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LED’s don't flicker, yet sometimes they do, why is this? If you live in Sydney it’s quite likely that you have either direct experience or you know somebody else who has.
WHY? - Mains Injection (ripple control)
In parts of Australia, Sydney in particular, the mains power supply is subject to an injection of a high frequency ‘pulse’ which is used by the power utilities to control various forms of ‘Off Peak’ electricity usage.
HOW? – the LED Driver. We know today that central to this problem is the LED Driver. The role of the typical LED Driver is to convert a 240V 50Hz alternating power supply to a direct current either with a constant current or a constant voltage. The circuitry required to do this will also maintain a high power factor and deal with ‘noise’ (abnormalities such as high frequencies) on the incoming power supply. This is where the specification of the driver takes on significance; not all drivers are made the same way!
A technique used to limit cost is to combine filtering and load control, the so-called single stage circuit. Design dependence means that the circuit can be optimised to handle ‘noise’ or it can be optimised to provide power factor control; the design CANNOT efficiently handle both tasks. Given power factor correction is invariably the priority the consequence is that the circuit will be slow to react to any mains borne ‘noise’. In consequence this ‘noise’ will pass through the device and on to the LED.
Circuitry capable of dealing with ‘noise’ and maintaining a high power factor is standard with all HARVARD CoolLED drivers, this requires the use of the two stage circuit design. The first stage acts as an electronic filter and provides power factor correction. The second stage is a switching converter, isolating transformer and fast acting control loop. Its job is to deal with any residual ‘noise’ that may be present before power is delivered to the LED.
There is no standard for flicker, IEEE 1789-2015 is the reference document used by industry.HARVARD CoolLED drivers meet the requirements herein across the full dimming range.


Posted on Tuesday, July 12, 2016 by Alistair Robertson
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