power mosfet IRF740 as a switch circuit ( switch 300 volts DC and 5amp)

[aliraza786]

hello i want to switch 300volts Dc by applying 5 volts at the gate. datasheet says it can switch 400 volts and 10 amp maximum current. but in my case load has just 2 ohm. in protious it is not switching by applying voltage at the gate. kindly guide me thanks , mosfet switch circuit is simple one . see the attachment.

 

[walkura]

If You apply +5 Volt to the gate it should start conducting, however there is a problem with your load.
Let's assume 2 Ohm of load and 0,5 Ohm RDSon (reality is worse)
At 300 Volt this means 120 Watt of heat your load and the mosfet has to dissipate 20% of this.
This is completely ignoring that You try to drive the mosfet with a low gate voltage and the positive temperature coefficient it has.
That means that the losses for your mosfet will in reality be worse.

The diode over the load gives the impression that You want to drive an inductive load (possibly with PWM)
Please give a little more information about your load.

As it is, it would burn your mosfet.
(IRF740 has only 10 Ampere rating which for sure wouldn't handle the 120 Amp's that Ohm's law would say for 2.5 Ohm at 300 Volt)
You will have to parallel mosfets (and ofcourse arrange proper cooling for them)

Best regards,
Walkura.

 

[aliraza786]

walkura you right .. but i want to tell you 300 volts can have maximum 5 ampare current because rectifre i use can not provide more then 5 amp. so we cannot calculate current with ohm formula. now tell me how to solve this issue.. thanks for your help.

 

[IanP]

walkura you right .. but i want to tell you 300 volts can have maximum 5 ampare current because rectifre i use can not provide more then 5 amp. so we cannot calculate current with ohm formula. now tell me how to solve this issue.. thanks for your help.

Your "issue" can be related to low Vgs - see the output curve ...
At Vgs<6V the IRF does nothing.
Normally you should apply at least Vgs=10V ...
:wink:
IanP

 

[aliraza786]

you are right Ianp... i do as you said this is the simulation picture but again it is not switching ... kindly check the picture .


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and one noice thing if i change the load resistance from 2(ohm actual ) to 1k just for checking ... and after this change it works properly .. but for 2 ohm load it is not switching

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picture of the circuit with load 2 ohm kindly check in this load it is not switching .