Protection of electric lighting devices. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Protection of electric lighting devices. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Lighting

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The article "Soft" load in the mains ("Radio", 1988, No. 10, p. 61) describes a device for "smooth" connection of the load to the AC mains. Such devices can be successfully used for switching electric lighting devices. As you know, the resistance of an incandescent lamp filament in a cold state is much less than in a heated one. That is why incandescent lamps most often fail at the moment they are turned on.

When the lamp is "softly" connected, the current through the filament increases smoothly, without reaching an extreme value, so the longevity of the lamp increases immeasurably. However, the implementation of these devices is associated with a number of difficulties. First, the use of high-capacity oxide capacitors is required, which, for safety reasons, must be rated for a voltage of at least 400 V. This leads to a significant increase in the dimensions of the device. Secondly, the fact that the switch is built into the device itself makes it necessary to lay additional lead wires.

In many cases, this complicates the design, since using the existing switch of the finished lighting fixture. (for example, a floor lamp or a chandelier with a button mounted on the power cord) is usually not possible. Bypass these difficulties allows the device described below. It (see diagram) is made in the form of a two-terminal network. This allows you to place the board with its parts in any convenient place by including in the gap the wire connecting the SA1 switch (available in the lighting fixture is suitable) with the HL1 lamp (or a group of lamps connected in parallel). The device can be combined with a wall switch - it can be "hidden" inside the chandelier, without the need for any

Protection of electric lighting devices

The use of the KT848A transistor, which has a large static current transfer coefficient and significant power, made it possible to get by with a relatively small capacitor C1. In addition, this transistor (it is used in the electronic switch 36.37.34 of the contactless ignition system of Samara and Tavria cars) is easy to purchase in automotive spare parts stores. It is one of the so-called "composite", therefore, it can operate at a relatively small base current, which made it possible to use a resistor R1 of a rather large resistance and, accordingly, reduce the capacitance of the capacitor C1. This made it possible to reduce the dimensions of the device.

With the types and ratings of parts indicated in the diagram, the turn-on delay of the HL1 lamp is approximately 100 ms, and the turn-off delay is 5 ms. This guarantees the necessary gradual heating of the lamp filament for any possible nature of the current switching by the SA1 switch. By the way, the set time delay for turning on the lamp is completely imperceptible; visually, the lamp ignition will still occur almost instantly.

With a lamp power of up to 100 W, the VT1 transistor can be mounted without a heat sink. With a larger value (maximum power rating of 300 W), a small heat sink will be required. Diodes KD202K can be replaced by others of the same series with a letter index from L to S. In some cases, it is structurally more convenient to use diode arrays of the KTs series, suitable for voltage and current. The described device has been operated by the author in a lighting chandelier for several years, and during this time it was not necessary to replace any of the lamps.

If it is necessary to switch lamps of even greater power, a trinistor power regulator assembled one by one from known circuits can be used as a protective device. The variable resistor of the regulator must be replaced by a circuit located in the diagram shown here between the common point of the cathodes of the diodes VD1, VD3 and the common point of the anodes of the diodes VD2, VD4; diodes are not needed. In this case, the operating voltage of the capacitor can be reduced, and the transistor VT1 can be replaced by a low-power low-voltage one, but with a possibly large current transfer coefficient. It is only important that they are designed for the stabilization voltage of the zener diode, which is usually used in power controllers with phase-pulse regulation. The HL1 lamp must be connected to the AC circuit (in series with a diode bridge or triac).

Author: V. Bannikov, Moscow; Publication: N. Bolshakov, rf.atnn.ru

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