A simple switching regulator. Scheme, description

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A simple switching regulator. 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 switching regulator described in the article by S. Kosenko "Designing a pulsed stabilized buck converter" ("Radio", 2005, No. 9, pp. 31-33) has good parameters. However, some of them can be improved while simplifying the device.

The scheme of the proposed version of the stabilizer is shown in fig. one.

A simple switching regulator

An n-channel IRL4 with a very low (2505 mΩ) channel resistance in the open state was used as a switching transistor (VT8). It is controlled by a generator containing two inverters. The first is made on transistors VT1, VT2, the second - on the microassembly VT3, containing two relatively powerful complementary MOSFETs, providing fast switching VT4. All this made it possible to increase the efficiency of the converter and obtain a wider (6...20 vs. 12...20 V in the prototype) range of input voltages. The output voltage of the device is 5 V, the maximum load current is 4 ... 5 A (determined by the resistance of the resistor R5).

The conversion frequency (set by the elements R1, R2, C2) is about 70 kHz, the duty cycle is about 8. In the stabilization mode, the frequency and duty cycle may increase slightly. The time spent by the key transistor VT4 in the open state does not exceed 2 μs.

After the input voltage is applied, the switching transistor VT4 begins to periodically open and the supply voltage is supplied to the output through the filter C3L2C5. With an increase in the current flowing through the open transistor VT4, to a value exceeding 4 ... 5 A, the voltage drop across the resistor R5 becomes sufficient to open the phototransistor U1.1 of the optocoupler U1. As a result, VT1 and the lower (according to the scheme) transistor of the assembly VT3 open, and VT2 and the upper transistor of the assembly close. A sharp decrease in the channel resistance of the lower assembly transistor provides a quick discharge of the gate-source capacitance VT4 and, as a result, its forced closing. When the transistor VT4 is open, the current flows through its drain-source section, and when the current is closed, caused by the EMF of the inductor, it flows through the diode VD3.

If for any reason the voltage at the load exceeds 5 V, the voltage drop across the resistor R7 will become more than 2,5 V, which, in turn, will lead to a sharp increase in the current passing through the integrated regulator DA1 and the LED of the optocoupler U1.2. As a result, the phototransistor of the U 1.1 optocoupler will be irradiated and the resistance of its emitter-collector section will decrease, causing, as in the case discussed above, a rapid closing of the switching transistor VT4 and a decrease in the output voltage of the stabilizer. Reducing the output voltage (relative to the set level) will resume the operation of the generator and it will be restored to its previous value.

The device is assembled on a printed circuit board made of one-sided foil fiberglass, the drawing of which is shown in Fig. 2.

A simple switching regulator

All resistors - MLT, capacitors - KM (C2, C4) and small-sized oxide firms Jamicon (the rest). The VT3 microassembly is mounted on the side of the printed conductors. The heat sink for the VT4 transistor and the VD3 diode is a 30x30 mm plate made of a 2,5 mm thick aluminum alloy sheet. Inductors L1 and L2, when self-made, can be wound on permalloy (MP140 grade) rings of sizes K19x11x4,8 and K10x6x4,5, respectively. The winding of the inductor L1 should contain 18 turns of the bundle of five pieces of wire PEV-2 0,5, and the inductor L2 - 7 turns of the bundle of four pieces of the same wire.

If the parts are in good condition and there are no errors in the installation, the device does not require adjustment and starts working immediately after turning on the power.

Author: M. Ozolin, Krasny Yar village, Tomsk region.

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