I made a DC POWER Supply 5 volts in my second year of college along with my friend divya alok(class mate).Below is the schematic made in proteus:
Power supplies are required everywhere, from industries to every household whether in urban areas or villages. They form the root of every digital as well as analog electronic item. Here, I demonstrate the construction of a conventional power supply using electronic components like diodes, BJTs FETs etc. The approach is easy to follow and can be used in many other applications. I have chosen +5V as our output voltage since majority of the circuits need such a source. Also to prevent any circuit damage like burning of components, I provided additional protection techniques which limit the output current.
The fundamental source of DC power is a battery or an electrochemical cell. A battery is basically a container carrying chemical reagents which undergo electrochemical reactions. These reactions provide a potential difference across its terminals; this potential difference is harnessed in cars, radios, inverters etc. Although batteries are highly useful devices they suffer from a number of problems. Due to prolonged usage the concentration of the chemical species reduces and the potential difference across their terminals decreases. There are further more constraints which undermines their practical use; their poor performance characteristics, low current ratings, fast discharge rates and also the fact that they are not economically and ecologically viable source of power (i.e. they are not biodegradable and are expensive to manufacture). Thus there's a need of an economically feasible and eco-friendly power source which can satisfy the needs of the industry as well as domestic demands and is easily available.
As an alternative to batteries, we use a source of 220 V 50 Hz from which we can fabricate a source of DC 5V. This source is easily available in India in every urban and sub urban household and in every industry. To get 5V out of AC 220V, the first step would be to step down the AC voltage to a lower level around 12V and then use a Bridge Rectifier to get a waveform which exists only in the positive direction. After this a peak filter i.e. a capacitor of sufficient capacitance will help in achieving the DC voltage.
The disadvantages of this circuit far outweigh its advantages. The voltage is constant for open circuit condition or light loads only. Also the circuit seems relatively simple and easy to fabricate. The disadvantages are that the output waveform has significant amount of ripple. The output voltage drops at heavier loads, i.e., when higher current needs to be drawn from the source which shows poor voltage regulation. To obtain a regulated supply from which we can obtain desired amount of current. Fortunately it is easy to construct stable DC supplies using negative feedback to compare DC output to a stable voltage reference. Such regulated supplies are in universal use, and can be simply constructed with integrated circuit voltage regulator chips, requiring only a source of unregulated DC input (from a transformer-rectifier-capacitor or a battery or some other source of DC input) and a few other components like diodes, BJT's and FET's.
Similar techniques can be used to make voltage regulators with discrete components, but because of availability of inexpensive high-performance regulator chips, there is advantage to using discrete components in new designs. Voltage regulators get us in the domain of high power dissipation, so we need to use techniques like over-voltage protection, current limiting and fold-back limiting to limit transistor operating temperatures and prevent circuit damage.
Circuit Parameters (objective)
· Output Voltage: 5V
· Maximum Current: 1A
· Fold-back Limiting enabled
· Short Circuit Current: 600mA
The µA723 Regulator: The µA723 regulator is an old voltage regulator designed by Bob Widlar in 1967. It offers flexibility and is easy to use and has good performance. The internal circuitry reveals that it contains a temperature compensated zener voltage reference, differential amplifier, series pass transistor, and current limiting protective circuit. High Current Regulator: The internal pass transistor allows maximum 150mA current, in addition the power dissipation must not exceed 1W at 25°C (less than ambient temperatures). Thus a 5V supply running at 12V input cannot supply more than 140mA. To construct a higher current supply, an external pass transistor must be used. It is easy to add one as a Darlington Pair with the internal pass transistor.
Fold-Back Current Limiting: For a regulator with simple current limiting, maximum transistor dissipation is when the output is shorted to ground. The situation is worse in cases when the dropout voltage is a smaller fraction of the supplied voltage. The brute force solution to this problem is to use massive heat sinks and transistors of higher power ratings and safe operation area. Even so, it isn't a good idea to have high currents flowing inside the circuit since other components may get damaged. The best solutions is fold-back current limiting, a circuit technique that reduces the output current under short circuit or overload conditions.
