Analysis of the first high power 132kHz CCM mode PSR power supply solution

On December 1, 2012, China will enforce the new electrical safety standard GB4943.1-2011, which requires that the primary and secondary electrical clearances of power supplies for equipment used at altitudes above 2,000 meters must be increased (multiplied by a multiplication factor of 1.48), and that warning labels must be affixed to power supplies that do not meet the strict creepage distance and electrical clearance requirements. This is good news for PSR (primary side regulator) devices, because PSR designs do not use optocouplers and feedback circuits.

Challenges of new safety regulations

Not long ago, Power Integrations (PI) launched the high-power LinkSwitch-HP IC series, whose no-load power consumption is less than 30mW, and the output power can reach up to 90W in an open-frame design, and the output power can reach up to 55W in a closed adapter (heat dissipation bottleneck). Li Zijun, senior manager of PI's marketing department, said that the new safety standards have brought challenges to the transformer, external capacitor and optocoupler parts in power supply design, especially optocouplers. According to the new regulations, larger package devices must be selected, which increases costs. The LinkSwitch-HP series launched this time is the first 132kHz CCM (continuous conduction mode) PSR solution on the market. The CCM mode can reduce output ripple, so that smaller output capacitors and voltage regulator diodes can be selected on the periphery, thereby reducing costs. "LinkSwitch-HP improves efficiency over the entire load range and reduces the size of the transformer and output filter," said Li Zijun. "The series uses an innovative multi-mode control engine to achieve a no-load input power of less than 30mW. Compared with the secondary side regulation (SSR) solution, the performance is similar but the BOM cost is lower."

Key Features

About ten years ago, PI launched the LinkSwitch product line, which uses innovative control algorithms and utilizes the characteristics of the main power transformer and output diode to determine the amount of power transferred from the primary side to the isolated secondary side. This PSR method does not require expensive optocouplers or the design of complex related feedback circuits, greatly reducing the number of components, saving space and cost, and enhancing reliability. Now, PSR solutions are basically adopted in many low-power applications such as mobile phone chargers. However, up to now, PSR has not been able to meet the constant voltage accuracy required by high-power products, so there are no PSR products in power products above 18W. LinkSwitch-HP adopts a unique multi-mode control architecture with a power range of 9W~90W, which directly extends the application of PSR solutions from mobile phones to tablet computers, LCD monitors, LCD TVs, set-top boxes, home appliances, and embedded power supplies.

Compared with the SSR solution, the PSR solution has more advantages in system-level cost savings.

The LinkSwitch-HP device automatically selects the control mode based on the prevailing line voltage and load conditions, thereby optimizing conversion efficiency and quickly responding to transient load requirements, while reducing output ripple and audio noise. CCM mode operation reduces RMS current, thereby improving efficiency and reducing heat dissipation. The 132kHz full-load operating frequency adopted by the device also allows the use of smaller magnetic cores and LC post-filter components. At 230 VAC, the LinkSwitch-HP IC can achieve a no-load power consumption of less than 30mW and an efficiency of more than 50% at an input power of 0.1W, enabling it to meet all global energy efficiency regulations, such as ErP (EuP), ENERGY STAR EPS V2.0 and EC Eco-Design Directive's external power supply Tier 2 requirements.

Function Configuration

The LinkSwitch-HP ICs feature comprehensive protection features including selectable current limit, programmable turn-off delay extension, and voltage ramp, voltage sag, overvoltage, overcurrent and overtemperature protection.

The LinkSwitch-HP series includes 5 ICs with different power and MOSFET sizes, and provides 2 package options. PI can provide two supporting evaluation demonstration boards according to customer requirements: RDK-321 (17W dual-output flyback converter for LCD displays) and RDK-313 (30W, 12V single-output universal adapter). Li Zijun said that the new device is now available in engineering samples and will be put into mass production at the end of August 2012.