Ramp Generator Circuit-using 555 Timer IC
We know that if a capacitor is charged
from a voltage source through a resistor, an exponential waveform is
produced while charging of a capacitor from a constant current source
produces a ramp. This is the idea behind the circuit. The circuit of a
ramp generator using timer 555 is shown in figure. Here the resistor of
previous circuits is replaced by a PNP transistor that produces a
constant charging current.
Charging current produced by PNP constant current source is
iC = Vcc-VE / RE
where VE = R2 / (R1 + R2) * VCC + VBE
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
Slope, s = I/C
No comments:
Post a Comment