Power Supplies for LED Driving
Including detailed examples of what works and why, this practical, hands-on book covers the design trade-offs involved in LED driving applications, from low-power to UB-LEDs and beyond.
TABLE OF CONTENTS Power Supplies for LED Driving
Chapter 15: Safety Issues
This chapter discusses electrical safety and readers are advised to obtain the latest requirements from their regulatory body or safety consultant. The information here is to show that many topics must be considered, rather than as a reference for design work. Optical safety is a concern, but it is outside the scope of this book and readers are advised to consult technical data supplied by LED manufacturers.
15.1 AC Mains Isolation
Safety isolation can only be achieved with a transformer. This transformer can be placed on the AC mains supply, or as part of the switching regulator circuit. Transformer isolation on the AC mains supply is bulky because the AC signal is operating at 50Hz or 60Hz.
Conversely, a transformer that isolates the output of a switching regulator can be very small because it is operating at the switching regulator frequency of typically 50kHz or more. If accurate current control is needed, additional electronics to control the LED current is needed and some form of isolated feedback is required.
For products connected to AC mains supplies, 1500V RMS (50Hz or 60Hz) isolation is usually required. Products for medical applications usually require a higher isolation voltage; LED lamps are sometimes found in operating theatres and in other medical applications.
15.2 Circuit Breakers
In the event of an over-current, the most common circuit breaker is a fuse. This is basically a piece of wire that is heated by the current flow. The wire eventually melts, thus breaking the circuit. Sometimes two...
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