Band Gap Reference: It involves generation of a voltage with positive temperature coefficient, the same as VBE's negative temperature coefficient so that the resultant voltage has nearly 0 temperature coefficient. If we use a simple current mirror whose transistors operate at different emitter currents. Using Eber's Moll Equation it is proved that output current has positive temperature coefficient. This current is passed through a resistor and VBE is added. So now when total voltage is equal to Silicon Band Gap Reference the circuit shows 0 temperature coefficient. The constant sources from the circuit can be used to provide any constant voltage which is used as a reference in place of zeners.
Negative Feedback: This is a process of feeding the output back to the input to cancel off some part of the input. Although it lowers the amplifier's gain but it improves the output characteristics to a much larger extent. The effects include reduction in distortion and nonlinearity of amplifier's gain function, increment in input impedance and decrease in output impedance. In fact, as more negative feedback is implemented, the resultant amplifier characteristics become less dependent on the open loop gain and more on the feedback network itself.
Load Regulation: It is defined as change in output voltage per unit change in load. A power supply should have very low load regulation so that its output voltage remains constant at any load desired.
Line Regulation: It is defined as change in output voltage with change in supplied unregulated voltage.
Output Impedance: It is defined as the open circuit voltage by the short circuit current. For practical voltage sources it should be as low as possible.
Input Impedance: It is the impedance seen from the input side by the voltage source. For voltage supplies, it should be as high as possible so that less power is dissipated and it provides higher efficiency.
• Fixed voltage regulators 7805, 7905 etc series which are only three terminal devices i.e. output, input & a ground. The end user has got nothing to do extra with these regulators since everything is already made.
• Variable voltage regulators are five terminals devices. In addition to the former cases they have to more terminals, the inverting and non-inverting terminals. As the name suggests these regulators can be used to obtain variable voltages as per our requirement. For example LM723, LM317. Unlike the fixed regulators which have the complete protection circuitry is inside the IC, the voltage regulators like LM723 need it externally.
Power supplies are required everywhere, from industries to every household whether in urban areas or villages. They form the root of every digital as well as analog electronic item. Here, I demonstrate the construction of a conventional power supply using electronic components like diodes, BJTs FETs etc. The approach is easy to follow and can be used in many other applications. I have chosen +5V as our output voltage since majority of the circuits need such a source. Also to prevent any circuit damage like burning of components, I provided additional protection techniques which limit the output current.
The fundamental source of DC power is a battery or an electrochemical cell. A battery is basically a container carrying chemical reagents which undergo electrochemical reactions. These reactions provide a potential difference across its terminals; this potential difference is harnessed in cars, radios, inverters etc. Although batteries are highly useful devices they suffer from a number of problems. Due to prolonged usage the concentration of the chemical species reduces and the potential difference across their terminals decreases. There are further more constraints which undermines their practical use; their poor performance characteristics, low current ratings, fast discharge rates and also the fact that they are not economically and ecologically viable source of power (i.e. they are not biodegradable and are expensive to manufacture). Thus there's a need of an economically feasible and eco-friendly power source which can satisfy the needs of the industry as well as domestic demands and is easily available.
As an alternative to batteries, we use a source of 220 V 50 Hz from which we can fabricate a source of DC 5V. This source is easily available in India in every urban and sub urban household and in every industry. To get 5V out of AC 220V, the first step would be to step down the AC voltage to a lower level around 12V and then use a Bridge Rectifier to get a waveform which exists only in the positive direction. After this a peak filter i.e. a capacitor of sufficient capacitance will help in achieving the DC voltage.
