Application examples for voltage regulators

Integrated fixed voltage regulator (78xx / 79xx)

For applications with constant voltage stabilization and low and stable current consumption, a simple circuit with a series resistor and Z-diode is sufficient. However, if larger currents, more precise and more stable voltage values ​​are required, integrated fixed voltage regulators are used. They consist of various stabilization circuits and several amplifier stages. In addition, they have an internal current limiter, which is triggered in the event of an overload or short circuit. In the event of a short circuit, the fixed voltage regulator automatically reduces its output voltage. If the short circuit is removed, the output voltage stabilizes again at its fixed value. A thermal protection circuit prevents the IC from being destroyed by overheating.

78xx / 79xx series

The best known fixed voltage regulators are the 78xx series for positive and the 79xx series for negative voltages. The output voltages of this series can be 5, 6, 8, 9, 12, 15, 18 or 24 V. In order for the voltage regulator to work, the input voltage must be at least 2 to 3 V above the output voltage. The input voltage for these controllers should not be more than 36 V. The difference between the input voltage and the output voltage should not be much higher than 3 V, otherwise the power loss on the fixed voltage regulator is too great. The power loss is noticeable as the development of heat. This requires cooling through a cooling plate.

Type description

The table shows the current consumption when cooling with a cooling plate or heat sink. If no cooling is possible, only about half of the current consumption is possible (rather less) without destroying the fixed voltage regulator through overheating.
The xx denotes the value of the output voltage in two numbers. So 05 would be 5 V. 12 would be 12 V.

descriptionCurrent consumption when cooling
78Lxx0.1 A
78Mxx0.5 A
78xx1 A
78Sxx2 A
78Txx3 A
78Hxx5 A

Pin assignment



The only necessary circuitry for the fixed voltage regulator is two capacitors. They should be connected to the fixed voltage regulator over a short distance at the input and output.
The rectifier circuit is located in front of this circuit. After the circuit is the rest of the circuit or the consumer.


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