Centre tapped Transformer

[Srinivasa Rao Beera]

We are using centre tapped transformer - 9V-0-9V /500mA for power supply. Circuit I made as below. For 200mA load , I am getting Vload is "4.5V" only. Let me know where is the issue , it has to work for load 9A/500mA right.

Or transformer is faulty, tried with two transformer , result is same.

 

[Harald Kapp]

I am getting Vload is "4.5V" only

I assume you used a multimeter in DC range to measure? Your supposed DC is superimposed by a large AC ripple. You need to apply a smoothing capacitor.

 

[Srinivasa Rao Beera]

I have added electrolytic capactor , sorry it has missed in circuit. still it is "4.5V" .

 

[(*steve*)]

Have you verified that the AC output of the transformer is 9-0-9 VAC?

 

[Srinivasa Rao Beera]

Yes , it is coming around 10Vac measured with multimeter in AC mode.

 

[(*steve*)]

So therefore about 20V across the ends of the windings?

What does it measure with the load connected

 

[kellys_eye]

The readings you give are consistent with a 4.5-0-4.5V (i.e 9V centre-tapped) transformer. This is NOT THE SAME as a 9-0-9V transformer.

Have you checked that the primary voltage is correct i.e. you're not running a 240V primary on a 120V supply?

 

[Srinivasa Rao Beera]

Here is the link for the transformer

http://www.shelfkey.com/orderProduct.aspx?prodid=4057&partno=TRANSFORMER-9-0-9VAC

 

[(*steve*)]

And your mains voltage is 230V?

 

[WHONOES]

Is the phasing of the transformer secondary's correct?
Using the notation: S = Start of winding and F = Finish of winding, the secondary must be connected in the order:
S, F, S, F. Otherwise the secondary's will effectively be in parallel which means that it is giving half wave rectification rather than full wave. If this is so, your output voltage will be 9V - forward drop of diodes, assumed to be 1V x 0.637 which calculates to 5.096V.

 

[73's de Edd]

That transformer construction automatically has the wiring done by the manufacturer, so that its going to have proper series phasing relationships.
Any chance that you made a boo-boo on one diodes polarity of installation, or that you have one open diode ?
How much capacitance is the main filter and is your load resistor in the order of 20 Ω' s ?

 

[WHONOES]

Are your measurements with or without a load?

 

[davenn]

Yes , it is coming around 10Vac measured with multimeter in AC mode.

when measured where ??


you should be getting ~ 18V across the transformer
or ~ 9V between the centre tap and either winding end

 

[WHONOES]

What diodes are you using and what value is you smoothing capacitor?

 

[(*steve*)]

As best I can tell, he is posting from a place that has 220V (ish) mains.

Or more accurately "is no longer posting from..."