AN2067 Datasheet, PDF (11/25 Pages) STMicroelectronics – LED manufacturers propose white LEDs inside a monolithic chip

AN2067
3
Transformer design
Transformer design
3.1
Primary inductance
The primary inductance is set to 0.5 mH, according to the output power required, and the
current capability of the VIPer53-E. The VIPer53-E software helps to define the number of
turns of the primary inductance. It provides a result of 52 turns, in 2 wires. A diameter of 0.4
mm has been chosen.
3.2
3.2.1
Primary auxiliary winding
To guarantee a correct operation, the VIPer53-E should be supplied with at least 12.8 V.
This winding is also used in forward mode. The turn ratio between primary winding and
primary auxiliary winding according to the minimum input voltage (100 V_DC) is 0.18.
0.21 is the value used with 11 turns on auxiliary. At maximum input voltage (400 V_DC), the
auxiliary supply is 85 V. This provides a constraint on the voltage regulator for the VIPer53-
E.
Secondary winding
The output voltage may vary from 4 V to 40 V, and the reflected voltage must not exceed
100 V. The turn ratio should be 0.5 (26 turns) in order to avoid current mode instability.
A diameter of 0.7 mm is provided by the VIPer53-E software.
3.3
Secondary auxiliary winding
This secondary auxiliary output must guarantee a voltage from 6 V to maximum 32 V
(supply voltage range of the TSM101). The turn ratio is 0.077 (4 turns). This provides a
supply voltage from 7.7 V up to 30.8 V, which is in line with the specification of the TSM101.
3.4
Transformer specifications
Table 2 shows the specifications of the power supply transformer.
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