Voltage regulator on a CMOS chip. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Voltage regulator on a CMOS chip. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Surge Protectors

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Power sources in which power elements operate in a key mode are more complicated than lithium sources with elements operating in an active mode, but their efficiency is twice or even three times higher than the efficiency of the latter. The efficiency of switching voltage regulators is high, since transistors in the closed and saturated states dissipate little power. In addition, the output does not require filters with large values of inductance and capacitance, since the ripple frequency is high (25...50 kHz). A switching voltage regulator with a constant switching frequency of the key element, but with a variable duration of its open state (PWM), is simpler than other types of stabilizers, and allows the use of low-frequency transistors.

The proposed switching voltage regulator with PWM (Fig. 1) contains a pulse-width modulator made on a K176LP1 CMOS chip [1]. This is a multi-purpose chip containing a set of CMOS transistors (three p- and three n-channel). Inverters DD1.1 and DD1.2. each of which is formed by two transistors placed in the K176LP1 chip, together with a resistor R4 and a capacitor C3 form a multivibrator. The other two transistors of the K176LP1 chip (n-channel and p-channel) are connected in parallel to the output of the inverter DD1 1 and resistor R4.

(click to enlarge)

At a high level at the output of DD1.1, the diode VD2 is open, and, neglecting its resistance, we can assume that the p-channel of the transistor is connected in parallel with the resistor R4, and the channel resistance decreases with decreasing control voltage. Similarly, the n-channel is connected in parallel with the resistor R4 at a low level at the output of the inverter DD1.1 and open VD3 (the resistance of this channel decreases with increasing control voltage). Since, at any value of the control voltage, the output resistance of one field-effect transistor increases and the other decreases, the average value of the resistance shunting resistor R4 over the period is constant, and the generator oscillation frequency is also constant, i.e. only the duty cycle changes (from 1 to 99% of the period of the operating frequency), and it is directly proportional to the amplitude of the control voltage.

A sequence of pulses modulated in duration is fed from the output of the pulse-width modulator to the base of the transistor VT2, which unlocks and locks the key transistor VT4. Diode VD4 provides a closed circuit for the current of the inductor L2 when the transistor VT4 is turned off.

The stabilizer, by changing the duty cycle of the output pulses, allows a change in the output voltage over a wide range. However, since the output voltage has a double noise level, filters are included at its input and output (chokes L1 and L3, capacitors C1, C4, C5).

The voltage stabilizer works as follows. Part of the output voltage taken from the potentiometer R8 controls the duty cycle of the pulses generated by the pulse-width modulator, i.e. the ratio between the durations of the open and closed states of the key transistor VT4. When the voltage at the output of the stabilizer decreases, the control voltage taken from R8 decreases. as a result, the key transistor VT4 is open longer, and the powerful diode VC4 is closed, and vice versa, with an increase in the output voltage, the key transistor VT4 is closed longer, and the powerful diode VD4 is open. As soon as the key transistor VT4 closes, the VD4 diode immediately opens. and the energy stored in the inductor L2 is given to the load. The output voltage is set by potentiometer R8. The stabilizer is placed on a 52x52 mm printed circuit board made of double-sided fiberglass. The drawing of the board is shown in fig. 2.

CMOS Voltage Regulator

In the stabilizer, instead of the KT908A transistor, you can use other powerful high-frequency transistors, for example, KT903A. or powerful low-frequency ones - KT803, KT805, KT808 At high load currents, the key transistor VT4 must be installed on a radiator to eliminate its overheating. As a VD4 diode, you can use a KD212 diode or a collector junction of a powerful high-frequency transistor. Inductors L1 and L3 are wound on pieces of a ferrite (600MN) rod 20 mm long and 8 mm in diameter. They contain 10 turns of wire PEV-2 01,2 mm. The inductor L2 is made on an armored ferrite (B26) core 2000MN with a gap between the cups of 0,2 mm. The L2 windings of the inductor are made of three PEV-2 00,2 mm wires twisted with a drill. The winding goes until the armor core is filled.

Literature

M.E. Anglin. C-MOS 1C forms pulsewkrth modulator. - Electronics, 1977. vol 50. No. 13, P126.
Seleznev V. Voltage stabilizer on the comparator. - Radio. No. 3. pp. 46-47.

Authors: V.Kalashnik, M.Eremin, R.Panov, Voronezh.

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