Patrick
I would be very wary of using the 4N33 in the high voltage supply line. I
know the spec says it isolates to lots of kV, but, if you plan to put the
device into a pcb or Vero, the distance between the high voltage and signal
voltage becomes very small between pads and you should be looking for at
least half inch. I would use a wide spaced opto here (sorry can't give you
a part number, the ones I am familiar with are triac couplers). If you
really want to use the 4N33 et al, then use them dead bug style with their
legs in the air and connect thin wires to each leg and arrange them to be as
far apart as possible. Use small diameter heat shrink to hold the wires in
place. It also worries me that a glitch could punch through the
inter-electrode barrier between the 2 sides, though someone else would be
better qualified on the opto structure to advise on this. The wide spaced
couplers might have less gain.
Another way to tackle the current sensing, though I haven't tried it: wrap
the ht wire around a long reed switch keeping the wire away from the reed
terminations. The glass gives very high isolation and you can adjust the
trip point by moving the reed in and out of the solenoid you've just made.
I don't know how many turns you would need but you can do all your
experimenting at low voltage of course. One note of caution on this
technique: don't feed the reed into a reactive circuit because the contact
can weld shut with even small current surges. You can fit a few 100ohms in
series with the reed to prevent this. One way of increasing the sensitivity
of the reed is to fit a small magnet nearby to give it a start, then your
current sensor needs less turns to get it to trip. Turning the reed axially
will adjust this magnetic bias. Sounds like fun to play with this.
It is possible to fit your opto sensor in the ground lead but this might
introduce other complications.
David
G3UNA
> Hi all,
>
> I'm back in the "business" after several very busy months and i'm
> continuing
> my 2m amplifier project. (4CX1500B)
> I'm still collecting parts and i will start with the power supplies.
>
> I made a diagram of my HV supply and i'ld be happy if you could look on it
> and say if everything seems OK.
>
> I added :
> - step-start
> - glitch protection
> - current overload detection
> - voltage lack detection
> - current measure
> - voltage measure (both with external meters)
>
> I used the components i've actualy found. For example, the K1 ON/OFF relay
> could better be a DPST instead of a SPST...
>
> The diagram can be seen here :
> http://tk5ep.free.fr/tech/PA2m/datas/HV%20supply.gif
> Patrick Egloff <pegloff@gmail.com>
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