When the buck topology is used, and the LED is connected in series with the inductor, there is no need for

any protection against an open circuit condition in the LED string. Open LED connection means no switching

and can be continuous. However, in the case of the buck-booster or the flyback topology the FC9910B may

cause excessive voltage stress of the switching transistor and the rectifier diode and potential failure.

In the case, the FC9910B can be disabled by pulling the PWM_D pin to ground when the over voltage

condition is detected.

Application Information (Continued)

FC9910B

2013. 08. 29

8/10

Revision No : 1

10. output Open Circuit Protection

Figure 4：Typical Application Circuit

0.2 Ω

AC Input

85-135V AC

68µ F,

160 V

750µΗ ,

LEDs

ES1B

FTK4N60D/F

coilcraft

BUSH-2820R5B

VIN

VDD

LD

PW M_D

GND

RT

CS

GATE

0.1µF,

250 V

0.1µF,

250 V

1n F,

250 V

1n F,

250 V

2A,

250 V

2R

NTC

1N4007

1N4007

1N4007

1N4007

FC9910B

68µ F,

160 V

1N4007

1N4007

1µF,

10V

optional for PFC

220nF,

400 V

LED(s) – a string of HB LEDs , 16 diodes

280 kΩ

1N4007*4 = DF06 / DF06S