This circuit, really inexpensive, dissipates about 300 mW @ 264 Vac. The typical wake-up time is 2.8 s

at 88 Vac and 0.8 s at 264 Vac. Should the wake-up time become an issue, a more expensive solution

would be adopted. The PCB is also able to accommodate an active start-up circuit that, under the same

conditions, dissipates less than 10 mW and provides 0.7 s and 0.2 s wake-up times respectively. The

schematic is shown in fig. 3 (R2 and R3 will be removed).

A further improvement of light load efficiency can be achieved by replacing the RCD clamp (C10, R21)

with a Transil. The suggested part is a 1.5KE150A. This slightly worsens efficiency at full load but allows

to save about 200 mW, currently dissipated on R21, at light load.

Application board evaluation: getting started

The AC voltage, from an AC source ranging from 88 VRMS to 264 VRMS, will be applied to connector

M1 (close to the top left-hand corner). The 200VDC and 80VDC outputs are located in connector M2

(top right-hand corner) while

±15VDC and 6.3VDC outputs are available at connector M3, near the bot-

tom right-hand corner.

Like in any offline circuit, extreme caution must be used when working with the application

board because it contains dangerous and lethal potentials. The application must be tested with

an isolation transformer connected between the AC mains and the input of the board to avoid

any risk of electrical shock.

Application board evaluation: results

In the following tables the results of some bench evaluations are summarised. Some waveforms under

different load and line conditions, as well as system’s transient response are also shown for user’s refer-

ence and to illustrate the operation of the standby function.

Table 4. Full load measurements

88

110

160

220

264

Pin [W]

105.4

103.5

101.5

100.6

100.3

Vout [V]

199.9

199.9

199.9

199.9

199.9

79.43

79.43

79.4

79.36

79.36

14.27

14.26

14.29

14.26

14.26

-14.41

-14.4

-14.36

-14.39

-14.38

6.65

6.65

6.65

6.65

6.65

Pout [W]

89.75

89.74

89.72

89.7

89.7

η [%]

85.2

86.7

88.4

89.2

89.4

Load conditions: 200V: 630

Ω; 80V: 600Ω; ±15V: 80Ω; 6.3V: 8Ω

88

110

160

220

264

Pin [W]

6.9

7

7

7.1

7.2

Load conditions: 200V: open; 80V: open;

±15V: 0.5W; 6.3V: 8Ω

88

110

160

220

264

Pin [W]

1.3

1.4

1.5

1.6

1.8

Pin [W] (*)

1.2

1.2

1.3

1.4

1.5

Load conditions: 200V: open; 80V: open; +15V: 0.5W; 6.3V: open

(*) With the active start-up circuit of fig.3

AN1132 APPLICATION NOTE

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