Transformer for voltage booster?

[HarryA1]

Hello from cold and snowy NE PA,

In my quest to convert 9 - 12 volts dc into 140 volts dc I purchased a "40W DC-AC 12V To 220V Step-up Transformer Boost Module Inverter" via Ebay. I also purchased a 220 volt to 120 volt 50-60 hertz step down transformer; the type travelers use.

But the inverter's output is 38.4k hertz!  So my transformer is useless here. I am wondering if one can find a transformer that will handle that frequency and is two to one?

I am driving a class D pulse amplifier that outputs 100 Volts peak at a current of 0.10 amperes max. The pulse is 0.4 ms duration at and interval  of 2 ms. So I am thinking that I need: 100v * 0.10 * 0.4/2 = 2.0 watts for the amplifier output so I am thinking about 10 watts for the amplifier and the conversion from 120 ac to 140 dc. 

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[audioguru2]

It is inefficient to boost the voltage too high then drop it down.

Why does the amplifier need a supply of 140V to produce only 100V? Won't the extra 40V cause lots of power waste as heat?

 

[HarryA1]

You points are well made; thanks.

On day one I found two voltage boosters on Ebay that gave more than 100 volts so I ordered both of them from China. The first  one I received was a 12v dc to 200 v dc. After connecting it up and adjusting it for 200 v I put a 100k resistor across the output  and got 2 volts output! It took a one mega-ohm load to keep 200 v.

The   second one (12v dc to 220 v ac) works well. I connected it to the 220v to 120v step down transformer and into a full wave bridge rectifier with a 100mfd capacitor and got 140 v dc; 9.6 volts input. With a 8.4 v NiMH rechargeable battery I get 128 v dc.
So I am happy with that  and  very surprised that the 50/60 hertz transformer works at all!