I was troubleshooting a circuit and found that a transistor BC547 is getting very hot and after a day or two it is completely burned out while keeping the circuit on continuously. Then i measured some voltages and currents around it and providing here. I also referred to datasheet of the transistor but couldn't solve the issue. Vce = 10.2V, Vcb = 9.5V, Vbe = 0.7V, Vc to gnd = 22.0V, Ve to gnd = 12.1V, Vb to gnd = 12.7V, Ic = 20mA, Ie = 20mA, Ib = 6.3uA, Here all the values are way below the max values. Then why is the transistor heating up. Do i need to check anything else. ANY HELP.
Well, you have 10.2 volts between collector and emitter and 20 mA flowing. That's a power of over 200 mW and it will get quite warm. If you don't have any circulating air (natural or forced) the transistor will just get warmer and warmer until is dies. There is also to consider that you might be operating this device in a naturally warm environment and this just adds to the woes.
Thermal resistance of the device is specified by Fairchild as being 200 degC/ watt so it will certainly rise at least 40 degC just on the power dissipation alone and, like I said, if there is no circulating air (or other cooling mechanism), it will continue to get hotter.