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Old 24th February 2012, 12:16 AM   #21
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locky_z

It would seem to me that a "crowbar" circuit or a Zener, or maybe a transzorb would protect sensitive input circuits?

Also I don't quite understand why the input to the tracer's current or voltage sense can't be scaled, the easiest being a simple divider, more complex with an external active circuit, and the collector voltage scaled with a DC amplifier?

Are you saying it won't work because you are not using ground on the "emitter" side?

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Old 24th February 2012, 06:22 AM   #22
locky_z is offline locky_z  China
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1.It use a op as follower,so it only operate at 40V.
2.It use differential amplifier and differential measurement,It requirements of high resistance matching degree, and I use calibration reduce the impact,
but if series resistor voltage divider too much, measure P type DTU will have error


My English level is low,and don't unstander what is mearn:
‘It would seem to me that a "crowbar" circuit or a Zener, or maybe a transzorb would protect sensitive input circuits?’
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Old 24th February 2012, 03:45 PM   #23
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Quote:
Originally Posted by locky_z View Post
1.It use a op as follower,so it only operate at 40V.
2.It use differential amplifier and differential measurement,It requirements of high resistance matching degree, and I use calibration reduce the impact,
but if series resistor voltage divider too much, measure P type DTU will have error


My English level is low,and don't unstander what is mearn:
‘It would seem to me that a "crowbar" circuit or a Zener, or maybe a transzorb would protect sensitive input circuits?’
Ok.

To keep from damage
To keep from breaking
To protect
To make maximum voltage not go too high
For test input voltage.

A circuit can be used for this
For this a Zener can keep voltage below
A "tranzorb" part will CLAMP maximum voltage
OR a circuit using a triac or SCR can be triggered at a maximum voltage

So no worry that too much voltage can destroy ADC or opamp.

IF I want to use unit for 200volt Vce, can not.
But If I use 10x DC opamp for Vce then I get 40vdc x 10 = 400vdc

But this is too much voltage for ITC 3.0

So, I want to use a circuit to make:

- test voltage higher (5x or 10x)
- scale, divide or adjust current sense back to ITC 3.0 regular 0-36vdc range when transistor is being tested This is 5x or 10x lower than actual voltage tested.
- it will display as 0-40 volt but will be higher!

Now ITC 3.0 "thinks" it is testing in regular range, but is really testing 5x or 10x more collector voltage




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Last edited by bear; 24th February 2012 at 03:50 PM.
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Old 25th February 2012, 05:50 AM   #24
locky_z is offline locky_z  China
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The curve tracer 3.0(CT3) have no high voltage protect because it not allowed outside measure voltage and can't measure outside input voltage.
The curve tracer 3.0(CT3) have 3 channel voltage generator inside ,It only handle less 40V.


If you replace the voltage generator,let it to output 100V,and change the divide scale of ADC, the CT3 can work more high voltage.

but another thing is you need a DC fllower that it can work under high voltage,the fllower is use to increasing the input impedance, without affecting the base current. but high voltage fllower not exist.
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Old 25th February 2012, 06:30 AM   #25
EUVL is offline EUVL  Europe
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Figure 6 of this TI Application Note will give you some idea how to do high voltage with an opamp :

http://www.ti.com/lit/an/snoa600a/snoa600a.pdf

Just take it as a friendly advice, as were all the advices we gave you a couple of years back.


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Old 25th February 2012, 11:23 AM   #26
locky_z is offline locky_z  China
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Quote:
Originally Posted by EUVL View Post
Figure 6 of this TI Application Note will give you some idea how to do high voltage with an opamp :

http://www.ti.com/lit/an/snoa600a/snoa600a.pdf

Just take it as a friendly advice, as were all the advices we gave you a couple of years back.


Patrick
I had research some 'Op booster' cricuit,They are not difficult.

But a difficult thing is the fllower, It need work in single supply, and Vicomm range need Vee+2~ Vcc-2,if use Op+booster,It is hard to do.
if use discrete component to make a single supply high voltage fllower,but It is difficult to guarantee the DC characteristics.
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Old 25th February 2012, 11:30 AM   #27
EUVL is offline EUVL  Europe
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I am sure you are aware that :

a) your DAC output would never be 120V, so you need a gain stage after that with negative feedback to reach high voltage;
b) there are many rail-to-rail opamps around that will output very close to the negative rail;
c) it is easy enough to make that circuit in Fig 6 single ended;
d) you are neither worried about distortion nor about high slew rate.


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Old 25th February 2012, 12:59 PM   #28
locky_z is offline locky_z  China
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Single supply high voltage AMP is easy.
But high voltage DC follower and work on single supply is no easy.

Could you show me a DC follower circuit that can work in high voltage and single supply?
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Old 25th February 2012, 02:34 PM   #29
EUVL is offline EUVL  Europe
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I can only guess that by follower you mean an output stage that can source or drain current, and NOT unity gain.
There is no need to use unity gain, as you already mentioned earlier.

If that is the case I do agree with you it is not so easy to make a single ended output stage that can both source and drain current.
But I do not think it is necessary to do so in this particular application.
For testing any MOSFETs and BJT's, Vce or Vds of +/-30V is sufficient for most purposes.
So people who want 100V want to use the Curve Tracer for Tubes.

But Tubes only have "N" types and no "P" types.
So you can make, as an adaptor to your current PCB, a HV current source with an opamp and 2 transistors (1x N-Mosfet small signal and 1x P-Mosfet power) for your C-channel only. You can still use your E-channel to drain the current.
I do not think you need HV for your B (or gate) channel, but then I am not a tube guy.


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Old 25th February 2012, 02:49 PM   #30
locky_z is offline locky_z  China
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There are not need E-channel AMP if only N type(or Tubes) be measured, direct use GND replacement E channel. This may Easy to designed,

Because P type need measure, so I add E-Channel AMP to drive the Emitter/Source.

The follower inrder to measure two voltage:Vb and Vc
Click the image to open in full size.

if Simple parallel resistance at Vc and Vb to GND,they may shunt the Ib and Ic,so measure may have error.

Because Vb and Vc's voltage swing is same as Power Amp output voltage swing,
The Power Amp output voltage swing is Gnd+2 ~ Vcc-2V,
If power supply less 40V,then direct use OP07 as follower,
If power supply more then 40V,It is hard to design the follower.

Last edited by locky_z; 25th February 2012 at 02:55 PM.
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