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Old 10th February 2004, 10:58 PM   #1
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Default Shorted power supply destroys amplifier

I have designed an amp with the Philips TDA2616. All is running well except for when the power supply to the amp is shorted, this destroy the amplifier every time. I have included kickback diodes on the output, but there is something else that needs protecting for this problem.
Any help?
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Old 11th February 2004, 07:55 AM   #2
Nuuk is offline Nuuk  United Kingdom
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We'll need to see full details of your circuit to suggest any fixes.
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Old 11th February 2004, 08:00 AM   #3
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Default Re: Shorted power supply destroys amplifier

Quote:
Originally posted by jpattison
I have designed an amp with the Philips TDA2616. All is running well except for when the power supply to the amp is shorted, this destroy the amplifier every time.
Any help?
The power supply must not be shorted...it almost allways result in catastrophic failure!!
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Old 11th February 2004, 08:16 AM   #4
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One question: How often do you plan on shorting your supply?
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Old 11th February 2004, 09:00 AM   #5
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A few weeks ago a Philips EE guy told me the main failure mode of these single chip poweramps is that one of the rail voltages is not there. Apparently these chips aren't protected against this (if this it at all possible).

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Old 11th February 2004, 11:59 AM   #6
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Quote:
All is running well except for when the power supply to the amp is shorted
J, why the h*** do you intentionally short a supply?
Wanted to save on the power switch?

This is definitely not a valid testing method to determine the supply's quality or the amps safety!

Quote:
Apparently these chips aren't protected against this (if this it at all possible).
Most Chip-Amps aren't even specified for supply voltages below a two-digit range. I'd expect shorting the supply would also cause currents from capacitors (or even the speaker) to flow through the low power part of the chip (maybe even in reversed directions).

Fully symmetric designs, OTOH, continue to work with one half of the symmetric supply taken down. Given an exact symmetry of both 'upper' and 'lower' half of an amplifier circuit, no parts of the circuit share 'common' currents. Thus, the 'failed' half of the signal waves is missing in the output signal, leaving it half-rectified.

Prof. Leach claims this for his design (in the FAQ section of his website) as a security benefit, in case one of the supply fuses blows due to overload.

I understand this to mean that both amplifier and speaker are inherently protected by this working principle, as both heat sink temperature and speaker voltage/current swing are reduced.

Quote:
but there is something else that needs protecting for this problem
Again, J, if your amp works with the supply not shorted, then your amp works at all! I understand that you're planning on protecting your design from as many failures as possible.

Would you like to explain why and when you expect an occasional supply short to happen (during normal use)?

edit:

Shorting a power amp's supply (even in low power amps) can be a major health risk. Not that I'm too picky about doing creative things with the own body, but I just had to imagine you , holding a lead in each hand, closing your eyes, shifting your hands towards each other, waiting for the bang...
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Old 12th February 2004, 09:08 AM   #7
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Default I think you are trying to discharge capacitor

I donīt used to reply in forums, but itīs familiar problem to me, this chip is destruyed inmediatly if you make a spark when you short your supply, (of course with unplugged supply!!!), or if you connect the dc output of the supply to your amplifier with residual charge in capacitors. Any spark destroy the chip.

If you try to discharge capacitor. the best option is to put a discharge resistors welded in paralel with capacitors (500 ohm for ejample)

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Old 12th February 2004, 10:42 AM   #8
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Default Re: I think you are trying to discharge capacitor

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Originally posted by jlcortes
I donīt used to reply in forums, but itīs familiar problem to me, this chip is destruyed inmediatly if you make a spark when you short your supply, (of course with unplugged supply!!!), or if you connect the dc output of the supply to your amplifier with residual charge in capacitors. Any spark destroy the chip.

If you try to discharge capacitor. the best option is to put a discharge resistors welded in paralel with capacitors (500 ohm for ejample)
In that case use permanentely a bledder resistor...(a resistor in paralel with caps) ...and when you turn off the amp ,the capacitor will be discharged in some minutes...
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Old 12th February 2004, 11:03 AM   #9
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Default Re: Shorted power supply destroys amplifier

Quote:
Originally posted by jpattison
I have designed an amp with the Philips TDA2616. All is running well except for when the power supply to the amp is shorted, this destroy the amplifier every time. I have included kickback diodes on the output, but there is something else that needs protecting for this problem.
Any help?
This was an interesting problem. You mean when you turn power off you want to disharge the power supply faster and the tool for this is a screwdriver or similar?

The solution is, as said above here, to have a controlled discharge current meaning using a resistor.

A golden rule is NOT to use a screwdriver when you want to discharge. Certain types of caps can actually become damaged due to these huge currents.

jpattison , can you tell more about your total setup and why you want to discharge? There are solutions for this.
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Old 12th February 2004, 11:09 AM   #10
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Default Re: Re: Shorted power supply destroys amplifier

Quote:
Originally posted by peranders

You mean when you turn power off you want to disharge the power supply faster and the tool for this is a screwdriver or similar?

Some people...like fire-works!!
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