My current PCB configurations are (10 series 4 parallel)x3 in parallel making 10 series and 12 parallel I am using Meanwell ELG-75-42 driver giving a voltage of 42V at 1800mA, and a power of 75W. It is a constant current + constant voltage driver.

While each LED is driven at 150mA dropping a voltage of 3.0V so a total of 1800mA and 30V,

LED specs
typical current-150mA
typical voltage-3.0v
maximum voltage-3.6v
As the voltage is going higher than maximum will it affect my LED's?

  • 1
    \$\begingroup\$ Take your time to read what you wrote and try and make it more structured. I can't understand what you are trying to say here. Oh, and schematics. Provide them, it's hard to help without being able to see what you are talking about. \$\endgroup\$ – Joren Vaes Jun 15 '17 at 12:22
  • 2
    \$\begingroup\$ Short answer, if you go over your rated voltage your LEDs will fail. Depending on how much, it's either quitly (they just stop working) or with a nice "pooof" and smoke and charred everything. \$\endgroup\$ – Joren Vaes Jun 15 '17 at 12:24
  • 1
    \$\begingroup\$ Please add some punctuation to the second paragraph and a question mark to the actual question so it's clear what exactly you are asking. There's a schematic button on the editor toolbar if required. \$\endgroup\$ – Transistor Jun 15 '17 at 12:24
  • \$\begingroup\$ If you're trying to actively control the voltage supplied to your LEDs you're already doing it wrong. LEDs are current controlled devices. Set your supply to provide the correct current and as long as it is capable of providing a high enough voltage to provide an acceptable Vf to your series string of LEDs, it will be fine. \$\endgroup\$ – brhans Jun 15 '17 at 12:33
  • \$\begingroup\$ @brhans The current I provide is fine calculated at 150mA which is the typical current for the LED. Query is about the driver being 75W and so the Voltage is 42V at 1800mA. My thinking is that the voltage each LED gets is 4.2V as 10 LED's are connected in series. The maximum voltage for the LED is 3.6V \$\endgroup\$ – Nihar Patel Jun 15 '17 at 13:03

It is important to understand that an LED is a current driven device. This means that when designing an LED circuit, we are concerned with setting the right current through the LED. It then happens that the LED has a voltage across it when driven at its rated current. This voltage can vary from LED to LED and that is what you are seeing in your LED datasheet. It is saying that when you drive the LED with 150 mA, it will have a voltage maximum of 3.6 volts across it but more typically it will be 3 volts.

While we drive the LED based on current, the voltage across the LED is an important number because it tells us that the supply for the LED must be capable of developing that voltage in order to supply the required current.

When LEDs are placed in series, the same current flows through each LED. Since they are in series, the voltage drop of each LED adds. So if you have 10 in series, the current through them should be set to 150 mA. The voltage across the string will then be 30 to 36 volts. But it is still the current that must be controlled.

The supply you are using will only limit its output current to 1.8 amps. If the current is less than this, it simply acts as a 42 volt supply. This means that you will need to add series resistors in each series string to limit the current to 150 mA in each. Since the series string will drop 30 to 36 volts at 150 mA, the series resistor must drop 6 to 12 volts at 150 mA. A 3 watt 82 ohm resistor would do the job.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.