Date:2011-09-11 17:41:24 (7 years 9 months ago)
Author:Werner Almesberger
Commit:b2c84810c6d47370015386a0dab55ed29f5fc987
Message:labsw/README: described situation with respect to high voltage

Files: labsw/README (1 diff)

Change Details

labsw/README
1Opto-isolated inputs
2--------------------
3
4The C8051F320 needs a current of at least 50 uA to drive an input low.
5The current transfer ratio of the opto coupler is 50% or better.
6Thus we need an input current of at least 100 uA.
7
8If we allow for a loss of at least 100 mV (yielding a minimum input
9voltage of 1.5 V), the protection resistor can be at most 1 kOhm.
10
11If the maximum power dissipation of the protection resistor is
12limited to 1 W, we can allow up to 30 mA into 1 kOhm +/- 10%.
13
14The maximum input voltage would thus be 30 V.
15
16
17Future changes for higher voltages
18----------------------------------
19
20The circuit is currently not designed for voltages exceeding about
2130 V between any two points !
22
23To allow the use with mains voltages, be it across the relays or be
24it as a difference in "ground" potential of separate loops, at least
25the following changes will be necessary:
26
27- air gaps must be 2 mm or larger (6 kV)
28- conducting elements closer than 2 mm must be isolated if high
29  voltage may exist between them
30
31In particular, this means:
32
33- the PCB must be coated
34- opto couplers may not share the same socket
35- the front opto coupler outputs need wider spacing
36- clearances need to be verified

Archive Download the corresponding diff file

Branches:
master



interactive