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Homemade driver for LED flashlight. Economic feasibility of using a “driver” in an LED flashlight? Important assembly details

The first part is about tuning and repairing a flashlight, introductory. Here we will consider the general structure of the average flashlight, the parameters of powerful LEDs and a bit of tedious mathematics associated with them.

So, you have an LED flashlight, but it’s burned out or you’re not satisfied with the brightness, or you want to convert it into a weapon flashlight. What options do you have? Let's figure it out.

Design of a spherical lantern in a vacuum.

The vast majority of flashlights consist of the following parts:

  1. body - a regular tube with threaded ends;
  2. battery - lives inside the case;
  3. end button - screwed into the body on a thread and used to turn on the flashlight. Sometimes the flashlight can be equipped with a second backdrop with a remote button;
  4. The head of the flashlight is screwed into the body and has a protective glass in front. Sometimes this part is collapsible (as in the photo, in two parts), sometimes not;
  5. light-emitting element - an LED unit, a light beam shaper, an LED heat sink and an LED driver combined into one unit. Sometimes it is produced integrally with the lantern head.

Light emitting element.

This same assembly can be of different designs. Heads for the Ultrafire WF-502B flashlight are very common, they are even sold in different types, different powers, with a bunch of functions, etc.
For example, fasttech.com. Flashlights with this type of element are good because you can buy several modules for different tasks and simply change them.

We’ll leave the LED alone for now, it deserves a separate consideration below, the driver too, in principle, but we’ll now look at the remaining details.

There are three types of light beam shaper:

1. lens- the simplest and least effective option, since not all of the crystal’s radiation is collected in the light beam. Very often the lens can be moved, changing the focusing of the light beam, which is the only advantage of this solution.


2. collimator- a part made of transparent plastic, made to obtain a beam with specified parameters. To do this, the collimator is made in such a way as to correspond to a certain design of the lens on the LED, so it will not be possible to install a collimator from one LED to an LED of another design - the parameters of the light beam will be different.

3. reflector- a design that comes from incandescent lamps and is adapted for LEDs. Simple, reliable and time-tested design. In general, the reflector, like the collimator, is optimized for a specific LED, but with less criticality. The right photo shows that the LED crystal is reflected by the entire area of ​​the reflector.

In practice, replacing the LED is quite possible, as is replacing the reflector. They come with a smooth surface, which gives a harder beam, and with a lumpy surface; I liked the latter better indoors.


The heat sink, also known as the housing, to which the reflector is often screwed and into which the LED driver is mounted. Typically, it is designed to install an LED on a substrate - an aluminum plate to which the LED is soldered. The photo shows all the mechanical components of the module. From left to right: reflector, heat sink, spring for the negative terminal (in contact with the flashlight body) and spring for the positive terminal (in contact with the battery positive). The last spring is soldered to the LED driver board.

LED parameters.


The main parameters in terms of lighting quality are the emission spectrum and brightness. , structurally this is determined by the quality and tricks of the phosphor. Alas, this parameter can vary greatly even for different series of the same manufacturer. And even Liao himself doesn’t know what Uncle Liao is spreading in his basement. Cheap flashlights with a hundred or so lumens are confidently inferior in terms of lighting quality (how the details of the illuminated object are clearly visible and how generally these details are legible to the eye) even with not very powerful halogen flashlights.

Serious guys represented by Cree provide the following graph for the emission of their XM-L series LEDs. Alas, these are average values; we don’t really know how uniform it is, whether there are dips there. Horizontal wavelength, vertical relative radiation power.


The graph shows three curves - for different color temperatures. It can be seen that LEDs with a lower temperature (red) penetrate into the infrared region (wavelength greater than 740 nm), but very, very little and not far away - only a few percent of the power is emitted there. This is the reason that it is impossible to make a decent IR flashlight out of any white LED flashlight by simply adding an IR filter (as is easily done with an incandescent flashlight). Formally it will shine, but the efficiency is non-existent.
Color temperature is a companion parameter directly related to the spectrum. Color temperature is defined as the temperature of a completely black body (such a cunning fetish of physicists) at which it emits radiation of the same color tone as the radiation in question. For daylight it is 6500K, for incandescent lamps 2700-4000K. The lower the color temperature, the more yellow the light has.

