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SG3525 PWM controller OCP cell

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ym58:
How does that cell work exactly ?
Does it produce some kind of delay (47uF/220nF ?) to the 'dis' output once a current limit has been reached on R9 (current sense) ?



I am myself triggering OCP thru a sense resistor in a Meishile 1000W/12V/87A SMPS (that I want to limit to 50A) but my OCP feedback cell is much simpler than this one (I am using an opamp comparing the voltage across the current sense resistor to a REF voltage then sending a HIGH signal to the shutdown input if Vshunt > threshold) and it works as far as current limiting is concerned.
But my cell keeps inducing an annoying 'click-click-click' sound somewhere within the SMPS !
--
Will such a cell prevent this drawback ?

jonpaul:
the overcurrent sense is designed to shut down the 3525, and after a dealy timeout to restart.

This creates a periodic start, stop cycle upon overload, very common technique especially in the 1980s ancient 3535 SMPS controller

Jon

ym58:
Yes, that's what I thought ...
A few questions though :
- Aside from the R9 value which is not quite convenient to source and swap (vous en conviendrez ;)), do you have any idea where within the cell a threshold adjustement could be implemented (I am thinking of making one of the 2.2K resistors adjustable but maybe I am mistaken) ?
- How does exactly work the delay-before-restart function, which capacitor (and resistor) are involved in the timeout process (and calculation) ?
- What's the use of the diode (not the Zener one !) ?
- Where possibly does the 'click-click-click' I mentioned in my OP come from ?
Merci.

Njk:

--- Quote from: ym58 on January 28, 2023, 01:27:25 pm ---- How does exactly work the delay-before-restart function, which capacitor (and resistor) are involved in the timeout process (and calculation) ?

--- End quote ---
I think you'll get the answer sooner if you change the picture adding reference to every component of the "OCP cell" circuit (like R1, C1, etc.)

jonpaul:
click....magnetostriction of transformer and magnetscs at START><OVERLOAD><Shutdown.

Repeats about 1/sec..1/5 sec

Very typical, see  Tektronix scope PSU repairs
j

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