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Encapsulated Transformers Queries

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Urahara

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Hi

Am looking at this range of transformers : https://docs-asia.electrocomponents.com/webdocs/0029/0900766b80029e0c.pdf

1) Can this be used as AC step down transformers? Plan to build a small regulated DC voltage power supply using it.

2) The transformer I am interested in has the following characteristics :
- input voltage : 230V/50-60Hz
- dual output : 2x8V / 2x0.062A

Am I correct then that the secondaries of this transformer can be configured in 3 possible configurations, using jumpers as needed :

a) In series : we get 16V with 0.062A
b) In parallel: we get 8V with 0.124A (2x0.062A)
c) No jumpers : we get 2 separate power source, each 8V, 0.062A

Correct? Thks!
 
Yes these transformers convert 230V to 16VAC or 8VAC.

You are correct about the jumper configurations.

The datasheet says the no load voltage multiplication factor is 1.8, so expect the voltage to be 14.4V for each 8V secondary when no load is connected.

The efficiency is a miserable 30% which is typical for a tiny 0.5VA transformer.
 
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Yes, you are correct.

I think that you are using the 1W transformer, and it is a little better than the 0.5 W transformer that Hero999 was looking at.

However, the voltage still rises a lot on no load, to 1.32 times the 8 V = 10.56 volts.

I suspect it might be higher than that. The regulation is usually better for larger transformers, but in that range the 1 W transformer seems to have better regulation than the 3.2 W one.

Other things to be aware of:-
1) Get the windings the right way round. The dots on the diagram show the ends of the windings that become positive at the same time.
2) The peak voltage will be 1.41 time larger than the RMS voltage, so it could be as large as 14.9 V on an unloaded 8 V winding. It is the peak voltage that determines how big the DC voltage is when the AC is rectified.
3) The terrible regulation means that the output voltage dips a lot when the output is loaded. If you are rectifying, the waveform looks just about square at full load.
 
Yes, I am looking at the 1W transformer.

For voltage regulation using LM78xx, datasheet usually specifies a min 2V difference btw input and desired voltage. Is it safe to use the no load secondary voltage by the transformer as a design basis? Thks!
 
You need to use both the on load and off load voltage.

You use the off load voltage when considering the maximum voltage ratings of the components and the on load voltage when considering the ripple and regulator dropout voltage.

What output voltage do you want and how much current to you intend to draw?
 
That transformer is no good for what you want, you need a 12V 100mA transformer.
 
yup, silly me! but understand the principles behind what you had earlier told me. will get the 1.5VA, 2x6V secondary transformer to be connected in series. that should give me 12V at 125mA. think that should work. thks!
 
That will be more than good enough for what you want.

You'll need an LM78L09, a bridge rectifier and a 150µF to 220µF capacitor rated at 35V.
 
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