According to personal observations, with LEDs with a lower color temperature, the details of the illuminated objects are better visible. At least for me. The disadvantage of warm white LEDs is their lower light output - they are less bright than their more “sultry” counterparts.

The second thing we are interested in is the brightness of the LED. Indicated in the documentation as brightness at a certain current through the LED. For example, for the already mentioned XM-L, the brightness of different currents is indicated. For example, XM-L T6 at 700mA (2W) has a luminous flux of 280 lumens (400 lm/A), at 1A it has 388 lm (388 lm/A), at 1.5A - 551 lm (367 lm/A), at 2A - 682 lm (341 lm/A). The specific brightness depending on the current is indicated in brackets. It drops by 17% when the current increases from 700mA to 2A. That is, the higher the current, the lower this specific brightness, that is, the lower the efficiency. By the way, it’s honestly clear from the schedule.


Another important parameter of an LED is its power. This is the maximum power that can be pumped into it. Of course, at maximum it will live less than at lower power, so it is better to “underfeed” it a little. In turn, power determines the maximum current through the LED. As a rule, the power and current through the LED are related by a nonlinear relationship, since they also depend on the voltage drop across the diode. Here's for XM-L: horizontally the forward voltage drop, vertically the current through the diode.


The voltage drop across an LED is typically on the order of 3 volts for a white LED and depends on the current through the LED. Let's look at the graph: at 200mA we have a drop of 2.7V, at 700mA - 2.9V, at 1A - 2.97V, at 1.5A - 3.1V, at 2A - 3.18V.

If you take tricky MC-E type LEDs with four crystals it will be 350mA - 3.1V, 700mA - 3.5V. Very powerful crystals of 10-20 W will have a voltage drop of about 10V, and even more powerful ones... well, maybe even more.

By the way, if we convert the specific luminosity depending on the current of these XM-Ls into luminosity depending on the power, we get that with a current I = 700 mA and a voltage drop U = 2.9 V, the power consumption is 2.03 W, and the luminous flux 280lm, that is 138 lm/W. We continue further and get 130, 118.5 and 107 lm/W for 1, 1.5 and 2 A current, respectively. The difference is 29%. So you're racking your brains about which mode to choose.

What does knowledge give us? At least an understanding of what kind of power a particular LED should have, what can be obtained from it, and what other LED can be used to replace a burnt-out flashlight LED. But the picture will not be complete without knowledge about LED power supply.

Flashlight power supply.


As a rule, flashlights use either lithium batteries (nominal voltage 3V, the same as the maximum and drops slightly when discharged) or lithium batteries (nominal voltage 3.7 V, and the minimum and maximum are approximately 3.2 and 4.2 V, You can read about batteries, there is information about the types and their differences).

By the way, I would avoid batteries like those in the photo above if possible. Low quality and greatly overestimated capacity (out of the declared 2500 mAh it would be good if there were 1800). It is better to take branded cells from Samsung and others. Good battery cells can be obtained from their laptop batteries - even those tortured by Narzan, they will be better than the Chinese ones. Although, even the Chinese have normal cells “inside”.

Sometimes AA batteries are used in LED flashlights, but they are not good at delivering the current needed to power powerful LEDs. That is, if the flashlight still has AA batteries, then it won’t be particularly possible to fix the problem with low brightness.

Drivers.

The vast majority of flashlights have one LED on board with a power of about 3 W. That is, it has a voltage drop of about 3 V and a current of about 1 A. To power such flashlights, one Li-Ion (or Li-Po) battery is sufficient. Such lamps can contain any driver circuits, even ordinary voltage-damping current sources. When installing lithium batteries, you will need as many as two of them, and the efficiency will drop catastrophically. It’s good that normal pulsed LED drivers have almost completely replaced cheap current sources. Flashlights that use multiple cells or batteries must have a pulse driver.

You can determine which driver is in front of you by the presence of a coil. If it exists, it's probably pulse driver. How good is it and what input voltage ranges does it tolerate? Here you will have to look for documentation for the microcircuit used in it. For example, for the middle driver in the photo above (sorry, it turned out badly), under a magnifying glass you can see the markings of the 2541B microcircuit and we managed to find documentation for it (in Chinese), it has an input voltage of 5 to 40 volts, but the efficiency is not indicated. In total, if we take a top-end LED with an efficiency of 30-40% and a good pulse driver (the efficiency will be about 90% in an ideal case), we get a flashlight efficiency of 27-36%. Not too bad.

