| Author |
Message |
yviswanathbe
Joined: 14 Jun 2007
Posts: 62
|
 24 Jul 2008 4:51 how to reduce noise ? |
|
|
|
Hi,
I have done a simple circuit for sensing current from the power supply using ADC0804 and AT89S8252 microcontroller and OP07 operational Amplifier.
I have given dual supply (+5,-5 V) to OP07.
Everything is fine but ADC is not giving correct values.
That is if current is 10A,ADC will show FF as per circuit and calculations.
But my ADC one time it is giving FF and next time it is giving some other value,means the value is not constant.
I guess some ripple or noise i need to reduce.
If so,Please help me how to reduce ripple in the circuit?
Thanks in Advance.
viswanath
|
|
| Back to top |
|
 |
RF-OM
Joined: 03 Aug 2007
Posts: 607
Helped: 113
Location: The Earth
|
| 24 Jul 2008 7:18 Re: how to reduce noise ? |
|
|
|
| If your current sensor is connected through cable or wires try to make a few turns of this cable around ferrite toroid with permeability that corresponds to your frequency. It creates a common mode choke and can help.
|
|
| Back to top |
|
|
yviswanathbe
Joined: 14 Jun 2007
Posts: 62
|
| 24 Jul 2008 8:47 Re: how to reduce noise ? |
|
|
|
Hi,
Thanks for replying.
I am not using current sensor here.
I have just connected the power supply in series to load using 75mV,10A shunt.
And i am amplifying the shunt input using OP-AMP.This Amplified voltage i am giving to ADC and measuring the digital value through Serial Port using Microcontroller.
This OP-AMP requires dual supply,so i have made a +5,-5 V powersupply on my board,i am guessing in this section ripple may cause...
I want to reduce this ripple or noise...
Thanks,
viswanath.
|
|
| Back to top |
|
|
RF-OM
Joined: 03 Aug 2007
Posts: 607
Helped: 113
Location: The Earth
|
| 24 Jul 2008 19:59 Re: how to reduce noise ? |
|
|
|
| There may be a lot of reason and may be not just one. You need to analyze you circuit and layout. It is hard to say something more detailed without such analysis.
|
|
| Back to top |
|
|
TekUT
Joined: 17 Jun 2008
Posts: 322
Helped: 22
|
| 25 Jul 2008 16:54 Re: how to reduce noise ? |
|
|
|
Post the circuit related the current sensing section.
Bye
Powermos
|
|
| Back to top |
|
|
madusnk
Joined: 30 Jun 2008
Posts: 16
|
| 28 Jul 2008 17:17 how to reduce noise ? |
|
|
|
sory 4 replying here I also have the same problem.
That is power supply noise.I f some one can post a circuit to reduse power supply noise(com mode and diff mode) it is a great help to me as well..
|
|
| Back to top |
|
|
TekUT
Joined: 17 Jun 2008
Posts: 322
Helped: 22
|
| 31 Jul 2008 19:58 Re: how to reduce noise ? |
|
|
|
Power supply noise can be a result of inject noise from the mains and noise build up from the power supply itself. If the power supply was a switch mode type may be you've to add filtering on the output to stop the noise at the switching frequency, if the noise came from the mains line into the supply you can put some filtering from the main before the supply input, a common mode coil should be enough.
Bye Powermos
|
|
| Back to top |
|
|
jhbbunch
Joined: 21 Feb 2006
Posts: 220
Helped: 16
|
| 01 Aug 2008 5:49 how to reduce noise ? |
|
|
|
Have you put the power supply on a scope and looked for an ac ripple, 60Hz in NA and 50Hz in europe? Have you hooked the ADC circuitry up to a DC battery supply to see if the ripple is still there? Because if it isn't there on a battery supply, then it is obvious that the DC is riding on an echo of the AC power supply input.
I had an instructor tell me years ago that a quiet DC power supply was a real art to make on a quantity basis. When he ran an electronics business he said they quit trying to make their own power supplies and just went out and bought ones they knew worked. Why? Because most of the problems they had with the equipment they made and sold came back to a noisy power supply.
I can also remember him yelling across the room more than once in our labs that the next time he had to help someone with a lab where the problem turned out to be a signal riding on a 60Hz power supply 'echo' he would fail the idiot.
I'm still not too sure why I passed.
|
|
| Back to top |
|
|
