MP4033—PRIMARY-SIDE–CONTROL, OFFLINE LED CONTROLLER WITH PFC

MP4033 Rev. 1.0

www.MonolithicPower.com

18

10/22/2014

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Output Over-Voltage Protection (OVP)

Output over-voltage protection (OVP) prevents

the components from over-voltage damage. The

auxiliary winding voltage’s positive plateau is

proportional to the output voltage, so the OVP

block monitors this auxiliary winding voltage to

apply an OVP function, as shown in Figure 7.

OVP signal is triggered, the gate driver turns off,

the IC works in its quiescent current mode. When

the VCC voltage drops below the UVLO

threshold, the IC shuts down and the system

restarts. The output OVP set point is calculated

as:

⋅⋅

=

+

aux

ZCD2

out _ ovp

ZCD _ OVP

sec

ZCD1

ZCD2

NR

VV

NR

R

Where:

Figure 7: OVP Sampling Circuit

To avoid switch-off spikes mis-triggering OVP,

shown in Figure 8.

Figure 8: ZCD Voltage and OVP Sampling

Cycle by Cycle Current Limit

There is cycle by cycle current limit on the S pin,

after a blanking time, the switching will be turn off

to limit the peak current value.

Primary Over-Current Protection (OCP)

The

S

pin

has

an

internally-integrated

comparator for primary side OCP. When the gate

is on, the comparator is enabled. Over-current

time. The IC shuts down and restarts after VCC

drops below UVLO. The OCP function block

diagram is shown in Figure 9.

Figure 9: Over-Current Protection Circuit

LED Short Circuit Protection (SCP)

When the LED Short Circuit occurs, IC reduces

the switching frequency to 7kHz. The output

power at this condition is limited at a safe range.

ZCD Pin Short Circuit Protection

pin short circuit. The MP4033 stops the switching

until VCC drops below UVLO and restarts. This

prevents the components from over-voltage

damage if LED load opens while ZCD pin shorts

at the same time.

Thermal Shutdown

To prevent IC from thermal damage, the MP4033

latches off the switching cycle when the junction

temperature is higher than 150°C. When the

VCC drops below UVLO, it restarts again .