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Document Number: 74254

S-60997–Rev. A, 12-Jun-06

Vishay Siliconix

SiP11203DB

generated by the Si9122. These timing signals drive

the positive and negative terminals of the primary

a step-down ratio of 4:3 for each secondary winding.

The secondary windings are center tapped, with a

capacitive filter placed at the center tap point, and rec-

tifier diodes anode-connected to ground, connected to

each end of the secondary windings. This arrange-

ment means that the timing information is coupled to

the SiP11203, while a bias voltage is also available at

the center-tap to power the SiP11203. This bias volt-

which powers the other internal circuitry on the

SiP11203. The voltage on one of the pulse transformer

secondary windings wrt ground is shown in Figure 6

(b). It can be seen from this that the center-tap voltage,

equal to the average value of the secondary voltage.

Magnetic Component

The main power transformer structure is illustrated in

Figure 7. The multilayer PCB layout is described in

Table 1. The primary magnetizing inductance is

between 11 µH and 15 µH, and the turns ratio is 4:1:1.

The core is a combination of an E14/3.5/5 core and its

associated I-plate in 3F3 material. The output filter

inductor structure is illustrated in Figure 8 and the mul-

tilayer PCB layout is described in Table 2. The inductor

has 2 sections of 3 turns connected in parallel, with a

custom ground center gap to yield an inductance value

between 850 nH and 900 nH. The auxiliary winding is

constructed of 10 turns, divided between 2 layers,

resulting in a 10:3 turns ratio between the auxiliary and

main windings. The core is a combination of an E14/

3.5/5 core and its associated I-plate in 3F3 material.

Figure 5. Converter efficiency over line voltage and load range

50

52

54

56

58

60

62

64

66

68

70

72

74

76

78

80

82

84

86

88

90

2 A

4 A

6 A

8 A

10 A

12 A

14 A

15 A

Io (A)

48 Vin

35 Vin

75 Vin

Start Up Waveform

Start Up Waveform

Output Voltage

(2 V/DIV)

(1 V/DIV)

1.00 mS/DIV

(a)

Output of pulse

tansformer (2 V/DIV)

(2 V/DIV)

1.00 µS/DIV

(b)

Figure 7. Power Transformer Structure

Primary

Secondary

Secondary

P1

P2

P3

P4

S1

S2

S3

S4