MV1012SC

27

6. Operations in abnormal situations

While the MV1012SC incorporates various protection functions, certain problems cannot be averted by the IC functions

alone. Provided below are some examples of typical abnormal situations. These are provided as a guide.

Always perform appropriate testing using the actual apparatus, including open-circuit and short-circuit tests, to check

operations in abnormal situations.

6.1 LED open-circuit

The MV1012SC has a latch-off function to protect against LED open-circuits using the auxiliary winding voltage and

Vcc_OVP function. For details, see [LED open-circuit protection using auxiliary winding] on page 16.

①

Auxiliary winding is used:

 The output voltage is detected indirectly using the auxiliary winding voltage, and the latch-off is performed with

the Vcc_OVP function.

②

Auxiliary winding is not used:

 The IC operates with the maximum on-time, Ton_max. Vo becomes nearly equal to Vi.

The withstand voltage of the output capacitor should be the same as that of the input capacitor.

6.2 LED short-circuit

If Vo becomes 0 V, the operation automatically switches to the restart operation from zero current detection. That

makes it possible to limit forcibly the current in the event of an LED short-circuit. After the short-circuit is resolved, the IC is

automatically reset and starts to operate with zero current detection.

If the formula below is fulfilled, the IC operates in continuous conduction mode, and a short-circuit current flowing to the

MOSFET or the fly-wheel diode is likely to increase. Make sure the actual apparatus is unaffected in such cases.

Figure 24 shows the ideal waveforms for the Svout and Svin pins in the event of an LED short-circuit. Make sure the

Svin voltage always exceeds the Svout voltage in the event of an LED short-circuit. To prevent false switching-on due to

noise, we recommend making the value of resistors R5 + R6 about 5% less than R7 + R8. For noise reduction, insert

capacitors C8 and C9. (See Sections 3.2.10 and 3.2.13.)

Figure 24 Svin and Svout pin waveforms in the event of an LED short-circuit

F

V

min

_

Ton

max

_

Toff

Vi





CAT.No.1A0602-1E