TSM101 datasheet(8/15 Pages) STMICROELECTRONICS

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Figure 4 : An Auxiliary Winding for TSM101 Power Supply

5 - IMPROVEMENT

5.1. High frequency compensation

Two R-C devices (R9 + C2 & R10 + C3) are used

to stabilize the regulation at high frequencies.

The calculation of these values is not easy and is

a function of the transfer function of the SMPS.

A guess value for the capacitors C2 and C3 is

100nF.

5.2. Power supply for TSM101

In applications requiring low voltage battery charge

or when the charger is in current regulation mode,

the outputvoltage can be too low to supply correctly

the TSM101.

The same problem occurs when the output is short-

circuited.

A solution to provide a quasi constant supply volt-

age to the TSM101 is shown at figure 4 : an auxiliary

winding is added at the secondary side of the

transformer.

This winding is forward coupled to the primary

winding, the voltage across it is directly proportional

to the mains rectified voltage, even if the flyback

voltage is close to zero.

As this auxiliary winding is a voltage source, it is

necessary to add a resistor (R11) on the cathode

of the rectifier (D3) to limit the current.

A low cost regulator (Q2 and Zener diode D4) is

used to power the TSM101. This is necessary with

autoranging SMPS with wide input voltages, for

example 90 to 240V without switching. In standard

SMPS with voltage range from 200 to 240VAC or

100 to 130VAC, this regulator can be removed and

replaced by the small power supply shown on

figure 5 (Raux, Caux, D2).

TSM101/A

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