20Amp upto 90V shunt Reg simpler version - diyAudio
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Old 8th June 2015, 07:19 AM   #1
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Default 20Amp upto 90V shunt Reg simpler version

Im thinking of a high current and higher voltage shunt reg for the power amplifier application. The actual reason is using just a bare trafo output with filter caps looks very common why cant one use a discrete but high current capable shunt reg still simpler can anybody imagine this? what are the practical complexities involved in this..

1. seems heat from the Mosfet which could be quite high but not in class A mode though but still the current draw would be somewhat higher > The reason why say 20Amp is mainly for the headroom.

2. Larger Mosfets or how it can handle such higher transients is little bit questionable.
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Old 8th June 2015, 07:44 AM   #2
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Old 8th June 2015, 07:46 AM   #3
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can we start from there?
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Old 8th June 2015, 10:11 AM   #4
AndrewT is offline AndrewT  Scotland
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what is the output voltage after passing 90A through the 1k pass resistor?
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Old 8th June 2015, 04:10 PM   #5
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Quote:
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what is the output voltage after passing 90A through the 1k pass resistor?
The values are not yet fixed there.
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Old 8th June 2015, 06:15 PM   #6
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what is the output voltage after passing 90A through the 1k pass resistor?
Its not 90A its 90V
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Old 15th June 2015, 05:34 AM   #7
MarianB is offline MarianB  Romania
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Have you thought about how much voltage drop is caused by a 1k resistor at 20A load current? That is I*R, it's the current multiplied by the resistor value in Ohms, and it is 20kV!...

As for the mosfet power device, the greatest stress on it it's at idle, or at very light load, where it needs to shunt all that 20A of current, to maintain the desired output, so the power dissipated by it would be 90V*20A, you do the math...

The conclusion is that a shunt regulator for those parameters is not a good idea, you simply waste too much power. If the load current is often much lower than those 20A specified than a better idea would be a series regulator, a linear one would be much simpler but still you would waste an important amount of power ( still not as much as a shunt regulator ), a switched one would be much more complicated but the power wasted would be much smaller. It all depends on what you need the most from it, and what your expectations are.
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Last edited by MarianB; 15th June 2015 at 05:37 AM.
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Old 20th June 2015, 07:18 AM   #8
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Yes 1k was not intentionally added it was just to place a resistor if any value one would recommend. Infact I was looking much for the noise reduction than proper static voltage regulation. I agree the series regulator having just a mosfet and then using a Jfet to control is better choice than shunting.

Yes the above circuit oscillates since we have two shunts at the output removed one and it stable.
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Old 21st June 2015, 04:38 AM   #9
MarianB is offline MarianB  Romania
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No single mosfet circuit would be able to handle the required parameters, probably not even a switching supply, let alone a linear supply...

I think you should first establish a firm set of parameters and keep them, say exactly what you need and for what you need it, where would the power for that supply come frome? A 50hz transformer? If so what are it's parameters ( voltage, power ); is it a switching power supply? and if so then what are it's parameters? What do you intend to power with those 90V at 20A? Be as generous as possible with this sort of details so we can guide you to make the best choice.
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Old 21st June 2015, 04:06 PM   #10
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Transformer R-core 50Hz to power up 300W into 8 ohm amplifier
not looking towards SMPS.

Im just looking for substantial noise suppression instead of using just Mains filter. Little bit of voltage regulation is also considerable.

Hence thought of using just a series regulator yes agree the fact that one mosfet will not do it so why not parallel them like two of them.
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