This is the circuit diagram of adjustable symmetric 1 to 24VDC, 1A Power Supply. This power supply give dual output positive and negatif output, you can adjust both positif and negative output (+1 to +24VDC and -1 to -24VDC). This kind of power supply also known as dual polarity power supply or splitted power supply which give positive anf negatif output.

This power supply can be used for universal usage, which required not more than 1A DC current. Please take a note that you should adjust the output voltage using general multimeter or DC voltmeter before use this power supply to protect the supplied devices.

Circuit Features:

• Low cost universal symmetric power supply
• Just add a suitable transformer and a heatsink
• Ideal for e.g. op-amp applications, amplifiers, …
• Trimmers can be replaced by potmeters to allow continuous adjustment of output voltage
• LED output indicators

Circuit Specifications:

• Positive and negative output adjustable between 1.2 and 24VDC
• Output current: up to 2 x 1A continuous (with suitable heatsink)
• Max. input voltage: 2 x 24VAC
• Very good line and load regulation
• Low ripple
• Short circuit protection
• Thermal protection

Circuit Manual of Adjustable Symmetric 1 to 24VDC, 1A Power Supply:

Adjustable Symmetrical Power Supply

1 file(s) 1.45 MB

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Kit Version:
This circuit available in kit version by valleman, you may purchase this kit online.

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:

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.

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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