Change voltage or PWM to dim LEDs?

Thread Starter

LikeTheSandwich

Joined Feb 22, 2021
151
I have some LEDs, and they are set up to run around 10V currently. They get progressively dimmer until about 7.5V where they go so dim they're like a tiny candle or less. Would I be better off using an adjustable voltage supply or PWM module to dim them? Which would be more effective/better for the LEDs, or is it about the same?
 
Last edited:

Ya’akov

Joined Jan 27, 2019
5,540
If you just need a particular output, choosing the supply voltage to get that would be the simplest approach. If you need continuous dimming, PWM Is the best way to get it.
 

Thread Starter

LikeTheSandwich

Joined Feb 22, 2021
151
If you just need a particular output, choosing the supply voltage to get that would be the simplest approach. If you need continuous dimming, PWM Is the best way to get it.
I need continuous dimming. I'm looking to adapt it for use with an 18V tool battery, so I'm thinking that I may need to go with voltage to avoid adding a second stage adjustment (buck convert the voltage, then PWM control for dimming vs adjustable buck conversion). Also I remembered wrong, the cutoff is around 7.5V.
 

Thread Starter

LikeTheSandwich

Joined Feb 22, 2021
151
So I went through the data sheet for this LED driver IC but I'm not an electrical engineer and I'm new to looking at data sheets like this. So there's a normal current set pin on this chip, but I don't quite understand how to use it. It seems I put a resistor between it and gnd, but how am I to know what value of resistor? I didn't see an explanation in the data sheet to say how to use it. For example, if I wanted to have nominal current be 3A (the limit on the chip), what value for Rset would I use? How about for 2A nominal current? And what page is that info on, so I can learn how to decode this info in the future?
 

Ian0

Joined Aug 7, 2020
4,882
Be patient, and read as far as page 11, where it says:
Iout = 0.1/Rset

so Rset = 0.1/Iout = 0.05Ω for 2A and 0.033Ω for 3A

But look at the application circuit on page 2, and the resistor doesn't go from SET to ground, it goes from SET to the positive supply.
 

Thread Starter

LikeTheSandwich

Joined Feb 22, 2021
151
Be patient, and read as far as page 11, where it says:
Iout = 0.1/Rset

so Rset = 0.1/Iout = 0.05Ω for 2A and 0.033Ω for 3A

But look at the application circuit on page 2, and the resistor doesn't go from SET to ground, it goes from SET to the positive supply.
Ah I'm not sure how I missed it, it even has a table there and everything. Thank you!
 

bassbindevil

Joined Jan 23, 2014
378
You can buy a PWM dimmer board on eBay for a couple of bucks; it uses a 555 and MOSFET (and comes with a panel-mountable pot with switch (like a radio volume control)). I'd suggest buying 5PCS since shipping isn't free and they're useful for other projects. (How about continuously adjustable RGB lighting?)
 
Last edited:

Thread Starter

LikeTheSandwich

Joined Feb 22, 2021
151
You can buy a PWM dimmer board on eBay for a couple of bucks; it uses a 555 and MOSFET (and comes with a panel-mountable pot with switch (like a radio volume control)). I'd suggest buying 5PCS since shipping isn't free and they're useful for other projects. (How about continuously adjustable RGB lighting?)
Do you mean stuff like this? Or something else?
 
Top