Hey there! first post here.
I've been working with LED strobe lights for a few months now and I'm looking to upgrade my system.
Currently, my system has 3 separate modules:
1) DC power supply: I have a 12V supply and a 90V low current boost converter for different light sources
2) Strobe Controller circuit
3) Teensy based pulse generator
The strobe control circuit is as simple as can be for now:
Use a mosfet as a low-side switch on the LED.
This means my LEDs are voltage driven instead of current driven. This has been fine while working with resistor laden LED strips, and even a couple cheap COB LEDs.
But now I have a new list of requirements:
1) Run of rectified mains: cheaper and less bulky than DC supplies
2) Adjustable current limit: In the case that my strobe pulses are too long, I don't want to burn out my LEDs
3) Strobe pulse width control with ~5us resolution
4) current limit up to 4A
5) Ideally, but not necessary: have a different current limit for fast pulses and slow pulses
I see 2 paths forward and I'd like to discuss the merits of each path before proceeding.
Path 1) All analog: Use an op-amp and current sense resistor to apply linear feedback to the mosfet gate. Apply strobe control pulses to the op-amp inputs
Advantages:
*) I've used this circuit topology before, and its easy to understand
disadvantages:
*) Need to generate a low-voltage supply rail for the op amp
*) mosfet dumps a lot of heat when its in linear mode
I'm sure this would work, but I'm tempted to take a more sophisticated route.
After disassembling some LED spotlights, I found a class of integrated circuit that uses PWM banging on the mosfet gate regulate the current. Some of them even integrate the mosfet, run directly off rectified mains, and have fancy power factor correction features (which I am not interested in for now). My strobe pulses are non periodic, so I can't just use a typical PWM interface at a fixed or variable frequency.
This leads me to path 2:
Path 2) Use an offline led driver circuit such as AL9910SP:
https://www.digikey.com/en/products/detail/diodes-incorporated/AL9910SP-13/2639280Advantages:
*) Runs directly off rectified mains
*) External PWM control pin for applying strobe pulse
*) Analog dim pin to set different current thresholds
Disadvantages:
*) New chip to work with, may take a few tries
*) I'm using the chip a bit off-label and there aren't too many resources to consult on this usage. For example, I may need to modify the LC network on the load for my use case.
My thoughts on how to adapt the AL9910 for my use case:
*) Operate at the highest PWM frequency (~300kHz)
*) Use an RC network at R_sense to get a different current limit for fast and slow pulses.
*) Omit the inductor L1, or choose a much smaller value, to get fast turn-off
Any thoughts on this topic?
Other IC suggestions?
Is my description coherent enough to discuss?