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Power Integrations Engineer Power Integrations ModeratorCurrent limit behavior
I have implemented primary side current limit using a resistor connected to the X pin of TOP246Y.
What happens when the power supply hits the designed current limit?
Does the current max out at the designed value or does the power supply reset?
3 replies | Created on Dec 21, 2010 08:05 AM by powerfly
powerfly
Hello powerfly,
The answers are in the specification:
http://www.powerint.com/sites/default/files/product-docs/top242.250.pdf
On page 3 you see the current limit comparator turning OFF the MOSFET when the current rises up the prescribed limit. It is not shutting down the power supply; it is current limit without auto-restart.
Cheers,
PI_Crusher
PI_Crusher | 278 posts That's exactly what I thought. But what's happening is different. When I reduce the load connected to the output of the Power supply, the PS is reset.
For TOP246Y, my designed current limit is 1.38A. When I connected a 6 ohm resistor across the output, the PS reset.
The first time this happened was when I connected the PS to the output of a rechargeable battery. The PS kept getting reset.
Does the TOP switch current limit work like a BJT current limit with a pass transistor and a another transistor which sinks the pass transistor base current when current reaches the limit?
powerfly | 45 posts Hello powerfly,
The MOSFET is turned OFF for the remaining of the switching cycle. The auto-restart condition is described on page 9, it is happening when the output is not any more in regulation. Use our design software to calculate the transformer, and check the output and feedback loop to see why the regulation is not maintained.
Cheers,
PI_Crusher
PI_Crusher | 278 posts 