Question

Describe the functional pin diagram of regulator IC 78XX and 79XX.

Answer 1

IC 78XX:

Explanation: 78XX series of IC regulators is representative of three terminal devices that are available with several fixed positive output voltages. It has three terminals labeled as input, output and ground. The last two digits (mark XX) in the part no. designate the input voltage. Above fig. shows a standard configuration of a fixed positive voltage IC regulator of 78XX series. The capacitor C1 is required only if the power supply filter is located more than three inches from the IC regulator. The capacitor C0 acts basically as a line filter to improve transient response.

IC 79XX: 

Explanation: 79xx series of voltage regulators are the commonly used negative voltage regulators. These are three terminal regulators and is available with fixed output voltages of -5V, -12V and -15V. These ICs have internal current limiting protection and thermal shut down protection to protect the ICs from overload conditions. IC 79xx is used in circuits as shown in the circuit. In order to improve stability two capacitors – C1 and C2 are used. The capacitor C1 is used only if the regulator is separated from filter capacitor by more than 3". It must be a 2.2 μF solid tantalum capacitor or 25μF aluminum electrolytic capacitor. The capacitor C2 is required for stability. Usually 1 μF solid tantalum capacitor is used. One can also use 25μF aluminum electrolytic capacitor. Values given may be increased without limit. Usually 1 μF solid tantalum capacitor is used. One can also use 25μF aluminum electrolytic capacitor. Values given may be increased without limit.