MV1012SC

19

5. Dimming characteristics

Figure 12 shows typical dimming characteristics for the MV1012SC.

Apply a DC voltage to the REF pin and adjust the voltage to enable linear dimming control. In addition, sending a PWM

switches operations from critical conduction mode to discontinuous conduction mode, allowing adjustments of the output

current to very low levels, even with linear dimming.

[A] frequency modulation region and [B] off-time modulation region shown in Figure 12 are automatically switched over

based on a comparison of Toff (CRM) and Toff (DCM) on the IC. Toff (CRM) is the off-time in critical conduction mode

(sum of toff1 worked out by the formula in Figure 5 on page 8 and the resonant period toff2). Toff (DCM) is the forced

frequency modulation region. When Toff (CRM) < Toff (DCM), the operating mode switches to the [B] off-time modulation

region. The REF pin voltage for switchover changes with input/output conditions, choke inductance, and other parameters.

Calculate the forced off-time Toff (DCM), using the following approximation formula as a guide.

The lower chart in Figure 12 shows a graph of REF pin voltage and off-time. The red curve represents Toff (CRM). The

green curve represents Toff (DCM).

Oscillation off region.

Operating mode

[A] Frequency modulation region

When Toff (CRM) > Toff

(DCM)

[B] Off-time modulation region

When Toff (CRM) < Toff

(DCM)

[C] Oscillation off region

)

V

7

.

0

V

V

24

.

0

(

]

s

[

9

.

9

-

V

9

.

45

35

.

64

)

DCM

(

Toff

REF

REF











（参考）

]

s

[

9

.

9

-

VREF

9

.

45

35

.

64

)

DCM

(

Toff







]

s

[

LC

(max)

Io

2

5

.

2

VREF

V

Vo

L

)

CRM

(

Toff

F

















Dimming ratio [%]

REF pin voltage [V]

REF pin voltage [V]

(Reference)

CAT.No.1A0602-1E