SA555DT Datasheet, PDF (12/20 Pages) STMicroelectronics – General-purpose single bipolar timers

Application information
NE555 - SA555 - SE555
4.3
Pulse width modulator
When the timer is connected in the monostable mode and triggered with a continuous pulse
train, the output pulse width can be modulated by a signal applied to pin 5. Figure 18 shows
the circuit.
Figure 18. Pulse width modulator
Trigger
4
2
8
7
VCC
R_A
Output
3
NE555
1
6
Modulation
Input
5
C
4.4
Linear ramp
When the pull-up resistor, R_A, in the monostable circuit is replaced by a constant current
source, a linear ramp is generated. Figure 19 shows a circuit configuration that will perform
this function.
Figure 19. Linear ramp
Trigger
R_E
4
8
2
7
NE555
2N4250
or equiv.
6
VCC
R1
C
Output
3
5
R2
0.01μF
1
12/20
Doc ID 2182 Rev 6