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Many times the hobbyist desires to have a simple, dual power supply for a project. Existing power supplies may be large either in power output or physical size. a simple Dual Power Supply is necessary.For most non-critical applications the best & simplest choice for a voltage regulator is the 3-terminal type.The three terminals are input, ground & output.

The 78xx & 79xx series can provide up to 1A load current & it have on chip circuitry to prevent damage in the event of over heating or excessive current. That is, the chip basically shuts down than blowing out. These regulators are cheap, simple to make use of, & they make it practical to design a method with plenty of P C Bs in which an unregulated supply is brought in & regulation is done locally on each circuit board.

This Dual Power Supply project provides a dual power supply. With the appropriate choice of transformer & 3-terminal voltage regulator pairs you can basically build a tiny power supply delivering up to amp at +/- 5V, +/- 9V, +/- 12V, +/-15V or +/-18V. You require to provide the middle tapped transformer and the 3-terminal pair of regulators you require:7805 & 7905, 7809 & 7909, 7812 & 7912, 7815 & 7915or 7818 & 7918.

The user must pick the pair they needs for his particular application.

Note that the + & - regulators do not must be matched: you can for example, use a +5v & -9V pair. However,the positive regulator must be a 78xx regulator, & the negative a 79xx. They have built in plenty of safety in to this project so it ought to give plenty of years of continuous service.

Transformer
This Dual Power Supply design makes use of a full wave bridge rectifier coupled with a centre-tapped transformer. A transformer with a power output rated at at least 7VA ought to be used. The 7VA rating means that the maximum current which can be delivered without overheating will be around 390mA for the 9V+9V tap; 290mA for the 12V+12V and 230mA for the 15V+15V. If the transformer is rated by output RMS-current then the worth ought to be divided by one.2 to get the current which can be supplied. For example, in this case a 1A RMS can deliver 1/(one.2) or 830mA.

Rectifier

They use an epoxy-packaged four amp bridge rectifier with at least a peak reverse voltage of 200V. (Note the part numbers of bridge rectifiers are not standardised so the number are different from different manufacturers.) For safety the diode voltage rating ought to be at least to times that of the transformers secondary voltage. The current rating of the diodes ought to be two times the maximum load current that will be drawn.

Filter Capacitor
The purpose of the filter capacitor is to smooth out the ripple in the rectified AC voltage. There's dual amount of ripple is determined by the worth of the filer capacitor: the larger the worth the smaller the ripple.The two,200uF is an appropriate value for all the voltages generated using this project. The other consideration in choosing the correct capacitor is its voltage rating. The working voltage of the capacitor has to be greater than the peak output voltage of the rectifier. For an 18V supply the peak output voltage is one.4 x 18V, or 25V. So they have selected a 35V rated capacitor.

Regulators

The unregulated input voltage must always be higher than the regulators output voltage by at least 3V in order for it to work. If the input/output voltage difference is greater than 3V then the excess potential must be dissipated as heat. Without a heat sink three terminal regulators can dissipate about two watts. A simple calculation of the voltage differential times the current drawn will give the watts to be dissipated. Over two watts a heat sink must be provided. If not then the regulator will automatically turn off if the internal temperature reaches 150oC. For safety it is always best to make use of a small heat sink even in case you do not think you will need.

C4 & C5 improve the regulators ability to react to sudden changes in load current & to prevent uncontrolled oscillations.

The mono block capacitor C2 & C6 across the output provides high frequency decoupling which keep the impedance low at high frequencies.

Two LED's are provided to show when the output regulated power is online. You do not must make use of the LED's in the event you do not require to. However, the LED on the negative side of the circuit does provide a maximum load to the 79xx regulator which they found necessary in the coursework of testing. The negative 3-pin regulators did not like a zero load situation. They have provided a 470R/0.5W resistors as the current limiting resistors for the LED's.

These protect chiefly against any back emf which may come back in to the power supply when it supplies power to inductive lots. They also provide additional short circuit protection in the case that the positive output is connected by accident to the negative output. If this happened the usual current limiting shutdown in each regulator may not work as intended. The diodes will short circuit in this case & protect the two regulators.

In recent years, the use of switch mode power supply (SMPS) has become more comon as more applications demand for greater power eficiency. It makes use of semiconductor (mostly MOSFET) fast switches to switch DC input that has been rectified at high frequency. The advantages of high frequency switching are that it reduces the size of inductor, capacitors & transformer used. Other advantages of switching power supply over linear power supply are :

1) High Efficiency (up to 90% and above for nice design).

