Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

FCC conducted emissions question

Status
Not open for further replies.
D

difflvl

Advanced Member level 4
Full Member level 1
Joined
Jun 14, 2006
Messages
110
Helped
12
Reputation
24
Reaction score
2
Trophy points
1,298
Activity points
1,985
Hi,

I had a device that was failing with the conducted emissions test of the FCC part 15b.

It was failing in the 800khz-1.2MHz range. I do not have a clock source of that frequency on my board, nor was I able to trace where it is coming from.

My question is this what can I add to my power supply circuit to reduce noise in the 1MHz region.

I have attached my power supply schematic below. It is a 3.3 V regulator with VIN being a 6volt wall wart.

Thanks
 

pls refer the attach pdf....

do not forget to press help me button
 

    D

    difflvl

    Points: 2
    Helpful Answer Positive Rating
Just place C6 100nF (X2 type) before D1. Or add new one (better)

difflvl said:
Hi,

I had a device that was failing with the conducted emissions test of the FCC part 15b.

It was failing in the 800khz-1.2MHz range. I do not have a clock source of that frequency on my board, nor was I able to trace where it is coming from.

My question is this what can I add to my power supply circuit to reduce noise in the 1MHz region.

I have attached my power supply schematic below. It is a 3.3 V regulator with VIN being a 6volt wall wart.

Thanks
Click to expand...
 

BasePointer said:
Just place C6 100nF (X2 type) before D1. Or add new one (better)

difflvl said:
Hi,

I had a device that was failing with the conducted emissions test of the FCC part 15b.

It was failing in the 800khz-1.2MHz range. I do not have a clock source of that frequency on my board, nor was I able to trace where it is coming from.

My question is this what can I add to my power supply circuit to reduce noise in the 1MHz region.

I have attached my power supply schematic below. It is a 3.3 V regulator with VIN being a 6volt wall wart.

Thanks
Click to expand...
Click to expand...

6 100nf caps will help with the 1mhz frequency range? I thought those values are good for higher frequencies. At the lab I tried adding more 100nfs and it didn't really do anything.
 

- What is your input voltage?
- What is the output current that you require?
- Does the power supplier have a load when testing?

You may use higher capacitor instead of 100nF (X2). For example electrolytic one.
Can you send graphical test output here?
 

The input voltage is 6VDC from a wall wart. Output current required is ~200-450mA. Yes it has load during testing.

I don't have the test output available but I was 18dBs over the limit at ~1MHz.
 

What clock sources are there in you design?
 

Clock sources are 14.7456mhz from crystal, 28.224mhz from another crystal and 4.032mhz from an IC.
 

difflvl said:
Clock sources are 14.7456mhz from crystal, 28.224mhz from another crystal and 4.032mhz from an IC.
Click to expand...

Did you try 100uF/25V or 1000uF/25V electrolytic instead of C6 100nF?
 

    D

    difflvl

    Points: 2
    Helpful Answer Positive Rating
Hi, reading the hole topic it seems like the wall wart power supply is causing problems. I might be wrong here. Are you are testing with the wall wart power supply to get a compliance certificate for the complete system. Perhaps you can try an other power supply if the one you are using is a switching power supply. It might be market CE and all the rest but most of them are not. I'm currently evaluating power supplies from china for a product. Some of them even fail on the input voltage requirement of 85 volt...

Regards
 

If possible ( cost available ), add an emc coil at test port. It has significant improvement.

Rogerynt
 

inventor(y) said:
Hi, reading the hole topic it seems like the wall wart power supply is causing problems. I might be wrong here. Are you are testing with the wall wart power supply to get a compliance certificate for the complete system. Perhaps you can try an other power supply if the one you are using is a switching power supply. It might be market CE and all the rest but most of them are not. I'm currently evaluating power supplies from china for a product. Some of them even fail on the input voltage requirement of 85 volt...

Regards
Click to expand...

If you have a list of a few wall warts that are good I would appreciate it.
 

difflvl, at the moment I have tried three different brands. But I can't test radiated emission. I don't have the equipment to do this. Here my customer is a bit upset about the price he has to pay to get a certificate...
Anyway, a good working and very low cost power supply can be found on: cnhitong.com
 

    D

    difflvl

    Points: 2
    Helpful Answer Positive Rating
Hi
you can try this method also put ferrite bead in series with the input power jack to reduce the conducted emission problem
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top