Unusual Transistors Circuits

Diod Transistors

Transistor as a Zener

Zener diodes connected as shown in Fig. 1 are carefully doped at manufacture such that they break down when a critical reverse bias voltage is applied and allows current to flow. The current is limited by the power ratings of the particular device employed.

Zeners are used to provide a voltage reference and any transistor can be employed to do the same job if connected as shown in Fig. 2.

Different transistors will produce different zener voltages and a series of tests can be done to establish what the typical zener voltage is for that device.

A suitable setup could be employed as shown below.

  A BC548B gives a zener voltage Vz = 8.2V

  A BC549B gives a zener voltage Vz = 10.8V

  A BC547B gives a zener voltage Vz = 9.1V

  A BC184 gives a zener voltage Vz = 8.2V

Using the Configuration in Practice

The above circuit Fig 4 could form the basis of a low power regulated power supply.

Vbe Multiplayer

Variable Reference Voltage Circuit

Fig. 5 shows a way of adjusting the voltage Vz to suit by adjusting the resistor values of R1 and R2.

Vz = Vbe((R1 + R2)/R2)

Better regulation can be achieved with a darlington configuration as shown below where it is used in a simple regulated supply, but now the voltage Vz becomes:-

Vz = 2Vbe((R1 + R2)/R2)

and the regulated output voltage becomes:-

Vo = Vz – Vbe

Other more circuits

any signal add to it vbe by Q1 and send it to Q2 so Q2 can read any signal
vce more stable than vbe because once vbe increased R2 incresed and keep palance
Vbe multiplayer with more stability