Power MOSFET Problem

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electro13

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Hi,

Sorry if the questions sound stupid!! I'm just confused and need help!

I'm working on a power inverter project, im using two Power MOSFETs 'FQP30N06', at 100KHz PWM, do I need a gate driver to control the FETs or connecting the gate directly to the PWM pin output from STM32F4 is enough? I tried connecting them directly from the pinout, the FETs where working fine for a while, but then I couldn't get any output from the drain, I'm guessing the FETs broke down, but is it possible to break a FET just by applying PWM?
 

electro13,

You must inform what circuit topology is used ( Push-Pull / Full-Bridge / etc... ).

+++
 

andre_teprom,

Im using Push-Pull topology connected to a centre tapped transformer to convert DC to DC!
 

You need 10v to 12v of gate drive for these MOSFET's. A uP with 3.3 volt I/O's will not drive them directly. Yes, you need a driver IC.

Don't let the STM part have too long an active MOSFET 'ON" period or you will saturate transformer and blow the supply fuse (or MOSFET if you don't have a fuse).
 

Try perform a simple test, just applying VCC to gate directly ( protecting with a 100R ).
Check if drain flows conduction now.

+++
 

A mosfet driver is required surely at 100khz microcontroller output is not be able to provide the gate drive required by the FET
 

theres alot of different driver ICs, I dont know which one to pick, for example which bridge type, or driver type! and is there a way to protect the MOSFETs from saturating using resistors or capacitors?

andre_teprom said:
Try perform a simple test, just applying VCC to gate directly ( protecting with a 100R ).
Check if drain flows conduction now.

+++
Click to expand...

I'll test this today and see! if I use a signal generator would that be enough gate voltage to work?

Thanks
 

electro13 said:
...is there a way to protect the MOSFETs from saturating using resistors or capacitors?
Click to expand...

Due you are under development stage, I suppose you are using a DC regulated power supply, with limit current protection, wright ?
That´s the standard procedure, and if the case, there is no need to do that you are asking.

+++
 

andre_teprom,

I've tried connecting VCC "12V" directly to the gate! and I got nothing out of the drain! shouldn't I get something close to 12 V out of the drain?
 

electro13 said:
andre_teprom,

I've tried connecting VCC "12V" directly to the gate! and I got nothing out of the drain! shouldn't I get something close to 12 V out of the drain?
Click to expand...
NOTING? how did you connect your mosfet ? it should work even with 5volt ..connect your source to ground and apply 5volt to gate via 1k resistor check you voltage between drain and vcc you should see 12v displayed on your meter screen.
 

the drain should give a low signal when the gate is charged. connect a bulb to supply positive and the drain. the bulb should light up when u put a gate signal.
 

yeah! I connected the drain to ground! now I connected it to vcc i got 5v out!! this means that the FET is working right? but if connect the PWM directly I dont get any output! so I need a gate driver?!

I tried using a signal generator to get the PWM at 100KHz and 11V connected to the gate using 1K resistor, I should get 100KHz and nearly 11V, but instead im getting around 1V from the drain at 100KHz? im confused shouldn't I get 11V?
 
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if this is a mosfet there should be no current flow from gait to drain. create a voltage divider, put a 10k res between mosfet source and ground, place another 10k from mosfet drain and supply. when mosfet is turned off you should measure supply at drain node of mosfet. when you apply a gate voltage the mosfet(assuming nfet) will turn on and you should see a voltage close to supply/2 at the drain.

-Pb

- - - Updated - - -

Also as far as can a PWM kill a mosfet, yes.
if the gate voltage is too large it could punch-through to the channel and get a shorting affect. also if the voltage difference between drain and source is too large you could get a punch-through and a shorting between drain and source would occur.
-Pb
 

would the voltage out of the drain be enough for the transformer to boost the voltage?
 

may i know why you connected the drain to ground?
 

you need to understand a mosfet, it is not a bjt. there is no current flow from gate to drain or gate to source.
the only current flow is drain to source. the fet can be connected in various manners, cs, cd(sf), cg. If this is a nmos mosfet, and you put 11V on the gate you are turning the device on, making the drain source a resistor essentially. if it is pmos mosfet, then putting a voltage on the gate turns the device off.making the drain/source an open.
 

im trying to connect the 2 nmos mosfets to a centre tapped transformer as part of the DC to DC push pull topology, i connected the drains to the transformer, the sources to ground and the gates to complementary PWMs shouldnt this work and give a higher voltage at the output of the transformer?
 

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