Astable 555 Multivibrator

Astable 555 Multivibrator
freq  Hz period Sec duty cycle Power Ra                                       kilo ohms                                 mega ohms                                  Rb                                       kilo ohms                                 mega ohms                                  Ct                                       uF                                 nF                                  LED1 LED2
Above in Gadget form, Astable 555 Multivibrator Gadget , for your Webpage or Google Home Page.

These are the formulae used by 555 and same is used in javascript without any change.

T1 = 0.693 (Ra + Rb) * Ct   charge time of Ct 

T2 = 0.693 (Rb * Ct)  discharge time of Ct

T = T1 + T 2    total period in seconds

F = 1 / T = 1.44 / ((Ra + (2 * Rb)) * Ct)   Frequency in Hertz

D = T 2 / T  duty cycle, multiply by 100 to get %.

Ct in farads and Ra-Rb in ohms.
The max power dissipation of 555 is 700mW so overload of more than 200mA will damage the device, connecting the battery in the reverse or wrong polarity will also damage device, ensure also Ra and Rb do not go less than 2.2K (use 4.7K minimum) as it may damage the discharge transistor at pin 7. The supply voltage can go upto 18V. For CMOS 555 like 7555 see the datasheet they are different.
the above circuit in pdf format  del00018.pdf
the cadsoft eagle source of the circuit  del00018.zip

datasheet of LM555 here pdf.
pdf links may take time to load in the browser, save file target to your disk is better.
If LEDs are not lighting up, refresh the page. Tested in Mozilla 1, Opera 5 and IE5 with javascript and images enabled.

Press the Red button below to turn on the circuit press it again to turn off. The 555 can source (LED2) or Sink (LED1) upto 200mA. It can even drive a small motor or lamp with diodes added to protect from inductive kickback.
Vary Ra, Rb and Ct with the controls given and see the change of frequency, period and duty cycle.

How to make an Astable or Free running Multi vibrator using 741 Op-Amp ?

Square Wave Generator using Op-Amp

jojo

September - 21 - 2009

8 Comments

 

op amp astable multi vibrator

The non-sinusoidal waveform generators are also called relaxation oscillators. The op-amp relaxation oscillator shown in figure is a square wave generator. In general, square waves are relatively easy to produce. Like the UJT relaxation oscillator, the circuit’s frequency of oscillation is dependent on the charge and discharge of a capacitor C through feedback resistor R,. The “heart” of the oscillator is an inverting op-amp comparator

The compa­rator uses positive feedback that increases the gain of the amplifier. In a comparator circuit this offer two advantages. First, the high gain causes the op-amp’s output to switch very quickly from one state to an­other and vice-versa. Second, the use of positive feedback gives the circuit hysteresis. In the op-amp square-wave generator circuit given in figure, the output voltage v_out is shunted to ground by two Zener diodes Z₁ and Z₂ connected back-to-back and is limited to either  V_{Z 2} or –V_{Z 1}. A fraction of the output is fedback to the non-inverting (+) input terminal. Combination of IL and C acting as a low-pass R-C circuit is used to integrate the output voltage v_out and the capacitor voltage v_c is applied to the inverting input terminal in place of external signal. The differential input voltage is given as v_in = v_c - β v_out

When v_in is positive, v_out = – V_z1 and when v_in is negative v_out = + V_z 2. Consider an instant of time when v_in < 0. At this instant v_out = + V_{z 2} , and the voltage at the non-inverting (+) input terminal is  β V_{z 2} , the capacitor C charges exponentially towards V_{z 2}, with a time constant R_f C. The output voltage remains constant at V_{z 2} until v_c equal β V_{z 2}.

When it happens, comparator output reverses to – V_{z 1}. Now v_c changes exponentially towards -V_z1 with  the  same  time  constant  and  again  the  output  makes  a  transition  from -V_z1 to + V_{z 2.} when v_c equals -βV_{z 1}

Let    V_z1 = V_{z 2}

The time period, T, of the output square wave is determined using the charging and discharging phenomena of the capacitor C. The voltage across the capacitor, v_c when it is charging from – B V_z to + V_z is given by

V_c = [1-(1+β)]e^-T/2τ

Where τ = R_fC

The waveforms of the capacitor voltage v_c and output voltage v_out (or v_z) are shown in figure.

When t = t/2

V_c = +β V_{z or} + β V_out

Therefore β V_z = V_z [1-(1+β)e^-T/2τ]

Or e^-T/2τ = 1- β/1+ β

Or T = 2τ log_e 1+β/1- β = 2R_f C log_e [1+ (2R₃/R₂)]

The frequency, f = 1/T , of the square-wave is independent of output voltage V_out. This circuit is also known as free-running or astable multivibrator because it has two quasi-stable states. The output remains in one state for time T₁ and then makes an abrupt transition to the second state and re­mains in that state for time T₂. The cycle repeats itself after time T = (T₁ + T₂) where T is the time period of the square-wave.

