1.5 - 35 Volt DC Regulated Power Supply

Here is the circuit diagram of regulated power supply. It is a small power supply that provides a regulated voltage, adjustable between 1.5 and 35 volts at 1 ampere. This circuit is ready to use, you just need to add a suitable transformer. This circuit is thermal overload protected because the current limiter and thermal overload protection are included in the IC.

Picture of the circuit:

1A Regulated Power Supply Circuit Schematic

Circuit diagram:

1A Regulated Power Supply Circuit Diagram

Transformer selection chart:

Transformer selection Guide-Table For Power Supply

Parts:

IC = LM317
P1 = 4.7K
R1 = 120R
C1 = 100nF - 63V
C2 = 1uF - 35V
C3 = 10uF - 35V
C4 = 2200uF - 35V
D1-D4 = 1N4007

Features:

• Just add a suitable transformer (see table)
• Great to power your projects and save money on batteries
• Suitable as an adjustable power supply for experiments
• Control DC motors, low voltage light bulbs, …

Specifications :

• Preset any voltage between 1.5 and 35V
• Very low ripple (80dB rejection)
• Short-circuit, thermal and overload protection
• Max input voltage : 28VAC or 40VDC
• Max dissipation : 15W (with heatsink)
• Dimensions : 52x52mm (2.1” x 2.1”)

Technical Specifications

• Input Voltage = 40Vdc max Transformer
• Output Voltage = 1.5V to 35Vdc
• Output Current = 1.5 Amps max.
• Power Dissipation = 15W max (cooled)

Note:

• It has not to be cooled if used for small powers. 28 Volt AC max is allowed for the input voltage.

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Electronic Fuse for DC Short Circuit Protection

This is an electronic fuse that protects the load against short circuit.

Project Description

Relays must be chosen with a voltage value equals to the input voltage. Don’t omit using the 100uF capacitor with appropriate voltage value with respect to the input voltage. If you can’t provide, you can use C106 instead of BRX46.

You can adjust the current with using 10K potentiometer. If you will use the fuse with very high currents, lower the 0R6 5W resistor value (ex. 0R47, 0R33, 0R22 or 0R1). Watt value of the resistor should be increased also.

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Transformerless Power Supply Circuit

This circuit will supply up to about 20ma at 12 volts. It uses capacitive reactance instead of resistance; and it doesn't generate very much heat.The circuit draws about 30ma AC. Always use a fuse and/or a fusible resistor to be on the safe side. The values given are only a guide. There should be more than enough power available for timers, light operated switches, temperature controllers etc, provided that you use an optical isolator as your circuit's output device. (E.g. MOC 3010/3020) If a relay is unavoidable, use one with a mains voltage coil and switch the coil using the optical isolator.C1 should be of the 'suppressor type'; made to be connected directly across the incoming Mains Supply.

They are generally covered with the logos of several different Safety Standards Authorities. If you need more current, use a larger value capacitor; or put two in parallel; but be careful of what you are doing to the Watts. The low voltage 'AC' is supplied by ZD1 and ZD2. The bridge rectifier can be any of the small 'Round', 'In-line', or 'DIL' types; or you could use four separate diodes. If you want to, you can replace R2 and ZD3 with a 78 Series regulator. The full sized ones will work; but if space is tight, there are some small 100ma versions available in TO 92 type cases. They look like a BC 547. It is also worth noting that many small circuits will work with an unregulated supply.

Circuit diagram:

Transformerless Power Supply Circuit Diagram

You can, of course, alter any or all of the Zenner diodes in order to produce a different output voltage. As for the mains voltage, the suggestion regarding the 110v version is just that, a suggestion. I haven't built it, so be prepared to experiment a little. I get a lot of emails asking if this power supply can be modified to provide currents of anything up to 50 amps. It cannot. The circuit was designed to provide a cheap compact power supply for Cmos logic circuits that require only a few milliamps. The logic circuits were then used to control mains equipment (fans, lights, heaters etc.) through an optically isolated triac.

