If I put my notes here, I might be able to find them again later!
Z-reg II improved simple Zener voltage regulator
I've added an additional RC filter stage (R3, C4 in the schematic below) before the Zener diode, substantially reducing the amount or ripple on the transistor base by cleaning up the voltage applied to the Zener reference. (The original Z-reg is described here.)
Circuit shows C2 with a value of 300 uF. Typically much larger values are used. I kept the filter capacitance to a minimum here to show circuit working with a reasonably high ripple (1 V p-p) on the input. The rectifier diodes used here are of no particular consequence, I just wanted the simulation to generate a realistic sawtooth for the input.
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OK, this doesn't do as much as I originally thought. The improvement is mostly below 100 Hz, whereas the ripple is mostly in the 100Hz-1kHz band. There's perhaps 3 dB less output ripple, but that's about it. You can verify this yourself in LTSpice, just cut the wire between C4 and the junction or R1-R3 and rerun the sim.
Circuit shows C2 with a value of 300 uF. Typically much larger values are used. I kept the filter capacitance to a minimum here to show circuit working with a reasonably high ripple (1 V p-p) on the input. The rectifier diodes used here are of no particular consequence, I just wanted the simulation to generate a realistic sawtooth for the input.
***
OK, this doesn't do as much as I originally thought. The improvement is mostly below 100 Hz, whereas the ripple is mostly in the 100Hz-1kHz band. There's perhaps 3 dB less output ripple, but that's about it. You can verify this yourself in LTSpice, just cut the wire between C4 and the junction or R1-R3 and rerun the sim.
Total Comments 2
Comments
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You can also try a small film cap near the gate to eliminate higher frequency switching stuff
Salas on his BiB for example is filtering his led reference with 0.22uF
A gyrator is also an interesting idea used by Matrin from acoustica
He uses it on the raw supply though to fix the high frequency limitations of the LM series, but it would be interesting to see it filtering the reference too...
Using 3-pin regulators off-piste: part 2Posted 22nd February 2015 at 11:44 AM by dimkasta
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Food for thought. I'll look into it!Posted 22nd February 2015 at 01:32 PM by rjm
