Cambridge spin-out CamSemi has announced its second chip, a novel primary-side regulated AC-DC flyback controller for wall plug power supplies.
“The C2140 series offers current and voltage regulation of +/-5% and targets high volume, universal input applications rated up to 8W,” said the firm.
Like its first offering, the C2470, the new chip is designed to cut cost by working with a generic high-voltage bipolar transistor rather than having mains on the die. Also like the 2470, the 2140 uses some unusual circuit techniques.
For example, the power transistor is emitter-switched instead of the usual base control, and there is no need for an opto-isolator despite the close output regulation.
Instead, output voltage voltage in inferred from the auxillary power winding “measuring at just the right moment”, a company spokesman told
Electronics Weekly. “The controllers algorithms combined with digital techniques to more accurately monitor the output voltage and provide tighter current regulation than has previously been possible.”
Quasi-resonant zero-voltage switching is used keep power losses down in the main bipolar transistor.
According to the firm, designs using the chips can meet the Energy Star 2.0 European code of conduct and other worldwide energy-efficiency regulations.
There are two devices: the 4W C2141PX2 and 8W C2142PX2, both available in SOT23-6 in volume now.
Programmable cable compensation of up to 10% allows voltage regulation at the far end of the cable, even with thin, cheaper, conductors. “The compensation is fully adjustable in the design phase allowing one standard design to be quickly modified to accommodate different cable lengths or gauges,” said CamSemi. “The controllers can also be adapted to match the required switching frequency of the end application by specifying one external component.”
The firm’s earlier C2470 series controllers are also novel - implementing the unusual resonant discontinuous forward converter topology.
This keeps the loss low even with a relatively slow bipolar main switch. However, the input-output voltage ratio of this topology is fixed like a transformer and so it is not suitable for universal mains inputs.
This limitation does not seem to have affected sales which the firm claimed hit 10 million in October. The introduction of the 2140 series adds universal input capability to CamSemi’s portfolio.