This powerful step-up/step-down regulator efficiently produces a fixed 9V output from input voltages between 3V and 30V while allowing a typical output current of up to 2A 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.
These step-up/step-down regulators take an input voltage from 3V to 30V and increase or decrease it as necessary to produce a fixed 9V output, 5V, 6V and 12V versions also available. 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 below), but it will be around 2A when the input voltage is close to the output voltage.
The S18V20F9 regulator family consists of the four fixed-output versions mentioned above along with two adjustable-output versions which we also stock. The different versions of the board all look very similar, so the bottom silkscreen includes a blank space where you can add your own distinguishing marks or labels.
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 6V output with fresh alkalines or a 4.0V output with partially discharged NiMH cells, can be used with the 5V version of this regulator to power a 5V circuit.
- A disposable 9V battery powering a 5V circuit can be discharged to under 3V instead of cutting out at 6V, 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 all possible combinations of input and output voltages (e.g. the quiescent current of the 12V version is approximately 4mA with 3V in, 1.5mA with 12V in, and 1mA with 30V in). The ENABLE pin can be used to put the board in a low-power state that reduces the quiescent current to between 10 and 20µA per volt on VIN (e.g. approximately 30µA with 3V in and 500µA with 30V 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 2.5V (typical).
- Input voltage: 2.9V to 32V1
- Fixed 9V output with 4% accuracy
- Typical maximum continuous output current: 2A (when input voltage is close to the output voltage; the Typical Efficiency and Output Current section below 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
1 32 V is the absolute maximum operating voltage; the recommended maximum operating voltage is 30V, 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; higher input voltages can destroy the regulator, so you should ensure that noise on the input is not excessive. 32V should be treated as the absolute maximum input voltage. Our recommended maximum operating voltage is 30V, which is the limit of the reverse voltage protection.
The regulator is enabled by default: a 100kΩ 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 30µA with 3V in and 500µA with 30V 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 labeled 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.
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 graph abive, these switching regulators have an efficiency of 80% to 90% for most combinations of input voltage, output voltage, and load.
Pololu manufacture these boards in-house at their Las Vegas facility, which gives the flexibility to make batches of regulators with customized components to better meet the needs of your project. For example, if you have an application where the input voltage will always be below 20V and efficiency is very important, they can make these regulators a bit more efficient at high loads by replacing the 30V reverse voltage protection MOSFET with a 20V one. They can also customize the set output voltage. If you are interested in customization and want at least a few dozen units, please contact us.
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 graph above show the output current 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.