LNK3209 auto restart?
Hi,
We are doing a 24V, 17W circuit with LNK3209. VAC input is 100-265VAC.
Pg 13 of AN-70 by Power Integrations says that we must put a capacitor across the upper feedback resistor, of value 470nF to 47uF. This, it says, is needed, because otherwise it wont start up within 50ms and so will hiccup OFF, before the output reaches 24V….and it will go in to auto-restart.
However, what if we no_load the output during startup?….then all that the LNK3209 has to do is charge up the output caps…and it may take a few auto-restarts to do this, but surely it will get there in the end?
As such, can we leave out the 470nF – 47uF capacitor?
AN-70
https://www.power.com/design-support/application-notes/an-70-linkswitch-tn2-design-guide
LNK3209 datasheet:
https://www.power.com/sites/default/files/documents/linkswitch-tn2_family_datasheet.pdf
Comments
Thanks, our load is a BLDC fan motor, fed through a HF bridge. As such, it appears as a resistive load.
The auto-restart can indeed, as you know, be triggered when the load is purely resistive, ....say if the output capacitor bank is very large.
AN-70 also says this......as you know, anything, that stops the vout getting to regulation level inside of 50ms, will trigger the auto-restart....not just non-resistive loads.
Hi,
Thankyou, Yes you are correct.
Regards,
Sigris
Hi,
Thank you for using PI-forums
AN-70 recommends that you add the capacitor when there is non resistive load. is your load non resistive?
the concern there is when powering up with loaded condition there will be a chance that it will not be in
regulation after 50 ms,
if you power it up at "MIN LOAD". all energy will be diverted to output cap and yes it will reach output (within regulation).
Yes, you can leave the cap out.
Regards,
SIGRIS