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Diode in Amplifier

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Dear Sir,
I want the constant current source 2SK117 not replaced by a resistor.

The operation of the power supply I understand, only the choice of the zener diode D3 and D4 is not clear to me, why would a designer to make that choice, I would like to understand.
It is for security reasons?.

Greeting,

Pim
 
Dear Sir,
I want the constant current source 2SK117 not replaced by a resistor.

The operation of the power supply I understand, only the choice of the zener diode D3 and D4 is not clear to me, why would a designer to make that choice, I would like to understand.
It is for security reasons?.

You would need to ask the designer, but I suspect the entire design (just like the amplifier) is deliberately over complicated, in the desire that it makes the designer look 'clever'?.
 
Dear Sir, I do not know the designer, but know that it is a commercial amplifier design.
Thank you for you time.

yours sincerely,

Pim
 
Dear Sir, I am busy with my amps, and I encounter the following problem.
There are mosfets as driver transistors used 2SJ76 and 2SK213, according to the data information of this mosfet there would be a built in * zener diode in it to the source gate voltage should not come above the 9 volt, but it turns out that there are also on the schedule of amp external zener diode is placed, I do not know if I should trust the been built in or external zener diode zener upon to place.
I will send you some pictures of the amplifier under construction.

Sincerely,

Pim Driessen
 

Attachments

  • Device under construction.pdf
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  • Supply Amplifier input amplifier.pdf
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  • Test set-up 1 amplifier.pdf
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  • Test set-up 2 amplifier.pdf
    250.8 KB · Views: 130
Most good audio amplifiers do not use a low noise regulated power supply because their circuit rejects power supply voltage changes and noise.
Most good audio amplifiers are not class-A heaters but instead use class-AB but new ones use class-D.
 
Hi,

MOSFETs are used in the output stage (at least) of the class D amplifier because they are very fast when used as a switching device and class D is basically a bipolar mode buck switching regulator that has an averaged response that can follow an audio signal.

As far as using them in a linear design, it's really up to the designer but again when used in the output stage it seems easier to get lower crossover distortion, if done right.

The design presented here just seems wayyyyy over complicated, and that tells me that maybe the design isnt that good to begin with anyway as i dont think anyone with a lot of experience in amplifier design would make such a complicated off the wall design unless it was for some very special purpose and a regular audio amplifier doesnt fit into that category.

The general rule here is that if you find a design that is much more complicated than most other designs you find for the same application, then there darn well better be something extraordinary about it to compensate for the extra complexity.
This extraordinary property can come as almost anything: a cheaper part, a more expensive but longer lasting part, a better high end response, a better low end response, etc., but if you cant find something great about it then it's not worth using the design.
 
Dear Sir,

Thank you for the response, but my specific question about mosfet 2SK213 and 2SJ76 is that there's a built-in zener 9V1 present, to the Gate and Source to limit voltage above 9,1 volt.
In the diagram is also a zener signed that is in parallel with the internal zener of 2SK213, my question is, 2 zeners in parallel can be?.

with greeting,

Pim
 
Hi,

When there are two zeners in parallel then the one with the lowest voltage will do all the work unless the voltages are close to each other, and then they will probably each draw some current with the lowest voltage one drawing more current than the other in the event of a voltage that goes higher than both voltages. If the voltages are vastly different then only one will draw current. So it should not hurt too much to put two in parallel as long as the second one is equal to or greater than the voltage of the first one that is presumably at the right voltage to begin with.

There is a secondary effect of capacitance, so there will be a little more capacitance but it will probably be minimal compared to the MOSFET gate source capacitance anyway.
 
I think the "extra" zener diodes are not there. The schematic shows them not connected and might be showing that they are built into the Mosfets.
If the "extra" zener diodes are actually part of the design then they can be installed when the original Mosfets are not available and ordinary Mosfets without them can be used.
I notice that all the semiconductors are Japanese. Which company makes this amplifier?
 
I think the "extra" zener diodes are not there. The schematic shows them not connected and might be showing that they are built into the Mosfets.
If the "extra" zener diodes are actually part of the design then they can be installed when the original Mosfets are not available and ordinary Mosfets without them can be used.
I notice that all the semiconductors are Japanese. Which company makes this amplifier?
The schedule is drawn by me, the zener diode is not connected because I had not yet decided whether I needed this zener
 
I think the "extra" zener diodes are not there. The schematic shows them not connected and might be showing that they are built into the Mosfets.
If the "extra" zener diodes are actually part of the design then they can be installed when the original Mosfets are not available and ordinary Mosfets without them can be used.
I notice that all the semiconductors are Japanese. Which company makes this amplifier?


Thanks for your explanation, I have chosen to do extra to place a zener diode next to the mosfet because it is never 100% sure that the zener in the mosfet really is 9 volts.


Sincerely,


Pim
 
Maybe Hitachi do not know what they are talking about in English or maybe we do not know what they are talking about.
Their datasheets show two zener diodes in opposite-connected in series from gate to source but the absolute maximum Vgs is plus or minus 15V like any other logic-level Mosfet that does not have zener diodes.
The datasheets say NOTHING about zener diodes.
 
Hi,

Most MOSFETs do not have "built in" zener diodes.

If you suspect that one type does and cant find any concrete data that confirms this, then you should do your own test.
Run the gate source voltage up with a current limiting resistor and voltage supply and see if the gate source acts like a zener. It's a pretty simple test and easy to do.

Also, zeners are not magic devices in that they can not limit the voltage under every possible circumstance. They also need some sort of current limiting. If they get too much current they could blow out pretty quick. In this circuit it looks like they are connected to some low impedances so you'll have to check that out. If they blow out you may not know it until something else blows out too.
 
With a resistor between + a drain of 100 ohms and a potentiometer 10 k between + and ground, the runner at the gate, I have run up to 16 volts between G and S, I measure the voltage zener not, so that's clear .
 
The absolute maximum allowed Vgs voltage is plus or minus 15V so you are lucky that your 16V did not destroy the Mosfet.
No zener diode? Then why does Hitachi show two zener diodes on their datasheets?
 

Attachments

  • Hitachi.png
    Hitachi.png
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With a resistor between + a drain of 100 ohms and a potentiometer 10 k between + and ground, the runner at the gate, I have run up to 16 volts between G and S, I measure the voltage zener not, so that's clear .

Hi,

Really you need a 10k resistor between the pot arm (runner as you put it) and the gate, measuring the gate voltage.
If there is a zener, at some point when you turn the pot the gate voltage will stop rising, assuming also source to ground.
You need resistance between the pot and gate to see this.

Interesting picture with the two zeners. With no additional information though we dont know for sure why they have them shown there. It would seem they are for gate protection, but who knows. Some may have this and some not. They could also be for ESD protection.
Some MOSFETS now have more built in protection devices too.

To test for the zeners is easy but the test has to be done in the right way to get sure results, and most of all the current should be kept low so the zener plateau can be easily noticed.
 
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