sense pin (13, ISEN). This can be accomplished by means of R24, currently not used. The offset will be

the partition of the reference voltage (pin 4, VREF) through R24 and R14. Consider that applying the off-

set may require the sense resistor R15 to be reduced, as shown in table 4. Increasing R15 is instead the

Table 4. Adjustment of the static standby thresholds

R24

open

100k

Ω

47k

Ω

33k

Ω

24k

Ω

R15[

Ω]

0.47

0.43

0.43

0.43

0.39

DC offset[mV]

0

50

100

150

200

8.3

6.2

5.1

3.6

2.5

13.3

11.9

12.3

11.1

11.5

Table 3. Transformer Specification (Part Number RDT20001, supplied by RD Elettronica).

Core

Philips EFD30x15x9, 3C85 Material or equivalent

Bobbin

Horizontal mounting, 12 pins

Air gap

≅ 0.7 mm for an inductance 2-6 of 400 µH

Leakage inductance

< 10

µH

Windings

Spec & Build

Winding

Wire

S-F

Turns

Notes

Pri1

AWG27

2-4

25

Sec (a)

AWG25

11-7

12

Bifiliar with Sec (b)

Sec (b)

AWG25

12-8

12

Bifiliar with Sec (a)

Pri2

AWG27

4-6

25

Aux

AWG32

3-1

10

Evenly spaced

Note: sec (a) and sec (b) are paralleled on the PCB

Figure 2. PCB layout: Silk + component side and bottom layer (top view); 1:1.25 scale.

AN1134 APPLICATION NOTE

4/9