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CC operation mode consulation regarding LNK-3

Posted by: IalJnI on Wed, 06/30/2021

Dear expert,

     Thanks for your rare time to take an explanation。I have the following serial question for datasheet.

Q 1:  In CC mode, what is adjusting max frequency?

Q 2:  For cable compensation,our device is how to sample output current in DCM or CCM mode.

Q3:   which frequency is frequency ratio basing on?

 Above request,have you detail resource explanation from theory by formula , waveform, etc.? as datasheet has simple content lead to don’t  deeply understand this content  when lack of PSR baisc knowledge.

Best regards!


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Submitted by PI-Hiro on Wed, 07/07/2021

Hi IalanJ,


When the power supply operates in constant voltage mode, voltage regulation is obtained using the ON/OFF method. As the load increases, the number of pulses also starts to increase until it reaches the maximum output current. At this point, the switching frequency is at its maximum and is the switching frequency set in PI Expert while designing the power supply. This is also the point where the power supply transitions to constant current mode. As this is the maximum output current of the power supply, further load demand will result to a decrease in the output voltage and in turn will also decrease the feedback pin voltage. As the feedback pin voltage decreases, the switching frequency decreases to maintain constant current regulation.


For cable compensation, the IC determines the output current from the switching pulses generated during operation.


This is a parameter used as a factory specification in manufacturing the IC.

In typical applications of the LinkSwitch-3, primary side regulation is used where the voltage on the bias winding is sensed to regulate the output. Since the number of bias winding turns is known upon design and construction, a relationship between the output voltage and bias winding voltage can be obtained from the transformer turns ratio. Since this method does not directly tap on the output voltage and is dependent on the construction of the transformer, output regulation cannot be expected to be very tight.