EngineeringSlash- The electronic projects,electronic project,electronic schematic,electronic design » Power Supply http://www.engineeringslash.com Engineering blog- electronic circuits , electronic projects,electronic schematic,electronic design,simple circuit and hobby circuits Tue, 09 Feb 2010 05:03:16 +0000 en hourly 1 http://wordpress.org/?v=3.3.1 LM317T Voltage Regulator with Pass Transistor http://www.engineeringslash.com/power-supply/lm317t-voltage-regulator-with-pass-transistor.html http://www.engineeringslash.com/power-supply/lm317t-voltage-regulator-with-pass-transistor.html#comments Mon, 08 Feb 2010 10:45:09 +0000 admin http://www.engineeringslash.com/?p=321 LM317T Voltage Regulator with Pass Transistor circuit 300x228Here is the circuit diagram for LM 317 T voltage regulator with pass transistor .

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    ]]>     http://www.engineeringslash.com/power-supply/lm317t-voltage-regulator-with-pass-transistor.html/feed 0     Simple Adjustable Voltage Source http://www.engineeringslash.com/power-supply/simple-adjustable-voltage-source.html http://www.engineeringslash.com/power-supply/simple-adjustable-voltage-source.html#comments Mon, 08 Feb 2010 10:21:50 +0000 admin http://www.engineeringslash.com/?p=317 Simple Adjustable Voltage Source circuit 269x300

    A simple but less efficient method of controlling a DC voltage is to use a voltage divider and transistor emitter follower configuration. The figure below illustrates using a 1K pot to set the base voltage of a medium power NPN transistor. The collector of the NPN feeds the base of a larger PNP power transistor which supplies most of the current to the load. The output voltage will be about 0.7 volts below the voltage of the wiper of the 1K pot so the output can be adjusted from 0 to the full supply voltage minus 0.7 volts. Using two transistors provides a current gain of around 1000 or more so that only a couple milliamps of current is drawn from the voltage divider to supply a couple amps of current at the output.

    The power consumed by the lamp will be only (3 volts * 1 amp) = 3 watts which gives us an efficiency factor of only 25% when the lamp is dimmed. The advantage of the circuit is simplicity, and also that it doesn’t generate any RF interference as a switching regulator does. The circuit can be used as a voltage regulator if the input voltage remains constant, but it will not compensate for changes at the input as the LM317 does.

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      ]]>       http://www.engineeringslash.com/power-supply/simple-adjustable-voltage-source.html/feed 2       Three Terminal Adjustable Regulator http://www.engineeringslash.com/power-supply/three-terminal-adjustable-regulator.html http://www.engineeringslash.com/power-supply/three-terminal-adjustable-regulator.html#comments Sun, 25 Oct 2009 10:31:07 +0000 admin http://www.engineeringslash.com/?p=29 Three terminal regulators are just right when we need a single fixed voltage. But they will be cumbersome as a hobbyist works with different voltages at different times and it becomes unwieldy to keep power supplies with a number of three terminal regulators.

      Wouldn’t it be better if we have an adjustable but regulated power supply, which can cater to all the voltages we need? And we have such a wonderful device where you can continually adjust your output DC voltage. Well! It is short circuit protected, has only three terminals and all other good things. LM317

      LM317

      LM317T is an adjustable 3 terminal positive voltage regulator capable of supplying around 1.5 amps over an output range of 1.25 to 37 volts. It also has built in current limiting and thermal shutdown features, which makes it virtually blowout proof. This is an excellent startup project with low ripple. With an easy adjustment of regulated voltage, it can be used as power source for most of the applications in the next chapters. Pin out is given in Figure 13.

      Circuit :

      Three Terminal Adjustable Regulator

      Rectifier part is same as shown in the earlier schematic of bridge rectifier. Transformer is changed to 18 V to get a better range of regulated voltages. 9-0-9 Transformer is used as it is difficult to get an 18 V transformer. Please change transformer rating as per your requirement and the capacitor also for higher voltage rating. It is preferable to use 2200 mfd. caps as larger value makes good, low ripple output voltage.