2) Output can be higher than input.
3) Able to operate over a variety of input power supply.
4) Able to have over output.

The setback of using SMPS compared to linear power supply is that it generates electrical noise which contributes to electromagnetic compatibility design issues & more part count.

Buck Converter SMPS

The SMPS circuit below from Power Integration makes use of LNK304 as its high frequency switch. Take note that this circuit is non isolated type which means that the output is not electrically isolated from the input & all testing ought to be completed using an isolation transformer to provide the AC line input to the board.

Make positive that you have electrical safety knowledge & experience before you embark on doing this project.

This Bipolar power supply for battery instruments . This is a simple circuit diagram, this circuit to generate regulated ± 5-V supplies from a pair of dry batteries, the circuit of Fig. 1 is commonly used. In order to give protection from inadvertent reverse connection of a battery, a diode in series with each battery would produce an unacceptable voltage drop. 

The more effective approach is to fit diodes Dl and D2 as shown in Fig. 2, in parallel with each battery. When the supply is switched off, there is the risk of a reverse bias being applied across the regulators, if there is significant inductance or capacitance in the load circuit. Diodes across the regulators prevent damage. When the power supply is switched on, the two switches do not act in unison. 

There is a probability that one or the other regulators will be latched hard off by the other. To prevent this, D3 and D4 are Zener diodes so that ± 5-V rails are pulled up by the batteries until the regulators establish the correct levels.

This is a Simple 0.5V Negative Supply Circuit Diagram. This simple circuit consists of two LEDs and a photo diode. It generates a negative voltage with a current level of a couple milliamps. It is ideal for supplying a negative rail to low power “rail to rail” op amp circuits, which need to have a true zero volts output. Note: This circuits is not particularly efficient. 

Unregulated power supplies contain four basic components: transformer, rectifier, filter capacitor, and a bleeder resistor. This type of power supply, because of Us simpticity, is the least costly and most reliable for low power requirements. The disadvantage is that the output voltage is not constant It will vary with the input voltage and the load current, and the ripple is not suitable for electronic applications. The ripple can be reduced by changing the filter capacitor to an LC (inductor-capacitor) filter but the cost to make this change would make use of the regulated linear power supply a more economical choice.

Here is a design guide from Linear Technology describing how to design boost power supplies that can work from as little as 0.7 volts. These constant voltage power supplies that can run off until nearly every last drop of power is consumed. [Link]

In this Dual Regulated Power Supply Circuit Diagram, the 7815 regulates the positive supply, and the 7915 regulates the negative supply. The transformer should have a primary rating of 240/220 volts for europe, or 120 volts for North America. The centre tapped secondary coil should be rated about 18 volts at 1 amp or higher, allowing for losses in the regulator. An application for this type of circuit would be for a small regulated bench power supply. 

Many times the hobbyist desires to have a simple, dual power supply for a project. Existing power supplies may be large either in power output or physical size. a simple Dual Power Supply is necessary.For most non-critical applications the best & simplest choice for a voltage regulator is the 3-terminal type.The three terminals are input, ground & output.

The 78xx & 79xx series can provide up to 1A load current & it have on chip circuitry to prevent damage in the event of over heating or excessive current. That is, the chip basically shuts down than blowing out. These regulators are cheap, simple to make use of, & they make it practical to design a method with plenty of P C Bs in which an unregulated supply is brought in & regulation is done locally on each circuit board.

This Dual Power Supply project provides a dual power supply. With the appropriate choice of transformer & 3-terminal voltage regulator pairs you can basically build a tiny power supply delivering up to amp at +/- 5V, +/- 9V, +/- 12V, +/-15V or +/-18V. You require to provide the middle tapped transformer and the 3-terminal pair of regulators you require:7805 & 7905, 7809 & 7909, 7812 & 7912, 7815 & 7915or 7818 & 7918.

The user must pick the pair they needs for his particular application.

Note that the + & - regulators do not must be matched: you can for example, use a +5v & -9V pair. However,the positive regulator must be a 78xx regulator, & the negative a 79xx. They have built in plenty of safety in to this project so it ought to give plenty of years of continuous service.

