Display Driver
Figure 11.27 shows op-amp circuits
that can be used to drive a lamp display or LED dis- play.
When the noninverting input to the circuit in Fig. 11.27
a goes above the inverting input, the output at terminal 1 goes to the positive saturation level (near 5 V in this example) and the lamp is driven “on” when transistor Q 1 conducts. As shown in the cir- cuit, the output of the op-amp provides 30 mA of current to the base of transistor Q 1 ,