MP4031—PRIMARY-SIDE–CONTROLLED, OFFLINE LED CONTROLLER WITH PFC

MP4031 Rev.1.03

www.MonolithicPower.com

14

5/8/2013

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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)

unit

between the S pin and the current-comparator

input blocks the path from the S pin to the current

comparator input during the blanking time. Figure

7 shows the leading-edge blanking.

t

Figure 7: Leading-Edge Blanking

Output Over-Voltage Protection (OVP)

Output over-voltage protection (OVP) prevents

component damage from over-voltage conditions.

The auxiliary winding voltage’s positive plateau is

proportional to the output voltage, and the OVP

monitors this auxiliary winding voltage instead of

directly monitoring the output voltage as shown in

Figure 8. Once the ZCD pin voltage exceeds

5.5V, the OVP signal triggers and latches, the

gate driver turns off, and the IC functions in

quiescent mode. When the VCC voltage drops

below the UVLO threshold, the IC shuts down

and the system restarts. The output OVP set

point can be calculated as:

aux

ZCD2

out _ ovp

sec

ZCD1

ZCD2

NR

V5.5

NR

R

⋅⋅

=

+

Where:

+

2uS

Blanking

Vcc

ZCD

Auxiliary Winding

OVP

signal

5.5V

Latch

Figure 8: OVP Sampling Circuit

To avoid switch-on spikes mis-triggering OVP,

around 2µs, as shown in Figure 9.

0V

T

OVPS

Sampling Here

Figure 9: ZCD Voltage and OVP Sampling

Overload Protection (OLP)

In the event of an output overload, the COMP

voltage rises. When the voltage reaches 5V, the

IC will shut down and restart until VCC drops

below UVLO.

Thermal Shutdown

To prevent internal temperatures from exceeding

150°C and causing lethal thermal damage, the

MP4031 shuts down the switching cycle and

latched until VCC dropping below UVLO and

restarts again.

TRIAC-Based Dimming Control

The MP4031 can be used in TRIAC-based

dimming application with the CS pin connected

directly to the S pin. The TRIAC dimmer usually

consists of a bi-directional SCR with an

adjustable turn-on phase. Figure 10 shows the

leading-edge TRIAC dimmer waveforms.