Wich current on Gate?

[Mr.Big]

I'm repairing a Switching Power Supply with 120A.
There is a Transistors before the Fet comes damaged.
It Oscilites with 72KHz
Betwenn GND and Basis to Tranistor I measure 11V
The FETs are STP80NF03L

Wich current are at the Gate with 72Khz and 11V
Will a BC856 work well??


The originales Tranistor SOT23 is marked with W2F

 

[ThirunavukkarasuThoondi]

Hi
transistor W2F can be replaced by High frequency transistor

 

[Mr.Big]

why High frequency? 72KHz isn't much?
And how much current are there?
The Switching suplly run many hours with highest current...I need a littel space from the maximum current from the transtor for long live

 

[KlausST]

Hi,

Betwenn GND and Basis to Tranistor I measure 11V

A transistor is not referenced to GND.
It is referenced to E, B, C.

--> give the voltage between C and E.

Klaus

 

[Mr.Big]

11V, I mean C and E

 

[KlausST]

Hi,

then I´d give a BC856 a try.But it is specified with 200mA peak current.

W2F: --> PMBT2907A --> 600mA peak current.
datasheet:

According NXP datasheet from 2004/Jan/16 the "W" means made in China.

Klaus

 

[Mr.Big]

Do you think it really is an PMBT2907A, I found many Transistors with this mark

 

[KlausST]

Hi,

many Transistors with this mark

"Many" isn't very descriptive..

..in SOT23?
..With very different specifications? or just different manufacturer and different names?

Klaus

 

[treez]

it sounds like you are saying that there is a totem pole gate drive using pnp/npn and that these are damaged?......maybe the gate drive circuit is wrong and it is damaging them, you should post the gate drive circuit