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

MP4033 Rev. 1.0

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21

10/22/2014

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Color Temperature and Brightness Control

for Warm Sunset Dimming application

The color temperature and brightness control

circuit is shown in Figure 16.

Figure 16: Color Temperature and Brightness

Control Circuit

The DIM pin of MP4033 outputs a driving signal

for external MOSFET. The DIM control logic is

shown in Figure 17.

Figure 17: Dim Signal Logic

DIM turn-on signal is the compliment signal of the

dimming turn-on signal. This means the longer

the dimming turn-on cycle, the smaller the DIM

turn-on cycle. When the dimming turn-on cycle is

greater than 70%, the DIM stays low, and the

string. As the dimming turn-on cycle decreases,

the DIM turn-on duty cycle proportionally

stays constant. This current balance achieves

color temperature and brightness control. The

by changing the resistance of Ra.

Dimming Depth Enlargement

Driving a MOSFET to pull down a resistor from

auxiliary winding to GND forms a dummy load,

which to help distribute the output current. The

DIM pin working timing makes the smaller

dimming duty cycle is, the bigger dummy load

distribution current is, the dimming depth is

enlarged. The dimming depth enlargement circuit

is shown in figure 18.

Figure 18: Dimming Depth Enlargement circuit

Programmable Thermal Fold-back (NTC)

The NTC pin is used as the LED programmable

thermal fold-back. A NTC resistor is connected to

this pin directly to monitor the LED temperature.

The LED current changes as the voltage drops

on NTC. Figure 19 shows the NTC curve.

Figure 19: NTC Curve

If the voltage on the NTC pin is lower than the

value, the minimum output current is determined

by the minimum on time of the main MOSFET.

(Equals to LEB time)

Analog Dimming with PWM Input

The MP4033 enables direct control of analog

dimming. Applying a PWM signal (>200Hz) on

NTC pin achieves analog dimming. The output

current will linearly change with the PWM duty

cycle from maximum to minimum. This feature

dramatically reduces the BOM cost for the PWM

dimming system.