The Simplest Circuit

We apperceive that if a capacitor is answerable from a voltage antecedent through a resistor, an exponential waveform is produced while charging of a capaci­tor from a connected accepted antecedent produces a ramp. This is the abstraction abaft the circuit. The circuit of a access architect application timer 555 is apparent in figure. Here the resistor of previ­ous circuits is replaced by a PNP transistor that produces a connected charging current.

When a trigger starts the monostable multivibrator timer 555 as shown in figure, the PNP current source forces a constant charging into the capacitor C. The voltage across the capacitor is, therefore, a ramp as illustrated in the figure. The slope of the ramp is given as