Modulating DC Signal From Standard Power Supply

[tarun172]

I need to modulate DC Signal from Standard Bench Power Supply with a 1Vpp 1KHz sinusoidal signal. Modulation by definition is multiplication of two signals. So, if I connect a signal generator and a standard bench power supply in series it should work right? or it shouldn't? When I do that I get is sinusoidal signal with DC offset. I did not see anything in the manual on this topic. Do I need a special type of power supply with this feature?

[tautech]

Current requirements ?

This is standard fare for most AWG's or do you only have a Sig gen ?

[danadak]

There are many ways to do this. If yiou need the power levels that
a signal generator cannot supply here are some approaches to the
problem -

1) If you power supply has remote sensing capability you could modulate
on the sense leads. This  of course depends on how much modulation you
want, common mode range of sense inputs.....

2) You could use a three terminal adjustable regulator, and modulate its
reference leg. Trial and error type of experiment.

What is -

1) Power level you need ?
2) Range of power supply Vout and/or Iout ?
3) Modulation frequency ?
4) Modulation waveform, type, sine, square, ramp....?

Regards, Dana.

[Seekonk]

Or put a transformer in series.  Not sure that modulating the feedback on a power supply will respond well at 1K.  Modulating a regulator chip does seem a possibility if a sufficient load, a pull down resistor may be needed on the output.  DC power amp module maybe.

[tarun172]

@ tautech : I need about 20-30 VDC with 30 mA max.

@ danadak: 1) Power level you need ? 30 VDC @ 30 mA Max
2) Range of power supply Vout and/or Iout ? 24-30 VDC
3) Modulation frequency ? 100 Hz - 10 KHz
4) Modulation waveform, type, sine, square, ramp....? Sine

I like modulating reference voltage idea. I am try that now. Connecting signal generator in parallel with power supply does not work. It goes in voltage overload mode.
                     

[james_s]

Trying to modulate the output of the power supply directly at such high frequencies is not likely to work, often there is significant capacitance in the output and the regulator is damped so that it doesn't glitch all over the place if there's a little dirt in the pot. I think what you want is an audio amplifier that you can drive with the signal generator. There are single ICs that should do what you want with just a handful of external parts.

[tautech]

@ tautech : I need about 20-30 VDC with 30 mA max.

Many AWG's can supply those kind of currents but the voltages are at the top end of most units these days.

A Siglent AWG accessory might be worth looking at, it's a 10W amp for use with any of the Siglent AWG's and is listed as able to supply a sinewave @ 25.4 Vpp.
A basic description of it is here:
https://store.siglentamerica.com/product/spa1010-10-watt-amplifier/

Manual link:
http://www.siglent.com/2014EnglishWebsite/Documents/UserManual/SPA1000_UserManual_UM60010-E01A.pdf
4.1 Mb

[tarun172]

Does anybody has any experience with Kepco Power Supply BOP Series? See link here:http://www.kepcopower.com/catalog/050-054-bop.pdf

[tarun172]

All,
     Thank you all for the help. After playing for a while, I found two ways of doing it:
1. Limit the current coming of power supply by adding a resistor in series.
2. You can use batteries in series which are usually current limited.

Both seems to work for me.