Description

The TinySwitch™ family uses a breakthrough design to provide

the lowest cost, high efficiency, off-line switcher solution in

the 0 to 10 W range. These devices integrate a 700 V power

MOSFET, oscillator, high-voltage switched current source,

current limit and thermal shutdown circuitry. They start-up

and run on power derived from the DRAIN voltage, eliminating

the need for a transformer bias winding and the associated

circuitry. And yet, they consume only about 80 mW at no load,

from 265 VAC input. A simple ON/OFF control scheme also

eliminates the need for loop compensation.

The TNY253 and TNY254 switch at 44 kHz to minimize EMI

and to allow a simple snubber clamp to limit DRAIN spike

voltage. At the same time, they allow use of low cost EE16 core

transformers to deliver up to 5 W. The TNY253 is identical to

TNY254 except for its lower current limit, which reduces output

short-circuit current for applications under 2.5 W. TNY255

uses higher switching rate of 130 kHz to deliver up to 10 W

from the same low cost EE16 core for applications such as PC

standby supply. An EE13 or EF13 core with safety spaced

bobbin can be used for applications under 2.5 W. Absence of

a bias winding eliminates the need for taping/margins in most

applications, when triple insulated wire is used for the secondary.

This simplifies the transformer construction and reduces cost.