If more than 20mA is required it is possible to increase C1 to 0.68uF or 1uF and thus obtain a current of up to about 40mA. But 'suppressor type' capacitors are relatively big and more expensive than regular capacitors; and increasing the current means that higher wattage resistors and zener diodes are required. If you try to produce more than about 40mA the circuit will no longer be cheap and compact, and it simply makes more sense to use a transformer. The Transformerless Power Supply Support Material provides a complete circuit description including all the calculations.

Web-masters Note:

I have had several requests for a power supply project without using a power supply. This can save the expense of buying a transformer, but presents potentially lethal voltages at the output terminals. Under no circumstances should a beginner attempt to build such a project.

Important Notice:

Electric Shock Hazard. In the UK,the neutral wire is connected to earth at the power station. If you touch the "Live" wire, then depending on how well earthed you are, you form a conductive path between Live and Neutral. DO NOT TOUCH the output of this power supply. Whilst the output of this circuit sits innocently at 12V with respect to (wrt) the other terminal, it is also 12V above earth potential. Should a component fail then either terminal will become a potential shock hazard.

MAINS ELECTRICITY IS VERY DANGEROUS.

If you are not experienced in dealing with it, then leave this project alone. Although Mains equipment can itself consume a lot of current, the circuits we build to control it, usually only require a few milliamps. Yet the low voltage power supply is frequently the largest part of the construction and a sizeable portion of the cost.

Author: Ron J - Copyright: Zen

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3-A Wide-input Adjustable Switching Regulator

The PTN78060 is a series of high-efficiency, buck-boost, integrated switching regulators (ISR) from good old Texas Instruments (TI). The caseless, double-sided package has excellent thermal characteristics, and is RoHs compliant. The PTN78060 devices operate from a remarkably wide input voltage range:

Note that the –A version supplies a negative output voltage. The devices provide high-efficiency stepdown voltage conversion for loads of up to 3 A. The PTN78060 devices are suited to a wide variety of general-purpose applications that operate off 12-V, 24-V, or tightly regulated 28-V dc power, hence are ideal for running low-voltage electronics from a very high power 24-V battery unit salvaged from an electric wheel chair and migrated into a robot.  The output voltage VO can be set to any value over a wide adjustment range using a single external resistor RSET, using the equation RSET = 54.9kΩ×(1.25V/VO–VMIN) – Rp  If pin 4 is left open, the output voltage defaults to the lowest value.

Limiting ourselves to the two positive-output regulators, for the -W version, VMIN and Rp are 2.5 V and 6.49 kΩ respectively; for the -H device, the values 11.824 V and 6.65 kΩ should be used. For the output to remain in regulation, the input voltage must exceed the output by a minimum differential voltage. Another consideration is the pulsewidth modulation (PWM) range of the regulator’s internal control circuit. For stable operation, its operating duty cycle should not be lower than a certain minimum percentage. This defines the maximum advisable ratio between the regulator input and output voltage magnitudes. For satisfactory performance, the operating input voltage range of the PTN78060x must satisfy the following requirements.

1. For PTN78060W devices supplying output voltages lower than 10 V, the minimum input voltage is (VO+2 V) or 7 V, whichever is higher.

2. For PTN78060Ws supplying output voltages of 10 V and higher, the minimum input voltage is (VO+2.5 V).

3. The maximum input voltage for PTN78060W is 10VO or 36 V, whichever is less.

4. For PTN78060H output voltages lower than 19 V, the minimum input voltage is (VO+3 V) or 15 V, whichever is higher.

5. For PTN78060H output voltages equal to 19 V and higher, the minimum input voltage is (VO+4 V).

 

As an example, the Table gives the operating input voltage range for some commonly used output bus voltages. The modules are protected against load faults with a continuous current limit characteristic. Under a load-fault condition, the output current increases to the current limit threshold. Attempting to draw current that exceeds the current limit threshold causes the module to progressively reduce its output voltage. Current is continuously supplied to the load until the fault is removed. Once it is removed, the output voltage promptly recovers. When limiting output current, the regulator experiences higher power dissipation, which increases its temperature. If the temperature increase is excessive, the module overtemperature protection begins to periodically turn the output voltage off.