Transformer
This Dual Power Supply design makes use of a full wave bridge rectifier coupled with a centre-tapped transformer. A transformer with a power output rated at at least 7VA ought to be used. The 7VA rating means that the maximum current which can be delivered without overheating will be around 390mA for the 9V+9V tap; 290mA for the 12V+12V and 230mA for the 15V+15V. If the transformer is rated by output RMS-current then the worth ought to be divided by one.2 to get the current which can be supplied. For example, in this case a 1A RMS can deliver 1/(one.2) or 830mA.

Rectifier

They use an epoxy-packaged four amp bridge rectifier with at least a peak reverse voltage of 200V. (Note the part numbers of bridge rectifiers are not standardised so the number are different from different manufacturers.) For safety the diode voltage rating ought to be at least to times that of the transformers secondary voltage. The current rating of the diodes ought to be two times the maximum load current that will be drawn.

Filter Capacitor
The purpose of the filter capacitor is to smooth out the ripple in the rectified AC voltage. There's dual amount of ripple is determined by the worth of the filer capacitor: the larger the worth the smaller the ripple.The two,200uF is an appropriate value for all the voltages generated using this project. The other consideration in choosing the correct capacitor is its voltage rating. The working voltage of the capacitor has to be greater than the peak output voltage of the rectifier. For an 18V supply the peak output voltage is one.4 x 18V, or 25V. So they have selected a 35V rated capacitor.

Regulators

The unregulated input voltage must always be higher than the regulators output voltage by at least 3V in order for it to work. If the input/output voltage difference is greater than 3V then the excess potential must be dissipated as heat. Without a heat sink three terminal regulators can dissipate about two watts. A simple calculation of the voltage differential times the current drawn will give the watts to be dissipated. Over two watts a heat sink must be provided. If not then the regulator will automatically turn off if the internal temperature reaches 150oC. For safety it is always best to make use of a small heat sink even in case you do not think you will need.

C4 & C5 improve the regulators ability to react to sudden changes in load current & to prevent uncontrolled oscillations.

The mono block capacitor C2 & C6 across the output provides high frequency decoupling which keep the impedance low at high frequencies.

Two LED's are provided to show when the output regulated power is online. You do not must make use of the LED's in the event you do not require to. However, the LED on the negative side of the circuit does provide a maximum load to the 79xx regulator which they found necessary in the coursework of testing. The negative 3-pin regulators did not like a zero load situation. They have provided a 470R/0.5W resistors as the current limiting resistors for the LED's.

These protect chiefly against any back emf which may come back in to the power supply when it supplies power to inductive lots. They also provide additional short circuit protection in the case that the positive output is connected by accident to the negative output. If this happened the usual current limiting shutdown in each regulator may not work as intended. The diodes will short circuit in this case & protect the two regulators.

This Variable DC Power Supply (Rise) Circuit Diagram project provides the schematic & the parts list needed to construct a simple DC Power Supply from an input power supply of 7-20 V AC or 7-30V DC. This project will come in handy in case you use plenty of batteries for your basic electronics project.

Two DC voltage outputs are available; is a fixed regulated 5V for TTL use. The other output is variable from 5V upwards. The maximum output voltage depends on the input voltage. The specified maximum input DC voltage to the regulator is 35V. The maximum input voltage must be two volts higher than the regulated output voltage.

 Variable DC Power Supply (Rise) Circuit Diagram

The DC Power Supply circuit is based around the 7805 voltage regulator. It's only three connections input, output & ground & it provides a fixed output. The last digits of the part number specify the output voltage, e g. 05, 06, 08, ten, 12,15, 18, or 24. The 7800 series provides up to one amp load current & has on-chip circuitry to close down the regulator if any attempt is made to operate it outside its safe operating area.It can be seen that there's in fact separate circuits in this power supply. 7805 is directly connected as a fixed 5V regulator. The second 7805 has a resistor divider network on the output. A variable 500 ohm potentiometer is used to vary the output voltage from a maximum of 5V up to the maximum DC voltage depending on the input voltage. It will be about 2V below the input DC voltage.

The capacitor across the output improves transient response. The giant capacitor across the input is a filter capacitor to help smooth out ripple in the rectified AC voltage. The larger the filter capacitor the lower the ripple.

