TWO STAGE INDICATOR DIMMING CIRCUIT CONTROLLED BY PWM BACKLIGHTING BACK FEED AND BACKLIGHT CONTROL.

摘要

A dimming circuit for an indicator switch has a control input, a dimming state and a non-dimming state. The dimming circuit is responsive to the presence of a backlight PWM signal at the control input of the dimming circuit to switch to the dimming state and responsive to the absence of the backlight PWM signal at the control input of the dimming circuit to switch to the non-dimming state. In the dimming state a high resistance of the dimming circuit is coupled in series with the indicator LED and a LED drive output of the function control module and in the non-dimming state a low resistance of the dimming circuit is coupled in series with the indicator LED and the LED drive output of the function control module. The high resistance has a resistance higher than the low resistance.