The inhibit feature can be used wherever there is a requirement for the output voltage to be turned off. The power module switches off the output voltage when the Inhibit control (pin 3) is pulled to ground,for example, by a switching FET. Finally, good attention should be paid to the quality of the capacitors on VI and VO as they determine the regulator stability and overall performance to a substantial degree. Summarizing the extensive information on capacitor selection found in the datasheets, the minimum requirement for C1 is 2.2 μF (!) worth of ceramic capacitors for the –W device and 14.1 μF (!!) for the-H device. Tantalum caps are not recommended.  Similarly, at the regulator output, C2 should be at least 100 μF worth of low- ESR electrolytics.

Datasheets:
http://focus.ti.com/docs/prod/folders/print/ptn78060h.html
http://focus.ti.com/docs/prod/folders/print/ptn78060w.html
http://focus.ti.com/docs/prod/folders/print/ptn78060a.html

Author : Luc Lemmens Copyright : elektor elector

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Deep Discharge Protection for Rechargeable Cells

With this circuit built into the power supply of a battery powered device, it will prevent the rechargeable cells from being completely drained when you forget to turn the equipment off. When the battery voltage drops below a preset limit (9.5 V in this example) the circuit will automatically disconnect the battery. Power is re-connected when the voltage rises above an upper threshold level (10.5 V here), this will typically occur after the equipment has been plugged into its recharging station.

The circuit is designed to use as little power as possible.The ICL7665 from Intersil forms the heart of the circuit. This IC contains two comparators together with a voltage reference and consumes just 3 μA. The circuit only uses one of the comparators, the values of resistors R1 to R3 shown in the diagram will cause the circuit to switch at the levels mentioned above. The comparator output switches the P-channel MOSFET T1 which in turn controls power to the load RLOAD.

Circuit diagram:

The switching threshold levels and hysteresis can be changed by using different values of resistor for R1 to R3. Increasing the value of R3 to 300 KΩ will raise the upper thresh-old level to 12.5 V. The ICL7665 data sheet gives examples of suitable resistor values that can be used here.  The PCB layout uses SMD components so the finished circuit takes up very little space  when installed in the equipment.  A fine-tipped soldering iron should be adequate to mount the components and there shouldn’t be any problems provided you do not choose to use very small resistor packages. Once the circuit has been tested the entire PCB can be protected by encapsu-lating it with a short length of heat shrink sleeving.

Data sheet IRL7665:  www.intersil.com/data/fn/fn3182.pdf
Data sheet IRLML6402:  www.irf.com/product-info/datasheets/data/irlml6402.pdf

Author : Tilman Küpper Copyright : elektor elector  -  7-8/2007

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Dual Power Supply 78xx-79xx

Many times the hobbyist wants to have a simple, dual power supply for a project. Existing powersupplies may be too big either in power output or physical size. Just a simple Dual Power Supply is required.For most non-critical applications the best and simplest choice for a voltage regulator is the 3-terminal type.The 3 terminals are input, ground and output.

The 78xx & 79xx series can provide up to 1A load current and it have onchip circuitry to prevent damage in the event of over heating or excessive current. That is, the chip simply shuts down rather than blowing out. These regulators are inexpensive, easy to use, and they make it practical to design a system with many PCBs in which an unregulated supply is brought in and regulation is done locally on each circuit board.

Circuit diagram:

Dual Power Supply Schematic Circuit diagram

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

Note that the + and - regulators do not have to be matched: you can for example, use a +5v and -9V pair. However,the positive regulator must be a 78xx regulator, and the negative a 79xx one. We have built in plenty of safety into this project so it should give many years of continuous service.  The user must choose the pair he needs for his particular application.

Parts :

Transformer

This Dual Power Supply design uses a full wave bridge rectifier coupled with a centre-tapped transformer. A transformer with a power output rated at at least 7VA should 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 value should be divided by 1.2 to get the current which can be supplied. For example, in this case a 1A RMS can deliver 1/(1.2) or 830mA.

Rectifier

We use an epoxy-packaged 4 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 should be at least three to four times that of the transformers secondary voltage. The current rating of the diodes should be twice 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. Theresidual amount of ripple is determined by the value of the filer capacitor: the larger the value the smaller the ripple.The 2,200uF is a suitable value for all the voltages generated using this project. The other consideration inchoosing the correct capacitor is its voltage rating. The working voltage of the capacitor has to be greater than thepeak output voltage of the rectifier. For an 18V supply the peak output voltage is 1.4 x 18V, or 25V. So we havechosen a 35V rated capacitor.

