In this post we will elaborately discuss how to build a simple LM based adjustable power supply circuit using minimum number of external components. As the name suggests a variable power supply circuit provides the user with a range of linearly varying output voltages through a manually controlled potentiometer rotation. A LM is a versatile device which helps an electronic hobbyist to build a variable voltage power supply quickly, cheaply and very efficiently.
It is the basic source of power that may be required for various electronic procedures, right from powering intricate electronic circuits to the robust electromechanical devices like motors, relays etc.
These may be built using discrete components like transistors, resistors etc. No matter what the type may be, a power supply unit should incorporate the following features to become a universal and reliable with its nature:. With the advent of chips or ICs like LM, L, LMLM, configuring power supply circuits with variable voltage output with the above exceptional qualities has become very easy nowadays. This IC is normally available in TO package and has three pin outs. The pin outs are very easy to understand, since it consists of an input, an output and an adjustment pins that just needs to be wired up with the relevant connections.
Adjusting the pot produces a linearly varying voltage at the output that may be right from 1. Though the shown design is the simplest one and therefore includes only a voltage control feature, a current control feature can also be included with the IC. The IC can be further enhanced for producing currents higher than its rated values. The diagram below shows how the IC can be used for producing more than 3 amps of current. The idea was built and tested by one of the avid readers of this blog Mr.
Steven Chiverton and used for driving special laser diodes which are known to have stringent operating specifications, and could be driven only through specialized driver circuits. The discussed LM configuration is so accurate that it becomes ideally suitable for all such specialist current and voltage regulated applications.
Referring to the shown circuit diagram, the configuration looks pretty straightforward, two LM IC s can be seen, one configured in its standard voltage regulator mode and the other in a current control mode.
To be precise the upper LM forms the current regulator stage while the lower acts like a voltage controller stage. The input supply source is connected across the Vin and ground of the upper current regulator circuit, the output from this stage goes to the input of the lower LM variable voltage regulator stage.
Basically both the stages are connected in series for implementing a complete foolproof voltage and current regulation for the connected load which is a laser diode in the present case. R2 is selected to acquire a range of around 1. The output voltage of a LM power supply circuit could be determined with the following formula:. You can ignore this. The current controlled voltage acquired from the upper stage is next applied to the lower LM voltage regulator circuit, which enables the desired voltage to be set anywhere from 1.
This is achieved by adjusting R4. The discussed circuit is assigned to handle not more than 1. The following lovely pictures were sent by Mr. Steven Chiverton, after the circuit was built and verified successfully by him. So far we have learned how to configure an LM for producing adjustable output using a pot, now let's understand how push buttons may be used for enabling digitally controlled voltage selection.
The innovation converts the traditional LM power supply design into a digital power supply design, by eliminating the low tech potentiometer which might be prone to wear and tear in the long run resulting in erratic operations and incorrect voltage outputs.
The modified LM design which would be allow it to respond to the push button selections can be seen in the following diagram:. The R2 resistors associated need to be calculated with respect to R1 ohms for setting up the intended push button selected voltage outputs. Pin 1 to pin 10 needs to be connected with the bases of the PNP associated with the LM circuit stage.
The above push button circuit using LM is specified with 10 outputs only, in order to get more selectable ranges, a couple of such IC LM could be cascaded together for upgrading the design with 20 selectable voltage outputs.
The LEDs as shown in the design may be optional, however these can be useful for indicating the relevant voltage levels as per the preferred selections. If you have anymore doubts regarding this LM push button operated power supply circuit, you can simply ask them through the comments.In this post we learn how to make a simple variable power supply circuit using transistor 2N and some other passive components.
It includes variable voltage and variable current feature, fully adjustable. A power supply circuit that does not include the features of a variable voltage and current control can by no means be considered truly versatile.
A variable workbench power supply circuit explained in this article is not only specified with a continuously variable voltage control but is also equipped with the feature of overload or continuously variable current control. The voltage variations are made by using the preset P2, through a feedback configuration employing the components D1, R7, T2 and P2. The inclusion of D1 makes it sure that the voltage can be lowered right down to 0.
If any other specific minimum value is required then the diode can be replaced by zener diode having the required specified value. Therefore in this variable power supply circuit using 2N transistor, the transformer being a 0 — 40 V, the output becomes variable right from 0.
The value of R4 is specifically becomes responsible for defining the maximum allowable output current. If you have any doubts regarding this variable voltage and current power supply circuit using transistor 2N circuit please do not hesitate to ask then through the comments below.
The above design was inspired from the following circuit which was designed and presented in the elektor electronics magazine by the elektor engineers:. The above designs were assessed and simplified with more effective results by Mr. The revised and simplified design can be viewed in the following diagram:. PCB Design for the above Circuit. William C. The key highlights of the circuit are: wide range output: 0.
