22W ac

Aug 13, 2023

Power Integrations has introduced a one-chip non-isolated LED driver for loads up to 22W.

Capable of working from inputs from 90 to 305Vac, it is triac (and trailing-edge) dimmable on nominal 110V supplies, but not on 230V supplies.

The dimming voltage is a clue here – this chip is aimed at commercial US installations where mains is split-phase and either 110V or double this. A future version will be optimised for dimming at 230V.

Called LYTSwitch-7, the firm claims dimmer compatibility without a bleeder resistor. “Designs do not require bleeders; employing simple, passive damping for TRIAC management,” said the firm.

86% efficiency is claimed for 230V operation – this is from a reference design called DER-561 (included in the data sheet) which is for a 7.5W design feeding 60V of LEDs from a 185-300V supply. Current regulation is +/-3% and efficiency stays above 80% right across the range. This design, using the LYT7503D, actually works up from 90V, and is dimmable at lower voltages. Power factor is 0.9.

Even though the package is an SO-8, operation has been stretched to 22W loads in some designs by allocating four pins to the mosfet source for conductive heatsinking. Space was freed-up by combining several control functions into a single pin, now called the multi-function pin.

The integrated mosfet is rated at 725V, and the main power inductor is a simple two-terminal inductor rather than a tapped inductor or transformer. 20 components total are required for a light bulb design. “A 725V mosfet delivers better withstand performance during line surges,” said Huberto Notohamiprodjo, director of product marketing at Power Integrations.

The firm has gone for a linear dimming curve rather than logarithmic, claiming that this is more power efficient and arguing that acceptability testing indicates users are happy a wide range of dimming curves so long as there is always some visible change of brightness when ever the control is moved.

Protection includes: automatic LED dimming if the bulb is over-heating (followed by shut-down if the temperature continues to rise), open-circuit, short-circuit, input over-voltage, output over-voltage, over-current and safe operating area (SOA).

“LYTSwitch-7 ICs meet international standards including: DOE Level 6 (external power supply), CEC Titles 20 and 24, Energy Star Lamps Program Requirements Version 2.0, NEMA SSL-7A and EN61000-3-2 C and D,” said the firm.

The output current has a high ripple factor, leading to 100 or 120Hz strobing. “The LYSTwitch-7 can be paired with external ripple-reduction circuits to achieve low output ripple in applications or geographies that may require it, the very high efficiency of LYTSwitch-7 is helpful in reducing the impact on efficiency that these circuits have,” said Power Integrations’ director of training Andrew Smith.

As the design is non-isolated, applications are expected where users cannot touch the LEDs – inside light bulbs and sealed luminaires.

Three reference designs have been prepared, all dimmable and non-isolated: