MP4056—TRIAC DIMMABLE, NON-ISOLATED OFFLINE LED CONTROLLER WITH APFC

MP4056 Rev.1.01

www.MonolithicPower.com

17

11/9/2016

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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 Figure5.

Initially,

VCC

charges

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

This cycle repeats until the auxiliary winding

voltage is high enough to power VCC.

If any fault occurs during this time, the switching

and the internal charging circuit stops, and VCC

internal re-charge is enabled to auto-restart.

Vcc

Internal

Charging Circuit

And Regulates the VCC

Auxiliary Winding Takes Charge

Fault happens

Gate

Switching Pulses

Figure 5: VCC Timing Sequence

Auto Start

The MP4056 contains an auto starter that starts

timing when the MOSFET turns off. If ZCD fails

will automatically send a turn-on signal to avoid

unnecessary shutdown.

Minimum OFF Time

MP4056 operates with a variable switching

frequency; the frequency changes with the

instantaneous input line voltage. In order to limit

the maximum frequency and get a good EMI

performance, the MP4056 employs an internal

minimum off time.

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 pin during the blanking time.

Figure 6 shows the leading-edge blanking.

t

Figure 6: Leading-Edge Blanking