Help me connect DP-241-7-36 transformer to my 230V mains

• Sep 2, 2011

• #1

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Hello.
I wan to build this power supply
I have DP-241-7-36 transformer **broken link removed**
Is that OK for this circuit?
Also, I'm not sure how to connect it to my 230V mains, there are four terminals F2, S2, F1, S1 how do I connect it?
I know those are silly questions, but I'm having hard time finding some good explanation of transformers, when I google for transformers most results are some car-robots from out of space

tnx.

 

• Sep 2, 2011

• #2

Raza

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Re: transformer question

Hi,
Make a short (jumper) between S2-F1 and apply your mains supply to S1-F2. O n the secondary side or the other side connect the center tag to Ground the other two tags (side ones) to AC and AC terminals on the bridge rectifier.
Your transformer is 18-0-18 (or 36 volts center tapped) volts out and 220 volts input capable of supplying 1.5 ampere current.
Hope this helps. For any further query contact back.

 

• Sep 2, 2011

• #3

keith1200rs

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Re: transformer question

S = start, F = finish. For 220V operation connect the S of on winding to the F of the other e.g. F2 to S1 and then put 220V across F1/S2. That puts the windings in series in the correct phase i.e. As if it was one continuous primary winding.

For 110V you would want the windings in parallel so F1 to F2 and S1 to S2.

Keith

 

• Sep 2, 2011

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Re: transformer question

Thank you guys, transformer input makes sense to me now.

OK, if it is 18-0-18, does it mean I can build dual output(LM317, LM337) with max around -15/+15 output? Or single output(only LM317) around +35?

 

• Sep 2, 2011

• #5

FvM

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Re: transformer question

OK, if it is 18-0-18, does it mean I can build dual output(LM317, LM337) with max around -15/+15 output? Or single output(only LM317) around +35?

Click to expand...

Basically yes, but for operational overload and short circuit protection, you'll need to refer to LM317H for the 35V regulator. There's still a risk, that the input voltage exceeds LM317H voltage maximum of 60V. The design should be still safe with expectable mains overvoltage of e.g. 10 percent.

 

• Sep 2, 2011

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Re: transformer question

Actually I'm not sure what kind of power supply I should build for myself What do you guys advise?

On my stock i have:
this LM317
this LM337
this 5V regulator
And a mentioned transformer.

I'm mainly playing around with microcontrollers, so I was thinking about having 1 fixed 5V output(for most uC I'm using) and one regulated up to ?? for other stuff, is this a good Idea?

TIA

 

• Sep 2, 2011

• #7

keith1200rs

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Re: transformer question

Why not make it provide +5V fixed and +/-variable up to say 12V?

Keith.

 

• Sep 2, 2011

• #8

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Re: transformer question

Do you mean something like this?:


If so, can i connect another 5V fixed reg. in the same manner to power my volt meter that will monitor regulated outputs?

 

• Sep 2, 2011

• #9

keith1200rs

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Re: transformer question

Yes that is the idea.

Keith

 

• Sep 2, 2011

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Re: transformer question

Thanks Keith.
In next few days I'll try to draw a full schematic and will post it here for check

Thank you all for your help!

 

• Sep 2, 2011

• #11

Raza

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Re: transformer question

Hi,
Yes you can build a DUAL supply unit as you showed in attached image. Even you can build 5V regulator but on LM78xx series there are some thing to take care. For example 7805 has its maximum input voltage as 36 volts. In your case if you use 18 volts (center tap to one side of secondary side) it will be 18x1.14=25.452 volts. It is fine but same time you have to consider the load current of the regulator. If you draw 1 ampere at 5.0 volts when the input voltage to the regulator is 25 volts the loading wattage of the regulator will be 25-5x1=20 watts (watts of heat), means you need a huge heat sink or a forced air cooling. You can not use single supply input to 78xx series as 36x1.414=50.904 volts, much higher from the allowed input volts.
Any further assistance, if needed, is welcomed.

 

• Sep 2, 2011

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Re: transformer question

Thanks Raza! Appreciate your help.

One more silly question: what is the 1.14 multiplier?

TIA

 

• Sep 2, 2011

• #13

keith1200rs

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Re: transformer question

Should be 1.414 - the square root of 2. The height of the peak of an RMS sine wave.

Keith.

 

• Sep 3, 2011

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Re: transformer question

Now for bridge questions
I have bunch of 1N5819TP schottkys, but I'm not sure if I can use them.
According to datasheet max RMS voltage is 28V. If my transformer is 2x18 I think it should be OK - only 18V RMS will go through each diode, right?
Also, I'm not sure about current: avg.=1A, peak=25A is this enough for me?

If they're not good enough i have one of those heavy-duty bridges. It's 800V, 2.7A without heat sink, can I use it or are there any drawbacks in using 800V bridge to rectify 30V?

To sumarize, which should i use: 1N5819TP, D10XB80 or should i buy something else.

TIA

 

• Sep 3, 2011

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Re: transformer question

If you are going to play with micro-controllers you may also consider to add a 3.3V regulator. I have a similar general purpose supply with following parameters :

+/- 15 V, 5A equal blocks
+/- 12 V, over 10A for positive, 1A for negative
+/-5 V, over 20A for positive, 1A for negative
+ 3.3V, over 20A

The amps depend on your needs. I used switch mode supplies rated for several amps, my 5V is more than 20A. Yes, a lot of power, but I want to be able to supply any circuit and especially powerful LEDs. Switch mode supplies are very powerful for their size and weight, but also very noisy. So if you play with analogue circuits, consider using well filtered linear regulator, like LM7812 with additional chokes.