HV507 Common line: diode protection and current limiting about dsky_el_replica HOT 5 CLOSED

If I were going to redesign it, I'd add a current-limiting resistor to each line immediately at the IC's output. Then, downstream of the current limiting resistors, 8 or 16 lines could be joined together for better drive strength. I would not build it as shown in #2, since even if all lines are switched exactly at the same time, mismatch in output transistors causes problems (ie the IC is destroyed). The clamp diode is good insurance, so I'd keep all that as-is.

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Well, I'm not sure I have the stomach that scale of a redesign at this point -- the driver PCB is really packed (at least for my skill level). Some substantial layout changes would be required to add the resistors next to the chip as you suggest. Am I quoting the right value for the resistors - 47K?
I was going to use 0.2W resistors (the HV507 data sheet rates the output of each line at 0.5mA).
Thanks for your support!

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You can add the resistors to the segment board -- same step as placing and reflowing the board-to-board connectors. I think you'll definitely want to add resistors to at least the 8 or 16 common lines -- don't connect them directly together as shown. It may work for a while, but it's probably not a good plan. Ideally, the resistors would be added to every segment, but it's likely that it will work fine only putting resistors on the commons only. The resistors will dissipate very little average current, so 0402 or even 0201 would be fine. Don't worry about the power rating. 47K minimum. Maybe even go 100K. I'm sorry for the lack of precision in my design -- it's not a problem of missing documentation, but rather a lack of having a completely final ready-for-production design. There are still some small tweaks needed.

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Thanks! will do.

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I toyed with adding resistors to the Segment board last night (image below).

I'm going to think more about your suggestion to place them on the Driver board instead. I'll try to commit to a choice this week.

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