Bicycle generator voltage regulator. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Regulators of current, voltage, power

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When cycling in the dark, the voltage generated by the bicycle generator ("dynamka") is often used to power the bicycle headlight. The variable speed of rotation of the generator shaft causes a change in the brightness of the lamp. In principle, you can take two light bulbs of different power and switch them depending on the speed of movement so that there is always light.

At a low speed of the bike, a low-power bulb will provide at least some visibility of the road. But if you increase the speed, it will immediately burn out from overvoltage. To prevent this from happening, you need to quickly switch the bulbs, which is very difficult to do manually. The proposed device will help out (Fig. 1).

(click to enlarge)

While the voltage at the output of the diode bridge VD1 ... VD4 does not exceed 2,5 V, the thyristor VS1 is closed, since the voltage across the capacitor C1 is less than the opening voltage. A current passes through the EL2 lamp and resistors R1, R2, which is insufficient for EL2 to glow, but opens the VT1 transistor. As a result, the EL1 lamp lights up. The voltage on it is less than at the output of the diode bridge, since part of the voltage drops on the open transistor VT1. When the voltage at C1 reaches the opening threshold VS1, it fires, the lamp EL2 lights up, and EL1 goes out, so the transistor VT1 closes. Due to the divider R1-R2, complete closing of VT1 is ensured.

When the bicycle slows down and the generator voltage decreases, the reverse switching occurs when the thyristor VS1- closes. To charge the capacitor C1 and fix the voltage on it, the VD5 diode is used. Therefore, the switching of light sources occurs when the average value of the supply voltage changes, and not in each period of its pulsations.

The values ​​of the resistors R1 and R2 are selected for reasons of minimum energy consumption with reliable opening of the transistor VT1. When it is completely closed with the thyristor VS1 open, no energy is consumed on it, and when it is completely open with the thyristor closed, the minimum energy is spent on heat (the transistor is selected with a minimum voltage drop in the open state). Therefore, if the transistor VT1 (when the EL1 light is on) noticeably heats up, i.e. is in the active area, you need to reduce the value of R2, and if it is ajar when EL2 is on, you need to reduce R1. If switching lamps occurs at a voltage less than 2,5 V, you need to increase the value of R3, and vice versa.

Unfortunately, lamps have a limited service life and burn out even if all operating modes are observed.

In the described scheme, the burnout of one light bulb does not lead to the combustion of the other. True, if a powerful EL2 burns out, then a low-power EL1 will not glow, since there will be zero voltage at the base of VT1. But if a low-power EL1 burns out, then the work of a powerful EL2 will not change from this.

In this scheme, almost all the energy goes into the light sources. The inevitable loss of energy on the transistor, thyristor and bridge diodes is reduced to a minimum.

For this, old germanium diodes with a minimum voltage drop across them are used. Instead, you can use any diodes or diode bridges with an operating current of at least 300 mA. However, with a larger voltage drop across them, the brightness of the lamps will decrease. The glow of the EL1 lamp will also weaken when using another transistor VT1. The thyristor also reduces the current through the powerful EL2 lamp, therefore, at the same power and driving speed, it glows weaker in the circuit. But this can be regarded as an advantage of the circuit, since at high speed an overload of a powerful lamp occurs.

The circuit is easily assembled by surface mounting on the headlight reflector from the outside.

The transistor, thyristor and capacitor are glued to the reflector near the lamp socket, and the resistors and the VD5 diode are soldered between them. If the headlight reflector is conductive, insulating pads are needed under the parts to isolate them from the bike body, to which one of the alternator contacts is connected. The reflector for the other bulb (if it is conductive) must also be insulated from the body of the bike. Usually modern reflectors are plastic, and it is not necessary to insulate them. It is not recommended to apply a positive potential to the bicycle body, as this increases its corrosion.

You can get by with one headlight. Then, after mounting and testing the circuit, the additional lamp is fixed as shown in Fig. 2. The reflector can be plastic or conductive, because the lamps are directly connected to each other according to the scheme. It is convenient to use a low-power lamp 1 with a thinned glass bulb diameter so that the filaments of two lamps 1 and 2 are located as close as possible to each other at the focus 3 of the reflector 4. A powerful lamp 2 is screwed deeper into the socket 5 or the latter is moved away from the focus.

Lamp bulb 1 touches bulb bulb 2.

The cartridge of the second lamp 6 is glued or soldered along the contour of the hole 7 drilled in the reflector. This arrangement of the lamp 1 allows it to be changed. Lamp 2 is easily screwed in and out when lamp 1 is unscrewed. In the headlight, the reflector should be positioned with the drilled hole downwards (as shown in Fig. 2). In this case, the filament of lamp 1 is shifted down from focus 3, and the light flux from it is directed at a slight angle downward relative to the light flux created by lamp 2. As a result, it turns out that from lamp 1 - "dipped beam", and from lamp 2 - "far ".

Author: V.Solonin, Konotop, Ukraine

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