Ac to AC converter - help needed

[Manju_Bhat]

Hi Friends,

I have an uinversal AC input , 85v to 265v . I need to design for constant 120v AC output supply for heater application. But i do not want to use Auto transfomrer , since i have a size constraint on my board/product.  I was just thinking of using universal AC to PFC circuit , after that one full bridge inverter would suffice the requirement.  But Converting AC to DC and again back to AC ..may create a lot of efficiency related issue.  Is there any way of  achieving this ? Can some body give me the circutry ?

Input : Universal AC : 85V to 265V AC
Output : 120V constant AC , with 2kw power delivery.

please share me the schemtics if you have.

thanks in advance.
-Manju

[Hero999]

Why does it need to be AC?

It's a heater so it doesn't make any difference whether it's AC or DC, just use a standard off the shelf 120VDC power supply and run the heater off it.

A more crude solution is to use a 120VAC transformer with two primaryies designed to take 133V and connect them in series when the input exceeds 130V and parallel when it drops below 120V. This will reduce the voltage range to 85V to 132V but that will still mean the power to the hear will only be 1kW when it's run off 85V and will be 2.4kW when run off 130V so it's still not good enough.

[Manju_Bhat]

Hi Hero999 ,

thanks for your reply.

But i am not allowed to use any auto transformers or any transformers in which size is the issue.
and how to maintain 120V when the input is 85v ?

though heaters works on RMS or DC , requiremnt is to cotrol the heaters through PWM with 120V AC excitation.

So is there any way for this ? Can i get a topology for this ?
Can you share some reference designs for this requirement .

thanks
manju

[Hero999]

You won't be able to maintain 120V with 85V with a transformer, if the heater is overrated for what you need and you've got good temperature control, the lower voltage shouldn't matter. anyway I accept a transformer is not a sensible solution so lets forget about it.

There's no easy way to do want without a transformer, the only way is to use DC.

PWM is ideal for DC and should work with no problem; a standard DC motor controller board can be used for the purpose.

DC also has the advantage of being safer than AC: the peak votlage is lower, it's less likely to cause ventricular fribulation, an off the self DC supply will be isolated from the AC side and the safey standards are much less stringent for 120VDC than for 120VAC.