Torex Semiconductor Ltd. has developed the XC9401 series C type off-line controllers for LED lighting that feature an improved current-sense (Isen) voltage accuracy. The new series C device achieves an Isen voltage accuracy of 0.34V±2.5% compared with ±5% for the earlier type A and B designs. The improved Isen voltage accuracy was achieved as the result of a re-designed comparator circuit. The Isen accuracy of 0.34V±2.5% is achieved without the need for special external components, but higher accuracies are possible using precision current-sense resistors. Operation within the range 85- to 270-Vac or from 85- to 270-Vdc input is possible by optimizing external components.
The dimming range of the type C controller is 1% to 100%. Using selected components to match the circuit configuration, a wide variety of specifications can be realized. Fixed-off time control is used as the basic method, and with detecting the current that flows to the external power MOSFET, the current flowing to the LED is monitored and stable power for LED lighting is supplied.
The circuit configuration of the A type is designed to achieve a high power factor by synchronizing the LED current with the input voltage (sine wave). In this circuit configuration, a high capacity, high breakdown voltage electrolytic capacitor is not necessary after the bridge rectifying circuit from the AC input. An input filter removes high-frequency switching noise from the ac line, and therefore a low capacity ceramic capacitor can be used.
The B type holds constant the peak current that flows to the external power MOSFET due to switching, and is thereby able to maintain a constant LED current. By keeping the LED current constant, this circuit configuration makes it possible to achieve a stable light source with high efficiency.
The C type further enhances the peak current detection accuracy of the B type, adding greater flexibility in the selection of external components and a higher LED current stability. The general purpose SOT-25 package is used for this C type.
This series is an environment-friendly product that complies with the EU RoHS Directive and is Pb-free. For the XC9401C type, the "TOREXsim." web simulator provides powerful technical support that lets users check detailed operation at any time. Engineers can change constants and select components online, run a simple operation test that creates a simulated waveform, and create, save, and print a BOM list that forms a summary of the results. The simulator can be accessed from the Torex Semiconductor website.