consumption of the op-amp itself is 0.02 mA let at 4 Volts = 0.08 mW
= 1.88 mW - significantly less than 36 mW.

About the components.

Any low-power op-amp with a low minimum supply voltage can work in place of the KR1446UD2; the OP193FS would be better suited, but it is quite expensive. Transistor in SOT23 package. A smaller polar capacitor - type SS for 10 Volts. The inductance of CW68 is 100 μH for a current of 710 mA. Although the cutoff current of the inverter is 1 A, it works fine. It achieved the best efficiency. I selected the LEDs based on the most equal voltage drop at a current of 20 mA. The flashlight is assembled in a housing for two AA batteries. I shortened the space for the batteries to fit the size of AAA batteries, and in the freed-up space I assembled this circuit using wall-mounted installation. A case that fits three AA batteries works well. You will need to install only two, and place the circuit in place of the third.

Efficiency of the resulting device.
Input U I P Output U I P Efficiency
Volt mA mW Volt mA mW %
3.03 90 273 3.53 62 219 80
1.78 180 320 3.53 62 219 68
1.28 290 371 3.53 62 219 59

Replacing the bulb of the "Zhuchek" flashlight with a module from the companyLuxeonLumiledLXHL-NW 98.
We get a dazzlingly bright flashlight, with a very light press (compared to a light bulb).

Rework scheme and module parameters.

StepUP DC-DC converters ADP1110 converters from Analog devices.

Power supply: 1 or 2 1.5V batteries, operability maintained up to Uinput = 0.9V
Consumption:
*with switch open S1 = 300mA
*with switch closed S1 = 110mA

LED Electronic Flashlight
Powered by just one AA or AAA AA battery on a microcircuit (KR1446PN1), which is a complete analogue of the MAX756 (MAX731) microcircuit and has almost identical characteristics.

The flashlight is based on a flashlight that uses two AA size AA batteries as a power source.
The converter board is placed in the flashlight instead of the second battery. A contact made of tinned sheet metal is soldered at one end of the board to power the circuit, and at the other there is an LED. A circle made of the same tin is placed on the LED terminals. The diameter of the circle should be slightly larger than the diameter of the reflector base (0.2-0.5 mm) into which the cartridge is inserted. One of the diode leads (negative) is soldered to the circle, the second (positive) goes through and is insulated with a piece of PVC or fluoroplastic tube. The purpose of the circle is twofold. It provides the structure with the necessary rigidity and at the same time serves to close the negative contact of the circuit. The lamp with the socket is removed from the lantern in advance and a circuit with an LED is placed in its place. Before installation on the board, the LED leads are shortened in such a way as to ensure a tight, play-free fit “in place.” Typically, the length of the leads (excluding soldering to the board) is equal to the length of the protruding part of the fully screwed-in lamp base.
The connection diagram between the board and the battery is shown in Fig. 9.2.
Next, the lantern is assembled and its functionality is checked. If the circuit is assembled correctly, then no settings are required.

The design uses standard installation elements: capacitors of the K50-35 type, EC-24 chokes with an inductance of 18-22 μH, LEDs with a brightness of 5-10 cd with a diameter of 5 or 10 mm. Of course, it is possible to use other LEDs with a supply voltage of 2.4-5 V. The circuit has sufficient power reserve and allows you to power even LEDs with a brightness of up to 25 cd!

About some test results of this design.
The flashlight modified in this way worked with a “fresh” battery without interruption, in the on state, for more than 20 hours! For comparison, the same flashlight in the “standard” configuration (that is, with a lamp and two “fresh” batteries from the same batch) worked for only 4 hours.
And one more important point. If you use rechargeable batteries in this design, it is easy to monitor the state of their discharge level. The fact is that the converter on the KR1446PN1 microcircuit starts stably at an input voltage of 0.8-0.9 V. And the glow of the LEDs is consistently bright until the voltage on the battery reaches this critical threshold. The lamp will, of course, still burn at this voltage, but we can hardly talk about it as a real light source.

Rice. 9.2Figure 9.3

The printed circuit board of the device is shown in Fig. 9.3, and the arrangement of elements is in Fig. 9.4.

Turning the flashlight on and off with one button

The circuit is assembled using a CD4013 D-trigger chip and an IRF630 field-effect transistor in the “off” mode. the current consumption of the circuit is practically 0. For stable operation of the D-trigger, a filter resistor and capacitor are connected to the input of the microcircuit; their function is to eliminate contact bounce. It is better not to connect unused pins of the microcircuit anywhere. The microcircuit operates from 2 to 12 volts; any powerful field-effect transistor can be used as a power switch, because The drain-source resistance of the field-effect transistor is negligible and does not load the output of the microcircuit.

CD4013A in SO-14 package, analogue of K561TM2, 564TM2

Simple generator circuits.
Allows you to power an LED with an ignition voltage of 2-3V from 1-1.5V. Short pulses of increased potential unlock p-n junction. The efficiency of course decreases, but this device allows you to “squeeze” almost its entire resource from an autonomous power source.
Wire 0.1 mm - 100-300 turns with a tap from the middle, wound on a toroidal ring.

