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This article describes a circuit arrangement which generates a negative voltage from a positive source.
English (United States)
This text was extracted from a PDF file.
This is the abbreviated version, containing approximately
90% of the total text.
Page 1 of 1
Positive to Negative Voltage Converter
This article describes a circuit arrangement which generates a negative
voltage from a positive source.
Portable electronic products are frequently constrained to a single polarity
power source (i.e., battery). In cases which require a negative voltage source, it
is necessary to generate that voltage from the positive source. The circuit
arrangement disclosed herein generates a negative voltage from a positive
source by the use of an astable multivibrator as a charge pump, two steering
diodes and two capacitors.
The present circuit arrangement is shown in the drawing. The astable
multivibrator must have a push/pull output and must be capable of providing all
the voltage and current required by the output load at V-. On the positive side of
the cycle of the astable multivibrator output capacitor C1 discharges through
diode CR1 to ground leaving the positive side of the capacitor at one diode drop
above ground. Diode CR2 is reverse biased and blocks current flow into C2. On
the negative side of the cycle the node at the junction of CR1, CR2, and C1
becomes negative. Since CR1 is reverse, current cannot flow through it.
However, CR2 is forward biased and conducts until capacitor C2 is negative
enough to cause diode CR2 to turn off. Capacitor C2 is an integrating capacitor
whose voltage ends up being opposite in polarity but of equal magnitude to the
astable multivibrator output minus two diode drops.