The disadvantages of this circuit far outweigh its advantages. The voltage is constant for open circuit condition or light loads only. Also the circuit seems relatively simple and easy to fabricate. The disadvantages are that the output waveform has significant amount of ripple. The output voltage drops at heavier loads, i.e., when higher current needs to be drawn from the source which shows poor voltage regulation. To obtain a regulated supply from which we can obtain desired amount of current. Fortunately it is easy to construct stable DC supplies using negative feedback to compare DC output to a stable voltage reference. Such regulated supplies are in universal use, and can be simply constructed with integrated circuit voltage regulator chips, requiring only a source of unregulated DC input (from a transformer-rectifier-capacitor or a battery or some other source of DC input) and a few other components like diodes, BJT's and FET's.
Similar techniques can be used to make voltage regulators with discrete components, but because of availability of inexpensive high-performance regulator chips, there is advantage to using discrete components in new designs. Voltage regulators get us in the domain of high power dissipation, so we need to use techniques like over-voltage protection, current limiting and fold-back limiting to limit transistor operating temperatures and prevent circuit damage.
Circuit Parameters (objective)
· Output Voltage: 5V
· Maximum Current: 1A
· Fold-back Limiting enabled
· Short Circuit Current: 600mA
The µA723 Regulator: The µA723 regulator is an old voltage regulator designed by Bob Widlar in 1967. It offers flexibility and is easy to use and has good performance. The internal circuitry reveals that it contains a temperature compensated zener voltage reference, differential amplifier, series pass transistor, and current limiting protective circuit. High Current Regulator: The internal pass transistor allows maximum 150mA current, in addition the power dissipation must not exceed 1W at 25°C (less than ambient temperatures). Thus a 5V supply running at 12V input cannot supply more than 140mA. To construct a higher current supply, an external pass transistor must be used. It is easy to add one as a Darlington Pair with the internal pass transistor.
Fold-Back Current Limiting: For a regulator with simple current limiting, maximum transistor dissipation is when the output is shorted to ground. The situation is worse in cases when the dropout voltage is a smaller fraction of the supplied voltage. The brute force solution to this problem is to use massive heat sinks and transistors of higher power ratings and safe operation area. Even so, it isn't a good idea to have high currents flowing inside the circuit since other components may get damaged. The best solutions is fold-back current limiting, a circuit technique that reduces the output current under short circuit or overload conditions.
Band Gap Reference: It involves generation of a voltage with positive temperature coefficient, the same as VBE's negative temperature coefficient so that the resultant voltage has nearly 0 temperature coefficient. If we use a simple current mirror whose transistors operate at different emitter currents. Using Eber's Moll Equation it is proved that output current has positive temperature coefficient. This current is passed through a resistor and VBE is added. So now when total voltage is equal to Silicon Band Gap Reference the circuit shows 0 temperature coefficient. The constant sources from the circuit can be used to provide any constant voltage which is used as a reference in place of zeners.
Negative Feedback: This is a process of feeding the output back to the input to cancel off some part of the input. Although it lowers the amplifier's gain but it improves the output characteristics to a much larger extent. The effects include reduction in distortion and nonlinearity of amplifier's gain function, increment in input impedance and decrease in output impedance. In fact, as more negative feedback is implemented, the resultant amplifier characteristics become less dependent on the open loop gain and more on the feedback network itself.
Load Regulation: It is defined as change in output voltage per unit change in load. A power supply should have very low load regulation so that its output voltage remains constant at any load desired.
Line Regulation: It is defined as change in output voltage with change in supplied unregulated voltage.
Output Impedance: It is defined as the open circuit voltage by the short circuit current. For practical voltage sources it should be as low as possible.
Input Impedance: It is the impedance seen from the input side by the voltage source. For voltage supplies, it should be as high as possible so that less power is dissipated and it provides higher efficiency.
• Fixed voltage regulators 7805, 7905 etc series which are only three terminal devices i.e. output, input & a ground. The end user has got nothing to do extra with these regulators since everything is already made.
• Variable voltage regulators are five terminals devices. In addition to the former cases they have to more terminals, the inverting and non-inverting terminals. As the name suggests these regulators can be used to obtain variable voltages as per our requirement. For example LM723, LM317. Unlike the fixed regulators which have the complete protection circuitry is inside the IC, the voltage regulators like LM723 need it externally.
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