power on?

skodaboy · 19th April 2012, 09:47 PM

Hi i have buit standed power supply set up for my ESP active crossover using 7815/7915 regulators.when i turn on nothing happens but if i unplug then plug back in i get power.
any ideas why this might be happening?

Mooly · 20th April 2012, 06:51 AM

Do you mean the voltage regulators fails to produce output ?

There can be a problem if one regulator "starts" before the other. Have you tried reverse biased diodes across each regulator output to ground.

skodaboy · 20th April 2012, 10:07 AM

hi

i hAVE NO DIODES ON THIS ITS JUST SIMPLE bridge ,largecap , regs followed by 0.1uf caps then 10uf caps .

epicyclic · 20th April 2012, 10:41 AM

Mooly is suggesting you put reverse biased diodes IN .....something like 1N4001 (reverse biased ) from each rail to earth after the regs on the regulated output sides . This will probably cure your problem......especially if your following circuitry has rail capacitors connected directly from rail to rail.

DF96 · 20th April 2012, 10:49 AM

Is this caused by the regulators latching into 'protection' mode?

A circuit diagram might help. We are good at guessing, but why should we have to?

skodaboy · 20th April 2012, 01:08 PM

Hi put in diodes as per national data sheet.diodes position with banded end towards positive rail.
It seems to be better will turn on first time.
but after switching off it will only come back on within 3 seconds or after 10 seconds.
the times it doesnt come on and is switched off it powers up briefly as the power drains away

Mooly · 20th April 2012, 04:57 PM

You can also try two more diodes... it's a recognised method... by fitting one across each reg between input pin and output pin.

For the 78 reg the banded end goes to the input pin of the reg and the other end to the output pin.

For the 79 reg the NON banded end goes to the input pin and the banded end to the output pin.

Leave the other diodes in place.

This odd problem, and I must admit it's never happened to me, can also be fixed by sometimes using a different brand of reg. But that's not really the answer.

DF96 · 20th April 2012, 07:59 PM

Would a soft-start circuit help, by slowing things down?

skodaboy · 20th April 2012, 10:35 PM

hey thanks for advice guys.
working well enough in normal use but still a strange one.
i think a have another reg to try.
they get pretty hot by the way!the trafo is 15v to match so should be too much!

imix500 · 20th April 2012, 11:23 PM

You have them on heatsinks right?

19th April 2012, 09:47 PM	#1
skodaboy diyAudio Member Join Date: Mar 2010 Location: Tasmania	power on? Hi i have buit standed power supply set up for my ESP active crossover using 7815/7915 regulators.when i turn on nothing happens but if i unplug then plug back in i get power. any ideas why this might be happening?

20th April 2012, 06:51 AM	#2
Mooly diyAudio Moderator Join Date: Sep 2007	Do you mean the voltage regulators fails to produce output ? There can be a problem if one regulator "starts" before the other. Have you tried reverse biased diodes across each regulator output to ground. __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*

20th April 2012, 04:57 PM	#7
Mooly diyAudio Moderator Join Date: Sep 2007	You can also try two more diodes... it's a recognised method... by fitting one across each reg between input pin and output pin. For the 78 reg the banded end goes to the input pin of the reg and the other end to the output pin. For the 79 reg the NON banded end goes to the input pin and the banded end to the output pin. Leave the other diodes in place. This odd problem, and I must admit it's never happened to me, can also be fixed by sometimes using a different brand of reg. But that's not really the answer. __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*

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20th April 2012, 10:07 AM	#3
skodaboy diyAudio Member Join Date: Mar 2010 Location: Tasmania	hi i hAVE NO DIODES ON THIS ITS JUST SIMPLE bridge ,largecap , regs followed by 0.1uf caps then 10uf caps .

20th April 2012, 10:41 AM	#4
epicyclic diyAudio Member Join Date: Jan 2012	Mooly is suggesting you put reverse biased diodes IN .....something like 1N4001 (reverse biased ) from each rail to earth after the regs on the regulated output sides . This will probably cure your problem......especially if your following circuitry has rail capacitors connected directly from rail to rail.

20th April 2012, 10:49 AM	#5
DF96 diyAudio Member Join Date: May 2007	Is this caused by the regulators latching into 'protection' mode? A circuit diagram might help. We are good at guessing, but why should we have to?

20th April 2012, 01:08 PM	#6
skodaboy diyAudio Member Join Date: Mar 2010 Location: Tasmania	Hi put in diodes as per national data sheet.diodes position with banded end towards positive rail. It seems to be better will turn on first time. but after switching off it will only come back on within 3 seconds or after 10 seconds. the times it doesnt come on and is switched off it powers up briefly as the power drains away

20th April 2012, 07:59 PM	#8
DF96 diyAudio Member Join Date: May 2007	Would a soft-start circuit help, by slowing things down?

20th April 2012, 10:35 PM	#9
skodaboy diyAudio Member Join Date: Mar 2010 Location: Tasmania	hey thanks for advice guys. working well enough in normal use but still a strange one. i think a have another reg to try. they get pretty hot by the way!the trafo is 15v to match so should be too much!

20th April 2012, 11:23 PM	#10
imix500 Proud Union Member diyAudio Member Join Date: Mar 2004 Location: Nashville, TN	You have them on heatsinks right?

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