PowerIntLinkSwitch-II系列电源方案

Power Integrations公司的LNK603-606/613-616 LinkSwitch-II系列产品是用于电源适配器和充电器的节电和精确的CV/CC开关控制器.它包括了高压功率MOSFET和电源控制器.它用ON/OFF来控制输出电压,而开关频率用来调整输出电流,从而提供恒流特性. LinkSwitch-II系列中的控制器包括振荡器,反馈电路(检测和逻辑电路),6V稳压器,超温保护,频率抖动,限流电路, 上升边缘消隐,电感修正电路,用于恒流调整的频率控制和用于CV控制的ON/OFF状态机.本文介绍了LNK603-606/613-616 LinkSwitch-II系列的主要性能,方框图以及多种应用电路图和所用材料清单(BOM).

Energy-Efficient, Accurate CV/CC Switcher for Adapters and Chargers.The LinkSwitch-II combines a high voltage power MOSFET switch with a power supply controller in one device. Similar to the LinkSwitch-LP and TinySwitch-III it uses ON/OFF control to
regulate the output voltage. In addition, the switching frequency is modulated to regulate the output current to provide a constant current characteristic. The LinkSwitch-II controller
consists of an oscillator, feedback (sense and logic) circuit, 6 V regulator, over-temperature protection, frequency jittering, current limit circuit, leading-edge blanking, inductance correction circuitry, frequency control for constant current regulation and on/off state machine for CV control.

Inductance Correction Circuitry
If the primary magnetizing inductance is either too high or low the converter will automatically compensate for this by adjusting the oscillator frequency. Since this controller is designed to operate in discontinuous-conduction mode the output power is
directly proportional to the set primary inductance and its tolerance can be completely compensated with adjustments to the switching frequency.

Constant Current (CC) Operation
As the output voltage and therefore the Flyback voltage across the bias winding increases, the feedback pin voltage increases. The switching frequency is adjusted as the feedback pin voltage increases to provide a constant output current regulation. The constant current circuit and the inductance correction circuit are designed to operate concurrently in the CC region.

Constant Voltage (CV) Operation
As the feedback pin approaches VFBth from the constant current regulation mode, the power supply transitions into CV operation. The switching frequency at this point is at its
maximum value, corresponding to the peak power point of the CCCV characteristic. The controller regulates the feedback pin voltage to remain at VFBth using an on/off state-machine. The feedback pin voltage is sampled 2.5us after the turn-off of the high voltage switch. At light loads the current limit is also reduced to decrease the transformer flux density.

Output Cable Compensation
This compensation provides a constant output voltage at the end of the cable over the entire load range in CV mode. As the converter load increases from no-load to the peak power point (transition point between CV and CC) the voltage drop introduced across the output cable is compensated by increasing the feedback pin reference voltage. The controller determines the output load and therefore the correct degree of compensation based on the output of the state machine. Cable drop compensation for a 24 AWG (0.3 ?) cable is selected with CBP = 1uF and for a 26 AWG (0.49ohm) cable with CPB = 10uF.

Auto-Restart and Open-Loop Protection
In the event of a fault condition such as an output short or an open loop condition the LinkSwitch-II enters into an appropriate protection mode as described below.

In the event the feedback pin voltage during the Flyback period falls below 0.7 V before the feedback pin sampling delay (~2.5us) for a duration in excess of ~450 ms (auto-restart ontime (tAR-ON) the converter enters into Auto-restart, wherein the power MOSFET is disabled for 4 seconds (~8% Auto-Restart duty cycle). The auto-restart alternately enables and disables the switching of the power MOSFET until the fault condition is
removed.