L7818CV-DG

Description

The L78 series of three-terminal positive regulators is available in TO-220, TO-220FP,D²PAK and DPAK packages and several fixed output voltages, making it useful in a wide range of applications.

These regulators can provide local on-card regulation, eliminating the distribution problems associated with single point regulation. Each type embeds internal current limiting, thermal shutdown and safe area protection, making it essentially indestructible. If adequate heat sinking is provided, they can deliver over 1 A output current. Although designed primarily as fixed voltage regulators, these devices can be used with external components to obtain adjustable voltage and currents.

Features

   1. Output current up to 1.5 A

   2. Output voltages of 5; 6; 8; 8.5; 9; 12; 15; 18;24 V

   3. Thermal overload protection

   4. Short circuit protection

   5. Output transition SOA protection

   6. 2 % output voltage tolerance (A version)

   7. Guaranteed in extended temperature range (A version) 

Application information

1 Design consideration

The L78 Series of fixed voltage regulators are designed with thermal overload protection that shuts down the circuit when subjected to an excessive power overload condition,internal short-circuit protection that limits the maximum current the circuit will pass, and output transistor safe-area compensation that reduces the output short-circuit current as the voltage across the pass transistor is increased. In many low current applications,compensation capacitors are not required. However, it is recommended that the regulator input be bypassed with capacitor if the regulator is connected to the power supply filter with long lengths, or if the output load capacitance is large. An input bypass capacitor should be selected to provide good high frequency characteristics to insure stable operation under all load conditions. A 0.33 µF or larger tantalum, mylar or other capacitor having low internal impedance at high frequencies should be chosen. The bypass capacitor should be mounted with the shortest possible leads directly across the regulators input terminals.

Normally good construction techniques should be used to minimize ground loops and lead resistance drops since the regulator has no external sense lead.

The addition of an operational amplifier allows adjustment to higher or intermediate values while retaining regulation characteristics. The minimum voltage obtained with the arrangement is 2 V greater than the regulator voltage.

Fixed output regulator

1. Although no output capacitor is need for stability, it does improve transient response.

2. Required if regulator is located an appreciable distance from power supply filter.

Block diagram

Pin connections (top view)