Smooth ignition of an incandescent lamp. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Lighting
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The device provides protection of the lighting lamp from current surges at the moment of switching on and smooth heating of its filament, as well as adjustment of the maximum load power. Its advantage over some similar ones, for example, those published in [1, 2], is its simplicity combined with sufficiently high reliability.
The method of pulse-phase control of the trinistor, described in [3], was taken as a basis (see diagram). The principle of operation of such a device is well known to readers of Radio, and therefore we will only consider in detail the operation of the newly introduced automatic load power control circuit, consisting of a VD4 diode, capacitor C1 and resistors R2, R3.
Immediately after being connected to the network, capacitor C1 begins to be charged by current pulses flowing through resistor R2, diode VD4 and resistor R3. The peak value of the voltage at point A is not yet enough to open the unijunction transistor VT1, so it is closed, naturally, so is the trinistor VS1. At this time, no current flows through the load EL1. As the capacitor C1 charges, the value of the impulse voltage at point A increases. When it reaches the transistor opening threshold, the capacitor C1 begins to discharge through its emitter-base junction, as a result of which short pulses opening it are sent to the control electrode of the trinistor.
The power dissipated in the load is determined by the phase shift between the control pulse and the beginning of the period of the anode voltage of the SCR, as well as the frequency of the control pulses, since at the beginning of the process one pulse is formed for several periods of the mains voltage. These two parameters that determine the operation of the trinistor depend on the charging rate of the capacitor C2, i.e., on the peak voltage at point A and the resistance of the input part of the variable resistor R4. As the capacitor C1 charges (after 1 ... 2 s), the average current flowing through the diode VD4 decreases so much that in the future this circuit does not have a noticeable effect on the operation of the device. The maximum power supplied to the load is determined by the total resistance of resistors R2 and R4 and can be approximately 5 ... 90% of the rated load power. As practice shows, such a range of power adjustment for incandescent lamps is quite enough.
Resistor R7 is designed to discharge the capacitor C1 after disconnecting the load from the network. It is advisable to supplement the device with an SF1 reed switch, which accelerates the discharge of this capacitor, and mechanically connect the magnet controlling its contacts to the SA1 switch. Resistor R8 limits the current through the reed switch.
A device of arbitrary design can be assembled in a housing of relatively small dimensions. With a load power of more than 100 W, the trinistor should be installed on the heat sink, and the VD1 rectifier bridge should be replaced with a more powerful one, for example, assembled on four D245 diodes.
Trinistor KU201L will be replaced by KU201K, M, KU202L-N. Diode VD4 - any of the KD522, KD521, KD503 series. All fixed resistors - MLT, variable resistor R4 -SPZ-4a. Capacitor C1 - oxide K50-6, C2 - any small-sized.
Due to the fact that the device has direct contact with the network, the shaft of the variable resistor R4 must be equipped with a handle made of insulating material.
An unmistakably assembled device does not require adjustment.
Literature
- 1. Bzhevsky L. Light regulator with time delay. - Radio, 1989, No. 10, p. 76.
- 2. Leontiev A., Lukash S. Voltage regulator with phase-pulse control. - Radio, 1992, No. 9. With. 43. 44.
- 3. Fisher E., Getpand Kh. B. Electronics - from theory to practice. - M.: Energy, 1980, p. 71,72.
Author: D. Pankratiev, Tashkent, Radio 9-97; Publication: N. Bolshakov, rf.atnn.ru
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