Intelligent lighting switch. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Lighting

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The device is designed to turn on and off the light in rarely visited utility rooms. It implements a branched algorithm of work. The fact is that utility rooms are mainly visited for two purposes - "for a long time" and "for a short time". When they enter the room "for a long time", the door is usually immediately closed behind them. If the room is entered "for a short time" (for example, in the pantry for a jar of cucumbers), then the door is usually left open so that when leaving, you do not have to "kiss" with the closed door.

Therefore, the device works according to two algorithms:

• the door remains open for more than 3 s (this time can be changed), then after the door is closed, the light goes out (it turns on immediately after the door is opened);
• the door was opened and closed in less than 3 seconds - the light will continue to burn and go out only after the door is opened and closed again.

In both modes, the light turns off only after the door is closed.

As a door position sensor, the SB1 button (Fig. 1) of the MP-9 type with a pusher is used (it was widely used in the tape transport mechanisms of Soviet tape recorders).

Fig.1. Schematic diagram of the switch (click to enlarge)

The button can be replaced with a magnet-reed switch pair, but if the reed switch has closing (rather than switching) contacts, one more resistor will have to be added to the circuit (Fig. 2).

Ris.2.

Schmitt trigger DD1.1 (Fig. 1) dampens the bounce of the contacts of the SB1 button; from its output, the signal is fed to the input of the DD1.2 element that controls the load (incandescent lamp) and the logical part of the device.

While the door is closed, there is a logical "1.1" at the output of the DD1 element; when it is open, a logical "0" appears there, which sets the DD1.2 element so that "1" appears at its output, turning on the load (EL1 lamp) , the generator on the element DD1.3, and allowing the counter DD2. At the same time, the trigger DD3 is reset through the differentiating chain C3-R3.1. A logical "3.1" appears at the direct output of DD0, it enables the operation of the DD3.2 trigger at input C and maintains a logical "1" at the DD1.2 output, regardless of the SB1 button, i.e. the lamp will continue to light.

After about 3 s (with the position of the SA1 switch indicated on the diagram), a “single” pulse front appears at the input C of the DD3.1 trigger, and information about the contact position of the SB1 button is written to the trigger. If the door is still open, a "1" appears at the trigger output, and as soon as the door closes, the EL1 lamp goes out.

When the door is closed by this time, the state of the direct output of the trigger DD3.1 will not change (logical "0"), and the lamp will continue to burn. Immediately after the door is closed, a positive voltage drop appears at the output of the DD1.1 element, and a logical "3.2" is set at the direct output of the counting trigger DD0. Lamp EL1 continues to glow.

So it will be until the existence of the door is again remembered. When you open it, nothing will happen, and when you close it with the next pulse, the logical "3.2" is set at the output of the trigger DD1. Thanks to the differentiating chain C4-R4, the same level appears at the output of the trigger DD3.1. At both inputs of the element DD1.2 - "1", at its output - "0". The lamp goes out, the generator stops, the counter is reset.

A so-called "watchdog timer" has been added to the device. It is needed to limit the glow time of the EL1 lamp, i.e. to save electricity. The function of the watchdog timer performs the trigger DD3.2 together with the counter DD2. The maximum lamp duration depends on the position of switch SA2 and can be 7, 14 or 28 minutes. As soon as the time limit expires, "2" appears at the corresponding output of the counter DD1. Through the VD1 diode, it is written to the DD3.2 trigger and, through the C4-R4 chain, switches the DD3.1 trigger, which extinguishes the lamp.

The high-voltage part of the device is assembled on a triac VS1, a high-voltage transistor VT1 and a diode bridge VD2 ... VD5. It is this circuit configuration that was chosen to achieve greater efficiency and reduce the control current. Despite the fact that the minimum unlocking current for the triac used in the circuit (TS106-10) is 10 ... 30 mA, the short-circuit current of the bridge diagonal on diodes VD2 ... VD5 does not exceed 0,5 mA. This is due to one of the features of thyristors: to transfer them to the open state, a very short current pulse is needed, after which the voltage at the control electrode becomes 1 V less than the voltage at the anode. That is, in this circuit, a significant current through the transistor VT1 (20 ... 30 mA) flows only at the beginning of each half-cycle (about 1/40 part), and the rest of the triac is open, and the current flowing through the transistor is close to zero. Therefore, the average value of the opening current for the half-cycle "decreased" by a factor of 40.

All this is true only if the transistor VT1 operates in the key mode. If the resistance of its collector junction decreases smoothly, then with a "half-open" transistor, the average value of the current flowing through it is much more than 0,5 mA, and it heats up more.

The high-voltage part of the circuit works like this. At a high level at the output of the element DD1.2, the capacitor C5 is slowly charged through the resistor R5, the resistance of the collector-emitter junction of the transistor VT1 gradually decreases, and the lamp EL1 gradually flares up. During the switching on and off of the lamp, a rather significant power is released on the transistor VT1, but if you do not increase the capacitance of the capacitor C5 and maintain the interval between switching on the lamp for more than 2 ... 3 s, a radiator is not needed for it. When the lamp is lit at full heat, the temperature of the transistor body rises by about 15 ° C.

