How to get 120V Constant AC from 120-277 V Varying AC voltage

You don't say how much power you need, but one relatively easy and inexpensive way is this:

Wide ranging AC --> Universal input AC to 12VDC power supply --> DC to AC inverter

Paul Mathews

Jayesh wrote:

Hi, i need it to work in this range i.e to be precise on universal supply. I need this to be given to a thermal protector ( 4 leads) iam not sure of its rating thats what iam searching for. If by any chance u know of thermal protector then plz tell me . Sincerely Jayesh Thanks for ur reply

hi whats a variac with servo can u plz elaborate it for me i wud be thankful to u Jayesh

i dont wanna useany magnetic circuits i want to be purely electronics so no transformer. thank u jayesh

thanks for the help what u think of using and AC/AC converter thanx jayesh

What you need is whats called a power conditioner i believe, the circuit is probably way to complicated to consider for a one off. however maybe you could use a variac with a servo ?

Colin =^.^=

A variac is a variable transformer, its usualy is a big cylindrical heavy thing with a big knob on the top wich alows you to vary the output voltage, its basicaly a toridal transformer with the conductors exposed so that a carbon brush can be moved acros them to conect a particular turn to the output thus seting the turns ratio and input to output voltage ratio.

If the input voltage changes so does the output voltage but you can turn the knob to compensate.

A servo is a motor conected to electronic feedback control unit. you could use this to monitor the output voltage and turn the knob automaticaly, however i dont know if this will work quickly enough for you needs. it might also be dangerous if the supply droped and then shot up quickly. it was just sugested as an "alternative" idea.

Another type is an auto tap changing transformer wich uses thyristors to conect the output to a particular tap to compensate for change in voltage. these are used in electricity substations.

however the wide range might be a problem.

I think would be better to go for a power conditioner (but not the cheap simple protection type), these are basically a AC->DC converter folowed by an DC->AC converter. I would imagine these would be available in the wide input range but wouldnt be cheap.

Colin =^.^=

Theres quite a lot of products if u google "AC voltage regulator"

As for a circuit it depends what power level and tolerance is required, but its the sort of thing that you would need quite a bit of experience to build.

Unless you could get a circuit diagram of a comercial unit you would be unlikly to get a schematic that is gauranteed to work.

However it would be quite easy to come up with a rough circuit by picking out circuits from aplication notes for most of it, all you need is input filter, ac->dc rectification, smoothing, switch mode isolation stage (if needed), sinewave generator fed into a class-D output stage (probaly best to use a micro here and add fualt handling and anything else fancy) oh and an output filter.

Would be interesting and chalenging but i doubt its all that useful for many people to have built their own.

Colin =^.^=

I gues that'l be fine, i think youl find theres a lot of similarity in the way they operate inside anyway.

Colin =^.^=

Does the output have to be a sine wave?

If not, a "light dimmer" like circuit would be the simplest way to get what you want. The output would be good for running things like light bulbs that don't care much about the wave form.

If the load power is very little, a circuit that uses thermistors in a voltage divider and a resistor to warm them up can be made to work and is very cheap.

Turning the AC into DC and them back to AC is likely to be the easiest way to go if you need a sinewave at much power.

hi i do need a sine wave of 120V ac constant i may also need feedback control isnt it so as to verify and accordingly fire the triac. can u help me on control ckt. thanks jayesh

Not with what you've specified.

You either (a) want a sinewave OR (b) use the triac. Doing a sinewave output with triacs is more bother than not using triacs.