hello all
I have a problem with my PCB board where my BC547 switching transistor is overheating and sometimes blowing out. I don't know what might be the cause because anytime I replace it and I put it on the system for a long time, I find myself in a similar situation where I have to replace the transistor again.
Help out!

 

What's its average and on resistance? Is there a way you can substitute two BC547 for the one and get enough air to both heatsinks? I can imagine a few circumstances in which the gain walks up and you get parasitic gain (pushing down on real gain and making it look like 150 ohms) from too high a gate.

 

Hello,

@Niu_X_Tang , The used transistor is not a mosfet.
The BC547 is a BJT, wich needs a base current to act as a switch.
@simon mugo , Can you post a schematic, so we can see if the base current is enough to switch.
Also, what current are you switching. The BC547 collector current is limited to about 100 mA absolute maximum.
The rule of thumb would be that Ib = Ic/10, to have a good saturation of the transistor.
If the driven current is at the limit, better use a stronger transistor.
The BC337 would be a good candidate, as the max collector current is 800 mA.

Bertus

 

Post a schematic or I can’t help you.

 

1. You could try using a heat sink , it will help with heat dissipation specially as you're saying that it takes long time till it blow out.
2. Use your multi-meter and measure the current through the collector , maybe it is exceeding the BJT rating..
3. The base current could be too high, measure it using a multi-meter
4. You could also use BC337 as suggested by bertus.