555 Negative Voltage Generator
This circuit is supplied as a hobby project. I get frequent requests for help indicating that there is often a need to generate a negative voltage for RS-232 type interfaces or other circuits when there is only a +5 or +12 volt source that is readily available. I have encountered the same problem. There are commercially available answers for such problems but they are usually cumbersome, expensive, not readily available when you need them, and they are not really adaptable to all situations.
For me, the solution came in the form of a 555 IC project back in the late 70s and early 80s. It is for all practical purposes, a quickie negative voltage generator. There is nothing new or particularly clever about the design as it is based on one of the most popular and versatile ICs ever produced. The parts are plentiful and cheap, two of my hobby criteria for projects; usually they are all part of any electronics workshop junk box. The circuit is very straight forward and easily adaptable to various requirements. The circuit can be used to generate twice the supply voltage by reversing the polarity of the diodes and the output capacitor. See our detailed explanation of serial communications.
The Schematic
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Load (Ohms)
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I in (mA)
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V out (V)
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Iout (calc) (mA)
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The Calculations
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| infinite | 20 | 10.9 | 0 |
| 2200 | 30 | 9.1 | 4.1 |
| 446 | 60 | 8.5 | 19 |
| 248 | 95 | 4.3 | 17 |
| 240 | 100 | 8.2 | 34 |
| 96 | 175 | 6.2 | 54 |
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Version 1.0.1
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