5 V Voltage Regulator: 7805 Reference Guide

The 7805, also known as LM7805, is a 5 V regulator integrated circuit (IC). It is a 3-terminal positive voltage device, which provides a regulated fixed dc output. This component usually has a built-in guard for short-circuit protection, and thermal over-loads. Due to improvements in IC technology, there are variations of this component and consequently it is possible to obtain low-dropout (LDO) versions.

As you can see, it has a simple pinout arrangement where the centre pin is common and connects to ground, whilst the leftmost pin is the input, and the rightmost pin is the output. The capacitor at the input terminal is usually 0.33 µF, whilst the capacitor at the output terminal is 0.1 µF. The quiescent current of a regular 7805 is typically 5.2 mA at 25 °C. The image above shows a rare and original 1980s voltage regulator with gold terminals made by Motorola. High specifications components are usually used in military and spacecraft applications.

Low Dropout

For use with 9 V battery power applications, a high efficiency LDO voltage regulator should be used. The best one that performs a good job is the KA78R05C by Fairchild Semiconductor, which has a dropout voltage below 0.5 V. This is a four-pin device, where the additional pin performs the function of disabling the IC for power conservation. The use of this disable pin is optional.

Applications

• Power supply for Raspberry Pi
• Automotive
• Embeded Computers
• Arduino Power Supply
• Breakout Board Power Supply

7805 Versions

Here is a very small list of the different versions and models that are currently available from different manufacturers. This regulator IC and its capabilities vary between versions and therefore it is better to consult its documentation when using it. Some voltage regulators can provide a maximum output current of 1 A, whilst others can provide 1.5 A. All regulators in the above list are in a TO-220 package and provide a fixed voltage output at 5 V.

Buy

You could get these at RadioShack and many online stores. The cheapest voltage regulators in a standard TO-220 package are usually MC7805CT-BP and MC7805CTG. Both regulators are monolithic ICs designed for fixed voltage regulation, and low dropout. Both versions provide internal current limiting, and thermal overload protection.

If you are a teacher, requiring a large quantity then you most probably want to look for the MC7805CT-BP by Micro Commercial Components, which is selling for a few pence at Farnell. There is also the very cheap MC7805CTG by On Semiconductor, which is is often available online.

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