Designing Embedded Hardware, 2nd Edition

LM78xx Regulators

There are literally thousands of voltage regulators available. Probably the most commonly used are the LM78xx linear regulator series made by several manufacturers such as Fairchild (http://www.fairchildsemi.com), Semelab (http://www.semelab.co.uk), and ST Microelectronics (http://www.st.com). They typically come in a TO-220 package (Figure 5-3) and have a metallic attachment point for a heatsink, such as the one shown in Figure 5-4. The regulator is normally mounted flat against the circuit board, and the pins are bent 90 degrees downward.

The part number designates the output voltage. For example, an LM7805 provides a 5 V regulated output, while an LM7812 gives a regulated 12 V output. They can provide an output current of up to 1 Amp (and as much as 2.2 Amps peak), with a quiescent current of between 5 mA and 8 mA. They also feature overload and short-circuit protection. Table 5-1 lists the regulators, their input voltage ranges and their output voltages.

Figure 5-3. LM78xx

Figure 5-4. Heatsink

Table 5-1. LM78xx voltage regulators

Part	Output (V)	Input range (V)
LM7805	5	7–25
LM7806	6	8–25
LM7808	8	10.5–25
LM7809	9	11.5–25
LM7810	10	12.5–25
LM7812	12	14.5–30
LM7815	15	17.5–30
LM7818	18	21–33
LM7824	24	27–38

The ...