555 transistor characteristic curve tracer circuit diagram

As shown in the figure is the circuit of a 555 transistor characteristic curve tracer. To describe the characteristics of a transistor, two voltages are required. One is the step wave applied to the b electrode to generate different Ib, and the other is the sawtooth wave on the c electrode. Its period corresponds to the step wave to depict the Ic-Vcc characteristic curve.

As shown in the figure, 555 and R1, R2, and C1 form an astable multivibrator with an oscillation frequency of f=1.44 (R1+2R2) C1. The parameter in the figure is f=1100Hz. C2 and R3 form an integrating circuit to generate a sawtooth wave, which is emitted and output through VT4, and then added to the vertical "Y" input of the oscilloscope and the c-pole of the tube under test. C3, D1, VT1~VT3, C4, etc. form a staircase wave generator. Every 5 oscillation cycles, the charging voltage on C4 turns on VT3 and C4 discharges, forming 5 steps. Every time C4 is charged, the emitter voltage of VT2 decreases a little, forming a step. The step wave is added to the b pole of the tube under test through R4. The tube to be tested is VTx in the figure. The IV characteristic curve observed after connecting to the oscilloscope is shown in Figure b.

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