15VAC to regulated +15/-15v irregular behaviour

Thread Starter

jacopo1919

Joined Apr 12, 2020
41
Hello. i need an advice regarding a power supply i'm trying out.
it is from Elliot sound products ESP : https://sound-au.com/project05-mini.htm

i didn't want to zombify this thread even if is related (same circuit) to this one.
https://forum.allaboutcircuits.com/...gulated-15-15v-circuit-question.131169/page-3

So..
as adviced in the ESP page, i connected Ground and AC2 to my 15VAC trasformer. (full-wave voltage-doubler type)
it works, i get the result as shown if the picture BUT mystery arrives now:

from time to time (more or less once every 4/5 time that i switch it on.. kind of randomly), the regulated +15V doesn't work (measuring from pin 3 of the 7815). it remains 0v.
why such a thing happens? and why just sometimes?

i also attach a picture of what happens when i switch off the circuit (in case of the above mentioned malfunction):
the unregulated - 20V and the regulated -15V slowly decrease towards ground as expected,
the positive at 0v and the unregulated +20V stay still untill the negative rails go down to around -2v and then instantly the ''regulated'' drops at +15V for one second and then both descend towards 0v .

i hope the last part is clear and thanks in advance if someone can help me out.

EDIT: this will be more explanatory than words:
 

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Last edited:

ericgibbs

Joined Jan 29, 2010
12,901
hi 1919,
Is the highlighted text a typo.?
Do you have a load connected when the malfunction occurs.?
If Yes, what is the load.?
E
Quote:
from time to time (more or less once every 4/5 time that i switch it on.. kind of randomly), the regulated +15V doesn't work (measuring from pin 3 of the 7815). it remains 0v.
why such a thing happens? and why just sometimes?

i also attach a picture of what happens when i switch off the circuit (in case of the above mentioned malfunction):
the unregulated - 20V and the regulated +15V slowly decrease towards ground as expected,
 
Last edited:

KeithWalker

Joined Jul 10, 2017
1,779
from time to time (more or less once every 4/5 time that i switch it on.. kind of randomly), the regulated +15V doesn't work (measuring from pin 3 of the 7815). it remains 0v.

i also attach a picture of what happens when i switch off the circuit (in case of the above mentioned malfunction):
the unregulated - 20V and the regulated +15V slowly decrease towards ground as expected,
the positive at 0v and the unregulated +20V stay still untill the negative rails go down to around -2v and then instantly the ''regulated'' drops at +15V for one second and then both descend towards 0v .
Are you surer your explanation is correct? Under the fault condition, you state that there is no voltage out from the +15V regulator.
When you switch it off, you state that "the regulated +15V slowly decrease towards ground as expected". These two statements contradict each other.
It sounds as though the positive regulator is going into current overload shutdown. This could occur if you turn on the power shortly after turning it off, before C3 is discharged. The sudden surge of charging current into C9 could trigger the current overload protection in the regulator. This could be caused by having a load connected to the +15V supply to discharge C9, or C9 may be faulty and not hold its charge.
 

Thread Starter

jacopo1919

Joined Apr 12, 2020
41
hi 1919,
Is the highlighted text a typo.?
Do you have a load connected when the malfunction occurs.?

E
Quote:
from time to time (more or less once every 4/5 time that i switch it on.. kind of randomly), the regulated +15V doesn't work (measuring from pin 3 of the 7815). it remains 0v.
why such a thing happens? and why just sometimes?

i also attach a picture of what happens when i switch off the circuit (in case of the above mentioned malfunction):
the unregulated - 20V and the regulated +15V slowly decrease towards ground as expected,
Hi. the second one yes. i meant -15v and i corrected now, the first one is correct. as you can see in the picture (picture named ''unregulated fail'') the probe n.4 (light blue) stays on Ground/0V instead of been +15V.
there is a load attached, yes.
 

