duty cycle of 50 in the prior art example the drain voltage vd is maintained at ten volts independent of the gate voltage which varies alternately u2014 zero or ten volts with some finite rise and fall rate in the present invention the drain voltage vd is raised to ten volts when the gate voltage is raised to ten volts and the drain voltage is dropped to zero volts when the gate voltage is dropped to zero volts thus there is less u201c wear u201d on the drive tft 22 because there is less often a voltage differential between the gate voltage i e voltage between the gate and the source and the drain voltage i e voltage between the drain and the source this extends the life of the driving tft 22 to twice or longer than in the prior art where there are more often such voltage differential 0020 fig5 illustrates the variation of vth over time of the driving tft 22 at thirty five degrees celsius according to the prior art triangles and according to the present invention gray hashed circles black circules and diamonds the vertical axis indicates the variation in the threshold voltage vth and the horizontal axis indicates the operating time in hours in the illustrated example the gate voltage and the drain voltage are changed at a duty cycle of 50 in the prior art the drain voltage vd is maintained at ten volts independent of the gate voltage which varies alternately u2014 zero or ten volts in one example of the present invention indicated by the gray hashed circles the drain.