Voltage regulators are used for providing a stable supply voltage, free of noise and AC ripple, to power a circuit.
Different types include:
The simplest and best known regulators are the 78xx and 79xx series, where xx is the desired output voltage. They have three pins: input, output and ground. 7805 will get you 5V on the output pin, as long as you supply an input voltage of at least 2-3V more. 79xx Series are for negative output voltages, but they work the same. These "building blocks" are great for making a simple and stable power supply.
Important: always place a 100nF capacitor between the output pin and the ground pin. Otherwise the regulator could start oscillating.
Variants:
The following table has links for 7805 only, since those are the most popular!
The LM2931T (TO-220 high current) and LM2931Z (TO-92 low current) LDOs are 78XX pin-compatible, and available in 5V, 3.3V, or adjustable voltages. Much lower drop-out voltage than 7805, much higher input voltage limit, with built-in battery reversal protection and over-voltage protection. Nice when you want an 78xx upgrade!
Image | Part # & Datasheet | Description | Package notes | Distributor |
---|---|---|---|---|
LM2931 | . | Packaged in SOP-8, TO-92 or TO-220. | Widely avaiable from many suppliers and manufacturers. |
The 1117 series regulators are similar to the 7805 series, but have a lower dropout. The pinout is NOT the same, they are NOT drop-in replaceable!
The following table has links for the 1117-3.3 and 5.0 only, since those are the most popular. 1117 Datasheet
Basically the same as the 78xx regulator, but adjustable. It also has three pins: input, output, adjust. A voltage divider (2 resistors) is connected to the output pin and ground to create a reference voltage. This reference voltage is connected to the adjust pin. The regulator will adjust the output voltage, until the reference voltage is 1.25V. By altering one of the resistors of the voltage divider, you can adjust the output voltage.
Image | Package | Part # | Vout @ Iout | Distributors | Eagle library part |
---|---|---|---|---|---|
TO-92 | MCP1700-330 | 3.3V @ 250mA The highest current output we could find in a TO-92 pkg | Mouser | adafruit:MCP1700 |
The 7660 is a voltage converter capable of converting a positive voltage in the range of +1.5V to +10V to a negative voltage of −1.5V to −10V
Image | Part # & Datasheet | Description | Package notes | Distributor |
---|---|---|---|---|
. | LCM7660 | Charge pump based step-up/voltage inverting chip. Provides a low-current voltage at either -Vin or 2Vin, using only capacitors. Suitable for providing a negative rail for low-power op-amp circuits, or a low-current stepped-up supply for programming voltages on flash-based microcontrollers. | Available in MSOP-8, PDIP-8, SOP-8. | Widely available from many suppliers and manufacturers. |
Image | Package | Part # | Distributors | Eagle library part |
---|---|---|---|---|
MAX756-CPA | DC/DC Boost 3.3V or 5V or adj out | Digikey Mouser Maxim Direct | adafruit:MAX756 | |
" | LT1302(CN8-5) | DC/DC boost In 3V, 5V or adjustable | Newark Linear Direct | adafruit:LT1302 |