Help needed in push-pull circuit for Inveter.

[koolguy]

A multimeter is not an oscilloscope. The 12Vp-p square-wave might measure 6VAC on a cheap multimeter because it simply averages the voltage.

I think you are right b'coz i have notice that while measuring the output from 4047 with respect to gnd and Vcc was giving something ~5.5V. so, is MOSFET getting satisfying gate trigger to turn it complete

 

[audioguru]

I don't know why you connected only one Mosfet instead of connecting both Mosfets.

The square-wave inverter circuit is extremely simple so its output voltage changes when the load current changes because it has no voltage regulation circuit.

 

[koolguy]

I don't know why you connected only one Mosfet instead of connecting both Mosfets.

I have connected single MOSFET just for testing.

 

[audioguru]

I have connected single MOSFET just for testing.

But a push-pull output does not work properly if it is not connected properly.

 

[koolguy]

Do you think is MOSFET getting right gate pulse to turn fully ON??

 

[audioguru]

Do you think is MOSFET getting right gate pulse to turn fully ON??

You forgot to post your schematic so nobody knows.

The transformers in your photos look cheap and tiny so maybe your inverter will have an output of 50W or 75W.

 

[koolguy]

The 100ohms and 47ohms resistance at gate is not connected rest of circuit is same!!

 

[audioguru]

The 47 ohm resistor in series with each Mosfet's gate mounted at the gate pin is very important to prevent the Mosfet from oscillating at a high frequency.

Change the 10k resistors to 100k because the Cmos CD4047 has trouble driving a load as low as 10k.

Without having the 100 ohm resistor then voltage spikes might cause the zener diode and the CD4047 IC to blow up.

 

[koolguy]

OK, i will do these changes thanks.

The transformers in your photos look cheap and tiny so maybe your inverter will have an output of 50W or 75W.

The transformer i am using is 12-012V at 500mA. so do you think it can give 50watt??


Anyway how to make voltage regulation circuit for this inverter??

 

[audioguru]

The 24V/500mA transformer can produce 24V x 0.5A= 12W because it is a cheap tiny one.
You need to learn the basics of electronics to make voltage regulation using pulse-width-modulation which can also make a sine-wave.

 

[koolguy]

You need to learn the basics of electronics to make voltage regulation using pulse-width-modulation which can also make a sine-wave.

I have done PWM speed control of DC motor.....anyway if we will change the width of pulse then it is obvious that freq and duty cycle will also change, then what to do??

 

[audioguru]

It is easy to change the width of the pulses without changing the frequency. Then the duty-cycle changes and the average output voltage is regulated.

 

[koolguy]

Can you explain how freq will be constant and if duty cycle is change then push-pull ckt will not work as it should be..

 

[audioguru]

I have never made, bought or used an inverter because my electricity is reliable.
Inverters are sold to people who go away to camp, hunt or fish. I don't doo dat.

I think no manufacturer makes a poor quality square-wave inverter anymore, today they are modified sine-wave or pure sine-wave.
A pure sine-wave inverter can use a class-D digital amplifier IC driving Mosfets or it can use a microcontroller to make the PWM.

A modified sine-wave is actually a modified square-wave and it has narrow pulses that reach to the peak voltage of a sine-wave and the peaks have their width adjusted for voltage regulation.
The freqiency does not change.

Here is the waveform and schematic of a modified sine-wave inverter without voltage regulation and with voltage regulation:

 

[koolguy]

Can you please explain the first figure why NAND gate is used and its working with 4047..?

 

[audioguru]

Can you please explain the first figure why NAND gate is used and its working with 4047..?

Where is a NAND gate? Look at the datasheet of the CD4001 NOR gates.
The second image shows the function of a NOR gate: When both inputs are low then the output is high.
When the output is high then its attached Mosfet turns on. Then the transformer output produces the modified sine-wave shown.

 

[koolguy]

The second image shows the function of a NOR gate: When both inputs are low then the output is high.
When the output is high then its attached Mosfet turns on. Then the transformer output produces the modified sine-wave shown.

SO, ading NOR gate will do anything extra in circuit then before??

 

[audioguru]

SO, adding NOR gate will do anything extra in circuit than before??

The original circuit had a square-wave output. The peak voltage of the square-wave is 0.707 times lower than the peak voltage of the sine-wave from the mains so many electronic products and motor speed controllers WILL NOT WORK.

The circuit with the NOR gates has a modified sine-wave output that has the same peak voltage as the sine-wave from the mains.
The voltage of the transformer is also a little different.

This is the "modified sine-wave":

 

[koolguy]

OK, I have seen that the center tap transformer 12-0-12V of higher current then ~4A are not easily available in market but simple 12-0V transformer of higher current rating can be found easily....can we use these transformer for inverter by any mean??

 

[audioguru]

Edit: Modern transformers have two low voltage windings so they can be connected in series with or without a center-tap or can be connected in parallel.

My local store has hundreds of name-brand transformers. Digikey.com stocks thousands. If I order by phone or online from Digikey then it is delivered to me the next morning.
The modified sinewave transformer is 9V-0-9V so that the peak voltage is the same as the sinewave peak voltage from the mains.

You can make a simple square-wave inverter and use a transformer with a single winding without a center-tap if you switch both ends of the winding like this Japanese (100VAC) one (it is simple so it does not have voltage regulation):