Propeller Head Plaza

Posted by jneutron (A) on August 23, 2006 at 12:57:11

In Reply to: Re: Hey JC..what is " vector stimulus on the VI space."..do you know? posted by john curl on August 23, 2006 at 12:06:45:

JC: ""
Another $25 word or phrase in order to impress the locals? ""

Nope. You seem hung up on impressing people. That is not my problem, but yours..

Good thing you asked for an explanation. It is of course, something that YOU as a designer, should be aware of. Guess since you don't know the words, I'll explain..

All power amplifiers operate in four quadrants..two are pure resistive, pos voltage, pos current, neg v and neg I.. quads 1 and 3.

All power amplifiers have to operate in the other two quads, as reactive loads force that. Pos drive, neg current.and versa visa...this is the SOA issue of course.

If you draw the VI space, with voltage as the horizontal axis, and current as the vertical, you see that a resistive load crosses zero, and travels in 1 and 3.

Use of some fancy shmancy test waveform that is entirely uncontrolled, needs the load to push the output into 2 or 4. There is absolutely no control here..IOW, anarchy.

By using two ARB generators, it is trivial to force the out into quad 2 and 4, and it is easy as pie to force the amp from one location on the VI plane, to another. Select the starting point, say quadrant 1 500 watts into 4 ohms, then force the arbs to move the output to another location in VI space. THAT is a vector move, where you have a direction from point 1 to point 2.

If you choose to, you can force the positive pass transistors into heavy dissipation in quad 1 via the amps input, then quickly push the amp into quad 2 by the second arb forcing the outputs.

You can preset dissipation, dwell, whatever, and then move (vector) to another position in space. And you can even work the first arb during or after the vector move, to see how long it takes the DUT amp to recover from the vector move. The moves can be any rate desired, they can be sines, whatever..

It tests everything JR alludes to, and it does it fast, repeatable, and accurately. Accuracy being the key.

Obviously, you've never worked with automatic test and data aquisition, have you?.. It can be hairy, I will admit, but with a coupla arbs and a pc, it can produce some excellent tests that would otherwise be impossible. As a designer of amps, I would have thought you knew about this stuff..guess I was wrong..

BTW..by using this setup with rudimentary programming, you can find the line haversine coupling, the ripple coupling, and the pos/neg rail coupling to the feedback divider.. Easy..

Cheers, John