LED flashlight with adjustable brightness and Beacon mode

The power supply of the microcircuit - generator with adjustable duty cycle (K561LE5 or 564LE5) that controls the electronic key, in the proposed device is carried out from a step-up voltage converter, which allows the flashlight to be powered from one 1.5 galvanic cell.
The converter is made on transistors VT1, VT2 according to the circuit of a transformer self-oscillator with positive current feedback.
The generator circuit with adjustable duty cycle on the K561LE5 chip mentioned above has been slightly modified in order to improve the linearity of current regulation.
The minimum current consumption of a flashlight with six super-bright white LEDs L-53MWC from Kingbnght connected in parallel is 2.3 mA. The dependence of the current consumption on the number of LEDs is directly proportional.
The "Beacon" mode, when the LEDs flash brightly at a low frequency and then go out, is implemented by setting the brightness control to maximum and turning the flashlight on again. The desired frequency of light flashes is adjusted by selecting the capacitor SZ.
The performance of the flashlight is maintained when the voltage is reduced to 1.1v, although the brightness is significantly reduced
A field-effect transistor with an insulated gate KP501A (KR1014KT1V) is used as an electronic switch. According to the control circuit, it matches well with the K561LE5 microcircuit. The KP501A transistor has the following limit parameters: drain-source voltage - 240 V; gate-source voltage - 20 V. drain current - 0.18 A; power - 0.5 W
It is permissible to connect transistors in parallel, preferably from the same batch. Possible replacement - KP504 with any letter index. For IRF540 field-effect transistors, the supply voltage of the DD1 microcircuit. generated by the converter must be increased to 10 V
In a flashlight with six L-53MWC LEDs connected in parallel, the current consumption is approximately equal to 120 mA when the second transistor is connected in parallel to VT3 - 140 mA
Transformer T1 is wound on a ferrite ring 2000NM K10-6"4.5. The windings are wound in two wires, with the end of the first winding connected to the beginning of the second winding. The primary winding contains 2-10 turns, the secondary - 2 * 20 turns. Wire diameter - 0.37 mm. grade - PEV-2. The choke is wound on the same magnetic circuit without a gap with the same wire in one layer, the number of turns is 38. The inductance of the choke is 860 μH

One day, on the Internet, I came across a fairly simple converter circuit for powering LEDs from one AA battery. After assembly, I was upset because the circuit turned out to be inoperative. In half an hour, the circuit was brought into working condition, the ratings of the radio components were changed, and unnecessary parts were removed, and the result was a fairly high-quality converter that is capable of powering LEDs with a power of up to 1 Watt.

The circuit itself consists of 4 parts and a throttle. Fortunately, a ready-made SMD choke was found (soldered from the radiotelephone board), but making it is also not a problem. The choke can be made on a ring from fluorescent lamps (available on all energy saving boards), contains 15 turns of wire 0.15 - 0.2 mm.

Unfortunately, I never found a direct conduction transistor in the SMD version and a powerful bipolar transistor of the KT818 series was used, but for compactness I highly recommend using SMD transistors. The second reverse conduction transistor, literally any one will do, for example the well-known KT315.

The basic resistor is 1 kilo-ohm, it is also advisable to use it in the SMD version.
A 1000 picofarad capacitor is not critical, you can deviate by 50% in one direction or another (it worked for me even with a 0.1 microfarad capacitor, but the LED will glow weaker).

For demonstration, the circuit was assembled on a breadboard. The current consumption is 35 - 40 mA, but it increases sharply if you power the LEDs at 1 watt; the circuit does not allow more, since the maximum output current at peak is 300 mA.

The circuit starts at 0.7 volts. The maximum supply voltage is no more than 2.5 volts; if you supply more, the circuit simply will not work. The output voltage is 3.8 volts at the specified inductor parameters.

List of radioelements

Designation	Type	Denomination	Quantity	My notepad
	Bipolar transistor	KT315A	1	To notepad
	Bipolar transistor	KT818A	1	To notepad
C1	Capacitor	1 nF	1	To notepad
	Resistor	1 kOhm	1	To notepad
L1	Inductor		1	To notepad
HL1	Light-emitting diode		1

Without a doubt, LEDs are by far the most economical and durable light sources. New devices of this class that have appeared in recent years have produced a kind of revolution in the field of lighting and illumination. LED lamps have become widespread in everyday life, coming along with compact fluorescent lamps (CFLs) to replace uneconomical and short-lived incandescent lamps, and today they are increasingly replacing CFLs. Unfortunately, despite manufacturers’ assurances of durability, estimated at many tens of thousands of hours, LED lamps sometimes fail, much earlier than expected. And the reason is often not the quality of the LEDs, but, most likely, the stinginess of manufacturers: in order to save on the cost of lamps, the LEDs in them are forced to work under extreme conditions, at current values close to the maximum permissible, which has a noticeable effect on the rate of degradation of the crystal and phosphors, as well as lamp reliability. And if you consider that due to the small dimensions of the lamps, unsatisfactory cooling conditions for LEDs are added to the above, it is not surprising that sometimes such lamps fail after just a few hours of operation.

