Dublin-based fab-less chip company Ikon Semiconductor has jumped into the competitive LED light bulb market with its first product: a dimmable single-stage ac-dc converter.
Like iWatt's new chip for non-dimmable bulbs (see page??), Ikon has resistor-programmable power factor correction (PFC).
"The feature allows customers to trade-off PFC against output ripple. For example, in residential applications >0.7 is all that is required," Ikon CEO Conor McAuliffe told Electronics Weekly. It can set up to 0.95.
For extremely compact or lowest-cost implementations, the chip, dubbed IKS2053, can run without an electrolytic capacitor on the output.
"It is single-stage, so this has eliminated the electrolytic on the bridge rectifier," said McAuliffe. "On the output, the electrolytic is optional, it depends on how much ripple you can accept. If the customer wants to minimise ripple, they can add electrolytic, but it is not required."
The chip is low-voltage CMOS, and mostly digital.
"We don't have a processor of any kind, it is essentially digital logic implementing some mathematical equations that need to be implemented - digital filters and state machines," said McAuliffe. "If there is a multiplication required, we have a digital multiplier. If there is a divider required, we have a digital divider."
iWatt, and Power Integrations in some of its products, also use the state-machine approach.
Like CamSemi and iWatt, Ikon uses an external mains-voltage switch. In this case a mosfet.
"In future we will look at bipolar transistors, and look at integrating a bipolar transistor or mosfet," said McAuliffe. "On-silicon or in-package is not decided yet."
This first chip is aimed at bulbs from 1W to 15W, working with both leading-edge and trailing-edge dimmers.
Dimmer compatibility is something all LED bulb chip makers are tackling, and is as long as a piece of string.
Ikon has identified 70 dimmer makers offering 400-500 models and is working through, starting with the most widely used.
"It is quite a time-consuming process," said McAuliffe. "With a good dimmer, feedback from customers is that it will be able to dim down to less than 10%. If you can get 5%, that is fantastic. We are targeting to be able to go below 5% with all dimmers. Worst case 10%."
Damping and bleeding - two dimmer compatibility issues - are dealt with, with both passive bleeding, or active bleeding using an additional external transistor to switch the resistors and capacitors.
Potential flicker is handled by an internal algorithm "to give smooth dimming without visible flicker over whole range", claimed McAuliffe.
IKS2053 will operate from 85-265V, start up on <20μA, claims the firm, can hit >85% efficiency, and is protected from over-voltage, over current and over temperature.
Solutions can be small enough to fit in the challenging GU10 envelope, and the firm will be demonstrating a GU10 at trade shows - the firm will be at Strategies in Light in Santa Clara.