And an example linear driver in the same photo in the lower right corner. All electronic components come down to a protective diode and several parallel operating linear current sources. You can estimate its efficiency as the ratio of the output voltage to the input voltage. If we power the circuit from a battery, we get a maximum voltage of 4.2V, a nominal voltage of 3.7V. Most likely it will not reach the minimum - the driver needs a minimum voltage drop of half a volt to work. So, we consider 3/4.2 = 70%. However, since it will shut up without using the battery, it must be used with a pair of lithium batteries (2 to 3V). Then the efficiency will be 3/6=50%. Not very curly, considering the efficiency of the crystal is 20-30% and, as a consequence, the efficiency of the entire flashlight is 10-15%. I hope it is clear that linear drivers should be avoided?...

Drivers are often installed in flashlights that support several operating modes- full power, average, reduced and all sorts of blinkers. In the photo there is such a driver at the bottom left. Moreover, in cheap models these modes are switched by briefly opening the circuit. That is, you lightly press the button - the flashlight goes out and when released it works in a new mode. I can’t stand them; for me, no mode switch is better than this one.

Not always, but in some models it is possible to wean the flashlight from this behavior and convert it to work with a remote button (in the form of a weapon flashlight). But this is a separate topic.

The standard RT4115 LED driver circuit is shown in the figure below:

The supply voltage should be at least 1.5-2 volts higher than the total voltage across the LEDs. Accordingly, in the supply voltage range from 6 to 30 volts, from 1 to 7-8 LEDs can be connected to the driver.

Maximum supply voltage of the microcircuit 45 V, but operation in this mode is not guaranteed (better pay attention to a similar microcircuit).

The current through the LEDs has a triangular shape with a maximum deviation from the average value of ±15%. The average current through the LEDs is set by a resistor and calculated by the formula:

I LED = 0.1 / R

The minimum permissible value is R = 0.082 Ohm, which corresponds to a maximum current of 1.2 A.

The deviation of the current through the LED from the calculated one does not exceed 5%, provided that resistor R is installed with a maximum deviation from the nominal value of 1%.

So, to turn on the LED at constant brightness, we leave the DIM pin hanging in the air (it is pulled up to the 5V level inside the PT4115). In this case, the output current is determined solely by resistance R.

If we connect a capacitor between the DIM pin and ground, we get the effect of smooth lighting of the LEDs. The time it takes to reach maximum brightness will depend on the capacitor capacity; the larger it is, the longer the lamp will light up.

For reference: Each nanofarad of capacitance increases the turn-on time by 0.8 ms.

If you want to make a dimmable driver for LEDs with brightness adjustment from 0 to 100%, then you can resort to one of two methods:

  1. First way assumes that a constant voltage in the range from 0 to 6V is supplied to the DIM input. In this case, brightness adjustment from 0 to 100% is carried out at a voltage at the DIM pin from 0.5 to 2.5 volts. Increasing the voltage above 2.5 V (and up to 6 V) does not affect the current through the LEDs (the brightness does not change). On the contrary, reducing the voltage to a level of 0.3V or lower leads to the circuit turning off and putting it into standby mode (the current consumption drops to 95 μA). Thus, you can effectively control the operation of the driver without removing the supply voltage.
  2. Second way involves supplying a signal from a pulse-width converter with an output frequency of 100-20000 Hz, the brightness will be determined by the duty cycle (pulse duty cycle). For example, if the high level lasts 1/4 of the period, and the low level, respectively, 3/4, then this will correspond to a brightness level of 25% of the maximum. You must understand that the driver operating frequency is determined by the inductance of the inductor and in no way depends on the dimming frequency.

The PT4115 LED driver circuit with constant voltage dimmer is shown in the figure below:

This circuit for adjusting the brightness of LEDs works great due to the fact that inside the chip the DIM pin is “pulled up” to the 5V bus through a 200 kOhm resistor. Therefore, when the potentiometer slider is in its lowest position, a voltage divider of 200 + 200 kOhm is formed and a potential of 5/2 = 2.5V is formed at the DIM pin, which corresponds to 100% brightness.

