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Forum section: electronics / projects

author: The_Almighty_Bacon_Lord
author_rank: Contributor
timestamp: March 03, 2016, 03:23:04 pm
content: Delete Delete Delete

author: Wirehead
author_rank: Regular Contributor
timestamp: March 03, 2016, 03:26:21 pm
content: What you ordered is a LED driver, what it does is give a constant current at 32V. What you want to do is keep that voltage at 32V; but limit the current. Nothing a simple pot will doLook around for some current limiting schematics

author: Buriedcode
author_rank: Super Contributor
timestamp: March 03, 2016, 04:47:24 pm
content: What LED driver are you using?You won't need a 50W potentiometer, because, hopefully, the constant current LED driver will allow you to set the current using a voltage, or at least a small signal resistance. If you're getting 32V from 3 lithium batteries (3 x 3.7-4.2 = 11.1-12.6V) then I'll assume this is a boost converter, that uses a current sense resistor to keep its output current constant.Post what LED, and what driver you are using, and I'm sure you'll get more responses.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: March 03, 2016, 04:50:11 pm
content: PWM is the ordinary way to control the brightness of LEDs like this.A potentiometer controls pulse width of a 555 astable multivibrator which drives the gate of a mosfet which switches the 32VDC supply to the LED.

author: IanB
author_rank: Super Contributor
timestamp: March 03, 2016, 05:31:13 pm
content: Quote from: The_Almighty_Bacon_Lord on March 03, 2016, 05:22:29 pmYou don't want to be doing PWM if you are assembling building blocks. As someone previously mentioned you want to use a driver with a dimming control (or output current adjustment) built into it.Look at the driver specifications for that feature and then check the documentation for how to use it.

author: hlavac
author_rank: Frequent Contributor
timestamp: March 03, 2016, 07:25:27 pm
content: The driver you bought doesnt look very useful for this application.The problem with dimming LEDs is there is a very small range of voltage where the current varies wildly and LED goes from not lit to burnedThe correct way is usually to regulate current instead of voltage - that gives you more linear-ish control of the brightness.There are two basic ways to do that:One is regulating the current using some sort of analog circuitry (negative feedback loop with op-amp) and resistor to detect and control the current.Advantage of analog current control is the LED is not blinking so its suitable as lighting for photography / video recording.Disadvantage is it has more power losses (gets hot) and some LEDs tend to change color on different brightness levels.Other is the PWM control (pulse width modulation) where you have a fixed maximum allowable current (maybe set with small resistor and constant voltage supply) and you switch the LED on and off quickly, varying the ratio between on and off.Advantages are less losses and thus longer battery life, constant color.Disadvantage is the flickering that can cause weird interference patterns when there are two light sources PWM switched using similar but not identical switching frequency.For your setup you probably need a 38V /1.5A power supply as the voltage required by the LED is pretty high.You could use a beefy 5Watt 1.5Ohm resistor to limit the current, and some kind of MOSFET to switch the LED on/off, controlled by either a 555 timer based PWM circuit or small cheap microcontroller

author: Siwastaja
author_rank: Super Contributor
timestamp: March 03, 2016, 07:31:45 pm
content: Quote from: hlavac on March 03, 2016, 07:25:27 pmIt looks exactly the right thing, because of this:QuoteWhich is exactly what said product is. As long as it's operating as specified, of course.For OP, the only really useful answer is:Any way of dimming an LED requires some sort of support from the LED constant-current driver.You already have the potentiometer you are asking for, installed on that PCB, marked "CI" in the PCB silkscreen!You can replace it with an external one. Or, as I would recommend, find the maximum current which is OK for the LEDs, then connect an external potentiometer in series with the original one, so that the original pot limits the maximum, and your external pot goes downwards from there.

author: Mr.B
author_rank: Unknown
timestamp: March 03, 2016, 07:35:49 pm
content: Quote from: Siwastaja on March 03, 2016, 07:31:45 pmIt doesn't look like the right thing to me.It is a BUCK supply...How is the OP going to get 32v from 3 lithium batteries?He needs a BOOST supply... Preferably with PWM control.

author: Siwastaja
author_rank: Super Contributor
timestamp: March 03, 2016, 07:37:34 pm
content: Quote from: Mr.B on March 03, 2016, 07:35:49 pmOh, I ignored that issue. Yes, indeed. It's probably a proper driver (adjustable constant-current operation), but wrong type for the OP. Good catch.