Applying PWM to load while controlling its current

[farzadlatifeh]

Hey there
I have an electrolysis cell to produce brown's gas from water, in the process gas barrier decreases efficiency of cell while it may consume huge amounts of current too.
So, I need to apply PWM pulses to increase electrode efficiencies and control current consumption in one circuit.
I have this current limiter example "circuit one"
And this simple PWM generator "circuit two"
But I have no clue how to couple them in one circuit for load full control, I mean can I just use one FET in series with load that PWM circuit controls it? Is that so simple though? Or I should do some modifications to reach the target!
If anyone here can help me, I'll be really appreciated.

 

[duke37]

Q1 is always turned off, it needs several volts on the gate to turn on. You could use a p-channel for Q1
A low pass filter is shown. Will this compete with the 555 output frequency and just give a smoothed output.
I see no circuit to turn Q1 on and off quickly to minimise heating in the transistor.
What is brown's gas, is that the colour or should it be Brown's gas?

 

[Alec_t]

As suggested on another forum, you could PWM another FET in parallel with Q2.