![]() The MOSFET T2 circuit controls, which helps to make Tr2 transformer work offers floating drive and galvanic isolation for the upper IGBT. However, the original threshold of UC3845 should to set as low as possible. It never goes below 13.5V and further helps to protect IGBT from desaturation. The source initiates the power and starts working on 14.1V. The circuit is further powered with the help of the zener diode, which actually helps to reduce the supply voltage and even helps to shift the UVLO threshold of lower 7.9V and upper 8.5V to 13.5V and 14.1V respectively. The UC3845 control circuit results to 47 duty cycle (Max.) with the output frequency of 50 kHz. The auxiliary supply on the other hand uses TNY267 circuit and R27 facilitates protection from under-voltage of auxiliary power. It is ideal to select R1 so that the voltage at the fan and the relay coil limits to 12V. ![]() The power is obtained via the resistor from 17V auxiliary supply. The relay coil and fan, taken from AT or ATX power supply is powered from 12V. The mains voltage goes straight through the EMC filter which is further checked and filtered on C4 capacitor.Īs the capacity is high (50 amps), the inflow in the limiting circuit with Re1 switch and also on R2. Written and Submitted by: Dhrubajyoti Biswas Using IC UC3845 as the Main Controller The switching supply is powered with IGBT transmitters and is further controlled by UC3845 circuit.
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