How the scheme works

At the first moment of time, when the input voltage is applied, the current through R and L is zero and the output switch built into the microcircuit is open. The current through the LEDs begins to gradually increase. The rate of current rise depends on the magnitude of the inductance and supply voltage. The in-circuit comparator compares the potentials before and after resistor R and, as soon as the difference is 115 mV, a low level appears at its output, which closes the output switch.

Thanks to the energy stored in the inductance, the current through the LEDs does not disappear instantly, but begins to gradually decrease. The voltage drop across the resistor R gradually decreases. As soon as it reaches a value of 85 mV, the comparator will again issue a signal to open the output switch. And the whole cycle repeats all over again.

If it is necessary to reduce the range of current ripples through the LEDs, it is possible to connect a capacitor in parallel with the LEDs. The larger its capacity, the more the triangular shape of the current through the LEDs will be smoothed out and the more similar it will become to a sinusoidal one. The capacitor does not affect the operating frequency or efficiency of the driver, but increases the time it takes for the specified current through the LED to settle.

Important assembly details

An important element of the circuit is capacitor C1. It not only smoothes out ripples, but also compensates for the energy accumulated in the inductor at the moment the output switch is closed. Without C1, the energy stored in the inductor will flow through the Schottky diode to the power bus and can cause a breakdown of the microcircuit. Therefore, if you turn on the driver without a capacitor shunting the power supply, the microcircuit is almost guaranteed to shut down. And the greater the inductance of the inductor, the greater the chance of burning the microcontroller.

The minimum capacitance of capacitor C1 is 4.7 µF (and when the circuit is powered with a pulsating voltage after the diode bridge - at least 100 µF).

The capacitor should be located as close to the chip as possible and have the lowest possible ESR value (i.e. tantalum capacitors are welcome).

It is also very important to take a responsible approach to choosing a diode. It must have a low forward voltage drop, short recovery time during switching, and stability of parameters as the temperature of the p-n junction increases, in order to prevent an increase in leakage current.

In principle, you can take a regular diode, but Schottky diodes are best suited to these requirements. For example, STPS2H100A in SMD version (forward voltage 0.65V, reverse - 100V, pulse current up to 75A, operating temperature up to 156°C) or FR103 in DO-41 housing (reverse voltage up to 200V, current up to 30A, temperature up to 150 °C). The common SS34s performed very well, which you can pull out of old boards or buy a whole pack for 90 rubles.

The inductance of the inductor depends on the output current (see table below). An incorrectly selected inductance value can lead to an increase in the power dissipated on the microcircuit and exceeding the operating temperature limits.

If it overheats above 160°C, the microcircuit will automatically turn off and remain in the off state until it cools down to 140°C, after which it will start automatically.

Despite the available tabular data, it is permissible to install a coil with an inductance deviation greater than the nominal value. In this case, the efficiency of the entire circuit changes, but it remains operational.

You can take a factory choke, or you can make it yourself from a ferrite ring from a burnt motherboard and PEL-0.35 wire.

If maximum autonomy of the device is important (portable lamps, lanterns), then, in order to increase the efficiency of the circuit, it makes sense to spend time carefully selecting the inductor. At low currents, the inductance must be larger to minimize current control errors resulting from the delay in switching the transistor.

The inductor should be located as close as possible to the SW pin, ideally connected directly to it.

And finally, the most precision element of the LED driver circuit is resistor R. As already mentioned, its minimum value is 0.082 Ohms, which corresponds to a current of 1.2 A.

Unfortunately, it is not always possible to find a resistor of a suitable value, so it’s time to remember the formulas for calculating the equivalent resistance when resistors are connected in series and in parallel:

  • R last = R 1 +R 2 +…+R n;
  • R pairs = (R 1 xR 2) / (R 1 +R 2).

By combining different connection methods, you can obtain the required resistance from several resistors at hand.

It is important to route the board so that the Schottky diode current does not flow along the path between R and VIN, as this can lead to errors in measuring the load current.

The low cost, high reliability and stability of driver characteristics on the RT4115 contribute to its widespread use in LED lamps. Almost every second 12-volt LED lamp with an MR16 base is assembled on PT4115 (or CL6808).

