Rectangular pulse generator

The difference between a rectangular pulse generator and a square wave is that the high level and low level of a square wave occupy equal time (i.e. the duty cycle is 50%), while the rectangular pulse does not.

Figure 5.3-35 is a rectangular pulse generator circuit with adjustable duty cycle and its working waveform. The working principle of the square wave generator is shown in Figure 5.3-34. This circuit uses the unidirectional conductivity of the diode to separate the C charging and discharging circuits. Due to the different charging and discharging time constants, a rectangular pulse is formed. The time constant RC when C is charged is

The potentiometer RW in the figure can change the duty cycle of the output rectangular pulse in the range of about 1% to 99%. When adjusting the duty cycle, Y0 remains unchanged.

In the circuit diagram shown in Figure 5.3-34A, if R4 is not grounded but connected to the external control signal U1, as shown in Figure 5.3-36, the width of the output pulse will be modulated by U1, which becomes a simple adjustable width rectangular pulse generator.

It can be seen from the above formula that TO is related to U1, which is undesirable. However, if U1 < UZ, R4> R3, the periodic variation angle TO caused by U1 is very small. For example, if U1=0.2UZ, R4=2R3, the angle TO/TO=0.6%.