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Curve Tracer Project .:. Part 2

Homebrew Curve Tracer

This is the advanced version of the simple Curve Tracer. It offers a current limiter, and a base/gate Driving Section.

Circuit Description

The Device uses 3 transformers to generate 4 AC voltages and 3 DC voltages. The 4 AC voltages are in series, and a switch selects between 0 - 20 - 40 - 60 - 80 V. This voltages is rectified and then passes a current limiter which may be adjusted from 5 mA to 50 mA.

current limiter

The design is straightforward, the main focus was on easy design. Of course, an LM-10 would have a lower voltage drop, but the cost is 10 times higher :-( It follows a relais to switch the polarity. (NPN or PNP). This voltage is then applied to the collector or drain of the transistor. This voltages also is the [HORIZONTAL DEFL.] A shunt (R23,10Ω) in connection with an 10x amplifier (IC2a) amplifies the voltage drop at the shunt to give a 100mV / 1mA reading. [VERTICAL DEFL.] The 3rd transformer is used to generate an impulse to trigger the counter (74HC191) which counts from 0 to 7.

Impulsformer Counter with R2R Network

The output of this counter forms with an R2R-network a staircase which is amplified to 7 Vpp. (adjusted with R20). This staircase is inverted with IC6a and another relais switches between the polarity (NPN or PNP). In case a fet is to be analysed, a switch selects between 0.5 V/DIV and 1.0 V/DIV. In case a bipolar transitor is to be analysed, a voltage controlled current source generates the drive current. This is done by IC6c,d. The 3rd transformer also generates the supply voltages of -12V, +5V, +12V.

Measurement / Handling

The handling is almost self explanatory. In this section we will show some measurents and how to obtain them.

[LEFT] BY 228 Diode   [RIGHT] Resistor

BY228 Resistor

[LEFT] Varistor EPCOS S20K30    [RIGHT] Capacitor 100µF


[LEFT] Transformer, primary    [RIGHT] BC141-16, Base Drive : 10µA, 40V, 5mA

Trafo BC141-16


I get a lot of emails concerning R8.

R8 is used to define the current for BJT's. IC4 together with the R2R Network produce a staircase waveform. With R10 this can be adjusted to 1V/step.

IC6d and IC6c generate a current. (I=U/R)

You can use any switch you have. I used one with seven positions to generate a Base Drive of 10-20-50-100-200-500-1000 microAmp /DIV

Therefore I used the following Resistors: 100kR-50kR-20kR-10kR-5kR-2kR-1kR

Schalter Schalter

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t1 = 3941 d

t2 = 401 ms

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