Low-pass Filter?

[audioguru2]

Can i use the 1N5401 for the diode ?

For the modified 500W inverter project the 1N5401 diode is rated for 100V/3A so will be fine for D1 and D2.

the voltage at the primary side of the transformer should be 12V AC right ?

No. The primary has 24Vp-p so the transformer should be rated at 12V - 0V - 12V which is 24V center-tapped.

 

[ray99mond]

Thanks for your great reply

I measured the voltage between "12V to 0" and i get 24VAC
and same result for the "0 to 12V"

I didn't connect to a transformer yet for safety purpose....

so is the reading correct ? or should be 12VAC instead of 24VAC?

 

[audioguru2]

I don't know what your transformer is connected to. The mains? The project?
I don't know what was not connected to a transformer yet.
The project produces a square wave output that most meters won't measure accurately.

 

[ray99mond]

sorry for confusing, I built this 500W inverter but not yet connect the transformer to that circuit yet. and the 24VAC is come from the circuit which should be connected to the transformer.

sorry for drawing it wrongly.

 

[audioguru2]

The project doesn't have a regulated output voltage. It will change with the load.

 

[ray99mond]

the voltage will change with the load?
the project is using 12v-0-12v to 220 transformer, so the circuit circuit should generate 12VAC at the primary side of the transformer right ?

My problem is why i get 24VAC instead of 12VAC...
Thanks

 

[audioguru2]

With a 14V fully charged car battery, one 12V wire of the transformer will be driven to about 2V and the other 12V wire will swing to 26V. Then the oscillator reverses the voltages. So each transformer wire has 24Vp-p when measured from the 14V center tap.

If you connect the high voltage winding to a 220VAC sine-wave, then each wire of the low voltage winding will be 12VAC which is 34Vp-p when measured from the center tap.

 

[ray99mond]

I see... thanks for your explanation .. ;D

btw I have a 3A step down transformer from 240VAC (primary) to 12v-0-12v (secondary) for the rectifier system, can i use it as the step up transformer for this circuit? 12v-0-12v become the primary side while the 240VAC as the secondary side?

 

[audioguru2]

If your transformer's 24V output is rated at only 3A then the transformer's max rating is only 72 VA. Using such a small transformer in a 500W circuit wastes many parts. Just the operating power of the circuit without a load will probably overload the transformer.

Here is the modified project stripped down for a 100W load. With your small transformer its max is 72W.

View attachment 38496

 

[ray99mond]

actually the transformer that i am using now is a 240V to 12V  step down transformer for my rectifier circuit.

I need this inverter for my UPS project, so this 500W inverter is suitable...
so what kind of transformer i should get to support 500W output? 20A transformer?

 

[audioguru2]

actually the transformer that i am using now is a 240V to 12V

 

[ray99mond]

for backup computer for a short while only..
btw, the secondary transformer output is 240V,
240V x 2A = 480VA right?
why time the 2A with the primary voltage; 12v ?

 

[audioguru2]

for backup computer for a short while only.

I don't know if a computer's power supply will work from a square wave.
I wouldn't use a simple low cost inverter on my computer.

the secondary transformer output is 240V,
240V x 2A = 480VA right?
why time the 2A with the primary voltage; 12v?

Your transformer is probably rated as a voltage step-down transformer with a small 24V/2A output. That is only 48VA. A 480VA inverter will draw 40A from 12V and therefore needs a huge transformer.

 

[ray99mond]

audioguru, do you have any pure sine wave 12V to 240V inverter ?

Thanks

 

[audioguru2]

Hi Raymond,
An inverter with a pure sinewave output would be expensive and complicated. It would operate with PWM like a class-D audio amp.
I don't need an inverter with reliable nuke generating stations all around me and Niagara Falls nearby.

 

[ray99mond]

Hi audioguru,

1. how come the -TRG (pin6) of the CD4047 is not ground like +TRG (pin8)?
2. The output of the Q (pin10) & -Q (pin11) is a square wave right, then what is the function of LM358? square wave generator?
3. what is the function of 2SC1061 and 2N3055?
4. why connect 12VDC to the pin2 of the center tap transformer?

Thanks

 

[audioguru2]

1. how come the -TRG (pin6) of the CD4047 is not ground like +TRG (pin8)?

On the datasheet it shows that it must be wired that way to oscillate.

2. The output of the Q (pin10) & -Q (pin11) is a square wave right, then what is the function of LM358? square wave generator?

The LM358 is a dual current amplifier. The output current from Cmos logic devices like a CD4047 is very low.

3. what is the function of 2SC1061 and 2N3055?

They are current amplifiers.

4. why connect 12VDC to the pin2 of the center tap transformer?

The transformer is used push-pull.

 

[ray99mond]

i got a problem here,
i constructed such circuit and i am able to get a square wave output (without connecting to transformer yet), however once i connected to the transformer, the IC CD4047 burned.
may i know what is the problem? or i really need to add a fuse there?

 

[audioguru2]

A CD4047 is destroyed much quicker than a fuse can blow. It is a supply voltage spike that causes the damage. A fuse slowly protects against current overload.

The very low impedance of a car battery as a supply for the project has proven to keep supply voltage spikes down.

The addition of a 100 ohm resistor feeding positive power to the CD4047 and a 16V zener diode across it will protect it. 

 

[ray99mond]

is it add a resistor at the VDD pin 14 of CD4047? zener diode is placed parallel with the resistor ?