In many modern stabilizers to improve their quality indicators used operational amplifiers, having a large coefficient gain and stable characteristics. However, a relatively simple modification the traditional scheme of transistor stabilizer allows to improve considerably its specifications and to avoid some of the difficulties encountered the design of the stabilizers with the use of the shelter (especially in devices with regulation of the output voltage within a wide range). High ratio stabilization of the described power supply unit (Fig. 3.4) due to the application of amplifier with dynamic load.
The reference voltage source is assembled on a field-effect transistor, which gives the opportunity to reduce the output resistance of the regulator and get deep regulation of the output voltage.
Main technical characteristics:
- The input voltage stabilizer - 30 In;
- The limits of regulation of the output voltage - 1...29 In;
- The maximum load current, 2 A;
- Coefficient of voltage - 60 dB;
- Output impedance 5...10 mω.
The voltage regulator consists of two amplifiers with dynamic load serial control. First collected on transistors V13, V12, where V13 included in the common-gate circuit, and V12 - collector: the second - in transistors V14, V15 V14 - common-emitter, and V15 - collector). The feedback signal from the engine resistor R9, is applied to the source of the transistor V3 is enhanced without inverting the phase and fed to the base of transistor V14. Transistor V13 operates in a mode close to the cutoff current. The voltage between the source and the gate is in the stabilizer of a model.
Chain R2, R3, V11 only serves for temperature compensation circuit the drain of the transistor V13 (without it when closed to ground the gate of this the transistor of the output voltage is changed to 3...5% in temperature range 20...50°C). With the collector of the transistor V14 proinvertirovanny and the amplified signal is transmitted to the base of a powerful regulatory transistor V15. The control element is powered by a parametric stabilizer the Zener diode transistor V10 and V9. To obtain a higher coefficient of use the voltage of the main rectifier V1...V4 stabilizer on the transistor V9 is powered by a voltage multiplier diodes V5 V8 and... the capacitors C1, C2. A multiplier connected to the secondary winding of the transformer T1.
Lamp H1 is used to limit the collector current through the transistor V9, V14 and the base current of the transistor VI5 during a short circuit in the load circuit, and for indicating overload. At the time of overload due to the increasing base current of the transistor VI5 there is a decrease in voltage at the input of the parametric stabilizer up to level 30 In where the stress falls almost entirely on the lamp H1 minus the voltage drop across the transistors V9, V14 and the emitter transition transistor V15. The current on this circuit does not exceed 120...130 mA, which is less than the maximum allowable for its elements.
In the stabilizer used wire variable resistor with a valid the power dissipation of 3 W (PPB-3, HTP-40). Transistor V13 need to pick up with a small value of the initial current flow, only then the lower bound of the output voltage stabilizer will be close to 1 V. the drain Current of the transistor at a voltage between the drain and the source 10 and the shutter is closed off at its source, must be in 0.5...0.7 mA. When mounting the stabilizer between the diode V11 and the transistor V13 it is necessary to ensure good thermal contact, which is enough to glue their corps. Transistor V15 is desirable to choose a large static the current transfer ratio base.
Also indicated in the diagram, you can use silicon transistors series CT, CT, CT, CT, CT, CT (V12), CT, CT (V14), transistors KT815, CT with any letter index, CTB (V9), CTA, CTA, with any CT letter index (VI5).
The stabilizer can be used germanium transistors MPA, and any from the series N, N, N, N (V12), GT, GT, P...P (V14). Instead KS527A you can apply the Zener D, DD (two in series), D, DV (three in series). Transistors V9 and V14 is desirable to set on small radiators (with a useful area of 20... 30 cm2). For the transistor VI5 need a radiator.
To facilitate the thermal regime of this transistor provides stepwise the voltage change at the input of the stabilizer switch S1, a current capacity 2 A. In position 1 at the input of the stabilizer serves 15 In and in position 2 to 30 V. When the toggle switch is in position 2 and the load resistance is close to the minimum stable voltage should not be set less than 15 V.
Mains transformer are wound on the magnetic core of the transformer TC-60. Primary the winding is left unchanged, secondary rewound; it contains 200 turns (100 turns on each coil) of PEV-2-1,16.
Sometimes occurs in the stabilizer of the high-frequency generation can be suppressed or increasing the value of capacitor C6, or switching in the transistor base circuit V15 the resistor 5...10 Ohm 1 watt. To ensure stable operation of the stabilizer installation you want to perform conductors minimum length having a large cross-section of the conductor.
Author: A. P. Seman