From The Circuit Designer's Companion, Second Edition

The power supply is a vital but often neglected part of any electronic product. It is the interface between the noisy, variable and ill-defined power source from the outside world and the hopefully clear-cut requirements of the internal circuitry. For the purposes of this discussion it is assumed that power is taken from the conventional ac mains supply. Other supply options are possible, for instance a low-voltage dc bus, or the standard aircraft supply of 400Hz 48V. Batteries we shall discuss separately at the end of this chapter.

7.1 General

A conceptual block diagram for the two common types of power supply linear and switch-mode is given in Figure 7.1.

Figure 7.1: Power supply block diagrams

7.1.1 The linear supply

The component blocks of a linear supply are common to all variants, and can be described as follows:

  • input circuit: conditions the input power and protects the unit, typically voltage selector, fuse, on-off switching, filter and transient suppressor

  • transformer: isolates the output circuitry from the ac input, and steps down (or up) the voltage to the required operating level

  • rectifier and reservoir: converts the ac transformer voltage to dc, reduces the ac ripple component of the dc and determines the output hold-up time when the input is interrupted

  • regulation: stabilises the output voltage against input and load fluctuations

  • supervision: protects against over-voltage and over-current on the output and signals the state of the power supply to other circuitry; often...

Products & Services
Power Supplies
Power supplies are electrical devices that deliver electric power to one or several loads. They generate the output power by converting an input signal into an output signal.
DC Power Supplies
DC power supplies accept an input power and output the desired form of DC power. Common types of DC power supplies include linear power supplies, switching power supplies, DC-DC converters, and silicon controlled rectifier (SCR) type power supplies.
Rectifier diodes are designed for use in rectification circuits. Rectifiers are used to convert AC to DC.
Switching Power Supplies
Switching power supplies are DC sources that use a switching element (normally a power transistor) to generate the desired voltage. Switching power supplies are also called switch-mode products or switching mode power supplies (SMPS).
AC Power Sources
AC power sources provide alternating power and typically have adjustable output values for the testing of component response at various voltages, current and frequency levels.

Topics of Interest

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6.1 INTRODUCTION As previously mentioned, the direct-off-line switchmode supply is so called because it takes its power input directly from the ac power lines, without using the rather large...

Electronic equipment requiring dc power must adjust the ac input to a usable level with transformers or switching transistors and use a rectifier stage to convert the ac to dc. Primary...

Y. M. Lai, Ph.D., Department of Electronic and Information Engineering, The Hong Kong Polytechnic University, Hong Kong 23.1 Introduction Power supplies are used in most electrical equipment. Their...

A rectified voltage (or current) is a voltage with a DC value not equal to zero and without any change in polarity.  A pure sine wave has a DC (or average) value of zero because the signal...

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