Circuit to amplify square wave

Without getting into too much detail, look at a switching power supply with a dual primary/secondary transformer. Any car audio amp over 50W or so will have one you can use as an example. Just cut and paste the sections you need.

There are a couple very good books at your local Borders or Barnes and Noble bookstore that cover this very topic if you need to design something from scratch.

Ge0rge

If you have only a single +8V supply, your output is constrained to be bounded by 0V and +8V.

"OpAmp" implies relatively low power output, why "...over a hundred amperes"?

What does "amplify" mean? -5V to +5V input produces what range of outputs? Centered at +4V? Minimum always at 0V?

?????

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

I do need build the circuit from scratch. Do you of a specific book which addresses this problem? I looked in "The Art of Electronics" by Horowitz - couldn't find what I'm looking for.

-SD

opamp is not my idea - it's just hear-say. I don't even know whether an opamp needs to be used in the first place.

I need to pass high currents through my load (here, an electromagnetic actuator). The desired current is not steady, but periodically switching between +A amperes and -A amperes at frequencies up to 100 Hz. The actual value of the current A is variable - I will gradually be increasing it in steps until my load burns out. The value of the current through the load is of importance to me, not the voltage drop across it. I used the word amplify to signify that a high power circuit is being driven by a function generator, a low power device. I guess 'amplify' is not the right word in this situation; my bad - a square wave pulse on the input side of a solid state relay acts as a gate only, and its actual amplitude does not influence the output current or voltage.

I am pretty sure that all I need is the 8V DC power supply box. We used to have a box made by a company (which probably doesn't exist now!) which did exactly what I want, and using the exact same power supply that I have. It's just that it doesn't work and probably parts of it are stolen/missing.

If someone could point me to a book, say, which has this explained, or sketch an quick and dirty circuit diagram, that'll be invaluable.

-SD

O.. and by the way, I plan to regulate the current magnitude A by either toning down the voltage from the power supply to something below

8V, or alternatively, keeping the 8V fixed and connecting a potentiometer in series with my load.

Your idea of using a solid-state relay (or a pair of them) is valid then. Many general-purpose function generators have a TTL-level "sync" output that could be used; if you are stuck with +/-5V and the SSR can't handle the input you can always use a blocking diode:

------>|---o------- From | To SSR signal .-. generator | | | | '-' | | === GND created by Andy´s ASCII-Circuit v1.24.140803 Beta

Things to check for on your SSR are the response speed (100Hz is 10ms, the relay should be capable of a fraction of that), current handling ability, and ON resistance. If you can't find a DPDT solid state relay (do such things exist) to reverse your power then you'll have to make an 'H' bridge out of four individual ones. This will create a definite danger of turning on both relays in one leg of the 'H', causing what Zsa-zsa Gabor would call "shoosht through" and the rest of us would call "smoke".

"Amplifier" is more or less correct here -- what folks were fishing for was whether you needed to take +/-5V and turn it into +/-100V at 1mA, or if you wanted 0V, 8V at 100A -- which appears to be what you want.

You are looking for a heavy-duty, low voltage, low speed (thankfully) 'H' bridge. 'H' bridges are dirt common anywhere electrical watts are being turned into mechanical watts, so there's lots of choices out there.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

(8V)(100A) = 800 Watts. That's quite a big pot. If you can adjust the power supply that's probably the way to go.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

[snip]

Your description is clear as mud ;-)

But it sounds like an H-bridge on the output of your power supply might do what you want.

Can you post a block diagram with performance expectations either on newsgroup alt.binaries.schematics.electronic or on a URL?

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

"Simplified Design of Switching Power Supplies" By John D. Lenk

This is my favorite. It helped me design my first 3KW switcher for an automotive amp project I had going. Does a great job at the basics and gives plenty of examples.

The only problem I see you having is with the magnetics. You would be well served to consult with a transfomer company to get what you need.

Many other books exist and are on the shelves at Barnes and Noble or Borders. Just do what I did and do a search for "switching power supply" on either companies web site.

Ge0rge

Does this need to be a linear amplifier (output amplitude proportional to input amplitude) or must it output a constant, high amplitude, in spite of changes in input amplitude?

Just limit the negative excursion:

Signal Generator +5 ~ -5 ----[470R]---+--- SSR Input | ---K / \\ 1N914, 1N4148, etc --- | Signal Generator Ground --------------+--- SSR Input return

Good Luck! Rich

To be honest you clearly need a better grasp of the basics before you should consider switching 100 Amps or so.

What electronics experience *do* you have ?

Graham

Ahh yes, an H-bridge!!!

Ge0rge

Can you get at both of the leads of the load? Can you seperate the frequency source and the amplitude?

Consider this:

From variable -------+------------------------ supply ! ! O S1A O S2 / / ! ! ! ! +--------[ LOAD ]--------+ ! ! O S2B O S1B / / ! ! ------------+------------------------+

The switches can be arrays of MOSFETs.

--
--
kensmith@rahul.net   forging knowledge

Thanks to all those who replied. I think Ken Smith's circuit best does what I am trying to do. Ken, I know how to use solid state relays as switches in locations S1A, S2A, S1B and S2B in your circuit diagram. I have been told that MOSFETs do the same job (as the SSR's) but more effectively. I am not too sure how to connect the MOSFETs. An SSR has four terminals for low power input and return (function generator in this case), and high power input and return (here, the 8V power supply). So this makes sense. A MOSFET has only three, right?

high power input / signal generator -----| MOSFET \\ return

Where does sig generator return go? Another way of asking the same question is, if the two leads of the signal generator get connected across MOSFET gate and X, what is X? On the high power side, I assume that the two ends of the wire on which the MOSFET is 'mounted' get connected across MOSFET source and drain.

-SD

No sir. This seems to chop off one half of my input signal. I can easily produce the output of your circuit by halving the amplitude and adding an offset in my signal generator. I NEED a zero offset square wave (going from +a to -a volts) on the high power (output) side of the SSR (or any circuitry used). Thanks.