Jump to content
Electronics-Lab.com Community

12 V DC to a 220V AC Inverter AMplfier Design


Recommended Posts

hi audioguru and kachew,
its seems this topic become more complicated......i just want to ask is this inverter runs by 12vdc (input from 12V battery) and having ouput 240vac at the transformer output(output of circuit at the transformer secondary winding)? as i understand the transformer operates on Ac current and from the diagram as i understood this Ac current provided by 12 battery dc source and being switched by the mosfet to produce 12 to 0v alternating step current? is this correct?? ;D ;D as i understand the transformer cant be fed from a 12 dc battery directly....pls advice...
thanks for your reply.... ;D ;D

Link to comment
Share on other sites

  • Replies 195
  • Created
  • Last Reply

Top Posters In This Topic

Hi Morro,
The transformer is fed with AC from the Mosfets..
One side of the center-tapped low voltage winding has 12VDC applied to it from the Mosfets on that side, then that side turns off and the other side turns on, for a square-wave inverter. The DC current in the winding alternates from side to side. That makes AC in the high voltage winding of the transformer.

For a modified sine-wave inverter, there is a pause with no current between each side being driven alternately. The modified sine-wave inverter doesn't feed a stepped current to the transformer. It is 1 side on, then a pause with no current, then the 2nd side on, then a pause with no current, then it repeats. The DC current in the winding alternates from side to side. That makes AC in the high voltage winding of the transformer.

Link to comment
Share on other sites

hi audio guru,
  i now understand why you are called by that name. you answers are flawless. can u please help me answer the following questions?;

1. what are the functions of the two 1n5408 diodes connected back to back from the drain of the power mosfets to ground?.

2. can i achieve a back emf suppression by connecting the two diodes front to front and connect their cathodes to the positive of the battery?

3. lastly, is there no way one can connect a feedback to the cd 4047 to achieve a good voltage regulation as in sasi's sg3524 pwm inverter circuit?

Link to comment
Share on other sites


1. what are the functions of the two 1n5408 diodes connected back to back from the drain of the power mosfets to ground?

They are to protect against reverse-voltage spikes. But Mosfets already have diodes in them which is how they are made so I wouldn't add the 1N5408 diodes. Look at the diodes (zener diodes) in an IRF540 Mosfet.

2. can i achieve a back emf suppression by connecting the two diodes front to front and connect their cathodes to the positive of the battery?

That would cause smoke. When one side of the center-tapped transformer winding is grounded by a turned on Mosfet, then the other side must swing up to double the supply voltage due to transformer action (think about a teeter-totter). Your added diodes would short-circuit the voltage swing.

3. lastly, is there no way one can connect a feedback to the cd 4047 to achieve a good voltage regulation as in sasi's sg3524 pwm inverter circuit?

Not easily. The SG3524 is made to vary the pulse width by feedback but the simple CD4047 is not.

post-1706-14279143088157_thumb.png

Link to comment
Share on other sites

thanx audio guru. but sorry, some more questions;

1. does every power mosfet have the zener diode connected internally across their source to drain pins?

2. when using the cd4047 and cd 4001 ic for a simple msw inverter as done by kachew, what frequencies would be found at the output pins 10,11, and 13 respectively for an inverter of 50hz?

3.does the source to drain voltage(vds) matter when choosing power mosfets for inverter designs of supply voltages of between 24v and 48v?

4. can thyristors be used to substitute power mosfets in higher power inverter designs?

Link to comment
Share on other sites


1. does every power mosfet have the zener diode connected internally across their source to drain pins?

Every one that I have seen. It is part of how they are made. It is a very powerful zener diode so it is slow. For high speeds, a quicker diode is added.

2. when using the cd4047 and cd 4001 ic for a simple msw inverter as done by kachew, what frequencies would be found at the output pins 10,11, and 13 respectively for an inverter of 50hz?

Pins 10 and 11 are 50Hz opposite each other (one is high while the other is low).
Pin 13 is 100Hz.

3.does the source to drain voltage(vds) matter when choosing power mosfets for inverter designs of supply voltages of between 24v and 48v?

Of course the max voltage rating matters. In this push-pull inverter, the drains reaches to double the supply voltage due to transformer action (teeter-totter).

4. can thyristors be used to substitute power mosfets in higher power inverter designs?

I guess so. I have never seen one.
Link to comment
Share on other sites


as we know the mosfet is used as a switch rite...in the kachew's inverter diagram its shown there is 6 mosfet parallel in the diagram, can we reduce it to 2 mosfet and what is the effect for reducing it compare to 6 mosfet?

