Power Electronics
Accurate Power Supply Chip Cuts Components, Exceeds Efficiency Standards

Accurate Power Supply Chip Cuts Components, Exceeds Efficiency Standards

Power Integrations’ LinkSwitch-II family of ac-dc power conversion ICs feature a highly accurate primary-side control that simplifies the design of constant-voltage, constant-current (CV/CC) converters, while enabling power supplies to meet all worldwide energy-efficiency regulations such as ENERGY STAR 2.0. The ICs target applications such as chargers for cell phones and cordless phones, high-brightness LED drivers and other accurate CV or CC applications.

The LinkSwitch-II family consists of eight model numbers (LNK603/613, LNK604/614, LNK605/615, and LNK606/616) designed to implement power supplies with outputs ranging from 2.5 W to 5.5 W in adapter designs or 3.3 W to 6.1 W in open-frame designs. The chips are offered in three package options: 8-pin SOICs, SMDs, and DIPs.

LinkSwitch-II eases the design of accurate-output CV/CC converters by eliminating the need for optocouplers and all secondary-side CV/CC control circuitry as well as all control-loop compensation circuitry. By integrating all control and protection circuitry along with a 700-V MOSFET, LinkSwitch-II significantly reduces component count, space and system cost while increasing reliability (see the figure).

Output CV/CC tolerances of ±5% and ±10% respectively are achieved over a 0°C to 100°C temperature range. The ICs achieve these levels of accuracy by compensating for transformer inductance tolerances, input line variations, output cable voltage drop (on LNK61x models only) and external component temperature variations.

LinkSwitch-II also offers frequency jittering to reduce EMI filter costs. Protection and safety features include auto-restart output short circuit protection and hysteretic thermal shutdown. IEC 60950-1 HV creepage requirements between drain and all other pins are met and all single-point failures are handled safely.

In an example cellphone charger design with 5-V, 1-A output, LinkSwitch-II eases compliance with ENERGY STAR EPS 2.0 by achieving average efficiency levels of up to 75% at 25%, 50%, 75% and 100% loads across a 115-Vac to 230-Vac input range. The on/off control scheme employed in LinkSwitch-II, coupled with low IC power consumption and elimination of secondary-side current sense resistor and control circuitry, provides practically constant efficiency across the entire load range.

Meanwhile, no-load consumption is less than 30 mW when external bias is applied. That requires a bias winding on the transformer plus a diode and capacitor. Alternatively, the chip can be powered directly off the supply rail.

A charger designed with LinkSwitch-II has 9 fewer components compared to the previous generation of LinkSwitch and up to 15 fewer components when compared to discrete designs.

However, the comparison with first-generation devices such as LinkSwitch LT is not apples-to-apples because those devices are loosely regulated and do not include compensation for input line variations and output cable voltage drop. (A closer comparison for LinkSwitch-II would be with Power Integrations’ TinySwitch devices, which require optocoupler feedback.)

The cable-drop compensation in LinkSwitch-II reduces the cost of the output cable by minimizing its copper content without sacrificing output performance. It also works with a smaller transformer, which reduces the amount of copper and core material required.

All LinkSwitch-II family members are produced in halogen-free, RoHS-compliant packaging, which is increasingly being demanded by end customers such as Apple, Nokia Samsung and LG. For a copy of the data sheet, see http://www.powerint.com/link2product.htm.

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