short cirucit issue

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Sir,

    we made a 36w constant current circuit(50v/700ma) with the help of der289 and it is working fine. We conducted a short circuit test and the unit got shut down. After removal of short circuit , the circuit is working ok but with less output current. Before the SC test output current was 690mA and after test output current is 650mA only. The current sense resistor used was 0.33ohm(1ohm resistor3nos parallel+/-5%). Why this current is reducing after sc test? We removed the current sense resistor with a fresh 0.33ohm, circuit started working with 690mA. Kindly explain

Thanks

SDM

Hi SDM,

The power level and output voltage is high enough to change the characteristic of the sense reistor during hard short. For this kind of application use high pulse rating sense resistor.  Sample is:

http://www.bourns.com/pdfs/CRM0805_1206_2010.pdf

 

Regards,

PI-Jono