ROBOT.LK

Parts List:

1. R1 = 10K
2. R2 = 100K
3. R3 = 100 ohm
4. R4 = 50K potmeter, Linear
5. C1,C2 = 0.1uF
6. C3 = 0.01uF
7. C4 = 2700uF
8. Q1 = TIP41A, NPN, or equivalent
9. Q2 = TIP42A, PNP, or equivalent
10. L1 = 1uH
11. T1 = Filament transformer, your choice

This DC-to-AC inverter schematic produces an AC output at line frequency and voltage. The 555 is configured as a low-frequency oscillator, tunable over the frequency range of 50 to 60 Hz by Frequency potentiometer R4.
The 555 feeds its output (amplified by Q1 and Q2) to the input of transformer T1, a reverse-connected filament transformer with the necessary step-up turns ratio. Capacitor C4 and coil L1 filter the input to T1, assuring that it is effectively a sine wave. Adjust the value of T1 to your voltage.

The output (in watts) is up to you by selecting different components.

Input voltage is anywhere from +5V to +15Volt DC, adjust the 2700uF cap's working voltage accordingly.
Replacement types for Q1 are: TIP41B, TIP41C, NTE196, ECG196, etc. Replacement types for Q2 are: TIP42B, TIP42C, NTE197, ECG197, etc. Don't be afraid to use another type of similar specs, it's only a transistor...

If the whole thing is working, good. If not, relax and don't get frustrated. Do the following checks:

• You have connected the filament transformer in REVERSE yes?
• If not, disconnect the power and reverse. If you have, disconnect the transformer and measure the voltage after L1 and ground.
• Just in case, GROUND for this circuit is same as negative (-).
• Q1/Q2 are oposites, e.i. npn/pnp.
• Is your 555 perhaps defective? Disconnect R3 from pin 3 and check pin 3 for a pulse.
• Check your transistors to make sure they are not defective.

If we use high frequency , we can use a small tramsformer!
like SMPS power supplies.

Dear Friend,

Small transformers have low efficient in low frequencies like 50 Hz. Because their power density is low in low frequencies. If we want to obtain a 50Hz AC signal we can do switching with a high frequency as you have mentioned.
But to reduce the output A/C frequency to 50 Hz , we have to convert the high frequency AC signal again to DC and then can obtain a 50 Hz signal , by switching transistors in 50 Hz.

And if we want to make the transformer small , we can not use lamination core and core should be ferrite. Because
the magnetic properties of the ferrite are the main thing , that increase the power density , when have a high frequency signal.

Yes, definitely right! If you use high frequency, then you need a small transformer. This has suggested by one of my friends, Magneto gave you the details on how this works.

There is something a bit confusing to me, specificley how the transistors amperage rating will change the
maximum output current.

By using the TIP41 & 2A, will there be 6A of 120V available?

The other alternative I'm guessing is that 6A of 12V is allowed to go through the primary resulting in .6A of 120V out the other side.

This being true, would additional transistors be connected in parallel on each respective side to increase the output wattage?

I've already got a transformer rated at 800w, and 2n3055 15A transistors. If I was to use them with a bank of MJ2955, would it suffice to say that 5 connected together on each
side would allow 75A of 12V through the primary resulting in 900W of 120V available?

Best thing you could do is, do a little experiment with it. Since the circuit is not difficult to make, with a scope you could measure all ratings and adjust as you want.