DC to AC converter

[SanjayG]

I need a very simple
DC 12V
to
AC 12V 1.5 Amp. 50 Hz.
inverter.

Can somebody help me with a circuit ?

 

[Harald Kapp]

What waveform? Will a square wave be sufficient or do you need a sine wave?
What is you application? Why the need for AC?

 

[SanjayG]

We have a medical frequency generator from USA (we are in India), which uses 12V AC input.
I think quasi-Sine wave should be OK, but not square wave.

 

[kellys_eye]

Such low levels of AC could be generated using a simple oscillator and amplifier and give a true sine wave.

But if the equipment uses a 12V AC input it's likely to convert to DC inside anyway and the the AC adapter could be changed for a DC adapter at the appropriate voltage (around 15-16V). The internal bridge rectifier (an assumption - needs to be confirmed internally) would sort out any polarity issue.

 

[SanjayG]

Thanks. Can you give a Circuit diagram of an Oscillator+Amplifier which will generate 12V AC from a 12V DC voltage input ?

 

[davenn]

We have a medical frequency generator from USA (we are in India), which uses 12V AC input.
I think quasi-Sine wave should be OK, but not square wave.

so this begs the question
Why don't you just use a 240V ( or what ever your mains voltage is) to 12V AC plug pack ?? .... so simplistically easy

plenty of them on ebay etc

 

[hevans1944]

Thanks. Can you give a Circuit diagram of an Oscillator+Amplifier which will generate 12V AC from a 12V DC voltage input ?

@kellys_eye is saying you may not need it. Most medical electronics equipment runs internally on DC. One reason to build such equipment to operate from low-voltage AC is isolation (via a transformer) from the power line. Since only a step-down transformer is needed to provide an AC voltage that is easily rectified, filtered, and regulated, you may be able to provide rectified, filtered, and (perhaps) regulated DC in place of the 12 V AC input.

This would not bypass those built-in rectification, filtering and regulation functions, or replace them. Those functions would still exist inside the medical frequency generator, but instead of providing 12V AC, 50 Hz, power input, you would simply provide a DC power input of an appropriately higher voltage, necessary to account for the forward voltage drop of internal rectifiers in the medical frequency generator.

This will not work if the medical frequency generator has a transformer inside that requires 12 V AC for its operation.

But why do you want to power your medical frequency generator from a 12 V DC power source? Is it located far from mains power (240 VAC, 50 Hz, IIRC in India)? As @davenn stated in post #6 above, all you need is a step-down transformer (12 V AC plug pack) and access to utility power. OTOH, if AC power is unavailable and you have to operate using a car battery (or some such), you might still investigate whether the medical frequency generator will accept and operate directly from a DC source of appropriate voltage. A DC-to-DC boost converter is a lot less complicated than a 12 V AC, 50 Hz, sine-wave inverter, which you may not need.

 

[(*steve*)]

Having been to India several times, I'm thinking that the reason for this is to operate the equipment when the power is out.

The main problem is that 12VAC has a peak of +/- 17V.

We may need to know more about what the equipment does with the 12VAC.

 

[hevans1944]

We may need to know more about what the equipment does with the 12VAC.

Excellent observation! I hear that reliable mains power is a huge problem in India, only somewhat alleviated by the fairly recent availability of relatively "inexpensive" photo-voltaic solar array panels backed with automobile batteries.

Here in the USA, I needed some means to power my HP laptop while traveling on the road, so I purchased a 12 V DC to 120 VAC inverter. This allows me to plug my line-operated laptop power supply into the inverter while "on the road". My wife is driving the car of course. Please don't surf the Internet or text on your cell phone while driving! There is also a powered USB port on the inverter that keeps my cell phone charged while I use the cell phone "hot spot" feature to provide Internet connectivity for the laptop. I must confess all this is usually more trouble than it's worth because, when we pull into a motel for a night's rest, there is usually a WiFi Internet "hot spot" provided with the room.

Maybe my "solution" would work for the OP. Just add a small step-down transformer to the 120 VAC, 60 Hz, output to get 12 VAC. Frequency shouldn't matter if the medical frequency generator just uses the 12 VAC to create rectified DC inside the frequency generator. But, as @(*steve*) said, more information is necessary.