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Recent advances in measurement technology have made it not only possible to measure stability margins, but made it a quick and simple process.
When purchasing a power supply, the knowledgable buyer should specify the gain and phase margins of all feedback loops within a power supply.
Many designers think of control system feedback loop compensation only in terms of stable or unstable. In reality, there is an optimum error amplifier transfer function for any given loop crossover frequency and phase margin.
Military power supplies frequently require conducted susceptibility testing per MIL-STD-461. This paper describes the relationship between open-loop gain of the voltage feedback loop and input filter characteristics.
This paper details the principle of current mode control — a.k.a. the discontinuous mode flyback converter — how it is supposed to work, and what topologies come closest to truly representing the concept.
Parasitic elements do not show up on the schematic or parts list! This paper describes the application of computers to identifying and quantifying these parasitic elements. Actual test data are used.
Integrating a power supply into a new system is often left until late in the design cycle. This paper deals with the problems encountered and how vendors and users can effectively avoid and/or overcome these "last minute" obstacles.
Measurement of loop gain and loop phase shift versus frequency are necessary to determine the phase and gain margins and insure stability of the feedback loop. Measurement requires access to a point that may not exist in many low-cost computer power supplies. This paper presents techniques for overcoming this obstacle and obtaining loop data even where a single signal path is not accessible.
Before switching regulators came into such wide-spread use, oscillation was rarely a problem. Now, as switching regulators become lower in cost and more wide-spread in application, there are many instances where switching regulators serve as both source and load. This paper gives practical suggestions of design and testing criteria to assure stability under all operating conditions.
Power factor correction has become an increasingly necessary feature in new power supply designs. This paper discusses the necessary techniques, equipment, and procedures to perform these tests.
Power factor correction circuits often have two feedback loops. Both loops can have stability problems, and both loops can be tested for stability. This paper describes procedures for testing both loops and gives guidelines and examples for several PFC chips.
Step load testing does not measure critical parameters such as conditional stability. Measuring gain and phase of the feedback versus frequency requires finding a point in the loop to inject a test signal. This article describes this technique and gives examples of how to apply it to various types of integrated circuits.
Feedback loops aren't what they used to be. Here are some practical tips for dealing with the problems presented by modern topologies.
In power supplies with current mode control topology, the current feedback forms an internal digital loop that cannot be directly measured. This paper describes techniques for indirect measurement of the Bode plot of this feedback loop.
Distributed power systems can oscillate, especially when driving one power supply with another power supply. The input and output impedances of a power supply can predict this oscillation. Before looking at the specific details of the oscillation criteria we will review the basics of impedance.
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