Lm317 as a variable reg also has a variable performance that declines above 12v, from what ive read here and also what ive been able to verify via listening.
So im wondering if at much higher voltage, say 24, would lm7824 be performing better?
Also does 78xx series have an inductive output like lm317?
So im wondering if at much higher voltage, say 24, would lm7824 be performing better?
Also does 78xx series have an inductive output like lm317?
What exactly is it that concerns you at performance level for 317?
And what du you mean by "inductive output"?
The current limit? If so then yes, 78xx has the same characteristic as 317.
And what du you mean by "inductive output"?
The current limit? If so then yes, 78xx has the same characteristic as 317.
All NFB systems (even emitter/cathode followers) lose gain at high frequency, so the Z out increases, which is inductance.
Why bench-race? It would cost you $2 to buy and wire-up both LM317 and LM7624 and try.
Why bench-race? It would cost you $2 to buy and wire-up both LM317 and LM7624 and try.
LM317 is just a 1.25V regulator and any 78xx can be wired the same way to make it "variable". 7824 is not a common part like 7805 or 7812 so I would use 7812 with a 2:1 feedback divider. All of these are linear regulators with an input voltage limit about 40V, so they are suitable for low current from a raw supply that is about 6V higher than the output. They require an output capacitor with significant ESR for feedback stability, ie a ceramic cap is not suitable.
Both LM317 and LM7824 rely on bandgap references but LM317 has the ability to reduce the multiplied up noise with an external cap and LM7824 does not.
Look out for the effect of the ground pin current when you do that. The LM317 is designed to have only a very small current through the ADJ pin, while the 78xx series is not designed to have such a low current through the GND pin.
I think the consensus is that the 317 is higher performance as a regulator than a 78xx, some of the reasons are mentioned above.
Jan
Jan
A raw 317 is inferior when wired for 24V, but with the capacitors it has the potential to be significantly better
Low ESR caps for LM317 etc.
581-TAP105K035SCS 35V 1uf solid tantulum
80-A759BQ106M1VAAE90 35v 10uf organic polymer
Mouser part numbers only a computer would love
Interesting Note: The Whammy Class A, 25 watt kit uses 7815 with LEDs to lift the output to 17vdc
581-TAP105K035SCS 35V 1uf solid tantulum
80-A759BQ106M1VAAE90 35v 10uf organic polymer
Mouser part numbers only a computer would love
Interesting Note: The Whammy Class A, 25 watt kit uses 7815 with LEDs to lift the output to 17vdc
Low-ESR capacitors should work well for ADJ decoupling, but as far as the output capacitor is concerned, like steveu already wrote, an LM317 needs some ESR to stay stable. I'd rather use a run-of-the-mill electrolytic capacitor than a low-ESR one for the output.
The last bug I had in my valve DAC was an annoying high-pitched beep that sometimes came from the PCB and sometimes not. I hadn't a clue what it was until I read a remark about LM317's and output capacitor losses on this forum. I had used two 10 uF X5R ceramic capacitors for the output decoupling of a 1.8 V regulator with an LM317, which sometimes did and sometimes didn't make it oscillate. The piezoelectric capacitors also acted as loudspeakers. After I connected a cheap 47 uF aluminium electrolytic capacitor in parallel, it never beeped again.
The last bug I had in my valve DAC was an annoying high-pitched beep that sometimes came from the PCB and sometimes not. I hadn't a clue what it was until I read a remark about LM317's and output capacitor losses on this forum. I had used two 10 uF X5R ceramic capacitors for the output decoupling of a 1.8 V regulator with an LM317, which sometimes did and sometimes didn't make it oscillate. The piezoelectric capacitors also acted as loudspeakers. After I connected a cheap 47 uF aluminium electrolytic capacitor in parallel, it never beeped again.
Put a low value resistor inbetween the neg pin of the output elcap and the gnd. 2ohm or less. Not only is it a surefire guarantee vs oscillation it usually sounds better in treble.
I know elvee's denoiser thread recommends this too
I know elvee's denoiser thread recommends this too
It can be done with devices that have more than 3 pins. Same era dinosaur LM723 could be the man for the job. Low noise and at the same time higher current 24V PSUs can be made with it relatively easy because of the external pass transistor.
Interesting would be to compare designs with regards to performance. I know LM723 still is one of the better regulators so age does not say much. They do differ depending on brand though.
https://www.electroschematics.com/3v-to-24v-variable-power-supply/
BTW dinosaur LM350 is also 3A and pin compatible with LM317.
Interesting would be to compare designs with regards to performance. I know LM723 still is one of the better regulators so age does not say much. They do differ depending on brand though.
https://www.electroschematics.com/3v-to-24v-variable-power-supply/
BTW dinosaur LM350 is also 3A and pin compatible with LM317.
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I measured the output noise of a 317 at a load of c 300mA with a QA401 analyser and got wideband noise of 35uV which included the ripple components. The adjust pin is decoupled with a 100uF cap. This is pretty good performance IMV. To get the best out of IC regs like this, you do need to follow the data sheet recommendations but also make sure you have adequate decoupling around your PCB. There’s no point in designing a super reg otherwise.
(I don’t think the 723 is available anymore - it was a very quiet reg from the thermal noise aspect IIRC)
(I don’t think the 723 is available anymore - it was a very quiet reg from the thermal noise aspect IIRC)
You can always use a PNP emitter follower to raid the ground voltage - Self has an example of this in one of his books.
