Toshiba Laptop Power ON and Charger circuit problem.

[peter_england]

in battery charger section there is two Mosfets named AO4435 AND AO4409 if i remove the AO4409 MOSFET THEN the charger adapter pin shows me the 18volts reading and if i replace it then it shows 0 volts , and that AO4409 is got shorted I tested it . My question is what is the substitute Mosfet that i can use here and how to solve further shorting of this mosfet ? I have checked using AO4433 in place of AO4409 but it get shorted .pls help.

 

[pinout]

I'm sure you are correct, but just to check, are you finding the MOSFET component shorted after removal from the circuit?
if so check that your not measuring the inbuilt diode.

If the 'short' is when it is in the circuit, it could be the FET drive circuit is wrong and it is being forced on? If so this could be part of an 'over voltage' protection circuit.

As you can measure 18Volts (assuming this is the correct output voltage) with the mosfet removed, can you put a load on to check if it's regulating. This may help confirm the mosfet function.

 

[peter_england]

I have checked the MOSFET out of the circuit and it showing as shorted.can you please tell how to give load to the MOSFET? Thanks.

 

[pinout]

Without a circuit diagram I'm trying to understand what the MOSFETs function is.

If your power supply gives out 18V with the MOSFET removed, I'm suggesting you put a load on that to see if it regulates.

So assuming it normally outputs about 4 or 5A then test initially around 1A (so choose R around 18V/1A or 18R at say 25W rating on a heatsink), if successful you can then put more resistors on to check load performance.

If all this works, then the MOSFET must be some sort of overvoltage clamp and will need further investigation, but at least your PSU is functioning.

Is the MOSFET a dead short? Test with the meter leads both ways round as there is always a diode across the MOSFET.

After this I'm stumped without a circuit diagram.......