Relay voltage stabilizer. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Surge Protectors

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Often, to power, for example, TVs, especially in rural areas, you need a stabilizer that provides the rated output voltage with a deep decrease in the voltage in the network. In addition, for powering many types of consumer electronic equipment, a stabilizer is preferable that does not introduce distortions of the sinusoidal form of the output voltage. The stabilizer has four stages of output voltage regulation. This made it possible to significantly expand the stabilization zone - 160.250 V. At the same time, the output voltage remains within the limits for the supply voltage of television color image receivers.

The stabilizer circuit is shown in fig. 9.4.

The electronic unit of the device includes two switches on transistors VT1 and VT2, switching relays K1 and K2 and three threshold devices, each of which is a voltage divider of resistors and a zener diode. The first threshold device is R2, VD3, R3, the second is VD5, R4, R6, the third is R5, VD6, R6. The control unit is powered by a rectifier on diodes VD1 and VD2 with a filter capacitor C2. Capacitors C3 and C4 eliminate short-term changes (emissions) of the mains voltage. Resistor R1 and capacitor C1 - "spark arresting" circuit. Diodes VD4 and VD7 protect the transistors from the self-induction voltage of the relay windings, which occurs when the transistor switch is closed.

In the case of ideal operation of the threshold devices and the transformer, each of the four stages of regulation would provide a voltage range of 198 ... and changing the transfer coefficient of the transformer when changing its load mode. Therefore, for all three threshold devices, the output voltage intervals are selected narrowed - according to the output voltage of 231 ± 140 V (in the ideal case, 260 ± 215 V), because of this, the interval for changing the mains voltage is narrowed to 10 ... 215 V ( Fig. 15).

With a mains voltage of less than 185 V, the voltage from the rectifier on diodes VD1 and VD2 is not enough to open at least one threshold device - all three zener diodes are closed, and the position of the relay contacts corresponds to that shown in the diagram. With an input mains voltage of 160 V, the output voltage will be 198 V. The voltage at the load is equal to the mains voltage plus the voltage boost taken from the windings II and III of the T1 transformer. In the mains voltage range of 185 ... 205 V, the zener diode VD5 is open. In this case, the second threshold device comes into operation. The current flows through the relay winding K1, the zener diode VD5 and resistors R4 and R6. This current is insufficient to operate relay K1.

The voltage drop across the resistor R6 opens the transistor VT2 As a result, relay K2 is activated and contacts K2.1 switches the transformer windings so that now only winding II serves as a source of voltage boost. With a mains voltage in the range of 205 ... 225 V, the VD3 zener diode opens, that is, the current flows through the first threshold device. The transistor VT1 opens, as a result of which the second threshold device closes, and hence the transistor VT2, the relay K2 releases the armature. Relay K1 is activated and switches contacts. KM. With this state of the relay contacts, the load current bypasses the windings II and III of the transformer, that is, the voltage boost is zero. The mains voltage is repeated on the load - 205 ... 225 V.

In the range of mains voltage 225 ... 245 V, the zener diode VD6 opens. This means that the third threshold device comes into operation and both transistor switches turn out to be open; both relays are switched on - K1 and K2. Now the winding III of the transformer T1 is included in the load current circuit, but in antiphase with the mains voltage ("minus" voltage boost). In this case, the load will also have a voltage in the range of 205 ... 225 V. With a mains voltage of 250 V, the output voltage of the stabilizer will increase to 230 V, without exceeding the allowable limit of 220 V + 5%.

It can be seen from the previous description that the voltage limits of the control stages are determined by the stabilization voltage of the zener diodes included in the threshold devices. When setting the boundaries of the regulation steps, it is necessary to install a selection of zener diodes, which, as you know, are distinguished by a significant spread in the stabilization voltage. If it turns out that it is not possible to select a suitable instance, you can use the serial connection of a zener diode with one or two diodes (in direct connection). Instead of KS218Zh (VD5), you can use the KS220Zh zener diode. This zener diode must be double-anode. The fact is that in the mains voltage range of 225 ... 245 V, when the zener diode VD6 opens and both transistor switches are open, the circuit R4, VD5 shunts the resistor R6 of the threshold device R5, VD6, R6.

To eliminate the shunting action, the VD5 zener diode must be two-anode. The stabilization voltage of the VD5 zener diode should not exceed 20 V. The VD3 zener diode should be selected from the KS220Zh series (stabilization voltage is 22 V); you can use a chain of two zener diodes - D810 and D811. Zener diode KS222Zh (VD6) - for 24 V - can be replaced with a chain of zener diodes D810 and D813. The transistors in the stabilizer can be any of the KT3102 series. Diodes - also any of the indicated series. Relays K1 and K2 - REN34, passport HP4.500.000-01.

The transformer is made on the OL50 / 80-25 magnetic circuit made of steel E350 (or E360), the thickness of the tape is 0,08 mm. Winding I (for a rated voltage of 220 V) must contain 2400 turns of PETV-2-0,355 wire. Windings II and III are the same, 300 turns of wire PETV-2-0,9 (13,9 V). It is necessary to adjust the stabilizer with the real load turned on so that the response of the transformer T1 to the load is taken into account, since the transfer coefficient decreases slightly when switching from idle to full load mode.

When only one winding II is operating, the transmission coefficient will be less than at idle, and even less when windings II and III operate simultaneously. When only winding III works, the transmission coefficient is close to the idle mode, since in this case losses are compensated due to the "counter" current in it in the range of mains voltage values ​​​​225 ... 250 V. The change in the transmission coefficient causes a slight - by fractions volt - change in the voltage of switching on threshold devices. This small change, multiplied by the transformation ratio of transformer T1, shifts the limits of the output voltage already by a few volts. That is why it is necessary to set the limits of the control steps only with a load.

Author: Semyan A.P.

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