Regulators

The unregulated input voltage must always be higher than the regulators output voltage by at least 3V inorder for it to work. If the input/output voltage difference is greater than 3V then the excess potential must bedissipated as heat. Without a heatsink 3 terminal regulators candissipate about 2 watts. A simple calculation of the voltage differential times the current drawn will give the watts tobe dissipated. Over 2 watts a heatsink must be provided. If not then the regulator will automatically turn off if theinternal temperature reaches 150oC. For safety it is always best to use a small heatsink even if you do not think youwill need one.

Stability

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

Decoupling

The monoblok capacitor C2 & C6 across the output provides high frequency decoupling which keepsthe impedence low at high frequencies.

LED

Two LED's are provided to show when the output regulated power is on-line. You do not have to use theLED's if you do not want to. However, the LED on the negative side of the circuit does provide a minimum load tothe 79xx regulator which we found necessary during testing. The negative 3-pin regulators did not like a zeroloadsituation. We have provided a 470R/0.5W resistors as the current limiting resistors for the LED's.

Diode Protection

These protect mainly against any back emf which may come back into the power supply when itsupplies power to inductive loads. They also provide additional short circuit protection in the case that thepositive output is connected by accident to the negative output. If this happened the usual current limiting shutdownin each regulator may not work as intended. The diodes will short circuit in this case and protect the 2 regulators.

Source :www.electronics-project-design.com

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USB Converter

Does this sound familiar: you buy a small piece of equipment, such as a programming & debugging interface for a microcontroller, and you have to use a clunky AC wall adapter to supply it with power? It’s even worse when you’re travelling and there’s no mains socket anywhere in sight. Of course, you can use the USB bus directly as a power source if the supply voltage is 5 V. If you need a higher voltage, you can use the USB converter described here. This small switch-mode step-up converter can generate an output voltage of up to 15 V with a maximum output current of 150 mA.

The LM3578 is a general-purpose switchmode voltage converter. Figure 1 shows its internal block diagram. Here we use it as a step-up converter. The circuit diagram in Figure 2 shows the necessary components. Voltage conversion is achieved by switching on the internal transistor until it is switched off by the comparator or the current-limiting circuit. The collector current flows through coil L1, which stores energy in the form of a magnetic field. When the internal transistor is switched off, the current continues flowing through L1 to the load via diode D1. However, the voltage across the coil reverses when this happens, so it is added to the input voltage. The resulting output voltage thus consists of the sum of the input voltage and the induced voltage across the coil.

The output voltage depends on the load current and the duty cycle of the internal transistor. Voltage divider R5/R6 feeds back a portion of the output voltage to the comparator in the IC in order to regulate the output voltage. C5 determines the clock frequency, which is approximately 55 kHz. Network R4, C2 and C3 provides loop compensation. The current-sense resistor for the current-limiting circuit is formed by three 1-Ω resistors in parallel (R1, R2 and R3), since SMD resistors with values less than 1 Ω are hard to find. The output voltage ripple is determined by the values and internal resistances of capacitors C11, C8, C7 and C6.

 

The total effective resistance is reduced by using several capacitors, and this also keeps the construction height of the board low. L2, C1, C9 and C10 act as an input filter. Ensure that the DC resistance of coil L2 is no more than 0.5 Ω. Use a Type B PCB-mount USB connector for connection to the USB bus.  A terminal strip with a pitch of 5.08 mm can be used for the output voltage connector. Of course, you can also solder a cable directly to the board. Two additional holes are provided in the circuit board for this purpose. As we haven’t been able to invent a device that produces more energy than it consumes, you should bear in mind that the input current of the circuit is higher than the output current. As a general rule, you can assume that the input current is equal to the product of the output current and the output voltage divided by the input R5 and R6 for other output voltages:

6V:	R5 = 47k, R6 = 9,1k
12V:	R5 = 110k, R6 = 10k
15V:	R5 = 130k, R6 = 9,1k

voltage and divided again by 0.8. Specifically, with an output current of 100 mA at 9 V, the input current on the USB bus is approximately 225 mA. Finally, Figure 3 shows a small PCB layout for the circuit. All of the components except the connector and the terminal strip are SMDs.