The resistance of the current-setting resistor (in Ohms) is calculated using exactly the same formula:

R = 0.1 / I LED[A]

A typical connection diagram looks like this:

As you can see, everything is very similar to the circuit of an LED lamp with a RT4515 driver. The description of the operation, signal levels, features of the elements used and the layout of the printed circuit board are exactly the same as those, so there is no point in repeating.

CL6807 sells for 12 rubles/pcs, you just need to be careful that they don’t slip soldered ones (I recommend taking them).

SN3350

SN3350 is another inexpensive chip for LED drivers (13 rubles/piece). It is almost a complete analogue of PT4115 with the only difference being that the supply voltage can range from 6 to 40 volts, and the maximum output current is limited to 750 milliamps (continuous current should not exceed 700 mA).

Like all the microcircuits described above, the SN3350 is a pulsed step-down converter with an output current stabilization function. As usual, the current in the load (and in our case, one or more LEDs act as the load) is set by the resistance of the resistor R:

R = 0.1 / I LED

To avoid exceeding the maximum output current, resistance R should not be lower than 0.15 Ohm.

The chip is available in two packages: SOT23-5 (maximum 350 mA) and SOT89-5 (700 mA).

As usual, by applying a constant voltage to the ADJ pin, we turn the circuit into a simple adjustable driver for LEDs.

A feature of this microcircuit is a slightly different adjustment range: from 25% (0.3V) to 100% (1.2V). When the potential at the ADJ pin drops to 0.2V, the microcircuit goes into sleep mode with a consumption of around 60 µA.

Typical connection diagram:

For other details, see the specifications for the microcircuit (pdf file).

ZXLD1350

Despite the fact that this microcircuit is another clone, some differences in technical characteristics do not allow their direct replacement with each other.

Here are the main differences:

  • the microcircuit starts at 4.8V, but reaches normal operation only with a supply voltage of 7 to 30 Volts (up to 40V can be supplied for half a second);
  • maximum load current - 350 mA;
  • resistance of the output switch in the open state is 1.5 - 2 Ohms;
  • By changing the potential at the ADJ pin from 0.3 to 2.5V, you can change the output current (LED brightness) in the range from 25 to 200%. At a voltage of 0.2V for at least 100 µs, the driver goes into sleep mode with low power consumption (about 15-20 µA);
  • if the adjustment is carried out by a PWM signal, then at a pulse repetition rate below 500 Hz, the range of brightness changes is 1-100%. If the frequency is above 10 kHz, then from 25% to 100%;

The maximum voltage that can be applied to the ADJ input is 6V. In this case, in the range from 2.5 to 6V, the driver produces the maximum current, which is set by the current-limiting resistor. The resistor resistance is calculated in exactly the same way as in all of the above microcircuits:

R = 0.1 / I LED

The minimum resistor resistance is 0.27 Ohm.

A typical connection diagram is no different from its counterparts:

Without capacitor C1 it is IMPOSSIBLE to supply power to the circuit!!! At best, the microcircuit will overheat and produce unstable characteristics. In the worst case, it will fail instantly.

More detailed characteristics of the ZXLD1350 can be found in the datasheet for this chip.

The cost of the microcircuit is unreasonably high (), despite the fact that the output current is quite small. In general, it’s very much for everyone. I wouldn't get involved.

QX5241

QX5241 is a Chinese analogue of MAX16819 (MAX16820), but in a more convenient package. Also available under the names KF5241, 5241B. It is marked "5241a" (see photo).

In one well-known store they are sold almost by weight (10 pieces for 90 rubles).

The driver operates on exactly the same principle as all those described above (continuous step-down converter), but does not contain an output switch, so operation requires the connection of an external field-effect transistor.

You can take any N-channel MOSFET with suitable drain current and drain-to-source voltage. For example, the following are suitable: SQ2310ES (up to 20V!!!), 40N06, IRF7413, IPD090N03L, IRF7201. In general, the lower the opening voltage, the better.

