The lamp will last longer. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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The lamp will last longer. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Lighting

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Night or standby (with reduced brightness) lighting, which also makes it possible to significantly increase the service life of the lamps, can be implemented in different ways. Among the simple and reliable is the method using a quenching capacitor in the power supply circuit (Fig. 1). In this case, the capacitance C1 is calculated as a reactance to obtain the required voltage on the lamp EL1. Resistor R1 is needed to discharge the capacitor after disconnecting the circuit from the network. Its value is taken in the range of 100-500 kOhm.

The lamp will last
Rice. Fig. 1. Schematic diagram of night-time standby (with reduced brightness) lighting, which also makes it possible to significantly increase the service life of the lamps due to the introduction of additional (capacitive) resistance

Due to the non-linearity of the active resistance of the filaments and the real spread of the static parameters of the lamps themselves, the exact calculation of the capacitance of the capacitor C1 is quite difficult even for experienced specialists. However, the calculations can be significantly simplified by using approximate formulas. In particular, for an electrical circuit with low-voltage and low-power incandescent lamps (switching, from garlands, indicator and others with a voltage of 10-42 V and a current of up to 0,5 A), the ratio verified by practice is quite acceptable:

where: С is the capacitance of the additional (extinguishing) capacitor, uF; In - lamp rated current, A; Ul - the voltage that you want to get on the lamp, V; Us - voltage of the AC supply network, V.

When using typical incandescent lighting lamps, on the base or bulb of which the rated operating voltage (usually 220-240 V) and power consumption (10-200 W) are indicated, the coefficient in the numerator should be reduced to 1150, and In should be found using the known to everyone from school benches by Ohm's law.

As practice shows, in any case, it is better to calculate the capacitance of the quenching capacitor, taking into account the receipt of half of its rated voltage on the lamp. For example, if Un is 24 V, then Ul is recommended to be taken equal to 12 V. The approximately found value of C1 is subsequently specified - depending on the desired brightness of the lamp. At the same time, one should not forget about the nonlinearity of the resistance of the filament, which leads to the fact that a slight increase in the capacitance of the quenching capacitor sometimes causes a sharp increase in the voltage across the lamp, and a decrease threatens with an almost abrupt decrease in Ul.

In order to further simplify the procedure for calculating and selecting the quenching electric capacity, it is recommended to use ready-made data (Table 1), verified by practice for some types of lamps when connected to a household network (220 V, 50 Hz) in accordance with the scheme discussed above.

Table 1. Recommended values of quenching (additional) capacities for turning common types of lamps into super-reliable lamps operating in a 220-volt electrical network at a deliberately low filament voltage

It is worth emphasizing, I think, that voltage suppression with the help of capacitors really makes it possible to significantly increase the service life of lamps with a rather insignificant decrease in the brightness of the glow. In addition, this technical solution (unlike classical circuits based on powerful semiconductor diodes) does not lead to annoying 50 or 100 Hz flickering of the lighting itself ...

The lamp will last
Rice. 2. An ordinary table lamp can also serve as a night light, thanks to a slight refinement using a quenching capacitor

Additional benefits and conveniences can be obtained by embedding a quenching (additional) capacitor of the appropriate capacity in an ordinary table lamp, slightly modifying its switching circuit (Fig. 2). True, for this you will have to replace the regular two-pole toggle switch with a switch-button SA1 for three fixed positions.

Author: M.Gartsev

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