Hi All

Can anyone please suggest a topology that would enable a high voltage to be inverted: 175V to -175V (Power of 300W) in reference to the GND used in the circuit? Would really appreciate any suggestions.

Kind Regards

Art

 

Buck boost topology is inverting.

Buck Boost Converter

Bob

 

If it's an atx type of psu or transformer and diodes, it might be easily done by reversing the diodes output or adding extra diodes to make a Negative output.

 

Can you give a better description of what you are wanting? A schematic or some hints?

 

Can you give a better description of what you are wanting? A schematic or some hints?

schematic would be useful just something I can use a basis to work from

 

I think Shortbus was asking for artmaster547 to post a schematic and/or more info of what the starting point and end result are.

 

I think Shortbus was asking for artmaster547 to post a schematic and/or more info of what the starting point and end result are.

oh right at the moment this is conceptual no schematic has been designed yet just know the input and output and power

 

oh right at the moment this is conceptual no schematic has been designed yet just know the input and output and power

Can you simply connect your 175V supply backwards?

 

Can you simply connect your 175V supply backwards?

errm not quite sorry just to add more detail I am essential trying to create supply rails for a halfbridge/class D amplifier to get an AC waveform that goes between 175V and -175V

 

errm not quite sorry just to add more detail I am essential trying to create supply rails for a halfbridge/class D amplifier to get an AC waveform that goes between 175V and -175V

...and you have a 175V supply already available? How much current do you need?

 

...and you have a 175V supply already available? How much current do you need?

yep I have access to 175V, around 1.72A

 

I'm thinking it will be far easier to create a bi polar supply with ± 175 VDC rails from a transformer with a center tapped secondary. Unless you are very careful and diligent about controlling losses, one side of the supply will have considerably less oomph than the other, especially at high power levels. DC-DC converters tend to collapse under transient current demands.

 

I'm thinking it will be far easier to create a bi polar supply with ± 175 VDC rails from a transformer with a center tapped secondary. Unless you are very careful and diligent about controlling losses, one side of the supply will have considerably less oomph than the other, especially at high power levels. DC-DC converters tend to collapse under transient current demands.

ok thanks for the suggestion do these transformers take up a lot of space do you have any examples that can be purchased off the "shelf" so to speak?

 

I'm thinking it will be far easier to create a bi polar supply with ± 175 VDC rails from a transformer with a center tapped secondary. Unless you are very careful and diligent about controlling losses, one side of the supply will have considerably less oomph than the other, especially at high power levels. DC-DC converters tend to collapse under transient current demands.

Do you have any links to such transformers from Farnell/Mouser/RS/Digikey?

 

I think you will have some difficulty finding an off-the-shelf converter that runs at that voltage. Even a transformer for the voltages you require is going to be something of a problem. It is easy to get transformers with 120 volt or 240 volt secondaries, but there isn't much in between.

You don't say what frequency you want your AC output to be. Any chance of using an off-the-shelf transformer in the output circuit? - e.g. use a 1:2 step up transformer intended for 120 to 240 VAC. An ordinary iron core transformer will begin to get unhappy above a few hundred hertz, and you would probably need an oversized one for frequency lower than 50/60 Hz to keep the core from saturating.

Designing and building a converter is quite possibly a larger project than your main one.
Making one that runs "open loop" (unregulated, output voltage essentially tracks input voltage) wouldn't be hugely complex. A non-isolated voltage inverting "buck-boost" is reasonably simple. An isolated converter would require a transformer which you would almost certainly have to design and build yourself. Switchers look simple on paper, but when you start actually switching high voltages in a few nanoseconds, things can behave rather badly. Circuit board layout is critical and everything is in conflict with everything else.

This covers the basics quite well:
http://www.ti.com/lit/an/snva559a/snva559a.pdf

 

I was assuming something, but it should be asked: Must the load be referred to "ground" or would a bridge-tied load be acceptable?

 

I think you will have some difficulty finding an off-the-shelf converter that runs at that voltage. Even a transformer for the voltages you require is going to be something of a problem. It is easy to get transformers with 120 volt or 240 volt secondaries, but there isn't much in between.

You don't say what frequency you want your AC output to be. Any chance of using an off-the-shelf transformer in the output circuit? - e.g. use a 1:2 step up transformer intended for 120 to 240 VAC. An ordinary iron core transformer will begin to get unhappy above a few hundred hertz, and you would probably need an oversized one for frequency lower than 50/60 Hz to keep the core from saturating.

Designing and building a converter is quite possibly a larger project than your main one.
Making one that runs "open loop" (unregulated, output voltage essentially tracks input voltage) wouldn't be hugely complex. A non-isolated voltage inverting "buck-boost" is reasonably simple. An isolated converter would require a transformer which you would almost certainly have to design and build yourself. Switchers look simple on paper, but when you start actually switching high voltages in a few nanoseconds, things can behave rather badly. Circuit board layout is critical and everything is in conflict with everything else.

This covers the basics quite well:
http://www.ti.com/lit/an/snva559a/snva559a.pdf

Ok yeah I wanted to go down the route of DC-DC converter and then look at creating AC

 

I was assuming something, but it should be asked: Must the load be referred to "ground" or would a bridge-tied load be acceptable?

yep load has to be referred to ground

 

Do you have any links to such transformers from Farnell/Mouser/RS/Digikey?

I do not, but a standard isolation transformer will take 120VAC in and put just under 170V out. That should be close enough for you to experiment with. If you are dead set on 175 volts you can buy a toroid and some magnet wire and wind a custom transformer.

 

I do not, but a standard isolation transformer will take 120VAC in and put just under 170V out. That should be close enough for you to experiment with. If you are dead set on 175 volts you can buy a toroid and some magnet wire and wind a custom transformer.

I assume you mean the standard one puts out 120VAC, which yields roughly 170VDC only after rectification and ripple filtering.