• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Variable AC Power Supply

Status
Not open for further replies.

aryan_hr

New Member
Hi,
I need Variable AC Power Supply that I can control it through my program.
Voltage: 0 to 140V or max 200V
Current: 0 to 500 mA or 1 A max.
Frequency: 50 to 60 Hz.
One suggested, use NI D/A 1 V (out put sinwave) and then use Op-Amp and one Transformer (1 /1) to isolate from out put.

Any idea?

Regards,
Hamid,
 

crutschow

Well-Known Member
Most Helpful Member
You basic approach would work but you would need a 200W power audio amp to generate the 200W maximum power you want (200V @ 1A) to drive the transformer.

Also a typical 200W audio amp's output would be 40Vrms (200W into 8 ohms) so you would need a 1:5 ratio 200W transformer to generate the 200V. A 220V:48V transformer would be close (183V max if used in reverse).
 

Willbe

New Member
Use a step down 'former with a 1A primary rating in series with your load, with the 'former secondary feeding a Triac that shunts the secondary winding.
The more the Triac conducts the more current through the 'former primary.
 
Last edited:

Hero999

Banned
A servo controlled variac?
 

aryan_hr

New Member
Hero999,
Thanks for the reply.
Can you give me more information?
I have PhD in chemistry and my electronic knowledge is little.

Thanks,
Hamid,
 

unclejed613

Well-Known Member
Most Helpful Member
"back in the day"( 1979 or 1980 i think), Sony came out with an Application Note for one of their audio amplifiers. it was a real eyebrow raiser at the time :eek: but it works and sounds extremely similar to what you're trying to accomplish. the app note said to take one of their larger (300W into 8Ω) amplifiers and simply wire a transformer and an AC outlet box to the speaker terminals. then input a sine wave from an oscillator to the amp. the volume control of the amp becomes your "variac" control, and the oscillator allows you to generate "line voltage" at whatever frequency you desire. you could do the same thing with a soundcard and a suitable amplifier. Sony's app note also suggested using the amp in bridge mode for 220V output.
 
Last edited:

Leftyretro

New Member
"back in the day"( 1979 or 1980 i think), Sony came out with an Application Note for one of their audio amplifiers. it was a real eyebrow raiser at the time :eek: but it works and sounds extremely similar to what you're trying to accomplish. the app note said to take one of their larger (300W into 8Ω) amplifiers and simply wire a transformer and an AC outlet box to the speaker terminals. then input a sine wave from an oscillator to the amp. the volume control of the amp becomes your "variac" control, and the oscillator allows you to generate "line voltage" at whatever frequency you desire. you could do the same thing with a soundcard and a suitable amplifier. Sony's app note also suggested using the amp in bridge mode for 220V output.
I've suggested that method a couple of times, even though I've never actually tried it. It's not real efficient and I wouldn't recommend buying a new amp, but if you already had a old class AB direct coupled output audio amp it would be a quick and easy if not somewhat unusual solution. You wouldn't even need an output transformer if the rail to rail DC voltages for the amp fit within the peak to peak AC output voltage range you wished to cover, but few if any amps would be able to generate 120vac without an additional output transformer.

I wonder if one of the modern day high power class D audio amps would make the whole thing efficient enough to call it a good solution for a variable AC voltage source?

Lefty
 

unclejed613

Well-Known Member
Most Helpful Member
you would need an 1800W amp to get 120Vrms directly. using a class D amp, you would probably want to use one of the "ultralight" PA amps, like Peavey or QSC. if you use a "heavy iron" amp, such an amp would weigh about 200lb and some require dual power cords running from separate 20A circuits. i think the Sony amp in the App Note was driving a 220:120 transformer backwards to get the voltage, it might have been in bridge mode to get 60Vrms into the transformer. i don't think i would want to drive a complex load like a drill or another highly reactive device.

if you have an amp that's stable at 2 ohms, you could drive a 12V battery charger transformer backwards (we're talking a LARGE 12V transformer like a 20A secondary) to get the required output voltage. fortunately a transformer, even though it's somewhat reactive, will reflect a resistive load to the primary.
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top