This is the circuit diagram of 0-60V / 0-2A variable power supply. Of course this circuit used to cover the voltage range from 0 to 60V and current from 0 to 2A. The maximum current can be increased, if we add the power transistors needed. Note the power output, just to cite one example, if delivery 2A 12V source to have a voltage drop of 48V with 2A consumption giving us a dissipation of 100 watts, is not a heating source, so, care.

Close attention should be paid to the way in which the two transistors BC327 circuit current protection, which work in saturation cutting work, another deals only activate an LED indicator on-load when the voltage drop lights output and will have to press the RESET button provided for the case. This will activate the output voltage again.

As already mentioned, this source has an intensity control, which disconnects the output voltage. This does not mean that supports the intersection of the (positive and negative) output cables. We must avoid this situation if possible as this will cause the destruction of transistors and other circuit components, it should be noted that we are dealing with respectable power.

For example: 5V and 2A output, this represents 65V – 5V = 60V which must be dissipated by the output transistors 2A, are talking about the power loss of 120 watts as a small “electric fire” this heat, more heat produced by 10W consumption advantage, they must evacuate 130W between the radiator and a fan that helps to lower the temperature that produces this “heater”, otherwise, you can imagine the result.

This is variable DC power supply circuit, or we can call it adjustable DC power supply which give us a 1.2V-25V output voltage. The power supply schematic above is taken from the datasheet of regulator LM338K manufactured National Semiconductor. The circuit uses IC LM338K as the voltage regulator, so we will get the stable and regulated output. The regulator IC LM338K provides 5A output current max, and the voltage from 1.2 to 32V, it also featured the integrated thermal and short-circuit protection. Maximum voltage at input and output of the regulator is 35V .

The transformer current value depends your needs. For example, if you need 120W power output then you’ll need 5A transformer. 5A x 24V (full power) will give you 120W output power. Since this power supply circuit described to give us 1.2-25V DC output, then you must have transformer with 24V AC output.

For the diode, you have the choices whether use 4 diodes of single bridge diode. If you are have plan to use the PCB design in this post, then you have to use bridge diode. The value of diode is depend on the current value of transformer. For the example, if the circuit uses 3A transformer the you must use minimum 3A diode. The higher current value of diode, the price is more expensive of course…

The following images are the PCB layout design (bottom) and the component placement on the top. Don’f forget to use heatsink for LM338K to prevent overheat. I think every electronics hobbysts have high level of creativity, may be you’ll face some problems during the practice and you’ll solve the problem by yourself..

PCB Layout Design:

Component Placement:

Good luck…

Above schematic diagram is the circuit of the variable desktop power supply. Regulator IC LM317T is set up in its standard application. Diode D1 protects against polarity reversal and capacitor C1 is an additional buffer. The green LED (LED1) signifies the status of the power input. Diode D2 keeps the output voltage from increasing above the input voltage when a capacitive or inductive load is hooked up at the output. Similarly, capacitor C3 eliminates any residual ripple.

Connect a common digital voltmeter in parallel with the output leads to precisely set the wanted voltage with the support of variable resistor / potensiometer VR1. It is possible to also work with your digital multimeter in case the digital voltmeter isn’t around. Switch on S1 and set the needed voltage through potensiometer VR1 and start reading it on the digital voltmeter. Now the power supply is all set to be used.

The circuit could be built on a general purposed Printed Circuit Board (PCB). Refer refer to the following picture for the pin configuration of LM317, just before soldering it on the PCB.

When the circuit already build, then enclose the circuit inside a metallic box, the suggested power supply box shown below:

Then open up the case of the desktop computer and hook up the input line of is circuit to a free available (hanging) four-pin drive power connector of the SMPS properly.

This bench power supply features three solid-state DC power supplies. The first supply gives a +1.5 to +15 volts at 1 ampere. The second supply gives a -1.5 to -15 volts at 1 ampere. The third has a fixed 5V at 3 amperes. All? DC supplies are fully regulated. A special IC circuit keeps the output voltage within .2V when going from no? load to 1 ampere. The output is fully protected from short circuits. This supply is ideal for use in school labs,? service shops or anywhere a precise DC voltage is required.

Take a note that based on the diagram, this circuit require 120V AC to 17V AC Center Tapped Transformer. If your country use 220V AC home electric, you MUST change the Transformer 220-240V AC to 18V AC Center Tapped Transformer.

Power Supply Specification:

Output Voltage     : 1) 1.5-15VDC @ 1A
(at 120V input)    : 2) ?1.5 - ?15VDC @ 1A
                   : 3) 5VDC @ 3A
Output Regulation  : 200mV each supply
Line Regulation    : 100mV each supply
Ripple             : Max 5mV RMS
Current Protection : 1A limit 2-15VDC
                   : 3A limit 5VDC
Short Protection   : 1A limit 2-15VDC
                   : 3A limit 5VDC
Output Impedance   : .025W each supply

Here is the schematic diagram of bench power supply:

To know the step by step build the bench power supply circuit, download this instruction manual (kit manual):

Bench Power Supply xp620

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The circuit is based around the 7805 voltage regulator. It has only 3 connections (input, output and ground) and it provides a fixed output. The last two digits of the part number specify the output voltage, eg. 05, 06, 08, 10, 12, 15, 18, or 24. The 7800 series provides up to 1 amp load current and has on-chip circuitry to shut down the regulator (rather than blowing out) if any attempt is made to operate it outside its safe operating area. (If this happens to you, let the chip cool down & attach the heatsink.)

It can be seen that there are in fact two separate circuits in this power supply. One 7805 is directly connected as a fixed 5V regulator. The second 7805 has a resistor divider network on the output. A variable 500R potentiometer is used to vary the output voltage from a minimum 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 large 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 small applications the heat sinks will not be needed. The tab on the regulator will dissipate 2W at 25 degree Celcius just in air. (This is equivalent, for example, to an input voltage of 9V, an output of 5V and drawing 500 mA.) However, as your projects get bigger they will draw more current from the power supply and the regulators will operate at a higher temperature.

Download this hobby power supply circuit manual in PDF version from the following link:

Hobby Power Supply

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