6 Mosfets are not in parallel, 3 are in parallel on each side.
There is a very high current in the mosfets. Paralleling them allows them to share the current so each one gets 1/3rd of the total.
Paralleled Mosfets share the heat so each one gets nearly only 1/3rd of the dissipation.
You could use two more expensive Mosfets with lower on-resistance instead of paralleling cheaper Mosfets that have a higher on-resistance.
Link to comment
Share on other sites

  • 5 months later...

hi all,

i have tried the CD 4047 and i cant get the desired output from the Oscilloscope....can anyone pls help me?
i cant get the square wave pulse from it....i have connected a +12V supply  and ground (which is connected to -VE supply with a wire) from a DC power supply at my lab. i have connect it according to the design....any mistake there...if yes pls help me to correct it.... thanks alot :-* :-*

Link to comment
Share on other sites

There is no -VE supply in this project. The supply is +12V and 0V.

Did you make the wrong circuit or my corrected one? I don't know why my corrected one was deleted.

MODERATOR EDIT: THE VALUES FOR C AND R IN THE PROJECT ARE NOT INCORRECT VALUES. BOTH SETS OF C AND R WILL GIVE YOU 50HZ, AS WILL AN ENDLESS NUMBER OF OTHER VALUES.  -MP

Link to comment
Share on other sites

dear Au, i did the corrected version but still no avail, mayb the IC hav destroyed by me... cos i have wrongly connected the supply to the pin 13.... will it burn the ic? i will try with new IC of CD4047 to retry.... is there any other compatible IC can be used to replace this function generator IC? oh ya... i more question.... how can i modified the circuit and use the mosfet for amplification? as i know previous thread u told me that mosfet will get hot easily when amplification occur....so i have built another circuit which is 12V fan temperature control to cool my inverter circuit....can this be done??
thanks Au

Link to comment
Share on other sites


i did the corrected version but still no avail, mayb the IC hav destroyed by me... cos i have wrongly connected the supply to the pin 13.... will it burn the ic?

Pin 13 is an output and is not supposed to be connected to the supply. A high current would flow which might destroy it. Replace it.

is there any other compatible IC can be used to replace this function generator IC?

It is not a function generator IC. It is a common Cmos digital monostable/astable multivibrator that is made by most semiconductor manufacturers. Any square-wave oscillator and a digital inverter could replace it.

how can i modified the circuit and use the mosfet for amplification? as i know previous thread u told me that mosfet will get hot easily when amplification occur....so i have built another circuit which is 12V fan temperature control to cool my inverter circuit....can this be done??

Mosfets work better and are cooler in a simple square-wave inverter. The design is completely different (much simpler). The Mosfet stays cooler because it switches, it does not amplify.
This project uses ordinary transistors instead of Mosfets because the circuit is old and Mosfets are not available in The Philippines where it was used.
Link to comment
Share on other sites

hi Au,

how can i know how much currents flows in my circuit? izzit the same amount of current as shown in the datasheet for the mosfet? how many amps of current will flow to the transformer and what is the output amps and voltage as the modified sine wave circuit is recommeded by you....isnt the amps and voltage value for the circuit is controlled by the transformer? depends on the step up transformer voltage and amps rating since the mosfet is use to share and drawn current from the car battery?
thanks for your reply... :-* :-*

Link to comment
Share on other sites

The stepup of the transformer determines the output voltage of an inverter that is simple and doesn't have voltage regulation.
The load determines the current in the transformer, in the Mosfets and from the battery.

The Mosfets are just switches that draw DC power from the battery and pass AC power to the transformer:
1) For a 500W square-wave inverter about 100W of heat will be produced, so 600W must be taken from the battery. The battery current and average Mosfets current is 600W/12V= 50A.
2) The 100W of heat must be dissipated mostly in the Mosfets so they must be properly heatsinked.

Link to comment
Share on other sites

dear AU,

from your explaination i know abit of transformer thanks...but how can i know or make the output to have desire voltage regulation? but putting the desired  value of resistor at the drain of the mosfet there? can u prove it by calculation so i can have better understanding on the circuit and the operation of the mosfet...
thanks again

Link to comment
Share on other sites

You cannot use a resistor in series with the transformer to reduce the output voltage, the high current will create too much heat. Use Pulse-Width-Modulation at a high frequency to control Mosfets which adjust the average voltage that is applied to the transformer.
Then since you will have PWM, you might as well apply a sine-wave to control the average voltage.

Link to comment
Share on other sites

no no... i dint mean that....i mean how much mosfet will draw current from the battery? and what is the desired output Amps at the output of the trans? how we can determine the output amps....as i know the amps is dependent on how much load we have in the circuit.....
any calculation can prove how many amps in the circuit and the output at the transfomer?
thanks

Link to comment
Share on other sites

If your inverter is efficient then it doesn't waste much power as heat because its Mosfets switch nearly completely on and off and do not operate linear.

Power= Volts x Amps. Amps= Power/Volts.
Input power from the battery = output power to the load plus heating power.

Example again:
500W inverter with a 500W load. 100W of heating. Total power from the battery= 600W. Total current from a 12V battery = 50A. Current in the Mosfets on each side= 50A max.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share


×
  • Create New...