Power transistor gets heating up??????

hi all!.....

I am using the power transistor which withstand continuous DC current upto 1A.

i am using it to the 200mA resistive load.... at 30V DC supply...

for that 200mA load the power transistor gets so much heat... what is the problem...........

i attached the power transistor data sheet... please refer.....!...

Please note that here:
Power = Vce * Ic (negleting Vbe * Ib)

Do you have an idea about Vce?

Added:
Or you may like showing the components that bias the SMD PNP transistor.

karthickb3e said:

hi all!.....

I am using the power transistor which withstand continuous DC current upto 1A.

i am using it to the 200mA resistive load.... at 30V DC supply...

for that 200mA load the power transistor gets so much heat... what is the problem...........

i attached the power transistor data sheet... please refer.....!...

Click to expand...

@25C temp:
1A is not continuous! Its max 1A! and max voltage is 80V.

As KerimF said, we need to know how much power the transistor is dissipating in your circuit.

For example, if the transistor has an average Vce of 15V, at 200mA, then the power dissipation is 3 watts. That's quite a lot for a small component - do you have a good heatsink area of copper with the transistor well soldered to it?

The datasheet gives a value of 14K/W, with a 6cm² tinned mounting pad. So, if you have provided that, then the temperature of the transistor will still rise to 42K above ambient assuming the above example dissipation. If you have not provided that, then the part could get very hot with even a small amount of dissipation.

KerimF said:

Please note that here:
Power = Vce * Ic (negleting Vbe * Ib)

Do you have an idea about Vce?

Added:
Or you may like showing the components that bias the SMD PNP transistor.

Click to expand...

Vce= 30V
and Ic = 200mA


what this....

Added:
Or you may like showing the components that bias the SMD PNP transistor i dont understand

karthickb3e said:

Added:
Or you may like showing the components that bias the SMD PNP transistor i dont understand

Click to expand...

Show us your circuit schematic, so that we can determine how you are using the transistor and why it is getting hot.

Sorry

at 30V DC supply...

Click to expand...

I thought that your supply, for both Vce and the load, is 30V.

If Vce=30V and Ic=200mA, it means the tiny SMD transistor should dissipate 6W!
I would be surprised if it is still alive

Actually, we need always considering at least the following three limits:
Voltage
Current
Power dissipated

You just missed the 3rd one.

On the other hand, if you let Vce = 50V and Ic = 500mA and the duty cycle of these two be equal to 2% then:
Pdis = 50 * 0.5 * 0.02 = 0.5W only which is not bad as 6W though Vce and Ic are higher.

Kerim

KerimF said:

Sorry I thought that your supply, for both Vce and the load, is 30V.

If Vce=30V and Ic=200mA, it means the tiny SMD transistor should dissipate 6W!
I would be surprised if it is still alive

Actually, we need always considering at least the following three limits:
Voltage
Current
Power dissipated

You just missed the 3rd one.

On the other hand, if you let Vce = 50V and Ic = 500mA and the duty cycle of these two be equal to 2% then:
Pdis = 50 * 0.5 * 0.02 = 0.5W only which is not bad as 6W though Vce and Ic are higher.

Kerim

Click to expand...

thanks for all responses...... and also special thanks to KerimF... i miss the the power dissipation calculation.......................

---------- Post added at 08:58 ---------- Previous post was at 08:51 ----------

On the other hand, if you let Vce = 50V and Ic = 500mA and the duty cycle of these two be equal to 2% then:
Pdis = 50 * 0.5 * 0.02 = 0.5W only which is not bad as 6W though Vce and Ic are higher.


i using the transistor for 20usec ON TIME and 230usec OFF TIME... (total time= 250us (ie)frequency= 4Khz) for that also the transistor heats up from your formula Pdiss= 0.48 only... then how its get more hot.............................

and also it makes noise (switching sound) how should i control noise................


is any mistake i done ....... please help me.........

See this doc about power dissipation according to SMD package :

http://www.irf.com/technical-info/appnotes/an-994.pdf



A Method to Determine How Much Power a SOT23 Can Dissipate

http://ww1.microchip.com/downloads/en/appnotes/00792a.pdf