Hello, I was trying to build a variable dc supply (100V to 440V DC). I took this inverter circuit and changed the Transformer T2 with a 12-0-12 440V 2A transformer and T1 with a 440V - 12V step down chopper. The output was 315V but it did not vary. What modifications should I use?
I also tried the voltage doubler circuit using capacitors on the 220V inverter output - but it didn't work. I am new and inexperienced with high voltages. Please help. Thanks.

 

What actual electronic experience do you have to start with?
How many things have you built before? If this is a first,
My advice is DONT!
You are dealing with lethal voltage there, and at a high power too.

More info is required anyway.
Is this a mains driven supply?
And is the output a 100V min to 400V max? (Your description could be 100V in and 400V out.)
So, input supply=?

Does it need to be regulated?
If not, a mains Variac driving a transformer/rectifier will be easy.

 

What actual electronic experience do you have to start with?
How many things have you built before? If this is a first,
My advice is DONT!
You are dealing with lethal voltage there, and at a high power too.

More info is required anyway.
Is this a mains driven supply?
And is the output a 100V min to 400V max? (Your description could be 100V in and 400V out.)
So, input supply=?

Does it need to be regulated?
If not, a mains Variac driving a transformer/rectifier will be easy.

Hello, I am trying to build an Inverter running from a 12V 7000mAH battery. Output should be 100V-400V dc (regulated) with maximum current of 2A. I have some experience with electronics. But not comfortable in high voltages. BTW the circuit from instructables - I have made it and it works perfectly. Output voltage is around 50V t0 220V. Please help modify it for a 400 Voltage supply.

 

A 440V x 2A supply is 880Watts, not counting losses. So more like 1KW.
That really is a bit much to run from a 12V battery. You are talking 60 to 80 Amps from the battery.
Assuming your battery can supply that current, and it probably will not, you will only get a couple on minutes run time.
I really do think you are trying something that is not really practical.
What is you load and application?

 

A 440V x 2A supply is 880Watts, not counting losses. So more like 1KW.
That really is a bit much to run from a 12V battery. You are talking 60 to 80 Amps from the battery.
Assuming your battery can supply that current, and it probably will not, you will only get a couple on minutes run time.
I really do think you are trying something that is not really practical.
What is you load and application?

Well, sorry for the confusion, I don't know much about coils and transformers. The supply I require should be able to output 100V to 400V DC with Maximum current of 2A (load dependent current flow). But the transformer spec is 200W. So at 400V the maximum current output will be 500mA. Is it right?

Edit: Can I use voltage-multipler like this in a 220V Inverter??

 

Yes, if the transformer you are going to use is 200Watts, the max current will be 500ma.
So you need a bigger transformer for a start.
Using a voltage multiplier will increase the voltage but not the power. In fact there will be extra losses added to the circuit.
What is you load and application that needs 100 to 400V?
That may help with the design. But starting from 12V is not a good idea unless you really have no choice.
I still do not know what you intend to use this for and that will impact on the design.
It will be much better to run your inverter at a higher frequency as you are after DC out as you rare not tied to 50 or 60 hz.
How well regulated does the output need to be?

 

Yes, max current will be 500mA at 400V output. But it can also be 2A at 100V output, right?
200W looks sufficient for now.
If voltage multipliers can work with lower currents that may also be fine by me. (needs testing)
Another 12V battery can be added to make the voltage as 24V - 25V. But more battery means heavier setup.
As for the usage - I need to supply high voltage in some tests in our lab. Our requirement is actually more - maybe around 1kV. I am trying to achieve 400V peak voltage now in this inverter

 

To get a bigger voltage out, you need to change the transformer secondary to give a bigger output ideally double the secondary windings, then i would change the feedback loop to look at the output of the 400V with an opto-coupler and Tl431 zener.

 

To get a bigger voltage ou, you need to change the transformer secondary to give a bigger output ideally double the secondary windings, then i would change the feedback loop to look at the output of the 400V with an opto-coupler and Tl431 zener.

Thank you, that's exactly what I tried, but looks like the feedback isn't working. I didn't implement any optocoupler though. Used a chopper instead. Can you share the optocoupler feedback circuit, I would like to try it out as well.

 

Thank you, that's exactly what I tried, but looks like the feedback isn't working. I didn't implement any optocoupler though. Used a chopper instead. Can you share the optocoupler feedback circuit, I would like to try it out as well.

Your circuit is really poor, i would use a different chip, like the TL494, but you need to remove the transformer that feeds the feedback and everything on pins 1, leave the two 4k7 resistors on pins 16,2 these set the reference point at 2.5V, so your feedback voltage on pin1 needs to be adjusted to give 2.5V when your output is at 400V, you can use a simple resistor divider with a 22K preset resistor, and a 1.6Meg resistor on pin 2 from the output of the transformer using a bridge rectifier to test it, then modify it with the opto-coupler circuit like this....

 

Thanks sir, for your nice circuit. I'll try to change mine accordingly. What I understood is that I have to supply 2.5V to the feedback pin 1 and vary it down to reduce the output.
Can I supply 2.5V from another 5V supply using a 10k/10k resistor divider and a pot divider after that removing the feedback transformer?

 

The whole point of the feedback to pin 1 is that it is a sample of the required output, not from another power supply. As the output volts go up, the "2.5V" to the feedback pin goes up too, so the controller backs off the switching a bit to bring the volts on the feedback pin back to 2.5V. In a similar way, when the load current on the output increases, the output voltage goes down, and so does the volts on the feedback pin. So now the controller increases the switching to bring the 2.5V back.
So, no, do not use an extra 5V supply for the feedback. It must be a sample from the output to work, moving up and down as thew output does.
To change the output volts, the % sample of the output volts needs to be changed.
So for instance, if your feedback circuitry divided the output by 10, the power supply would give you 25V out.
And if it was 1/100, the output would be 250V. There are various ways of extracting this sample for the feedback.
I just go an email about this design suite. It may be worth a try...
http://www.st.com/content/st_com/en/support/resources/edesign.html?ecmp=tt5740_gl_enews_sep2017

Oops! I see now you are not referring to the circuit above.
Still, the comments about the feedback operation still apply so someone may find it helpful.
I need to read a bit better in future.

 

Thanks sir, for your nice circuit. I'll try to change mine accordingly. What I understood is that I have to supply 2.5V to the feedback pin and vary it down to reduce the output.
Can I supply 2.5V from another 5V supply using a 10k/10k resistor divider and a pot divider after that removing the feedback transformer?

No the 2.5 V is a stable source provided by the chip, using two resistors of equal value, you can have any reference voltage on pin 2, and when the output voltage is regulated down to this value on pin 1, the output is stable, ..

 

Thanks, got it. Found another nice article on the IC that I am using.
https://www.homemade-circuits.com/2013/01/understanding-sg3525-ic-pin-outs.html

@Dodgydave I am using a 12-0-12 input, 440-0 output transformer (similar to T1 in your circuit) but with another secondary output of 24-0. I am giving feedback from this.
As I was studying your circuit, what will happen if there is no Rx? like in no load condition? How can I vary the output then?

 

If you have no load the transformer output may not be stable enough, i would use a dummy load to draw 500mA on the 400V output, and use the 24V output to set the feedback voltage, as long as the transformer is a tight coupling both outputs should be regulated.