replace relay with mosfet

[Afzal hossain]

Dear Experts,
I am trying to using a P-channel mosfet(irf-9640) to switch a gsm module Input power where I am currently using a 5v relay.In case of relay , module is working fine.In case of mosfet,module getting stop while trying to register to a network.irf-9640 is a power mosfet and its current limit is -11A .gsm module gets very small amount of current (<30ma) while starts and at this stage the module is running which indicates that mosfet is being able to supply this current . While gsm modul try to get register to network, it needs few more current (50-60ma) and in that case it's getting stop seems mosfet is not being able to carry this little current . I am switching mosfets gate by a avr micro-controller.

Please help me to find the problem or give me any other option to replace the relay .Thanks in advance .

 

[milan.rajik]

Post the circuit.

 

[esp1]

H Afzal,
The datasheet shows the possible range of Vgs threshold could be as high as -4V.

So -5Vgs in the worst case could give only a few milli-amps of Ids.
Try to find a PMOS FET with a Logic level Vgs control voltage.

E

 

[Afzal hossain]

Hi esp1,
Thank you for your helpful reply.new I am clear about the scenario .I've got fet according to your advice.2sj160-62.

 

[FvM]

You'll need a logic-level FET. A small one like Si2323 should already works.

 

[aliraza786]

you need word on the gate drive circuit i think if you gate is not driven accurately then this problem can happen.use totem pole transistor configuration to drive the gate and then post the results.
or try to use N-Channel mosfet like IRF740 always most your real schematic to get better results thanks.

 

[KlausST]

Hi,

A high side P channel MOSFET should work.

But there are high side power switches, ofthen used to switch power for USB at the device side.
Look for USB power switch.

They have built in protection and switch on inrush current limit.

Klaus

 

[Afzal hossain]

Thank you guys for your valuable suggestions . I thing I got the solution . My knowledge in electronics is very poor.I am facing one more problem.As far I know, mosfet is voltage driven.Is there any problem if high current(transient current made by 24v battery about 30A )strikes on mosfet gate. I am connecting the p- channel Mosfet gate (si2323) to a a 24 battery and using voltage divider to apply 3.5v to the gate. please give me your valuable suggestion .

 

[FvM]

First time you mention 24V. Si2323 isn't suited for that high voltage. Previous posts assumed that the problem is a too low gate voltage. But apparently it's wrong gate control circuit. Too bad that you didn't post a schematic.

 

[Afzal hossain]

Hi FvM,
My first purpose where I wanted to drive the mosfet gate by a mcu is served.I think it will be okey if I drive si2323 gate with a mcu. As your opinion, it will not be save to drive si2323 gate by 24v supplied by a 24v car battery though I divided 24v so that the gate voltage will be about 3.5v.If this is not okey , i think I can use 2sj160-62 mosfet for this purpose.My concern is trisiend current made by battery during the starting of vahicle which will strike the mosfet gate.
please suggest me if 2sj160-62 is ok for this purpose and what will be the situation in case of transient current.

 

[KlausST]

Hi,

a schematic could clarify what you mean.


Klaus

 

[D.A.(Tony)Stewart]

Hey Asfzal,

anytime you ask a question,

Always specify the input and output parameters , everyone starts any GOOD design with specs or even just to solve a problem.

- in this case for voltage and current range and maybe impedance
- plus time and frequency domain parameters
- plus any environmental issue like conducted and radiated noise from a auto starter motor.

Do you know to choose an RC filter to suppress noise to the gate and supply?
Always ensure the FET switch chosen meets the worst case requirements. There are over 20k part numbers to choose from.

try again just for practice here , even though I think we eventually understand your issue.