Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Building a 12Vdc to 120VAC converter

Status
Not open for further replies.

eliasib

Newbie level 3
Joined
Sep 23, 2018
Messages
4
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
36
Hello friends; thank you for allowing me to be member of this wonderful electronic site. I write you because I want you to help me build a DC to AC inverter. I have a Transformer which I took out of an inverter for computer use. This transformer has a 12VAC input with 120/220VAC output. I know there are many diagrams in internet but I wanted to use a pwm TL494 (I have many of them) and looking for a schematic to build the converter with the parts I have, I have always found push pull configurations (for center tap transformer) but mine has no center tap. I am thinking of using a full bridge converter but I am not sure about that. If you have any suggestion to my request, I will thank you a lot. God bless you
 

Can you confirm what is the proper switching frequency for your transformer? Did the unit apply PWM at a rapid frequency, to the primary?

Or did the unit apply 50-60 Hz at 12V to the primary? This could make a difference how you choose the best topology.
 

Not enough information, you should be more specific and more people will understand your question, so higher chances of being helped.

I assume you want to generate a 120V 60Hz sine wave signal. How much power are you planning to use? I think TL494 won't fit in your application, as its main use is high frequency PWM generation.

The circuit you must be talking about is for a SMPS, which uses high frequency transformers with several windings, I assume your transformer is a simple one (2 windings).

I recommend you to use a fixed 60Hz oscillator with a diode based sine-wave shaper (it's only 2 diodes and a resistor), with a power driver to connect the secondary winding. The efficiency won't be good but it's a simple way to get what you want.
 

Hello. Thank you very much for answering me. Excuse me for not being specific. The frequency is 60Hz and the inverter will not be used for high power applications but for connecting cellphone chargers, iron tip or any small appliance with little current demanding.. What happens is that the electric energy is often cut off so I need a small dc/ac inverter to power the appliances described above but I want to make use of the electronic parts I have because it is very difficult to buy them here. Thank you for your help.
 

cellphone chargers, iron tip or any small appliance with little current..

Most likely a waveform of AC square waves is suitable. Here is a simple H-bridge inverter. The clock pulses can come from a 555 timer IC.
I adjusted transformer specs so that I got reasonable performance at 60 Hz.

inverter clk-driv 4 transis 12VDC to 117V sq waves 300 ohm load.png

- - - Updated - - -

The zener diodes reduce inductive spikes in the simulation. However a hardware circuit ought to have a proper snubbing network.
 
Thank you Brad for helping me.. The circuit is very interesting. I will use a 60Hz oscillator based on Ne555 to drive the transistors. I found other circuit built with a CMOS IC but I will post it so you can check it. Thank you
 


It's a very simple circuit, but I wouldn't be that quiet. Transient periods will generate huge losses between both transistors of each driver.

The square wave goes from 0 to 12V (aprox.) in a very short period of time, when the signal will take every voltage value between these given two. Whenever it's higher than 0.7V and lower than 11.3V both transistors are switched on, so if by miracle they don't burn up, they will heat a lot and waste energy which is precious in this application (battery supplied).

I would use the opposite configuration instead, a NPN in the high side and a PNP in the low side, a simple voltage follower as each H-bridge driver. This will need an additional transistor to invert one driver's input so it's high when the another is low.
sddsasd.png
Proposed circuit. Sorry about lack of values for 555 oscillator but I don't have time to calculate them, you can use an online calculator. Keep in mind that Rc and Rd (charge and discharge resistors) shouldn't be higher than 100K. Always prefer keeping frequency beneath 60Hz because most phone chargers are designed to operate between 50-60Hz and not higher frequencies, so if in the calculator you get "57Hz" it's more than OK, even because of the components tolerance value (error) you could get 55 or 60Hz once the circuit is mounted in the PCB.
The transistors you're going to use are D'arlington arrays, such as TIP135 or TIP122 or that family, they are cheap and accesible.

I recommend you to mount it in a PCB since breadboard contacts are very poor for driving high currents.

Hope being helpful.
 

BrunoArg and Brad, I thank you very much for your help. Once I finish mounting this circuit, I will upload it. I will follow each suggestion. Thank you very much
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top