In addition, higher extension of the output range becomes feasible through the inclusion of T4 between the IC and the series pass transistor. T3 works like an output current controller. When P1 is rotated totally anti-clockwise, T3 restricts at 0. The limiting circuit becomes inactive when P2 is moved completely clockwise. The regulator circuit specifically operates in the following manner.
The IC CA analyzes the output voltage given to the non-inverting input with respect to a reference voltage at the inverting input. The output voltage of the regulator is reduced with a potential divider to protect against damage to the IC. The reference voltage is determined by P2, which needs to be a top-notch part, since any kind of noise upon its slider arm will probably be transferred to the regulator output terminals.
The IC is made up of 4 transistors applied as diodes or zener and another transistor for cutting down the output impedance of the reference circuit. The reference IC furthermore provides a stepped down supply voltage for powering CA This feature necessitates the use of each ICs in the regulator stage; if IC1 is removed can result in the break down of IC2. Each of the transistors shown in the diagram must be rated with a breakdown voltage of a minimum of 55 volts.
If you have any circuit related query, you may interact through comments, I'll be most happy to help!This is attained by adding two resistors R1 and R2 as shown in figure.
Circuit diagram. C1 is the filter capacitor the thumb rule is uF per amp at Hz. For 2 amps 50Hz is uF. C2 is a HF decoupling capacitor to avoid HF instability. C3 is for reducing the output impedance of the power supply such that no instability in the connected load due to power supply common impedance effect. The power supply here is only 9V output. If you used a V supply then you will get all the voltages mentioned in the article.
Even if you get the voltages out after inputting 12V plus, the whole idea of boost is defeated, especially when the current this contraption will eck out is a measly ma or less. This article is misleading.
Sorry bro. It gives 3. I think they are enough. Ckt is checked 5 times. Help needed guys. Author john. Regulated DC power supply October 7, How to fix the values of the capacitors? What is their use?
Seetharaman 6 years ago. Hi Jov 25volts will do. Pat 7 years ago. Vikas dabas 8 years ago. Submit Type above and press Enter to search. Press Esc to cancel.Have you ever tried to design a variable regulated power supply? This article describes you how to design a variable power supply circuit.
Till now we have seen a lot of power supply circuits, but the main advantage of this power supply circuit is that it can vary the output voltage and output current. For smaller voltages, we normally use batteries as a reliable source. Instead of using batteries, which have a limited lifetime, a variable DC power supply can be used which is implemented in this project. It is a robust, reliable and easy to use variable DC power supply.
The working of the circuit is as follows. A transformer is used to step down the AC supply to 24V at 2A. A bridge rectifier is used to convert this voltage to DC.
Depending on the settings of the POT, the ADJ pin of LM receives a small portion of the output voltage as feedback and the output voltage is varied. With the help of this variable DC power supply, the output voltage can be varied from 1. This circuit can be used as a reliable DC source and acts as a replacement for batteries. It is important to attach the voltage regulator IC LM to a heat sink as it tends to get hotter during operation.
The above circuit uses only 15 v transformer at the input, so it can be varied maximum up to 15V. In order to increase the up to 30v input of 30v should be applied. Although the voltage regulator LM protects the circuit from overheating and overload the Fuses F1 and F2 are used to protect the power supply circuit.
The rectified voltage at capacitor C1 is around So we need to use all the capacitors which are rated at 50v in the circuit.
Pot RV1 allows us to vary the output voltage between 0 to 28V. The minimum output voltage of the LM voltage regulator 1. In order to get 0V at the output, we are using 3 diodes D7, D8, and D9. Here 2N transistors are used to get more current.
Variable High Power “Resistor” For Power Supply Testing
Pot RV2 is used to set the maximum current available at the output. LM is the 3 pin series adjustable voltage regulator. This regulator provides output voltage ranging from 1. This IC is easy to use and requires only two resistors to provide the variable supply.
It provides internal current limiting, thermal shut down and it provides more line and load regulation as compared to fixed voltage regulators. Because of all these features, this IC is mostly used in a variety of applications.
This circuit is studied theoretically and may require some changes to implement it in practice. The fixed voltage regulator is used to offer fixed voltage at the output terminal and does not depend upon the input voltage supplied.
Here is the circuit producing variable voltage Power supply designed using fixed voltage regulators. Imagine that the resistor which is attached between the com terminal and the output terminal of the regulator has a value of ohm R1. This implies that the value of current is Among the rotary switch and ground, there is some amount of standby current of 2. Hence about Now assume that from the circuit we need 5V to 12V.
With the regulator output, we directly got the 5V minimum. While if there is a need for 12V then between com and output 5V is available and for the rest 7V, we need to select the appropriate value of the resistor.
Hence we have to attach a resistor of ohms with ohms so to obtain the wanted output i. While it is difficult for us to get such a value of the resistor in the market so we can use the nearby value of the resistor i.So to get through such problems I introduce a high current variable voltage power supply circuit which can drive 10A of load, the current handling capacity can be increased simply by connecting 2N power transistors in parallel.
