MV1012SC

6

2. Explanation of basic operations

The MV1012SC is a critical conduction mode (CRM) step-down chopper control IC. Figure 1 shows the circuit

little recovery current for the diode and lower losses and noises than a PWM circuit. Meanwhile, disadvantageously, the

oscillation frequency changes dramatically as the output current (LED current) changes, resulting in poorer dimming

characteristics and efficiency.

The MV1012SC detects Id, converted to a voltage, with the current detection pin (CS pin). When it reaches the CS

reference voltage, the MV1012SC turns the MOSFET off (peak current detection). The IC performs CRM control in this

(zero current detection) and turns the MOSFET on. The voltages on both ends of the choke (① and ② in Figure 2) are

divided with resistors and input to the Svin pin and the Svout pin to achieve CRM operations without auxiliary winding.

Additionally, the off-time modulation prevents the frequency increasing during dimming and achieves constant high

efficiency and dimming characteristics during deep dimming. (See Section 5 [Dimming characteristics] on page 19.)

Figure 1 CRM step-down chopper circuit

Figure 2 MOSFET and diode current waveforms of the CRM step-down chopper and voltage waveforms

on both ends of the choke

Ip

Io

Vi

Vo

Detect

intersection

Id

Delay in detection by IC + gate delay

0

0

CAT.No.1A0602-1E