I am working on an Active Clamp Forward converter. Schematic is given here: P-spice model of forward converter


  1. Output voltage-5V
  2. Input voltage 26..42V
  3. frequency=500KHz
  4. Output power=10W

It is working fine in open loop, but in closed loop I am getting a ripple in output Voltage of 2.5 Volts Peak to peak.

Voltage waveform is given below: waveformOutput voltage

I have designed controller considering settling time and load disturbance rejection. Here is the bode plot of my plant Gvd(s) and my plant+Controller.Bode Plots What should I do to reduce the ripple in output voltage.

Note1: to implement the controller TL431 and opto-coupler 4N25 are used.

Note2: No ripple is seen in the simulation.

  • \$\begingroup\$ It's very likely the fast-lane disconnection is not working as it should. You have to properly decouple the LED current from \$V_{out}\$ via an intermediate circuit. The Zener diode is supposed to do the job but the 82-ohm resistance is way too low to reject anything. An active shunt regulator would do a better job. Did you solve this issue since then? See there onsemi.com/pub/Collateral/AND9173-D.PDF how I turned the fast lane off with another TL431. \$\endgroup\$ – Verbal Kint Mar 13 at 13:12

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