      Pulsating DC output from the bridge is now filtered by the 2200uF capacitor and fed to TN’-put terminal (1) of LM317 regulator. The output of this regulator is varied via the ‘Adj’ pin(3) and the 5K variable resistance or preset pot meter (Rl) connected to it. The regulator uses an internal Zener diode to provide a fixed reference voltage of 1.2 volt across the external resistor R2. Hence the lower end of output voltage is limited to 1.2 volts. C2 is 47uF decoupling capacitor to filter out the transient noise. Metal tab of LM317 is connected internally to the ‘Output’ pin (2). The circuit diagram is shown in Schematic 5.

      Construction

      Use a small Vero board to fix all the components, cut the tracks where not required and solder the pins. Mount the LM317 regulator on a heat sink. However it can be screwed to the metal case of the enclosure box with the mica insulator and the nylon washer with the mounting screw as shown in Figure 12.

      Use a little of heat sink compound on the metal tab and mica insulator as it helps to transfer heat between LM317 and case or heat sink.Use a metal box of suitable size and fix the veroboard and transformer. Mains wire is connected to the primary side of the transformer and taken out. Carefully insulate the mains joints. Mains switch is not shown in the schematic. You may add one if it is required. 5k linear potentiometer is fixed at the casing. Measure the voltages and mark them suitably on a dial fixed on the face of the casing with appropriate indication of the voltage. LED is also fixed on the casing to indicate the power supply.

      Use a small Vero board to fix all the components, cut the tracks where not required and solder the pins. Mount the LM317 regulator on a heat sink. However it can be screwed to the metal case of the enclosure box with the mica insulator and the nylon washer with the mounting screw as shown in Figure 12.
      Use a little of heat sink compound on the metal tab and mica insulator as it helps to transfer heat between LM317 and case or heat sink.
      Use a metal box of suitable size and fix the veroboard and transformer. Mains wire is connected to the primary side of the transformer and taken out. Carefully insulate the mains joints. Mains switch is not shown in the schematic. You may add one if it is required. 5k linear potentiometer is fixed at the casing. Measure the voltages and mark them suitably on a dial fixed on the face of the casing with appropriate indication of the voltage. LED is also fixed on the casing to indicate the power supply.

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      ]]>       http://www.engineeringslash.com/power-supply/three-terminal-adjustable-regulator.html/feed 0       Three Terminal Regulators- Unadjustable http://www.engineeringslash.com/power-supply/three-terminal-regulators-unadjustable.html http://www.engineeringslash.com/power-supply/three-terminal-regulators-unadjustable.html#comments Thu, 22 Oct 2009 10:12:55 +0000 admin http://www.engineeringslash.com/?p=25 These are simple, effective and interesting integrated circuits. They are short circuit protected, can stand up to 32V, have thermal protection and they can easily deliver regulated voltage with 1 amp of current. In these ICs, the last two digits give you the regulated voltage they deliver, 7806 gives you 6 volts and 7812 gives you 12 volts and so on. These are available from most of the manufacturers and are cheap. They are connected after the conventional power supply. There should be 3V more than the required voltage at the input for proper regulation. You need 9V for a 7806 regulator. Use this circuit whenever single regulated voltage is required. Pinout and heat sink mounting procedure are given in figure 11 and Figure 12 respectively.

      ele

      regulator unadjustable

      solder the three terminal regulator after the bridge. Connect the input pin (1) after the bridge and capacitor. Connect the common terminal (2) to the negative rail and you have the regulated voltage at the output (3). 47 uF capacitor (C2) is required if the regulator is placed faraway from the main power supply.

      Metal bodies of these ICs are connected to the ground (common) terminal. Follow the mounting procedure as given below and fix a small aluminum plate to remove the heat and to improve its current capability. (This is a standard practice to mount heat sinks on ICs, transistors, SCRs, and triacs, etc.) By now you must have caught up with the art of soldering and the IC should be soldered well and fast.

      Schematic 4 shows a 9V regulator appended to 12V power supply of the earlier bridge power supply of 12V DC.

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      ]]>       http://www.engineeringslash.com/power-supply/three-terminal-regulators-unadjustable.html/feed 0       Regulated Power Supplies http://www.engineeringslash.com/power-supply/regulated-power-supplies.html http://www.engineeringslash.com/power-supply/regulated-power-supplies.html#comments Sun, 18 Oct 2009 09:53:06 +0000 admin http://www.engineeringslash.com/?p=22 Unfortunately our hobby circuits work on different voltages and a power supply with single voltage will not be sufficient. Simplest way would be to buy a multi-tapped transformer and connect the voltage taps with a suitable switch. These transformers are available with taps of 1.5,3,4.5,6,9,12V. We need a single multi throw switch (as many throws as there are taps). With 9-6-0-6-9 transformer and with a double pole double throw switch, you can get 6 and 9V DC. With the same transformer, and with a double pole six throw switch, it is possible to get 3, 6, 9, 12, 15, 18 V. Switches and multi-tapped transformers are difficult to procure; cumbersome and even unavailable at some places.

