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.