Hi,
I'm currently working on a high current (Max 10A) limiter. I've taken a look around to see what other people are doing and figured the best approach would be to use a MOSFET as a switch and an Opamp/resistor for the feedback. The output from the Opamp (or comparator in this function) goes to the Data input of a 74175 Flip Flop. This FF is clocked at 100kHz and reset at 10kHz. The idea being that if the current goes above the set value the OpAmp goes high (or high enough) and the FF clears the output upon a rising edge of the clock. The inverted output is tied to the MOSFET...
See image of this circuit here: http://www.solveering.com/freestuff/files/currentLim.jpg
The issue I have is that the MOSFET (a IRFZ44) gets way too hot...
What am I missing? I would like to keep the part count to a minimum and am prepared to sacrifice accuracy of the limit but I would like to keep the maximum heat generated by the FET below about 1-2W. Having the 74HCT175 gives a fairly steep rising edge (~700ns) and using a higher current driver (TC1427) gets this down to about 250ns but the FET still gets really hot.
Any comments? Am I missing something?
I'm currently working on a high current (Max 10A) limiter. I've taken a look around to see what other people are doing and figured the best approach would be to use a MOSFET as a switch and an Opamp/resistor for the feedback. The output from the Opamp (or comparator in this function) goes to the Data input of a 74175 Flip Flop. This FF is clocked at 100kHz and reset at 10kHz. The idea being that if the current goes above the set value the OpAmp goes high (or high enough) and the FF clears the output upon a rising edge of the clock. The inverted output is tied to the MOSFET...
See image of this circuit here: http://www.solveering.com/freestuff/files/currentLim.jpg
The issue I have is that the MOSFET (a IRFZ44) gets way too hot...
What am I missing? I would like to keep the part count to a minimum and am prepared to sacrifice accuracy of the limit but I would like to keep the maximum heat generated by the FET below about 1-2W. Having the 74HCT175 gives a fairly steep rising edge (~700ns) and using a higher current driver (TC1427) gets this down to about 250ns but the FET still gets really hot.
Any comments? Am I missing something?