The InnoSwitch™3-CE family of ICs by POWER INTEGRATION has revolutionized power supply design, enabling highly efficient, very compact power supplies for consumer products such as set-top boxes, networking adaptors, wireless speakers and game terminals. Similar to other members of the InnoSwitch3 family, InnoSwitch3-CE parts feature a primary side Quasi-Resonant (QR,) Continuous and Discontinuous Conduction Mode (CCM/CDM) flyback controller and a 650 V primary side power MOSFET. The benefits of secondary side regulation are achieved without optocouplers via the FluxLink™ isolated feedback link which also facilitates very precise control of secondary synchronous rectification.
Accuracy and efficiency for consumer products
With up to 94% flat-across-load efficiency that virtually eliminates heatsinks, excellent noise immunity and very low output ripple, InnoSwitch3-CE devices allow smaller power supplies to be embedded within a wide range of consumer products which have previously used external adapter power supplies. High switching efficiency is complemented by extremely low power consumption in standby - less than 15mW, no load - enabling power supply designs that meet existing and proposed global energy efficiency regulations.
InnoSwitch™3-CE provides overvoltage and overcurrent protection
A comprehensive array of protection and safety features have also been integrated into the InnoSwitch3-CE family that improve performance and reliability. These include synchronous rectification (SR) MOSFET, short circuit protection, line input over-voltage and under-voltage protection, open loop and pin-short, latching or hysteretic over-temperature protection as well as output over-current, and over-voltage protection.
Technology Features of InnoSwitch™3-CE
The figure illustrates the important technical features integrated into the new InnoSwitch3 family that result in the exceptional efficiency and reliability of these devices. InnoSwitch3-CE ICs incorporate POWER INTEGRATIONS’ propriety inductive coupling communications link, FluxLink. Using this technology, InnoSwitch3-CE ICs are able to accurately control the operation of the primary side switch with secondary side synchronous rectification to maximise efficiency. Accurate control prevents potentially damaging cross conduction or “shoot through”, even as load changes force the power supply to repeatedly transition between DCM and CCM operating modes. In addition, FluxLink is a safe barrier-crossing technology that is approved worldwide to provide galvanic isolation between the primary side high voltage and the low voltage secondary side. This removes the need for unreliable discrete isolation components such as optocouplers to provide feedback.
The primary side quasi-resonant flyback controller employs a combination of on-off control, variable frequency and variable current control techniques to achieve flat efficiency across the entire load range. This approach allows the InnoSwitch3 CE family to provide virtually noiseless power solutions delivering up to65 W – well beyond the power capability of traditional on-off control schemes. The secondary side consists of a controller, transmitter circuit magnetically coupled to the primary side receiver, via the FluxLink feedback link, Constant Voltage (CV) and Constant Current (CC) control circuits for output voltage and current regulation, synchronous rectifier driver and numerous safety features that can be selected to provide either an auto-restart or latching shutdown fault response.
Excellent output voltage regulation (better than +/- 3 % across line and load) and output current regulation (better than +/- 5 % across line and load is achieved by secondary sensing. The secondary side controller directs the operation of the primary side, initiating a primary side switching cycle only when it has finished its own switching cycle. QR or valley-switching forces the integrated primary side MOSFET to turn on at the minimum MOSFET drain-source voltage, induced by the DCM ring. This significantly reduces switching losses and EMI. Excellent noise immunity enables designs using the InnoSwitch3-CE to achieve class “A” performance levels for EN61000-4 suite; EN61000-4-2, 4-3 (30V/m),4-4, 4-5, 4-6, 4-8 (100A/m) and 4-9 (1000A/m), making regulatory compliance straightforward with integrated designs.
The flyback design using the InnoSwitch3-CE
The schematic of a typical flyback design using the InnoSwitch3-CE shown in the following figure demonstrates the level of integration achieved. The schematic shows a universal input (90 VAC – 265 VAC) 36 W output power supply which delivers a well-regulated 3 A 12 V output.
The high voltage X-capacitor, C1, and common mode choke, L1, form a common mode filter and the line input is full wave rectified by bridge rectifier, BR1. Smoothing and filtering is performed by a π filter formed by capacitors C2, C3 and inductor, L2. Thermistor, RT1, limits inrush current and varistor, RV1, provides protection from line surge. The INN3166 InnoSwitch3 IC is self-starting using an internal high voltage current source which charges C6 - the primary side bypass capacitor connected to the BPP Pin. During normal operation, the primary side of the controller is powered from the auxiliary winding off the transformer, T1, via the diode, D2, and filtered by resistor, R5, and capacitor, C5. Line voltage is monitored via resistors R1 and R2 which feed a current into the high voltage V Pin that is proportional to the DC voltage across C3. This signal is used to provide accurate line overvoltage and undervoltage protection information whilst consuming less than 3mW.
Secondary side rectification is performed by the synchronous rectification (SR) FET, Q1. An RC snubber network comprising of R6 and C11 damps any high frequency ringing across the SR FET that may result from leakage inductance of the transformer windings and secondary parasitic capacitance. Q1 turn-on is controlled the winding voltage sensed at the Forward Pin (FWD) via R7. In CCM operation, the power MOSFET is turned off the instant before the secondary controller initiates a new switching cycle on the primary side via the FluxLink communications medium. In DCM operation, the power MOSFET is turned off when the voltage drop across the MOSFET falls below zero. Secondary side control of the primary side MOSEFT ensures that it is never turned on simultaneously with the secondary side SR FET. This accurate control allows an InnoSwitch3 circuit to operate in both DCM and CCM modes. This seamless transition greatly simplifies the design and optimization of power solutions for applications with widely varying loads.
Output voltage is sensed via the potential divider formed by resisters R8 and R9 with the midpoint connected to the Feedback Pin (FB). Zener Diode, VR1, along with R12 provides secondary side output over-voltage protection. When the Zener starts to conduct it is detected as a fault condition by the secondary Bypass (BPS) Pin. Output current information is generated across R11 and monitored by the ISense (IS) Pin that has a low threshold voltage of 33mV to reduce losses.
Compact package for reinforced isolation
The InnoSwitch3-CE is available in the new compact InSOP 24D package that provides reinforced isolation up to 4,000 V and carries UL1577 and TUV (EN60950) safety approval. All parts are 100% production tested for HIPOT and partial-discharge.
More details can be found on the POWER INTEGRATIONS’ website along with an online selection tool "Build Your Own InnoSwitch". This tool guides designers to the InnoSwitch device that is equipped with the features that best matches their need.