Voltage stabilizer 40/3-30 volts 2 amps with double protection. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Voltage stabilizer 40/3-30 volts 2 amps with double protection. 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 proposed stabilizer has separate protection against overcurrent and short circuit. In the event of a short circuit at the output of the stabilizer, the protection unit on VT3 is triggered (Fig. 1). In case of overcurrent, protection is activated on VS1 and K1.

Rice. 1. Voltage regulator circuit (click to enlarge)

The electronic protection unit is triggered when the load current creates a voltage drop across the resistor R6 sufficient to open the thyristor VS1, i.e. when the voltage difference between the control electrode and the thyristor cathode reaches approximately 1 V. The resulting negative voltage pulse through the diode VD3 enters the base of the transistor VT3 and practically closes it, and therefore the regulating transistor VT1. At the same time, the VD3 diode protects the VT3 transistor from getting a positive voltage from the anode circuit of the thyristor to its base.

However, the electronic protection system still does not completely protect the transistor VT1 from thermal breakdown by residual current, especially if the transistor has already been heated during operation, or the SB1 button has not been pressed for a long time.

To prevent thermal breakdown of the transistor VT1, an electromagnetic protection system is used, which operates a few milliseconds (depending on the relay K1 used) after the thyristor VS1 opens. Then relay K1 is activated. Its contacts K1.1 close the VT3 base to the negative conductor of the power source, and the contacts K1.2 turn on the HL2 LED - a protection action indicator. After eliminating the cause of the overload, it is enough to briefly press the SB1 button to restore the previous mode of operation of the power supply without disconnecting the device from the network.

A constant voltage of 40 V is supplied to the input of the stabilizer from the rectifier. The output stabilized voltage from 3 V to 30 V is set by resistor R2. The maximum load current is 2 A. The load current is controlled by the PA1 head by switching SA1.

The stabilizer parts are mounted on a board made of foil fiberglass (Fig. 2 and 3) and on the front panel of the power supply housing. Regulating transistor VT1 is installed on the heat sink. The KT825A transistor can be replaced with KT825B, G; QT818V, G, VM, GM; KT814G - on KT814V, B; KT816B, V, G; KT315V - on KT315G, D, E.

Voltage stabilizer 40/3-30 volts 2 amps with double protection. PCB - side of printed conductors
Rice. 2. PCB - side of printed conductors

Voltage stabilizer 40/3-30 volts 2 amps with double protection. PCB - mounting side
Rice. 3. PCB - mounting side

Thyristor KU202K is replaced by KU201V...KU201L, KU202V...KU202N. Instead of the D220A (VD2) diode, D219, D220, D223, KD102, KD103 with any letter indices are suitable, and instead of the KD105B (VD3, VD4, VD5) diode, KD106A or any other silicon one with a forward current of up to 300 mA and a reverse voltage of at least 50 IN.

Variable resistor R2 - any type with characteristic A. Relay K1 - RES48A (passport RS4.590.206) or another with two groups of switching contacts, triggered at a voltage of not more than 30 V.

Resistor R6 is made in the form of several turns of constantan, nichrome or manganin wire wound around the housing of the MLT-1 resistor. Its resistance is determined by the value of the operating current, which, in turn, depends on the voltage at the control electrode of the thyristor, at which it opens. So, for example, if 2 A is taken as the maximum protection trip current, and the thyristor opens at a voltage on the control electrode of about 1 V, the resistance of the resistor R6 should be (according to Ohm's law) close to 0,5 Ohm. It is possible to use resistors of the C5-16 type of appropriate power.

More precisely, the resistance of the resistor is adjusted to the selected protection trip limit in this order. An ammeter and a wire-wound variable resistor with a resistance of 25 ... 30 ohms connected in series are connected to the output of the stabilizer. The corresponding voltage from the rectifier is supplied to the input of the stabilizer, and a voltage of 2 ... 10 V is set at the output with resistor R15. Then, with a variable resistor that acts as a load equivalent, a current equal to 2 A is set on the ammeter, and by selecting the resistance of resistor R6, the protection system is activated .

In amateur radio practice, there are often circumstances when, from overload with currents of a lower value, for example, 50 or 100 mA, it is necessary to protect not only the voltage regulator itself, but also the device powered by it. In this case, it is desirable to have a stepped protection system, made, for example, according to the scheme shown in Fig. 4. Here, the resistor R6.1 of the first stage, designed for a minimum protection current of 50 mA, is permanently connected to the stabilizer, and resistors R2 ... R6.2 of four other stages are connected in parallel with the SA6.5 switch: 100 mA, 500 mA, 1 A and 2 A.

Voltage stabilizer 40/3-30 volts 2 amps with double protection. Stepped protection system
Rice. 4. Step protection system

The resistors indicated on the diagram are approximate. More precisely, they can be calculated only by knowing the opening voltage of the thyristor operating in the stabilizer. This voltage can be measured as follows. Set the engine of the variable resistor R2 to the lowest (according to the diagram) position and connect the control electrode of the thyristor to it, unsoldering it from the right (according to the diagram) output of the resistor R6.1. Then turn on the power and slowly increase the voltage at the control electrode of the thyristor with resistor R2. At the moment the thyristor opens, as indicated by the LED, measure this voltage with a voltmeter.

Resistors R6.2...R6.5 are mounted directly on the contacts of switch SA2. Resistors RS1 and R12 are selected specifically for the existing measuring device.

Literature

O. Lukyanchikov. Voltage stabilizer with double short circuit protection in the load. - Radio, 1986, N9, p.56.
A. Bizer. Protective devices for power supplies. - Radio, 1977, N2, p.47.
Y. Timlin. Dual bipolar power supply. - To help the radio amateur, vol. 71. - M.: DOSAAF, 1980
V.Borisov. Stabilized power supply. - Radio, 1979, N6, S.54.

Author: Yu.Kurbakov, Tula; Publication: cxem.net

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