Switching step-down stabilizer, 35-46 / 5,1-30 volts 4 amps. Scheme, description

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Switching step-down stabilizer, 35-46 / 5,1-30 volts 4 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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Your attention is invited to a laboratory power supply, developed on the basis of the KR1155EU2 microcircuit.

The scheme of the device is shown in fig. 4.63. It differs little from the standard switching circuit, and the positional designations of the elements are the same. This circuit implements a control method with a fixed pulse repetition period, i.e. pulse-width control. Capacitor C1 - input filter. It has a larger capacitance than indicated in the typical switching circuit, which is due to the relatively large current consumption.

Switching step-down stabilizer, 35-46 / 5,1-30 volts 4 amps

Main technical characteristics:

input unstabilized voltage, V.....35...46;
regulation interval of the output stabilized voltage, V.....5,1...30;
maximum load current, A ..... 4;
range (double amplitude) of output voltage ripples at maximum load, mV.....30;
control interval for current protection operation, A.....1...4.

Resistors R1 and R2 control the current protection level. Their maximum total resistance corresponds to the maximum protection operation current, and the minimum resistance corresponds to the minimum current. With the help of capacitor C4, the stabilizer is smoothly started. In addition, its capacitance determines the restart period when the current protection threshold is exceeded.

Resistor R5 and capacitors C5, C6 are elements of frequency compensation of the internal error amplifier. Capacitor C3 and resistor R3 determine the carrier frequency of the pulse-width converter. Capacitor C2 sets the time between a sharp decrease in the output voltage (caused by external causes, for example, a short-term output overload) and the transition of the RESO signal (pin 14 DA1) to a state corresponding to normal operation, when the transistor connected between the RESO and GND pins inside the microcircuit closes .

Resistor R6 provides an open collector load for this transistor. If you plan to use the RESO signal with its binding to a voltage different from the output voltage of the stabilizer, then the resistor R6 is not installed, and the open collector load is connected inside the RESO signal receiver. Resistor R4 provides zero potential at the input IN HI (pin 6 DAI), which corresponds to the normal operation of the microcircuit. The stabilizer can be turned off by an external high TTL level signal by applying it to this pin.

The use of the KD636AS diode (its total allowable current significantly exceeds that required in this stabilizer) allows you to increase the efficiency by 3 ... 5% with a slight increase in the cost of the device. This leads to a decrease in the temperature of the heat sink and, consequently, to a decrease in its dimensions and weight.

Resistors R7 and R8 are used to regulate the output voltage. When the slider of the resistor R7 is in the lower position according to the diagram, the output voltage is minimal and equal to the reference voltage of the DA1 chip, respectively, when in the upper position the output voltage is maximum. The trinistor VS1 opens with a CBO signal (pin 15 DA1) if the voltage at the CBI input (pin 1 DA1) exceeds the internal reference voltage of the DA1 chip by approximately 20%. This is how the load is protected from overvoltage at the output.

All oxide capacitors K50-35, except C1 - K50-53. Capacitor C6 - ceramic K10-176, the rest are film (K73-9, K73-17, etc.). All fixed resistors are C2-23. Variable resistors R2 and R7 are SDR ~ 4a with a power of 0,25 W. They are mounted on the board using brackets. Choke L1 is wound on two folded annular K20x12x6,5 magnetic cores made of permalloy MP 140. The winding contains 42 turns of PETV-2-1,12 wire wound in two layers: the first - 27-28 turns, the second layer - all the rest.

The stabilizer is assembled on a board made of one-sided foil fiberglass. The board drawing is shown in fig. 4.64.

Switching step-down stabilizer, 35-46 / 5,1-30 volts 4 amps

The microcircuit, diode and trinistor are fixed on the same heat sink. In this case, the microcircuit in most cases can not be isolated from the heat sink surface, since its flange is connected to pin 8 (GND). Diode and trinistor must be isolated from the radiator. Pay special attention to the mains transformer and rectifier. The transformer is designed for an output power of at least 150 W and an open-circuit output voltage of approximately 33 V.

At maximum load, it is permissible to reduce the output voltage by no more than 1,5 V relative to the open circuit voltage. The rectifier is selected for a current of 3 ... 3,5 A with a total voltage drop across its diodes of not more than 2 V. The rectifier (in the case of a monolithic version) or individual diodes can be mounted on the same heat sink as the stabilizer.

Author: Semyan A.P.

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