Pololu Step-Down 9V, 300mA Voltage Regulator D24V3F9

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The compact (0.4″ × 0.5″) D24V3F9 switching step-down (or buck) voltage regulator takes an input voltage between 11V and 42V and efficiently reduces it to 9V while allowing for a maximum output current of 300mA. The pins have a 0.1″ spacing, making this board compatible with standard solderless breadboards and perfboards.


This buck (step-down) voltage regulators generate lower output voltages from input voltages as high as 42V. They are switching regulators (also called switched-mode power supplies (SMPS) or DC-to-DC converters) and have a typical efficiency between 80% to 90%, which is much more efficient than linear voltage regulators, especially when the difference between the input and output voltage is large. This regulator is also available with a fixed 3.3V, 5V, or 12V output, and two versions are available for each voltage, one with a 300mA maximum output current (D24V3Fx) and one with a 600mA maximum output current (D24V6Fx):

The regulator has short-circuit protection, and thermal shutdown prevents damage from overheating. The board does not have reverse-voltage protection.

If you need more output current, consider our D15V35F5S3 and D15V70F5S3 3.3V/5V step-down voltage regulators, which can typically deliver a continuous 3.5 A and 7 A, respectively.


  • Input voltage: [output voltage + dropout voltage] to 42V (see below for more information on dropout voltage)
  • Fixed 9V output with 4% accuracy
  • Maximum output current: 300mA
  • 550kHz switching frequency
  • 2mA typical no-load quiescent current (20 μA typical quiescent current with SHDN = LOW)
  • Integrated over-temperature and over-current shutoff
  • Small size: 0.5″ × 0.4″ × 0.1″ (13 mm × 10 mm × 3 mm)

Using the Regulator


The buck regulator has four connections: shutdown (SHDN), input voltage (VIN), ground (GND), and output voltage (VOUT).

The SHDN pin can be driven low (under 0.3 V) to turn off the output and put the board into a low-power state that typically draws 20μA. The SHDN pin can be driven high (above 2.3V) to enable the board, or it can be connected to VIN or left disconnected if you want to leave the board permanently enabled.

The input voltage, VIN, should exceed VOUT by at least the regulator’s dropout voltage (see below for graphs of dropout voltages as a function of the load), and you must ensure that noise on your input does not exceed the 42 V maximum. Additionally, please be wary of destructive LC spikes (see below for more information).

The output voltage, VOUT, is fixed and depends on the regulator version: the D24VxF3 version outputs 3.3V, the D24VxF5 version outputs 5V, the D24VxF9 version outputs 9V, and the D24VxF12 version outputs 12V.

The four connections are labeled on the back side of the PCB, and they are arranged with a 0.1″ spacing along the edge of the board for compatibility with solderless breadboards, connectors, and other prototyping arrangements that use a 0.1″ grid. You can solder wires directly to the board or solder in either the 4×1 straight male header strip or the 4×1 right-angle male header strip that is included.

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 above, this switching regulator typically has an efficiency of 80% to 90%.

Note that the above graphs apply to both the 300mA and 600mA versions, which is why the x axis extends to 600mA. You should not expect to get more than 300 mA from the 300 mA versions (D24V3Fx).

Typical Dropout Voltage

The dropout voltage of a step-down regulator is the minimum amount by which the input voltage must exceed the regulator’s target output voltage in order to ensure the target output can be achieved. For example, if a 5V regulator has a 1V dropout voltage, the input must be at least 6 V to ensure the output is the full 5V. The graph above shows the dropout voltages as a function of the output current.

LC Voltage Spikes

When connecting voltage to electronic circuits, the initial rush of current can cause voltage spikes that are much higher than the input voltage. If these spikes exceed the regulator’s maximum voltage (42 V), the regulator can be destroyed. In our tests with typical power leads (~30″ test clips), input voltages above 20 V caused spikes over 42V. If you are connecting more than 20 V or your power leads or supply has high inductance, we recommend soldering a 33μF or larger electrolytic capacitor close to the regulator between VIN and GND. The capacitor should be rated for at least 50 V.

More information about LC spikes can be found in our application note, Understanding Destructive LC Voltage Spikes.


Size: 0.4″ × 0.5″ × 0.1″1
Weight: 0.5g1

General specifications

Minimum operating voltage: 10.5V2
Maximum operating voltage: 42V
Maximum output current: 300mA
Output voltage: 9V
Reverse voltage protection?: N
Maximum quiescent current: 2mA3


1 Without included optional headers.
2 For small loads; input voltage must be at least 11V to get 250mA and 12.5V to get the full 300 output.
3 While enabled (SHDN = HIGH) with no load. Current draw is approximately 20 µA when SHDN = LOW.
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