Help me here: inverter

[burhanmz]

hello everyone.
its a simple in-efficient inverter with the basics config (roughly over 150W)...
it works, but my problem is cross over distortion.

when i try to put loads such as energy saver bulbs, they flicker. although resistive loads are ok.

Audio Guru posted a circuit with diodes in place at the setting transistors.

i used different transistors, darlington TIP122. since i need roughly 2amp to drive the power transistors, i voltage divider biased my setting transistors...
so where am i suppose to insert diodes to overcome distortion, so that both pair of transistor are just on for a fraction of a second..


here is rough sketch... (dont mind the drawing, i'll make on in some circuit program and post it again)

thanks in advance to those who help..

 

[audioguru]

hello everyone.
Its a simple in-efficient inverter with the basics config (roughly over 150W)...
it works, but my problem is cross over distortion.

It has a square-wave output, not a sine-wave so it doesn't have any crossover distortion.
It has a voltage loss of at least 3.5V with a 300W load so a 10V transfoemer must be used and the transistors waste at least 74W.
Two Mosfets should be used instead of the transistors.

Many products don't work with a square-wave.

 

[burhanmz]

yes i know, there are centain drops...
but whether it be square or sine, cross over distortion does occur, i checked with both waves on an oscilloscope...

thats why i went for the little bit of smoothing using the oldest OPAMP. it will convert square wave form into sine.. since 10 and 11 outputs of cd4047 produces 180degree out of phase wave froms, i get a really good sine and cosine from the OPAMPS.

so back again to how to overcome cross-over distortion, and make this a class AB amplifier. i know a diode drop at the setting transistors will do it, as is indicated in text books. but i am not getting any result when i do insert diodes..

what to do? because even though the present circuit works (with poor line regulation!), loads like energy saver and tube lights flicker at operation.

and if someone can tell me how to improve its voltage regulation, it would be so good of them.

 

[Nigel Goodwin]

You're still deluding yourself, as Audioguru said, your problem isn't crossover distortion, it's because it's a rubbish design.

Adding lowpass filters between the oscillator and the transistors isn't going to help, and it's going to DRASTICALLY reduce the output capability and efficiency of the inverter.

 

[audioguru]

The resistors in the lowpass filters have a value that is too low for a CD4047 to drive. Use 20k or more then decrease the capacitors to 0.2uF and 0.4uF or less.

The 12k and 3.3k resistors are not doing anything because the opamps are driving the output transistors. The opamps are poor filters because they are clipping. The transistors are also clipping.
There is no negative feedback so the entire amplifier is extremely distorted. Negative feedback would also provide voltage regulation.

The peak voltage swing into half of the transformer is about 9V. Then the peak output from the transformer is only 90V for a 12V-0V-12V/120V transformer or only 172.5V for a 12V-0V-12V/230V transformer.
Without clipping distortion the voltage from the transformer is only 63.6V RMS for a 12V-0V-12V/120V transformer or only 122V for a 12V-0V-12V/230V transformer.

The transformer receives about 9V peak from the transistors so the low voltage winding must be 9V x 0.707= 6.4V-0V-6.4V if the waveform is not distorted.

Your idea wastes half the power from the battery because the transistors are linear instead of switching. Your transistors would get extremely hot.
Modern inverters use Pulse-Width-Modulation at a high frequency to allow their Mosfets to switch on and off with low heat, then the waveform is in many steps which are easily filtered into a pure sine-wave. The frequency is high so a small lightweight transformer is used. Negative feedback is uased for voltage regulation.

 

[burhanmz]

can you please suggest me some books for power amplifiers (specially class D) and PWM.

also.. can u post a circuit pic of a working good enough MOSFET made inverter.
i'd be grateful for your help...

 

[audioguru]

Like I said in your PM, my electricity is reliable so i don't need an inverter. Buy a cheap Chinese one.

 

[Mathieu3545]

May anyone help me with a circuit of Analogue Ohmmeter and Analogue AC voltmeter

 

[audioguru]

May anyone help me with a circuit of Analogue Ohmmeter and Analogue AC voltmeter

You hijacked this thread. It is about an inverter, not about your meters.

Please make your own thread about your meters.

 

[fsmyth]

There are some examples at:
https://hmin.tripod.com/als/andysm/pages/pwrsupp9.html
<als>