AL1663S-13 datasheet(9/15 Pages) DIODES

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AL1663/AL1663R

Document number: DS38466 Rev. 2 - 2

9 of 15

www.diodes.com

March 2017

AL1663/AL1663R

Application Information (Cont.)

5. Over Temperature Protection (OTP)

The AL1663/AL1663R has build-in over temperature protection (OTP) function. When the temperature goes up to +165°C, the over temperature

protection will be triggered, which leads to a latch mode protection. When OTP happens, the system need to be powered off and on again to

restart.

Output Constant-current Control

According to the definition of mean output current, the mean output current can be obtained as below.

ONS

MEAN









Where IO_MEAN is the mean output current; ISP is secondary peak current of transformer;

tONS is discharge time of secondary side of transformer; tSW is the switch period.

According to the principle of AL1663/AL1663R close loop control, the voltage of RCS will be sampled when switch is turned off and the value will

be held until discharge time tONS is over. It can be described by following formula:

ONS

REF









Where IP is primary peak current of transformer; RCS is current sense resistor which is shown as Figures 1 and 2.

tONS is discharge time of secondary side of transformer; tSW is the switch period. VREF is internal reference voltage that is equal to 0.3V.

The peak current at secondary side has following relationship with primary side peak current, if the effect of the leakage inductor is neglected.



Where NPS is the turns ratio of Flyback transformer (NPS=1 for Buck-boost); IP is the primary peak current of the transformer.

According to these above formulas, the mean output current can be induced finally by below expressions.

REF

O MEAN







Where IO_MEAN is the mean output current; RCS is current sense resistor which is shown as Figures 1 and 2;

VREF is internal reference voltage that is equal to 0.3V; NPS is the turns ratio of Flyback transformer (NPS=1 for Buck-boost);

Therefore, the constant output current control can be realized with appropriate parameter design.

PF and THD compensation circuit

For normal application, AL1663/AL1663R can provide high PF and low THD. But there is a phase difference between input current and input

voltage especially at high input voltage, thus PF and THD may not be the best situation. The below circuit can optimize this situation by reducing

the phase difference. VBUS is connected to the voltage point after rectifier. In normal application resistor RN1 is usually a several hundred k

resistor, RN2 is a

hundred Ω resistor, CN1 is a several µF capacitor. PF and THD can be improved by debugging these components.

COMP

Ccomp

Rcomp

VBUS

CN1

RN1

RN2

Figure 3. PF and THD Optimization Circuit

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