Positive Voltage Regulator 18V-7818

The 7818 is a widely used voltage regulator that provides a fixed positive output voltage of +18V. It is part of the 78XX series of voltage regulators, which are designed for easy implementation in various electronic circuits to provide a stable output voltage.

Key Features

• Fixed Output Voltage: Provides a regulated output voltage of +18V.
• Input Voltage Range: The maximum input voltage is typically +35V, but for optimal performance and to avoid thermal overload, it is advisable to keep the input voltage to around +20V-25V.
• Output Current: Capable of supplying output currents up to 1A, depending on input-output voltage difference and thermal conditions.
• Thermal Protection: Includes built-in thermal overload protection, which shuts down the output if the device overheats.
• Short Circuit Protection: The regulator can protect itself if the output is short-circuited.
• Low Dropout Voltage: Good performance even with a lower voltage differential between input and output.

Pin Configuration

The 7818 voltage regulator is typically housed in a TO-220 or TO-3 package. Here’s a typical pin configuration for the TO-220 package:

Copy       +-----------+
    1  | Input     |  3
    2  | Ground    |  2
    3  | Output    |  1
       +-----------+

Pin Description

1. Input (Pin 1): This pin receives the input voltage. It should be greater than +18V and can typically handle input voltages up to +35V.
2. Ground (Pin 2): This pin is connected to the ground of the circuit.
3. Output (Pin 3): This pin provides the regulated output voltage of +18V.

Basic Operation

The 7818 voltage regulator works by taking a higher input voltage and regulating it down to a fixed output voltage. Here’s a simplified operation:

1. Input Voltage: Connect a voltage source of at least +20V to the Input pin (but not above +35V).
2. Regulation: Internally, the regulator uses feedback to adjust its output to maintain a steady 18V output despite variations in input voltage or load conditions.
3. Output Voltage: The regulated +18V output will be available at the Output pin, delivered to the load.

Typical Application Circuit

An example application circuit for the 7818 regulator is shown below:

Copy    +Vin       +------+
    (+20V to 35V)    |
        |             |
        |    +-----+  |
        +----| 7818 |---- +Vout (+18V)
        |    +-----+  |
        |             |
       GND          GND

Capacitor Recommendations

To stabilize the output and improve transient response, it is generally recommended to use output and input capacitors:

• Input Capacitor (C1): Typically a 0.33 µF capacitor should be connected between the input pin and ground to filter out noise from the input voltage.
• Output Capacitor (C2): A 0.1 µF capacitor is generally used between the output pin and ground to improve the transient response and overall stability.

Applications

The 7818 voltage regulator can be used in:

• Power supply circuits for powering various electronic devices.
• Audio amplifiers and processors.
• Microcontroller and microprocessor power supplies.
• General-purpose power supply applications in hobbyist and industrial projects.

Advantages

• Ease of Use: Simple to implement with minimal external components required.
• Reliability: The built-in protection features enhance reliability and longevity.
• Cost-Effective: Widely available and usually inexpensive.

Considerations

1. Heat Dissipation: The 7818 can generate heat depending on the input-output voltage difference and load current. Adequate heatsinking may be required to prevent thermal shutdown.
2. Input Voltage Limitations: Do not exceed the maximum input voltage to avoid damaging the regulator.