Joinwin Electronics HK Limited518031About Join WinJoinwin Electronics HK Limited FLAT/RM 29, 22/F, YAN’S TOWER, 25-27 WONG CHUK HANG ROAD,ABERDEEN HONGKONG Shenzhen ZhongYiYingTong Technology Limited Room 1610, Block A, Overseas Decorative Building, Zhenhua Road,Huaqiang North Street, Shenzhen, 518031Join-Win will be your one-stop purchasing assistant. Join together, achieve win-win!Joinwin Electronics HK Limited518031About Join WinJoinwin Electronics HK Limited FLAT/RM 29, 22/F, YAN’S TOWER, 25-27 WONG CHUK HANG ROAD,ABERDEEN HONGKONG Shenzhen ZhongYiYingTong Technology Limited Room 1610, Block A, Overseas Decorative Building, Zhenhua Road,Huaqiang North Street, Shenzhen, 518031Join-Win will be your one-stop purchasing assistant. Join together, achieve win-win!Joinwin Electronics HK LimitedJoinwin Electronics HK LimitedJoinwin Electronics HK LimitedJoinwin Electronics HK LimitedJoinwin Electronics HK LimitedJoinwin Electronics HK LimitedJoinwin Electronics HK LimitedJoinwin Electronics HK LimitedJoinwin Electronics HK LimitedJoinwin Electronics HK LimitedJoinwin Electronics HK LimitedJoinwin Electronics

Home
News
555 Monostable Circuit Simulation

555 Monostable Circuit Simulation

September 22 , 2023 0

The 555 Timer is a low cost, reliable, external resistor and capacitor, which can be used to realise pulse generation and conversion circuits such as multi-harmonic oscillator, monostable trigger and Schmitt trigger.
It internally includes two voltage comparators, three 5K ohm equal value of the electric coupling voltage divider resistor 555 timer name is also derived from this), an RS generator, a discharge tube T and power output stage, which provides two reference voltages
CC/3 and 2VCC/3.

Monostable 555 Simulation Function

Its individual pin functions are as follows:

Pin 1: Negative external power supply VSS or ground, normally ground.
Pin 2: Low trigger terminal TR.
Pin 3: output terminal Vo
Pin 4: is the direct zero clearing terminal. When this end is connected to a low level, the time base circuit does not work, at this time, regardless of TR, TH level, the time base circuit output is "0", this end should be connected to a high level when not in use.
5 feet: VC for the control voltage. If this terminal external voltage, you can change the internal reference voltage of the two comparators, when the terminal is not in use, the terminal should be strung into a 0.01μF capacitor ground, in order to prevent the introduction of interference.
Pin 6: High trigger terminal TH.
Pin 7: Discharge terminal. This terminal is connected to the collector of the discharge tube and is used to discharge the capacitor when the timer is used.
Pin 8: external power supply VCC, the range of VCC for bipolar time base circuit is 4.5 ~ 16V, and the range of VCC for CMOS time base circuit is 3 ~ 18V. 5V is generally used.

Working Principle of Monostable Trigger　　

The monostable trigger is characterised by a steady state and a transient state. Under the action of the trigger signal, the circuit will flip from the steady state to the transient steady state, which is a state that cannot be maintained for a long time. Due to the action of the RC delay link in the circuit, the circuit will return to the steady state after a period of time and obtain a rectangular waveform with a pulse width of tw at the output. In a monostable flip-flop, the output pulse width, tw, is the duration of the temporary steady state, the length of which depends on the parameters of the circuit.
The monostable flip-flop circuit and waveforms are shown in Fig. 1, which is composed of NE555. Figure R, C for the external timing components, the input trigger signal ui connected to the low-level trigger terminal (2 feet).

　　Steady state, the output uo is low, that is, no trigger signal (ui is high), the circuit is in a stable state - the output is low. Under the action of ui negative pulse, the low-level trigger terminal gets lower than (1/3) Vcc, the trigger signal, the output uo is high, the discharge tube VT cut-off, the circuit enters the transient steady state, the timing starts.

　　During the temporary steady state, power supply + Vcc → R → C → ground, the capacitor charging, charging time constant T = RC, uc according to the exponential law. When the capacitor voltage uc rises to (2/3) Vcc, 6 terminal for the high level, the output uo becomes low, the discharge tube VT conduction, timing capacitor C charging end, that is, the end of the temporary steady state. The circuit returns to the steady state uo is low. When the second trigger pulse arrives, the above process is repeated. The operating waveform is shown in Fig. 1(b).

Simple touch switch circuit

As shown in Figure 2 for a simple touch switch circuit, the IC is an integrated NE555 timer, which constitutes a monostable trigger, when the hand touch a piece of metal, the low-level trigger terminal is lower than (1/3) Vcc trigger signal, the output uo is high, light-emitting diode is bright, the discharge tube VT cut-off, the circuit enters the transient steady state, the start of the timer. After a certain period of time tw = 1.1RC, light-emitting diode off. The principle circuit can be used for bedside lamps, bathrooms and other places.

NE555 timer for other applications of the circuit

NE555 timer is used in addition to monostable triggers and polyharmonic oscillators, but also applied to Schmitt trigger. As shown in Figure 3 for the light-controlled lighting circuit , the principle of operation is: when the photodiode 2CU2B by the light, its internal resistance becomes smaller, 555 timer 2 feet and 6 feet higher than the voltage of 2Vcc/3, 3 feet of the output is low, the relay is in the off state, the lights do not light. When the night photodiode 2CU2B can not get light or light weak, its internal resistance becomes large, 555 timer 2 feet and 6 feet of voltage is lower than the Vcc / 3, 3 feet output high level, the relay is electrically suction, the light is on. In order to prevent the relay disconnected to produce a higher electric potential and damage to the 555 timer, increase VD5, VD6 to protect the circuit.