  Radio and Electronics (DED Philippinen, 66 p.)  10. BLOCKS OF RADIOS / -1- / POWER SUPPLIES  10.5. STABILIZATION  10.5.5. METHODS OF STABILIZATION  (introduction...) 10.5.5.1. PARALLEL-STABILIZATION 10.5.2.2. SERIES STABILIZATION

### 10.5.5.1. PARALLEL-STABILIZATION

Here the overall current drawn from the supply will be kept constant by a component giving way for a current in a second path as soon as the voltage tends to increase above 6 V. fig. 102

PARALLEL CONTROL STABILIZING CIRCUIT USING A ZENERDIODE EXCLUSIVELY

the most simple circuit to achieve the parallel stabilization is to connect a so called ZENERDIODE in parallel to the load.

FUNCTION:

Let us first have a closer look to the characteristics of a zenerdiode. The characteristics of one called B6Z2 is shown in fig. 105. It is easy to see, that the zenerdiode has a very flat characteristics first (which means a very high resistance) and from a special point on it has an extremly steep-characteristics (which means a very low resistance). fig. 105

The working points between which the diode is useful for stabilization are found at the borders of delta-V.

Taking the second part of the characteristics for a moment theoretically totally vertical, the zenerdiode looks like a contact closed as soon as the voltage at its terminals is exceeding a special limit (the zenervoltage).

Even though this is only a theoretical view, it shows us what the zenerdiode is going to do in the simple stabilization circuit: It will let flow a big amount of-current as soon as the zenervoltage is exceeded.

That means too: the voltage at its terminals is changing only very slightly while the current changes tremendously - as seen in fig. 105 fig. 106 shows this rather simple circuit containing a Zenerdiode, which is able to do the job rather well. fig. 106

The overall current flowing in the circuit is kept constant here by the zenerdiode.

The next chapter will show us by graphical means how this is working by using the characteristics of the zenerdiode.

GRAPHICAL DERIVATION OF THE FUNCTION OF A SIMPLE PARALLEL CONTROLLED STABILIZATION.

fig. 107 shows the typical graph of a Zenerdiode connected in series to a resister (here the internal resistor of the voltage source or even a special series resistor) fig. 107

If there is a load-resistance lower than infinite it can be represented by one of the graphs shown in fig. 108. fig. 108

As we know, the graph is as steeper as lower the resistance represented is. If both components - Rload and the zenerdiode - are connected in parallel, there are passing two currents through them in parallel. If we want to know the overall current flowing through both components, we can find that easily, by constructing the overall characteristics, of both, by adding the vertical represented currents. fig. 109 fig. 110

The characteristic obtained by that method is shown in fig. 109. is the overall-characteristics of zenerdiode and loadresistor in parallel. fig. 109

If we return now the characteristics of the internal resistor back to our field, we can easily read from it, how much voltage will be found at different load resistors.

Homework;

By using fig. 110 find out, what the voltages at the load are, with the different loadresistance.

Find out what voltage would appear with the same voltage source and the given load resistors, without a stabilizing circuit. Plot the stabilized and the unstabilized voltage over the load currents. figure