The compact (0.4? × 0.5?) D24V5F5 synchronous buck voltage regulator takes an input voltage of up to 36 V and efficiently reduces it to 5 V while allowing for a maximum output current of 500 mA. This regulator offers typical efficiencies between 85% and 90% and has a very low dropout, so it can be used with input voltages as low as a few hundred millivolts above 5 V. The pins have a 0.1? spacing, making this board compatible with standard solderless breadboards and perfboards.
These buck (step-down) voltage regulators generate lower output voltages from input voltages as high as 42 V. 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.
The regulator has short-circuit protection, and thermal shutdown prevents damage from overheating. The board does not have reverse-voltage protection.
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 20 ?A. The SHDN pin can be driven high (above 2.3 V) 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 3.3 V, the D24VxF5 version outputs 5 V, the D24VxF9 version outputs 9 V, and the D24VxF12 version outputs 12 V.
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 below, this switching regulator typically has an efficiency of 80% to 90%.
Pololu step-down voltage regulator D24VxF5 - efficiency
Note that the above graphs apply to both the 300 mA and 600 mA versions, which is why the x axis extends to 600 mA. 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 5 V regulator has a 1 V dropout voltage, the input must be at least 6 V to ensure the output is the full 5 V. The following graphs show the dropout voltages for the eight D24VxFx regulators as a function of the output current:
Typical dropout voltage of Pololu step-down voltage regulator D24VxF5
As you can see from the last two graphs, the dropout voltage of the low-current 9 V and 12 V versions (D24V3F9 and D24V3F12) spikes as the output current nears the 300 mA limit.
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 42 V. If you are connecting more than 20 V or your power leads or supply has high inductance, we recommend soldering a 33?F 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.
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