Driving leds

Submitted by Dan on Sat, 01/04/2020 - 03:02


After been using all your good advice to other peoples projects its now my time to ask. Thank you for allways being really helpfull in this forum.

Being a noob like me sometimes makes it hard to ask the right question, so instead I'll try to explain what I want to archieve.

I'm gonna build a led-grow-panel. I bought 20 3w, 700ma leds in different colours(=different voltage needs).

I also bought some cheap constant-current step-down led drivers which allows me to set the output voltage (like these https://a.aliexpress.com/FB0AKvHm). The idea is to have 4 strings of 5 leds in series (=voltage needs of about 14-16 v in each string, depending on the colours in that string).

Then I was about to buy a decent powersupply with decent current (since it'll be driving other parts of the project simultaniously). I won't be buying cheap high-voltage-stuff as I'm too nervous of the firehazard of the cheap stuff. So it turned out to be rather expensive. Then I found my old X-box 360 power supply which is able to drive 16,5a 12v. 12v is great for the other parts of my project, the current-ratings are well on the safe side (and its free) so I'm gonna stick with that.

To drive the led-strings I would need approx. 18v (because of the consumption from the led-driver). So I was thinking of adding a step-up-booster like this:

12v psu -> 18v step up -> cc led driver -> led

Just seems silly to step down-step up-step down. And I cant really seem to find cheap high current/wattage step-up-modules that's not constant current.

So to make a long story short: I have a 12v16,5a psu and i want to drive 20 3w 700ma leds with different voltage ratings.What would your approach be?

Thank so much for your help.




Lets break down the project for better understanding.

Can you share the detailed LED strip schematic? And forward voltage vs current information?

For example, One of type LED has 2.3V Vf at 300mA of current and the other type has 2.7V Vf at 300mA of current.

You will get this info in the respective Vf/I curve in the LED datasheet.

I am concern about the LED strip configuration first, because it is your load, and your each and every circuit will be made to support this load.

  Joined February 12, 2018      696
Monday at 02:11 PM



Driving LEDs is relatively simple and, unlike fluorescent or discharge lamps, they do not require an ignition voltage to start. Too little current and voltage will result in little or no light, and too much current and voltage can damage the light-emitting junction of the LED diode. A typical LED forward voltage.

The simplest circuit to drive an LED is through a series resistor. It is commonly used for indicators and digital displays in many consumer appliances, though this circuit is not particularly energy-efficient because energy is lost in the resistor. An LED has a voltage drop specified at the intended operating current.

  Joined November 07, 2019      124
Thursday at 04:25 PM