1000 Volt Application Question
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Posts: 46,084
I have a couple different questions.
1. Does anyone know of a high voltage mux? Should be able to handle 0-1000vdc @ 5ma.
··· Yes, I realize you can divide the voltage down and then mux it. But, it would be convenient to········
··· measure is directly.
2. Does anyone have a favorite circuit for an adjustable current limit that can handle up to 1000vdc @ 5 ma?
··· ·I am looking at using a MOSFET with feedback via a current sense resistor·and an op-amp driving the gate.
··· ·I know I can do it if the·limit circuit is on the ground side. But, it would be more convenient to
···· do it on the positive side. But to do so would mean using a floating supply for the op-amp.·And the analog control
··· signal.···
Now that I have blown your minds, let me explain my application. If anyone is familiar with aluminum electrolytic
capacitors then ·this will make sense to you. During the aging of the capacitors they are powered by an adjustable ·0 to 1000vdc power supply and current limited. The current is set via a potentiometer which we would like to replace with an analog voltage(0-5vdc). Once the capacitor is fully charged the voltage across the capacitor should be the same as the HV supply. Then we have to discharge the capacitor using a variable current limit like the one used during the charge cycle. And then the cycle repeats. The idea is to allow the micro to control the charge and discharge rates. Each circuit would then be repeated n number of capacitors being tested.
Thank in advance!
Jon KreftJon Kreft
Jkreft@concentric.net
1. Does anyone know of a high voltage mux? Should be able to handle 0-1000vdc @ 5ma.
··· Yes, I realize you can divide the voltage down and then mux it. But, it would be convenient to········
··· measure is directly.
2. Does anyone have a favorite circuit for an adjustable current limit that can handle up to 1000vdc @ 5 ma?
··· ·I am looking at using a MOSFET with feedback via a current sense resistor·and an op-amp driving the gate.
··· ·I know I can do it if the·limit circuit is on the ground side. But, it would be more convenient to
···· do it on the positive side. But to do so would mean using a floating supply for the op-amp.·And the analog control
··· signal.···
Now that I have blown your minds, let me explain my application. If anyone is familiar with aluminum electrolytic
capacitors then ·this will make sense to you. During the aging of the capacitors they are powered by an adjustable ·0 to 1000vdc power supply and current limited. The current is set via a potentiometer which we would like to replace with an analog voltage(0-5vdc). Once the capacitor is fully charged the voltage across the capacitor should be the same as the HV supply. Then we have to discharge the capacitor using a variable current limit like the one used during the charge cycle. And then the cycle repeats. The idea is to allow the micro to control the charge and discharge rates. Each circuit would then be repeated n number of capacitors being tested.
Thank in advance!
Jon KreftJon Kreft
Jkreft@concentric.net
Comments
The only commercial HV muxes I'm aware of use relays...
You're usually better off with your current limiter on the low side, but
there are relatively reasonable ways to get power and signals across to a
floating subsystem if you must. One of my favorites: Use a pair of HV
capacitors in the 100~1000pF range to couple AC power, in the low MHz
range, to a bridge rectifier in the floating circuit. Fast rectifiers are
needed, but ordinary 1N4148 signal diodes are usually adequate. If load
current is only a few mA, your AC source could be a simple oscillator made
with CMOS logic gates (e.g. 4049).
You can couple a control signal this way too, by modulating the amplitude
of the AC source, but there's a more elegant method using an opto-isolator
with dual phototransistors or photodiodes (or an ordinary dual
optoisolator). The idea is to use one of the phototransistors in a local
feedback loop, forcing the output of the other phototransistor, when
equally loaded, to track the input signal. At least one manufacturer offers
a device that is optimized for this application-- see Infineon's IL300 data
sheet (linked on this page):
http://www.infineon.com/cgi/ecrm.dll/ecrm/scripts/prod_ov.jsp?oid=13976cat_o
id=-8198
====================================
1. Does anyone know of a high voltage mux? Should be able to handle
0-1000vdc @ 5ma.
Yes, I realize you can divide the voltage down and then mux it. But, it
would be convenient to
measure is directly.
2. Does anyone have a favorite circuit for an adjustable current limit that
can handle up to 1000vdc @ 5 ma?
I am looking at using a MOSFET with feedback via a current sense
resistor and an op-amp driving the gate.
I know I can do it if the limit circuit is on the ground side. But, it
would be more convenient to
do it on the positive side. But to do so would mean using a floating
supply for the op-amp. And the analog control
signal.
Now that I have blown your minds, let me explain my application. If anyone
is familiar with aluminum electrolytic
capacitors then this will make sense to you. During the aging of the
capacitors they are powered by an adjustable 0 to 1000vdc power supply and
current limited. The current is set via a potentiometer which we would like
to replace with an analog voltage(0-5vdc). Once the capacitor is fully
charged the voltage across the capacitor should be the same as the HV
supply. Then we have to discharge the capacitor using a variable current
limit like the one used during the charge cycle. And then the cycle
repeats. The idea is to allow the micro to control the charge and discharge
rates. Each circuit would then be repeated n number of capacitors being
tested.
===================================
Mike Hardwick, for Decade Engineering -- <http://www.decadenet.com>
Manufacturer of the famous BOB-II Serial Video Text Display Module!