SMD Regulator gets too hot

[DjKrish]

I have a cd player that has a problem of giving a plain siren sound after warm up say like 1 or 2 hours. It plays fine before that. No matter cd player is playing or idle, the siren sound continues. I check the audio signal output board and found out that theres a voltage regulator thats getting pretty hot. Not burning my finger but it is hot within a second or 2.

I checked for voltage as its a SMD 12V>5V regulator. Used digital MM and found incoming is 11.7V and output is 5.7V. Is that normal? Or the regulator fried? Should DC voltage be 100% accurate or can be plus minus a few percents? According to the datasheet, plus or minus it shouldn't be above 1% that's +/- 5.05V but here its showing 5.7V which is 14% higher than allowed

I have attached the datasheet for the regulator and also a schematic for the board.

[R_J]

Re: SMD Regulator gets too hot

You could have a bad cap (1uf/50v) on the output. If the output is not filtered properly they can start to oscillate.

[DjKrish]

Re: SMD Regulator gets too hot

You could have a bad cap (1uf/50v) on the output. If the output is not filtered properly they can start to oscillate.

But shouldn't the output leg show exactly 5v? Cause its a 12v>5V regulator.

[budm]

Re: SMD Regulator gets too hot

Not if it is oscillating.
Look at the output with the scope.

[DjKrish]

Re: SMD Regulator gets too hot

Not if it is oscillating.
Look at the output with the scope.

Thanks for the reply budm, sadly i dont have a scope. Only digital and analogue MM

[R_J]

Re: SMD Regulator gets too hot

Just find a 1 uf (or what ever value it is) and add it across the output and see if the voltage drops and it runs cooler.

[DjKrish]

Re: SMD Regulator gets too hot

As i suspected, it was indeed the regulator. Now the voltage is stable on the output after replacing a new one.

[budm]

Re: SMD Regulator gets too hot

Glad to hear that it is just the bad regulator not the oscillation due to bad filter caps or too much current drawn by the load.

[DjKrish]

Re: SMD Regulator gets too hot

Thats right, before was high voltage around 5.8V, after replacing stabilized to 4.8V which is normal.

[budm]

Re: SMD Regulator gets too hot

Thats right, before was high voltage around 5.8V, after replacing stabilized to 4.8V which is normal.

The spec of the IC indicates High precision output of +/- 1%,
So getting 4.8V instead of 5V is more than 1% tolerance, that is about 4% off, so may be there is still problem in the circuit.
From spec sheet:
"High Precision Output Vo ±1.0%"

[Sparkey55]

Re: SMD Regulator gets too hot

The spec of the IC indicates High precision output of +/- 1%,
So getting 4.8V instead of 5V is more than 1% tolerance, that is about 4% off, so may be there is still problem in the circuit.
From spec sheet:
"High Precision Output Vo ±1.0%"

When ever i see an instance of a voltage regulator whether linear or digital become hot or unstable I tend to first blame the input filter caps because of age or other problems with the caps. These are the most suspect components in my opinion.

[budm]

Re: SMD Regulator gets too hot

When ever i see an instance of a voltage regulator whether linear or digital become hot or unstable I tend to first blame the input filter caps because of age or other problems with the caps. These are the most suspect components in my opinion.

We already suggested OP to check the output and input caps, and look at the output with the scope.

[DjKrish]

Re: SMD Regulator gets too hot

The spec of the IC indicates High precision output of +/- 1%,
So getting 4.8V instead of 5V is more than 1% tolerance, that is about 4% off, so may be there is still problem in the circuit.
From spec sheet:
"High Precision Output Vo ±1.0%"

But the weird part is, i had 3 other same players and i tested the voltage and it all stands still at 4.8V. Weird? Or bad design?

[Sparkey55]

Re: SMD Regulator gets too hot

But the weird part is, i had 3 other same players and i tested the voltage and it all stands still at 4.8V. Weird? Or bad design?

Have you checked the calibration of the volt meter, is it in spec?

[DjKrish]

Re: SMD Regulator gets too hot

Have you checked the calibration of the volt meter, is it in spec?

I used 3 meters and it gives same reading

[Sparkey55]

Re: SMD Regulator gets too hot

I used 3 meters and it gives same reading

So? You could still have three meters out of calibration. Are you using the same set of meters leads each time you take readings? Find a three terminal voltage regulator preferably a 7805 and connect the +12v in from the amps power supply and measure the output (+5VDC) from the 7805 reg.

[DjKrish]

Re: SMD Regulator gets too hot

So? You could still have three meters out of calibration. Are you using the same set of meters leads each time you take readings? Find a three terminal voltage regulator preferably a 7805 and connect the +12v in from the amps power supply and measure the output (+5VDC) from the 7805 reg.

Yes all my meters are recently calibrated.

[Agent24]

Re: SMD Regulator gets too hot

Yes all my meters are recently calibrated.

Makes me think that maybe they've all recently been calibrated incorrectly, then.

Or, you could still have some kind of noise on the output of the regulator, which is causing the error.