17-07-2013, 04:14 PM
INVERTER
[attachment=56673]
INTRODUCTION
BASIS OF INVERTER :
The inverter is the dc to ac voltage converter device. In one simple inverter circuit, DC power is connected to a transformer through the centre tap of the primary winding. A switch is rapidly switched back and forth to allow current to flow back to the DC source following two alternate paths through one end of the primary winding and then the other. The alternation of the direction of current in the primary winding of the transformer produces alternating current (AC) in the secondary circuit.
The electromechanical version of the switching device includes two stationary contacts and a spring supported moving contact. The spring holds the movable contact against one of the stationary contacts and an electromagnet pulls the movable contact to the opposite stationary contact. The current in the electromagnet is interrupted by the action of the switch so that the switch continually switches rapidly back and forth. This type of electromechanical inverter switch, called a vibrator or buzzer, was once used in vacuum tube automobile radios. A similar mechanism has been used in door bells, buzzers and tattoo guns.
Output waveforms:
The switch in the simple inverter described above, when not coupled to an output transformer, produces a square voltage waveform due to its simple off and on nature as opposed to the sinusoidal waveform that is the usual waveform of an AC power supply. Using Fourier analysis, periodic waveforms are represented as the sum of an infinite series of sine waves.The sine wave that has the same frequency as the original waveform is called the fundamental component. The other sine waves, called harmonics, that are included in the series have frequencies that are integral multiples of the fundamental frequency.
The quality of the inverter output waveform can be expressed by using the Fourier analysis data to calculate the total harmonic distortion (THD). The total harmonic distortion (THD) is the square root of the sum of the squares of the
harmonic voltages divided by the fundamentals.
THEORY
ASTABLE MULTIVIBRATOR OPERATION :
When power is applied to the circuit one might expect both transistors to switch on because both of them have paths to their bases for current to flow (R2 & R3). If the supply voltage is not applied quickly, i.e. it increases from zero slowly, this can in fact happen but there is a technique to overcome this. However, in most cases the supply is established quickly enough and operation is as follows.
Because of inevitable differences in nominally similar components, and in particular the transistors, one of the transistors will conduct before, or more rapidly than, the other.
Unless stated otherwise any voltage mentioned in the following description implies that it is measured with respect to the negative pole of the supply (0V) and therefore the transistor emitters.
Let’s suppose that TR1 conducts first. It is held on by the current from the supply through R3 and its base-emitter junction. The voltage at its collector will be around +100 mV. Since both capacitors will not have any charge on them at switch on they will both have zero voltage across them. With +100 mV at the left hand plate of C1 and zero volts across it there will also be +100 mV at its right hand plate and therefore at the base of TR2. This is not sufficient to cause TR2 to conduct.
TR1 is conducting there will be +0.6V at its base. C2 has zero volts across it so TR2 collector will also be at +0.6V. Two things now start to happen. Both C1 and C2 start to charge. The right hand plate of C1 starts charging, through R2, from +100Mv towards +9V, and the right hand plate of C2, through R4, from +0.6V towards +9V. The next significant thing which happens is when the voltage on the right hand plate of C1, and therefore TR2’s base, approaches +0.6V.
[attachment=56673]
INTRODUCTION
BASIS OF INVERTER :
The inverter is the dc to ac voltage converter device. In one simple inverter circuit, DC power is connected to a transformer through the centre tap of the primary winding. A switch is rapidly switched back and forth to allow current to flow back to the DC source following two alternate paths through one end of the primary winding and then the other. The alternation of the direction of current in the primary winding of the transformer produces alternating current (AC) in the secondary circuit.
The electromechanical version of the switching device includes two stationary contacts and a spring supported moving contact. The spring holds the movable contact against one of the stationary contacts and an electromagnet pulls the movable contact to the opposite stationary contact. The current in the electromagnet is interrupted by the action of the switch so that the switch continually switches rapidly back and forth. This type of electromechanical inverter switch, called a vibrator or buzzer, was once used in vacuum tube automobile radios. A similar mechanism has been used in door bells, buzzers and tattoo guns.
Output waveforms:
The switch in the simple inverter described above, when not coupled to an output transformer, produces a square voltage waveform due to its simple off and on nature as opposed to the sinusoidal waveform that is the usual waveform of an AC power supply. Using Fourier analysis, periodic waveforms are represented as the sum of an infinite series of sine waves.The sine wave that has the same frequency as the original waveform is called the fundamental component. The other sine waves, called harmonics, that are included in the series have frequencies that are integral multiples of the fundamental frequency.
The quality of the inverter output waveform can be expressed by using the Fourier analysis data to calculate the total harmonic distortion (THD). The total harmonic distortion (THD) is the square root of the sum of the squares of the
harmonic voltages divided by the fundamentals.
THEORY
ASTABLE MULTIVIBRATOR OPERATION :
When power is applied to the circuit one might expect both transistors to switch on because both of them have paths to their bases for current to flow (R2 & R3). If the supply voltage is not applied quickly, i.e. it increases from zero slowly, this can in fact happen but there is a technique to overcome this. However, in most cases the supply is established quickly enough and operation is as follows.
Because of inevitable differences in nominally similar components, and in particular the transistors, one of the transistors will conduct before, or more rapidly than, the other.
Unless stated otherwise any voltage mentioned in the following description implies that it is measured with respect to the negative pole of the supply (0V) and therefore the transistor emitters.
Let’s suppose that TR1 conducts first. It is held on by the current from the supply through R3 and its base-emitter junction. The voltage at its collector will be around +100 mV. Since both capacitors will not have any charge on them at switch on they will both have zero voltage across them. With +100 mV at the left hand plate of C1 and zero volts across it there will also be +100 mV at its right hand plate and therefore at the base of TR2. This is not sufficient to cause TR2 to conduct.
TR1 is conducting there will be +0.6V at its base. C2 has zero volts across it so TR2 collector will also be at +0.6V. Two things now start to happen. Both C1 and C2 start to charge. The right hand plate of C1 starts charging, through R2, from +100Mv towards +9V, and the right hand plate of C2, through R4, from +0.6V towards +9V. The next significant thing which happens is when the voltage on the right hand plate of C1, and therefore TR2’s base, approaches +0.6V.