TNY264 Low Power Off-line Switcher

TinySwitch-II maintains the simplicity of the TinySwitch topology, while providing a number of new enhancements to further reduce system cost and component count, and to practically eliminate audible noise. Like Tiny Switch, a 700 V power MOSFET, oscillator, high voltage switched current source, current limit and thermal shutdown circuitry are integrated onto a monolithic device. The start-up and operating power are derived directly from the voltage on the DRAIN pin, eliminating the need for a bias winding and associated circuitry. In addition, the TinySwitch-II devices incorporate auto-restart, line under voltage sense, and frequency jittering.

An innovative design minimizes audio frequency components in the simple ON/OFF control scheme to practically eliminate audible noise with standard taped/varnished transformer construction. TNY264 fully integrated auto-restart circuit safely limits output power during fault conditions such as output short circuit or open loop, reducing component count and secondary feedback circuitry cost. An optional line sense resistor externally programs a line under-voltage threshold, which eliminates power down glitches caused by the slow discharge of input storage capacitors present in applications such as standby supplies. The operating frequency of 132 kHz is jittered to significantly reduce both the quasi-peak and average EMI, minimizing filtering cost.

Features of TNY264 Low Power Off-line Switcher

•  Fully integrated auto-restart for short circuit and open loop fault protection–saves external component costs

•  Built-in circuitry practically eliminates audible noise with ordinary varnished transformer

•  Programmable line under-voltage detect feature prevents power on/off glitches–saves external components

•  Frequency jittering dramatically reduces EMI (~10 dB) –minimizes EMI filter component costs

•  132 kHz operation reduces transformer size–allows use of EF12.6 or EE13 cores for low cost and small size

•  Very tight tolerances and negligible temperature variation on key parameters eases design and lowers cost

•  Lowest component count switcher solution