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LED FM Control
Artistic Licence has developed a new technique for the control of LED intensity. The technology is relevant to both single colour intensity colour and colour mixing applications.
Most existing production designs for LED colour mixing use a technique called Pulse Width Modulation (PWM). PWM is characterised by a fixed frequency control waveform, where the intensity of each LED colour is controlled by the width of the pulse.
This technology has been widely used in the first generation of LED colour mixing products. Whilst the technique works, it has a number of drawbacks:
- The response of control input to LED current is largely linear. As LEDs are non-linear devices, this does not produce a linear intensity response
- PWM is a fixed frequency system, this means that all LEDs switch on at the same time in the cycle. In larger systems this leads to asymmetric loading of the power source and can complicate EMC issues
- A number of patents have been issued covering the use of PWM in such applications.
The latest developments by Artistic Licence are intended to solve these problems.
The technique of Frequency Modulation uses the concept of a fixed width control pulse delivered at a variable frequency. As the frequency increases, the intensity of the LEDs is reduced. It is seen that the technique is inherently non-linear. However, the benefit is that this nonlinearity opposes the inherent non-linear LED response. The result is to increase the resolution over the low intensity end of the control range.
The power supply loading issue is also addressed by Frequency Modulation. As the frequency varies, the switch on point for each circuit varies in time. This effect reduces the asymmetric power supply loading.
Finally research suggests that this development has not been patented and is therefore open to the lighting industry.
The technique is clearly applicable to all forms of additive colour mixing including light sources other than LEDs. Additionally it is clear that the FM modulation could be set by local controls or by data generated by network control such as DMX512 or Ethernet.
Artistic Licence is not seeking any intellectual property protection for this development, but will be supplying a range of products and OEM modules that use the technique. The purpose of this short application note is to ensure that, by publication, this technique cannot be patented by others.
W D Howell
Artistic Licence (UK) Ltd
London 2002
See also:
- Go back
- Basics of LED technology
- Artistic Licence range of LED luminaires
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