| 简介 |
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.
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In addition to the conditions for auto-restart described above, if the sensed feedback pin current during the Forward period of the conduction cycle (switch “on” time) falls below 120 uA, theconverter annunciates this as an open-loop condition (top resistor in potential divider is open or missing) and reduces the Auto-restart time from 450 msec to approximately 6 clock cycles (90 us), whilst keeping the disable period of 4 seconds. This
effectively reduces the Auto-Restart duty cycle to less than 0.01%.
Over-Temperature Protection
The thermal shutdown circuitry senses the die temperature. The threshold is set at 142 °C typical with a 60 °C hysteresis. When the die temperature rises above this threshold (142 °C) the power MOSFET is disabled and remains disabled until the die temperature falls by 60 °C, at which point the MOSFET is re-enabled.
Current Limit
The current limit circuit senses the current in the power MOSFET. When this current exceeds the internal threshold (ILIMIT), the power MOSFET is turned off for the remainder of that cycle. The leading edge blanking circuit inhibits the current limit
comparator for a short time (tLEB) after the power MOSFET is turned on. This leading edge blanking time has been set so that current spikes caused by capacitance and rectifier reverse recovery time will not cause premature termination of the MOSFET conduction. The LinkSwitch-II also contains a “di/dt” correction feature to minimize CC variation across the input line range.
6.0 V Regulator
The 6 V regulator charges the bypass capacitor connected to the BYPASS pin to 6 V by drawing a current from the voltage on the DRAIN, whenever the MOSFET is off. The BYPASS pin is the internal supply voltage node. When the MOSFET is on, the device runs off of the energy stored in the bypass capacitor.
Extremely low power consumption of the internal circuitry allows the LinkSwitch-II to operate continuously from the current drawn from the DRAIN pin. A bypass capacitor value of either 1uF or 10uF is sufficient for both high frequency decoupling and energy storage.
The LinkSwitch-II dramatically simplifies low power CV/CC charger designs by eliminating an optocoupler and secondary control circuitry. The device introduces a revolutionary control technique to provide very tight output voltage and current regulation, ompensating for transformer and internal parameter tolerances along with input voltage variations.
The device incorporates a 700 V power MOSFET, a novel On/Off control state machine, a high voltage switched current source for self biasing, frequency jittering, cycle-by-cycle current limit and hysteretic thermal shutdown circuitry onto a monolithic IC.
Product Highlights
Dramatically Simplifies CV/CC Converters
Eliminates Optocoupler and all secondary CV/CC control circuitry
Eliminates all control loop compensation circuitry
Advanced Performance Features
Compensates for transformer inductance tolerances
Compensates for input line voltage variations
Compensates for cable voltage drop (LNK61X series)
Compensates for external component temperature variations
Very tight IC parameter tolerances using proprietary trimming technology
Frequency jittering greatly reduces EMI fi lter cost
Even tighter output tolerances achievable with external resistor selection/trimming
Advanced Protection/Safety Features
Auto-restart protection reduces power delivered by >95% for output short circuit and control loop faults (open and shorted components)
Hysteretic thermal shutdown – automatic recovery reduces
power supply returns from the field
Meets HV creepage requirements between Drain and all other pins both on the PCB and at the package
EcoSmart – Energy Effi cient
Easily meets all global energy efficiency regulations
No-load consumption <200 mW at 230 VAC and down to below 30 mW with optional external bias
On/Off control provides constant efficiency down to very light loads – ideal for CEC and ENERGY STAR 2.0 regulations
No current sense resistors – maximizes efficiency
Green Package
Halogen free and RoHS compliant package
Applications
Chargers for cell/cordless phones, PDAs, MP3/portable audio devices, adapters, LED drivers, etc.
图1.LinkSwitch-II系列功能方框图
应用案例:
图2.节电的USB充电电源电路图(平均效率74%,无负载输入功率小于40mW)
图3.无需偏压电源的LinkSwitch-II系列反激电源
图4.通用输入5 W CV/CC充电器电源
下表为通用输入5 W CV/CC充电器电源材料清单(BOM):
图5.采用LNK605DG的4.2W LED驱动电路图
来源：Power Integrations
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