A parametric stabilizer is the simplest version of a constant voltage stabilization circuit. It contains a small amount of parts and does not require any additional settings after the circuit is assembled. Allows replacement of circuit elements with numerous analogs, which simplifies assembly.
The main stabilization element is Zener diode (VD1) from ballast resistor (Rb), which limits the current through it to an acceptable level. The transistor, connected according to the emitter-follower scheme, acts as a "power-up" to increase the maximum current in the load. This is the main, basic part of the circuit of any parametric stabilizer (Fig. 1)
The input voltage must be greater than the output at least 3 volts - this is the voltage drop across the "emitter-collector" junction of the transistor. This voltage difference can be more than 3 volts, but should not be too large, as this will lead to excessive heating of the transistor even with a small value of the current in the load. The value of the output voltage, therefore, is set precisely by the zener diode, taking into account the voltage drop across the transistor.
The type of transistor is selected depending on the required maximum current in the load. For small currents (about 50... 200 mA), transistors of the type KT315, KT503 or similar imported ones. For currents of greater value, it is necessary, accordingly, to choose more powerful transistors, for example - KT815, KT819, KT829. In some cases (at currents over 1A) this transistor should be installed on a heat sink. A complete practical diagram of a power supply with a parametric regulator is shown in Fig. 2.
The table below shows the cell ratings for different values of the required output voltage. Zener diodes can be replaced with others with the required stabilization voltage.
The rectifier is assembled, as a rule, in a full-wave circuit, since this provides a greater efficiency of the entire circuit. Filtering capacitor C1 smoothes DC voltage ripple after the rectifier. Its capacity is better to choose large values. Capacitor C2, connected in parallel with the Zener diode, provides an additional reduction in the level of ripple.
It may have a small capacity value (10... 50 μF). At the output of the circuit, a smoothing capacitor with a capacity of 10... 50 μF. The more current the load will consume, the higher the capacities of all electrolytic capacitors must be.
Resistor R2 plays the role of a low-power load and, in principle, is not required in the circuit. But it should be noted that without this resistor, the voltage at the output of the stabilizer circuit will not correspond to the true voltage in the absence of a load.
Fuse FU is selected based on the maximum current in the load.
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