MT7603 datasheet(5/6 Pages) MAXIC

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MT7603

Maximizing IC Performance

Linear Constant – Current LED Driver

Rev. 1.00

Page 5

In general, D ≈ 0.5, so

PEAK

LED



 5

The final average LED current needs to be

fine

tuned/trimmed

according

the

measured results. In this case, the system

power factor (PF) can reach more than 0.9.

But the LED output current will increase with

the input voltage.

2) There is an electrolytic capacitor after the

rectifier bridge. After rectifying, the input

voltage substantially closes to DC voltage.

So, the LED output current equals to the

peak current,

PEAK

LED



as calculated in

Equation (1). In this case, the output current

is stable. But power factor is relatively lower.

Power Consumption and Heat

Dissipation

The voltage difference between input voltage

and output LED voltage can generate power

consumption, which is all undertaken by the

external power MOSFET. Hence the LED string

voltage and input voltage should be properly

configured to guarantee the power consumption

in a controllable range, or carry on other effective

thermal design solutions. For example to choose

the MOSFET in better heat dissipation package,

and to add a radiator for MOSFET, etc.

Over Temperature Protection

When the junction temperature exceeds Tfold

(typically 140 ℃ ), the LED output current is

gradually reduced. Thus, the output power and

thermal dissipation are also reduced, so as to

protect the LED lamps, and be able to extend the

system life. When the temperature is higher than

Tfold, the drop slope for the output current with the

temperature is about 4%/℃.

Linear Compensation

MT7603

integrates

Maxic

proprietary linear

compensation technique. The input voltage is

detected by the VLINE pin through a resistor

divider R1, R3, R4. The output current is

compensated when the input voltage varies, so

that the input power keeps stable. As shown in

Fig3.

Linear voltage

compensation

GND

VDD

VLINE

GATE

MT7603

Vin_ac

VLED+

VLED-

Fig.3 Linear compensation application circuit

For buy, please contact: info@chimicron.com

Skype:info@chimicron.com

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For buy, please contact: info@chimicron.com

Skype:info@chimicron.com

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