MV1012SC

15

3.3 Winding voltage supply

3.3.1

Configuration of a winding voltage supply

Using an auxiliary winding shown in Figure 9 protects the MV1012SC against output overvoltages caused (for instance)

by LED open circuits. Additionally, the operation is ensured even with specifications at which the output voltage Vo does

not exceed 10% of the maximum input voltage Vi. (See Section 3.2.6 [Selecting resistors for Svin and Svout pins] on page

12.)

When selecting components, select an auxiliary winding and a rectifier diode for the auxiliary winding.

Figure 9 Configuration of a winding voltage supply

3.3.2

Selecting the auxiliary winding (Nc)

If Vc represents the auxiliary winding voltage rectified and applied to the Vcc pin, Vc is obtained by the formula given

below. Considering changes in Vo due to dimming and changes in VF of the LED, select the turn ratio at which Vc voltage

falls within the range between 10 V and 16 V.

Np: Number of turns of inductor L1 [T]

Nc: Number of turns of auxiliary winding [T]

Depending on the turn ratio or the coupling condition of the winding, a surge voltage is generated in the auxiliary

winding, and Vc voltage may exceed the set level. Check with the actual apparatus to determine whether the Vc voltage is

between 10 V and 16 V.

3.3.3

Selecting the auxiliary winding rectifier diode (D3)

Vr, a reverse voltage represented by the following formula, is applied to D3. Note the withstand voltage when selecting

this component.

When the input voltage is at maximum, the reverse voltage applied to D3 is also at maximum. Use a fast recovery diode

(FRD) for D3.

(See Table 3 Recommended rectifier diodes.)

Vo

Vc

Np

Nc 

Np

Nc

Vi

Vr





CAT.No.1A0602-1E