5/18

AN1537 APPLICATION NOTE

Table 3. 45W, wide-range mains AC-DC adapter: list of modifications to the original design

45W AC-DC adapter: evaluation results

The following diagrams compare the performance of the original design ("standard standby") with that of the

modified one ("improved standby"). For reference, it has also been measured the input consumption after re-

placing the start-up circuit made up of R1, R2 and D3 with an active start-up circuit (see fig. 12).

To be noted in figure 4, the no-load consumption is < 0.6W @ 264Vac, then the adapter under test meets the

ECC limits, Phase 3 (< 0.75W @230Vac) with some margin even without the use of an active start-up circuit.

Figure 4. 45W AC-DC adapter: light load input consumption comparison

The diagram on the left in figure 5 shows the relationship between output current and switching frequency ob-

tained with the modified oscillator. The oscillator frequency is not much affected by the input voltage, as shown

also by the oscilloscope diagrams of figures 6 to 10: the internal propagation delay of the current sense pin is

ligible.

The diagram on the right in figure 5 illustrates the effect of temperature on both the oscillator frequency and the

no-load input consumption (@264Vac) in the temperature range 0-70°C: the variation is very limited.

Part

Original value

New Value

Part

Original value

New Value

R7

4.7

Ω

1

Ω

R20

5.6k

Ω

180k

Ω

R8

5.6k

Ω

22k

Ω

R21

348

Ω

3.16k

Ω

R19

6.8k

Ω

27k

Ω

---

5.9k

Ω

R12

24k

Ω

12k

Ω

R’

---

8.2k

Ω

R13

8.2k

Ω

12k

Ω

C7

220pF

3.3nF

R18

2.2k

Ω

20k

Ω

C14

470nF

4.7nF

R19

1.2k

Ω

---

D6, D7

---

1N4148

50

100

150

200

250

300

0.6

0.8

1

1.2

1.4

1.6

Vin [Vac]

Pin [W]

Pout = 0.5 W

fsw = 16 kHz

Tamb= 25 °C

standard standby

improved standby

improved standby

with active start-up (*)

50

100

150

200

250

300

0.4

0.6

0.8

1

1.2

1.4

Vin [Vac]

Pin [W]

Pout = 0.3 W

fsw = 13 kHz

Tamb= 25 °C

standard standby

improved standby

improved standby

with active start-up (*)

50

100

150

200

250

300

0

0.2

0.4

0.6

0.8

1

Vin [Vac]

Pin [W]

Pout = 0 W

fsw = 5 kHz

Tamb= 25 °C

standard standby

improved standby

improved standby

with active start-up (*)

(*) refer to the circuit shown in

the schematic of figure 12

(*) refer to the circuit shown in

the schematic of figure 12

(*) refer to the circuit shown in

the schematic of figure 12