Parts List:

(for UO = 9 V)
Resistors
R1,R2,R3 = 1Ω
R4 = 220kΩ
R5 = 82kΩ
R6 = 10kΩ
Capacitors
(SMD 1206)
C1 = 100nF
C2 = 2nF2
C3 = 22pF
C4 = 100nF
C5 = 1nF5
(tantalum SMD 7343)
C6 = 68μF 20V
C7 = 68μF 20V
C8 = 68μF 20V
C9 = 47μF 16V
C10 = 47μF 16V
C11 = 68μF 20V
Inductors
L1 = 820μH (SMD CD105)
L2 = 47μH (SMD 2220)
Semiconductors
D1 = SK34SMD (Schottky)
IC1 = LM3578AM (SMD SO8)
Miscellaneous
K1 = 2-way PCB terminal block, lead pitch 5mm
(optional)
K2 = USB-B connector

PCB layout, free download from Elektor website, 070119-1.pdf

Author : Jörg Schnyder  copyright : Elektor

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Switch-Mode 555 Supply

This switch-mode power supply is built around a 555 timer IC. It provides a maximum output voltage of 40 V with a 12-V input voltage. The voltage can easily be set using a Zener diode, and it must be higher than the input voltage (the minimum output voltage is always 12 V). The NE555 is used in an unconventional way here. In the normal configuration, the output of the oscillator IC is low longer than it is high. With the configuration used here, the output can be high for a shorter time than it is low. The NE555 switches FET T1 on and off.When T1 is conducting, energy is stored in L1. When T1 stops conducting, this energy is transferred to C1 and C2 via Schottky diode D1, so the voltage on these capacitors rises.

The voltage is limited by Zener diode D2.If the voltage rises above the Zener voltage,the current through the Zener diode causes T3 to conduct. This reduces the voltage on pin 5 of the NE555, which in turn decreases the relative duration of the high level on pin 3. T1 thus conducts for a shorter interval, so less energy is stored in L1 and the output voltage is stabilised.Current limiting is provided by R6, R5 and T2. If the voltage across R6 is more than 0.6 V, T2 starts to conduct. This drives T3 into conduction, causing the voltage to decrease in order to limit the current.

C5 and R7 provide a soft-start effect.The value of R1 can range from 22 kΩ for an output voltage of 15 V to 10 kΩ for an output voltage of 40 V.For the sake of safety, limit the Zener voltage to a maximum of 40 V. T1 and T2 can be rated for a maximum of 50 V. The FET is not critical; you may already have one in your spare parts bin that can switch enough current. If the coil becomes warm,the core is too small or the wire is too thin.The Schottky diode is the only component that is actually critical. Do not use an ordinary diode, since it will become much to

hot. You’re bound to find a Schottky diode in an old computer power supply (just check for a forward voltage of 0.2 V on the diode range of your multimeter).The supply shown here can deliver approximately 200 W. The input supply voltage can range from 7 V to 15 V.Don’t forget that the maximum voltage the NE555 can handle is 15 V.Finally, this power supply is not short circuit proof. A slow-blow fuse on the 12-V side is recommended.

Author : Martijn Geel Copyright :elektor elector

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To drive nixie tubes or neon lamps you need a DC power supply of around 170 volts for consistent and fast tube striking. But where to get such a supply? This simple switchmode converter provides the required voltage with enough current to supply most projects.

This kit allows you to make a very simple switchmode boost (step-up) converter for powering nixie tubes and similar displays that require voltages between 100 and 200 Volt DC. It uses very readily available parts which can be bought from almost any electronics components store should the need arise for replacements.

How it works :

The circuit is designed around one of the most common ICs on the planet—the 555 timer chip. While several decades old, this chip still finds uses in a great many areas, including simple converters like this one. The 555 is configured as an astable oscillator which oscillates at a frequency (around 45kHz) determined by resistors R1 and R2, and capacitor C2. The 555’output directly drives a high voltage MOSFET, Q1, that switches the current through an inductor, L1.

