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From: rahulponna on 10 Jul 2010 05:13



-------------------------------------


Hi,

Does anybody have any idea to design a AC to DC conversion circuit
without using diodes? We can use MOSFETs, but we would need a control
circuitory to switch ON and OFF the MOSFETs.
Is to possible to somehow use the secondary voltage of the transformer
to turn ON and OFF the MOSFETs?


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From: cbarn24050 on 10 Jul 2010 07:17
On Jul 10, 10:13 am, findprahul_at_yahoo_dot_co_dot...(a)foo.com
(rahulponna) wrote:
> -------------------------------------
>
> Hi,
>
>   Does anybody have any idea to design a AC to DC conversion circuit
> without using diodes? We can use MOSFETs, but we would need a control
> circuitory to switch ON and OFF the MOSFETs.
>   Is to possible to somehow use the secondary voltage of the transformer
> to turn ON and OFF the MOSFETs?
>
> ##-----------------------------------------------##
> Delivered via  http://www.electrondepot.com/
> Electronics Enthusiasts' Community of the Net
> Web and RSS access to your favorite newsgroup -
> sci.electronics.design - 397015 messages and counting!
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Chapter and verse http://www.national.com/vcm/national3/en_US/resources/power_designer/national_power_designer112.pdf
From: George Jefferson on 10 Jul 2010 09:47


"rahulponna" <findprahul_at_yahoo_dot_co_dot_uk(a)foo.com> wrote in message
news:bcdab$4c3839c0$43de0cc0$21965(a)news.flashnewsgroups.com...
>
>
>
> -------------------------------------
>
>
> Hi,
>
> Does anybody have any idea to design a AC to DC conversion circuit
> without using diodes? We can use MOSFETs, but we would need a control
> circuitory to switch ON and OFF the MOSFETs.
> Is to possible to somehow use the secondary voltage of the transformer
> to turn ON and OFF the MOSFETs?
>

Not directly in any efficient manner. You want to turn on the mosfets when
the voltage is 0. Thich mosfet depends on the direction(sign of the
derivative of the voltage). If the voltage is 0 for any long period of time
you actually wan the mosfets to be off. This also causes a problem for near
0 voltage.

It's better and easier just to use a controller. This way you can turn the
mosfets on much more effectively by having them alternatate once per
1/120s(to prevent oscillations) and monitor the transformer when it is off
to turn the mosfets off.

The good thing about using a controller is that you can easily create a
variable power supply PWM the mosfets among other things.



From: JosephKK on 14 Jul 2010 02:25
On Sat, 10 Jul 2010 09:13:36 +0000,
findprahul_at_yahoo_dot_co_dot_uk(a)foo.com (rahulponna) wrote:

>
>
>
>-------------------------------------
>
>
>Hi,
>
> Does anybody have any idea to design a AC to DC conversion circuit
>without using diodes? We can use MOSFETs, but we would need a control
>circuitory to switch ON and OFF the MOSFETs.
> Is to possible to somehow use the secondary voltage of the transformer
>to turn ON and OFF the MOSFETs?
>

There is always motor generator sets.
From: Jamie on 14 Jul 2010 11:24
JosephKK wrote:

> On Sat, 10 Jul 2010 09:13:36 +0000,
> findprahul_at_yahoo_dot_co_dot_uk(a)foo.com (rahulponna) wrote:
>
>
>>
>>
>>-------------------------------------
>>
>>
>>Hi,
>>
>> Does anybody have any idea to design a AC to DC conversion circuit
>>without using diodes? We can use MOSFETs, but we would need a control
>>circuitory to switch ON and OFF the MOSFETs.
>> Is to possible to somehow use the secondary voltage of the transformer
>>to turn ON and OFF the MOSFETs?
>>
>
>
> There is always motor generator sets.
Hmm
I've taken a PNP and NPN set to be biased via an AC signal to produce a
steady DC with no diodes..
The PNP simply derived the (+) directly with an R bypass over the
NPN.. the NPN circuit was decoupled via a 90 degree shift circuit which
also then, biased the PNP.. both were common E to the (+) and (-) rails..
I basically used that switch for a sensitive AC to DC switch which
produced a nice DC saturated switch with fast response..

It works find If you're working with a small range of freq..

Just a thought..




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