Laboratory switching power supply on the L4960 chip, 220 / 5-40 volts 2,5 amperes. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power Supplies

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The proposed compact power supply unit (PSU) is assembled on an L4960 integrated circuit from SGS-Thomson Microelectronics, which is an adjustable switching DC voltage regulator that provides an output current of up to 2,5 A at an output voltage of 5 ... 40 V. The microcircuit has built-in protection against overtemperature, overcurrent and short circuit in the load circuit. This unit is designed to power various electronic devices that consume power up to 25 watts.

The schematic diagram of the device is shown in fig. 1. The mains voltage 220 V through the fuse FU1, the contacts of the switch SA1 and the noise suppression filter C4L1L2C5 is supplied to the primary winding of the step-down transformer T1. The SA1 switch has a built-in indicator - a gas discharge lamp. Resistor R1 extends the life of the switch lamp and reduces its heating.

(click to enlarge)

The voltage of the secondary winding of the transformer through a self-healing fuse FU2 is supplied to the Schottky bridge rectifier VD4-VD7. The use of such diodes reduces the power loss on the rectifier and, accordingly, the heating of its elements, and also increases the rectified voltage on the filter capacitor C1 by approximately 3 V. Resettable fuse FU2 protects the transformer from overload in case of faults in the rectifier, DA1 chip, as well as in case of "errors" of its protection system.

The overload protection system of some integrated switching regulators, for example, LM2575T, LM2576T, may fail if a powerful stable current generator or other switching regulator of comparable power is connected as a load. Varistor RU1 protects the mains transformer and rectifier diodes from impulse noise and mains voltage surges. The output voltage is regulated by a variable resistor R5 in the range from 5 to 18 V. The upper position of the variable resistor slider according to the diagram corresponds to the minimum output voltage.

The operating frequency of the DA1 chip is about 95 kHz. The voltage shape at the output of the microcircuit (pin 7) is rectangular, the duty cycle of the pulses depends on the output, input voltages and load current. Resistor R6 and diode VD1 protect the microcircuit from damage, for example, when the variable resistor R5 is turned sharply or a charged high-capacity capacitor is connected to the PSU output. When the stabilizer output is overloaded, the protection built into the microcircuit turns off the output voltage and tries to start again after about 0,5 s.

Choke L3 - storage. The two-link filter C9-C12L4C17-C19L5C20-C22 reduces the ripple of the output stabilized voltage. The oxide capacitor C9, due to high-current high-frequency ripples, has an increased risk of degradation, therefore it is shunted with ceramic capacitors C10-C12. A similar solution applies to the oxide capacitor C3.

Relay K1 turns on the power of the HL3 LED at a load current of more than 1 A. This allows you to quickly track the increased power consumption, for example, UMZCH in silent mode. The release current of the relay contacts is about 0,6 A. The relay coil K1 is also part of the filter.

A voltmeter is made on the PA1 microammeter, VD8 zener diode and resistors R10, R11, which measures the output voltage of the power supply. Zener diode VD8 and resistor R11 provide "stretching" of the scale of the device RA1.

When the contacts of the switch SA2 are closed, the protection of the load and the stabilizer is provided by the built-in nodes of the DA1 chip, and in case of its malfunction, by the self-resetting fuse FU2. Resettable fuse FU3 for a current of 0,75 A is designed to protect low-power load nodes. The SA3 switch allows you to quickly disconnect the load from the PSU and thereby reduce the chance of damaging the powered equipment.

LEDs HL1, HL2 illuminate the scale of the device PA1. LED HL4 indicates the presence of voltage at the output of the stabilizer DA1, and HL5 - the presence of voltage at the load.

The power supply is mounted in a metal case measuring 178x160x49 mm from an old imported car radio. The case is preliminarily painted with black automotive varnish BT-577 and dried, first for 12 hours at room temperature, then twice for 40 minutes at 180°C and another 12 hours at room temperature. This mode prevents the appearance of bubbles on the surface. Drying the painted body only at room temperature can take up to six months. Before painting, 100 ... 200 ventilation holes with a diameter of 3 mm are drilled in the lower and side walls of the case.

Most of the design details are placed on two boards, fig. 2 and fig. 3. Mounting is carried out by hinged method. High-current connections are made with a copper mounting wire with a diameter of at least 1 mm. Pin 4 of the microcircuit, diodes VD2, VD3, capacitor C9 must be connected to the common wire with separate conductors. You need to connect the metal case of the device and the common wire at a point. indicated on the diagram with a grounding symbol (see Fig. 1). Proper wiring of power and signal circuits is extremely important for the perfect operation of the PSU.

