Mesa cards (7i76) field input pull-up resistor
- cts1085
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30 Nov 2016 15:53 #83486
by cts1085
Mesa cards (7i76) field input pull-up resistor was created by cts1085
I know that Peter has recommended PNP over NPN due to no extra parts needed but i find myself with NPN switches.
I also know that Peter has recommended a 2K 1W pullup resistor in these cases.
Is it feasible to use a higher resistance pull-up to lower the current draw when grounded?
In my case I am using 24v field Vcc
for example, a 15k 1/4watt resister still leaves 15v present (after voltage drop) - and the resistor stays cool.
Would a 10K work?
Just trying to reduce heat and current consumption i guess.
Thanks for chiming in...
I also know that Peter has recommended a 2K 1W pullup resistor in these cases.
Is it feasible to use a higher resistance pull-up to lower the current draw when grounded?
In my case I am using 24v field Vcc
for example, a 15k 1/4watt resister still leaves 15v present (after voltage drop) - and the resistor stays cool.
Would a 10K work?
Just trying to reduce heat and current consumption i guess.
Thanks for chiming in...
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- tommylight
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30 Nov 2016 15:56 #83487
by tommylight
Replied by tommylight on topic Mesa cards (7i76) field input pull-up resistor
It should work.
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- PCW
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30 Nov 2016 16:59 - 30 Nov 2016 17:05 #83493
by PCW
Replied by PCW on topic Mesa cards (7i76) field input pull-up resistor
4.7K would be about the highest i would trust for a 7I76 pullup
This would give ~20V in the high state and 24V field voltage.
A 4.7K resistor would dissipate ~ 1/8W at 24V so that should not be an issue
At 24 V the 7I76 input thresholds would be 16.8V (going high)
and 9.6V going low (60% and 40% of field voltage)
A 10K resistor will only pull the input up to ~16.5V so will not provide a valid high level
This would give ~20V in the high state and 24V field voltage.
A 4.7K resistor would dissipate ~ 1/8W at 24V so that should not be an issue
At 24 V the 7I76 input thresholds would be 16.8V (going high)
and 9.6V going low (60% and 40% of field voltage)
A 10K resistor will only pull the input up to ~16.5V so will not provide a valid high level
Last edit: 30 Nov 2016 17:05 by PCW.
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- cts1085
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30 Nov 2016 17:32 #83499
by cts1085
Replied by cts1085 on topic Mesa cards (7i76) field input pull-up resistor
Thank you very much!
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