MP4030—PRIMARY-SIDE-CONTROL, OFFLINE LED CONTROLLER WITH PFC

MP4030 Rev.1.02

www.MonolithicPower.com

14

4/16/2013

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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 enters quiescent

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

V5.5V

NR

R





Where:

+

Blanking

Vcc

ZCD

Auxiliary Winding

1

OVP

signal

Latch

2

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

Output Short-Circuit Protection (SCP)

In the event of an output short-circuit, the COMP

voltage rises. When the voltage reaches 5V, the

below UVLO.

Primary Over-Current Protection (OCP)

The ZCD pin has an internally-integrated

comparator for primary OCP. When the gate is

on, the comparator is enabled. Over-current

time. Then the IC shuts down and restarts until

OCP.