TNY268 only switch when power is plugged then stop switching , not sure of EN/UV pin being floating is correct
I am trying to design a simple power supply using TNY268 , I connected the circuit as in the attached schematic
Where the input of the attached schematic is connected to the output of a bridge and smoothing capacitor , I understood from the datasheet that at the beginning of each cycle the EN/UV pin is sampled to see if its pulled down , then the next cycle is disabled other wise its enabled , I Ignored the feed back optocoupler and left the pin floating (not pulled down) so that the duty cycle is always maximum , switching is not happening except when i connect the HV source then the switching stops
so why is switching stops , what I am missing or misunderstanding from the datasheet ? Is it necessary to use optocoupler ? Can I fix the duty cycle to always maximum and always switching on for testing/Educational purpose at the beginning ?
Thanks
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Hi,
It is necessary to use optocoupler. If you want high duty cycle, you may apply load on your output. Duty cycle will depend on the overall design of your power supply (VIN, VOUT, IOUT, transformer inductance, etc....)
Below is the link of an application notes for deeper understanding of TinySwitch operation.
https://www.power.com/sites/default/files/documents/an-90_tinyswitch-iii_family_design_guide.pdf
Regards,
Jedidiah