      Such schematics are not shown here as there are better ways to build circuits to get variable voltages. Also these power supplies suffer from a major draw back; poor voltage regulation, the voltage falls as more and more current is drawn and voltage also changes with mains voltage fluctuations.

      A 12 V power supply shown in Schematic 3 may show as much as 16.8 V without load and it may go down to less than 12 V as the load current is increased. This still can be and is safely used for most of the non-critical circuits, but it is an unstabilised supply.

      Why not build a regulated power supply, which doesn’t cost an earth but still gives very good results. Now for the time being, without going into details and complications of integrated circuits, we will use them for the pleasure and ease of using them and build a regulated power supply as a starter.

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      ]]>       http://www.engineeringslash.com/power-supply/regulated-power-supplies.html/feed 0       Full Wave Power Supply http://www.engineeringslash.com/power-supply/full-wave-power-supply.html http://www.engineeringslash.com/power-supply/full-wave-power-supply.html#comments Fri, 25 Sep 2009 09:18:41 +0000 admin http://www.engineeringslash.com/?p=7 Make a full wave rectifier, as it is cheaper and better than a half wave one and has less AC ripple. Full wave rectification can be accomplished by two ways, either by a center-tapped transformer using two diodes, or by a bridge circuit, which uses four diodes.

      full wave rectifier

      We need center tapped transformer as used in the earlier circuit. .As already described, in this transformer, you have three wires on the secondary side. Simply speaking in this transformer center wire is taken as zero reference; two outside wires give you equal voltages. Say for a 6-0-6 transformer, center wire gives 0 volts while both ends give 6 volts each. The circuit is shown in Schematic 2.

      Connect diodes, capacitor and resistor and LED just as in earlier project but follow the circuit is shown in the Figure below. Now if you wish to use the same 6-0-6 transformer, you will get 6V DC. If you wish to have 12 V DC by this method, you should get a 12 – 0 -12 transformer.

      Solder lOOOuf / 25Vcapacitor after carefully noting the polarity. Negative side of the pin is marked on the can. A light emitting diode along with lK-x/4 watt resistor in series with it is idded to indicate that the power supply is on.

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        ]]>         http://www.engineeringslash.com/power-supply/full-wave-power-supply.html/feed 0         Half Wave Power Supply http://www.engineeringslash.com/power-supply/half-wave-power-supply.html http://www.engineeringslash.com/power-supply/half-wave-power-supply.html#comments Fri, 18 Sep 2009 09:02:35 +0000 admin http://www.engineeringslash.com/?p=3 Half wave rectification is simplest, as it requires only one transformer, one diode and one capacitor, but we have added a LED to give power supply indication. A simple half wave rectifier for 12V is shown below

        half wave power supply

        500mA transformers are generally used for these circuits. Connect the primary wires to the mains chord after carefully insulating the joints. This transformer has three wires on the secondary side. AC voltage across both end wires is 12 and voltage across any one end wire and center wire is 6. So if both end wires are connected as shown in the present schematic the output DC voltage will be 12 and if any one of the end wires and center tap are connected the voltage will be 6.

        Take a Veroboard and solder all components on it except mains power supply. Solder IN4003 diode to one end of secondary winding making note of the cathode. Solder lOOOuf /25V capacitor. Please note the capacitor is polarized, which means that you should connect it one way only. Negative side of the pin is marked on the can. Add a light emitting diode to know that the power supply is on. Now use a 1K-1A watt resistor in series with it.

        LEDs are also polarized and marked. LEDs will not light up if they are connected in reverse. Take two pen light cells and connect the ends of a Red LED to positive and negative and then turn the leads over and try. (Forget the cathodes and anodes for the time being.) You will know that it works only one way. That also explains how a diode works. Do not connect them directly to 12 V  LEDs cannot work beyond 5 V and their current capability is extremely limited. Although they are very rugged devices, they must always be used with a current limiting resistor.

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