Introduction: Inverter: 5 VDC to AC With 555 Timer

This tutorial will walk you through how to invert a DC voltage signal into an AC voltage signal using a 555 timer, capacitors, resistors and transistors. Before we jump into the details, it’s important to understand the 2 main actions that are occurring in the circuit. First, the 555 timer is used to create a square wave from the DC signal, then 2 transistors, a capacitor and resistor are used to smooth and shift the square wave into an AC signal. The values of the resistors and capacitors directly connected to the 555 timer can be tuned to change the frequency of the square wave. The value of the capacitor and resistor to the right of the 2 transistors determine how severely the square wave is smoothed to produce the final AC wave. We will go into more detail on the function of each component in the following sections. Above is a picture of the overall circuit board after the build and the circuit in simulation. The simulation does not exactly match the built circuit because we had to tune the breadboarded circuit by replacing the 15 kOhm resistor with a potentiometer and modifying the 100 kOhm resistor to 90 kOhms.

Supplies

Parts List:

  • Breadboard
  • Assorted wires
  • 5V power supply
  • TS555CN - 555 timer
  • 2N3904 - NPN transistor
  • 2N3906 - PNP transistor
  • Resistors
  • 1 kΩ
  • 10 kΩ
  • 15 kΩ
  • 100 kΩ
  • 30 kΩ (x3)
  • 25 kΩ Potentiometer
  • Capacitors
  • 10 nF
  • 100 nF
  • 2.2 μF

Step 1:

Set up the breadboard by connecting the two power rails and two ground rails. Add power and ground connectors.

Step 2:

Place the 555 timer so it spans the gutter of the breadboard.

Step 3:

Connect Vcc and GND of the 555 timer to power and ground, respectively.

Step 4:

Connect the Control Voltage of the 555 timer to ground with a 10 nF capacitor.

Step 5:

Place the power and ground for the series resistors and capacitor.

Step 6:

Begin to connect them with a 10 kΩ resistor.

Step 7:

Next, add three 30 kΩ resistors in series to create an equivalent resistance of 90 kΩ.

Step 8:

Add a 25 kΩ potentiometer in series with the other resistors.

Step 9:

Connect the potentiometer and ground with a 100 nF capacitor.

Step 10:

Connect the Discharge pin of the 555 timer to the node between the 10 kΩ resistor and the equivalent 90 kΩ resistor.

Step 11:

Connect the Threshold pin of the 555 timer to the node between the 90 kΩ resistor and the 100 nF capacitor

Step 12:

Connect the Trigger pin of the 555 timer to the node between the 90 kΩ resistor and the 100 nF capacitor

Step 13:

Connect the Reset pin of the 555 timer to the Control Voltage pin of the 555 timer

Step 14:

Connect the Output pin of the 555 timer to a separate row of the breadboard

Step 15:

Connect the NPN transistor

  1. Base on the output from the 555 timer Output pin, with a 100 Ω resistor between
  2. Collector connected to Ground
  3. Emitter connected to an empty row of the breadboard

Step 16:

Connect the PNP transistor

  1. Base on the same node as the NPN Base
  2. Collector connected to Vcc
  3. Emitter connected to the same node as the NPN Emitter

Step 17:

Add the 1 kΩ resistor and 2.2 uF capacitor in series between the Emitter node of the transistors and Ground

Step 18:

Here is the final AC output with the tuned potentiometer: A 60 Hz signal with a peak to peak voltage of 3.26 V.