This is the circuit diagram of 5V DC regulated power supply which featured with short circuit protection system. There are 2 kind of output that are regulated 5V DC with short circuit protection and without circuit protection. The main circuit is protected from any damage due to short-circuit in the additional power supply circuit by cutting off the derived supply voltage. The derived supply voltage restores automatically when shorting is removed. An indicator LED is utilized to show whether short-circuit exists or not.

Power Supply Block:
This circuit works just like the ordinary DC power supply adapter, in the main power supply circuit, 230V AC from main home electric source is stepped down by transformer X1 (230V AC primary to 0-9V, 300mA secondary), then rectified by a fullwave rectifier comprising diodes D1 through D4 with bridge arrangement (you may use a single bridge diode), filtered by capacitor C1 and regulated by IC 7805 to give regulated 5V DC output (O/P1).

Short-Circuit Protection Block:
Transistors SK100 and BC547 are used to derive the secondary output of around 5V (O/P2) from the main 5V supply (O/P1).

The working of this circuit is quite simple. When the 5V DC output from regulator IC 7805 is available, transistor BC547 conducts through resistors R1 and R3 and LED1. As a result, transistor SK100 conducts and short-circuit protected 5V DC output appears across O/P2 terminals. The green LED (LED2)? lows to indicate the same, while the red LED (LED1) remains off due to the presence of the same voltage at both of its ends.

When O/P2 terminals short, BC547 cuts off due to grounding of its base. As a result, SK100 is also cut-off. Thus during short-circuit, the green LED (LED2) turns off and the red LED (LED1) glows. Capacitors C2 and C3 across the main 5V output (O/P1) absorb the voltage fluctuations occurring due to short-circuit in O/P2, ensuring disturbance-free O/P1. The design of the circuit is refer to the relationship given below:

R_B = (H_FE ? V_S) / (1.3 ? I_L)

where,

R_B = Base resistances of transistors of SK100 and BC547
H_FE = 200 for SK100 and 350 for BC547
Switching Voltage V_S = 5V
1.3 = Safety factor
I_L = Collector-emitter current of transistors

Build the circuit on a general purpose PCB and mount in a general circuit box. Connect O/P1 and O/P2 terminals on the front panel of the cabinet. Also connect the mains power cord to feed 230V AC to the transformer. Connect LED1 and LED2 for visual indication.

This circuit has been tested by the author, the circuit that already built is shown on the following image:

This is definitely an effective 4-output stage stabilized DC power supply unit for testing electronic circuits. It delivers very well regulated and stabilised output, that is important for most electronic circuits to provide good results. The circuit gives you an audio-visual indication if there is a short circuit in the PCB under test, so the power supply to the circuit “under test” could be cut-off instantly to protect the important components from damage.

The circuit gives you four different regulated DC outputs (12V, 9V, 6V and 5V) and an unregulated 18V DC output, that are selectable by way of rotary switch S2. The selected output is showed on the analogue voltmeter connected to the outputs rails.

The circuit works by using a typical 18V-0-18V, 500mA step-down transformer to deliver 18V AC. A rectifier diode comprising diodes D1 and D2 supplies 18V DC, that is smoothed by capacitor C1 and given towards the combination of regulator ICs (IC1 through IC4). The regulator ICs deliver fixed, regulated outputs of 12V, 9V, 6V and 5V, respectively, that are joined to the rotary switch contacts. This power supply is useful and effective for loads requiring up to 200mA current.

Complementary transistors T1 and T2 conduct in the event the power to the circuit is switched on. Full chosen supply voltage is obtainable at the collector of transistor T2, that is applied to power the load. LED3 signifies the presence of output voltage. The negative terminal of piezobuzzer PZ1 is joined to the output rail via LED2, so the piezobuzzer stays silent as its negative terminal is also at full supply voltage (selected). If there is a short circuit at the output, LED2 glows to activate the piezobuzzer.

A fuse-failure indicator distinguishes short circuit at the output and input failure. It includes a bicolour LED (LED1) and resistors R1 and R2. When power is available and also the fuse is intact, red and green halves of LED1 are effectively in parallel to output a yellowish light. When fuse fails, green LED goes off and red LED lights up to tell us fuse breakdown.

The circuit could be simply assembled on a general-purpose PCB. Use small heatsinks properly for all ICs to dissipate the IC temperature. The output voltage could be check out on a voltmeter. Assmble and mount the circuit inside a metal box / case with provisions for voltmeter, LEDs, rotary switch, and so on.

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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This power supply unit can be used for general purposes, as long as the maximum specifications are taken into account.

Power Supply Technical Data:

• Short circuit protected
• Overload protected
• Output voltage: adjustable 3 to 30V stabilized.
• Output current: max. 3A
• Output ripple voltage: 0.5mV.
• Input: 9 to 30V transformer, depending on the desired output

Download the manual of this circuit include the schematic and part list from the following link:

3-30V 3A power supply circuit manual

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Kit Version:

This is a dual regulated and stabilized power supply, usually used to supply amplifier circuit, it also known as split powersupply. There are 3 output that are (+) voltage, (0) Ground (normal), and (-) voltage. The current output max about 0.3-0.5 A. For higher current output, power transistor is needed.

Please take a note that this circuit require center tap transformer. for example, if you need 12v output, you should connect J1 to 15v transformer output, J2 connected to 0v and J3 connected to another 15V.

The IC works ac stabilizer and regulator. There are 2 types of IC that are:

• 78xx > for positive voltage
• 79xx > for negative voltage

“xx” is the voltage output from IC. example, use 7809 if you need +9VDC output and 7909 for -9VDC output. For 9V output, the IC? input voltage should be at least 12V. For 12V output, the input voltage at regulator IC should be at least 15V.

Do you need high current power supply without heavy and expensive transformer? Then, this circuit would be great choice for you.

This 13.8 Volt 20 A regulated transformerless power supply. 20A transformer is very-very expensive, large in size and very heavy in weight.

This power supply capable in delivers around 20Amps at 13.8V. For lower currents, a separate current limiting output, capable of 15ma up to a total of 20A has been added. Let us see what we have got here. The power transformer should be capable to deliver at least 25A at 17.5 to 20V. The lower the voltage, the lower power dissipation. The rectified current will be ironed by the C1, whose capacity should not be less than 40.000uF, (a golden rule of around 2000uF/A), but we recommend up to 50.000uF. This capacity can be built up by several smaller capacitors in parallel. The base of this design is a simple 12V regulator IC 7812.

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