Looking for a power supply that can be modulated

[davidd31415]

Hi,

I am looking for a power supply that can be modulated from 50 Hz to 20 kHz with a peak-to-peak voltage of 4 V. The supply must be capable of providing at least 1 A and have an internal resistance from 50 m? to 150 m?.

I have never worked with a power supply that could be modulated like this before and am mostly interested in where I should start looking for one. Specific brand names would be helpful. Are there certain terms that describe supplies such as these (modulate-able didn't get me far)?

Regards,

David

 

[melone]

It sounds like you're looking for an AC power supply.... What is the final application? 1A @ 4V @ 10kHz is rather intriguing.

 

[IRstuff]

Sounds like something more like a diode driver might be suitable:

http://www.analogmodules.com/Catalog/diode_dr.htm

TTFN

FAQ731-376

 

[ScottyUK]

Sounds like a job for a small audio amplifier. What form is the modulating signal - sine, square, pulse?


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

 

[Skogsgurra]

I salvaged an old Kepco +/-75 V at +/6 A from a lab environment. Not sure if it goes all the way up to 20 kHz full swing, but definitely for lower amplitudes. Use it a lot for dferent purposes. There are smaller ones.

eBay probably has them now and then.

Gunnar Englund

http://www.gke.org

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

 

[davidd31415]

The modulating signal is a sinewave.

The application is automotive testing (AC signal superimposed on DC to simulate battery and alternator).

I have a few Kepcos, TCRs, and Xantrex supplies- I was hesitant to use them since there isn't a specification for output frequency. I'll try them out and see what kind of results I get.

Thanks,

David

 

[VEBill]

Amplitude Modulated (AM) transmitter of classical design (as opposed to the newer digital architectures) typically did exactly that. They modulated the audio onto the "B+" power supply feeding the final stage.

But for PSRR (?) testing as you describe, I seem to recall that it is very common to use just a normal power supply, but fed through (in series) the secondary of an audio transformer where the primary of the audio transformer is fed with the required audio signal. The net result is that the DC supply has imposed upon it the audio modulation. You might have to tweak the voltage a bit for the DC resistance.

In Military testing, the specifications and standards typically include a detailed 'how to' for each test. Doesn't the automotive industry provide a similar degree of guidance in their specs and standards? If not, then perhaps you should look up the closest applicable military standard and see their recommended (or mandated) test set-up.

 

[Noway2]

VE1BLL, your suggestion is along the lines of what I was thinking. After reading your post, it reminded me very much of an experiment we did in a college lab making an AM transmitter and receiver.

My suggestion was going to to use a signal transformer, or at least one good up to the frequency of interest, and then drive the primary with a function generator via a transistor. You would need to tweak the circuit paramaters, but you should be able to use the transistor / transformer as a power amplifier to get the amperage up without excesively loading the function generator.

 

[VEBill]

I wouldn't bother with a 'transistor'; I'd just borrow an reasonable quality audio amplifier.

 

[richs]

Hi-

In place of VE1BLL's fine suggestion, I would subsitute a good quality audio transformer rather than a signal transformer. The power requirements suggested might lean to the former.

They should be relatively inexpensive and the 50Hz to 20KHz are well within the audio range for "high end" components.

Cheers,

Rich S.

 

[VEBill]

Ahem.

 

[bogeyman]

My solution to this problem, (we wanted 2v of 400hz and its harmonics on top of a 28v 2A DC supply) was inject the required signal (via a capacitor) into a resistor tied to the summing junction of the psu control amp, at the end of the voltage pot on a farnell L30B bench unit. It seemed OK up to about 30KHz.
Try it on one of your old linear psu's if you've kept any.

I would not reccomend using an audio amp unless it is rated for full power continuously, you will probably destroy the output stage.

 

[OperaHouse]

Power supplies are good at sourcing voltage, but not sinking it. The negative swing response will be determined by the load. The poster has not specified the DC (if that) voltage the signal will be imposed on. There are a number of cheap 300-600W PA amplifiers that would work well if modified for a DC input. I have seen HP and Kikusui power supplies on ebay that are basically a large op amp that can swing +&-.

 

[Skogsgurra]

It may have escaped you that David told us he has a few Kepco units. They will do the job.

Gunnar Englund

http://www.gke.org

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

 

[DanEE]

You might also check the current vintage Crown audio amplifiers.. and check with their engineering tech support...

They may still be able to be run in the mode the earlier DC300A amp could be used..

The Crown DC300A was called a "Laboratory Amplifier" as it could be used as a DC to 20khz DC servo amplifier.. There were DC balance controls behind the front panel that could be adjusted for high precision "critical applications" (their words)..

A little info on the DC300A..

http://www.broadcaststore.com/store/model_detail.cfm?id=8289

Their amps have a reputation for being bullet proof. still have one running strong that I bought in the early '80s..

http://home.4x4wire.com/deddleman/

 

[Comcokid]

I've had to do similar things in the past.

I Once disconnected the power amplifer from a small vibration table, and used it (carefully).

Another time, I had access to a wideband power amplifer from Krohn-Hite Corporation.

http://www.krohn-hite.com

At one time, I planned on building a test fixture for a similar application using Apex precision power OP-Amps

http://apex.cirrus.com/en/products/apex/index.html