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Electronics => Microcontrollers => Topic started by: ocset on December 06, 2017, 08:42:36 pm

Title: DALI TX opto should have greater CTR?
Post by: ocset on December 06, 2017, 08:42:36 pm

Hello,
Figure 5, page 3, of the following DALI application note (AN1465) shows optos being used to isolate both TX and RX DALI signals…. :D

AN1465 Application note:
http://ww1.microchip.com/downloads/en/AppNotes/01465A.pdf (http://ww1.microchip.com/downloads/en/AppNotes/01465A.pdf)

Though surely, the TX opto should be a TCLT1009 (CTR of TCLT1009 = 300%) and not a TCLT1000 (CTR of TCLT1000 = 50%)?   :-//

Also, surely the RX opto should be a TCLT1000, which it indeed is.  :clap:

The reason that the RX opto should be a TCLT1000 is because it has a lower capacitance seen at its emitter pin which means the rise time of the emitter can be quicker. Do you agree?  :-//

TCLT100X opto datasheet:
https://www.vishay.com/docs/83515/tclt1000.pdf (https://www.vishay.com/docs/83515/tclt1000.pdf)

Title: Re: DALI TX opto should have greater CTR?
Post by: CJay on December 06, 2017, 08:54:55 pm

DALI is only 1200BPS isn't it?

Not at all convinced it's necessary for it to be faster, I'm transferring 19200 BPS logic level serial through two CNY25s, the only extra components are a couple of pull up resistors per opto.

Title: Re: DALI TX opto should have greater CTR?
Post by: dmills on December 16, 2017, 05:45:36 pm

The usual problem with simple minded DALI is that the transmit edge is **overly fast** not too slow.

Check the standard, but as I recall there was a limit on how fact the line should fall when you transmit. 

regards, Dan.