The op-amp square-wave generator is useful in the frequency range of about 10 Hz -10 kHz. At higher frequencies, the op-amp’s slew rate limits the slope of the output square wave. The symmetry of the output waveform depends on the matching of two Zener diodes Z₁ and Z₂. The unsymmetrical square-wave (T₁ not equal to t₂) can be had by using different constants for charging the capacitor C to +V_out and -V_out

How to make an Astable or Free running Multi vibrator using 741 Op-Amp ?

 

op amp astable multi vibrator

The non-sinusoidal waveform generators are also called relaxation oscillators. The op-amp relaxation oscillator shown in figure is a square wave generator. In general, square waves are relatively easy to produce. Like the UJT relaxation oscillator, the circuit’s frequency of oscillation is dependent on the charge and discharge of a capacitor C through feedback resistor R,. The “heart” of the oscillator is an inverting op-amp comparator

The compa­rator uses positive feedback that increases the gain of the amplifier. In a comparator circuit this offer two advantages. First, the high gain causes the op-amp’s output to switch very quickly from one state to an­other and vice-versa. Second, the use of positive feedback gives the circuit hysteresis. In the op-amp square-wave generator circuit given in figure, the output voltage v_out is shunted to ground by two Zener diodes Z₁ and Z₂ connected back-to-back and is limited to either  V_{Z 2} or –V_{Z 1}. A fraction of the output is fedback to the non-inverting (+) input terminal. Combination of IL and C acting as a low-pass R-C circuit is used to integrate the output voltage v_out and the capacitor voltage v_c is applied to the inverting input terminal in place of external signal. The differential input voltage is given as v_in = v_c - β v_out

When v_in is positive, v_out = – V_z1 and when v_in is negative v_out = + V_z 2. Consider an instant of time when v_in < 0. At this instant v_out = + V_{z 2} , and the voltage at the non-inverting (+) input terminal is  β V_{z 2} , the capacitor C charges exponentially towards V_{z 2}, with a time constant R_f C. The output voltage remains constant at V_{z 2} until v_c equal β V_{z 2}.

When it happens, comparator output reverses to – V_{z 1}. Now v_c changes exponentially towards -V_z1 with  the  same  time  constant  and  again  the  output  makes  a  transition  from -V_z1 to + V_{z 2.} when v_c equals -βV_{z 1}

Let    V_z1 = V_{z 2}

The time period, T, of the output square wave is determined using the charging and discharging phenomena of the capacitor C. The voltage across the capacitor, v_c when it is charging from – B V_z to + V_z is given by

V_c = [1-(1+β)]e^-T/2τ

Where τ = R_fC

The waveforms of the capacitor voltage v_c and output voltage v_out (or v_z) are shown in figure.

When t = t/2

V_c = +β V_{z or} + β V_out

Therefore β V_z = V_z [1-(1+β)e^-T/2τ]

Or e^-T/2τ = 1- β/1+ β

Or T = 2τ log_e 1+β/1- β = 2R_f C log_e [1+ (2R₃/R₂)]

The frequency, f = 1/T , of the square-wave is independent of output voltage V_out. This circuit is also known as free-running or astable multivibrator because it has two quasi-stable states. The output remains in one state for time T₁ and then makes an abrupt transition to the second state and re­mains in that state for time T₂. The cycle repeats itself after time T = (T₁ + T₂) where T is the time period of the square-wave.

The op-amp square-wave generator is useful in the frequency range of about 10 Hz -10 kHz. At higher frequencies, the op-amp’s slew rate limits the slope of the output square wave. The symmetry of the output waveform depends on the matching of two Zener diodes Z₁ and Z₂. The unsymmetrical square-wave (T₁ not equal to t₂) can be had by using different constants for charging the capacitor C to +V_out and -V_out

12VDC to 220V 50Hz 500W Inverter Circuit

This is circuit Inverter 12VDC to 220V 50Hz 500W.

It easy to make and Low cost. Friends favorite circuit about the the inverter, because like working outdoors, or to backup storage to use when necessary. Most of this is circuit low power, which is not suitable for practical applications. My friends said that he would be about 500 Watt.

It is a good size. Use with television receivers and light bulbs as well. When looking for circuit. I get headaches. If you are a beginner or I can not buy expensive good quality circuits. Requires only one transistor. Or if you have free time. I want to build old circuit is alive again. This circuit will accommodate all your needs. It is a simple circuit. 

The same principle, I take battery voltage 12V to produce a oscillator about 100 Hz and pass to a two frequency divider circuit is only 50HZ. And drive a 10 ampere transformer with 10 x 2N3055 transistor in parallel. By a single transistor has 2A, when I use 10 transistors or 5 pairs of drive high current output. The complexity of circuit, but the principle is not it, and it is the number of transistors on a basic, easy to buy. You may be modified 100 watt power inverter To the size of transistors and transformers as well.

Source:circuitschematicelectronics