What sort of LED driver should I get/make?

Thread Starter

LikeTheSandwich

Joined Feb 22, 2021
151
OK, so here's my situation: I have an LED assembly that I want to drive using an 18V tool battery. In my testing, it seems that giving it a 7.5V-10V (at 10V it approaches 3A and 30W power) input range will give me the brightness range I want. Options I know I have:
  • Adjustable buck converter (probably modified with a "fine adjustment" pot to only have range between 7.5 and 10V)
  • Adjustable current driver (also probably modified to limit to about 3A output max)
  • PWM driver with a high power resistor (wouldn't be my first time, and this might be the easiest option, but will also give the least consisntency)
  • Find an LED driver online (I have looked on Banggood, AliExpress, eBay, and Amazon, haven't been able to find anything that looks like it'll work)
  • Use some sort of LED driver IC which allows both voltage regulation and a dimming input
So the bottom one is least appealing because it's the most work. Middle one is least consistent and probably least efficient, but it's the easiest and fastest for my needs. I haven't seen any complete LED drivers online that regulate voltage, are dimmable, have an output of 10V, and have a DC input. I've seen a few that meet 3 of those requirements, but their inputs are usually 120-277VAC.

So what is the best option? I don't mind spending a little bit of money, but it's not ideal if I don't have to.

EDIT: I have a bit of experience with making circuits, but I'd rather use something (mostly) complete. I also have experience with MCUs and Arduino IDE (which I find much preferable to using a 555 most of the time), so if there's a good/easy/cheap solution but it requires an MCU and some clever programming, that's an option to me.
 
Last edited:

Audioguru again

Joined Oct 21, 2019
4,688
Please post the datasheet for the extremely high power LEDs. The 7.5V to 10V voltage is much higher than a single LED so they must be in series string and maybe have some strings in parallel for the high current.

An LED is never powered from a voltage source, An LED sets its own voltage and is powered from a current regulator.
 

Thread Starter

LikeTheSandwich

Joined Feb 22, 2021
151
I have this LED assembly but I have bypassed the internal circuitry to access the LEDs directly, since that internal circuitry is constant current and does not allow for external dimming. I tested the voltage across the LEDs while operating with internal circuitry and it was about 8.4V across the LEDs (all LEDs are parallel, apparently operating at this voltage as I measured it across many diodes). Also the listing is absolutely false, they use about 12W normally, and I have a 2500 lumen light that is WAY brighter, but I added additional thermal compound and am comfortable with the idea of running the array up to around 30W or so. I edited OP to better reflect my component.
 

ronsimpson

Joined Oct 7, 2019
2,067
I don't have the right IC but here is one to be an example. If bucks a supply voltage down. Dimming is accomplished in either of two ways. If you play the the "Iadj" pin you can change the current in the LED. OR You can send a pulse signal from a "555" or something. The pulse frequency need to be higher than 100hz and the duty cycle will dim the light. It is constant current. (with dimming)
1638919623940.png
 

LowQCab

Joined Nov 6, 2012
2,054
Removing the internal Current-Limiting-Circuitry was a bad move.
With the original configuration, all You would have had to do is PWM the Input-Voltage.
If You can re-install the original Circuitry then do that first,
Creating a PWM-Dimmer is super easy.

Here is an option that You could use with raw LEDs ..........
( Schematic is from a different project )
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3A 50V Current Source FLAT .png
 

Thread Starter

LikeTheSandwich

Joined Feb 22, 2021
151
Removing the internal Current-Limiting-Circuitry was a bad move.
With the original configuration, all You would have had to do is PWM the Input-Voltage.
If You can re-install the original Circuitry then do that first,
Creating a PWM-Dimmer is super easy.

Here is an option that You could use with raw LEDs ..........
( Schematic is from a different project )
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View attachment 254509
I tried a PWM control on the lights, it doesn't work. The current limiting circuitry is also a buck converter, always providing a constant power output for varying 12-24V input.
 

LowQCab

Joined Nov 6, 2012
2,054
Reducing the Input-Voltage, ( with the factory configuration ),
whether by PWM, Filtered-PWM, or by Linear means,
will result in 1 of 2 results ......
You will get the expected, "somewhat linear" Dimming action,
or,
nothing will happen as You lower the Input-Voltage,
until, at a critical point, the Light just stops working.

Relatively Low-Frequency PWM, ( ~60hz ),
will probably work even with a factory Buck-Regulator in the Circuit.
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Thread Starter

LikeTheSandwich

Joined Feb 22, 2021
151
nothing will happen as You lower the Input-Voltage,
until, at a critical point, the Light just stops working.
That's what happened. I tried it with I think a 2kHz PWM module, identical to what I use on another LED project (but with a resistor).
How?
Can you show us the PCB for the Buck that is there now? Most I have used will PWM dim from an external source.
I just put PWM device in line with the input positive and negative on the light.

Here's the electronics. Only thing out of frame is a second inductor, same as the one you can see at the bottom of the picture (second one is below the one you see).
 

