Regulator performance is good or bad, dynamic resistance r can really mean?

Generally, the triode is forward-conducting and reverse-cut; the reverse voltage applied to the diode, if it exceeds the capability of the diode, the diode is broken down. However, there is a diode whose forward characteristic is the same as that of a normal diode, but the reverse characteristic is special: when the reverse voltage is applied to a certain degree, although the tube exhibits a breakdown state, a large current is passed, but it is not damaged, and This phenomenon is very reproducible; conversely, as long as the tube is in a breakdown state, although the electricity flowing through the tube varies greatly, the voltage across the tube changes very little to stabilize the voltage. This special diode is called a Zener.

Type regulator has 2CW, 2DW series, its circuit symbol in FIG 5--17 FIG.

Regulation characteristics of the regulator, can be used as shown in FIG. 5 a 18 volt-ampere characteristic curve is clearly shown.

The stability of the Zener diode can be expressed by its dynamic resistance r :

Obviously, for the same current change amount ΔI , the smaller the voltage change amount ΔU across the Zener diode, the smaller the dynamic resistance, and the better the performance of the Zener diode.

　　

A simple voltage regulator circuit composed of a silicon voltage regulator tube is shown in Figure 5- l ( a ). The silicon voltage regulator DW is connected in parallel with the load Rfz , and R1 is a current limiting resistor.

This circuit is a regulator of how to conduct it?

If the grid voltage rises, the output voltage Usr of the rectifier circuit also rises, causing the load voltage Usc to rise. Since the regulator DW Rfz parallel with the load, as long as Usc less root growth, it will cause a sharp increase in the current flowing through the regulator, such that I1 increases, limiting the voltage drop on the resistor R1 increases to counteract The rise of Usr keeps the load voltage Usc substantially unchanged. Conversely, if the grid voltage drops, causing Usr to drop, causing Usc to also drop, the current in the Zener diode is drastically reduced, causing I1 to decrease and the voltage drop across R1 to decrease, thereby offsetting the drop in Usr and maintaining the load. The voltage Usc is substantially unchanged.

If the Usr is constant and the load current increases, the voltage drop across R1 increases, causing the load voltage Usc to drop. As soon as Usc drops a little, the current in the Zener diode is rapidly reduced, so that the voltage drop across R1 is further reduced, so that the voltage drop across R1 is kept constant, and the load voltage Usc is stabilized.

In summary it can be seen, the current regulator plays a role in the automatic adjustment, the adjustment voltage limiting resistor plays a role. The smaller the dynamic resistance of the Zener diode, the larger the current limiting resistor and the better the stability of the output voltage.