This powerful step-up/step-down regulator efficiently produces an adjustable 4 V to 12 V output from input voltages between 3 V and 30 V while allowing a typical output current of up to 2 A when the input voltage is close to the output voltage and offering typical efficiencies of 80% to 90%. Its ability to convert both higher and lower input voltages makes it useful for applications where the power supply voltage can vary greatly, as with batteries that start above but discharge below the regulated voltage.
They are switching regulators (also called switched-mode power supplies (SMPS) or DC-to-DC converters) with a single-ended primary-inductor converter (SEPIC) topology, and they have a typical efficiency between 80% and 90%. The available output current is a function of the input voltage, output voltage, and efficiency (see the Typical Efficiency and Output Current section in the resources tab), but it will be around 2A when the input voltage is close to the output voltage.
The flexibility in input voltage offered by these regulators is especially well-suited for battery-powered applications in which the battery voltage begins above the desired output voltage and drops below the target as the battery discharges. Without the typical restriction on the battery voltage staying above the required voltage throughout its life, new battery packs and form factors can be considered. For example:
- A 4-cell battery holder, which might have a 6 V output with fresh alkalines or a 4.0 V output with partially discharged NiMH cells, can be used with the 5V version of this regulator to power a 5 V circuit.
- A disposable 9 V battery powering a 5V circuit can be discharged to under 3 V instead of cutting out at 6 V, as with typical linear or step-down regulators.
- The 6V version of this regulator can be used to enable a wide range of power supply options for a hobby servo project.
The no-load quiescent will typically be between 1mA and 5mA for most combinations of input and output voltages, though the combination of a very high output voltage and a very low input voltage (e.g. when boosting from 3V in to 24V out) can result in quiescent currents on the order of a few dozen milliamps.
The ENABLE pin can be used to put the board in a low-power state that reduces the quiescent current to between 10 and 20 µA per volt on VIN (e.g. approximately 30 µA with 3 V in and 500 µA with 30 V in).
This regulator has built-in reverse-voltage protection, over-current protection, thermal shutdown (which typically activates at 165°C), and an under-voltage lockout that causes the regulator to turn off when the input voltage is below 2.5 V (typical).
For similarly powerful boost-only regulators, consider the U3V50ALV regulator, which are typically more appropriate if you know that your input voltage will always be lower than your output voltage.
- Input voltage: 2.9 V to 32 V
- Output adjustable from 4V to 12V
- Typical maximum continuous output current: 2A (when input voltage is close to the output voltage; the Typical Efficiency and Output Current section in the resources tab shows how the achievable continuous output current depends on input and output voltages)
- Integrated reverse-voltage protection (up to 30V), over-current protection, over-temperature shutoff, and under-voltage lockout
- Typical efficiency of 80% to 90%, depending on input voltage, output voltage, and load
- Four mounting holes for #2 or M2 screws
- Compact size: 1.7″ × 0.825″ × 0.41″ (48 × 15 × 10.5 mm)
- Smaller holes for 0.1″ header pins and larger holes for terminal blocks offer several options for connecting to the board
32 V is the absolute maximum operating voltage; the recommended maximum operating voltage is 30 V, which is the limit of the reverse voltage protection.
Using the regulator
This step-up/step-down regulator has four connections: input voltage (VIN), ground (GND), and output voltage (VOUT), and ENABLE.
The input voltage, VIN, should be between 2.9 V and 32 V. Lower input voltages can cause the regulator to shut down or behave erratically; , so you should ensure that noise on the input is not excessive. 32 V should be treated as the absolute maximum input voltage. Our recommended maximum operating voltage is 30 V, which is the limit of the reverse voltage protection. Additionally, we recommend keeping the sum of the input and output voltages below 55 V; see the Setting the Output Voltage section below for more information.
The regulator is enabled by default: a 100 kΩ pull-up resistor on the board connects the ENABLE pin to reverse-protected VIN. The ENABLE pin can be driven low (under 0.7 V) to put the board into a low-power state. The quiescent current draw in this sleep mode is dominated by the current in the pull-up resistor from ENABLE to VIN and by the reverse-voltage protection circuit, which will draw between 10 µA and 20 µA per volt on VIN when ENABLE is held low (e.g. approximately 30 µA with 3 V in and 500 µA with 30 V in). If you do not need this feature, you should leave the ENABLE pin disconnected. Note that the SEPIC topology has an inherent capacitor from input to output; therefore, the output is not completely disconnected from the input even when the regulator is shut down.
The connections are labelled on the back side of the PCB, and the board offers several options for making electrical connections. You can solder the included 2-pin 5mm-pitch terminal blocks to the two pairs of larger holes on the ends of the board. Alternatively, if you want to use this regulator with a solderless breadboard, 0.1″-pitch connectors, or other prototyping arrangements that use a 0.1″grid, you can solder pieces of the included 9×1 straight male header strip to the 0.1″-spaced smaller holes (each large through-hole has a corresponding pair of these smaller holes). For the most compact installation, you can solder wires directly to the board.
The board has four mounting holes intended for #2 or M2 screws. In applications where mounting screws are not used and wires are soldered directly to the board, the insulated part of the wires can be passed through the mounting holes for strain relief. The picture above shows an example of this with 20 AWG wire, which was close to the limit of what would fit through the mounting holes.
Setting the output voltage
The output voltage can be adjusted using a multimeter and a light load (e.g. a 10 kΩ to 100 kΩ resistor). Turning the potentiometer clockwise increases the output voltage. The output voltage can be affected by a screwdriver touching the potentiometer, so the output measurement should be done with nothing touching the potentiometer (also, note that touching parts of the board with your finger can affect the output voltage). The following graph shows the approximate output voltage as a function of the potentiometer position:
Output voltage settings for Pololu adjustable step-up/step-down voltage regulators S18V20ALV (blue line) and S18V20AHV (red line).
Note: We recommend against using this regulator in situations where the sum of the input and output voltages exceeds 55 V. For example, if your input voltage could reach 30 V, you should keep the output voltage setting under 25 V. It is typically not very practical to use the AHV version of this regulator beyond about 24 V out
The trimmer potentiometer is not rated for continual adjustment back and forth; the intended application is to set the output voltage a few times in its life.
Typical efficiency and output current
The efficiency of a voltage regulator, defined as (Power out)/(Power in), is an important measure of its performance, especially when battery life or heat are concerns. As shown in the graphs below, these switching regulators have an efficiency of 80% to 90% for most combinations of input voltage, output voltage, and load.
S18V20ALV (4-12 V) efficiencies for various combinations of VIN and VOUT:
The maximum achievable output current of the board varies with the input voltage but also depends on other factors, including the ambient temperature, air flow, and heat sinking. The graphs below show output currents at which this voltage regulator’s over-temperature protection typically kicks in after a few seconds. These currents represent the limit of the regulator’s capability and cannot be sustained for long periods, so the continuous currents that the regulator can provide are typically several hundred milliamps lower.
During normal operation, this product can get hot enough to burn you. Take care when handling this product or other components connected to it.