Minimal Parts LED driver

Thread Starter

HazenAL

Joined Sep 1, 2020
15
I want to design a LED driver that is compact and uses mostly SMD components. It will run 1 LED at 700 mA and 3 V, and be user dimmable with a PWM signal (0-100%) as well. Additionally, It will plug into a USB port to run off of 5 V.
My question is that which design will yield the least amount of SMD components?
The IC I've found is the ILD6070 (datasheet), which has a built-in PWM generator in which it's duty cycle can be controlled by applying 0.61 - 2.43 V. On the other hand, it can be supplied with a separate PWM signal.
The solutions that I can think of are:
  1. A linear regulator that's adjustable
  2. A PWM generator IC
  3. A timer like the 555, but this adds the most parts
 

wayneh

Joined Sep 9, 2010
17,153
I want to design a LED driver that is compact and uses mostly SMD components. It will run 1 LED at 700 mA and 3 V, and be user dimmable with a PWM signal (0-100%) as well. Additionally, It will plug into a USB port to run off of 5 V.
My question is that which design will yield the least amount of SMD components?
The IC I've found is the ILD6070 (datasheet), which has a built-in PWM generator in which it's duty cycle can be controlled by applying 0.61 - 2.43 V. On the other hand, it can be supplied with a separate PWM signal.
The solutions that I can think of are:
  1. A linear regulator that's adjustable
  2. A PWM generator IC
  3. A timer like the 555, but this adds the most parts
I don't see how you could possibly beat a purpose-built IC like the one you linked. I'd be nervous running that particular device at its max current rating continuously. It might be fine but it'd be great to find another IC with a little higher rating.
 

Thread Starter

HazenAL

Joined Sep 1, 2020
15
I don't see how you could possibly beat a purpose-built IC like the one you linked. I'd be nervous running that particular device at its max current rating continuously. It might be fine but it'd be great to find another IC with a little higher rating.
Okay. How should I apply a voltage to the IC? Linear regulator with a pot?
 

Papabravo

Joined Feb 24, 2006
16,773
Okay. How should I apply a voltage to the IC? Linear regulator with a pot?
Words do not do what you have in mind any justice at all. Draw it up. Schematics are the lifeblood of engineering.
I think you have bigger problems than that with using the chip. How did you plan to select the inductor?
Anything with an inductor drawing 0.7 Amperes is unlikely to be either small or compact.
 

Ian0

Joined Aug 7, 2020
3,186

Papabravo

Joined Feb 24, 2006
16,773
https://www.diodes.com/products/power-management/led-drivers/
is a good place to look for a variety of LED drivers. There are buck regulators in SOT25 packages which take either analogue or PWM dimming inputs.
including this one
https://www.diodes.com/assets/Datasheets/AL8861.pdf
which will switch 1A and is in a package less than 3mm square.
It does reach the stage where the size of the semiconductor becomes irrelevant in comparison to the size of the inductor.
I think that might be why you seldom see an inductor on a chip. (LOL)
 

crutschow

Joined Mar 14, 2008
27,697
Here's the LTspice simulation of a simple PWM circuit that uses one CD40106 Schmidt-trigger hex Inverter package to generate a PWM circuit with duty-cycle controlled by a pot.
It doesn't go completely from 0% to 100% but very near (<1% to >99%), if that's sufficient [shown for 0%(green trace), 50%(yellow trace), and 100%(red trace) pot settings].
5 of the inverters are paralleled to better drive the high gate capacitance of the MOSFET.

The N-MOSFET must be a logic-level type device (Max Vgs(th) <2V).
These can be found with low Rds(on) in SMD packages.

Edit: Changed to CD40106 circuit for better MOSFET gate drive.

1619889571627.png
 
Last edited:

Sensacell

Joined Jun 19, 2012
2,890
I would go with the ILD6070.

With one LED, and 5V supply, the datasheet graph shows using a 10 Microhenry inductor.
10 uH inductors can be very small, you need one with a saturation current of around 1 amp.

You are not going to brew up a smaller or more efficient driver than this.

You can use a simple pot to create the DC control voltage to dim the LED via its internal PWM generator.
 
Top