Consider the possibility of restoring a 7 W Elektrostandard lamp. Its appearance and the view of the driver board from the side of the printed conductors are shown in Fig. 1. First, you should find the burnt-out LED in any way and close it with a jumper. Next, you need to reduce the current through the LEDs. To monitor the current, a sensor consisting of two SMD resistors connected in parallel is used (circled in red in Fig. 1). To reduce the current, you need to unsolder them and solder a new one with a resistance of 2 Ohms in place of any of them. After such repairs, the power and luminous output of the lamp will decrease somewhat, but it will be able to work for a long time. The above is fully applicable to similar 15 W lamps (Fig. 2). On their board, to reduce the current through the LEDs, you need to unsolder one of the 5.6 Ohm resistors (also circled in red).

Rice. 1. Elektrostandard lamp

Rice. 2. Elektrostandard lamp

But sometimes it is impossible to restore the lamp due to a controller failure. In this case, the LEDs can be powered from another source. Below we consider the option of connecting a board of LED lamps with a power of 5 or 7 W to a twelve-volt source (for example, a car battery). Depending on the rated power, these lamps have 12 or 16 LEDs installed, respectively. Such a lamp can be useful for an emergency or car lamp. Since the LEDs are connected in series on the board, and I didn’t want to change the connection diagram by cutting printed conductors and installing wire jumpers, it was decided to make a converter that increases the battery voltage to the level necessary for the LEDs to glow with normal brightness (in this case, up to 35 or 48 V, respectively). ).

A diagram of a simple converter assembled from widely available and inexpensive parts is shown in Fig. 3. Using a Schmitt trigger DD1.1, a master oscillator operating at a frequency of about 25 kHz is built according to a standard circuit. Elements DD1.2-DD1.6 connected in parallel invert the generator signal and increase its load capacity, providing fast charging and discharging of the capacitance of field-effect transistor VT2. The microcircuit is powered from the lamp power supply through a linear voltage regulator DA1, connected according to a standard circuit. The current sensor is resistor R5.

Rice. 3. Circuit of a simple converter

The stabilization circuit works as follows. If the current through the LEDs becomes greater than required, transistor VT1 opens, shunting the input of the Schmitt trigger DD1.1 with resistor R1. In this case, the duration of the control pulses supplied to the gate of the field-effect transistor VT2 decreases, and the duration of the pauses between them, on the contrary, increases. As a result, the current through the LEDs decreases. Current stabilization is carried out in the range of input voltage values from 9 to 15 V, which is quite sufficient for a battery and car lamp. Resistor R3 serves to discharge capacitor C4 after turning off the converter (without it, the LEDs would glow faintly for a long time after turning off the power).

All parts of the device are placed on a printed circuit board (Fig. 4), made of fiberglass foil on one side. Transistor VT2 does not need a heat sink, but if its body heats up noticeably during operation, you can, in addition to the contact pad on the board used as a heat sink, to which its drain pin is soldered, provide it with a small U-shaped heat sink made from a flattened piece of copper wires with a cross section of 2.5 mm 2 and a length of 20 mm. You can solder it either to the indicated area on the board (next to the transistor) or to the heat-sinking flange of the transistor itself. The appearance of the finished unit is shown in Fig. 5. The additional heat sink for the LED panel is made of aluminum alloy sheet, its appearance is also shown in this picture.

Rice. 4. Printed board and parts on it

Rice. 5. Appearance of the finished unit

A few words about the details. In addition to what is indicated in the diagram, any low-power transistor can be used as VT1 n-p-n structures for surface mounting. Field-effect transistor (VT2) - any with a drain current of at least 2 A and a drain-source voltage of at least 80 V, designed to control logical levels. Possible replacement of the 74НСТ14 (DD1) microcircuit - from the 74НСТ14 or 74АС14 series. Instead of the RGP10J (VD1) diode, you can use a 1N4007, but it will heat up noticeably and the efficiency will decrease. Diodes of the KD226 series operate practically without heating. Throttle L1 is industrially manufactured in a cylindrical body, its type is unknown, and its appearance is shown in Fig. 5 (black cylinder in the lower left corner of the board).

If you cannot find a 5 V SMD integrated stabilizer, you can build a parametric stabilizer on a zener diode into the power circuit of the DD1 microcircuit. You can place it and a ballast resistor with a resistance of 1 kOhm on the microcircuit seat.

A device assembled from serviceable parts requires virtually no adjustment. When you first turn on the converter, it is advisable to power it from a laboratory unit with an adjustable output voltage, gradually increasing it, starting from 5 V. If the LEDs do not light, you should check the polarity of their connection and the serviceability of the parts.

Next, you should check the range of input voltage values at which the current is stabilized through the LEDs. You can try to increase the efficiency of the converter by selecting the inductance of inductor L1. When setting up, you should remember that an open LED circuit can lead to breakdown of the field-effect transistor, so you need to be very careful.

Finally, the converter board should be coated with two layers of XB-784 varnish, this will protect it from moisture. When operating such a lamp, remember that when connecting it to a power source, the polarity must be observed.