* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Uses of the Astable Multivibrator
Stray voltage wikipedia , lookup
Transmission line loudspeaker wikipedia , lookup
Alternating current wikipedia , lookup
Electrical ballast wikipedia , lookup
Time-to-digital converter wikipedia , lookup
Spark-gap transmitter wikipedia , lookup
Voltage optimisation wikipedia , lookup
Current source wikipedia , lookup
Power inverter wikipedia , lookup
Mains electricity wikipedia , lookup
Voltage regulator wikipedia , lookup
Regenerative circuit wikipedia , lookup
Power electronics wikipedia , lookup
Immunity-aware programming wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Wien bridge oscillator wikipedia , lookup
Integrating ADC wikipedia , lookup
Two-port network wikipedia , lookup
Capacitor discharge ignition wikipedia , lookup
Oscilloscope history wikipedia , lookup
Flip-flop (electronics) wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Current mirror wikipedia , lookup
Buck converter wikipedia , lookup
Schmitt trigger wikipedia , lookup
Astable Multivibrator Introduction An astable multivibrator, often called a free-running multivibrator, is a rectan- gular-wave generating circuit. Unlike the monostable multivibrator, this circuit does not require any external trigger to change the state of the output, hence the name freerunning. An astable multivibrator can be produced by adding resistors and a capacitor to the basic timer IC, as illustrated in figure. The timing during which the output is either high or low is determined by the externally connected two resistors and a capacitor. The details of the astable multivibrator circuit are given below. Cont..., • Pin 1 is grounded; • pins 4 and 8 are shorted and then tied to supply +Vcc, output (VOUT is taken form pin 3; • pin 2 and 6 are shorted and the connected to ground through capacitor C, • pin 7 is connected to supply + VCC through a resistor RA; • and between pin 6 and 7 a resistor RB is connected. • At pin 5 either a bypass capacitor of 0.01 • F is connected or modulation input is applied. Astable Multivibrator & Waveforms 2) Astable Multivibrator(Oscillator) 8 UCC charge R1 . R2 first uC=0 + uC – . 5KΩ 5 6 2 . . V A >2/3 <1/3 5K Ω UUCC CC VB . 7 5K Ω T . 1 discharge (grand) 4 10 + + C1 10 + + C2 01 RD Q SD Q RD=1 SD=0 uO 13 +VCC uC 2/3UCC R1 . R u . 2 C 5 8 4 6 3 2 71 . C 1/3UCC t uO uO t tp1 =(R1+R2)C ln2=0.7(R1+R2)C tp2 =R2C ln2=0.7R2C T=tp1+tp2 =0.7(R1+2R2)C Duty Cycle = tp1/T tp1 tp2 Astable Multivibrator Operation In figure, when Q is low or output VOUT is high, the discharging transistor is cut-off and the capacitor C begins charging toward VCC through resistances RA and RB. Because of this, the charging time constant is (RA + RB) C. Eventually, the threshold voltage exceeds +2/3 VCC, the comparator 1 has a high output and triggers the flip-flop so that its Q is high and the timer output is low. With Q high, the discharge transistor saturates and pin 7 grounds so that the capacitor C discharges through resistance RB with a discharging time constant RB C. With the discharging of capacitor, trigger voltage at inverting input of comparator 2 decreases. When it drops below 1/3VCC, the output of comparator 2 goes high and this reset the flip-flop so that Q is low and the timer output is high. This proves the autotransition in output from low to high and then to low as. Thus the cycle repeats. 555 Timer Astable Multivibrator Circuit Cont.., This circuit diagram shows how a 555 timer IC is configured to function as an astable multivibrator. An astable multivibrator is a timing circuit whose 'low' and 'high' states are both unstable. As such, the output of an astable multivibrator toggles between 'low' and 'high' continuously, in effect generating a train of pulses. This circuit is therefore also known as a 'pulse generator' circuit. Cont.., In this circuit, capacitor C1 charges through R1 and R2, eventually building up enough voltage to trigger an internal comparator to toggle the output flip-flop. Once toggled, the flip-flop discharges C1 through R2 into pin 7, which is the discharge pin. When C1's voltage becomes low enough, another internal comparator is triggered to toggle the output flip-flop. This once again allows C1 to charge up through R1 and R2 and the cycle starts all over again. C1's charge-up time t1 is given by: t1 = 0.693(R1+R2)C1. C1's discharge time t2 is given by: t2 = 0.693(R2)C1. Thus, the total period of one cycle is t1+t2 = 0.693 C1(R1+2R2). The frequency f of the output wave is the reciprocal of this period, and is therefore given by: f = 1.44/(C1(R1+2R2)), wherein f is in Hz if R1 and R2 are in mega ohms and C1 is in microfarads. Behavior of the Astable Multivibrator The astable multivibrator is simply an oscillator. The astable multivibrator generates a continuous stream of rectangular off-on pulses that switch between two voltage levels. The frequency of the pulses and their duty cycle are dependent upon the RC network values. The capacitor C charges through the series resistors R1 and R2 with a time constant (R1 + R2)C. The capacitor discharges through R2 with a time constant of R2C 13 Uses of the Astable Multivibrator – Flashing LED’s – Pulse Width Modulation – Pulse Position Modulation – Periodic Timers (see mushroom timer in the experiment). 14