Time relay for lamp. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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The proposed device is designed to automatically turn off incandescent lamps after a specified period of time after switching on. It differs from those previously proposed in various literature by its simplicity, the use of only a widespread element base, two-stage ignition and smooth lamp extinction, and extremely low power consumption in standby mode.

The schematic diagram of the device is shown in the figure.

When you first turn on the network, the capacitor C1 is discharged, the field effect transistor VT2 is open and shunts the emitter junction of the transistor VT1. The transistor VT1 and the trinistor VS2 are closed at this time, the voltage at the output of the diode bridge VD1 is maximum, and the current flowing through it is not enough to open the triac VS1. The EL1 lamp is not lit, the device is in standby mode.

When the transistor VT1 is closed, capacitor C2 is charged through the circuit VD8, R2. The voltage across this capacitor is stabilized by the transistor VT3 at 6...8 V.

When the SB1 button is closed, the capacitor C1 is relatively quickly charged from the capacitor C2 through the resistors R9, R5 and the emitter junction of the transistor VT1. The positive gate-source voltage of the transistor VT2 begins to exceed the cutoff voltage, the field-effect transistor closes, the high-voltage transistor VT1 opens, and therefore the low-power trinistor with a low control current VS2 also opens. At the beginning of each half-wave of the rectified voltage, a current pulse flows through the circuit R1, VD1, control electrode VS1, sufficient to open a powerful triac.

The EL1 incandescent lamp lights up, but not completely, until the button is released, the effective voltage on the lamp is about 70 ... 75% of the supply voltage. After releasing the button, 98% of the power is supplied to the lamp, i.e. the lamp glows at full intensity. This two-stage ignition of the lamp favorably affects its service life.

Capacitor C1 is gradually discharged through resistor R7. When the voltage across it approaches the cutoff voltage, the field-effect transistor starts to open, the current through the emitter junction of the transistor VT1 gradually decreases, therefore, the transistor VT1 gradually closes, the trinistor VS2 and the triac VS1 on each half-wave of the alternating voltage open with a gradually increasing delay - the lamp EL1 slowly goes out .

The HL1 LED, connected in series with the resistor R6 and the emitter junction of the transistor VT1, is designed to illuminate the switch when the relay is in standby mode.

The device uses resistors MLT, S2-23 of the corresponding power. Resistor R3 can be made up of several lower power resistors connected in parallel. R8 can be replaced by two 510 W 0,125 kΩ resistors in series.

The maximum holding time that can be achieved depends on the quality of the capacitor C1. The author used a niobium oxide-semiconductor capacitor type K53-4 10 μF 15 V with a leakage current of 150 nA at a voltage of 10 V and a case temperature of 25 ° C. With such a capacitor, the lamp glows for 10 minutes. You can try to use similar capacitors with low leakage current K53-1, K53-1A. Very good results are also obtained when conventional RUBICON oxide capacitors are used. With capacitor 22uF 50V - 9 minutes, 100uF 63V - 40 minutes. Unfortunately, domestic K50-35 capacitors have one or two orders of magnitude higher leakage currents, so it is difficult to obtain good results when using them. Capacitor C2 can be installed with a capacity of 100 ... 200 μF with a leakage current at a voltage of 10 V of not more than 10 μA.

Instead of a KD102B diode, it is permissible to use any low-power silicon, for example, the KD510, KD522, KD521 series. The VD1 diode bridge can be replaced with KTs402, KTs405 with indices A-B or four diodes KD102B, KD105 (B-G). Triac VS1 is replaced by TS112-10, TS112-16 or any other for the corresponding current and voltage of at least 400 V. Before installation in the assembled structure, it is advisable to check the triac for the cathode-anode current with the cathode and control electrode leads connected together and the case temperature 25 °C. For any voltage polarity of 300 V, the triac current should be no more than 20 μA. If it exceeds this value by more than an order of magnitude, then this instance of the triac may turn out to be unreliable in operation, which will manifest itself as spontaneous flickering and even complete ignition of the lamp.

The LED can be replaced with any of the AL307, AL336, KIPD21 series with sufficient brightness at a current of 1 mA.

The high voltage transistor VT1 is replaced by KT969A, 2SC2330. A field-effect transistor with an n-type channel KP103Zh to obtain long exposures must have a low cutoff voltage, preferably no more than 1,5 V. In addition, an instance with an initial drain current of more than 1 mA should be selected. The bipolar transistor VT3 is replaced by any of the KT315 series.

With a lamp power of more than 40 W, the triac is installed on a heat sink. With the triac KU208G, the load power can be up to 1000 watts. The temperature of the triac housing during long-term operation of the device with the lamp on should not exceed 45 ... 55 ° С. With a lamp power of less than 300 W, the finished device easily fits in the installation box of the switch for internal wiring. At the same time, if a modern switch with a flat design is used, it can not be dismantled. If its key will play the role of the SB1 button, a small spring should be installed under it for self-return, for example, from the P2K button.

If it is necessary to adjust the exposure time, the resistor R7 is replaced by a variable one, with a resistance of 4,7 ... 10 MΩ. The wire from the resistor R9 to the button SB1 must have a minimum length or be shielded.

The fuse FU1 must be rated for a current 2 ... 3 times the operating current of the applied incandescent lamps.

The minimum power of the connected incandescent lamps depends on the type and specific instance of the triac used. Sometimes there are instances that work confidently with an active load with a power of more than 3 ... 5 watts. The first switching on and adjustment of the assembled time relay should be carried out with a lamp with a power of 40 ... 60 W.

Literature

1. Drobnitsa N. Electronic devices for radio amateurs. - M.: Radio and communication, 1986, p. 4-11.
2. Nechaev I. Automatic - energy saving. - Radio, 1995, No. 12, p. 46.

Author: A.Butov, village of Kurba, Yaroslavl region

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