Practical Electronics for Inventors, Third Edition, 3rd Edition

12.10.2   Using Logic to Drive External Loads

Driving simple loads such as LEDs, relays, buzzers, or any device that assumes either an on or off state is relatively simple. When driving such loads, it is important to first check the driving logic’s current specifications—how much current, say, a gate can sink or source. After that, you determine how much current the device to be driven will require. If the device draws more current than the logic can source or sink, a high-power transistor typically can be used as an output switch. Figure 12.137 shows some sample circuits used to drive various loads.

FIGURE 12.137

In Fig. 12.137a, LEDs can be ...