The resistance of the resistor R5 should be as high as possible, but such that the lamp EL1 reaches full heat. Resistor R6 cannot be removed - without it, the lamp will only burn half-heartedly. The capacitance of the capacitor C5 can be reduced, but it is undesirable to remove it, because. at the output of the DD1.2 element, pulses are formed with sudden voltage drops that will “pull” the lamp, which will adversely affect its “life”.

The device is powered directly from the AC mains through a simple rectifier on the VD6 diode and a current limiter - resistor R7. The current consumed by the device is extremely small: practically from zero in "sleep" mode to 350 μA with the lamp on. This made it possible to choose a fairly high-resistance resistor R7. It dissipates power, a little more than 0,05 W, but the power of this resistor should be 0,25 W or more - then there will be more chances that it will not be pierced by high voltage. The resistance of the resistor R7 can be increased up to 300 kOhm.

In the circuit, as DD1, the author used the HEF4093BT chip f. Philips in a surface mount case. A feature of this microcircuit is a very small through current during switching, due to which a working generator on the DD1.3 element consumes less than 7,2 mA at a supply voltage of 0,1 V.

The same generator, but assembled on the domestic analogue K561TL1, consumes more than 1 mA under the same conditions. This is due to the fact that digital CMOS microcircuits are not designed to work with a smoothly varying (analogue) signal, and at some "average" input voltage, through currents occur. Schmitt triggers have switching hysteresis, so there is no through current in their output stages. But, unfortunately, this does not apply to their input stages. Therefore, if you use a domestic microcircuit, then you may need to reduce the resistance R5 by 10 ... 7 times. At the same time, the power dissipated by it and the current consumed by the device will sharply increase.

When the device is connected to the network, the voltage across the capacitor C6 due to the significant time constant τ = R7-C6 increases slowly. At this point, the direct output of the trigger DD3.1 is low, i.e. EL1 lamp is on. Since the supply voltage increases very slowly, the base current of the transistor VT1 also slowly increases. The power dissipated by the collector junction of the transistor is maximum exactly when it is “half open”, and in this circuit it can reach 5 ... 10 watts. Those. the transistor can simply "burn out". Therefore, it is advisable to turn on the device in the network with the EL1 lamp unscrewed. It can be screwed into the cartridge only after 5 ... 10 s after switching on. However, with the ratings R5 ... R7, C5, C6 indicated in the diagram and a slowly flaring lamp, the temperature of the transistor case (without a radiator) rises by about 60 ... 70 ° C.

A device correctly assembled from serviceable parts does not need to be configured. If you are using a DD1 chip from another company (all other microcircuits can be any CMOS structures), then you do not need to solder the VD7 zener diode initially. Power is supplied to the circuit through a milliammeter from a constant voltage source (corresponding to the stabilization voltage of the zener diode), and the inputs of the DD1.1 element are connected to the "+ U" wire. With the help of an LED or in any other way, they are convinced of the operation of the DD1.3 generator, after which the readings of the device are read.

The resistance of the resistor R7 is calculated by the formula:

R7 = 100/I (KOhm), where I is the current in mA.

It is advisable to round the resulting resistance value down - after all, the VD7 zener diode also needs to "eat" something.

The supply voltage of the circuit depends only on the stabilization voltage of the zener diode VD7, and can be from 3 to 18 V. The lower the supply voltage, the lower the current consumed by the DD1.3 generator. Its frequency increases with decreasing supply voltage. When changing the supply voltage, it is necessary to change the resistance of the resistor R5 in the same direction (the selection of its value was discussed above). The capacitance of the capacitor C1 must be such that the element DD1.1 completely suppresses the bounce of the contacts of the button SB1; it is undesirable to reduce it. The values ​​​​of the resistor R1 and both chains C3-R3 and C4-R4 can be any of the ranges indicated on the diagram - nothing depends on them. Diodes VD2 ... VD6 can be any, designed for a reverse voltage of at least 400 V and a forward current of more than 0,1 A. The VT1 transistor can be replaced with a KT9115, the VS1 triac with any other. With an EL1 incandescent lamp power of less than 200 ... 300 W, a triac radiator is not required.

Instead of a bipolar transistor VT1, you can use any high-voltage field with an n-type channel. In this case, no changes to the scheme are required. Resistor R6 can then be short-circuited, and the resistance of resistor R5 can be increased several tens of times. At the same time, it is necessary to reduce the capacitance C5 by the same amount. However, it (C5) can be removed completely - for modern field-effect transistors, the slope of the characteristic is quite significant, and it is difficult to achieve the effect of a smooth "burning up" of the light bulb. If you use a powerful bipolar or field effect transistor, then the VS1 triac is not needed. But then on the radiator, in addition to the transistor, you need to "plant" diodes.

The switches SA1 and SA2 are made in the form of tracks passing on the printed circuit board near the corresponding outputs of the DD2 chip. Their "contacts" are closed with a drop of solder using a soldering iron. It is impossible to connect several outputs of the DD2 chip together!

The device has a transformerless mains supply. Be careful when setting up. The common wire (body) in the diagram is drawn to simplify the graphics. In no case should it be connected to the device case or grounded.

Author: A.Koldunov, Grodno; Publication: radioradar.net

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