4–25 An emergency indicator light uses a 10-V, 2-W incandescent lamp. It is to be ON when a digital output is high ð5 VÞ.

The digital circuit does not have sufficient power to turn on the lamp directly. However, as is common practice, a transistor driver is used as a digital switch. Select RB in the circuit of Figure P4–25 so as to drive the transistor into saturation causing it to act as a short circuit between the lamp and ground when the digital output is high. The Thévenin equivalent for the digital circuit is also shown in the figure.

Transcribed Image Text:

VD + +10 V iLamp Lamp 10 V @ 2W RD RB ww www Digital circuit VD=5V = 50 V = 0.7 V RD=500 2 FIGURE P4-25