Create The Future Entry

Electrical power plants supply around 20% of their output for lighting. LED lighting can reduce this demand by around 80%, however this is not perfect. Driver efficiencies are typically 80-90% and low cost solutions often suffer from high flicker, inability to dim by legacy dimmers, poor colour rendering and unnecessarily limited life. A method has been developed increasing the driver efficiency close to 99% whilst reducing flicker to imperceptible levels, improving colour rendering, extending the already considerable lifetime, with Power factor controlled to 0.99 and low cost. This relies on near-zero voltage switching to reduce switching losses in a single stage boost converter, and running (machine-loadable, no hand assembly) low-mid power LED’s in series at low controlled current with distributed cooling.

The circuit shows the deceptively simple arrangement, where a Mosfet M is switched to ground via a current sense resistor to build up current in an Inductor L. M is switched off fast at zero volts, at a peak current set by a signal proportional to the difference between the supply voltage and current such that the current waveform taken is forced to match the voltage waveform, hence high power factor and very low harmonics. A small Capacitor Cres across M limits the slew rate across M so that has little dissipation. When Cres charges to the peak voltage on the storage capacitor Cs, the current through L reverses so the voltage across M resonates with L and Cres towards 0V. A valley detector switches on M again slowly at the lowest point and near-zero current, again with minimal losses. There is also little conducted or radiated EMI as slew rate is limited and boost diode Db recovers gently during this period. The current through Cres is also used to supply the internal circuitry at near-zero loss.

The voltage on Cs supplies a current through the series LED’s measured in Rs; its voltage is compared against reference Vref, which can vary according to any phase-control or self-dimming by optional user-adjustable photosensor (with antiresonant circuitry to avoid oscillations), such that the LED current is controlled. Cs is a long-life capacitor running at very low ripple current due to its high voltage, so has minimal self-heating resulting in lifetime longer than the LED’s, which exhibit minimal flicker.

The series of small low cost LED’s allows for distributed cooling with optionally either PCB plane or additional small cheap formed copper strip soldered adjacent to each LED. This reduces the junction thermal resistance to very low levels so that natural convective cooling through thin plastic (no large metal heatsink) and minimal driver losses (1%) combine to keep temperature rises so low lifetime is hugely extended. Optional addition of saturated colour red/green/cyan LED’s distributed in the chain provides CRI>90 especially R9, at much higher efficiency than high-red phosphors provide.

Example: 600x600mm 3000Lm panel light normally 36-40W( ?70-80Lm/W) takes just 18.75W (160Lm/W). Life > 200,000Hrs with existing LM80 specified LED’s. Amortized lifetime cost