Bias power requirement of TNY287 Flyback SMPS controller

[treez]

Hi,
We are using the TNY287 for a offline isolated Flyback SMPS (10W), and we are powering the TNY287 from a bias winding. (schem attached)

Page 6 of the datasheet says we must supply 1mA to the TNY287, however page 12 says that the TNY287 requires 550uA.

Page 15 of the datasheet states that if TNY287 us supplied with over 4mA , then it will shut down.
Please advise if the TNY287 requires 550uA or 1mA?
We need to know, because when our secondary is light loaded, our bias coil collapses from 24V down to 14V.........we want to set the feed resistor (R18) to as low value as possible (feed resistor is the resistor that feeds the BP/M pin from the bias coil) so as to reduce dropout of the bias coil in light load as much as possible.

If the 550uA figure applies, then we can set the feed resistor to 11k, but if the 1mA figure applies, then we must set the feed resistor to 6k2.
If we set the feed resistor to 6k2, then when the secondary is loaded, and the bias coil thence goes up to 24V, then we are feeding the TNY287 perilously close to the 4mA maximum.
Please advise the actual bias current draw of the TNY287.

TNY287 datasheet:
https://ac-dc.power.com/sites/default/files/product-docs/tinyswitch-4_family_datasheet.pdf

 

[KlausST]

Hi,

Page 6 of the datasheet says we must supply 1mA to the TNY287, however page 12 says that the TNY287 requires 550uA.

TNY287 includes a shunt voltage regulation. This means you need to supply the 550uA for the circuit plus the current for the shunt regulator.
This means 450uA are used for the shunt clamp to operate correctly.

Please advise if the TNY287 requires 550uA or 1mA?

In this case the circuit is current driven.
You need to ensure that the current is within 1mA ... 4mA.

Klaus