Transformer Data

[pjshah72]

Hi,
How can I decide Transformer for AC to DC conversion? (What are the parameters/factors?)
Let's take an example of 230Vac to 24vdc with 2amp. I am thinking to make simple switch mode power supply design.

My first thing is to know how to decided transformer? (My input range is 85-265Vac but mostly it is 110vac or 220vac).

Any guidance will really appreciated.

Thank you,
pjshah72

 

[MikeMl]

Are you asking about a transformer to be used with a "linear" or "switch-mode off-line" switching power suppply?

Do you require isolation from the 120Vac line side to the load side?

If you are thinking of a switch-mode supply, this is not a project that a novice should tackle. If a linear supply, have at it...

 

[alec_t]

I am thinking to make simple switch mode power supply

If you want simple your best bet is to buy a ready-made SMPS. It would probably be cheaper, too.
What switching frequency were you intending to operate the transformer at? That would be one factor in choosing a suitable ferrite core.

 

[KMoffett]

I think with that question, a 85-265Vac to 24vdc with 2amp SMPS is out of your league, as it won't be "simple" or cheap. And certainly not this cheap:**broken link removed**

Ken

 

[pjshah72]

Thanks everyone for the response.

I would like to just make testing circuit and here in the US, we have 110Vac, 60Hz so lets keep this is an input of my supply.
So Input is 110Vac with 60Hz.
looking for output 24Vdc (+/-12Vdc) with 2amp.

Yes isolation is required between input and output (load side). I know SMPS would not be a cheaper and I am fine with it.
I wanted to first learn how to choose transformer and bridge rectifier for my circuit. Once I satisfied with transformer and bridge rectifier then I will do further steps.

If I am not wrong, we can decide liner or smps method after bridge rectifier stage, is it true?

Thank you for your comments.
pjshah72

 

[ronv]

So you want plus and minus 12 volts with each at 2 amps?

 

[pjshah72]

I think 24V is equal to +/12V??

 

[KMoffett]

I think 24V is equal to +/12V??

No...24VDC is a single output that requires one regulator circuit. +/-12VDC are two outputs that require two regulator circuits.

Ken

 

[pjshah72]

ok so I will go with +24Vdc as a single output.
But again I was asking help on transformer and bridge rectifier.

Thank you,
pjshah72

 

[KMoffett]

Do you have a design that you're intending to implement? Can you post a schematic?

Ken

 

[pjshah72]

sure. I have attached here.

 

[ronv]

Yes that's true but the transformer is different.

Easy is a bit more expensive, while cheap is hard. So take a look at this transformer and the attached circuit. We can add the regulators if it looks ok to you. (easy one)

https://www.mouser.com/ProductDetai...ha2pyFaduhrVUM3P3AW%2bNGCy7bpe0dB0sRLod32h7A=

 

[ronv]

It would also get easier (and cheaper) If it was 1 amp instead of 2.

 

[pjshah72]

Yes that's true but the transformer is different.

Easy is a bit more expensive, while cheap is hard. So take a look at this transformer and the attached circuit. We can add the regulators if it looks ok to you. (easy one)

https://www.mouser.com/ProductDetai...ha2pyFaduhrVUM3P3AW%2bNGCy7bpe0dB0sRLod32h7A=

Hi ronv,
I appreciated your post.
I would like to know how to select transformer and bridge rectifier. So if I use your suggested then how do I know the calculations? (why this transformer only?)
How about bridge rectifier?

 

[KMoffett]

Pretty much any transformer rated for 105-120VAC/60Hz primary, and a secondary rated at 24VAC/2A (or greater A) or 24VAC CT/2A (or greater A) or Dual 12VAC/2A (or greater A) will work. Any bridge rectifier or for diodes rated at higher than 1.4 x 24V and a current higher than ~4A. Now, if you are going to add a 24V or two 12V regulators you will need secondary voltages of greater than 24VAC. Say about 28VAC.
Specific component spec's require specific user requirments.

Ken

 

[pjshah72]

Pretty much any transformer rated for 105-120VAC/60Hz primary, and a secondary rated at 24VAC/2A (or greater A) or 24VAC CT/2A (or greater A) or Dual 12VAC/2A (or greater A) will work. Any bridge rectifier or for diodes rated at higher than 1.4 x 24V and a current higher than ~4A. Now, if you are going to add a 24V or two 12V regulators you will need secondary voltages of greater than 24VAC. Say about 28VAC.
Specific component spec's require specific user requirments.

Ken

Thanks Ken.
Can you explain me how did you calculate ratings for diodes/rectifier? (I got that rectifier should be 4A (higher than my current which is 2A.)

 

[ronv]

Since you want +/_ supplies it is easiest to use a center tap transformer. The transformer current needs to be higher than your load because of the diodes and the capacitor that has to be charged - so 2.8 amps. It will get hot at full load.
The voltage needs to be high enough that with the filter caps the voltage stays high enough so that there is room for the voltage drop across the diodes and the regulator that follows. So in your case the caps will charge to the peak voltage (17.8 volts) then discharge down to about 15.4 volts because of the load. A smaller capacitor will let the voltage fall further a bigger one less.
The diodes need to be able to handle the maximum current on a continuous basis and the peaks needed to charge the cap. I think I used 3 amp diodes. I used schottky diodes because the are more efficient. They need to withstand the maximum voltage which in your case is about 36 volts - so the ones I used may be a little low at 40 volts - a 50 or 75 volt one would be better.

 

[KMoffett]

OK, maybe a little reading will help:
http://paginas.fisica.uson.mx/horacio.munguia/aula_virtual/Cursos/Instrumentacion%20I/Documentos/Reg%20de%20Voltaje%20SGS.pdf
**broken link removed**
**broken link removed**

It will give you some of the math behind for selecting components for a "raw"(unregulated) DC power supply.

Ken

 

[ChrisP58]

If I am not wrong, we can decide liner or smps method after bridge rectifier stage, is it true?
pjshah72

No. the two types of supplies are very different.

In a SMPS, you rectify the input AC first, giving you ~170 Volts DC (for a 120VAC input). Then you use a pwm controller to send pulses of that DC through a transformer. Then to a second rectifier stage to make your DC output.

A linear PS will have a (much larger) transformer at the front of a single rectifier stage. The tx secondary will be about 16 or 18 VAC for a 24V DC output.

 

[pjshah72]

No. the two types of supplies are very different.

In a SMPS, you rectify the input AC first, giving you ~170 Volts DC (for a 120VAC input). Then you use a pwm controller to send pulses of that DC through a transformer. Then to a second rectifier stage to make your DC output.

A linear PS will have a (much larger) transformer at the front of a single rectifier stage. The tx secondary will be about 16 or 18 VAC for a 24V DC output.

Hi Chris,
If possible could you explain operation (SMPS) with the voltage number at each stage? Consider input as 110ac, 60hz and output is 24vdc 2amp.

Thank you.