Strange error in transformer voltage supply

[rahulbs]

Hi Everyone,

I am getting a strange error with the transformer power supply. I am adding it to a rectifier circuit.

When I check AC voltage of transformer without connecting it to the bridge rectifier, the reading in the multimeter showed 14V

But when I check reading after connecting the transformer to the rectifier. I added the location where I am checking the reading in the above circuit diagram.

it is giving me a reading of only 4V. I don't know what is happening.

Is my transformer is bad? I am using a 12v step down transformer.

please help me.

thanks

 

[betwixt]

Something isn't right.
Just to be sure - can you confirm you are measuring AC across the transformer in both cases, with and without the rectifier connected.
Are you getting the 9V at the output? If you are, you are measuring wrongly somewhere, it cannot produce 9V when the input is only 4V RMS.

Brian.

 

[FvM]

I am using a 12v step down transformer.

Please show circuit details. Is 12 V winding isolated or is there a connection to other circuit parts, e.g. DC ground?

 

[KlausST]

Hi,

I would like to see a photo with your setup, wiring, meter, reading ..

Klaus

 

[D.A.(Tony)Stewart]

It looks like a diodes are all rotated and shorting the transformer making the diodes warm.

Also backwards are the symbols on the schematic for C1, C3.

Simulating your failure may look like below

 

[KlausST]

Hi,

diodes in schematic of post#1 are correct.

Klaus

 

[rahulbs]

Hi Everyone,

thanks for replying. I checked a few things in the circuit.

so there are two circuits on two different pcbs.

One circuit provides 9V using 7809 and another circuit which is a voltage divider on a separate zero pcb is connection to the first pcb for the power supply.

What is observed is when I connect the voltage divider circuit to power supply and check the AC voltage on the first PCB(power supply), the voltage varies according to the resistance of POT on voltage divider circuit. When I turn knob of the POT, the AC voltage varies from 4v to 14v

But when I disconnect the voltage divider circuit the AC voltage on power supply remains at around 14v.

I think the POT of the voltage divider is connected to ground pin of the ic 7809 which is causing this voltage variance.

But, I don't know exactly why it is happening.

Please advice.

thanks

 

[betwixt]

I'm even more puzzled now.
If there are two PCBs, what is on each board, show us the construction or at least add a dividing line on the schematic.
To my mind, the voltage divider looks wrong, as shown and with no load connected, the output voltage will adjust between 0V and 8.182V. Any load current will drop the output voltage. If a 100K potentiometer is wired in the ground pin of the 7809, and that isn't what is shown, the output will vary between 9V and something higher but most of the adjustment will be at the end of the potentiometer rotation. Even then the output will drop under load because of R1.

What exactly are you trying to achieve?

Brian.

 

[D.A.(Tony)Stewart]

Hi,

diodes in schematic of post#1 are correct.

Klaus

FWIW, My comment on diodes was the physical swap of AC and DC ports which matched my simulation to show a his fault, not a fault in the schematic

Tony

@rahulbs For clarity show all AC DC measurements