Electronics > Projects, Designs, and Technical Stuff
Tips on reducing ripple voltage on linear regulator
sahko123:
currently ive it down to around 15mv by adding 10uf to the zener and am going to add a capacitor multiplier to the negative side as well. ill get back on results
sahko123:
as it turns out my probing was one of the issues |O the actual figures are 9.6mVpp and 2.6mVRms at roughly 1.2A
Ian.M:
That's getting over-complex. I've done a LTspice sim of a modified version of your circuit that has under 30uV ripple out for 1V pk-pk ripple in, costing you three diodes and some extra or bigger caps.
Most of the improvement is due to increasing the AC loop gain by bypassing the upper arm of the feedback divider and powering the reference Zeners from the regulated output (apart from during startup). It also uses a diode and reservoir cap to reduce the ripple at the capacitance multiplier input (and boost the average voltage), and has various tweaks to RC time constants to get the corner frequency for LF ripple rejection well under 100Hz.
sahko123:
How would you power the zener from the regulated output though my idea would be to have a 47k or so resistor from collector to emitter of pass element to get some voltage at the regulated output to start the zener initially but I think this'll defeat the point. Also what do you mean by bypassing the upper arm? Is it capacitoelr bypassing? (sorry replied from phone went on computer and noticed spice file)
David Hess:
Power the regulator circuits from the output rather than the input, or from another regulator. Watch out for ground loops. Fix the current sink although if the other changes are made, it can be replaced with a resistor. Just fixing the current sink might be enough to solve your problem.
Is a completely discrete circuit required? Just replacing your discrete error amplifier with an operational amplifier and making the other changes would greatly improve performance.
I prefer the configuration shown below for high performance regulation. Notice that the error amplifier and reference are powered from the regulated output. The integrated regulator used as a pass element provides fault protection but could be replaced with discrete transistors. If a completely discrete design is required, I would still base it off of this topology.
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