The Ultimate Power Supply Filtering

[aviherman5]

Hello, good people of the internet!

I was wondering about creating The Ultimate Power Supply Filtering in a pedal.

it would have:

1) minuscule voltage drop (<= .1v)
2) the best ground and 60hz hum filtering
3) be suitable for <=100ma current draw
4) reverse polarity protection
5) reasonable overvoltage protection (i.e. 18v->9v pedal and not blow up)

All of this is assuming an isolated 9v input voltage

Any ideas or existing schematics out there?

Thanks for all the help!

AH

[antonis]

1) and 2) are incompatible.. 

For mains hum prevention you have to be generous to both reservoir cap size and rectified voltage minimum level, taking into account the worst case scenario..
(electrolytic caps tolerance and mains lowest RMS voltage..)

[iainpunk]

get the biggest, fattest, lowest resistance, highest inductance choke you can find. then, add MOSFet polarity protection.

cheers

[aviherman5]

get the biggest, fattest, lowest resistance, highest inductance choke you can find

By 'choke,' you mean this:


In terms of ohms and henrys, what are we looking at for your ideal choke?

Thanks!

[bartimaeus]

just use polyfuse style reverse voltage protection and call it a day. imho it doesn't make sense to put too much power filtering inside an individual pedal. filter the power at the power supply itself instead.

[Rob Strand]

1) and 2) are incompatible.

I think by < 0.1V drop he means 0.1V drop under load and not 0.1V dropout.
[antonis might be right to read this as dropout see reply #9]

As stated any basic regulator design with some reverse protection will work.
Ultimate implies some sort of over the top performance.

For < 100mA do want to add short circuit protection that limits to 100mA?
The smaller regulators can limit at low current but they can't actually
produce the rated output because they overheat at normal usage currents.
You can fix the overheating problem with larger regulators but then you
loose the low valued current limit.  The other way is to feed the smaller
regulators with a lower input voltage derived off a larger pre-regulator.

[antonis]

I think by < 0.1V drop he means 0.1V drop under load and not 0.1V dropout.

Possibly but should he refer on voltage regulation percentage then..??

[Jarno]

Hello, good people of the internet!

I was wondering about creating The Ultimate Power Supply Filtering in a pedal.

it would have:

1) minuscule voltage drop (<= .1v)
2) the best ground and 60hz hum filtering
3) be suitable for <=100ma current draw
4) reverse polarity protection
5) reasonable overvoltage protection (i.e. 18v->9v pedal and not blow up)

All of this is assuming an isolated 9v input voltage

Any ideas or existing schematics out there?

Thanks for all the help!

AH

Are you asking for best practices? If not, what problem are you trying to solve?

[niektb]

Doesn't achieve the low voltage dropout but I think it's neigh impossible to get good low-noise regulation without room to regulate

https://electrical.codidact.com/posts/279580
Scroll a bit down to get the "capacitance multiplier + current limiter + voltage limiter". I think thats the best you get without diverging to complexer solutions like  op-amp or IC-based (such as LDO).

Or you just get a LT3080 with a pot-adjusted voltage, call it a "sag" feature and everybody is happy, who needs headroom anyway 

[Rob Strand]

Possibly but should he refer on voltage regulation percentage then..??

You can say it as a voltage or a percentage.

The post is titled "power supply *filtering*".  He doesn't actually imply any voltage regulation.

So maybe you called it correctly as dropout and then like you said (1) and (2) are incompatible.
(So I'll retract my view until the op says otherwise.)

[antonis]

You don't have to retract anything, Rob..
(after all, it's just a chilled discussion about something "ultimate"..)

[Rob Strand]

You don't have to retract anything, Rob..
(after all, it's just a chilled discussion about something "ultimate"..)

Well it's more of chilled retraction than an utltimate one 

[anotherjim]

Power supply with filtering?
This...

[iainpunk]

get the biggest, fattest, lowest resistance, highest inductance choke you can find

By 'choke,' you mean this:


In terms of ohms and henrys, what are we looking at for your ideal choke?

Thanks!

that one s a bit small for power supply filter purposes, i was thinking more around the size of a microwave transformer. ideally less than 4 ohms and more than 10 Henries.

for guitar pedals, a 1n400x series diode and a 10u capacitor is generally enough.

cheers

[aviherman5]

Can I use a gyrator to simulate the inductor?


https://www.epanorama.net/documents/telecom/gyrator.html

[antonis]

Unfortunately, No..!!

Both 'cause simulation doesn't correspond to actual current demand and 'cause gyrator refers to grounded inductor..
(the later is part of HIGH pass filter..)

[iainpunk]

you can use a 'capacitance multiplier' if you want a transistor in the power supply, but a gyrator is like a inductor to ground, while the power supply inductor is in series with the power path. also, how are you going to power the gyrator cleanly enough to work here at all, it can't filter its own power, and needs really clean power.

cheers
edit: Antonis was just a bit quicker

[Rob Strand]

I think we have actually hit the point that antonis made where requirements (1) and (2) are incompatible.

The capacitance multiplier circuit has *at least* one Vbe drop (0.65V) usually a bit more due to the base resistor.

The key point is the circuit cannot boost the voltage and make the output voltage higher in the dips of the ripple.   By deliberately adding more dropout you can filter a higher amount of ripple.

The problem was discussed here,

https://www.diystompboxes.com/smfforum/index.php?topic=126170.0

and this thread has a simulation that shows if the ripple exceeds the deliberate dropout the circuit no longer filters.

https://www.diystompboxes.com/smfforum/index.php?topic=127644.msg1225116#msg1225116

The gyrator circuit from Electronics world cannot boost the output voltage either.  In fact the circuit is very similar to a capacitance multiplier.   It has same problem that you need to add dropout for it to work.  The difference is you add DC resistance to the inductor to make more drop.  I haven't compared it against the capacitance multiplier but it will be similar, perhaps a little worse off, for dropout.