I noticed a lot of people have been asking for power supplies for LEDs.
Unfortunately, linear power supplies are often not an option, especially when dealing with high power modules (>100W) that are now available. The main problem is inefficiency, and getting rid of heat. They are also an issue because the power transistors can be hard to get hold of.
So, I have designed a primitive switch-mode buck-converter based LED power supply. But it is not voltage controlled, it is current controlled. I have not fully tested this design yet, but it should work. A few changes might be required with the diode-AND logic, because I did not simulate that part; it might not provide enough current to turn the TIP122 all the way on or off.
The core of this design is based on the LM339, a quad voltage comparator. (You can also substitute a LM393 dual comparator, but the LM339 is more common and I have a few so I spec'd that in.) An oscillator is gated with a control signal which turns on an off a TIP122, a power darlington transistor. Many components in this can be changed or substituted for alternate parts if necessary; it's not critical.
The efficiency under full load is about 75-80%, and under light load (<20mA) is 45-50% (calculated from simulations; this does not include the logic current which may be greater.) It uses a current shunt (10mΩ) on the low side to sense current and the current is set using coarse and fine potentiometers. The current ranges from zero to about 2.5 amps (with a limit of 5 amps), depending on the choice of inductors, capacitors, diodes and transistors. At high currents, a fan is recommended, and so is good heatsinking. Due to the high efficiency usually only a heatsink is required for lower current levels.
Power input can vary from +8V to +24V. Recommended power ratings for any power supply are usually 30% to 50% greater than the LED's rating, for safety and due to losses in the supply. For lower power levels, a 9V battery may be used. I will probably design a portable version of this with a limited current range for testing LEDs, maybe zero to 500mA.
One important point of note is that you should never connect the LED backwards because the supply can easily exceed the Vrrm of the LED and fry it, especially if set to a high current level. And, usefully, this supply is not just limited to LEDs. It will work with any kind of device, whether or not they have a non-linear response to voltage, like an LED.
Additions I may make to this are:
Unfortunately, linear power supplies are often not an option, especially when dealing with high power modules (>100W) that are now available. The main problem is inefficiency, and getting rid of heat. They are also an issue because the power transistors can be hard to get hold of.
So, I have designed a primitive switch-mode buck-converter based LED power supply. But it is not voltage controlled, it is current controlled. I have not fully tested this design yet, but it should work. A few changes might be required with the diode-AND logic, because I did not simulate that part; it might not provide enough current to turn the TIP122 all the way on or off.
The core of this design is based on the LM339, a quad voltage comparator. (You can also substitute a LM393 dual comparator, but the LM339 is more common and I have a few so I spec'd that in.) An oscillator is gated with a control signal which turns on an off a TIP122, a power darlington transistor. Many components in this can be changed or substituted for alternate parts if necessary; it's not critical.
The efficiency under full load is about 75-80%, and under light load (<20mA) is 45-50% (calculated from simulations; this does not include the logic current which may be greater.) It uses a current shunt (10mΩ) on the low side to sense current and the current is set using coarse and fine potentiometers. The current ranges from zero to about 2.5 amps (with a limit of 5 amps), depending on the choice of inductors, capacitors, diodes and transistors. At high currents, a fan is recommended, and so is good heatsinking. Due to the high efficiency usually only a heatsink is required for lower current levels.
Power input can vary from +8V to +24V. Recommended power ratings for any power supply are usually 30% to 50% greater than the LED's rating, for safety and due to losses in the supply. For lower power levels, a 9V battery may be used. I will probably design a portable version of this with a limited current range for testing LEDs, maybe zero to 500mA.
One important point of note is that you should never connect the LED backwards because the supply can easily exceed the Vrrm of the LED and fry it, especially if set to a high current level. And, usefully, this supply is not just limited to LEDs. It will work with any kind of device, whether or not they have a non-linear response to voltage, like an LED.
Additions I may make to this are:
- A milliammeter/ammeter based on a panel meter of some kind. The voltage can be taken from the internal feedback loop.
- External voltage input for adjusting current.
- Portability (see above.)
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