View Full Version : My Intelligent Curve Tracer
02-01-2012, 10:59 AM
It use USB or RS232 interface communication with PC and show the semiconductor curve in PC screen.
It can measure BJT's Ic->Hfe curve
Can measure Vce-Ic curve
measure some semiconductor transmission curve,such as Vbe-Ic / Vgs-Id
also FETís Vds-Id curve measure,Even can study Vgs & Rds relationship
Upper is six IRF630 Vds-Id curves,their Vgs is 5V 6V 7V 8V 9V 10V.
The Vds-Id curve only show Vds=0~1V range,so you can use systemís calculate function get the slope value,
The window in the central show six curveís slope, Measurement unit is V/mA, multiplicate 1000 is Rds,
So under Vgs=10V,Rds is 0.000334649870637804*1000=0.334ohm
Some diode V->I curve
fllower is TL431 in all current range V-I curve
if you plug TL431 into socket B and E,and change the measure condition,you can see less current VI curve. The following figure , Y-axis is only 0~0.38mA
the Intelligent Curve Tracer is more powerful,It can measure 3 terminal voltage regulatorís Vi-Vo / Io->Vo Curve
02-01-2012, 11:04 AM
Intelligent Curve Tracer Principle
Before talking about my Intelligent Curve Tracer principle,I talk about the general measure curve principle by MCU first.
The general measure diagram as in Figure
Mcu control Channel B/C DAC and OCL power amplifier to driving the DTU, And measure four voltage(VBH/VB/VC/VCH) by ADC, and then calculate the Ib/Ic/Vce/Vbe and then draw the Vbe-Ic/Vce-Ic/Ic-Hfe curve.
Because of the need for the measure of P and N type semiconductor,so all the voltage are bipolar.
But considering the component selection, Most of the DAC and ADC can only output or measure unipolar voltage,bipolar ADC price will be very expensive.
Considering the cost of it, it uses unipolar ADC/DAC a lot cheaper, choice scope is much extensive.
So if we use unipolar ADC/DAC to design the curve tracer,we need some additional circuit:
1.four amplifier,It’s gain is –1, purposes to change negative voltage to positive voltage,so that the ADC can handle.
2.two amplifier to offset DAC to bipolar voltage;
3.Need biporlar power supply, but the DTU’s vce voltage range is only half of the total supply voltage;
4.Need 8 channle ADC to measure vbh1/vbh2/vb1/vb2/vch1/vch2/vc1/vc2;
My intelligent Curve Tracer in the above principle to make an improved, Using the" three voltage amplifier to drive DTU, the DTU emitter isn’t connect to ground, but from a voltage source,.
The emitter voltage source(Channel E Power Amp) is very critical, completely solve the shortcomings of the above,.
Measure NPN BJT,We set Channel E Power Amp to output 2.5V, and set Channel B/C Channel power amplifier to output more then 2.5V,such as B channel is 5V, C channel is 20V,so the NPN can work. We measure the Ve/Vbh/Vb/Vc/Vch then calculate the Vbe/Vce/Ib/Ic/Hfe and draw the curve.
If measure PNP BJT,We set Channel E to output 40V, and set Channel B/C Channle to output less then 40V,so PNP can work. We also measure the Ve/Vbh/Vb/Vc/Vch then calculate the Vbe/Vce/Ib/Ic/Hfe and draw the curve.
If measure N type J-FET,We connect JFET’s source to E, grid to B, Drain to C. and set E channel output 10V,and set B Channel is from 2.5V to 10V, and set C Channel output from 10 to 40V. This means that the JFET’s Vgs is –7.5 to 0V,and Vds is from 0 to 30V. This is the JFET normal operating voltage range.
You look back above example, All the measure voltage are unbipolar,so DAC and ADC are just use a unipolar model device.
And the solution only need a 40V unbipolar power supply, and the DTU Vce range can be from 0 to 40V.
02-24-2012, 08:45 AM
i work on my own curve tracer hw, but would like to make it compatible with your sw, it will support higher ce voltage (55-58V max, at 500ma), i use the opa547 for the final stage, which has a very nice current limiter embbeded inside the ic and a pic for usb, ad, da and control.
i like your pc sw, could you forward the sw to my email apollo2mond(at)gmx.de, I will need the sw sources for some modifications and to implement the interface protocol, maybe i will port it towards Qt in future.
many thanks, uwe from germany
02-24-2012, 02:18 PM
Sorry The software and fireware is not Open source.
The opa547 not suit in my circuit,because it is not a single supply opamp,It can't run under single power supply.
And my curve tracer need two fllower, and need Vicomm range is Vee+2~Vcc-2,Few OP can run over 40V. So I design it only runoperate under 40V