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Power Integrations Engineer Power Integrations ModeratorWhy restriction on V to C resistance?
I'm designing a TOP-JX supply, that can be powered either from an universal AC line or from a PFC output. The TOP must turn on with <=50VAC and work up to 440Vdc input.
In order to reduce no-load power, I want to use very high Rls values. But because of the low startup voltage I need a high resistance from V to C; high compared to the app note values. According to page 21 and figure 23 of AN47, I shouldn't exceed 300kR for Rcv if I want auto-restart to act properly.
I found that if I keep the standard 4MR from the AC line to the V pin, I need Rcv=392kR to make the startup be ~50VAC. There is virtually no hysteresis on the shutdown AC voltage. Other than auto-restart, are there any other effects if Rcv is >300kR? Is this not a recommended configuration?
If Rcv should always be <300kR, is my only option to lower Rls to less than 4MR so I can use a smaller Rcv?
EvanShultz
I believe Rcv higher than 390k affects only the auto restart function. Of course, Rcv will affect the line sense resistor value and thus line over voltage, under voltage and line feed forward will be affected too.
Since Rcv need to be lower than 390k, Below 4Mohm line sense resistor is a solution. Although it is very possible that this issue can be solved with extra circuit,the no load always suffer, and thus it does not make a lot sense.
PI-Cochrane | 54 posts 