In everyday life and in professional activities in all areas, various electronic devices are widely used. Their performance is ensured by a constant voltage source, which is powered by an alternating current network. The mains voltage often "walks" within wide limits, and without special measures, all these changes are directly reflected in the output voltage. This does not in the best way affect the functioning of the electronic device. To overcome this drawback, a number of circuit solutions are used to stabilize the output voltage of the source. The functions of a key component of the vast majority of stabilization circuits are performed by a zener diode.
Zener diode features
Zener diode (in foreign literature often referred to by the name of the inventor as the Zener diode) is a semiconductor diode that is operated in reverse bias mode. Due to the corresponding structure of the pn junction at a voltage value that reaches a certain threshold voltage, it begins electrical breakdown, as a result of which the current rises sharply with a very small change in the voltage drop across the junction, as shown in Figure 1. This area is working for the zener diode.
Standardized parameters
The manufacturer specifies in the technical data a number of parameters that are necessary when designing stabilization circuits.
Required:
- stabilization voltage;
- maximum current.
The convenience of using Soviet zener diodes is noticeably facilitated by the fact that the stabilization voltage is explicitly entered into their index. For example, the designation KS147 denotes a silicon zener diode with a stabilization voltage of 4.7 V.
The simplest stabilization scheme
The simplest so-called. The parametric stabilization circuit is shown in Figure 2 and is assembled from a zener diode and a limiting resistor R. It works as follows. When, for example, an increase in the input voltage by ΔU, the current through the zener diode immediately increases, as a result of which ΔU drops to R and the input voltage of the chain remains unchanged.
The strong side of the circuit in Figure 2 is normal performance both with a smooth and a sudden change in the input voltage. To further increase the quality of stabilization during impulse input actions, a large capacitor is often included in parallel with the zener diode.
Serviceability check
Checking the health of a zener diode is similar to checking a conventional diode and is performed with a multimeter: the element must demonstrate a large resistance in one direction and a small one in the other, Figure 3. This is due to the fact that the breakdown voltage is noticeably higher than the output voltage of the tester in the resistance measurement mode.