P-Channel MOSFET Operation

[Ishaan Karnik]

I am planning to use a PMOS as a primary switch to supply voltage and current to my circuit.
Circuit Condition :

1. Input Voltage Range : +10VDC to +36VDC
2. Input Current : > 27 Amps. (preferably > 30 Amps.)
3. Micro-Controller Available only after complete power up

The problem I am facing is that V_g-s Absolute Rating is +/- 20V.
I have checked more than 500 PMOS but this limitation for V_g-s exist in all.
As the input is from battery and decays over time Zener diode and Resistive Voltage Divider are not feasible.
Project is still in design phase any practical changes in design are still permissible.
Any Suggestion.

Regards,
Ishaan Karnik.

 

[FvM]

As the input is from battery and decays over time Zener diode and Resistive Voltage Divider are not feasible.

Zener diode doesn't sound bad as a first approach. Besides maximum gate voltage, which seems quite easily to satisfy, you should think about minimum gate voltage according to the MOSFET characteristic and intended Rds,on.

 

[Ishaan Karnik]

Zener diode doesn't sound bad as a first approach. Besides maximum gate voltage, which seems quite easily to satisfy, you should think about minimum gate voltage according to the MOSFET characteristic and intended Rds,on.

With Zener I am getting a problem of minimum gate voltage, hence I scraped I the idea.
Any other solutions.

 

[FvM]

If you have a minimum gate voltage problem, it hasn't to do with zener diode rather than too low supply voltage. There's no reason why a zener circuit would not pass the full supply voltage to the gate, if required. (reasonable design presumed)

So if the supply voltage is too low, you'll need to think about a voltage boost circuit.

 

[Ishaan Karnik]

If you have a minimum gate voltage problem, it hasn't to do with zener diode rather than too low supply voltage. There's no reason why a zener circuit would not pass the full supply voltage to the gate, if required. (reasonable design presumed)

So if the supply voltage is too low, you'll need to think about a voltage boost circuit.

Consider the two following scenario :
(1) When battery is supplying +36VDC, then we need a Zener to maintain above 16 Volts to avoid damage.
(2) When battery is supplying +24VDC, then the Voltage maintained by the Zener at the gate (+16VDC), will cause the V(gate-source) to be less than required (approx. 8 VDC).
The problem will be most acute when battery voltage is 16-17VDC.
Minimum Operation Voltage required >10 VDC.

 

[FvM]

Series connection isn't a reasonable way to use a zener diode for this problem. Consider a clamp cicrcuit instead (series resistor, zener diode between gate and source).

 

[Jason Cai]

Ishaan Karnik
If I were you,maybe i will use a delay as the primary switch
Certainly,if you need a high-frequency switch,delay isn't suitable for you