Power supply +/-15V for OpAmp

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#24
I would not put R1 and R2 on the output side of the regulators, you have introduced a voltage drop that varies with the load current. Use a CRC on the input side to reduce HF noise, but not on the output (unless noise is more important than regulation).
 
#26
Data sheets for 78xx/79xx regulators also show as best practice (last time I looked) a reverse-biased diode between output and input, which can provide protection at turn-off if there are capacitve loads which could cause voltage on the output side to exceed input voltage, which could damage the regulator.

Negative regulators in particular do not regulate well if very little current is drawn by the load, they will drop out of regulation unless a few mA are drawn. I would add a resistor from each rail to ground to ensure a few mA load no matter what the main load does; this also helps to discharge those caps.
 
#29
nezbleu said:
Data sheets for 78xx/79xx regulators also show as best practice (last time I looked) a reverse-biased diode between output and input, which can provide protection at turn-off if there are capacitve loads which could cause voltage on the output side to exceed input voltage, which could damage the regulator.

Negative regulators in particular do not regulate well if very little current is drawn by the load, they will drop out of regulation unless a few mA are drawn. I would add a resistor from each rail to ground to ensure a few mA load no matter what the main load does; this also helps to discharge those caps.
Click to expand...

Sounds good, I will put there 4K7 and led with nice amber light.
Hm, I will check datasheet again. Thanks!
 
#33

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#34
nezbleu said:
I would not put R1 and R2 on the output side of the regulators, you have introduced a voltage drop that varies with the load current. Use a CRC on the input side to reduce HF noise, but not on the output (unless noise is more important than regulation).
Click to expand...

Correct, I missed that. The idea of the regulator is to create a voltage source with very low output impedance - an ideal battery, if you want.
Those resistors destroy that and undo the great work of the regulator.

Jan
 
#35
It all depends on what's more important in the given application, best voltage stability / low frequency output impedance or lowest noise. It's not like a worst-case 10 ohm impedance near DC would be terribly terrible for a lot of uses - the caps would be dominating at AC anyway. It's not what you want for a DAC reference or similar, but ordinary opamp circuits with decent PSRR should be just fine either way.
 
#37
If you need a low-noise supply in a pinch, an RC filtered 78xx/79xx actually isn't bad. It combines the ripple rejection of a regulated supply with the low noise of a passive RC job and doesn't need any exotic parts. Back in the early/mid-1970s, hi-fi integrated amps used nothing but tons of RC filtering, and they worked! (It was the first regulators that caused some nasty surprises, as they weren't low-noise and circuitry tended to have low PSRR.)

Put in two sets of outputs for both filtered and direct output, and everyone's happy.
 
#40
wiseoldtech said:
The standard 7815/7915 arrangement is good, however I add a bit of "tweak" to it by adding a single transistor and zener before each regulator as a "capacitance multiplier".
Dead quiet result as if a battery was there.
Click to expand...

Sadly, I don't have to many skills, so I have no idea how it should be connected. And I have to say, a 'minimal' circuit is what I would like to have. I am thankful anyway 😉
 
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