Dimmer Switch: Description and Operation

GF54.30-P-2010S Setting Switch And Controls Illumination, Function







The brightness of the switch and controls illumination can be adjusted using the instrument, switch and controls illumination dimmer (A1r1) of the instrument cluster (A1). Control is adjusted based on the pulse-duty factor at "Terminal 58d".

Signal flow:
- If the standing lamps are switched on, the left front SAM control unit (N10/6) relays the message "standing lamps ON" on the interior compartment CAN.
- The instrument cluster (A1) receives this message and relays the message "duty cycle term. 58d" on both the interior compartment CAN and on the engine compartment CAN.
- Various control units receive this message and supply the lamps of the switch and controls illumination with the square-wave voltage U58d.







Pulse-duty factor Terminal 58d
The lamps of the switch and controls illuminations are supplied with a square-wave voltage U58d:
- The lamps are energized during the time (t1) which is then followed by a pause. After the pause the lamps are energized again and so on. The change occurs so quickly as to remain imperceptible to the human eye.
- The ratio of times t1 to T is called the duty cycle, where T is the constant cycle duration and t1 is the time during which power flows during a cycle.
- The higher the on/off ratio (i.e. the longer the power flow duration t1)), the greater the average power and therefore the brighter the lamps.

The diagram shows the voltage characteristic U58d as applied to the outputs "term. 58d" of the various control units. The upper and lower diagrams illustrate a duty cycle of 80% and 40%, respectively.

A duty cycle of 100% corresponds to normal direct voltage. Power is not supplied when the duty cycle is 0%.

Advantages of this type of brightness adjustment:
- Considerably more efficient
- The brightness of the lamps remains independent of the number of lamps
- Each control unit that is connected to the interior compartment CAN or engine compartment CAN can actuate the lamps with the brightness specified by the instrument cluster (A1).

When the standing lamps are OFF, the instrument cluster (A1) sends the message "duty cycle, term. 58d=0%".

When the standing lamps are ON, the sent duty cycle can be adjusted from 12 - 100% using the instrument, switch and controls illumination dimmer (A1r1).