adjustable 1.25v to 30v using lm317 & lm337
The dual power supply name suggests the whole idea about systems, where it produced two output, here we use lm317 and lm337 regulator ICs which is to build the dual power supply circuit.
What is a dual power supply
In electronic terms dual power supply means, the supply used to provide two supply terminals such as positive and negative. At Circuits like op-amp based amplifiers, both negatively and positively powered supply is a must for inverting and non-inverting part of the op-amp.
Circuit wish dual power supply is the same as a normal rectifier but the only difference is its positive and negative terminal had a common ground, this is the reason why both these terminals act like a dual-sided power supply.
Applications like amplifiers nature of the audio signal are always include two parts due to this, the negative and positive side of the input signal must have to amplify separately, in such case dual power supply is used.
In some particular circuits normal power supplies are not apt for the operation, more specifically op-amp ICs need these dual power supplies.
In this article we explain the variable dual power supply circuit, we need a constant output from this circuit, for that we use 78xx, 79xx regulator ICs. But our project is to build a bench of power supply for our common use.
At its output, we have 1.25v to 30v dc supply with 1.5amp maximum current.
LM317 is an adjustable voltage regulator IC, thus a constant output is taken from it by placing a fixed value resistor with the Lm317 IC.
This is a simple dual power supply circuit consists of LM317 regulator IC as the main component, normally a dual power supply build with two blocks with a positive and negative block.
LM317regulator IC will be working as a positive block, thus LM317 regulator ICs input pin 3, output pin2 and adjustable pin1, so input connected to pin3, it regulates voltage using adjustable pin1 which is connected to variable resistor RV1 and R1 resistors, variable resistor vary output voltage start from 1.5v to 30v, and the values selected for the RV1 resistor is 4.7k or 5k. C1 capacitor is used to further filtration of output.
Proteus-based circuit simulation video is included with this article, it is much useful for those who wish to build the circuit.
LM337 regulator IC also has the same features as LM317, but this particular IC had an extra feature to make the negative voltage at the output, this is the reason why we use LM337 IC here at this circuit.
LM337 based regulator circuit acts as negative block at the circuit, which is to provide negative supply voltage at the dual power supply. A negative block consists of the same components as a positive block but the pin indications will change as pin3 input, pin2 output, and pin1 for adjusting.
LM337 regulator circuit input section is just opposite of positive block, so the input voltage will reverse its polarity, thus the output voltage produced is negatively charged, and this is how negative output is generated at the circuit.
dual power supply circuit diagram
dual power supply-Circuit explanation
At the input stage, we convert 230v ac into 18-0-18 AC and then convert AC to DCusing BRIDGE IC, after the rectifier section, we remove ripples with C1 and C2capacitors.
LM317regulator provide +ve voltage supply
LM337regulator provide –ve voltage supply
RV1 variable resistor has to adjust to varying +VE supply
RV2will be adjusted to make –ve supply variation
The transformer had to set a maximum of 1.5amp current, is because of maximum output current delivered by IC is also 1.5amp.
dual power supply components
dual power supply PCB
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