Many motorists use in the car with various equipment supply voltage 3...9 V. the voltage is not less than 12 V. It would seem that it may be easier to assemble the stabilizer on the chip, for example, CAN. But if such chips or other integrated stabilizers in your disposal not? In this case, use a transistor counterparts powerful Zener, which collect simple parametric stabilizer.
Offer one of the variants of such devices. Its main technical features: maximum load current of 250 mA minimum output the voltage is 3 V, the maximum output voltage of 9.5 V.
Transistor VT1, HL1 led and resistors R1, R2 collected current stabilizer for the source of the reference voltage VD1 (see diagram). Part of the exemplary voltage with a resistive divider R3R4R6 served on a composite transistor VT2VT3, operating as an emitter follower. Output voltage adjust variable resistor R6.
The device is equipped with fixed resistors MLT (except R5). AC resistor - any. Ballast resistor R5 - wire (PE, sew, etc.). It resistance and power calculated by the formulas:
RB=(Uвх min-Uвых max)/IR max;
P=(Uвх max-Uвых min)2/RB,
where Uвх max, Uвх min, respectively, maximum and minimum input voltage; Uвых max, Uвых min - maximum and minimum output voltages; I n max is the maximum load current.
Capacitor - any oxide for a rated voltage not less than specified. The transistor VT3 is chosen from the series CT, KT; it should be installed on a small heat sink, including the wall of the metal casing the stabilizer. The Zener diode VD1 - at any voltage 8...9 V.
Author: V. Sevastyanov, Voronezh