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Pololu 3.3V 500mA Step-Down Voltage Regulator D24V5F3

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The compact 10 x 12.7mm (0.4″ × 0.5″) D24V5F1 synchronous buck voltage regulator takes input voltages up to 36V and efficiently reduces them to 3.3V while allowing for a maximum output current of 500mA. This regulator offers typical efficiencies between 75% and 90%. The pins have a 0.1″ spacing, making this board compatible with standard solderless breadboards and perfboards.


The D24V5Fx family of buck (step-down) voltage regulators generates lower output voltages from input voltages as high as 36V. They are switching regulators (also called switched-mode power supplies (SMPS) or DC-to-DC converters) and have a typical efficiency between 80% to 93%, which is much more efficient than linear voltage regulators, especially when the difference between the input and output voltage is large. These regulators have a power-save mode that activates at light loads and a low quiescent (no load) current draw, which make them well suited for low-power applications that are run from a battery. These regulators are available in eight different fixed output voltages:

The different versions of this regulator all look very similar, so the bottom silkscreen includes a blank space where you can add your own distinguishing marks or labels. This product page applies to all eight versions of the D24V5Fx family.

The regulators feature short-circuit/over-current protection, and thermal shutdown helps prevent damage from overheating. The boards do not have reverse-voltage protection.


  • Input voltage:
    • 3V to 36V for output voltages of 1.8V and 2.5V
    • [output voltage + dropout voltage] to 36V for output voltages of 3.3V and higher (see below for more information on dropout voltage)
  • Fixed 1.8V, 2.5V, 3.3V, 5V, 6V, 9V, 12V, or 15V output (depending on regulator version) with 4% accuracy
  • Maximum output current: 500mA
  • Typical efficiency of 80% to 93%
  • 500kHz switching frequency (when not in power-save mode)
  • 200μA typical no-load quiescent current
  • 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 0.4 V) to turn off the output and put the board into a low-power state. There is a 100kΩ pull-up resistor between the SHDN pin and VIN, so if you want to leave the board permanently enabled, the SHDN pin can be left disconnected. While the SHDN pin is being driven low, the current draw of the regulator is dominated by the current through the pull-up resistor and will be proportional to the input voltage. (At 36V in it will draw about 360μA.)

The input voltage, VIN, powers the regulator. Voltages between 3V and 36V can be applied to VIN, but for versions of the regulator that have an output voltage higher than 3V, the effective lower limit of VIN is VOUT plus the regulator’s dropout voltage, which varies approximately linearly with the load (see below for graphs of dropout voltages as a function of the load). 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 D24V5F1 version outputs 1.5V, D24V5F2 version outputs 2.5V, the D24V5F3 version outputs 3.3V, the D24V5F5 version outputs 5V, the D24V5F6 version outputs 6V, the D24V5F9 version outputs 9V, the D24V5F12 version outputs 12V, and the D24V5F15 version outputs 15V

The four connections are labeled on the back side of the PCB and 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. This family of switching regulators typically has an efficiency of 80% to 95%, though the actual efficiency in a given system depends on input voltage, output voltage, and output current. See the efficiency graph in the above thumbnail near the top of this page for more information.

In order to achieve a high efficiency at low loads, this regulator automatically goes into a power-save mode where the switching frequency is reduced. In power-save mode, the switching frequency of the regulator changes as necessary to minimize power loss. This could make it harder to filter out noise on the output caused by switching.

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 6V to ensure the output is the full 5V. Generally speaking, the dropout voltage increases as the output current increases. See the “Details” section below for more information on the dropout voltage for this specific regulator version.

The graph above shows the typical efficiency of this regulator 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 (36V), the regulator can be destroyed. In Pololu tests with typical power leads (~30″ test clips), input voltages above 20V caused spikes over 36V.

If you are connecting more than 20V 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 50V.

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

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