DC-AC InverterDC-AC InverterBy: Dave KresockBy: Dave Kresock

4/24/084/24/08

Original Design That I FoundOriginal Design That I Found

The op-amp and the and gate work together to assure the TX1 and TX2 are not on at the same time.

Optoisolators are used to isolate the logic side from the power side

Inverter Concept DiagramInverter Concept Diagram

Inverter Control Circuit

Transformer

To Transformer 120 Vac OutIn From 12 Vdc

Source

Original CircuitOriginal Circuit

Logic Side Power Side

Circuit Component FunctionsCircuit Component FunctionsLogic SideLogic Side

The 555 timer, along with R3, R4, and C1 are designed to provide the J-k flip-flop with a 120 Hz The 555 timer, along with R3, R4, and C1 are designed to provide the J-k flip-flop with a 120 Hz frequency based on the following equation:frequency based on the following equation:

f = 1.44/[(R3+R4)*C1]f = 1.44/[(R3+R4)*C1]

Therefore: Therefore: R3 = [1.44/(f*C1)] = R4R3 = [1.44/(f*C1)] = R4

Using a 1kUsing a 1kΩΩ resistor for R4: R3 resistor for R4: R3 = [1.44/(120*1= [1.44/(120*1µ)] – 1000 = 11,000µ)] – 1000 = 11,000ΩΩ

Since the inverter will be powered from a 12 Vdc source, Inductor L1 is needed as a buffer Since the inverter will be powered from a 12 Vdc source, Inductor L1 is needed as a buffer between the battery and the supply pins of the ICs.between the battery and the supply pins of the ICs.

The J-K flip-flop provides the precise 50% duty cycle that will be applied to turn on each transistor The J-K flip-flop provides the precise 50% duty cycle that will be applied to turn on each transistor at alternating frequency of 60 Hz.at alternating frequency of 60 Hz.

Circuit Component FunctionsCircuit Component FunctionsPower SidePower Side

Transistors Q1 and Q2 determine how much wattage the inverter can supply. This inverter is Transistors Q1 and Q2 determine how much wattage the inverter can supply. This inverter is designed for approximately 100W.designed for approximately 100W.

Diodes D1 and D2 protect the transistors when they turn off and the magnetic field collapses. Diodes D1 and D2 protect the transistors when they turn off and the magnetic field collapses. This is a safe way to dissipate the energy stored in the inductance of the primary winding.This is a safe way to dissipate the energy stored in the inductance of the primary winding.

WaveformsWaveformsChannel 1 (Blue) = Output of the Q-pin of Flip-FlopChannel 1 (Blue) = Output of the Q-pin of Flip-FlopChannel 2 (Red) = Output of the Q/-pin of Flip-FlopChannel 2 (Red) = Output of the Q/-pin of Flip-Flop

Note the alternating waveforms and 50

% duty cycle.

WaveformsWaveformsChannel 1 (Blue) = TX1 DrainChannel 1 (Blue) = TX1 DrainChannel 2 (Red) = TX2 DrainChannel 2 (Red) = TX2 Drain

This is an area for concern.

As TX1 turns on, it’s instantaneous. However, as TX2 turns off, it’s much slower.

WaveformsWaveformsChannel 1 (Blue) = TX1 DrainChannel 1 (Blue) = TX1 DrainChannel 2 (Red) = TX2 DrainChannel 2 (Red) = TX2 Drain

With both transistors on for 200µS, (2.5%), the current is doubled

WaveformsWaveformsChannel 1 (Blue) = Output of the Q-pin of Flip-FlopChannel 1 (Blue) = Output of the Q-pin of Flip-Flop

Channel 2 (Red) = Output of the TransformerChannel 2 (Red) = Output of the Transformer

Transformer Output:

120 Vac @ 56 Hz

Unnecessary ComponentsUnnecessary Components

Let there be light!Let there be light!