Experimental results

In order to validate the above considerations, an experimental example will be given. It concerns a 40W,

wide-range mains power supply for an inkjet printer, whose design has been optimized following some of

the guidelines here presented, and evaluated on the bench.

Fig. 13 shows the schematic with indication of the relevant parts. The 28V output powers the stepper

motors while the 12V output supplies the printhead. When the printer is idle these two outputs are not

loaded. The 5V section supplies the logic circuits as well as the

µcontroller that must be operating also

when the system is idle.

The system operates at 100 kHz at nominal load. This value is set by the parallel of the 22 k

Ω and the

5.6 k

Ω resistors connected at pin 2, along with the 3.3 nF capacitor placed between pin 2 and ground.

When the output load is decreased so that the input power falls below about 8W, the output of the error

nally the 5.6 k

Ω resistor, so that the capacitor is charged through the 22 kΩ resistor only and the oscilla-

tor frequency is changed to about 20 kHz.

The system works in standby at 20 kHz as long as the input power does not exceed about 9 W. When

the load current increases and this power is exceeded, the output of the error amplifier overcomes the

Ω resistor, thus switching the oscillator fre-

quency back to 100 kHz.

4700pF 4KV

4700pF 4KV

4.7M

STP4NA60

4N35

220

2 x 330

µF

35V

1K

0.022

µF

2.7K

3.9K

28V / 0.7A

GND

470

µF

16V

BYW100-50

BYW98-100

BYW100-200

4.7M

12V / 1.5A

5V / 0.5A

C02

C01

F01 AC 250V T1A

85 to

265 Vac

BD01

2.2

LF01

56K

10

22

13

1K

12

470pF

11

0.47

1/2 W

33

µF / 25V

8

9

14

15

22

330K

47K

2

3

4

1

0.1

µF

22K

3.3 nF

16

7

330 nF

470

470pF

6

BAT46

TL431

L5991

STTA106

5

5.6K

N1

N2

N3

N4

Naux

5.6K

5.6K

2 x 470

µF

16V

5.1K

270K

100

µF

400V

BZW50-100

1N4148

56K

Figure 13. 40W Power Supply for inkjet printers. Electrical schematic

TRANSFORMER SPECS.

CORE:

EDT29x16x10, 3c85 material, 1.4mm air gap

Prim. Induct:

260

µH

N1:

51 T, AWG26

N2:

11 T, AWG25

N3:

10 T, AWG20

N4:

4 T, AWG25

Naux:

10 T, AWG32

AN1049 APPLICATION NOTE

16/24