Setting switch and controls illumination, function - GF54.30-P-2010Q

Model 209.3 /4 

Presentation of duty cycle 

Fig 1: Presentation Of Duty Cycle

Courtesy of MERCEDES-BENZ USA

Duty cycle term. 58d 

The lamps of the switch and controls illumination are controlled by a square-wave voltage U 58d (see figure above).

• The lamps are supplied with power during the time t₁ which is then followed by a pause. After the pause the lamps are supplied with power 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 duty cycle (i.e. the longer the power flow duration t₁ ), the greater the average power and therefore the brighter the lamps.

The figure shows the shape U_58d , as applied to the outputs circuit 58d of the various controls units.

The upper curve represents a duty cycle of 80 %, while the lower one represents a duty cycle of 40 %.

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
• Every control unit connected to the interior CAN or engine compartment CAN can actuate lamps with the intensity specified by the instrument cluster (A1).

When the standing lamps are OFF, the instrument cluster (A1) sends the message "circuit 58d duty cycle = 0 %". When the standing lamps are ON, the sent duty cycle can be adjusted from 12 to 100 % using the instrument lighting rheostat and reset button (A1r1).

Function prerequisites: 

The switch and controls illumination is activated by the following components:

• Switching on vehicle lighting (so long as standing lamp is active).
• With automatic driving lights, via the rain/light sensor (B38/2). When the standing lamp is switched on, the overhead control panel control unit (N70) does not use the position of the instrument lighting rheostat and reset button (A1r1) as a controlled variable and the rain/light sensor (B38/2) is ignored.

When automatic driving lights are on, the brightness of the switch and controls illumination is determined via the rain/light sensor (B38/2).

Its signals are evaluated by the overhead control panel control unit (N70) and the brightness is thus regulated via the control unit.