The LM7805 is a popular voltage regulator integrated circuit that provides a stable 5 volts output voltage from an input voltage source that can be higher than 5 volts. It is part of the 78xx series of voltage regulators produced by various manufacturers.
Schematic
The manufacturer advises incorporating capacitors both on the input and output sides of the voltage regulator.
From the Datasheet
Components in the circuit:
D1: Schottky diode, used as Protection diode.
This will help protect the circuit if we connect the power supply the wrong way.
C1: The input capacitor (Electrolytic type) is particularly crucial when the regulator is situated far from the power supply filter. This capacitor serves to stabilize the input voltage by mitigating any fluctuations or noise present in the supply
C2: This is a bypass capacitor (Ceramic type) located in parallel to C1 on the input side.
This will be a small ceramic capacitor which is typically 0.1uF. The purpose of this capacitor is to filter out the noise and high frequency distortions from the power supply. As we might not always get a perfectly flat DC supply.
C3/C4: These are going to help ensure we have a clean output on our connected circuit.
J1/J2: Terminal blocks to connect the wires.
PCB Layout
3D Model
When planning a circuit using the LM7805 voltage regulator, there are several special considerations to keep in mind to ensure proper operation and reliability:
- Input Voltage: The LM7805 requires an input voltage higher than the desired output voltage. Ensure that the input voltage falls within the specified range for the LM7805 variant you are using. Typically, it should be at least a few volts higher than the desired output voltage (e.g., 7-35V depending on the specific variant).
- Input Capacitor: To ensure stability and reduce input voltage fluctuations, it’s recommended to include a capacitor (typically electrolytic/ceramic) on the input side of the regulator. The datasheet usually specifies the minimum required capacitance and the type of capacitor.
- Output Capacitor: Similarly, a capacitor (typically ceramic or tantalum) should be connected on the output side of the regulator to improve transient response and stability. Again, the datasheet provides guidance on the required capacitance.
- Heat Dissipation: The LM7805 may dissipate significant power, especially when dropping a high input voltage to 5 volts at high currents. To prevent overheating, it’s advisable to mount the LM7805 on a heat sink if the power dissipation is substantial. The datasheet provides thermal resistance values to help calculate the required heat sink size.
- Output Current: The LM7805 is available in various current ratings. Ensure that the chosen variant can supply the required output current for your application without exceeding its maximum rating. If the required current is too high, consider using a different voltage regulator with a higher current rating or using additional regulators in parallel.
- Bypass Capacitor: To further improve stability and transient response, a small ceramic capacitor (typically in the range of 0.1µF to 1µF) should be connected between the regulator’s input and ground pins and between the output and ground pins.
- Input Protection: Depending on the application, it may be necessary to include input protection circuitry such as a reverse polarity protection diode or a transient voltage suppressor (TVS) to protect the regulator from voltage spikes or reverse polarity connections.
- Load Regulation: Consider the load regulation requirements of your application, which refer to how well the regulator maintains a stable output voltage under varying load conditions. The LM7805 typically has good load regulation characteristics, but it’s essential to ensure that it meets the requirements of your specific application.
By considering these factors and following the guidelines provided in the LM7805 datasheet, you can design a reliable and efficient circuit using this voltage regulator.