Soft turn off high beam. Scheme, description

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Soft turn off high beam. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic devices

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At night, when two cars are passing by, the driver perceives the switching of the main beam of the headlights of his car to the low beam at the first moment as a sharp decrease in the illumination of the road, which makes him strain his eyesight and leads to rapid fatigue. It is also more difficult for oncoming drivers to navigate in an environment with sharp changes in the brightness of the light in front. This ultimately reduces traffic safety.

The driver's fatigue during night driving can be noticeably reduced by a smooth (within 3 ... 4 s) turning off of the high beam when switching it to the low beam. The industry produces the PDB-1 device intended for this purpose, however, it has large dimensions and weight, dissipates significant power and cannot be used on vehicles with halogen lamps and a four-headlight lighting system (for more details, see the article "Without loss of visibility", - Behind the wheel, 1983, No. 10, p. 30).

Fig.1 (click to enlarge)

Figure 1 shows a diagram of an automaton for smooth switching off the main beam, which is free from these shortcomings. Time voltage diagrams explaining the operation of the machine are shown in fig. 2.

Soft turn off high beam
Ris.2

The generator on the operational amplifier DA1.1 generates a triangular voltage with a frequency of 150 ... 200 Hz (graph 1 in Fig. 2). which is fed to the non-inverting input of the op-amp DA1.2. While the main beam is on (in the position of the foot light switch SA2, shown in the diagram), the capacitor C2 is discharged through the resistor R7, the diode VD3 and the low beam filament of the EL1 lamp (the diagram shows one lamp out of two) and the voltage at the output of the op-amp DA1.2 is about 10,5 V. Transistor VT1 is open at this time, and transistors VT2. VT3 are off, since the collector and emitter of the transistor VT3 are closed by the contacts of the switch SA2.

After switching the high beam to the low beam, the high beam spirals remain switched on through the opened transistors VT2 and VT3. Capacitor C2 starts charging (graph 2 in Fig. 2) through resistors R7 and R9. An increasing voltage appears at the inverting input of the DA1.2 op amp, and rectangular pulses with a constant frequency and increasing duty cycle appear at the output (graph 3). They switch transistors VT1--VT3 accordingly. and the effective value of the voltage on the filaments of the high-beam lamps gradually decreases to zero.

When switching light from near to far, capacitor C2 quickly discharges through the R7VD3 circuit. Diodes VD1, VD2 and resistor R6 serve to limit the voltage between the inputs of the op-amp DA1.2; stabistor VD4 and resistors RIO, R12 - for reliable closing of transistors. Trimmer resistor R9 allows you to adjust the high beam extinction time in the range from 1 to 4 ... 5 s. The device can be turned off with the SA1 toggle switch.

The described device is connected in parallel with the light foot switch as shown in fig. 1. The cross section of the connecting wires is at least 1,5 mm2.

The device uses resistors OMLT and SPZ-16 (R9), capacitors KM-5 and K50-6 (C2). The GT806A transistor can be replaced with any other of this series or GT701A. If the current consumed by the high beam coils does not exceed 10 A (two-headlight cars with conventional lamps), then P806A, GT210A transistors can be used instead of GT810A. Instead of the KT816B transistor, KT816V, KT816G or GT905, GT906 with any letter index are suitable; instead of KT815B - KT815V, KT815G. KT817B, KT817V. KT817G, KT801B. The stabistor KS119A can be replaced by three series-connected diodes KD102A or D220, D223, KD522A. It is undesirable to replace the K157UD2 microcircuit, since it is capable of operating in a wide range of supply voltages.

All parts, except for the SA1 toggle switch, are placed on a fiberglass board measuring 110x65x2 mm. Mounting is performed using tinned brass bushings, flared in the holes of the board. Transistors VT2, VT3 are installed on a heat sink with a surface area of at least 40 cmXNUMX. The assembled device is fixed under the dashboard to the left of the steering column.

Immediately after switching the light, the brightness of the main beam abruptly decreases slightly due to the fact. that the filaments of the lamps are turned on through the resistance of the open transistor VT3, and then the lamps go out smoothly.

The device can also be used on vehicles with an on-board network voltage of 24 V. To do this, it is necessary to connect the OMLT-11 resistor with a resistance of 2 Ohms in series with the R120 resistor. replace the stabistor KS119A with a zener diode D814G and use capacitor C2 for a voltage of 50 V. The device was tested on a GAZ-24 car and showed good results.

Author: A. Khrisanov; Publication: N. Bolshakov, rf.atnn.ru

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