Introduction

The main aim of this article is to provide a guide on how to design an essential +/- 9V dual power supply. This is done from a 3V supply prototype, and the main element used for the design is the 555 timer IC. The dual supply is handy since it boosts and inverts from a single power source. Therefore, a circuit does not need to have several power sources. A rectifier diode system converts the 555 timer IC's output square pulse to negative and positive.

+/-9V Dual Power Supply from 3V Circuit Diagram

Necessary Components

• C1 1 470p C_Small Capacitor_THT:C_Radial_D4.0mm_H7.0mm_P1.50mm Unpolarized capacitor, small symbol
• C2, C4 2 10u C_Polarized_Small_US Capacitor_THT:C_Radial_D4.0mm_H7.0mm_P1.50mm Polarized capacitor, small US symbol
• C3, C5 2 4.7uF C_Polarized_Small_US Capacitor_THT:C_Radial_D4.0mm_H7.0mm_P1.50mm Polarized capacitor, small US symbol
• D1, D2, D3, D4 4 1N4007 1N4007 Diode_THT:D_DO-41_SOD81_P7.62mm_Horizontal 1000V 1A General Purpose Rectifier Diode, DO-41
• J1 1 3V Screw_Terminal_01x02 282834-2:TE_282834-2 Generic screw terminal, single row, 01x02, script generated (kicad-library-utils/schlib/autogen/connector/)
• J2 1 +9V Conn_01x02 Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical Generic connector, single row, 01x02, script generated (kicad-library-utils/schlib/autogen/connector/)
• J3 1 -9V Conn_01x02 Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical Generic connector, single row, 01x02, script generated (kicad-library-utils/schlib/autogen/connector/)
• R1 1 1k R_Small_US Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P5.08mm_Horizontal Resistor, small US symbol
• R2 1 10k R_Small_US Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P5.08mm_Horizontal Resistor, small US symbol
• U1 1 LM555xN LM555xN Package_DIP:DIP-8_W7.62mm Timer, 555 compatible, PDIP-8

Building and Functioning

Constant non-discrete square output pulses are oscillated by a boost converter circuit timer IC 555, built in a stable multi-vibrator mode. Usually, the timing resistor and the timing capacitors determine the oscillating frequency. The formula below represents this;

Some additional information for the equations include RA = R1, RB = R2, and C = C1.

Two distinct rectification configurations involving diodes and capacitors will be utilized to achieve positive and negative voltage conversion. The output signal generated by the timer IC is directly fed into these rectification setups. As square pulses exhibit positive and negative components, rectification is essential to eliminate the undesired portions. In the first rectification circuit, the negative part is eliminated, resulting in a +9V output, while the second rectification circuit removes the positive aspect to yield a -9V output. Capacitors C3 and C5 are employed to manage voltage charging and discharging cycles triggered by the square pulse.

Pin Design and IC 555 Functions

An 8-pin dual in-line package timer IC is being utilized in this prototype circuit. The Timer IC 555 is known for its exceptional stability and can accurately generate time delays or oscillations. It can operate within a voltage range of 3 volts to 12 volts. When the timer IC 555 is configured in the astable mode (pins 2 and 6 are connected), it becomes a self-triggering device operating as a multi-vibrator without external intervention.

In this configuration, an external capacitor, C1, charges through the combined resistance of R1 and R2 and discharges through R2. Consequently, the duty cycle is determined by the ratio of these two timing resistors. During its operation as an astable multi-vibrator, capacitor C1 undergoes charging and discharging cycles, oscillating between 1/3 Vcc and 2/3 Vcc.

Uses of the +/-9V Dual Power Supply from 3V

• Op-Amp Circuits: Provides dual-voltage rails for amplifiers and signal conditioning.
• Audio Amplifiers: Used in portable audio devices and headphone amps.
• Instrumentation Amplifiers: Enables precise signal acquisition.
• Signal Processing: Vital for DSPs, ADCs, and DACs.
• Biasing Circuits: Supports correct component operation.
• Mixed-Signal Circuits: Ensures compatibility.
• Test Equipment: Common in oscilloscopes and function generators.

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