Published October 6, 2023
Masashi Nogawa, Sr. Member of Technical Staff, Qorvo
In this article, we’re taking a short break from talking about Power Supply Ripple Rejection (PSRR) to look at another key topic in voltage regulation: output impedance (ZOUT). While PSRR is an important measure of how well a voltage regulator handles noise from the power supply, output impedance tells us how well a regulator can maintain a stable output voltage when the load changes.
Voltage Regulator Basics: A Look Back
In the past, most voltage regulator datasheets focused on two main parameters:
- Line Regulation: How steady the output voltage stays when the input voltage changes.
- Load Regulation: How steady the output voltage stays when the load (current demand) changes.
These are still important, but as electronics have advanced, we’ve learned that other factors, like output impedance, are just as crucial for understanding how a voltage regulator performs.
What is Output Impedance?
Output impedance is a way to measure how much a regulator resists changes in current demand from the load. When a regulator has low output impedance, it can respond quickly and keep the voltage steady, even if the load changes suddenly.
Unlike line or load regulation, output impedance depends on frequency. This means it varies with how fast the current demand changes, making it especially important in systems with high-speed processors or other components that draw power in quick bursts.
Why Output Impedance Matters
- Handles Changing Loads Better:
Many modern electronics don’t draw a constant amount of power. Processors and other devices often switch between low and high power modes. A regulator with low output impedance can keep the voltage steady during these changes. - Reduces Noise and Ripple:
Lower output impedance helps to smooth out unwanted noise and ripple in the power supply, which keeps sensitive circuits running reliably. - Works Well with Capacitors:
Output impedance affects how the regulator works with external components like capacitors, which are used to further stabilize the power supply. A well-designed regulator will have an output impedance that complements these components.
Measuring Output Impedance
To measure output impedance, engineers use tools like network analyzers. These devices apply a small signal to the regulator’s output and measure the resulting voltage and current to calculate ZOUT. The results are often shown in a graph that plots impedance against frequency, giving a clear picture of how the regulator performs.
Read the full article here – Load Regulation ?VOUT/?IOUT and Output Impedance ZOUT | Microwave Journal
Published on Microwave Journal.com
