I have recently been working on making a lab bench power supply which has a maximum power output of 240W.
I have been able to write simple code for the feedback and set a precise voltage from the touch screen and rotary encoder.
This is the schematic of the project so far:

As you can see I have not yet been able to add current limiting. I know how to measure current with a shunt, but that will be part of the current limiting section. I do not want he limiting to be linear eg. limiting current with the lm317, because that would waste tons of energy as heat.
I found something here: https://www.microsemi.com/document-...iting-techniques-for-switching-power-supplies
but I would not know how to implement it in this circuit to get working results.
I have 4 digital pins available one of which is PWM capable, and 4, 10-bit ADC input pins.
Any help would be greatly appreciated.
Tom

 

hi Tom,
I get a site error message for your link.

Look up 'fold back current limiting'

Eric

 

hi Tom,
I get a site error message for your link.

Look up 'fold back current limiting'

Eric

Thanks Eric,
Wouldn't that be linear? The microsemi site is not working, but here is an archive of the page I sent:
https://web.archive.org/web/2016040...iting-techniques-for-switching-power-supplies

 

Also, could it be possible that with my original circuit, I could just add a shunt at the + output and then wire it up to the adc, and output various different PWM signals to the gates of the BUCK p-channel, and BOOST n-channel mosfets with certain duty cycles to create a variable voltage and current source which is not regulated/limited linearly. I guess the code for limiting the current would be similar to that used to regulate the voltage (ie. Voltage too high, decrease duty cycle). Is this so?

 

hi T,
These PDF's shows a method of fold back current limiting for SMPS.
A simple alternative, for a bench power supply, would be an over current trip, which would have to be manually reset, after the load which is causing the problem has been disconnected.

You could also consider say, a thermistor temperature measurement of the power FET's, checking for overheating and reduce the PWM On period.

E

 

hi T,
These PDF's shows a method of fold back current limiting for SMPS.
A simple alternative, for a bench power supply, would be an over current trip, which would have to be manually reset, after the load which is causing the problem has been disconnected.

You could also consider say, a thermistor temperature measurement of the power FET's, checking for overheating and reduce the PWM On period.

E

Thanks, I'll try it out.