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confusion in getting Negative output from the SMPS

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chirag2239

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Negative output in SMPS in attached image

Hello Experts,

Here I have attached an image of one of the section I am having. I am having little confusion in this diagram. I am having doubt in this 3 unit. in first 2, I need -85V and -93V respectively. Where in 3rd, I need -12V. I am confused here that does the arrangement of components are correct or not?

I have a doubt that will this arrangement give negative voltage? Here, the capacitor is place in reverse polarity. And is this enough to change the voltage to negative from positive? Or it will need some more changes?

Please check the image.

Thanks.
Chirag
 

Attachments

  • correction.PNG
    correction.PNG
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Re: Negative output in SMPS in attached image

Do you want the +-85V to be a bipolar supply? With a common ground? Then you need to create the effect of a center-tap secondary. This is done by orienting diodes so they point toward the transformer. That is how they steer current to produce a negative supply.

This simulation appears to do the above. Notice the ways that it is different from your schematic.

 

Hello Experts,

Here I have attached an image of one of the section I am having. I am having little confusion in this diagram. I am having doubt in this 3 unit. in first 2, I need -85V and -93V respectively. Where in 3rd, I need -12V. I am confused here that does the arrangement of components are correct or not?

I have a doubt that will this arrangement give negative voltage? Here, the capacitor is place in reverse polarity. And is this enough to change the voltage to negative from positive? Or it will need some more changes?

Please check the image.

Thanks.
Chirag
 

Attachments

  • correction.PNG
    correction.PNG
    78.6 KB · Views: 89

Re: Negative output in SMPS in attached image

Hi. Thanks for the reply.
I do not want bipolar +-85V. But I need it from separate coils as I need 0.2A constant from +85V and -85V coils each. If I will do with center tap, then it may be the possibility to current be divided. And not each coil will get exact 200mA. It could be a possibility. So I want it from the separate coil.

My one question is that if I will reverse the diode then do I need to change the polarity of the capacitor? And please let me know if there would any changes required or not.
 

Re: Negative output in SMPS in attached image

The schematic in post #1 has wrong polarity of coil, diode and output capacitor for the channels intended to give negative voltage.
 

Re: Negative output in SMPS in attached image

FvM said:
The schematic in post #1 has wrong polarity of coil, diode and output capacitor for the channels intended to give negative voltage.
Click to expand...

Can you please guide me in this issue for the solution? Please tell me how I can change this to negative voltage?
 

The schematic is wrong!
D10 and D11 are shown reversed and the capacitors C29 and C32 are also reversed.

Brian.
 

Re: Negative output in SMPS in attached image

Correct the faults I listed in my previous post.
 

Re: Negative output in SMPS in attached image

Hi, the level shifting pdf in the link is a nice, simple, and practical explanation about generating negative voltages (and level shifting upwards).

https://www.trekinc.com/pdf/6001_Voltage_Level_Shifting.pdf

I think what was meant about the coil polarity is that the secondary dot has to be in the opposite place to the primary dot (not both level, but diagonally opposing, if that's a clear description). Please correct me if I'm wrong.
 

Re: Negative output in SMPS in attached image

I don't see the relation of the present problem to level shifting. It's just about how to connect a separate coil, rectifier, capacitors to generate a negative voltage.
 

Re: Negative output in SMPS in attached image

Frankly speaking.. With your such a meaningless answer, I am not getting you. You told that change the polarity and I asked you that how it should be? ANd you told that correct them as per your instruction.

But how? I am looking for your reply is how and which component would be at which place and how. You can do it by paint addition.
 

Ok thanks.
What about C31 and C28? Are they in correct polarity? I have placed them in reversed polarity. + polarity to GND and -Polarity to positive output. Is this correct?

someone told that inductor is also in incorrect polarity. But I do not think so.
 

But how? I am looking for your reply is how and which component would be at which place and how. You can do it by paint addition.
Click to expand...
If a component has two terminals and I tell you to change the polarity, how many possibilities are there to connect it differently?

As already stated in post #5, the polarity of this three components as to be also flipped.

correction1.png

someone told that inductor is also in incorrect polarity. But I do not think so.
Click to expand...
Not the inductor, but the transformer coil, presumed it's not driven by a symmetrical push-pull switch.
 

Re: Negative output in SMPS in attached image

Hi,

The pdf was for chirag2239 to have a visual representation for diode and capacitor orientations for positive and nevative applications, as they didn't seem to have understood the correction provided, no intention of confusing them with a document about level shifting, just to see the principle in pictures.
 

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