Adjustable stabilizer 30/3-25 volts 2 amps. Scheme, description

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Adjustable stabilizer 30/3-25 volts 2 amps. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Surge Protectors

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The article describes a voltage stabilizer, in which the voltage drop across the regulating transistor is minimal and, accordingly, the power consumed by the stabilizer is reduced. Its use is especially useful for powering electronic equipment from galvanic cells and batteries.

Almost any electronic device requires a stabilized power supply. Stabilizers are easy to build on well-known KR142EN series microcircuits or discrete elements. But for the successful operation of such stabilizers, it is necessary that the voltage drop, i.e., the value by which the supplied supply voltage exceeds the stabilized one, be at least 2 ... 3 V. This leads to the problem of high power dissipation on the regulating transistor, since in In this case, he needs a "top margin" of a few volts.

The proposed stabilizer retains its properties at a voltage between the collector and emitter of the regulating transistor, equal to the saturation voltage (0,1 ... 0,5 V, depending on the load current).

Main technical characteristics maximum load current -2 A; maximum input voltage - 30 V; output voltage range - 3...25 V; stabilization factor - 150.

This is a compensation stabilizer with a regulating transistor VT1 connected in series (see diagram). A comparator is assembled on the op-amp DA2. The exemplary voltage is created by a stable current source on a field-effect transistor VT2 and a zener diode VD2 and is fed to the inverting input of the op-amp. The non-inverting input receives a voltage from the divider R3R4, proportional to the output. The op-amp compares these voltages, and the necessary control signal appears at its output, which is fed to the DA1 microcircuit, which contains four identical p-type MOSFETs. Each transistor has the same parameters as a discrete transistor of the KP304 series: open resistance - no more than 100 ohms. the slope of the characteristic is approximately 4 mA / V.

All transistors of the microcircuit are connected in parallel so that it turns out, as it were, one transistor operating as a source follower. This is done to increase the allowable source current of such a transistor, which can reach 80 mA. The slope also increases to 16 mA/V. The "composite" MOSFET, having a low channel resistance, effectively controls the regulating transistor VT1. It can be seen that the potential of the emitter VT1 will always be higher than the potential of the base, this ensures the operation of the stabilizer even at a very low voltage between the emitter and the collector (saturation voltage).

Resistor R1 limits the maximum current of the transistors of the DA1 chip, its value should not exceed 80 mA. Resistor R2 and diode VD1 are needed to start the stabilizer when the power is turned on. Then these elements practically do not affect the operation of the device. Variable resistor R3 set the required output voltage. Its lower limit is equal to the stabilization voltage of the VD2 zener diode (for KS133A it is approximately equal to 3,3 V), and the upper limit can be determined by the formula U = 3,3 • R3 / R4.

With an input voltage of not more than 25 V, the K547KP1B microcircuit can be used in the stabilizer, and less than 15 V - K547KP1V. Transistor VT1 - any pnp structure with a permissible collector current of more than 3 A and a permissible collector-emitter voltage of at least 35 V, for example, KT816B-KT816G, KT818B-KT818G. In place of VT2, transistors of the KPZOZ or KP307 series are applicable. Instead of OU K140UD1208, K140UD6 or K140UD7 will do; in this case, exclude the resistor R5. Diode VD1 - any low-power silicon.

A stabilizer assembled from serviceable parts and without errors does not need to be adjusted.

(click to enlarge)

Author: A. Zavrichko, Novoshakhtinsk, Rostov Region; Publication: cxem.net

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