Dependent inclusion of electrical and radio devices. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches

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The device is designed to automatically turn on one electronic device when another is turned on. The first of them is usually called the slave, and the second - the leader. A device of similar purpose was published by the author in the Radio magazine more than three years ago (see Radio, 1996, No. 8, p. 51). Its disadvantage was that an electromagnetic relay was used as a key. The new version is simpler, the functions of the keys in it are performed by triacs. This imposes certain restrictions on the types of devices used, but this will be discussed below.

A schematic diagram of a device for dependent switching on devices with a power of 100 W or more is shown in fig. 1. Triac VS1 is connected to socket XS1 for connecting a slave device. The master is connected to socket XS2. When it is in the off state, no current flows through the device, the triac is closed and the slave device is de-energized. When the master device is turned on, current begins to flow through the diodes VD1-VD5 and the voltage that appears on them (through the resistor R1) is fed to the control electrode of the triac. With a positive half-wave of the mains voltage, the current flowing through the host device will pass through the diodes VD1, VD2, and a positive voltage will be applied to the control electrode of the triac, which will open it.

With a negative half-wave of the mains voltage, the current will flow through the diodes VD3-VD5 and a negative voltage will be applied to the control electrode of the triac. In this case, it will already be opening. Diodes VD1-VD5 and resistor R1 limit the amount of current through the control electrode of the triac. Since the values ​​of positive and negative control voltages are different for the triac used here, the number of diodes connected in series for the positive and negative half-waves of the current is not the same. The current through the master device, at which the triac opens, is 50 ... 100 mA, therefore, on the slave device, the mains voltage does not appear at the very beginning of the half-cycle, but with some time delay.

The amount of delay depends on the power of the master. The presence of a delay leads to a decrease in the voltage on the slave device by about 7 ... 10, and sometimes more percent. In addition, since the holding current of the triac usually exceeds 100 mA, the minimum power of the slave devices in relation to the described device must be at least 100 watts. The maximum power of the master device is determined by the maximum allowable current through the diodes VD1-VD5 and can reach 1 kW, and the slave - 250 watts. If these diodes and a triac are installed on heat sinks, then these powers will increase to 2 ... 3 kW and 1,1 kW, respectively.

For low-power slave devices (50 W or less), you can use the device, the circuit of which is shown in fig. 2. Two thyristor optocouplers VS1, VS2 are used here, which in turn open each with its own half-wave of mains voltage. They are controlled by the current flowing through the master device. This current alternately flows through the emitting diodes of the optocouplers and opens the photothyristors. Diodes VD3-VD6 and resistor R1 limit the current through the emitting diodes. The maximum power of the master device is determined by the type of diodes VD3-VD6 and in this case is 400 watts. It can be easily increased by using more powerful diodes, such as those in the device shown in fig. 1.

The device, the schematic diagram of which is shown in fig. 1, assembled on a printed circuit board made of one-sided foil fiberglass (Fig. 3). It contains all the details, including sockets XS1, XS2. The printed circuit board of the device shown in fig. 2 is shown in fig. 4. These boards can simultaneously function as the front panel of the device, but in this case, all parts must be covered with an insulating material.

The device (see Figure 1) can use any silicon rectifier diodes rated for the current drawn by the host. In the device (see Fig. 2), diodes KD105B, D226B (VD1, VD2) and similar are applicable. Diodes VD3-VD6 should also be selected based on the maximum current consumed by the host device.

In order for the slave device to have normal voltage, the thyristors in the device must open at the beginning of each half-cycle of the mains voltage. This means that the master device must draw current during the entire half-cycle of the mains voltage. Such devices can be heating (without thyristor power regulators) or lighting (with incandescent lamps and also without regulators). If the masters are radio engineering devices powered by a rectifier and consuming current near the maximum voltage, then the mains voltage will be supplied to the slave devices not at the beginning, but approximately in the middle of each half-wave of the mains voltage. In the case when the functions of the slaves are performed by heating or lighting devices, they work with reduced power. If the slave is a radio device, for example, a power supply with a step-down transformer and a rectifier, which consumes current at maximum voltage, then it will work normally.

Setting up the device (see Fig. 1) is reduced to selecting the minimum number of series-connected diodes VD1-VD5, in which the triac turns on steadily at the beginning of each half-cycle of the mains voltage. In this case, the voltage on these diodes should not exceed 6 V. The device is set up in the same way (see Fig. 2), while it is necessary to select the number of VD3-VD6 diodes connected in series.

Author: I. Nechaev, Kursk

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