The DC/DC Book Of Knowledge
RECOM´s DC/DC Book of Knowledge is a detailed introduction to the various DC/DC converter topologies, feedback loops (analogue and digital), test and measurement, protection, filtering, safety, reliability, constant current drivers and DC/DC applications. The level is necessarily technical, but readable for engineers, designers and students.
The function of any AC/DC or DC/DC converter module is to meet one or more of the following requirements:
- To match the secondary load to the primary power supply
- To provide isolation between primary and secondary circuits
- To provide protection against the effects of faults, short circuit or over heating
- To simplify compliance with safety, performance or EMC legislation.
Chap. 1: Power Regulation
Modern AC/DC and DC/DC converters are designed to provide efficient power conversion to deliver a controlled, safe and well-regulated DC power supply for a variety of electronic instruments, devices and systems. It's not all too long ago that a transformer, rectifier and linear regulator was the main technology in power conversion, but just as the LED is slowly replacing the light bulb, so is the DC/DC converter gradually edging out the linear regulator and the primary-side switching controller is replacing the simple 50Hz mains transformer.
Chap. 2: Feedback Loops
Some of the most important design criteria in dc/dc power conversion design are the calculations and methodologies involved in the feedback loop compensation. If the feedback loop parameters are not properly calculated, the converter can exhibit instability or regulation failure.The function of a feedback loop in a DC/DC converter is to maintain the output at a fixed value which is dependent on a reference value only – i.e. it is independent of load, input voltage or environmental variations.
Chap. 3: Understanding Datasheet Parameters
Every respectable manufacturer supplies a technical datasheet with their product that details at the very least the basic operating parameters, overall dimensions and pin connections, but to compare one DC/DC converter with another just relying on the datasheet information often requires interpretation rather than just a simple comparison of numbers.
Chap. 4: DC/DC Converter Protection
As mentioned in the Preface, one of the functions of a DC/DC converter is to protect the application. At the most simple level, this protection consists of matching the load to the primary power supply and stabilising the output voltage against input overvoltages and undervoltages, but a DC/DC converter is also a significant element ensuring system fault protection. For example, output overload limiting and short-circuit protection not only stops the converter.
Chap. 5: Input and Output Filtering
All DC/DC converters have an output ripple voltage due to the charging and discharging of the output capacitor with each pulse of energy from the internal oscillator. This output ripple has a frequency of either the same or double the main oscillation frequency, depending on the topology, and is typically in the 100-200kHz region. Superimposed on this ripple voltage are switching voltage spikes with a much higher frequency, typically in the MHz range.
Chap. 6: Safety
The main aims of the various safety standards and regulations are to prevent injury, loss of life or damage to property by defining levels of protection against the following potential dangers: Electric Shock, Hazardous Energy, Fire and Smoke, Physical Injury, Radiation and Chemical Hazards. The terms “danger” and “hazard” are often used interchangeably.
Chap. 7: Reliability
Almost since the advent of electronics, it has been vital for the user to know how long such devices will work properly. Since no one is able to know the future, statistical methods to predict the reliability of components, assemblies or devices have been developed.
Chap. 8: LED Characteristics
The first rule of war is “know your enemy”. It is the same principle with Solid State Lighting (SSL) – if you don’t understand how an LED behaves, don’t be surprised when your application doesn’t succeed. LEDs are non-linear devices. If a low voltage is applied to an LED it does not conduct.
Chap. 9: DC/DC Application Ideas
Many applications require DC/DC conversion. So many, that it is estimated that the world market will exceed 35 billion dollars by 2020. But for many circuit designers, the DC/DC converter is a “black box”; a component to fulfil a function just like other components such as inductors or transistors.
Chap. 10: Magnetics
The 10th chapter covers the fundamentals of inductor and transformer magnetics, including terminology, core saturation, air-gapped inductors, core geometry, core losses, the skin effect and proximity effect. Worked examples of buck and boost DC/DC converter designs show how to correctly dimension the magnetic components and how to calculate the losses in the magnetic core and switching elements.