 Pulse width modulation
Before we get to the topic, have you ever heard of the lamp of the lighting controller? Yes, there are, in the strictest engineering terms. Do you still know the lamp pictured above? It is the double filament lamp that has been
used for a long time. Two functions in one glass bulb, one coil with 5W and the other with 21W.
Here you can see how it is switched. In principle there are two connections if we ignore the common ground across the bulb socket. To ensure that they are not mixed up, the small pins on the left and right are at different
heights so that the light bulb can only be used in one position.
The two power levels are assigned to the taillight and brake light, although indicators and rear fog lights also operate at 21W. The former is available in combination, for example on two-wheelers, but the latter is not. Of
course, halogen lamps or conversion to LED are also possible here, whereby even the original socket can be retained.
But this is about a somewhat larger campaign that was introduced at VW, for example, shortly after the turn of the millennium, namely, in principle, abolishing the second coil and supplementing the remaining one, of course
the stronger one, with electronics. So a coil designed for 21 watts should be made to shine as weakly as one with 5 watts.
To say it straight away, a resistor is ruled out because it converts expensive electricity generated by a generator into heat in a rather pointless manner. No, this is where the PulsWidthModulation
comes into play. The prerequisite is that all switches pass on their position to the on-board power supply control unit and the lamp is controlled from there for both functions.
Please note the units on the x-axis and note the speed at which the electricity, 12 volts for cars and 24 volts for trucks, is switched on and off. Here it is a ratio of 50:50, which can be described as a duty factor of 50 percent,
i.e. the percentage of switch-on time to the total duration.
In our case, the desired result is significantly closer to the ratio of 5 to 21 watts in just under a quarter of the time. The result would be the same as if a second, weaker filament were to light up in the glass bulb. And despite
the stronger filament, the energy required is as great as with the smaller one.
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