Introduction

The LM317/LM337 symmetrical power supply circuit is an electronic setup for meeting the voltage requirements of both positive and negative circuits. Powering circuits requiring dual polarity voltages is no problem for this flexible, low-cost circuit. It uses two voltage regulators, an LM317 for positive voltage and an LM337 for negative voltage. It has a simple construction procedure, making it a good choice for a wide range of applications that need access to both positive and negative voltage.

Circuit Diagram

Necessary Components

• 2200uF/50V Polarized capacitor, small US symbol C1,C3 CP_Radial_D16.0mm_P7.50mm
• 100nF Unpolarized capacitor, small symbol C2,C4,C7,C10 C_0402_1005Metric
• 10uF Polarized capacitor, small US symbol C5, C8 C_0402_1005Metric
• 470uF Polarized capacitor, small US symbol C6,C9 CP_Radial_D10.0mm_P5.00mm
• 1N4007 1000V 1A General Purpose Rectifier Diode, DO-41 D1,D2,D3,D4 D_DO-41_SOD81_P10.16mm_Horizontal
• LED_Small Light emitting diode, small symbol D5,D6 LED_D3.0mm
• Fuse_Small Fuse, small symbol F1,F2 Fuse_0402_1005Metric
• Conn_01x03_Pin Generic connector, single row, 01x03, script generated J1 PinHeader_1x03_P2.54mm_Vertical ~ Generic connector, single row, 01x02, script generated J2,J3 PinHeader_1x02_P2.54mm_Vertical
• 200R Resistor, small US symbol R1,R3 R_0402_1005Metric
• 4.7k Resistor, small US symbol R2,R4 R_0402_1005Metric
• 5k Potentiometer RV1,RV2 Potentiometer_Bourns_3296W_Vertical
• LM317_SOT-223 1.5A 35V Adjustable Linear Regulator, SOT-223 U1 SOT-223-3_TabPin2
• LM337_SOT223 Negative 1A 35V Adjustable Linear Regulator, SOT-223 U3 SOT-223-3_TabPin2

Using LM317 and LM337 to Fabricate a Dual Power Supply Circuit

Using the LM317 and the LM337, you can easily build a balanced power supply. The circuit uses two voltage regulators, the LM317 and the LM336, connected in parallel to produce a balanced output voltage. The circuit also includes a filter capacitor and a voltage adjustment resistor, which may be adjusted with a potentiometer or a precise multi-turn trim pot. Even though a precision multi-turn trim pot was used, it is important to note that a potentiometer can be connected to the CN2 and CN3 ports as well.

Mounting the ICs necessitates the use of heat sinks. However, a lesser current-rated transformer is permissible, with the condition that it sets the maximum current for the power supply, as long as the specs include a 12+12 to 28+28 VAC output and a minimum of 1.5A. The maximum voltage will be about 1.4% higher than the input voltage to the transformer. In other words, a 12VAC transformer can only produce up to 16.8VDC, but a 28VAC transformer can produce up to 39VDC. The output of a practical symmetrical power supply can be adjusted anywhere from 1.25V to 33VDC by adjusting the secondary winding of a 24+24 VAC/2A transformer.

The Circuit’s Fabricated PCB diagram

Advantages of utilizing a Symmetrical Power Supply Circuit that has both LM317 & LM337

• Provides symmetrical voltage output for applications like audio amplifiers.
• Offers continuous current output for relevant applications.
• Allows adjustable, regulated voltage output to match project requirements.

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