my power amp not work how to fix it?

my power amp not work how to fix it?

in this picture i draw signal sine wave by measurement of scope but observe upper signal not have sine wave why?


i'm test at 12Vdc supply but i want use 220Vdc supply

I doubt you will have enough bias current to the MJE350 when you are using a +12V and -12V supply.

I would also be very wary of using +220V and -220V (or +110V / -100V if thats what you mean). What is this amplifier to be used for?

Brian.

At least R45 must be definitely changed for higher supply voltages.

I don't see how that circuit can work at all. Note that all the MOSFETs are N-channel. Maybe Q4 is supposed to be a phase splitter, but that's not a good way to make an output stage, even if the resistor values are fixed.

Then again, Q6 and Q8 are probably supposed to be P-channel, in which case R13 and R20 are their source resistors. That still does'nt explain Q4, R47 and R48 though. They'd need to be rearranged to bias the output stage.

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Maybe the circuit's supposed to look like this. That would be a better start anyway.



p.s. I think the MOSFET symbols are wrong, but I don't want to spend all day redrawing this.

I was puzzled too, that's why I asked it's purpose. The supply voltage seems way too high for audio work but the input and feedback circuits suggest it's for low frequency use. I thought it might be part of a motor drive circuit but I would expect it to have some output protection if it was. Maybe it's 'theoretical' but never simulated or built and the design flaws haven't been exposed yet.

Brian.

betwixt said:

I was puzzled too, that's why I asked it's purpose. The supply voltage seems way too high for audio work but the input and feedback circuits suggest it's for low frequency use. I thought it might be part of a motor drive circuit but I would expect it to have some output protection if it was. Maybe it's 'theoretical' but never simulated or built and the design flaws haven't been exposed yet.

Brian.

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thank you for Reply every one

I want to use mini signal generator 20 - 400 Hz and 0 - 12 V sine wave to power Mosfet Amp to 0 - 220V sine wave and sent to high voltage transformer



picture this block diagram my project

jengsyber
from experience of having built a number of 3 Phase versions of what you are trying to achieve, the solution is to have a bridge mode Amplifier circuit capable of driving very low load impedances.
This then is used to drive a suitable transformer to achieve your desired output.

A suitable output Voltage for a single channel of your Amplifier channel can be of the order of 55 Volts RMS with power supplies of +/- 85 Volts DC. Output is then 110VAC in bridge mode.
Two, or better still three, stage VI protection is a 'must'!

You will definitely need to add emitter followers after the Voltage Amplifier stage of the amended circuit provided by godfreyl to drive the Output FET gate capacitance and replace R45 with a Constant Current source.
Tail current for your input long tailed pair will also benefit from a constant current source, or at the very least use a Zener to stabilise the current.

You don't specify what load is being presented to the secondary of your transformer, but you must allow properly for the adverse Power Factor of it with a suitable number of Output devices and heatsinking.

Hope this assists
Mik

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jengsyber
you will find this paper available at: http://hifisonix.com/safe_operating-_area/soaprot_12-03-2012/
very useful in designing your protection circuitry

Mik

It sounds like you are making a heater instead of making a sinewave inverter.
If you learn how to design or copy a linear Mosfet power amplifier then you will know that it heats almost the same amount as the load. A waste of power.

A real sinewave inverter uses Pulse-Width-Modulation (PWM) to make a stepped sinewave then its output Mosfets switch completely on and off at a high frequency. Since when they are switched on and the voltage across them is very low then they do not get hot and when they are switched off and do not conduct then they also do not get hot. The high frequency steps are easily filtered out.

It sounds like you are making a heater instead of making a sinewave inverter.
If you learn how to design or copy a linear Mosfet power amplifier then you will know that it heats almost the same amount as the load. A waste of power.

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For a number of applications, linear power amplifiers are still reasonable. I don't know if it's the case for the present application, but you shouldn't exclude the option. The theoretical efficiency of an ideal class-B amplifier with resoistive load is 78.5 %.

I think that at least for a power range up to 500 W or 1 kW, linear amplifiers can be still considered as straightforward and very ruggedized solution.

Audioguru said:

It sounds like you are making a heater instead of making a sinewave inverter.
If you learn how to design or copy a linear Mosfet power amplifier then you will know that it heats almost the same amount as the load. A waste of power.

A real sinewave inverter uses Pulse-Width-Modulation (PWM) to make a stepped sinewave then its output Mosfets switch completely on and off at a high frequency. Since when they are switched on and the voltage across them is very low then they do not get hot and when they are switched off and do not conduct then they also do not get hot. The high frequency steps are easily filtered out.

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I want pure sine wave 0 - 400Hz, PWM can make sine wave to 400Hz ? if it can make but resolution duty over 8bit ?
first my think I want design with PWM but scary it not 400Hz or resolution not over 8 bit

second my think use power mosfet because respond high freq. and not have deadtime

You can make a PWM sinewave with as many bits as you want. But 8 bits at 400Hz is a frequency that class-D PWM audio amplifiers work at.

Audioguru said:

You can make a PWM sinewave with as many bits as you want. But 8 bits at 400Hz is a frequency that class-D PWM audio amplifiers work at.

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wow!! class-D PWM amplifiers I think look good idea but i can design class-D amplifiers for more power volt out at 220V ?

You could use a normal class D audio power amplifier, and step up the output with a toroidal power transformer.

A class-D amplifier is expensive because its parts must make maybe 8 bits at 10kHz. Then the clock is at the very high frequency of 2.56MHz if my calculation is correct.
But a class-D amplifier for a sub-woofer goes to only about 200Hz, uses a much lower frequency clock and will cost much less.

Audioguru said:

A class-D amplifier is expensive because its parts must make maybe 8 bits at 10kHz. Then the clock is at the very high frequency of 2.56MHz if my calculation is correct.

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No. "Bits" don't come into it. They can run at much lower frequencies than that.

Texas Instruments make high quality class-D power amplifier ICs. Their PWM frame-rate is typically 384kHz. Their output power is 400 Whats and the distortion is very low.