When the FET is on, current flows from V+ through the inductor to ground. As the current in the inductor builds up, the FET then turns off.When the FET turns off, the current flowing through the inductor tries to continue to flow but can’t flow through the FET, so the voltage on the FET’s drain terminal rises until the ultrafast diode, D1 becomes forward biased. This allows the energy contained in the coil to be dumped into the high voltage capacitor, C4.

This cycle continues until the voltage across C4 reaches a value set by trimpot VR1. R4, R5 and VR1 form the feedback divider for the circuit, and are chosen such that the voltage across C4 is divided down to around 0.7 volts. This voltage is applied to transistor Q2, a BC547. When the voltage across C4 rises to the point where the voltage from the divider is enough to turn Q2 on, then Q2 pulls down the Control pin of the 555, stopping it from oscillating and shutting down the converter. As soon as this happens, the voltage across C4 begins to fall, as does the voltage into the base of Q2, and so Q2 turns off, allowing the converter to restart. This is how the circuit regulates the voltage, and in practice it works quite well. Resistor R6 and capacitor C3 form a simple snubber network, while C1 is the main reservoir cap for the circuit. And that’s about all there is to it!

Building it :

Well, there is not much to say here, just get the components in their appropriate places and the right way around (for the polarised components like the diode, electrolytic capacitors, transistors and IC) and solder them into place. Make sure there are no shorts between IC pins or other places on the board. When you have checked and double checked your work, you can then give the unit a test.

The smoke test :

Place the board on an insulating surace (clean, dry wood or plastic is fine) and, after making sure the trimpot is centred, connect a 9 to 12 volt DC source to the input terminal block. It is best to use a current limited supply to start with, in case there is a problem. Do not connect the circuit to a battery or other high current supply without having tested it first! Now, take your multimeter and check the output voltage. It could be anywhere between 100 and 200 Volt DC. If there is no voltage on the output, check that the 555 is oscillating (you do have a logic probe of course!). If not, find the problem and fix it. Once you get a high voltage output,make sure it is adjustable from around 100 volts to 200 volts. The lower limit varies somewhat with different components, one prototype couldn’t be adjusted below 145 volts.

Note that, as the kit is supplied with a 400 volt MOSFET, the output can exceed 200 volts, The final test involves connecting a load to the supply, such as a nixie tube via a 22k resistor. If the supply drives the load, then you’re in business! Of course, turn the supply off and allow the voltage to drop to a safe level before making any connections! Note that the voltage will vary a bit with load, but it should not swing by more than a few volts from 0 to 10mA load.but don’t use the kit for voltages above this.

Parts :

U1=555 timer
Q1=IRF740
Q2=BC547
D1=UF4004
C1=330uF 16V
C2=2.2nF
C3=100pF
C4=2.2uF 250V
R1=56k
R2=10k
R3=1k
R4=470ohm
R5=220k
R6=2.2k
VR1=1k trimpot
L1=100uH
TB1,=TB2 2-way terminal block
SOC1=8 pin IC socket
PCB1=Circuit board High voltage label

Warning!

This circuit, while not as dangerous as mains power, provides enough energy to potential kill a person should they be connected between the high voltage output and ground in the right way, so be careful when working on this circuit! Always, turn off the power and wait for the high voltage output to drop before making any changes to the circuit. When completed, the circuit must be mounted inside an insulated case with properly insulated terminals to prevent anyone accidentally coming into contact with the high voltage output!

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9 Volt 2 Amp PSU Circuit

A simple 9 Volt 2 amp supply using a single IC regulator.

The circuit will work without the extra components, but for reverse polarity protection a 1N5400 diode is provided at the input, extra smoothing being provided by C1. The output stage includes C2 for extra filtering, if powering a logic circuit than a 100nF capacitor is also desirable to remove any high frequency switching noise.

Circuit diagram:

 9 Volt 2 Amp PSU Circuit Diagram

Notes:

There is little to be said about this circuit. All the work is done by the regulator. The 78S09 can deliver up to 2 amps continuous output whilst maintaining a low noise and very well regulated supply.

