A Quick Guide to Voltage Regulation

Key Takeaways

• Learn the basics and three types of voltage regulation

• How voltage regulation behaves in transmission line systems

• A discussion on voltage regulation technologies, including linear and switching regulators

Power supply units such as these have built-in voltage regulators that are capable of supplying a steady voltage over a range of input voltages and connected loads

Voltage regulation is an incredibly important aspect of electronics and power engineering. Ensuring that the voltage magnitude between the sending and receiving end of a component remains constant is critical for keeping our devices operating as intended. Voltage regulation is the concept of providing a near-constant voltage over a range of load conditions. This can refer to passive properties such as the voltage drop over a transmission or distribution line, or an active intervention through a voltage regulating circuit. We’ll be taking a closer look at voltage regulation over transmission lines and discussing different methods of active voltage regulation.

Quantifying Voltage Regulation

The quality of a system’s voltage regulation capabilities can be defined by three different parameters:

• Line regulation is the system’s ability to maintain a constant output voltage regardless of the input voltage delivered to the regulator. The equation below is the ratio of the change in output over the corresponding change in input. 

• Load regulation is the system's ability to maintain a constant output voltage regardless of the size of the load. Percent voltage load regulation is defined as the ratio of the difference between an unloaded and fully loaded circuit over that of a fully loaded circuit. 

• Temperature dependence is the system’s ability to maintain constant output voltage regardless of temperature variations, which may occur from devices that produce a lot of heat (such as transistors).

Voltage Regulation in Transmission Lines

Real transmission lines have nonzero resistance and nonzero reactance. Therefore, when loaded, the transmission line can act as a voltage divider, leading to some small, albeit non-zero, voltage drops across the line. When loaded with the largest load intended for the circuit, there will be a maximum current through the line, and therefore a maximum voltage drop across the transmission – this is a fully loaded condition. The no-load voltage is measured with the receiving ends of the transmission line in an open circuit configuration.

Higher quality and more reliable transmission lines are closer to ideal lines with small or zero resistance, capacitance, and/or inductance. Depending on the transmission line’s properties, there may be a phase shift or magnitude decrease of the signal as it travels through the transmission line. Take a closer look into transmission line operation and layout for more on transmission line behavior.

Voltage Regulator Circuits

Voltage regulator circuits aim to maintain a fixed output voltage regardless of variations in the input voltage or load conditions. Generally, voltage regulators are connected to power supplies that may have variations in output voltage. More sensitive components such as microprocessors, digital components, or other loads are connected to the output of the regulator and can depend on it to supply a fixed voltage.

Voltage regulators are most commonly used for DC-to-DC conversion, but some are also capable of AC-to-AC conversion or AC-to-DC conversion. The two main types of voltage regulator topologies are linear and switching.

• Linear regulators operate with generally lower efficiency, with excess input power being converted to heat.
• Switching regulators operate with higher efficiency but require more complex components. 

Linear Regulators

Linear regulators use an active pass device such as a MOSFET or BJT that is controlled by a high-gain amplifier. To keep the output voltage constant, the linear regulator controls the pass device’s resistance by comparing an internal voltage with a sample of the output voltage. The error-correcting feedback loop controls the pass element to drive this difference to zero. Linear regulators will always step down the voltage so the output voltage will always be below that of the input voltage. Linear regulators are often easier to design, more cost-efficient, and offer low output noise. They generally also require the addition of a few external components, oftentimes just a capacitor.  

Switching Regulators

Switching regulators are generally more complex but offer higher efficiency. They require selecting specific external component values such as inductors, caps, feedback resistors or FETs, and have tunable loops for stability. Switching regulators can act as step-down converters or step-up converters – or even both. These regulators are more efficient and can handle a wider range of currents and voltages.

Types of switching regulators include step-down or step-up converters. Step-down converters take a large input voltage and maintain a small steady output voltage. Boost converters that step-up take a lower input voltage and create a higher output voltage. A buck-boost converter combines both of these aforementioned types and provides an output voltage of a range of input voltages that can either be greater or less than the output.

Cadence offers a suite of PCB design and analysis tools that can support your voltage regulation efforts. Leading electronics providers rely on Cadence products to optimize power, space, and energy needs for a wide variety of market applications. To learn more about our innovative solutions, talk to our team of experts or subscribe to our YouTube channel.