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Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
I want to use a linear power amplifier covering typical T.C. frequencies, 200 to 500 kHz initially, ideally 10 Hz to 1 MHz to match my sig-gen. 10 Wrms minimum but 50 to 100W rms is better. I do not want the PA. to become a major sub-project. I have designed and built working power amplifiers for audio and r.f. so I thought it would be quite simple :)
My first attempts at design result in brute-force designs that are not simple or efficient. so Has anyone a simple design, or seen a cheap module, 50 to 100 Wrms, 10 Hz to 1 MHz ?
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
That is similar to the LT1210 that I was considering (but I am reluctant to use any LT products because they were rude when I requested a (different) sample, unlike TI etc.) good to 10 MHz or more but 1 A into 10 Ohms is only 5 Wrms ... I want more .... 10x more
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
Yea Sulaiman, I beat you to this one. I've been working on this for a while.
If you have the money you can contact Amp-line for a brick power module, or you can buy the whole amp in a box, but they are a bit expensive.
This is a mos amplifier that operates in current mode, 28V rms into any load because the impedance is low, then they just match it into a transformer to up the voltage.
I've been playing with their design for a long time, but its a miserable design. The front end op-amp is discontinued, and the whole thing is difficult to get to operate without it becoming overly hot.
The main problem with their topology is the op amp feeds a class B driver and causes quite a bit of signal distortion. The main issue is there needs to be a better voltage amplification stage to effectively split the signal to both phases, and achieve the ~2.6V offset between the N and P mos. They took the shortcut favoring shunting diodes instead.
It would probably work if I had the correct op amp, but all I have is the replacement AD847, which does not behave properly in this circuit, its unstable.
I've been playing with it for 2 years, it would probably have been cheaper to just buy a power module already built and tested, but I think they want $500 for one, give them a call.
I don't know if you could implement DC offset to correct for the conduction difference in the P vs. N mos, maybe, I don't know.
I was shooting for a balanced amplifier with equal output. I suspect their modules are compressed on the positive going cycle, and un-distorted on the negative going cycle, but I never had enough money to buy the amp or module.
The main mos are 2sJ162 and 2sk1058. Some audio sites still have these, but they are somewhat hard to find sources for.
A clean design would be nice, and I would continue with the struggle, but I'm burned-out enough with work at the moment, and I have some power supply projects I'm working on.
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Linear Amplifier for T.C. frequencies