I happened to design variable power supply schematic diagram for my inverter battery for safe and quick charging. My 30Ah lead acid inverter battery takes more time for constant voltage charging when I use a LM variable voltage regulator.
This is due to its lower output current. So I connected a power transistor which helps to increase the current without varying the voltage. The maximum input to this DC variable power supply is 37 volts. You can buy this circuit from our Circuits Gallery Store.
This circuit will not work, only one of the 2n transistors will carry the lions share of the current. There are no required caps in this schematic? How would you go about adding a power indicator led to this? Whenever i connect load at output the output voltage at emitter reduces while the current increases.
I regulate a 3. I require a constant voltage of 3. Based on my research they said synchronous voltage regulator is the most efficient compare to linear regulator…. Dear Sir, first of all thnx for this circuit i want a circuit where i have to connect gps and gsm with car battery and output current should be 2A of regulator IC so tell me can this circuit can i use and can i replace lm with ic.
At 1v and 10 amps out with 30v in, you would need to dissipate watts. A 2n on a decent size heatsink can only dissipate 30 watts, so yoare going to need 10 of them. The emitters of the s should have a 0. Needs a fuse in the output. I want to be able to adjust the power for a motor between 2 and 3. What will happen if I use a power source of only 3.
Thanks in advance! Hi can this circuit power an 5 amp drawing electromagnet. So my question is with the above modification will it power even electromagnets??? Thank you. I needed better regulation than LM could provide for charging 4 x 1. So I did not need a 2N Voltage output just varied from 6.
Hello, I need a little help troubleshooting my test circuit. Im testing the circuit and the voltage does vary at the output with the potentiometer.
Emitter of the pwr Transistor. This happens without a load.Note that all these links are external and we cannot provide support on the circuits or offer any guarantees to their accuracy. Some circuits would be illegal to operate in most countries and others are dangerous to construct and should not be attempted by the inexperienced. Amplified zener regulator.
Voltage and current regulated power supply.
Variable Power Supply 0-24V
Simple switching power supply mains operated. Alkaline battery charger. Dry cell battery charger. Power Supply Resumption Alarm using timer. Solid-state voltage indicator with high voltage cutout. Capacitor voltage stepper using timer. Low Voltage Alarm for batteries and other volatile DC power sources. Voltage Monitor using UA operational amplifier. Expanded Scale Battery Volt Meter. Battery Low Voltage Beeper. Low Cost Universal Battery Charger. Regulated Power Supply Circuits.
Basic Solid State Relays. LM Thermostat circuit diagrams. Transformer Secondary Voltage Reduction. Low Battery Voltage Cutout Circuits. Efficient unipolar stepper motor driver only uses power when it makes a step. Alternative power source for Magellan GPS receivers. Battery voltage monitor using an LM op-amp. A Variable power supply with adjustable current limiting. Dynamo Current and Voltage Regulator. General purpose portable DC power supply using rechargeable C cells.
Bench power supply that allows a number of varying output voltages to be preset.Variable voltage power supply is essential for any electronic hobbyist to begin their electronics lessons.
For different applications you may need different voltages. So it becomes impossible to use multiple fixed power supplies all the time. Also this variable power supply circuit ensures the protection of other circuit parts from voltage fluctuations. So in this article we will teach you how to build a variable power supply on your own. Why to buy when you can make one of your own easily using very little components?
You can connect the output to a multimeter for displaying the voltage. This supply unit uses a LM3 17 voltage regulator IC. The rectified output from the full wave bridge rectifier is fed to a LM regulator IC.
By changing the value of potentiometer used in this circuit, the output voltage can be controlled easily. Note: For safety, use this circuit to get a maximum of 30 volts. Click on the image for enlarged view.
See below how I have integrated this circuit to a multimeter to show instantaneous reading. Let us know through the comment box below if you have any trouble in setting up a similar one.
Thank you. Khadija, when you rectify an Ac voltage to Dc, the dc value you get will be 1. Hope this is helpful. The link to buy gives a error. Apparently there is no DNS entry for services.HOW TO MAKE A VARIABLE POWER SUPPLY ( VOLTAGE AND CURRENT CONTROL )
The ohm resistor is burning in my circuit. In other words how much load it can carry? Hi Zaima wajid 1. Use equation 2. The 1kohm resistor and potentiometer is burning in my circuit. Polarities are all ok,every thing is according to the circuit diagram.
Variable Voltage, Current Power Supply Circuit Using Transistor 2N3055
The registor R1 is getting heated up with a odour within seconds after tryin turning ou the circuit ON. The circuit is working fine giving out 30volts on digital multimeter until the load is connected. As soon as the load is connected its directly dropping down to 2.