Attachments

ronsimpson

Joined Oct 7, 2019
2,067
I just put PWM device in line with the input positive and negative on the light.
Not how it works.
Go back to post #4 there is a pin-2 "DIM". The bottom trace is the "dim" PWM signal. The top trace is the LED current. The constant current is turned on/off by the PWM signal. (totally different than the PWM that keeps the current constant)
So there are two PWM signals. One that changes duty cycle to keep the current constant when the input voltage changes or when the LEDs get hot and change voltage. The second PWM turns on/off the constant current source. If the LED only emits light 1/2 of the time it looks dim. (assuming the dimming frequency is faster than you can see)
1638938258259.png
I can not see the numbers on the IC.
 

Thread Starter

LikeTheSandwich

Joined Feb 22, 2021
151
Not how it works.
Uhh...yeah...I know...that's why I said it didn't work. Also, I'm not certain that my original description of the circuit being "constant current" was accurrate. But in any event, without modifying or bypassing the built in circuit, I cannot make it dim in any effective manner. I imagine that figuring out how to modify it would be a bigger task than I would want, which is why I'm asking what's going to be the most effective way to drive the LEDs directly, given I want them to be dimmable, I need a voltage source that will go up to 10 volts, and I'm going to be using an 18V battery.
 

LowQCab

Joined Nov 6, 2012
2,054
I already provided a simple solution in Post-5 that will handle up to 5-Amps per Chip,
with 3 LED string configuration examples.
( That particular Schematic was set up for ~50-Volts, but 18-Volts will work just fine ).

The part number is LT1074IT#06PBF-ND, and DigiKey has ~100 in-stock, for ~$18.10 each.
Also Required is an Inductor p/n M1409-ND for ~$3.80, ~100 in-stock.
You will also need 1-Diode, 1-Capacitor, and 1-Resistor.

This will give You efficient Current Regulation, and an "On-Off" input.

In addition to this,
You will need a simple PWM-Circuit,
made with 1-Dual-Op-Amp,
to provide Dimming-Control.

Do You need help in understanding how it works ?
Are You capable of building a simple Circuit on a Perf-Board ?
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.
 

Thread Starter

LikeTheSandwich

Joined Feb 22, 2021
151
I already provided a simple solution in Post-5 that will handle up to 5-Amps per Chip,
with 3 LED string configuration examples.
( That particular Schematic was set up for ~50-Volts, but 18-Volts will work just fine ).

The part number is LT1074IT#06PBF-ND, and DigiKey has ~100 in-stock, for ~$18.10 each.
Also Required is an Inductor p/n M1409-ND for ~$3.80, ~100 in-stock.
You will also need 1-Diode, 1-Capacitor, and 1-Resistor.

This will give You efficient Current Regulation, and an "On-Off" input.

In addition to this,
You will need a simple PWM-Circuit,
made with 1-Dual-Op-Amp,
to provide Dimming-Control.

Do You need help in understanding how it works ?
Are You capable of building a simple Circuit on a Perf-Board ?
.
.
.
I don't understand how this will work. I have provided a PWM signal to the internal circuitry before, but it somehow modified it and kept the output constant once over a minimum (very low) threshold. How will this circuit in #5 trick the internal circuitry into doing some sort of dimming?

Also for that price I could just get a buck converter to 10V, then a separate PWM board to dim, for much cheaper and easier install (even if a bit less efficient).
 

LowQCab

Joined Nov 6, 2012
2,054
You stated earlier that You had removed the factory Buck-Converter.
Do You have a working Light, or has it been rendered "non-working" at this point ?

In any case, the CURRENT must be regulated first, NOT the Voltage.
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Thread Starter

LikeTheSandwich

Joined Feb 22, 2021
151
You stated earlier that You had removed the factory Buck-Converter.
Do You have a working Light, or has it been rendered "non-working" at this point ?

In any case, the CURRENT must be regulated first, NOT the Voltage.
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Oh I thought you were saying to wire back in the built weekcircuit.

The lights work fine.
 

LowQCab

Joined Nov 6, 2012
2,054
Is the Circuit-Board made in such a way that You can easily re-wire the LEDs into
any appropriate configuration, without any other components complicating the Circuitry ?
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LowQCab

Joined Nov 6, 2012
2,054
That's not really a complete answer ..........
Are there ANY other Components that You can NOT easily remove or bypass ?
What should be left behind are basically bare LEDs,
( possibly in several groups or "strings" ).
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Thread Starter

LikeTheSandwich

Joined Feb 22, 2021
151
That's not really a complete answer ..........
Are there ANY other Components that You can NOT easily remove or bypass ?
What should be left behind are basically bare LEDs,
( possibly in several groups or "strings" ).
.
.
.
Not sure how it's not complete. No, there's no other components I can easily remove or bypass, either using the whole built in circuit, or just the plain LEDs with no circuitry (all LEDs are parallel, no series).
 
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