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LinkSwitch-HP Entering Failsafe Mode under very light load conditions ?

Posted by: Markus Meng on

Dear Support,

 

I use the LinkSwitch-HP LNK6773V for a 5..7Watt ACDC Supply. Secondary side is 24VDC. Connecting to the 230VAC main line everything seems to work. Once everything is settled and a light load condition exists on the secondary side, the switch enters kind of hybernate mode pulsing 2..3 times within a certain interval. Suddenly this mode stops the secondary voltage drops and switch enters kind of fail mode. In this mode the switch tries with one pulse every 1.6..2 second. However the secondary never comes back to the nominal 24VDC output voltage. When I then disconnect the 230VAC line (!) the switch starts working and generates 24VDC output voltage as long as there is enough energy in primary side caps after the rectifier.

 

We really need a stable output voltage under very light load conditions. If a connect a 2..5W resistor accross the 24VDC output voltage, the switch enters periodic switching and everything works. No loss of regulation no entrance of hybernate or fail safe mode of the switch.

 

Q : What do I need to change in order to make sure the ACDC converter is not stopping to work under very light load conditions? In my application I can't just add a heat resistor ?

 

br

Markus

 

Attachements :

 

- The schematics of the ACDC converter

- A Scope-Shot Measurement

- The Calculation I made for this ACDC converter

 

Legend of the Scope-Shot :

 

Channel 1 (Green) : the generated 24VDC output voltage (+-5%)

Channel 2 (Magenta) : Measured on the secondary side just before the anode of the recifier diode D203 (See Schematics)

 

 

Comments

Submitted by Markus Meng on 01/20/2014

Dear All,

 

I could track down the problem. The SW Release 9.0.5.1 was buggy in terms of the transformer calculation regarding the Bias Windings. The number of bias windings for HP Chip was to high resulting in an early trigger of the bus line overvoltage protection function if the supply was connected to the 230VAC mains.

 

I did discover by accident when I did update to the 9.0.6.3 version of "PIXls Designer 9" Tool. Without changing anything the Bias windings is no one less resulting in proper operation of the power supply is being connected to the 230VAC lines.

 

br

Markus