LED Dimmer IC Recommendation?

Thread Starter

SoBuggy

Joined Aug 21, 2022
7
Hey everyone, I'm working on making a custom headlamp for myself and want to have dimming functionality without using a microcontroller. I came across the IC FM2819 (data sheet attached) which has the characteristics I'm looking for, but it isn't available for purchase on DigiKey, Mouser, or the like. Do you have any ideas/recommendations for a similar IC that controls a bright SMD LED on battery power?
Cheers!
 

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Ya’akov

Joined Jan 27, 2019
6,853
The CN5711 is a good option if you are able to keep the current requirements under 1.5A or so. It can be adjusted with either a variable resistor or a PWM signal.

Since it has picky thermal layout requirements, you might consider getting one of these very cheap modules and replacing the on-board trimmer with a variable resistor of your own. Possibly a digital potentiometer which generally will give you up to 256 steps from low to high resistance and could be operated with two pushbutton switches. This would be more environmentally robust than a physical potentiometer. There are digital pots with non-volatile memory that keep the last setting.

The bare chips are also readily available if you want to do it yourself, but only in SOP-8. It would still be worth buying the module since it would be a good example for the layout.
 

Thread Starter

SoBuggy

Joined Aug 21, 2022
7
Thanks for the replies so far. Sorry, I should have added more details in my initial post. Here’s some relevant details.
Battery = 4.5v (3xAAA batteries)
LED current max 3A
LED forward voltage 3.05v @ 1.5A
Data sheet of LED of interest is attached.
I’m looking to have a single button for control to do something similar to

Button PressLED State
1Max brightness
2Dim brightness
3Dimmest brightness
4Off
 

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Thread Starter

SoBuggy

Joined Aug 21, 2022
7
Thanks for the recommendations :)I’ll take a look into this chip and how a digital potentiometer could be added. In first looks, this looks like a good solution.
 

MisterBill2

Joined Jan 23, 2018
13,707
If the power source is only the three AAA batteries, and the LED current is anywhere near an amp, the battery life will be quite short. One very simple choice would be selecting the number of LEDs powered to give a low/medium/high choice. That could even be done with no electronics.
 

ronsimpson

Joined Oct 7, 2019
2,519
You are not getting that kind of power from AAA batteries.
There might be an on-bright-dim-dimmer-off IC but I don't know of one. We used an 8 or 6 pin microcomputer to do that.
I used a micro like these ATTINYxxx and PIC10Fxx and PIC16Fxx.
The micro drives the "dim" pin on the PWM.

Here is a typical power supply for a torch/flashlight.
1661176915913.png
 

MisterBill2

Joined Jan 23, 2018
13,707
I do have an LED flashlight that uses a pack of three AAA cells. It has a fairly bright beam , as well as the option of selecting lower intensity modes and a flashing mode. All controlled by a single chip buried in a small blob of epoxy. The current draw is much less than the three amps, and still the battery life is not even a single hour.
So the concept sort of works BUT the battery life is pitiful.
 

ronsimpson

Joined Oct 7, 2019
2,519
You have probably noticed the type of AAA batteries makes a big difference when pulling that much current.
single chip buried in a small blob of epoxy
It is unlikely you will find that part.

I have designed several different versions of this. The PWM is inside the metal part.
1661183055770.png
Here is the on-dim-off button. The "computer" is inside the red button.
1661183259019.png
brightness
Much of what you think is brightness comes from the reflector design.
1661183487183.png[/quote]
 

MisterBill2

Joined Jan 23, 2018
13,707
Certainly a good reflector arrangement aims all of that "brightness" in the desired direction. But all of that light comes from the LED, and all of the power comes from the battery. And no matter how excellent the design, the efficiency will not exceed 100%. My points being, first, that the control scheme is complex and not easily copied, and second, that there is not a whole lot of power in a stack of three AAA cells.
Probably Lithium technology AAA cells would deliver more, I have not seen them, though.
 
I have made several versions of this. Mostly using microcontroller with a hardware PWM module which drives the switch of a boost converter. You can get microcontrollers that will run on a single AA cell but two is a lot easier. You could use an ADC to make current or voltage measurements but it's not really essential to close the loop. I've attached a schematic for a simple and minimal version. You would usually think of a MOSFET for something like this but they typically require a gate voltage higher than what you'll have when the batteries approach end-of-life. So I used a BJT. Also of note, the switch timing is bit-banged in this version so I didn't even need a PWM peripheral. The power is always turned on and the microcontroller is in a low-power sleep mode. When the user pushes the "on" button, it resets the micro. The firmware the counts down 30 minutes and shuts off the light and puts the uC to sleep again until the next time. Let me know if you want the PCB project. It's in Altium.
 

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Thread Starter

SoBuggy

Joined Aug 21, 2022
7
This is all really great information everyone. Thanks for all the insights. I have some ideas to think through now. Using an attiny microcontroller is looking like the best option for my skill level.
Oh and I should have said the 3A draw for the LED is the max it can take but it looks to produce sufficient light at lesser current.
 

