AC voltage regulator option. Scheme, description

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AC voltage regulator option. 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 Mustek Power Mate 625 AC voltage stabilizer failed. In the process of searching for the cause of the malfunction, it turned out that the circuit of the device is in many respects similar to the circuit of the electronic relay regulator described by G. Gadzhiev in [1]. After reviewing other publications in the Radio magazine, it was decided not to repair the failed device, in which electromagnetic relays were used to switch the autotransformer windings, but to try to make a stabilizer based on electronic switches [2-5]. The device described in [5] was taken as a basis.

Due to the lack of a power autotransformer with the same number of taps as the one used by the author in this device (the outputs I have are much smaller), the circuit had to be slightly changed (Fig. 1). Instead of the encoder on the elements of the K561LP2 microcircuit, an imported encoder CD4532B [6] was used, paired with a decoder of the same CD4028B series (analogous to K561ID1). From additional stabilization of the exemplary voltage with the help of a parametric stabilizer (in the prototype - R4VD3) he refused - the integrated voltage regulator DA1 (from the 7812 series) maintains the output voltage within quite acceptable limits.

For a more complete use of the change in the amplitude U_x (without scaling losses) a VD1 zener diode is used. A threshold device has been added on the zener diode VD2 and transistors VT1, VT2, which turns off the stabilizer from the network when the permissible voltage value is exceeded. To simplify the adjustment, the dividers at the inputs of the comparators, made up of constant resistors that require selection, are replaced by multi-turn tuning resistors R7-R10. Triac switches are supplemented with so-called snubbers (shunting triacs with serial RC circuits), which prevent erroneous switching on of triacs, which can occur from mains interference. Otherwise, the scheme does not differ from that described in [5].

Rice. 1. Diagram of the device (click to enlarge)

The T2 step-down transformer I used has a mains winding with two taps and two secondary ones (44 and 48 V) with taps from the middle. Four control channels are left in the stabilizer (this is quite enough for the city). Prior to final assembly, the characteristics of the autotransformer were measured with a load of 500 W in the network or load switching options. The step-down windings were connected in accordance with the network according to the autotransformer circuit. In the first version of the stabilizer, the load was switched without the use of damping circuits. The stabilizer worked, but failed (the operation of this option with snubber circuits was not tested). In the working version, the switching of windings with a constant connection of the load is selected. Due to its inductive nature, a damping circuit (R27C7-R30C10) is used in each channel.

In accordance with the technical characteristics of the CD4028B microcircuit, the maximum output current of one channel is 10 mA, in connection with which MOS3063 optotriacs are used with a turn-on drain of not more than 5 mA.

To power the device and receive the control voltage U_x a separate transformer T1 with built-in thermal fuse RH01-83 (250 V, 2 A, 83 ^оC), indicated on the diagram as FU2. FU1 is a fuse in the primary circuit of this transformer, FU3 is a resettable fuse of a failed stabilizer.

The types of zener diodes VD1 and VD2 depend on the parameters of the transformer T1 (primarily on its transformation ratio). At the maximum "working" mains voltage (in this case, 250 V), the voltage across the tuning resistor R11 relative to the common wire should be about 12 V (microcircuit supply voltage), and at the minimum, the VD1 zener diode should not exit stabilization mode. In the author's device, with a mains voltage of 250 V, the voltage at the output of the VD3 rectifier rises to 32 V, and at 170 V it drops to 24 V, therefore, a KS1V zener diode is used as VD520 (stabilization voltage - 19 ... 21 V). To operate the protection at a voltage of 260 V, a zener diode KS210Zh was selected (stabilization voltage - 9 ... 11 V).

The details of the device are mounted on three printed circuit boards made of foil fiberglass. Fixed resistors - any small-sized, tuning - multi-turn wire (for example, SP5-2), capacitor C2 - KM, C7-C10 - K73-17, the rest - imported oxide. We will replace the BC547C transistor with any of the KT3102 series, and the BC557C - from the KT3107 series. To switch the windings of the T2 transformer, it is desirable to use triacs of the BTA41 series, since all their outputs are isolated from the mounting flange, and this allows them to be installed without insulation on a common heat sink, which is necessary when the load power is more than 300 ... 500 W. Together with transformers T1, T2, the boards are placed in the case of the failed Mustek Power Mate 625 stabilizer (Fig. 2).

AC Voltage Regulator Option
Rice. 2. Stabilizer Mustek Power Mate 625

The assembled stabilizer maintains the voltage on the supplied load within the permissible deviation from the nominal value (± 10%) when the mains voltage changes from 180 to 250 V. The approximate value of the mains voltage is indicated by one of the HL3-HL6 LEDs. If the voltage deviates beyond the specified limits, the load is turned off, and one of the LEDs HL1, HL2 lights up on the front panel of the device, showing in which direction the voltage has changed (it is large or small, respectively).

If the transformer allows, the number of control channels can be increased (by increasing the number of comparators and triac cells accordingly). The operation and configuration of the device basically do not differ from those described in the article [5].

Literature

Gadzhiev G. Electronic-relay voltage regulator. - Radio, 2009, No. 10, p. 23.
Godin A. Variable voltage stabilizer. - Radio, 2005, No. 8, p. 33-36.
Ozolin M. Improved control unit of the AC voltage stabilizer. - Radio, 2006, No. 7, p. 34, 35.
Gadzhiev G. Powerful load optosimistor switch. - Radio, 2010, No. 10, p. 33.
Gadzhiev G. AC voltage stabilizer. - Radio, 2013, No. 2, p. 20,21.
CMOS 8-Bit Priority Encoder. - URL: ti.com/product/CD4532B/technicaldocuments.

Author: E. Aksenov

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