How to Select a Voltage Regulator

All electronics projects need power. Power can come from either stored energy in a battery, or directly from mains AC voltage or DC power from renewable sources such as solar energy. Power Management ICs (PMICs) help manage the power requirements in a system including scaling voltages, battery charging, and DC-DC conversion. Choosing the right PMIC can make a difference in whether the final product becomes successful or not. An integral part of any PMIC solution is a voltage regulator. Voltage regulators provide a constant output voltage from a higher or lower input voltage. In this blog, let’s look at the variety of voltage regulators, how to choose them, and how Octopart data can help you make the decision to choose the right voltage regulator for your project. This is a follow-up on our series of blogs on how to select a capacitor,resistor, inductor, connector, IC packages and MCUs.
How to Select a Voltage Regulator

Voltage Regulators

Voltage regulators provide a stable DC voltage during operation of a system. Voltage regulators can receive power from either mains AC voltage from wall outlets or from batteries in electronic devices. Batteries discharge almost linearly with time and voltage regulators are needed to maintain stable power supply for electronic systems. This can be seen below:
In addition to powering circuits, a precise DC voltage is often used as a reference to which voltage signals are compared to make decisions. If this reference voltage is not very stable and fluctuates a lot, it affects the decision making of a system. NOTE: Input voltage and supply voltage are sometimes used interchangeably, as voltage regulators use supply voltage as their input.
Let’s dive into some of the most common parameters that are used to choose a voltage regulator. We’ll take Texas Instruments’ TPS76733 as an example to learn about the parameters that drive the decision to choose a particular regulator.

  1. Output voltage:  Output voltage is the constant voltage that you expect the voltage regulator to regulate voltage at. A regulator takes a noisy input and regulates it to a particular voltage, for example, 3.3V.
  2. Accuracy: Accuracy refers to how much the output voltage changes across temperature and load current.
  3. Load current: Load current refers to the maximum output current expected from the voltage regulator by the load system.
  4. Efficiency: The efficiency of a regulator is given by a ratio of output power to input power which is proportional to the ratio of output voltage to input voltage. Dropout voltage of a regulator limits how close the output can be to the input. The lower the dropout voltage, the more efficient the linear regulator will be. Switching regulators have a theoretical hundred percent efficiency, but is in practice limited by the resistance of FET switch, diode voltage drop and ESR of both inductor and output capacitor.
  5. Dropout voltage: Dropout voltage is only applicable for linear regulators. It is the smallest possible difference between output and input supply voltage while remaining in the intended operating range of the voltage regulator. For TPS76733, the dropout voltage is 350 mV. For getting the correct output of 3.3V, input voltage has to be at least 3.65V as can be seen below:
  6. Power Supply Rejection Ratio:  Power Supply Rejection Ratio or PSRR refers to the ratio of change in output voltage to change in input supply voltage. For example, if there is a 1mV ripple in power supply at 1kHz and it translates to output ripple of 1uV, the PSRR is 60dB at 1kHz. As you can see below, higher frequencies have lower PSRR, and thus have a greater chance of getting coupled into the output.
  7. Line regulation:  Line regulation is PSRR at DC or zero frequency. It means that if there is a 1V offset at power supply and if output voltage changes by 1mV, you get a line regulation of 1mV/V. In the plot of dropout region above, it’d be the slope of the output voltage to input voltage in the regulation region.

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