MP4034 – OFFLINE LED DRIVER

MP4034 Rev. 1.02

www.MonolithicPower.com

10

12/4/2013

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OPERATION

Figure 2: Simplified Flyback Converter

Startup

Initially, the IC is self-supplying through the

internal high-voltage current source, which is

drawn from the Drain pin. The internal high-

voltage current source will turn off for better

threshold. Then the transformer’s auxiliary

winding takes over as the power source. When

stops switching and the internal high-voltage

current source turns on again. See Figure 3 for

the start-up waveform.

Figure 3: VCC UVLO

Transformer Design

Figure 4: Isolated Flyback LED Driver

The MP4034 ensures that the circuit operates

in discontinues conduction mode (DCM). When

flowing

through

transformer’s

primary-side

0

Figure 5: Current Waveform

stored in the inductor is given by:

2

MPK

S

1

PL

I

f

2

=

××

Then inductance of coupling inductor is then:

O

M

2

PK

S

2P

L

If

×

=

×× η

estimated efficiency.

When MP4034’s internal switch turns off, the

secondary-side diode and decrease linearly, as

shown in Figure 5.

17.3 V

6.3V

Vcc

Drain

Switching Pulses

Regulation Occurs Here

Auxiliary Winding Takes Charge

High voltage

current source

ON

OFF