Transformer T1 - TP-30-2 from a portable black-and-white TV "Youth". With such a transformer, at a mains voltage of 220 V, the power supply provides an output voltage of 12 V at a load current of 2 ... 5 A. At a higher voltage, the maximum output current decreases linearly to 0,5 A at an output voltage of 18 V. To increase the output current to 2,5 A at a voltage of 18 V, a transformer with an overall power of at least 60 W and an open-circuit voltage on the secondary winding of 22 ... 27 V should be used. But such a transformer may not fit in the case of the indicated dimensions

The L4960 chip is mounted on a ribbed duralumin heat sink with a total cooling area of ​​100 cm2 (one side), isolated from the case.

The inductor L3 is wound on a K32x20x6 ring magnetic circuit made of 3000NM ferrite. The winding contains 30 turns of a home-made litz wire, made up of 33 pieces of wire PEV-2 0,13. Before winding in the magnetic circuit, it is necessary to make a non-magnetic gap, for which the ring is broken in a vice into two parts and glued with instant superglue. After that, the ring is successively dried for 2 hours at room temperature and 6 hours at a temperature of 60°C. Then the ring is overcast with varnished cloth and the winding is wound in two layers. Between the layers you need to lay one layer of varnished cloth. If the power supply is designed for increased output power (18 V, 2,5 A), then either two such rings glued together or a larger magnetic circuit must be used. A non-magnetic gap is required. The throttle is installed in a rectangular hole on the circuit board and fixed with silicone sealant. It is permissible to use any similar choke with an inductance of 150,3 ... 50 μH. The rest of the chokes are industrial. L1, L2 - LCHK-007, L4, L5 - NSNK-007 on H-shaped ferrite magnetic cores, designed for a current of at least 3 A, with a winding resistance of not more than 30 mOhm.

Role K1 is self-made, 23 turns of PEV-2 0,51 wire are wound on a reed switch bottle. КЭМ-2 Switch SA1 - IRS-101-1 A3 or IRS-101-12С with built-in glow discharge lamp. Switch SA3 - push-button for a current of at least 3 A, for example, KDC-A04T, SDDF-3 Similar domestic switches. PKN41-1-2 have a significantly shorter service life and a tighter return spring.

LEDs HL1, HL2 - RL50-WH744D white glow (8000 mCd), they can be replaced by any with increased light output. A translucent matte light-diffusing film is installed in front of their lenses. LEDs HL3 - RL30-RD314S red, HU - RL30-YG414S green, HL5 -RL30-HY214S yellow glow colors can be replaced with similar ones, for example, from the KIPD66 series.

Diodes SR306 can be replaced by SR360, MBR360, 31DQ06 Instead of the UF4004 diode, any of the 1N400x, UF400x, KD247, KD243, KD209 series will do. Replace BZV55C-3V6 zener diode with 1N4729A, TZMC3V6, G2S3.6.

Variable resistor R5 is an imported small-sized one with a linear characteristic of the dependence of resistance on the angle of rotation. The body of the variable resistor is connected to a common (negative) wire, but must be isolated from the body of the structure. The signal wire coming from the variable resistor R6 must be shielded. The rest of the resistors are any type of general purpose appropriate power. Varistor RU1 - MYG10-471 can be replaced with a similar disk FNR-10K471. FNR-14K471 TNR10G471. Capacitors C1, C2 - ceramic for a rated voltage of at least 50 V. Capacitors C10-C12, C17, C21, C22 - ceramic for a rated voltage of at least 25 V. Capacitors C13-C16 - ceramic or film for a rated voltage of at least 50 V. Capacitors C6, C7 - film. Oxide capacitors - imported analogues of K50-68. Capacitors C4, C5 - imported ceramic for a rated voltage of at least 400 V AC or 630 V DC. The safety of the PSU operation largely depends on the quality of these capacitors. Capacitors K15-5 can be used for an operating voltage of at least 1600 V

Microammeter RA1 - M68501, from a domestic tape recorder. A variant of the scale of the device with dimensions of 40x20 mm is shown in fig. 4.

The scale is drawn in the easy-to-learn Nero Cover Designer program, a graphical vector editor from the Ahead Nero software package version 8. The scale is calibrated in the working position of the device.

A view of the layout of nodes in the PSU case is shown in fig. 5.

Accurately made from serviceable parts, the power supply starts working immediately and requires almost no adjustment. If necessary, by selecting the resistor R2, set the upper limit of the output voltage and by selecting the resistor R10 - the required sensitivity of the voltmeter.

A small level of electromagnetic radiation from the power supply unit and voltage ripples at its output allowed the author to put on this power supply unit a self-made pocket double-circuit powered by it. VHF radio receiver, assembled in the first half of the 90s on the K174XA34 chip. Radio reception is carried out in a reinforced concrete house on a built-in telescopic antenna without any interference and squeaks from a distance of 30 km from the radio tower.

Author: A. Butov, p. Kurba, Yaroslavl region

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