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Class AB amplifier

T

Tim Williams

Jan 1, 1970
0
John Larkin said:
There's a tube, still in use by Kepco or somebody, that's a nice 8KV
pentode. And the old color teevees had a shunt regulator tube that was
good to 25 kv or something absurd.

Either:
The 6BK4C (and similar types), a beam triode -- so constructed to prevent
ions from destroying the rare earth oxide cathode, it was used as a shunt
regulator to control the high voltage directly;
Or, a pulse shunt regulator like the 6HS5, also a beam triode with very low
perveance but very high current and voltage capacity and gain. These were
used to control the height of the flyback pulse as it took place (at the
sweep tube's anode, so big peaky voltages!), thereby regulating HV.

Tim
 
P

Phil Hobbs

Jan 1, 1970
0
John said:
I've used a 1B3 HV diode as an active regulator element, with the
control being the filament voltage.

John
Brr. Bet that died of cathode inactivity pretty fast--you'd have been
exceeding the space charge limit 100% of the time, no?

Cheers,

Phil Hobbs

Honorary President,
American Society for Prevention of Cruelty to Cathodes
 
J

Jamie

Jan 1, 1970
0
Simon said:
Hi,

I'm looking for a push-pull output stage design for a single +500v rail
supply. It would need to drive no more than 1mA.

I guess that complementary design with bipolar PNP transistors are out,
since I can't find any PNP devices that have a reasonable margin.

What's the best way to go? A quasi-complementary output stage using only
NPN transistors, or design using MOSFETs? And can someone provide a
reference or url to a sample design or either transistor type?

Thanks
Simon
Are you looking for a bridged output using all NPN's HV transistors
by any chance?

I did something like that years ago for a beam deflection circuit
on a Irradiation circuit. We didn't use HV transistors in that circuit
how ever, It could be applied here.
It was a bridged output using all NPN's (4). Inverted drivers to
isolate the HV for the low voltage OP-AMPS we were using.
In our circuit, we were only dealing with 80 Volts but the Op-amps
could only handle 36 max.
Feed back was voltage divided and the (+) input was offset a bit from
the norm to compensate for that division factor.

One op-amp to drive the source NPN side while the other referenced the
source driver side in a voltage comparator mode to drive the sink NPN
output.
2 sets of these joined with a phase split circuit to drive the
magnetic coils.

That's a general run down, I would have to dig out the print and scan it
if there is any interest.

P.S.
If did run a little warm :)
 
J

John Larkin

Jan 1, 1970
0
Brr. Bet that died of cathode inactivity pretty fast--you'd have been
exceeding the space charge limit 100% of the time, no?

Cheers,

Phil Hobbs

Honorary President,
American Society for Prevention of Cruelty to Cathodes


The worst was a neon sign transformer-1B3 rectifier-oil cap bank for a
flashtube, charging to just under the spontaneous breakdown level, 7-8
KV maybe. The abuse level - high filament voltages to get fast
charging - must have been extreme. It never failed, after maybe a year
of moderate use.

I was a weird kid.

John
 
J

John Larkin

Jan 1, 1970
0
Either:
The 6BK4C (and similar types), a beam triode -- so constructed to prevent
ions from destroying the rare earth oxide cathode, it was used as a shunt
regulator to control the high voltage directly;
Or, a pulse shunt regulator like the 6HS5, also a beam triode with very low
perveance but very high current and voltage capacity and gain. These were
used to control the height of the flyback pulse as it took place (at the
sweep tube's anode, so big peaky voltages!), thereby regulating HV.

Tim


I was thinking of the 8068. I think.

John
 
J

John Larkin

Jan 1, 1970
0
Duh, invoke a +1000V supply. At 1mA, it's *practically* static
electricity, no one will notice. ;-)

Tim

Well, how close to the positive rail would you want it to swing?

Do the math.

John
 
F

Frithiof Andreas Jensen

Jan 1, 1970
0
Simon Burley said:
Hi,

I'm looking for a push-pull output stage design for a single +500v rail
supply. It would need to drive no more than 1mA.

I guess that complementary design with bipolar PNP transistors are out,
since I can't find any PNP devices that have a reasonable margin.

What's the best way to go? A quasi-complementary output stage using only
NPN transistors, or design using MOSFETs? And can someone provide a
reference or url to a sample design or either transistor type?


Maybe a differential amplifier output stage? Similar to the one a bit down
the page here: http://web.jfet.org/vclk/
 
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