Re: microprocessor controlled SMPS

From: Ian (${send-direct-email-to-news1021-at-jusme-dot-com-if-you-must}_at_jusme.com)
Date: 06/07/04 

Date: Mon, 07 Jun 2004 14:23:56 GMT

I've used a PIC to run a flyback SM converter, using a logic-level MOSFET driven directly
from the PWM output. Feedback is via potential divider straight to the comparator input.
Simple bang-bang software control loop to maintain approximately the required output voltage,
triggered off the PWM timer interrupt to sample the output voltage at an appropriate point in
each cycle (away from the flyback spike) and up/down the PWM duty accordingly.

For protection a beefy 200V zener across the HV output to protect the output cap (target
voltage 180V) and a thermal fuse on the MOSFET in case the PWM output gets stuck on
(experience indicates that the MOSFET gets hot quickest in this state :-)

Works great. I did have worries about zapping the PIC I/O lines with inductive spikes from the
transformer, but so far it's clocked up several 10's of hours running without a problem.

<http://projects.jusme.com/cgi-bin/projects/projects/files.pl?tab:files&id:nixieclock1>

(P104V2R1-MCU.pdf is the controller schematic) 

-- 
Ian

Relevant Pages

  • Re: Looking for opinions on LED dimmer circuit
    ... MOSFET is nearly useless, if you really built the circuit as drawn above, because when the PWM output is low, the MOSFET will be on, but the PWM will be sinking all the current that flows through the MOSFET, and when the PWM output is high, there will be no potential from the drain to the source, and hence no current flowing. ... So you could just as easily remove the MOSFET from your circuit above, and replace it with a short circuit and there would be no change in behavior. ... what purpose the IRF510 serves in your circuit as drawn? ...
    (sci.electronics.design)
  • Re: Looking for opinions on LED dimmer circuit
    ... I don't think your circuit makes any sense. ... >>> MOSFET is nearly useless, if you really built the circuit as drawn ... >>> and when the PWM output is high, there will be no potential from the ... connected between 24 VDC and the gate. ...
    (sci.electronics.design)
  • Re: microprocessor controlled SMPS
    ... >Simple bang-bang software control loop to maintain approximately the required output voltage, ... >voltage 180V) and a thermal fuse on the MOSFET in case the PWM output gets stuck on ... what I am missing is a small resistor in the source of the power MOSFET ... controller, to shut down the drive if Idrain exceeds some value. ...
    (sci.electronics.design)