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Does this Digital output design correct?
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SiliconWizard:

--- Quote from: Danesh_SA on January 02, 2020, 06:25:16 pm ---I think add discrete free wheel diode is much relaible for this chip!
what do you think?(and why you say "DO NOT USE BOTH the internal diodes (i.e. pin 10) and the discrete diodes.")

--- End quote ---

Not sure why. DS states a typical Vfd of 1.7V for the internal clamp diodes. Adding discrete external diodes in parallel should work as the typical discrete diodes for this will have a much lower Vfd, thus conducting first?
MarkF:

--- Quote from: Danesh_SA on January 02, 2020, 06:25:16 pm ---I have another big concern!
when i check related topics,a few days ago,i noticed someone had issue with ULN2803 internal free wheel diodes on each outputs,he said  THESE ARE NOT ROBUST FOR INDUCTIVE LOADS SUCH AS BIG 24V RELAYS,AND IT CAUSES ULN2803 BURN!
I think add discrete free wheel diode is much reliable for this chip!
what do you think?(and why you say "DO NOT USE BOTH the internal diodes (i.e. pin 10) and the discrete diodes.")

--- End quote ---

I avoid putting diodes in parallel.
If you want external diodes on the outputs, use something like a UF4004.
The 1N4148 you showed before are signal diodes and NOT appropriate for this application.
Yansi:
(unrelated to ULN2803 or whatever:) Bullshit. If the switched current is below what 4148 can handle, there is nothing wrong in using 4148 as the backemf protection for a say 50mA relay.

Neither do I believe internal diodes of ULN2803 are not enough to handle some relay switching, if the currents are within the datasheet limits.  I have used a lot of ULN2003 ICs in the past, never had one failed in a relay switching application.

Maybe if you buy inferior cheap crap from fleabay...
Danesh_SA:
Whats wrong with paralell diodes(internal diodes and  discrete diodes,both of them) ?
BAV70 is another option,i see alot in industrial products used for free wheel diode to handle back EMF .
@yansi do you use discrete diodes for ULN2003 and ULN2803 for your switching applications or just rely on internal diodes?
Yansi:
Only internal ones. No reason to add extra ones.  Used for relays up to about 50mA coils without issues.  Don't see a reason to add external ones.
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