Thread Starter

jacopo1919

Joined Apr 12, 2020
41
Are you surer your explanation is correct? Under the fault condition, you state that there is no voltage out from the +15V regulator.
When you switch it off, you state that "the regulated +15V slowly decrease towards ground as expected". These two statements contradict each other.
It sounds as though the positive regulator is going into current overload shutdown. This could occur if you turn on the power shortly after turning it off, before C3 is discharged. The sudden surge of charging current into C9 could trigger the current overload protection in the regulator. This could be caused by having a load connected to the +15V supply to discharge C9, or C9 may be faulty and not hold its charge.
hi. you are correct, that doesn't make sense but was a typo. i wrote +15V instead of -15V. i corrected now.

the fault doesn't occur when i switch on and off shortly after, i actually have to wait something like 5 seconds and then when i switch on again, i have this behaviour.
it definitely looks like the positive regulator shuts down somehow though.
 

KeithWalker

Joined Jul 10, 2017
1,779
Does the load have a large capacitor connected across its input? That would contribute to your problem.
C1, C2, C3 and C4 have no discharge path once the voltage falls to below the input threshold of the regulators. If they are in really good condition, they may hold their charge for a long time, which could initiate your fault condition. A 1 megohm resistor across each one will supply a discharge path for them and may solve your problem.
 

Thread Starter

jacopo1919

Joined Apr 12, 2020
41
Does the load have a large capacitor connected across its input? That would contribute to your problem.
C1, C2, C3 and C4 have no discharge path once the voltage falls to below the input threshold of the regulators. If they are in really good condition, they may hold their charge for a long time, which could initiate your fault condition. A 1 megohm resistor across each one will supply a discharge path for them and may solve your problem.
both audio input /audio out have a 10uF capacitor.
what do you mean precisely with across each one?
 

Thread Starter

jacopo1919

Joined Apr 12, 2020
41
Hello. i need an advice regarding a power supply i'm trying out.
it is from Elliot sound products ESP : https://sound-au.com/project05-mini.htm

i didn't want to zombify this thread even if is related (same circuit) to this one.
https://forum.allaboutcircuits.com/...gulated-15-15v-circuit-question.131169/page-3

So..
as adviced in the ESP page, i connected Ground and AC2 to my 15VAC trasformer. (full-wave voltage-doubler type)
it works, i get the result as shown if the picture BUT mystery arrives now:

from time to time (more or less once every 4/5 time that i switch it on.. kind of randomly), the regulated +15V doesn't work (measuring from pin 3 of the 7815). it remains 0v.
why such a thing happens? and why just sometimes?

i also attach a picture of what happens when i switch off the circuit (in case of the above mentioned malfunction):
the unregulated - 20V and the regulated -15V slowly decrease towards ground as expected,
the positive at 0v and the unregulated +20V stay still untill the negative rails go down to around -2v and then instantly the ''regulated'' drops at +15V for one second and then both descend towards 0v .

i hope the last part is clear and thanks in advance if someone can help me out.

EDIT: this will be more explanatory than words:
i attached a video for this: blue and violet are are unregulated, yellow and light blue the regulated
 

KeithWalker

Joined Jul 10, 2017
1,779
The positive voltage regulator is going into overload shutdown as I mentioned above. If the regulator or C9 are not causing the problem then it is being caused by the load you have connected to the supply. As it powers up, something in the load is drawing too much current and causes the shutdown. Do you have a circuit diagram of the amplifier you are powering with this supply?
 

Thread Starter

jacopo1919

Joined Apr 12, 2020
41
i tried removing all the ics and the problem doesn't occur anymore! i am using 15 ne5532 ( 6 of them had to be tl072 but i mixed them up) plus occasionally 6 leds .. so i am drawing much more current then expected. both 10R, 1W resistors burned as well. now will try switching to tl072 and see what i can do with all that current request.
 
Last edited:

Thread Starter

jacopo1919

Joined Apr 12, 2020
41
tried adding a 10R,1W resistor in parallel for more current and removed 5 ic and leds ( actually 10 tl072 left)
but i still run into the issue.
 

KeithWalker

Joined Jul 10, 2017
1,779
I can not offer any suggestions because I have no idea what your amplifier circuit is. All I know is that it contains a lot of op-amps and some LEDs,
 
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