Negative voltage generator using 555

Negative voltage generator.
I originally designed this circuit in order to repair an Icom 701. It is a fairly standard application of the ubiquitous 555 chip. The output is dependant on the supply voltage and the load, you will not get -9v out with 10v in for example. There is no such thing as a free lunch, and the diodes drop some volts. Replacing silicon diodes with Schottky types will improve things a little.  With a bit of imagination it can be constructed in a very small volume. 

The available current is quite small, about 20mA maximum into a 500R load. Efficiency around 30%. If I recall correctly, the 701 needed just a few uA, so well within the capability of this circuit.

Having recently purchased an SSB i/f PCB that needs -ve volts on the mixers and op-amps, I searched my notebook for
the schematic and made an electronic copy on my Samsung tablet, using the amazing app, SCHEMATIC.

Update .. Aug 2017   I found this to be rather noisy with the Telrad receiver PCB. I removed it and spent some time biasing the MC1496 mixers for single supply operation. 


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