For tiny applications the heat sinks won't be needed. The tab on the regulator will dissipate 2W at 25 o C in air. (This is equivalent, for example, to an input voltage of 9V, an output of 5V & drawing 500 m A.) However, as your projects get bigger they will draw more current from the power supply and the regulators will operate at a higher temperature and a heat sink will be needed. You can basically add voltage & current meters to it and put it in to an appropriate plastic case connected to a transformer.

Trouble Shooting Procedure

An LED has been put in to the output of the fixed 5V regulator to indicate that the circuit is working. Poor soldering is the most likely reason that the circuit does not work. Check that all the soldering is done properly. Check that all parts are in their correct position on the PCB. Other items to check are to make sure that the regulators, electrolytic capacitor & bridge rectifier are inserted in the correct orientation.

This is a Variable 5 to 20V DC Supply Circuit Diagram. If you are looking for a low drop voltage regulator that can provide a power supply of 1A with an output voltage of between 5V and 20V DC, National Semiconductor LM2941 Low Dropout Adjustable Regulator is that you can pick to make use of. It's a typical dropout voltage of 0.5V which means that the input supply need only must be 0.5V DC over the desired output voltage. 

 

Its other features include internal short circuit current limit and reverse battery protection. As shown in the schematic below, the regulator has five pins which consists of the ON/OFF control, Input Voltage, Output Voltage, Ground & Adjustable pins. ON/OFF is used for the purpose of switching on & off of the regulator. The capacitors C1 & E1 are to be placed as close as feasible to the regulator. 

The output of the circuit can be varied by varying the worth of potentiometer VR1 from 5V DC to 20V DC. The input voltage is limited from five.5V DC to 30V DC. Resistor R1 must be greater than 1K. The worth of the VR1 that needs to be set is calculated from the formula given below: 

VR1 = R1[(Vout/1.275) - 1] ohm

 If R1=1K, Vout = 5V, VR1 should be set to 2.9K ohm. 

 If R1=1K, Vout = 20V, VR1 should be set to 14.7K ohm

In recent years, the use of switch mode power supply (SMPS) has become more comon as more applications demand for greater power eficiency. It makes use of semiconductor (mostly MOSFET) fast switches to switch DC input that has been rectified at high frequency. The advantages of high frequency switching are that it reduces the size of inductor, capacitors & transformer used. Other advantages of switching power supply over linear power supply are :

1) High Efficiency (up to 90% and above for nice design).

2) Output can be higher than input.
3) Able to operate over a variety of input power supply.
4) Able to have over output.

The setback of using SMPS compared to linear power supply is that it generates electrical noise which contributes to electromagnetic compatibility design issues & more part count.

Buck Converter SMPS

The SMPS circuit below from Power Integration makes use of LNK304 as its high frequency switch. Take note that this circuit is non isolated type which means that the output is not electrically isolated from the input & all testing ought to be completed using an isolation transformer to provide the AC line input to the board.

Make positive that you have electrical safety knowledge & experience before you embark on doing this project.

This Power Pulse Using by LM350 and NE555 Circuit Diagram can use to drive lamp,power LED,DC motor etc. Adjust R5 for output amplitude.Adjust R1 for output power .The LM350 is adjustable 3-terminal positive voltage regulators is capable of supplying in excess of 3A over a 1.2V to 33V output range.This circuit requires 5-15V power supply.

 

Maxim describes various SMPS regulator topologies for battery powered systems. Isolated and non-isolated topologies are covered. This tutorial presents an overview of regulator topologies for battery-powered equipment. The discussion covers linear regulators, charge pumps, buck and boost regulators, inverters, and flyback designs. The importance of peak current is explained, and schematics of each topology are shown. [Link]

There are some applications, such as double-ended sensors and audio amplifiers that require a negative voltage for operation. With limited space on today’s system boards, creating a dedicated negative supply rail would add to the cost and space of the PCB. Hence, it makes sense to generate the required negative voltage from existing positive supply rails in the system.

One such solution using a traditional synchronous step-down regulator is provided by Texas Instruments in an application note entitled “Creating an Inverting Power Supply Using a Synchronous Step-Down Regulator”1. It shows you how to generate a negative voltage from a positive input voltage to the synchronous buck regulator. [Link]

 

The MAX17116 includes two current-mode 1.4MHz switch mode power-supply (SMPS) regulators for active-matrix organic light-emitting diode (AMOLED) displays. The positive supply is provided by a step-up regulator with a synchronous rectifier. The negative supply is provided by an inverting regulator with a synchronous rectifier.[Link]