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UC3845: UC3845 IC TEMPERATURE

prasanth Chigurupati
Prodigy 20 points
Part Number: UC3845

Hello,

I am using UC3845 PWM IC for flyback topology for 24v5 amps Output .Here I noticed while continuous current of 4amps @24V IC getting heat, around 80 degree centigrade.

Input Voltage :40VDC

Output Voltage  24V @ 5AMPS.

Vcc Start 27K & 18V 0.5W Zenner

VCC voltage : 15V

VCC Resistance : 22 ohm.

MAX DUTY CYCLE:39%

So, kindly let me know the why IC getting high temperature

  • +1
    TI__Guru 72935 points

    Hi,

    You need to check the VCC dc voltage and dc current of UC3845 then calculate the power. This power is the reason to cause UC3845 IC temperature increase. To reduce the temperature you need to reduce the power into VCC. So you need to find why the VCC has that much current and voltage. For voltage, VCC = 15V, you can reduce it 2 or 3 volt so help reduce the power, Reduce switching frequency can help reduce power into VCC. You can also consider external driver for MOSFET. 

    So if 80C is not acceptable you need to find ways such as from above to reduce power in to VCC (and VC if you use 14 pin package). After the power into VCC and Vc reduced, the temperature will be reduced.