Here are some key features of the LED driver on the QX5241:

  • maximum output current - 2.5 A;
  • Efficiency up to 96%;
  • maximum dimming frequency - 5 kHz;
  • maximum operating frequency of the converter is 1 MHz;
  • accuracy of current stabilization through LEDs - 1%;
  • supply voltage - 5.5 - 36 Volts (works normally at 38!);
  • output current is calculated by the formula: R = 0.2 / I LED

Read the specification (in English) for more details.

The LED driver on the QX5241 contains few parts and is always assembled according to this scheme:

The 5241 chip comes only in the SOT23-6 package, so it’s best not to approach it with a soldering iron for soldering pans. After installation, the board should be thoroughly washed to remove flux; any unknown contamination can negatively affect the operation of the microcircuit.

The difference between the supply voltage and the total voltage drop across the diodes should be 4 volts (or more). If it is less, then some glitches in operation are observed (current instability and inductor whistling). So take it with reserve. Moreover, the greater the output current, the greater the voltage reserve. Although, perhaps I just came across a bad copy of the microcircuit.

If the input voltage is less than the total drop across the LEDs, then generation fails. In this case, the output field switch opens completely and the LEDs light up (of course, not at full power, since the voltage is not enough).

AL9910

Diodes Incorporated has created one very interesting LED driver IC: the AL9910. It is curious in that its operating voltage range allows it to be connected directly to a 220V network (via a simple diode rectifier).

Here are its main characteristics:

  • input voltage - up to 500V (up to 277V for alternating);
  • built-in voltage stabilizer for powering the microcircuit, which does not require a quenching resistor;
  • the ability to adjust brightness by changing the potential on the control leg from 0.045 to 0.25V;
  • built-in overheating protection (triggered at 150°C);
  • operating frequency (25-300 kHz) is set by an external resistor;
  • an external field-effect transistor is required for operation;
  • Available in eight-legged SO-8 and SO-8EP packages.

The driver assembled on the AL9910 chip does not have galvanic isolation from the network, so it should be used only where direct contact with the circuit elements is impossible.

An old flashlight with a Duracell pen was collecting dust on a shelf for a long time. It ran on two AAA batteries for an incandescent light bulb. It was very convenient when you need to shine light into some narrow slot in the body of an electronic device, but all the convenience of use was canceled out by the “zhor” of the batteries. It would be possible to throw away this rarity and look in stores for something more modern, but... This is not our method...© Because Ali bought an LED driver chip, which helped convert the flashlight to LED light. The modification is very simple, which even a novice radio amateur who knows how to hold a soldering iron in his hands can master... So, for those who are interested, welcome to Cat...

The driver chip was purchased a long time ago, more than a year ago, and the link to the store already leads to “emptiness,” so I found a similar product from another seller. Now this driver costs less than I bought it for. What kind of “bug” with three legs is this, let’s take a closer look.
First, here's a link to the datasheet:
The microcircuit is an LED driver capable of operating from low voltage, for example, one 1.5V AAA battery. The driver chip has a high efficiency (efficiency) of 85% and is capable of “sucking” the battery almost completely, down to a residual voltage of 0.8V.
Driver chip characteristics

under the spoiler


The driver circuit is very simple...


As you can see, in addition to this “bug” microcircuit, only one part is needed - a choke (inductor), and it is the inductance of the choke that sets the LED current.
For a flashlight, instead of a light bulb, I selected a bright white LED that consumes a current of 30 mA, so I needed to wind a choke with an inductance of 10 μH. The driver efficiency is 75-92% in the range of 0.8-1.5V, which is very good.

I will not give a drawing of the printed circuit board here, because there is no point; the board can be made in a couple of minutes, simply by scratching the foil in the right places.


The choke can be wound, or taken ready-made. I wound it on a dumbbell that came to hand. When making it yourself, you need to control the inductance using an LC meter. As a housing for the driver board, I used a two-cc disposable syringe, inside of which there is enough space to place all the necessary components. On one side of the syringe there is a rubber stopper with an LED and a contact pad, on the other side there is a second contact pad. The size of the syringe piece is selected according to location and is approximately equal to the size of an AAA battery (pinky, as it is popularly called)


Actually assembling the flashlight


And we see that the LED shines brightly from one battery...


The assembled pen-flashlight looks like this


It shines well and the weight of the flashlight has become less, because only one battery is used, and not two, as it was originally...

