Prev: Jon-Archi collaboration, test results:
Next: Mosfet switching times ?
From: Tim Williams on 14 Jul 2010 13:03
"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_(a)charter.net> wrote in message news:Xzk%n.13500$0A5.7390(a)newsfe22.iad...
> 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 yesterday, I invented a chopper circuit which performs synchronous rectification with 2N3904s. DC in, DC out, doesn't matter which direction. It should work a few tenths of a volt negative as well (i.e., a true ideal transformer for small signals).

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
From: Michael Robinson on 14 Jul 2010 22:54

"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_(a)charter.net> wrote in message
news:Xzk%n.13500$0A5.7390(a)newsfe22.iad...

snip

> 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..


Could you please draw a diagram?


From: Jamie on 15 Jul 2010 18:42
Michael Robinson wrote:
> "Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_(a)charter.net> wrote in message
> news:Xzk%n.13500$0A5.7390(a)newsfe22.iad...
>
> snip
>
>
>> 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..
>
>
>
> Could you please draw a diagram?
>
>
I would have to do one in Spice and spit it out here.

The above circuit description is a rough draft of what I did..

The original circuit used 2 PNP's from the (+) rail and one NPN
circuit. The input signal was cap decoupled because of the signal
source would've otherwise biased the first PNP to saturation...

A basic R from the base to the (+) rail and R in series to the cap
of the input signal.

The 90 degree shift was a basic T network with cap and R which then
input to a buffer amp, this amp then switched on the second PNP.

Both collectors of the PNPs are joined and both Emitters are joined
to the (+) rail.. The second PNP base(B) is part of the 90 degree shift
buffer stage. The (B) r for that transistor simply was the collectors R
for the buffer stage which was inverted.

The shift was calculated for the lowest frequency of interest to
insure the time domain would cross over at 90 degrees. Higher
frequencies didn't need the shift to be exact due to the tome constants
put in place
for the final switch signal.

So when all said and done, I was able to get a wider pulse at the
final output with a short gap in the signal. A final cap on the end into
a comparator gave me the near perfect DC on/off I was looking for..

Basically I created a speed switch from a Eddy current motor that
needed to have a very fast on response when the rotor started to turn
with a very narrow gap in the pulse stream and voltages below .5 volts
into a compressed safety circuit..

This was done years ago and I later on did basically the same thing
using a 555 timer which worked out just fine...


This circuit isn't any good for a linear DC representation of AC levels.


I hope this was helpful enough, its a lot to do in Spice. I could
look up the old print in the files at work when I return monday
and photo scan that area and then post it. I will need to look in
dirty place to find that one, yuk...

First  |  Prev  | 
Pages: 1 2
Prev: Jon-Archi collaboration, test results:
Next: Mosfet switching times ?