Combine AC and DC signal (15A)

[CarlosR2022]

It is easy to combine two lower power signal into 1 signal using inverted-summing opt-amps circuit.

Now I would like to combine these 2 signals,
4v DC signal with a 0.5V AC (but its current is 30A - very high). What is the best way/ device to combine these signals.

 

[VEBill]

Is this an actual practical application? Who would use those "signals" and not be willing to use an extra set of wires? The cable can't be very long at 0.5 volts and 30 A.

It's non-trivial, so please provide more details about the specific application.

 

[DHambley]

With a very high-power op amp (or discrete circuit) you can put 0.5A AC on top of 30A AC but, like VE1Bill wrote, what is the application?

 

[Henneshoe]

With the information given so far, I would look into using an isolation transformer. I think it would be smaller, cheaper, and simpler than a solid state circuit. See attached schematic.

 

[Henneshoe]

I did a little looking, and a 30A transformer is actually a bit bigger and more expensive than I originally thought. Maybe it is worth looking into solid state.

 

[CarlosR2022]

I would like to design a power supply that has the ability of "sensor" input from other devices and automatically adjust the supply voltage (From 0-10V)

Think gets hard because I do not want to supply a purely DC signal. I want to have a small AC signal runs on top of the DC signal but the combination signal must supply a high current (I want at have least 30A)
(0-10VDC)+/-0.5VAC ~30A

 

[ScottyUK]

What you are describing is basically the power stage of a servo amplifier. There are plenty application notes available on the net which might be a good starting point.


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If we learn from our mistakes I'm getting a great education!

 

[VEBill]

So it's a low voltage, high current DC Power Supply with an AC signal entering the power supply by the same terminals.

(You can avoid much confusion by not using the word "signal" to refer to the output from a power supply.)

It all depends on the frequency of the AC control signal. If it is on its own frequency that is reasonably high, and is separate from the line frequency, separate from any switching frequency, and separate from any noise induced by the load, then it becomes easy to extract it.

But if you're contemplating using AC at the same 50/60 Hz frequency as the noise and ripple on the output, then it's going to be difficult to extract the information accurately.

Also, a DC power supply is typically designed to "fight" any AC on the output. It'll be an ultra low impedance load when you try to impose low frequency AC into the output pins of a DC power supply whose purpose in life is to keep noise off the output.

 

[Skogsgurra]

I use a KEPCO 'power opamp' for that purpose - I feed a signal from a function generator (DC plus function superimposed) to its analogue input and get (in my case) +48 V with desired frequency and waveform superimposed. I do not use more than around 5 amperes output, but you can have much more. Look at

http://www.kepcopower.com/bophi.htm

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[VEBill]

I must be misinterpreting his posts. Disregard my responses.

 

[OperaHouse]

It is not that hard if you want to impose 60 hz.. I got an old toroid power transformer and wound about 6 turns on it of #10 wire to supply 20-30A to test current relays. Seems that was about a 1/2 volt. Just put that secondary in series with your DC power supply and and apply 120V AC to the toroid primary. Suggest several really large caps 100,000 uF at least on the output of the DC supply. An AC supply can provide other frequencies. My transformer was less than 5 inches in diameter.

 

[OperaHouse]

A transformer from an old PC power supply will work in the 20-40 khz range if you want to induce higher frequency noise.

Any 30A power supply is going to have remote sensing. Sense and power are usually internally connected with about a 100 resistor so it doesn't go wild if the sense is disconnected. Just feed a signal into that sense pin through a capacitor and resistor. Most supplies should handle the low frequencies pretty well.