Hi Everyone,
I have a requirement for a variable 0.1 to 3 Volt high current PWM circuit.
Firstly would the attached circuit be suitable? and secondly;
What mosfet would be suitable? assuming my circuit below;

 

Hi Everyone,
I have a requirement for a variable 0.1 to 3 Volt high current PWM circuit.
Firstly would the attached circuit be suitable? and secondly;
What mosfet would be suitable? assuming my circuit below; View attachment 331815

Not many MOSFETs will be fully ON at 3V.
You would have to search for ones with very low VgsTH.
I think that you would need a MOSFET driver to provide a fast enough switch on/off at any frequency above 100Hz or so, because a 30A MOSFET would have a lot of gate capacitance.

 

Many people when looking for a low voltage MOSFET, they look at Gate Threshold Voltage. In this example it is in the range of 1.0 to 1.5 to 2.0 volts. But that is very misleading.

Look at the graph below left. This part (average part with a Vgs(th) of 1.5) will not be turned on well at 3.0V. You need 3.5V to turn on well at 30A. Because you don't know if the part in your hand is a 1.0 or 2.0V part, I think you should have a Gate On voltage of 5.0V or higher.
Again, when choosing a MOSFET look at the Drain Current & DSv & Vgs. This will help you pick a good part and Gate voltage.

 

The first thing to take care of is having a ~100-plus-Watt Power-Supply,
and a huge Storage-Capacitor in the ~100KuF -plus range.

Then figure-out how you're going to generate ~10 to ~15-Volts to fully turn on the Gate of the FET.
( Even a "Logic-Level" FET will usually require at least ~5-Volts for full Gate turn-on ).
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.
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The first thing to take care of is having a ~100-plus-Watt Power-Supply,
and a huge Storage-Capacitor in the ~100KuF -plus range.

Then figure-out how you're going to generate ~10 to ~15-Volts to fully turn on the Gate of the FET.
( Even a "Logic-Level" FET will usually require at least ~5-Volts for full Gate turn-on ).
.
.
.

I have the PSU already ... My requirement is based on replacing faulty circuitry in a Chemical agitator, retaining as much of the original (heating in this case), circuitry as possible.
As to your second "suggestion"; worst case scenario is that I use a small boost converter supplying a mosfet driver and force a couple of paralleled logic level mosfets into saturation in conjunction with the above 555 PWM circuit.

 

Remember to keep the PWM-Frequency to a moderate level to reduce the
required Switching-Current for the FET-Gate(s).
.
.
.

 

The first thing to take care of is having a ~100-plus-Watt Power-Supply,
and a huge Storage-Capacitor in the ~100KuF -plus range.

Then figure-out how you're going to generate ~10 to ~15-Volts to fully turn on the Gate of the FET.
( Even a "Logic-Level" FET will usually require at least ~5-Volts for full Gate turn-on ).
.
.
.

I was going to suggest that a separate power supply to provide enough bias to do the required switching. Certainly the control will need a higher voltage and current.

 

And, generally speaking,
if You must add-on a separate Power-Supply to switch the Gate(s),
it would be a better plan to not use Logic-Level-FET(s), but stick with standard ~15V VGS FET(s).
They will be cheaper, and will generally have more favorable specifications than Logic-Level-FET(s).
.
.
.

 

I use a small boost converter supplying a mosfet driver and force a couple of paralleled logic level mosfets into saturation in conjunction with the above 555 PWM circuit.

Use transistor IRF2903Z, $3.41 for 10 pcs/lot, $1.03 delivery.
In circuit below, with V_IN=3 V, V_GS=17 V, I_D=33 A (at R_LOAD=0.09 Ω),
V_DS(on)=33 mV, so R_DS(on)=1mΩ, transistor dissipates about 1 W.

https://forum.allaboutcircuits.com/threads/cant-figure-this-circuit-out.201291/post-1916067
ADDED:
File "TL431A.zip" - .asu and .lib

 

Use transistor IRF2903Z, $3.41 for 10 pcs/lot, $1.03 delivery.
In circuit below, with V_IN=3 V, V_GS=17 V, I_D=33 A (at R_LOAD=0.09 Ω),
V_DS(on)=33 mV, so R_DS(on)=1mΩ, transistor dissipates about 1 W.
View attachment 332120
https://forum.allaboutcircuits.com/threads/cant-figure-this-circuit-out.201291/post-1916067

This is flippen brilliant ... Thanks @Danko