Dirty, non insulated half wave power supply design circuit?

Thread Starter

taith

Joined Apr 1, 2017
28
I want to make as efficient as possible DC power source from available 24v AC mains insulated source
I want to ditch diodes in favor of MOSFET design, just not sure how to drive gate to result with desired effect
Zrzut ekranu z 2020-03-02 12-28-44 (kopia).png
 

KeithWalker

Joined Jul 10, 2017
1,062
I want to make as efficient as possible DC power source from available 24v AC mains insulated source
I want to ditch diodes in favor of MOSFET design, just not sure how to drive gate to result with desired effect
There is a problem with MOS FET bridge rectifier circuits: Do not use it as the rectifier in front of a capacitor-input power supply! In a conventional rectifier bridge, the diodes prevent the backflow of current from the power supply input capacitor as the applied voltage drops below the voltage on the capacitor. With this design, the MOSFETs act like switches rather than one-way valves for current flow. They don’t care which way current flows, hence the input capacitor of the power supply will be discharged to near zero volts with each half-cycle of the applied AC power! This limits the power supply applications for this circuit to inductive- or resistive-input designs.

Regards,
Keith

MOSBRG.jpg
 

crutschow

Joined Mar 14, 2008
25,133
You could use a MOSFET bridge driver IC which will work with a capacitive load, such as one of these, which uses all N-MOSFETs.
Also here's a circuit that uses an LM339 comparator to control the MOSFETs, which uses two N-MOSFETs and two P-MOSFETs.
 

Thread Starter

taith

Joined Apr 1, 2017
28
What if I'd like to use 5x3w power LEDs at voltage range between 3.2-2.9V, that is 16-14.5V peak current 700mA
And I'm not looking for bridge rectifier, I'd like to be able to drive gate to set voltage to value I want
If it can't be done with capacitor, would using inductor be practical?
 

KeithWalker

Joined Jul 10, 2017
1,062
What if I'd like to use 5x3w power LEDs at voltage range between 3.2-2.9V, that is 16-14.5V peak current 700mA
And I'm not looking for bridge rectifier, I'd like to be able to drive gate to set voltage to value I want
If it can't be done with capacitor, would using inductor be practical?
That is a very different set of parameters to what you first stated.
What do you plan on using to control the duty cycle of the supply?
Why does it have to be as efficient as possible?
Have you checked on-line? There are lots of AC light dimmer circuits that could be adapted to what you want.
 
Last edited:
Top