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This free-running oscillator
circuit generates a triangle waveform, the rising and falling slopes of
which may be set
by completely independent controls. Simultaneously the 555 output (pin
3) provides a rectangular waveform at low impedance that is synchronised
with the triangle waveform.
Assuming
the 555 output is low, the output of constant-current source 01 is shorted
to earth via diode D3. and diode D5 is reverse biased. During this time
current source 02 linearly discharges the timing capacitor C through D6,
D4 being reverse biased. Eventually the voltage on C falls to 1/3Vcc (set
by the internal potential divider that biases the two comparators in the
555) and the 555 output goes high. Now the output of 02 is shorted away
from the timing |
capacitor,
and 01 is allowd to linearly charge it up; when the capacitor voltage reaches
2/3Vcc the 555 Output goes low again, and the cycle |
repeats.
The biasing networks R1D1 and R2D2 compensate for the changes in |
