Simulation analysis of working characteristics of 1 Schmidt trigger
In PSPICE's schematic drawing editor, the graphic symbol and pin diagram of 555 timer are shown in figure 1, where pin 1 is the male terminal, pin 2 is the trigger terminal, pin 3 is the output terminal, pin 4 is the reset terminal, pin 5 is the control voltage input terminal, pin 6 is the threshold terminal, pin 7 is the discharge terminal of the internal transistor, and pin 8 is the power terminal.
The Schmitt trigger circuit composed of 555 timers drawn by PSPICE schematic drawing editor is shown in Figure 2. The input signal V 1 is a triangular wave, which is realized by piecewise linear source VPWL, and its amplitude varies linearly between 0v and 5v. Pin 8 is connected to a DC voltage source Vcc=5V. The transient analysis function of PSPICE is used for simulation. Time domain transient analysis refers to calculating the transient response of the circuit output under the action of a given input excitation signal, and its essence is to calculate the time domain response. The transient analysis parameters are set to record data from 0 time to 4s, and the maximum step length is 5 ms. The voltage waveform of the output terminal Vout and the input voltage waveform of 555 are shown in Figure 3. As can be seen from Figure 3, the circuit can convert the input triangular wave into a square wave output. When the input triangular wave voltage increases and the output level changes, the corresponding mosfet is about 3.33 V, while when the input triangular wave voltage decreases and the output level changes, the corresponding mosfet is about 1.67 V, that is, the upper mosfet is different from the lower mosfet, and the input and output have hysteresis characteristics. After changing the input signal into sinusoidal signal, the input and output voltage waveforms (as shown in Figure 4) still show hysteresis characteristics, and the upper mosfet and the lower mosfet are still 3.33 V and 1.67 V respectively, which is the working characteristics of Schmidt trigger circuit. The simulation results are consistent with the theoretical calculation results of upper mosfet 2Vcc/3 and lower mosfet Vcc/3. Obviously, the Schmitt trigger circuit composed of 555 timer has the advantages of simple structure and convenient use.
Simulation analysis of working characteristics of monostable flip-flop 2
Monostable flip-flops are widely used in pulse shaping, delay and timing. The monostable trigger circuit composed of 555 timer drawn by schematic diagram is shown in Figure 5. The input signal Vi is a PULSE voltage source (Vpulse), and its parameters are set as follows: V 1=5 V, V2=0V, PER (period) = 1 ms, and PW (pulse width) = 0.3ms. For monostable flip-flops, pulse is only used as an external trigger pulse, and its amplitude and pulse width will not affect the output signal. Through transient analysis, the output voltage waveform as shown in Figure 6 is obtained, in which the voltage across the capacitor C 1 is similar to sawtooth wave, and the square wave is the voltage waveform of the output terminal Vout of 555.
As can be seen from fig. 6, the capacitor c 1 has an automatic charging and discharging process. Before the capacitor c 1 is charged from 0 V to about 3.33 v, the output of 555 timer keeps high level. Once the capacitor is charged to 3.33 V, the output of 555 switches to low level immediately, and then the capacitor c 1 starts to discharge rapidly from 3.33 V to 0 V, and then a new charging and discharging process begins. A periodic rectangular pulse with a pulse width of about 1.75 ms can be obtained at the output terminal Vout of 555, which is consistent with the theoretical calculation value of1.1× r1. And the width of the output pulse is independent of the pulse width and amplitude of the input signal VPULSE.
Simulation analysis of working characteristics of three-harmonic oscillator
Multi-oscillator is a self-excited oscillator, which can automatically generate rectangular pulses without external trigger signal after the power supply is turned on. The multivibrator circuit composed of 555 timers drawn by the schematic diagram is shown in Figure 7. Start PSPICE transient analysis function. Observing the terminal voltage of capacitor C 1 and the voltage of output terminal Vout of 555, we get the waveform as shown in Figure 8. We find that the output voltage Vout of 555 in Figure 8 always remains at a high level, and the expected oscillation will not occur.
The multivibrator composed of 555 theoretically meets the starting conditions, and the output oscillation period is about [R 1+2×R2]×C 1×ln2, and the duty cycle is about [(r1+R2)/(r1+2× R2)].
3. Analysis of the reasons why 555 multivibrator does not start in1pspice.
The analysis shows that the reason why the 555 multivibrator in PSPICE can't start vibration lies in the starting source and the actual oscillation circuit.
This is my opinion on designing VI, calculating the periodic mean and variance of a triangular wave signal, and displaying the triangular wave on the waveform diagram.