# Control loop analysis

## Modulation in power converter

Pulse width modulation (PWM), pulse duration modulation (PDM) or frequency modulation are at the heart of almost any switched mode power supply or industrial drive. Analyzing and optimizing the underlying modulation function is important for assessing the function of the control loop. Rohde & Schwarz oscilloscopes feature dedicated analysis functions that are ideal for this task.

## Test solutions for stability analysis

### Converter control supply test

Bode plots are an important tool for verifying control loop stability of switched mode power supplies. Today, this functionality is also provided by oscilloscopes. This application information shows how.

### Tips and tricks on stability testing

This application note describes how to measure the control loop stability of switch-mode power supplies. It explains the main concept and practical applications while guiding the user through the process. The measurement is illustrated with a Rohde and Schwarz buck converter reference board, designed with Texas Instruments.

### Control loop stability

This webinar deals with measuring the control loop stability of switch-mode power supplies. It discusses the main measurement concept, emphasizing the main topics and describing the measurements from a practical point of view. It also presents proper measurement setups and advises on key solution differentiators.

### Practical tips for accurate bode plot measurements

This online guide describes how a bode plot created with an oscilloscope can be used to ensure the stability of a switched-mode power supply. Included is a wealth of practical tips for choosing suitable equipment, setting up measurements, running tests, and interpreting the results.

## Test solutions for modulation analysis

### Analyzing pulse width modulation

The track function of the R&S®RTM3000 and the R&S®RTA4000 oscilloscopes demodulate the PWM signal, extracting the underlying modulation signal in a track waveform. They plot the results of any given value against time, providing a clear view of PWM parameter changes over a relatively long period.

### Case study: Startup analysis

Resonant converters often use a much higher start frequency than the resonant frequency. This limits the resonant current, but also lengthens the startup phase. This application card shows how to analyze the startup phase of a resonant converter using the PWM frequency track function.

Related applications

#### DC/DC converter evaluation

This application note evaluates the main dynamic behaviors of a DC/DC buck converter. The test procedures and measurements described determine whether the converter operates in a safe manner and whether it meets its design goals for startup time, inrush current, peak inductor current, inductor behavior, output ripple and ripple spectrum.

#### Harmonic analysis with R&S®Scope Rider

An ideal electrical supply would deliver a constant frequency, sinusoidal voltage waveform with unvarying magnitude. Real power supplies deviate from this behavior due to varying system loads, transients and outages. Insufficient power quality can lead to failures of machinery, electric control systems or computers connected to the electrical supply network. Power quality measurements characterize the harmonic pollution, reactive power and load imbalance of power supplies.

Related topics

Efficiency testing

EMI debugging and analysis

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