Here's a short review... Using a driver chip, you can convert almost any rare flashlight to be powered by a single 1.5V battery. If you have any questions please ask...

I'm planning to buy +73 Add to favorites I liked the review +99 +185

LEDs for their power supply require the use of devices that will stabilize the current passing through them. In the case of indicator and other low-power LEDs, you can get by with resistors. Their simple calculation can be further simplified by using the LED Calculator.

To use high-power LEDs, you cannot do without using current-stabilizing devices - drivers. The right drivers have a very high efficiency - up to 90-95%. In addition, they provide stable current even when the power supply voltage changes. And this may be relevant if the LED is powered, for example, by batteries. The simplest current limiters - resistors - cannot provide this by their nature.

You can learn a little about the theory of linear and pulsed current stabilizers in the article “Drivers for LEDs”.

Of course, you can buy a ready-made driver. But it’s much more interesting to make it yourself. This will require basic skills in reading electrical diagrams and using a soldering iron. Let's look at a few simple homemade driver circuits for high-power LEDs.


Simple driver. Assembled on a breadboard, powers the mighty Cree MT-G2

A very simple linear driver circuit for an LED. Q1 – N-channel field-effect transistor of sufficient power. Suitable, for example, IRFZ48 or IRF530. Q2 is a bipolar NPN transistor. I used 2N3004, you can use any similar one. Resistor R2 is a 0.5-2W resistor that will determine the driver current. Resistance R2 2.2Ohm provides a current of 200-300mA. The input voltage should not be very high - it is advisable not to exceed 12-15V. The driver is linear, so the driver efficiency will be determined by the ratio V LED / V IN, where V LED is the voltage drop across the LED, and V IN is the input voltage. The greater the difference between the input voltage and the drop across the LED and the greater the driver current, the more the transistor Q1 and resistor R2 will heat up. However, V IN should be greater than V LED by at least 1-2V.

For tests, I assembled the circuit on a breadboard and powered it with a powerful CREE MT-G2 LED. The power supply voltage is 9V, the voltage drop across the LED is 6V. The driver worked immediately. And even with such a small current (240mA), the mosfet dissipates 0.24 * 3 = 0.72 W of heat, which is not small at all.

The circuit is very simple and can even be mounted in a finished device.

The circuit of the next homemade driver is also extremely simple. It involves the use of a step-down voltage converter chip LM317. This microcircuit can be used as a current stabilizer.


An even simpler driver on the LM317 chip

The input voltage can be up to 37V, it must be at least 3V higher than the voltage drop across the LED. The resistance of resistor R1 is calculated by the formula R1 = 1.2 / I, where I is the required current. The current should not exceed 1.5A. But at this current, resistor R1 should be able to dissipate 1.5 * 1.5 * 0.8 = 1.8 W of heat. The LM317 chip will also get very hot and will not be possible without a heatsink. The driver is also linear, so in order for the efficiency to be maximum, the difference between V IN and V LED should be as small as possible. Since the circuit is very simple, it can also be assembled by hanging installation.

On the same breadboard, a circuit was assembled with two one-watt resistors with a resistance of 2.2 Ohms. The current strength turned out to be less than the calculated one, since the contacts in the breadboard are not ideal and add resistance.

The next driver is a pulse buck driver. It is assembled on the QX5241 chip.


The circuit is also simple, but consists of a slightly larger number of parts and here you can’t do without making a printed circuit board. In addition, the QX5241 chip itself is made in a fairly small SOT23-6 package and requires attention when soldering.

The input voltage should not exceed 36V, the maximum stabilization current is 3A. The input capacitor C1 can be anything - electrolytic, ceramic or tantalum. Its capacity is up to 100 µF, the maximum operating voltage is no less than 2 times greater than the input. Capacitor C2 is ceramic. Capacitor C3 is ceramic, capacity 10 μF, voltage - no less than 2 times greater than the input. Resistor R1 must have a power of at least 1W. Its resistance is calculated by the formula R1 = 0.2 / I, where I is the required driver current. Resistor R2 - any resistance 20-100 kOhm. The Schottky diode D1 must withstand the reverse voltage with a reserve - at least 2 times the value of the input. And it must be designed for a current not less than the required driver current. One of the most important elements of the circuit is field-effect transistor Q1. This should be an N-channel field device with the minimum possible resistance in the open state; of course, it should withstand the input voltage and the required current strength with a reserve. A good option is field-effect transistors SI4178, IRF7201, etc. Inductor L1 should have an inductance of 20-40 μH and a maximum operating current not less than the required driver current.