Author : Andy Collinson Copyright : zen22142

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Variable DC Power Supply Circuit Diagram

Voltage Range: 0.7V to 24V, Current Range: 50mA to 2A

A variable dc power supply is one of the most useful tools on the electronics hobbyist's workbench. This circuit is not an absolute novelty, but it is simple, reliable, "rugged" and short-proof, featuring variable voltage up to 24V and variable current limiting up to 2A. You can adapt it to your own requirements as explained in the notes below.

Circuit Diagram :

Variable DC Power Supply Circuit Diagram

Parts:

P1 = 500R
P2 = 10K
R1 = 2.2K-1/2w
R2 = 2.2K-1/2w
R3 = 330R
R4 = 150R
R5 = 1R-5W
C1 = 35V-3300uF
D1 = 1N5402
D2 = 1N5402
D3 = 5mm Red Led
C2 = 63V-1uF
Q1 = BC182
Q2 = BD139
Q3 = BC212
Q4 = 2N3055
SW1 = SPST Mains Switch
T1 = 36VCT-Transformer

Notes:

• P1 sets the maximum output current you want to be delivered by the power supply at a given output voltage.
• P2 sets the output voltage and must be a logarithmic taper type, in order to obtain a more linear scale voltage indication.
• You can choose the Transformer on the grounds of maximum voltage and current output needed. Best choices are: 36, 40 or 48V center-tapped and 50, 75, 80 or 100VA.
• Capacitor C1 can be 2200 to 6800µF, 35 to 50V.
• Q4 must be mounted on a good heatsink in order to withstand sustained output short-circuit. In some cases the rear panel of the metal box in which you will enclose the circuit can do the job.
• The 2N3055 transistor (Q4) can be replaced with TIP3055 type.

Source : www.redcircuits.com

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Simple 5V Power Supply Digital Circuit

This circuit is a small +5V power supply, which is useful when experimenting with digital electronics. Small inexpensive wall tranformers with variable output voltage are available from any electronics shop and supermarket. Those transformers are easily available, but usually their voltage regulation is very poor, which makes then not very usable for digital circuit experimenter unless a better regulation can be achieved in some way. The following circuit is the answer to the problem.

This circuit can give +5V output at about 150 mA current, but it can be increased to 1 A when good cooling is added to 7805 regulator chip. The circuit has over overload and therminal protection.

Circuit diagram:

 power supply Circuit diagram

The capacitors must have enough high voltage rating to safely handle the input voltage feed to circuit. The circuit is very easy to build for example into a piece of veroboard.

 Pinout of the 7805 regulator IC

• 1. Unregulated voltage in
• 2. Ground
• 3. Regulated voltage out

Component list

7805 regulator IC
100 uF electrolytic capacitor, at least 25V voltage rating
10 uF electrolytic capacitor, at least 6V voltage rating
100 nF ceramic or polyester capacitor

Summary of circuit features

• Brief description of operation: Gives out well regulated +5V output, output current capability of 100 mA



• Circuit protection: Built-in overheating protection shuts down output when regulator IC gets too hot



• Circuit complexity: Very simple and easy to build



• Circuit performance: Very stable +5V output voltage, reliable operation



• Availability of components: Easy to get, uses only very common basic components



• Design testing: Based on datasheet example circuit, I have used this circuit succesfully as part of many electronics projects



• Applications: Part of electronics devices, small laboratory power supply



• Power supply voltage: Unreglated DC 8-18V power supply



• Power supply current: Needed output current + 5 mA



• Component costs: Few dollars for the electronics components + the input transformer cost

Modification ideas

More output current

If you need more than 150 mA of output current, you can update the output current up to 1A doing the following modifications:

• 
  
  Change the transformer from where you take the power to the circuit to a model which can give as much current as you need from output
  
  



• 
  
  Put a heatsink to the 7805 regulator (so big that it does not overheat because of the extra losses in the regulator)
  
  

Other output voltages

If you need other voltages than +5V, you can modify the circuit by replacing the 7805 chips with another regulator with different output voltage from regulator 78xx chip family. The last numbers in the the chip code tells the output voltage. Remember that the input voltage muts be at least 3V greater than regulator output voltage ot otherwise the regulator does not work well.

source :tkk

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