I want to make a voltage comparator , It should compare between 5 different voltages (about 15, 13, 11, 10, and 8.5) the pulse duration is about 15-30 ms,
what op-amp do you suggest for me to use as a comparator??
Supply voltage(s) and current available, regulated or unregulated?
Comparator output voltage and current drive required?
Internal or external reference voltage?
regulated +/- 15V, 100mA Supply for each comparator
output on display (LED or 7 segment driver or maybe microcontroller) not decided yet
reference will be zener diode for standard voltages, or using voltage divider (separate supply on the same board)
Please note that the input which will be compared with the reference will have sort duration (15-30 ms)
So you want to have a circuit that detects 5 different voltage levels with a duration of 15 msec? This would require 5 compare circuits and some way to sample each to detect for a true condition, then latch the true condition.
I am not getting what your trying to do, can you paint the big picture?
i'm making a tester that will receive a discharge of capacitor (thats why the duration is in msec) i want to determine the capacitor charge level.
The capacitor is (42uf 6 KV), discharging it will be on voltage divider the divider output is the input of the comparator. I need a suggestion for this comparator , I've already tried the 741 but, as you probably know, was a big faliure
As far as comparators go, the LM339 (quad, 16 mA output), or the LP339 (quad, 30 mA output) are standard and can be used for the comparison function.
I've already tried the 741 but, as you probably know, was a big faliure.
The 741 should work, as far the part itself goes, except it cannot drive an LED (output current is only a couple of mA). You should post that circuit, and then we can know.
the 741 in my circuit triggers a monostable 555 circuit, so output current was not my problem, I think it's because the input voltage many times so close to supply voltage
How can a comparator compare 5 diff values? Two analog signals must be compared first and then the higher valued signal with the next and so on...
A comparator just indicates if the input signal is higher or lower when compared to a trip point. i.e. the actual value of the input signal is not reproduced at the output... Am I right?
How can a comparator compare 5 diff values? Two analog signals must be compared first and then the higher valued signal with the next and so on...
A comparator just indicates if the input signal is higher or lower when compared to a trip point. i.e. the actual value of the input signal is not reproduced at the output... Am I right?
No not wattage, are they rated for the voltage.... You can't use a normal resistors on even 2 thousand volts, common resistors are only rated for 200 volts or so. You have to use long strings of smaller resistors to balance the voltage to bellow their limits or they don't act like resistors properly when high voltage is applied, it'll arc right through or around the dielectric.
**broken link removed**
This website explains the construction of 50kv resistor chains but is equally valid for 2000 volts. 2KV can arc 2 centimeters in dry air, I'm sure it's well past the dielectric breakdown voltage of a common resistor. If your resistors aren't marked SPECIFICALLY saying they're safe to use at 2kv's figure they're only good for 200, and derate 100% for saftey. 42u at 2kv will discharge through a 100ohm load in 10ms's with a peak power of 40kw and 84 joules.
Thanks Sceadwian, I've totally missed this point, It's my first HV project.
I'll study this issue and read the link you send and be back... thanks again
Think about it this way Atto. The 'starting' energy of defibrillators is around 100 joules. Not to mention more than enough to cause small resistors and IC's to explode. If you don't know what you're doing with high voltage one day you won't log on, and I won't wonder where you went =O
I accidentally set a board with a 80u 300volt charged cap on my pair of jeans once and even through the pants it was enough to cause my muscle to contract. I've brush my dry hand up against one as well and it felt like a slap to the face, and that' 300 volts. You do that with 2kv and you better hope there's someone around to call the peramedics.
They do it in test probes all the time but I would sure watch what your doing with 2000 volts and hook up you're test eq before powering up and never touch any thing with both hands
the 741 in my circuit triggers a monostable 555 circuit, so output current was not my problem, I think it's because the input voltage many times so close to supply voltage