MP4060—TRIAC Dimmable PFC, PSC LED Controller for 200-265VAC LEDs

MP4060 Rev. 1.0

www.MonolithicPower.com

17

5/27/2015

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Power-Factor Correction

MULT is connected to the tap of a resistor divider

from the rectified instantaneous line voltage,

driving a sinusoidal multiplier output. This signal

provides the reference for the current comparator,

which shapes the primary peak current into a

sinusoid and has the same phase with the input

line voltage. This guarantees a high power factor

(see Figure 4).

Inductor current

Multiplier output

Figure 4—Power-factor correction

The multiplier’s maximum output voltage to the

limit the cycle-by-cycle current. The multiplier’s

to ensure a turn-on signal during the TRIAC

dimming-off interval, which pulls down the

rectifier input voltage and accurately detects the

dimming phase.

VCC Timing Sequence

The VCC timing sequence is shown in Figure 5.

Initially, VCC is charged through the internal

charging circuit from the AC line. When VCC

charging, the control logic initializes, and the

internal main MOSFET begins to switch. The

auxiliary winding takes over the power supply.

However, the initial auxiliary winding positive

voltage may not be large enough to charge VCC,

causing VCC to drop. Instead, if the VCC voltage

charging circuit triggers and charges VCC to

winding voltage is high enough to power VCC

If any fault occurs during this time, the switching

and the internal charging circuit stop, and VCC

internal re-charge is enabled to auto-restart.

To simplify the power supply circuitry, an external

charging diode is applied between D (the source

of the external power MOSFET) and the VCC

capacitor (see Typical Application). D takes over

the VCC power supply at normal operation,

without an auxiliary winding. If any fault occurs,

the system re-starts after the input AC line

powers down/up again.

Figure 5—VCC timing sequence

Auto Start

The MP4060 contains an auto starter that starts

timing when the MOSFET turns off. If ZCD fails

the starter sends a turn-on signal to avoid an

unnecessary shutdown.

Minimum off Time

The MP4060 operates with a variable switching

frequency. The frequency changes with the

instantaneous input BUS voltage. In order to limit

the maximum frequency and get good EMI

performance, the MP4060 employs an internal

minimum off-time limiter.

Leading-Edge Blanking

In order to avoid premature switching-pulse

termination due to the parasitic capacitances

discharging when the MOSFET turns on, an

internal leading-edge-blanking (LEB) time is

introduced on S. The current comparator blocks

the input path from S during the blanking time

(see Figure 6)