SD4844 Silan Microelectronics, SD4844 Datasheet - Page 8

• Manufacturer Part Number: SD4844
• Description: (SD4840 - SD4844) Current Mode PWM Controller
• Manufacturer: Silan Microelectronics

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6.
The output is shutdown if voltage at Vcc exceeds the threshold and this state is kept until the circuit is powered
on reset.
7.
FB voltage increase if there is overload and the output is shutdown when FB voltage is up to the feedback
shutdown voltage. This state is kept until the circuit is powered on reset.
8.
During each cycle, the peak current value is decided by the comparison value of the comparator, which will not
exceed the peak current limited value to guarantee the current on MOSFET will not be more than the rating
current. The output power will not increase if the current reaches the peak value to limit the max. output power.
The output voltage decreases and FB voltage increases if there is overload and corresponding protection occurs.
9.
That secondary diode is short, or the transformer is short will cause this event. At this time, once it is over current
in spite of the leading edge blanking (L.E.B) time, protection will begin after 350nS, and is active for every cycle.
When the voltage on the current sense resistor is 1.6V, this protection will occur and the output is shut down.
This state is kept until the under voltage occurs, and the circuit will start.
10. Thermal Shutdown
If the circuit is over temperature, the over temperature protection will shut down the output to prevent the circuit
from damage. This state is kept until the under voltage occurs, and the circuit will start.
HANGZHOU SILAN MICROELECTRONICS CO.,LTD
Http: //www.silan.com.cn
Over Voltage Protection
Overload Protection
Peak Current Limit Cycle By Cycle
Abnormal Over Current Protection
SD4840/4841/4842/4843/4844
REV:1.2
Page 8 of 11
2008.12.17