how does this work??
how does this work??
(OP)
I am reverse engineering a circuit that switches
a 200 volt peak to peak ac voltage with a single bipolar
transistor rated with a Vce breakdown of 400v.
In the off position the base can be considered tied
to the emmitter by external circuitry.
When turned on by a base current the transistor
conducts current in both directions , collector
positive for a half cycle and then collector negative
for a half cycle.
A constant current through the base emitter junction
is maintained when on.
The current is low level, approx 20ma
Can a bipolar transistor live with this type of
use ????
a 200 volt peak to peak ac voltage with a single bipolar
transistor rated with a Vce breakdown of 400v.
In the off position the base can be considered tied
to the emmitter by external circuitry.
When turned on by a base current the transistor
conducts current in both directions , collector
positive for a half cycle and then collector negative
for a half cycle.
A constant current through the base emitter junction
is maintained when on.
The current is low level, approx 20ma
Can a bipolar transistor live with this type of
use ????





RE: how does this work??
The low current is what allows it to work, since the reverse beta is usually quite low, compared to the forward beta.
TTFN
RE: how does this work??
The usual base-emitter breakdown voltage is about 6V max.
I can' believe 200V.
Most likely the transistor is in the diagonal of a diode bridge which may be as small as a few mm. square (
dissipation <<30 mW)
<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032
RE: how does this work??
I forgot about transistors still having gain in
opposite polarity.
If the load were more it probably would die.
RE: how does this work??
RE: how does this work??
RE: how does this work??
I haven't found any high voltage transistors that have VEBO much more than 6V, but that's dictated by the configuration of the low resistivity emitter diffusion. If the emitter junction was designed to mirror the doping profile of the collector-base junction, you'd get symmetrical breakdown characteristics as well as symmetrical, but pitifully low betas.
TTFN
RE: how does this work??
that worked fine. Several times. Not that I would do that!!
Why are we talking about the VBE??? Just because nbucska miss read the original post?? :)
RE: how does this work??
I have used one transistor AC switch AC but for only a few Vpp.
<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032
RE: how does this work??
modeled as a capacitor in series with a
resistor.
The transistor does break Vbe in the reverse direction
but for only one cycle.
RE: how does this work??
<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032