Static d.c-d.c converter

A Type 555 timer and some passive components can provide a small converter to provide a negative output of 12 V at a few milliamperes. The 555 is connected as an astable with a rate of 125 kHz. Network C1-D2-05-D3 forms a cascade circuit that supplies a negative direct voltage. Since in the design it was required that neither a transformer nor a coil was used, the efficiency of the converter is not high: not more than 16% at an output current of 20 mA. However. in battery-powered equipment requiring a negative supply at only a few mA, that is no hardship. Note, however, that even unloaded. the converter draws a current of about 15 mA. The output voltage has a ripple of about 0.6 V p-p, which can be suppressed with the aid of a resistor-zener diode network or a low-drop regulator at the output.

Static d.c-d.c converter Schematic diagram

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