The proposed 12 V DC to 120 V AC inverter circuit is essentially a push-pull audio amplifier, as illustrated in the diagram below. A 5 volt square wave serves as the "input" or reference signal.
The output is a 340-volt AC signal with a peak-to-peak voltage of 340 volts. To match the DC reference signal, the feedback signal is rectified. The upper three FETs are switched on on one half of the AC waveform, while the lower three FETs are controlled on the other. In most 120-volt AC outlets, one side is grounded and the other is "LIVE."
The voltage on the LIVE side changes between - 170 and +170 volts.
The output of the inverter is somewhat unique. One side of the AC cycle is close to ground, while the other is at +170 volts. The condition is inverted during the second part of the cycle.
How it Works
Counter IC2 divides the clock signal by four to generate a 75-Hz inverter frequency, while op-amp IC1-a and its respective parts generate a 300-Hz clock oscillator. To eliminate transformer saturation, 75 Hz is utilized instead of 60 Hz.
Some electric clocks might run faster at this frequency, although most of the other electronic equipment would function normally.
The reference signal's timing and the error-amp signal's actuation to the right combination of FETs are controlled by the decade counter IC2.
The output of buffer IC1-c is high while IC2 pin 3 becomes high.
The error amp signal can now approach Q1, Q2, and Q3 due to the reverse biasing of D1. IC2 pin 4 is low at the very same moment, causing the output of buffer IC1-d to be low.
This turns off the gates of Q4, Q5, and Q6 by grounding them. Q7 is turned off since pins 2 and 7 of IC2 are similarly low. The non-inverting input of the error-amp (IC1-b) now has a 5 volt reference from regulator IC3.
R12 and C2 reduce the rising time of the reference signal to prevent output overshoot, and R15, R25, and C3 control the error amp's strength and frequency responsiveness. Subsequently, pin 2 of IC2 swings high, turning Q7 on and pulling the reference signal to ground.
The FET gates are grounded and pins 3 and 4 of IC2 are now low, shutting them off. The remaining three FETs are now switched on as pin 4 of IC2 gets high. The reference signal subsequently climbs to 5 volts, and the second half of the AC output waveform is obtained.
The next clock pulse triggers IC2 pin 7 to go high, turning off all FETs and setting the reference to zero. The next clock pulse resets IC2 and a new cycle starts.
R7, C8, and D7 create a filter which safeguards the CMOS electronics from alternating spikes and input polarity reversal. R9 and C4 filter output spikes, and R18-R21 are pre-load resistors that help the inverter stay stable while there is no load connected.
Despite the fact that the FETs lack current-equalizing source resistors, they divide current quite evenly. (When a FET "hogs" current, it warms up and its on resistance rises, resulting in lower current being pulled.)
How to Test
To run this 12 V to 120 V inverter circuit correctly, it must be initially powered by a 1 amp current-limited power source. In case you there isn't one, attach it to about 12 volts DC and pay attention for smoke or unexpected malfunctions.
You'll notice an alternating DC signal if you hookup an oscilloscope ground to inverter chassis ground and the probe to the intersection of D3 and D6. A frequency of 70 to 90 Hz is recommended.
If this isn't, you may change the value of R27 to make it so. Trimmer R17 should be adjusted at 180 volts peak.
If you're using a DVM or a VOM, attach it to the AC outlet of the inverter and tune R17 to 120 volts AC. Next, you would want to do a full -power testing.
A 12.6 volt, 10 amp power supply or a vehicle battery would be required for this. A 120-volt, 40-watt light bulb works well as a test load. The inverter will provide 150 volts peak with a 12.6-volt input, that would register around 105 volts on a DVM.
The output would be 115 volts AC with a 14.2 volt battery DC input supply, and is what a vehicle alternator provides.
From powering low-power AC electronics on a family vacation to recharging your camera batteries as you travel to your next holiday site, we're confident you'll find countless applications for your 12V to 120 V inverter at home or on the highway!
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