Soft start Power supply circuit.

john May 6, 2009 No Comments
Description. Here is the circuit diagram of a simple soft start power supply using the well known voltage regulator IC LM317.Here the IC is wired in soft start mode in which the output of the IC gradually increases to the desired output voltage .When the input voltage is given to the IC , the capacitor C1 starts to charge and the current from the adjust pin (pin2) of the IC increases.The output voltage of the IC at any time...
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12V 15A voltage regulator

john May 4, 2009 13 Comments
Description. Here is the circuit diagram of a powerful 12V regulator that can deliver up to 15 A of current.The common voltage regulator IC 7812(IC1) is used to keep the voltage at steady 12V and three TIP 2599 power transistors in parallel are wired in series pass mode to boost the output current. The 7812 can provide only up to 1A and rest of the current is supplied by the series pass transistors. The 15A bridge B1 does the...
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Delayed ON LED

john April 17, 2009 2 Comments
Description. Here is very simple circuit in which the LED becomes ON only after a preset time the power supply is switched ON. When the power supply is switched on the transistor will be OFF. The capacitor now charges via the preset R3 and when the voltage across C1 is sufficient, the transistor switches ON and LED glows. The ON delay depends on the value of POT R3 .You can increase the time delay by increasing the resistance of...
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5V power supply with overvoltage protection.

john March 31, 2009 9 Comments
Description. For circuits using TTL ICs the supply voltage is a great concern and a slight increase in supply from the rated 5V may damage the IC. Using fuses alone does not solve the problem because a fuse may take several milliseconds to blow off and that’s enough time for the IC to get damaged. In this circuit a crowbar scheme is used in which a triac short circuits the power supply and burns the fuse. The burning time...
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Adjustable regulator using L200

john March 31, 2009 3 Comments
Description. Here is the circuit diagram of an adjustable voltage regulator using IC L200. L200 is a monolithic integrated adjustable voltage regulator IC having features like current limiting, thermal shut down, power limiting, input over voltage protection etc. Here the regulator is designed to produce an output adjustable between 2.85V to 15V at 1A.The resistors R1 and R2 determines the output voltage. The resistor R3 determines the limiting value of output current, here 1A. Capacitors C1 and C2 does...
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Blown fuse indicator circuit

john March 31, 2009 3 Comments
Description. Here is a simple scheme for adding a blown fuse indicator to your existing power supply circuit. This is done by just adding a resistor and LED to the existing circuit. The LED and resistor are connected in series and this combination is connected in parallel to the existing fuse. When the fuse is intact, it offers a low resistance and so the voltage drop across it will be not sufficient enough to glow the LED. When the...
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12V & 5V Combo power supply

admin September 9, 2008 43 Comments
Description. This is a simple approach to obtain a 12V and 5V DC power supply using a single circuit. The circuit uses two ICs 7812(IC1) and 7805 (IC2) for obtaining the required voltages. The AC mains voltage will be stepped down by the transformer T1, rectified by bridge B1 and filtered by capacitor C1 to obtain a steady DC level .The IC1 regulates this voltage to obtain a steady 12V DC. The output of the IC1 will be regulated...
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Negative reference voltage generator

admin August 26, 2008 1 Comment
Description. The circuit given below shows a negative reference voltage supply.The reference voltage can be set to precise values by R2. The circuit operates in the same manner as the positive reference voltage supply circuit shown previously.The circuit is nothing but  an inverting DC amplifier based on IC uA741.The circuit operates on a negative power supply and produces a negative reference voltage at the output. Circuit diagram with Parts list. Notes.  Assemble the circuit on a good qualtiy PCB...
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Positive reference voltage generator

admin August 26, 2008 1 Comment
Description. The circuit given below is a variable positive voltage reference supply.The reference voltage can be set to precise values by R2.Basically the circuit is a DC amplifier based on op-amp uA 741.The negative feedback is given via the zener diode. Circuit diagram with Parts list. Notes. Assemble the circuit on a good quality PCb or common board. Mount the IC1 on a holder. The POT R2 can be used for adjusting the output voltage. The formula for determining...
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Voltage splitter using Op-Amp

admin March 3, 2014 1 Comment
Description. A simple circuit for converting a floating dual power supply is shown here.The circuit is based on a uA 741 op-amp. The input supply is splitted by the voltage divider circuit formed of R1 & R2 ,and given to the non-inverting input of the IC1. The output (Pin 6) is connected to the inverting input of the IC itself. This type of circuit consumes less standby current compared to conventional resistor only voltage splitters. Circuit diagram with parts...
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