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Hello,
I use the LM3481 as a Flyback-Controller. I observed a high inrush current of the Flyback-Converter when the LM3481 starts switching, the duty-cycle is also very high (aprox. 90 %).
My question is how the soft start Feature is implemented in the LM3481, becasue it seems there is no soft start. There are some screenshots below wich show the start up Phase of the
Flyback-Converter.
The Flyback-Converter has the following specification:
Vin = 5.5 V to 15.5 V
Vout = 6.1 V
Pout = 1.5 W
Lp = 23µH
Np:Ns = 12:14
Schematic:
Test condition:
Vin = 5.5 V, no load
primary current (ip) (CH3), Vgs (CH1), Vin (CH4), LM3481:COMP (CH2):
Overview of Vout (CH3), Vgs (CH1), Vin (CH4), LM3481:COMP (CH2):
Primary current (ip) (CH3), Vgs (CH1), LM3481:COMP (CH2), Vin (CH4). The screenshot Shows he waveforms when the converter finally stabilizes:
Regards
Adam
Hi Adam,
When the FB pin of the LM3481 grounded there is no soft-start functionality. For a flyback design this can be implemented on the secondary side by soft-starting the voltage reference. Please see the schematic below.
Thanks,
Garrett
