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AN-6920MR

Integrated Critical-Mode PFC / Quasi-Resonant Current-Mode PWM Controller FAN6920

Fairchild Semiconductor 

AN-6920

[STEP-B5] Design the Over-Temperature

Protection Circuit

The adjustable Over-Temperature Protection (OTP) circuit

is shown in Figure 20. As can be seen, a constant sourcing

current source (IRT) is connected to the RT pin. Once VRT is

lower than 0.8V for longer than 10ms debounce time,

FAN6920 is latched off. RRT can be determined by:

0.8V = (RRT + RNTC @OT ) ×100µ A

(41)

Figure 20. Adjustable Over-Temperature Protection

and External Latched-off Function

(Design Example) Assuming the resistance of NTC at over-

temperature protection point is 4.3kΩ;

RRT

= 0.8V - 4.3kΩ = 3.7kΩ

100µ A

APPLICATION NOTE

© 2010 Fairchild Semiconductor Corporation

Rev. 1.0.0 • March 10, 2011

13

www.fairchildsemi.com

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