[[upsilon].sub.T] - vector of the

turns ratio of control transformers,

Therefore, a reliable control system is required to adjust the voltage of HVS with respect to the voltage of LVS of the converter so that the voltage ratio of the HVS with LVS is close to the transformer

turns ratio.

Beside the duty cycle another design factor is provided to enlarge the voltage gain in proportion to the winding

turns ratio. Thus the converter can easily attain high voltage gain;

Therefore, in this application the transformer

turns ratio has to be selected for the converter to operate with minimum duty cycle under these operating conditions.

With this circuit structure, it results in a large transformer

turns ratio, which makes the transformer design complex and leads to a large leakage inductance.

To illustrate the

turns ratio selection process, first consider the boost or step-up mode.

Megger, one of the world's leading manufacturers and suppliers of test equipment and measuring instruments for electrical power applications, now offers a rugged, handheld, battery-operated TTR tester (transformer

turns ratio).

For example, for high step-down voltage conversion, it requires a transformer with high

turns ratio or it has to reduce the duty ratio of the switches.

In addition, the lead set used with the MTO300 series instruments is the same as that used with Megger's three-phase transformer

turns ratio test sets, which makes it possible to perform both resistance and

turns ratio tests after making just one set of connections to the transformer.

The two transformers [T.sub.a] and [T.sub.b] with

turns ratio [N.sub.a] and [N.sub.b] transform the two edge impedances to the feed point ([x.sub.0], [y.sub.0]).

The ADSL line transformers, part numbers BX2258 and BX2358, have an inductance value of 5.0 milli henries and

turns ratio of 1:1 while part numbers BX2259 and BX2353, have an inductance value of 5.0 micro henries and

turns ratio of 1:2.125.