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Ya’akov

Joined Jan 27, 2019
6,853
This is all really great information everyone. Thanks for all the insights. I have some ideas to think through now. Using an attiny microcontroller is looking like the best option for my skill level.
Oh and I should have said the 3A draw for the LED is the max it can take but it looks to produce sufficient light at lesser current.
The cool thing about using an MCU is the ability to make revisions and add features. For example, as a little challenge you could add a “soft start” effect for some polish where the lamp fades up instead of just coming on. (and fades out as well). Also, you could add a sensor for an adaptive mode so if something reflective is close by (e.g.: reading something on paper) the light automagically dims itself to prevent blinding you.

The possibilities are limited only by imagination. Versions 2–n could be really neat stuff.
 

Thread Starter

SoBuggy

Joined Aug 21, 2022
7
I have made several versions of this. Mostly using microcontroller with a hardware PWM module which drives the switch of a boost converter. You can get microcontrollers that will run on a single AA cell but two is a lot easier. You could use an ADC to make current or voltage measurements but it's not really essential to close the loop. I've attached a schematic for a simple and minimal version. You would usually think of a MOSFET for something like this but they typically require a gate voltage higher than what you'll have when the batteries approach end-of-life. So I used a BJT. Also of note, the switch timing is bit-banged in this version so I didn't even need a PWM peripheral. The power is always turned on and the microcontroller is in a low-power sleep mode. When the user pushes the "on" button, it resets the micro. The firmware the counts down 30 minutes and shuts off the light and puts the uC to sleep again until the next time. Let me know if you want the PCB project. It's in Altium.
Thanks for the info :) I’m thinking I’ll do something similar to this with PWM to change the brightness. I don’t think I need the Altius project but if it’s easily available to send I can take a look at your layout.
 

Thread Starter

SoBuggy

Joined Aug 21, 2022
7
The cool thing about using an MCU is the ability to make revisions and add features. For example, as a little challenge you could add a “soft start” effect for some polish where the lamp fades up instead of just coming on. (and fades out as well). Also, you could add a sensor for an adaptive mode so if something reflective is close by (e.g.: reading something on paper) the light automagically dims itself to prevent blinding you.

The possibilities are limited only by imagination. Versions 2–n could be really neat stuff.
Haha I love it! Always looking for the next improvement. And yeah the ability to change functionality through software makes the project exciting. I’ve been wanting to make this headlamp with a PIR sensor for when I go camping so at night the headlamp could sit outside and turn on if an animal comes too close to the tent.
 

Ya’akov

Joined Jan 27, 2019
6,853
Haha I love it! Always looking for the next improvement. And yeah the ability to change functionality through software makes the project exciting. I’ve been wanting to make this headlamp with a PIR sensor for when I go camping so at night the headlamp could sit outside and turn on if an animal comes too close to the tent.
Sounds like a great and fun way to learn new things about programming, circuits, and LEDs. I look forward to updates and questions for the very knowledgable people here who are always ready to help with everything from PCB design, to mechanical design, to programming, to component choice.

I hope, too, that you become a regular here, paying forward the help as is the custom in this place. If you know one more thing than someone else you are a teacher, if you know one less thing, you are a student—we are all, always, both.
 

bassbindevil

Joined Jan 23, 2014
631
How about a flashlight driver based on ATtiny13 and AMC7135 drivers? NANJG105C for example. IIRC it comes with enough 7135s to drive an LED at 2.8A, but there are other NANJG models with lower current (fewer 7135s). A variety of modes can be selected using soldered jumpers, or it can be reprogrammed with custom firmware. I swapped one of these into a flashlight and I found the basic L/M/H with memory for last brightness was exactly what I needed, so haven't attempted reprogramming. There's lots of info on these at https://budgetlightforum.com/node/23523
These drivers are for a single LED powered from a 1S lithium cell.

Oh, never mind, you don't want a microcontroller? Well, the generic driver chips tend to have annoying modes that include strobe and SOS, no memory for last mode used, and no low setting for when you want to see up cloe without burning out your eyes, or just want to conserve battery life. And if they do have a Low setting, the low PWM frequency makes for irritating flicker (and interferes with digital cameras). But, if price is more important than usability, you can buy the FM2819 on Aliexpress.
 
This is all really great information everyone. Thanks for all the insights. I have some ideas to think through now. Using an attiny microcontroller is looking like the best option for my skill level.
Oh and I should have said the 3A draw for the LED is the max it can take but it looks to produce sufficient light at lesser current.
3 amps is quite a bit for AA cells. Maybe an 18650 Li-ion cell? Also, if it's a single LED with a forward voltage of a couple of volts, you may want to use a buck topology to boost the current from your batteries. Buck converters are typically more efficient than boost converters as well.
 

Thread Starter

SoBuggy

Joined Aug 21, 2022
7
Sounds like a great and fun way to learn new things about programming, circuits, and LEDs. I look forward to updates and questions for the very knowledgable people here who are always ready to help with everything from PCB design, to mechanical design, to programming, to component choice.

I hope, too, that you become a regular here, paying forward the help as is the custom in this place. If you know one more thing than someone else you are a teacher, if you know one less thing, you are a student—we are all, always, both.
Thanks, I'll keep an eye out for posts where I can contribute some knowledge.
 
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