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Pulse-powered current limiter

Started by Piotr Wyderski ●February 18, 2022
Reply by Jasen Betts ●February 21, 20222022-02-21
On 2022-02-18, Piotr Wyderski <bombald@protonmail.com> wrote:

> Hi,
>
> I am experimenting with white LED COBs and wanted to power them from a 
> constant current source while still having the PWM dimming capability.
> The current limiter should be located next to the diode and the lamp 
> "interface" should be regular two wires. In other words, the current 
> limiter should be capable of being powered from a +12V/open drain source 
> with the PWM frequency of ~400Hz.


Putting two high impedances in series is asking for trouble.

perhaps shunt the LED current instead of cutting the power to the
current regulator, or arrange the current limiter to tune its limit
according to a PWM input

-- 
  Jasen.
Reply by Piotr Wyderski ●February 21, 20222022-02-21
Jasen Betts wrote:


> Putting two high impedances in series is asking for trouble.


The trouble can be caused only by energy stored in stray inductance or 
an EMP from a nearby lightning. TVSes on both ends will handle both 
cases nicely.

	Best regards, Piotr
Reply by Piotr Wyderski ●February 21, 20222022-02-21
piglet wrote:


> Thanks, yes I understood it within a few minutes of my first reply, it 
> should work fine - as you then proved!


Fine is an understatement. I didn't expect this sort of performance from 
a couple of dirt cheap components. It works perfectly well even at 10V 
and there is no (reasonable) upper limit - just the regular cooling 
constraints apply. Selected for implementation. :)

Thank you all for your help.

	Best regards, Piotr
Reply by piglet ●February 21, 20222022-02-21
On 21/02/2022 7:16 pm, Piotr Wyderski wrote:

> piglet wrote:
> 
>> Thanks, yes I understood it within a few minutes of my first reply, it 
>> should work fine - as you then proved!
> 
> Fine is an understatement. I didn't expect this sort of performance from 
> a couple of dirt cheap components. It works perfectly well even at 10V 
> and there is no (reasonable) upper limit - just the regular cooling 
> constraints apply. Selected for implementation. :)
> 
> Thank you all for your help.
> 
>  &nbsp;&nbsp;&nbsp;&nbsp;Best regards, Piotr
> 


You are very welcome, I enjoyed it and it is good to have on-topic posts 
to read!

The 431 packs a lot of gain into a dirt cheap part, folk even use them 
as op-amps with a well defined input offset voltage!

piglet