The number of parts of this driver is very small, all of them are compact in size. The result may be a fairly miniature and, at the same time, powerful driver. This is a pulse driver, its efficiency is significantly higher than that of linear drivers. However, it is recommended to select an input voltage that is only 2-3V higher than the voltage drop across the LEDs. The driver is also interesting because output 2 (DIM) of the QX5241 chip can be used for dimming - regulating the driver current and, accordingly, the brightness of the LED. To do this, pulses (PWM) with a frequency of up to 20 KHz must be supplied to this output. Any suitable microcontroller can handle this. The result may be a driver with several operating modes.

 (13 ratings, average 4.58 out of 5)

I've been eyeing these chips for a long time. Very often I solder something. I decided to take them for creativity. These microcircuits were purchased last year. But it never came to the point of using them in practice. But not long ago, my mother gave me her flashlight, bought offline, to repair. I practiced on it.
The order included 10 microcircuits, and 10 arrived.


Paid on November 17, received on December 19. Came in a standard bubble bag. There's another bag inside. We walked without a track. I was surprised when I found them in my mailbox. I didn't even have to go to the post office.


I didn't expect them to be so small.

I ordered microcircuits for other purposes. I won't share my plans. I hope that I will have time to bring them (plans) to life. Well, for now it’s a slightly different story, closer to life.
My mother, while walking around the shops, saw a flashlight at a good discount. What she liked more about the flashlight or the discount, history is silent. This flashlight soon became my headache. She used it for no more than six months. Six months of problems, then one thing, then another. I bought her three others to replace this one. But I still had to do it.


Although the flashlight is inexpensive, it has a number of significant advantages: it fits comfortably in the hand, is quite bright, the button is in the usual place, and it has an aluminum body.
Well, now about the shortcomings.
The flashlight is powered by four AAA type cells.


I installed all four batteries. I measured the current consumption - more than 1A! The scheme is simple. Batteries, button, 1.0 Ohm limiting resistor, LED. Everything is consistent. The current is limited only by the 1.0 ohm resistance and the internal resistance of the batteries.
This is what we have in the end.


It's strange that the nameless LED turned out to be alive.


The first thing I did was make a pacifier from an old battery.


Now it will be powered by 4.5V, like most Chinese flashlights.
And most importantly, instead of resistance I will install the AMC7135 driver.
Here is the standard connection diagram.

This chip requires a minimum of wiring. Among the additional components, it is advisable to install a pair of ceramic capacitors to prevent self-excitation of the microcircuit, especially if there are long wires going to the LED. The datasheet contains all the necessary information. There are no long wires in the flashlight, so I didn’t actually install any capacitors, although I indicated them in the diagram. Here is my scheme, redesigned for specific tasks.


In this circuit, a large current will no longer flow through the switch button in principle. Only control current flows through the button and that’s it. One less problem.


I also checked the button and lubricated it just in case.

Instead of resistance, there is now a microcircuit with a stabilization current of 360 mA.


I put everything back together and measured the current. I connected both batteries and accumulators, the picture does not change. The stabilization current does not change.


On the left is the voltage on the LED, on the right is the current flowing through it.
What did I achieve as a result of all the alterations?
1. The brightness of the flashlight practically does not change during operation.
2. Relieved the load on the flashlight on/off button. Now a tiny current flows through it. Damage to contacts due to high current is excluded.
3. Protected the LED from degradation due to high current flow (if with new batteries).
That, in general, is all.
Everyone decides for themselves how to properly use the information from my review. I can guarantee the veracity of my measurements. If anything is unclear about this review, please ask questions. For the rest, send me a PM, I’ll definitely answer.
That's all!
Good luck!

And I would also like to draw your attention to the fact that my flashlight has a switch on the positive side. Many Chinese lanterns have a switch on the negative side, but this will be a different circuit!

I'm planning to buy +59 Add to favorites I liked the review +58 +118