Voltage regulator with PWM

Hi,
I have realized this circuit to adjust a DC voltage with a PWM signal ...

What do you think?

The PWM signal frequency that must have?

Thank You.

This circuit will not work unless the 230V is from a transformer winding that is floating. the standard AC mains has the neutral earthed at the supply transformer and is always close to earth, i.e. 0 -> 6V AC, depending on the total supply current from that supply transformer. Also as the earth current is equal to the output current , this circuit would trip a RCD.
If would be helpful if the circuit was redrawn with inputs on the left and outputs on the right.
Frank

Thank You ...
I followed your suggestions ...
but the circuit still does not work ...

Makes more sense when there is an input transformer.

As it controls the trigger time of T5, the PWM period must start synchronous to the AC line frequency and the PWM frequency must be the same as the line frequency, probably 50Hz or 60Hz.

Brian.

Hi,

applying to the circuit a signal PWM-S with a frequency of 50hz,
I should have the signal out of VCC equal to a square wave at the same frequency of the PWM-S?

I can make the measure even without applying the load?

Yes, but I'm not sure what you are trying to achieve. The circuit uses phase control so either you have to use the PWM very slowly, like an on/off switch to control the average output power to the load or you have to synchronize the PWM to the zero crossing of the AC and set the trigger points within a single cycle of the AC. You do not show any method of detecting the zero crossing point. Using an opto-isolator with built in zero-crossing detection limits you to the speed of the AC line frequency.

If you are expecting to simply use the PWM ratio to control the voltage it will not work because from the first zero crossing during the first PWM pulse until the next zero crossing the triac will continue to conduct.

Brian.

why this circuit does work? :bang:

Even without a load? :evil:

I don't think you are understanding how a triac works. When connected to a MOC3083 or a MOC3043 the circuit works like a relay. When you pass current through the LED side of the opto-coupler, it waits until the next zero crossing point then makes the triac conduct. It stays conducting until the LED is off and the AC voltage falls to zero, in other words at the next zero crossing point. You can't turn the triac on and off at any time with the PWM signal you can only turn it on when the LED is conducting (PWM is high) and at the same time the AC crosses the zero point. When it is turned on, no matter what you do with the PWM, it will continue to conduct until at least the next zero crossing. Normally this kind of circuit is used like a power switch, it may turn on for anything from a few AC cycles to hours or days then turn off for a similar period. You can't use it to control the voltage leaving the circuit but you can use it to control how long the full output is turned on and off for in multiples of half AC cycles.

Brian.

If you want to do a higher frequency PWM from the AC line then you need to use a solid-state DC switch (opto isolator with power MOSFET output).