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From: JosephKK on 27 Jun 2010 23:58
On Fri, 25 Jun 2010 22:09:02 -0500, legg <legg(a)nospam.magma.ca> wrote:

>On Fri, 25 Jun 2010 14:59:33 -0700 (PDT), Scott <smbaker(a)gmail.com>
>wrote:
>
>>I've attempted to build the circuit depicted here:
>>
>>http://www.instructables.com/files/orig/FVE/I3SC/FR123O01/FVEI3SCFR123O01.png
>>
>
>Looks POW-ful, to me.
>
>Please review the 494 spec.
>
>...and stop calling this rubbish a full-bridge flyback.
>
>RL

Agreed, full bridge flyback is a oxymoron self-contradiction.
From: Tim Williams on 28 Jun 2010 00:33
"JosephKK" <quiettechblue(a)yahoo.com> wrote in message news:md7g26175c6a1gtvj2b8g0jq80bvmmuc5g(a)4ax.com...
> Agreed, full bridge flyback is a oxymoron self-contradiction.

Not quite. There is one load condition where it actually counts as flyback. Of course, it's not very useful.

The load is none, so the flyback pulse dumps back into the supply.
http://webpages.charter.net/dawill/tmoranwms/Elec_SG3524_Osc1.jpg
(actually half bridge)

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
From: m II on 28 Jun 2010 17:43
Scott wrote:

> I've attempted to build the circuit depicted here:


While on the topic of mosfets...

I'd like to build a crude dc-ac inverter. I salvaged 10 12volt
batteries from a large office UPS.

I have a 7.5 KVA transformer with 120-120 centre tapped primary and
208/230/240 variable tap volt secondary.

I'd like to feed the centre tap on the transformer primary from the
battery bank then switch the outer legs of the same windings in an
alternate fashion, back to ground.

Getting a square wave output from this is pretty trivial.

I would like to get something resembling sine wave on the output.

Now, my problem. How can I get the mosfets to conduct as much sine
wave shaped current as physically possible without burning them up? I
understand that mosfets don't like being 'half on'.

I've been playing with an Arduino microcontroller and learned enough
to be able to set whatever frequency I need on a couple of pins. These
could switch the mosfets. Pulse Width Modulation is available.

If I could get 10 or 20 amperes throughput I'd be happy. Efficiency
isn't that critical, but should be reasonable. The closer to a true
sine wave, the better.

Any insights welcome.



mike
From: Martin Riddle on 28 Jun 2010 18:37


"m II" <c(a)in.the.hat> wrote in message
news:4c2917a7$1(a)news.x-privat.org...
> Scott wrote:
>
>> I've attempted to build the circuit depicted here:
>
>
> While on the topic of mosfets...
>
> I'd like to build a crude dc-ac inverter. I salvaged 10 12volt
> batteries from a large office UPS.
>
> I have a 7.5 KVA transformer with 120-120 centre tapped primary and
> 208/230/240 variable tap volt secondary.
>
> I'd like to feed the centre tap on the transformer primary from the
> battery bank then switch the outer legs of the same windings in an
> alternate fashion, back to ground.
>
> Getting a square wave output from this is pretty trivial.
>
> I would like to get something resembling sine wave on the output.
>
> Now, my problem. How can I get the mosfets to conduct as much sine
> wave shaped current as physically possible without burning them up? I
> understand that mosfets don't like being 'half on'.
>
> I've been playing with an Arduino microcontroller and learned enough
> to be able to set whatever frequency I need on a couple of pins. These
> could switch the mosfets. Pulse Width Modulation is available.
>
> If I could get 10 or 20 amperes throughput I'd be happy. Efficiency
> isn't that critical, but should be reasonable. The closer to a true
> sine wave, the better.
>
> Any insights welcome.
>
>
>
> mike

Check the Microchip site, I believe there's a appnote on a Sine UPS.

Cheers



From: Tim Williams on 28 Jun 2010 18:39
"m II" <c(a)in.the.hat> wrote in message news:4c2917a7$1(a)news.x-privat.org...
> I'd like to build a crude dc-ac inverter. I salvaged 10 12volt
> batteries from a large office UPS.
>
> I have a 7.5 KVA transformer with 120-120 centre tapped primary and
> 208/230/240 variable tap volt secondary.
>
> I'd like to feed the centre tap on the transformer primary from the
> battery bank then switch the outer legs of the same windings in an
> alternate fashion, back to ground.
>
> Getting a square wave output from this is pretty trivial.
>
> I would like to get something resembling sine wave on the output.

First, you need 160-170V supply, not 120, or an 85V winding.

> Now, my problem. How can I get the mosfets to conduct as much sine
> wave shaped current as physically possible without burning them up? I
> understand that mosfets don't like being 'half on'.
>
> I've been playing with an Arduino microcontroller and learned enough
> to be able to set whatever frequency I need on a couple of pins. These
> could switch the mosfets. Pulse Width Modulation is available.

Set up PWM values from a sine table, or use magic sinewaves (Don Lancaster's favorite).

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
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