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the diodes snub inductive spikes from the speaker... kind of redundant because the body diodes of the MOSFETS also serve the same function. the problem here is that most of the other transistors in the circuit need to have Vceo's of 1200V or more.
i think this may be closer to what you are looking for, the rest of the article is here... **broken link removed**
For us who are trying to help it would be very beneficial to know what the 5 ohm load is that needs a 330Khz input.
Without knowing what the load is what it works with and how it works its nearly impossible to know what type of power system to deign for.
Is it a 5 ohm inductive impedance, a capacitive load like a piezo electric device, a pure restive load, phase and waveform sensitive load, a LF RF antennae load, etc.
Its an amplifier to power a magnet, on a sensor used on oilrigs (im sorry i cant be more specific, but its most likely confidential), (Im guessing oilrigs can output the ammount of current that i need - in anycase that part really isnt my problem - I've just been given specifications). The signal is a pulse (a sync looking pulse), so its not going to be on for very long... So I dont really have to worry about it overheating. 95% of the time it works at 330kHz - but sometimes they do use it at lower frequencey's.
Yes I got that part but still "big electromagnet" is a rather vague definition.
Air core or iron core or ferrite core or something else?
What waveform is needed? Clean low distortion sine wave or some other form of wave?
Picking amplifier designs for an unknown output into a non specific load is rather difficult. The whole thing may not even need a high precision amplifier type drive system either.
From the technical stand point this whole thread reads a bit like this.
Hey guys I need a thing to make my other thing work with a small input signal and large output signal to go into an unspecified 5 ohm load. It needs lots of power and is expensive and confidential too.
The thing is putting out 600+ volts at 330 Khz is not that hard unless it has to be super clean and highly specific to an application.
As I stated earlier I have seen EM based drill pipe testing done first hand. The company I saw it at didn't need a high powered machine or electrical system to run their magneflux testing either.
Their whole testing system plus its computer ran off a common 5000 watt portable generator.
If the OP is needing 72 Kw to run his system either its not what I think he is doing or his system is very over built to do a basic and surprisingly common function found here in the oil fields.
Thats why I am curious as to what and why exactly he needs to run at that high of voltage and power levels for.
I looked at the PA95 again. It must be used at a gain of 10 (15 max) if you want to get 333khz out of it. For 600Vp-p output then the input must be at 60Vp-p.
The PA95 with a current amplifier after it might work.
What does the signal look like? I know you said sign wave but I need to know how many cycles!
30 posts and i still see no well defined set of specifications. if the frequency range is known (not just upper frequency of 330kHz) you may not need high voltage amp. perhaps you could use transformer to step it up for load, but the primary could be lower (at higer current of course).
30 posts and i still see no well defined set of specifications. if the frequency range is known (not just upper frequency of 330kHz) you may not need high voltage amp. perhaps you could use transformer to step it up for load, but the primary could be lower (at higer current of course).
I have designed many 1000 volts p-p amplifiers, with 330khz bandwidth, for driving grids and deflection plates. Using a auto transformer is a good idea. If the amplifier is only going to be used at 330khz then resonating the transformer will help greatly.
60A amplifiers are not a problem either. BUT 60A and 600Vp-p at 330khz is something a college student will not get done.
If the amplifier only drives one pulse every second I would build it very differently than if it needs to drive 330khz continuously.
The lack of specifications and the lack of understanding of what the amp will do, will keep this amplifier in the form of " ????? " and it will never get made.
For us who are trying to help it would be very beneficial to know what the 5 ohm load is that needs a 330Khz input.
Without knowing what the load is what it works with and how it works its nearly impossible to know what type of power system to deign for.
Is it a 5 ohm inductive impedance, a capacitive load like a piezo electric device, a pure restive load, phase and waveform sensitive load, a LF RF antennae load, etc.
Im told that we are to look at the load as 5 ohm resistive load. It is however a magnet as you said. Currently they use 100Vp-p i guess they just want one that is bigger and better
the "phase distortion (?)" is to be less then 0.5% and as low noise and crossover as possible. The amp only works with pulses - 4 duty cycles of a sinus way.... so it will only be on for a matter of micro seconds.
Thanks for the information. That is what I thought 4 cycles.
The load is 5 ohms. I know it is inductive but....
PNP transistors are not as good. 400V 8A MJE5852 is the part that comes to mind. I can't think of a bigger part.
Increasing the voltage from 100 to 600 volts is a problem. High voltage transistors are much slower.
The only transistors I know of are all used for switching and not for a linear amplifier.
High voltage transistors have a 'safe operating graph' in the data sheet. They were designed to operate full on or full off. They were never meant to operate at 3/4 voltage under current. You need to watch the SOA.
You also can't use the transistors at their max current. At these speeds you will probably use 1/2 you current just driving the capacitance in the transistors. At max current the current gain is about 3. To run fast you need to be using the transistors near where the current gain is highest.
Most of the audio amplifiers mentioned above have too many stages to do the job. They are using faster transistors and only wanting 20k to 100khz of speed. You need to keep the number of stages down.
Keep the voltage gain low in each stage. Remember a 3mhz transistor will only have a gain of 10 at 300khz.
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