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 IC1a and the other three
gates (wired in parallel) forms a square-wave generator. D1 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 milliampères, depending
on the positive supply voltage (see chart), despite the fact that three
gates are connected in parallel.
Download Skema
Negative Auxiliary Voltage
Password : asinan
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 IC1a, and R1 and C1 can then be omitted.