Low output ac need some understanding

[maicael]

i decided to test a 555 oscilator with 200hz and 50% duty cycle and an ic4017 inverter schematic using irfp fets for the power stage and 12-0-12 transformer which was removed from an sg3524 inverter.Now heres the stange thing,while using the sg5324 circuit i got 220VAC but when i tested the 555 timer and 4017 circuit i got 116VAC but upon testing the volatge at the gates it read about 3V for both the sg3524 and 555 inverter.
why is this so what could be wrong with the oscillator of the 555.i dont understand it.pls anyone with a clue.thanks

 

[alec_t]

If you post a schematic of your setup we may have a better understanding of your problem.

 

[audioguru]

The output of the very simple inverter is a square-wave but an ordinary multimeter is designed to show the voltage of a sine-wave which is completely different.
Most Mosfets switch well only when the gate voltage swing is 10V, so maybe your multimeter showed only 3V for the 10V or 12V square-wave.

 

[maicael]

Thanks so far but if it helps here is the schematic i tried.R1= 2k, R2=56k R3= 50k, C1=50nf.the transformer is 12-0-12 by the way

 

[audioguru]

The circuit is a Modified Sine-wave which is actually a Modified Square-wave.
The Mosfets are turned off for half the total time which causes the average output voltage to be about half, if the transformer is 10V-0-10V.
The peak voltages must be much higher, like the peak voltages of a sine-wave are 1.414 times higher than the RMS voltage.

 

[MikeMl]

What Audioguru is trying to say is that the duty cycle of each FET is only 25%

 

[maicael]

is there any advantage to using a 10-0-10/220v or 9-0-9/220v transformer over a 12-0-12/220v transformer

 

[audioguru]

is there any advantage to using a 10-0-10/220v or 9-0-9/220v transformer over a 12-0-12/220v transformer

When the voltage ratio of the transformer is higher then the output voltage of the transformer is higher.

A very cheap 220V to 12V transformer might actually be a 220V to 15V transformer with thin high resistance wires. Then when it is loaded its output voltage drops to 12V.

But turn it around and feed a 12V signal into its 15V winding and its output voltage will be only 176V instead of 220V.

 

[maicael]

pls what exactly happens in an inverter where the output voltage drops with load applied especially in inverters without voltage correction feedback.
what are the factors that cause the voltage to drop?

 

[alec_t]

Power out = efficiency x power in.
If efficiency and power in are constant then so is power out.
Power = volts x current.
So if load current increases, output volts must decrease.

 

[audioguru]

pls what exactly happens in an inverter where the output voltage drops with load applied especially in inverters without voltage correction feedback.
what are the factors that cause the voltage to drop?

1) Old, weak or uncharged battery. The battery voltage should not drop much when the inverter has a load.
2) Thin wiring that has fairly high resistance.
3) Poor quality or cheap transformer that has a lot of resistance.
4) Mosfets that do not have a very low on-resistance.

A cheap transformer produces 16V instead of 12V without a load because it has a lot of resistance, then its voltage drops to 12V with a load.
Reversed, it produces 12/16= 75% of the expected output voltage when loaded. Or the voltage might drop more if it saturates.

A high quality transformer produces 13V without a load, then its voltage drops to 12V with a load.
Reversed, it produces 12/13= 92% of the expected output voltage.

 

[maicael]

thanks for the insight.i really appreciate.One more thing when powering a 555 timer using a 12v source do we power it directly or use a regulator or some sort of resistor because i noticed that my 555 stops working after a while and i have to replace it.Am thinking its because of some sort of surge current or something as i power it directly.

 

[audioguru]

The datasheets for a 555 timer show minimum a 1uF and a 0.1uF supply bypass capacitors. In an inverter use 10uF and 0.1uF and they and the 555 should be fed 12v through a series 47 ohm resistor then the supply to the 555 is filtered so that voltage spikes will not touch it.

 

[maicael]

so basically i connect the 10uf to pin 8 of 555 and its other leg to ground, same goes for the 0.1uf then power all through 47ohms.here is the picture just to be sure what you mean.thanks

 

[audioguru]

Yes you are correct about the 10uF and 0.1uF caps and the 47 ohm resistor.