MV1012SC

16

Table 3 Recommended rectifier diodes (as of January 2015)

Product name

Withstand

voltage (V)

Io (A)

Cj (pF)

trr (ns)

Manufacturer

Package

M1FL20U

200

1.1

0.98

-

35

Shindengen

M1F

M1FL40U

400

1.5

1.2

11

25

Shindengen

M1F

D1FK60

600

0.8

1.3

11

75

Shindengen

1F

Placing a resistor R12 in series with D3 may reduce the effects of the surge voltage of the auxiliary winding on the Vcc

pin, and reduce Vc voltage increased by the surge voltage.

R10 should be 1 MΩ; R11 should be 220 kΩ.

The Svin and Svout pin waveforms are as shown in Figure 10 when an auxiliary winding is used.

Figure 10 Waveforms of Svin and Svout pins when an auxiliary winding is used

3.3.4

LED open-circuit protection using auxiliary winding

Using the auxiliary winding of the inductor L1 shown in Figure 9 provides protection against output overvoltages due

(for instance) to LED open-circuit. The Vcc pin performs the latch-off function when detecting an overvoltage. It disables

the operation when the Vcc pin voltage reaches 20.7 V (typical). If the auxiliary winding is wound with the polarity shown in

Figure 9, the auxiliary winding voltage is proportional to output voltage; thus, it is possible to indirectly detect an

overvoltage caused by LED open-circuit and to stop the operation.

The following formula gives Vovp, an output voltage at the time of latch-off:

If the difference between the input voltage Vi and the output voltage Vo is small, the Vcc voltage may not reach 20.7 V.

In this case, LED open-circuit protection by the auxiliary winding may fail.

C8

C9

1

2

R10

R11

D3

4

25kΩ

25kΩ

Comp

L1

Vccへ

Nc

Np

-

+

Clamped by the built-in diode

Around 1.5V

V

t

0

Around 0.3V

Vo

Vc

20.7

Vovp





Clamped by the built-in diode

CAT.No.1A0602-1E