Semiconductor stabilizer

The electrical break down mode of a p-n junction is used in semiconductor stabilizers for voltage stabilization. These diodes are made of silicon, which permits to get necessary CVC. Germanium is not a good material for such diodes, because they may have a thermal break down.

The stabilivolt voltage depends on current a little in the operating mode. The voltage dependence on current is specified by differential resistance of a stabilivolt in the operating region of its characteristic (from to )

This resistance is a few dozens or even a few Ohms.

A stabilivolt is connected in parallel to a load resistor R_lod in the stabilizing circuits, and a limiting resistor R_lim is connected in series with these elements. The resistance of R_lim must be much higher than the resistance of a stabilivolt R_dif. The ratio R_lim/ R_dif is higher, the voltage stabilization is better . Such stabilizer is called parametric.

Fig.3.9. Circuit diagram of the parametric stabilizer

The main goal of a voltage stabilizer in electronic devices is to keep a source voltage stable when a load current or mains voltage varies (fluctuates).

The input and output voltages of a stabilizer are connected by the equation:

Let’s consider voltage stabilization when the mains voltage E fluctuates.

Assume that mains (supply-line) voltage has increased by DE, then stabilivolt voltage and load voltage start to increase. A little increase in V_st initiates (provokes) abrupt growth of a stabilivolt current DI_st. The current flowing through the limiting resistor R_lim starts to increase as soon as stabilivolt current begins to increase, and it provokes increasing of the voltage drop across the limiting resistor.

The circuit maintains the equal changes: , i.e. .

Thus, when supply-line voltage increases a limiting resistor voltage will increase automatically due to a CVC peculiarity (Fig. 3.10), and this will compensate fluctuations of E.

Let’s consider voltage stabilization when the load current fluctuates. Assume, that current has increased, and then voltage drop across the limiting resistor V_lim has increased too. Further stabilivolt voltage starts to decrease, and this provokes abrupt decrease in stabilivolt current. When a load current increases by DI_ld, a stabilivolt current DI_st will decrease by the same value, but there will be no fluctuation of the current I₀.