Author Topic: Audio amplifier, purpose of diode  (Read 3395 times)

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Offline Simon123

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Audio amplifier, purpose of diode
« on: January 31, 2017, 06:56:05 pm »
Hello!

I would like to know, what is purpose of diode placed over 39R and 10-12R resistor?

Thanks



« Last Edit: January 31, 2017, 06:58:43 pm by Simon123 »
 

Offline KD0CAC John

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Re: Audio amplifier, purpose of diode
« Reply #1 on: January 31, 2017, 07:03:43 pm »
I am guessing to eliminate feedback / control of those transistors ?
 

Offline Kleinstein

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Re: Audio amplifier, purpose of diode
« Reply #2 on: January 31, 2017, 07:33:23 pm »
The diode is there to limit the voltage lost at the resistors in cases of high negative output currents. It also makes the transition a little more symmetric, having two PN junctions for both the negative and positive half - at least for higher current.

Sometimes one has the diode without the parallel resistor.
 

Offline mzacharias

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Re: Audio amplifier, purpose of diode
« Reply #3 on: January 31, 2017, 09:34:55 pm »
I have seen them "built-in" to some (Darlington) transistors, such as the 2SB1647 and it's complement 2SD2560. Not sure they qualify as "damper" diodes but that is how I think of them. (I'm a repair tech, not an engineer)
 

Offline Gary.M

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Re: Audio amplifier, purpose of diode
« Reply #4 on: January 31, 2017, 09:38:38 pm »
That is a Quasi-complementary output stage and the diode adds some symmetry reducing hf distortion. If you google Baxandall diode you might find more info.

Sent from my x600 using Tapatalk

 

Offline David Hess

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Re: Audio amplifier, purpose of diode
« Reply #5 on: February 01, 2017, 07:35:52 pm »
The diodes across the output transistors and their emitter resistors prevent the output from exceeding the supply voltages which can happen with an inductive load.  Some Darlington transistors have these diodes built in.  Power MOSFET body diodes fulfill the same function sometimes.

I was not familiar with the term Baxandall diode but after reading this post, I understand the idea.  It simulates the load provided by the base-emitter junction of the top output transistor on its driver on the lower driver which would otherwise see a different load.  It is not required in a fully complementary output stage.
 

Offline lordvader88

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Re: Audio amplifier, purpose of diode
« Reply #6 on: February 03, 2017, 02:20:39 am »
Guys please feel free to also explain from the beginning what these circuits and mini-circuits are actually doing. Hardly ever do I find videos of explanations through a circuit like this with any amount of step by step detail. And since so many non-EE don't get near enough detail.

So many small circuits and mini-circuits that I still don't know or recognize or really know what they are meant to do.
 


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