Back to the Future: Home electronics from the （recent） past 3

Published:2011/8/10 0:42:00 Author:Amy From:SeekIC

Negative Auxiliary Voltage

Ludwig Libertin

Some circuits need a negative supply volt­age that only has to supply a small cur­rent. Providing a separate transformer winding for this (possibly even with a rec­tifier and filter capacitor) would be a rather extravagant solution. It can also be done using a few gates and several pas­sive components.

The combination of gate ICla and the other three gates (wired in parallel) forms a square-wave generator. Dl and D2 convert the ac voltage into a dc voltage.

As a CMOS IC is used here, the load on the negative output is limited to a few milliamperes, depending on the positive sup­ply voltage (see chart), despite the fact that three gates are connected in parallel. However, as the figure shows, the negative voltage has almost the same magnitude as the positive input voltage, but with the opposite sign. If a clock signal in the range of 10-50 kHz is available, it can be connected to the input of ICla, and Rl and CI can then be omitted.

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