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AN6846

Applying SG6846 to Control a Flyback Power Supply with Surge Current Output

Fairchild Semiconductor 

AN-6846

Table 1. Comparison

Symbol

Parameter

Feedback Input Section

tD-OLP

Delay Time for Open-Loop Protection (RI = 26kΩ)

Over-Temperature Protection (OTP) Section

tDOTP-LATCH Over-Temperature Latch-off Debounce (RI = 26kΩ)

Current Sense Section

tD-SCP

Delay Time for output short circuit protection (RI = 26kΩ)

tD-OCP

VSTH (VIN=1V)

VSTH (VIN=3V)

VSTH – 2/3 (1/2)

Delay Time for Over-Current Protection (RI = 26kΩ)

Threshold Voltage for Current Limit

Threshold Voltage for Current Limit

Threshold Voltage for Over Current Protection

APPLICATION NOTE

SG6846A

SG6846B

SG6846C

SG6846G

1700ms

NA

110ms

100ms

100µs

100ms

7ms

1700ms

200ms

0.83V

0.7V

VSTH × 2/3

NA

110ms

1.1V

0.94V

VSTH × 1/2

Symbol

Parameter

Oscillator Section

VFB-N

FB Threshold Voltage For Frequency Reduction (RI = 26kΩ)

VFB-G

FB Voltage at Green-mode Minimum Frequency (RI = 26kΩ)

VFB-ZDC

FB Threshold Voltage for Zero-duty

SG6846A/B/C

2.1

1.6

VFB-G

SG6846G

2.8V

2.3V

2V

Figure 3. SG6846A/B/C PWM Frequency

Figure 4. SG6846G PWM Frequency

© 2008 Fairchild Semiconductor Corporation

Rev. 1.3.2 • 9/26/08

2

www.fairchildsemi.com

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