How can I eliminate AC leakage in my power supply for optimal performance?

[chaoseverlasting]

Im using the 7809 IC to get 9v regulated dc supply. However, I'm also getting about 14v ac in the output as well. I've tried putting a notch filter tuned to 60hz to remove the ac voltage, but its still there.

I'm using this power supply to power tl072 op amps and I'm worried that the ac voltage present will change the bias point or saturate the op amp.

Another thing is that the circuit I'm trying to implement basically modifies an ac signal. The leakage voltage present is significantly greater than the input signal (which is about 35-80mv) which will render the whole circuit useless.

How do I get rid of the ac voltage?

EDIT: I also badly need help in trouble shooting the circuit.

 

[vk6kro]

Voltage regulators contain high gain amplifiers and they can oscillate if there is not enough bypassing on the input and output terminals.

This is what is happening in your circuit.

The input and output leads should be bypassed with suitable capacitors.

A data sheet for the 7809 suggests 0.33 µF from the input to ground and at least 0.1 µF from the output to ground.
And the ground lead should be as short as possible.

 

[chaoseverlasting]

I've got 1000uf from input to ground and 470uf from output to ground using electrolytic capacitors. Should I lower these cap values?

Another thing is that the voltage from input to ground across the 7809 is almost 60v. I suppose this is from the 1000uf cap. Could it damage the IC?

 

[mdjensen22]

I've got 1000uf from input to ground and 470uf from output to ground using electrolytic capacitors. Should I lower these cap values?

Another thing is that the voltage from input to ground across the 7809 is almost 60v. I suppose this is from the 1000uf cap. Could it damage the IC?

7809 maximum input voltage = 35V (http://www.fairchildsemi.com/ds/LM/LM7805.pdf" )
Yes - that could damage the part.

 

[vk6kro]

The 470 µF from the output to ground should be removed and replaced with about a 0.22 µF ceramic. Big capacitors on the output stop the regulator responding quickly to output changes.

Put another 0.22 µF on the input, but you can leave the 1000 µF there if you like.
Electros are not very good at high frequencies, so the smaller 0.22 µF is a better bypass.

I like to use the miniature "monolithic" ceramic capacitors for this. These are often blue and about 3 mm square. They work well.

 

[cjameshuff]

14 VAC on the output and 60 V (DC, I hope) on the input of a 7809 sounds like you have worse issues than capacitor selection. What is your circuit? Are you sure it's wired correctly?

 

[chaoseverlasting]

14 VAC on the output and 60 V (DC, I hope) on the input of a 7809 sounds like you have worse issues than capacitor selection. What is your circuit? Are you sure it's wired correctly?

I'm sure that I've got the diagram right. The funny part is that when I change the transformer, then the dc voltage drops down to about 13v at the input and 9v at the output. The ac leakage is still around 12-14 VAC. I tried putting a notch filter after the power supply, but I get no output at all after that dc or ac. I stopped trying to figure it out last night after I shorted out two transformers. It didnt go down well with my parents when the MCB tripped twice in as many minutes.

 

[vk6kro]

It sounds like you either have something faulty or you have the circuit connected wrongly.

One possibility would be the bridge rectifier. Can you remove this from the circuit and test it?
Use the "diode" position on a digital multimeter.

With the power plug removed from the wall, check for DC conductivity between the primary and secondary of the transformer. There shouldn't be any.

You should have a local fuse (maybe 2 amps) in series with the primary of the transformer so you don't blow the house circuit breaker. Parents remember that for a long time and it destroys your credibility very quickly.
When you have that fuse installed, plug the transformer back into the mains with no bridge rectifier.

If the fuse blows, the transformer is probably faulty. If the fuse doesn't blow, measure the voltage coming from the transformer using the AC range on a multimeter. It needs to be about 10 to 12 volts.

When you have the bridge rectifier working, you need a capacitor across its output to filter the DC pulses.
If the existing capacitor had AC on it, it may be faulty, so you might need a new one. It has to be rated at more than the peak value of the DC pulses and it shouldn't be more than 5000 µF (or the charging current will be very high).

After all that is working, you can think about attaching a regulator to it.