BACKGROUND OF THE INVENTION Fig. 1 is a prior art circuit diagram for a lighting system of a motor vehicle. Fig. 1 shows a conventional circuit using a 12 V battery as power supply 1. Lamp 2 represents the load and driver 3 energizes lamp 2. Driver 3 provides current to lamp 2 through transistor TR5. Control 5, resistor R5 controls the current to TR5. This is a typical circuit for illuminating a VF display such as a radio dial. When lamp 8 comprises panel lights in a dashboard, PWM circuitry 7, driving transistor TRe is used to drive load 8. In the prior art circuit, adjusting two output curves to obtain the same illumination on both circuits would not be possible.

DISCLOSURE OF THE INVENTION This invention is an electrical circuit for a motor vehicle to control the illumination level of lighting loads which have different illumination to voltage transfer functions. The circuit claimed will allow the transfer function for the input means to output voltage to be adjusted to compensate for the difference in the transfer functions for each illumination load.

In the circuitry of this invention, a power supply such as a 12 volt battery supplies power to a pre-drive which in turn supplies power to drive which supplies power to a load. A variable DC voltage input

controls the pre-drive through an input resistor. The value chosen for the resistor sets the base current which, along with the emitter resistor, determines the gain of the pre-drive circuitry. The available gain controls the base current into the output driver which, in turn, supplies an output voltage to a load. The shape of the output curve is controlled by the available gain of both the pre-drive and drive circuitry. A second circuit is used with the scheme to power a second load. This illustrates the convenience of independent adjustment of two outputs that originate from a single input. In this case, the two output curves can be adjusted independently according to the characteristics of the individual loads.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a circuit diagram showing for a prior art circuit for a lighting system of a motor vehicle.

Fig. 2 is a block and circuit diagram of the circuit of our invention.

BEST MODE OF CARRYING OUT INVENTION In the circuitry of this invention, Fig. 2 shows a variable DC voltage input 10 controlling a pre-drive section 20 through an input resistor R2. The value chosen for R2, along with R,, determines the gain of the pre-drive circuitry. The available gain controls the base current into the output driver 30 which, in turn, controls an output voltage to the load R4. The shape of the output curve is controlled by the available gain of both the pre-drive 20 and drive 30 circuitry. Ra in the pre-drive circuitry supplies the power from 12 volt battery 1 to pre-driver 20.

PWM circuitry 50 shown illustrates the convenience of independent adjustment of two outputs that originate from a single control input 10.

In this case, the two output curves for load R4 and load R5 can be adjusted independently according to the characteristics of the individual loads.

This output scheme allows for output slope variation which can be utilized to better meet individual customer lighting curve requirements.

The ability to vary the slope also allows for better illumination tracking between two separate sources of illumination, such as incandescent and VF displays. One example of our circuitry's use is using the PWM circuitry to illuminate the panel bulbs in the vehicle and the DC output to provide a voltage to the radio dial. One switch 10 and our circuitry controls both loads. The use of a PNP bipolar transistor as a pre-drive allows for large output slope variability based on the values of resistors R1 and R2 used. This variability can be used to obtain better illumination tracking between the PWM and DC outputs.

The preferred embodiment of this invention is an electrical circuit for a motor vehicle comprising a power supply 1, a load R4 energized by a first amount of power supplied by the power supply, a driver 30 for controlling the amount of power supplied to the load R4, the driver being connected between the power supply and the load, a pre-driver 20 for supply the amount of power supplied to driver 30, pre-driver 20 being connected between the power supply 1 and the driver 30, wherein pre- driver 20 comprises a first resistor R, and a transistor Q1, power supply 1 being connected to first resistor R1, first resistor R1 being connected transistor Q1 and transistor Q1 being connected to driver 30, and a second connection between variable voltage input 10 and the pre-driver 20 for controlling pre-driver 30, wherein the second connection includes a second resistor R2, the second resistor R2 being connected between control 10 and transistor Q1 In the preferred electrical circuit, control 10 is a variable voltage input. Control 10 also could be rheostat switch or a potentiometer.

Driver 30 comprises a transistor Q2, transistor CL, being connected between pre-driver 20 and load R4. Load R4 typically is a VF display.

Second load R5 typically is incandescent bulbs and second driver 50 is

PWM circuitry. PWM circuitry is connected between power supply 1 and load R5. Control 10 is a variable voltage input controller which controls the amount of power the PWM circuitry supplies the incandescent bulbs.

In this example, load R4 has an illumination level and load R5 has a different illuminator level. Control 10 controls pre-driver 20 and PWM circuitry 50. Using this scheme controls the two output curves by independently adjusting the individual loads.