HVLED805 Description
Doc ID 18077 Rev 1 3/29
1 Description
The HVLED805 is a high-voltage primary switcher intended for operating directly from the
rectified mains with minimum external parts to provide an efficient, compact and cost
effective solution for LED driving. It combines a high-performance low-voltage PWM
controller chip and an 800V, avalanche-rugged power MOSFET, in the same package.
The PWM is a current-mode controller IC specifically designed for ZVS (zero voltage
switching) fly-back LED drivers, with constant output current (CC) regulation using primary-
sensing feedback. This eliminates the need for the opto-coupler, the secondary voltage
reference, as well as the current sense on the secondary side, still maintaining a good LED
current accuracy. Moreover it guarantees a safe operation when short circuit of one or more
LEDs occurs.
In addition, the device can also provide a constant output voltage regulation (CV): it makes
the application able to work safely when the LED string opens due to a failure.
Quasi-resonant operation is achieved by means of a transformer demagnetization sensing
input that triggers MOSFET’s turn-on. This input serves also as both output voltage monitor,
to perform CV regulation, and input voltage monitor, to achieve mains-independent CC
regulation (line voltage feed forward).
The maximum switching frequency is top-limited below 166 kHz, so that at medium-light
load a special function automatically lowers the operating frequency still maintaining the
operation as close to ZVS as possible. At very light load, the device enters a controlled
burst-mode operation that, along with the built-in high-voltage start-up circuit and the low
operating current of the device, helps minimize the residual input consumption.
Although an auxiliary winding is required in the transformer to correctly perform CV/CC
regulation, the chip is able to power itself directly from the rectified mains. This is useful
especially during CC regulation, where the fly-back voltage generated by the winding drops.
In addition to these functions that optimize power handling under different operating
conditions, the device offers protection features that considerably increase end-product’s
safety and reliability: auxiliary winding disconnection or brownout detection and shorted
secondary rectifier or transformer’s saturation detection. All of them are auto restart mode.
