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Table of Contents
Voltage regulators are used for turning input voltage to the desired output voltage to run a circuit off of.
Different types include:
- linear 'dropout' regulators: also called LDO regulators, these take a high voltage and create a 'dropout' to set the output to be some lower voltage. For example, 9V down to 5V the regulator creates a 4V drop. That drop is dissipated as heat. They are low cost, have varying input/output and dropout voltages as well as max current capability.
- switching regulators
- DC/DC converters
Linear 'dropout' regulators
78xx, 79xx
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 2-3V higher. 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.
- Pinout: Input - Ground - Output. Tab is connected to ground
- Output voltages 7805 → 5V, 7806 → 6V, 7809 → 9V, 7812 → 12V, 7815 → 15V
- Dropout: ~2V
- Input voltage: at least 3V higher than output voltages, max 17V to 30V.
- Current: max 1A (assuming that the power dissipation isnt too high for the package)
Variants:
- 78Lxx, 79Lxx: (the middle character is an 'L') max 100mA
- 78Mxx, 79Mxx: max 500mA
- 78Sxx, 79Sxx: max 2A
The following table has links for 7805 only, since those are the most popular!
LM2931-XX series
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. |
'1117-XX series
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!
- Output voltages: 1117-1.5→ 1.5v, 1117→1.8 → 1.8V, 1117-3.3 → 3.3v, 1117→5.0 → 5.0v, 1117 → adjustable!
- Dropout: ~1.0 V
- Input voltage: 1V above output voltage, up to 15V
- Current: 800mA (assuming that the power dissipation isnt too high for the package)
The following table has links for the 1117-3.3 and 5.0 only, since those are the most popular. 1117 Datasheet
LM317, LM337
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.
- Output voltage: min 1.5V, max 37V
- Input voltage: ???
- Current: max 1.5A
- Variants: LM350 - max 3A, LM338 - max 5A
Others
| 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 |
Switching regulators
| 7660 | 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. |
DC/DC converters
| 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 |
