Werner's Miscellanea
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Werner's Miscellanea Commit Details
Date: | 2011-09-11 17:41:24 (12 years 6 months ago) |
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Author: | Werner Almesberger |
Commit: | b2c84810c6d47370015386a0dab55ed29f5fc987 |
Message: | labsw/README: described situation with respect to high voltage |
Files: |
labsw/README (1 diff) |
Change Details
labsw/README | ||
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1 | Opto-isolated inputs | |
2 | -------------------- | |
3 | ||
4 | The C8051F320 needs a current of at least 50 uA to drive an input low. | |
5 | The current transfer ratio of the opto coupler is 50% or better. | |
6 | Thus we need an input current of at least 100 uA. | |
7 | ||
8 | If we allow for a loss of at least 100 mV (yielding a minimum input | |
9 | voltage of 1.5 V), the protection resistor can be at most 1 kOhm. | |
10 | ||
11 | If the maximum power dissipation of the protection resistor is | |
12 | limited to 1 W, we can allow up to 30 mA into 1 kOhm +/- 10%. | |
13 | ||
14 | The maximum input voltage would thus be 30 V. | |
15 | ||
16 | ||
17 | Future changes for higher voltages | |
18 | ---------------------------------- | |
19 | ||
20 | The circuit is currently not designed for voltages exceeding about | |
21 | 30 V between any two points ! | |
22 | ||
23 | To allow the use with mains voltages, be it across the relays or be | |
24 | it as a difference in "ground" potential of separate loops, at least | |
25 | the 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 | ||
31 | In 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 |
Branches:
master