You didn't yet state clearly what's the intended circuit operation. If it's hiccup current limit, you should tell the parameters. If it's permanent shutdown, there must be a bistable circuit and a reset means, e.g. by cycling the power.
Hi,
I may not have read enough on this subject. I had thought from what I understood that with a comparator, a voltage reference, a current shunt monitor and a sensing resistor it would be possible to control the gate of a pass device fully on or fully off. By extension, a timeout device or a latch to shutdown can be added between the comparator and the pass device to force the faulty circuit into shutdown and not hiccup mode.
Idea is:
Led current total: 100mA = Pass device on and LED strings and LED drive circuitry on.
Led current total: >124mA = Pass device off and LED strings and LED drive circuitry off.
The intended circuit operation is ultimately permanent shutdown. If the current rises above 124mA the LEDs and their drive circuitry should shut down (so as to not waste battery power which it does in current limiting).
Do these waveforms basically have the correct shape for hiccup mode when there is an overcurrent condition, please? I think so but I've never seen it so I want to check with an adult:
What did you mean by parameters for hiccup mode?
Thanks.
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The circuit is configured as a current-limiter and that's how it is functioning.
If you want the output to latch off after an overload then you need to add a latch.
Note that an N-MOSFET is acting as a source-follower to limit the current, which means the output will never be higher than the MOSFET Vgs(th) below the input.
If you want the output voltage to be equal to the input, a P-MOSFET should be used.
That will reverse the polarity of the current limit signal.
Changed it to a PMOS with a discrete NMOS inverter to invert comp output to correct level - much better, it reclaims about 2.5V headroom compared to the NMOS so great, thanks, super suggestion.
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If you want latched overcurrent protection then there
had better be a latch (SRFF) in the lineup somewhere.
I see none, so the mode is probably comparator chatter
(motorboating, similar to UVLO behaviors) which after
the filter looks like something continuous.
Which the user prefers, is a question. Needing to power-
cycle after every momentary current spike is not well
received in some circles.
Hi,
Yes, I agree in some ways, whenever I read about power cycling it conjures up images of some poor tech guy who has to drives hundreds of miles to some bleak, windswept, rainy place just to flick a trip switch every few days.
In this case, the user loves the idea. It's a(nother) torch I'll be using. Besides my unhealthy compulsion for torch circuits, as the end user I want it to go off if a string blows to alert me to the problem - let's hope it doesn't happen in the dark. Hiccup mode related to lighting devices is just annoying, frankly.