ST HVLED805离线反激LED驱动解决方案

ST HVLED805离线反激LED驱动解决方案

　　ST公司的HVLED805是具有初级检测的离线LED驱动器，包括了高性能低压PWM控制器和800V耐雪崩击穿的功率MOSFET,可直接连接到火线整流电压，恒流LED输出电流精度5%,不需要光耦器件，准谐振（QR）零电压开关（ZVS）工作，内部HV起动电路，能对LED串的开路或短路进行管理，主要用在AC/DC LED驱动器，LED替代灯（如E27, GU10）等。本文介绍了HVLED80主要特性， 应用框图以及多种性能测试电路。

　　HVLED805: Off-line LED driver with primary-sensing

　　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 primarysensing 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 MOSFETs 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-products safety and reliability: auxiliary winding disconnection or brownout detection and shorted secondary rectifier or transformers saturation detection. All of them are auto restart mode.

　　HVLED80主要特性：

　　800 V, avalanche rugged internal power MOSFET

　　5% accuracy on constant LED output current with primary control

　　Optocoupler not needed

　　Quasi-resonant （QR） zero voltage switching （ZVS） operation

　　Internal HV start-up circuit

　　Open or short LED string management

　　Automatic self supply

　　Input voltage feed-forward for mains independent cc regulation

　　HVLED80应用：

　　AC-DC led driver applications

　　LED retrofit lamps （i。e。 E27, GU10）

　　图1.HVLED80应用框图

　　图2.HVLED80关断态漏和源电流测试电路图

　　图3.HVLED80起动电流测试电路图

　　图4.HVLED80静态电流测试电路图

　　图5.HVLED80工作电流测试电路图

　　图6.HVLED80故障时静态电流测试电路图