HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Mar 25, 2012, 03:31 AM
Registered User
Joined Sep 2005
9 Posts
Discussion
EMI/RF, voltage Ripples, noise problem own power source

Hello,
There was few posts about that. But in these kind of subjects every project is individual problem to fix.

I'm trying to design a stabilized 5V on LM2576 (52kHz) for my lightning system.
max input 21V
max Iout 0,5A
based on ATmega8 switching on the darlington driver ULN2803 ports. Ports goes from driver to LEDs.
LM2576 works with inductor 470uH. Input Capacitors are tantal (tried 100uF to 680uF). Output capacitors are tanatal and electrolit (tried from 100uF to 3300uF - electrolits are LOW ESR JAMICON).
On the input wire I add small axial choke 0,33uH to minimize V ripple.

And I still get terrible noise (on the battery side). The noise on oscilloscope looks like around 40mVpp. But the servos rage when the Tx stands more than 1m (with antenna collapsed). Rx was connected to regulator linear BEC, regulator share the same battery as my module. So my conclusion: the noise is from V ripple from wire system.
It seams like the problem is while the LED are blinking. The current goes instantly from 300mA to 500mA sometimes.

I get a little help from Mr.RC-CAM to add ceramic capacitors 0,001 - 0,1uF.
And more to add common mode Toroid. But which one? On what frequencies or what uH should it have?

RC system is 35Mhz. Did not try on 2,4GHz, but if on 35Mhz will be ok, than on 2,4Ghz as well.

I would be very gratefull for your help!
Thanks
Maciek.
Poland/Europe
maciejbilu is offline Find More Posts by maciejbilu
Last edited by maciejbilu; Mar 25, 2012 at 04:23 AM.
Reply With Quote
Sign up now
to remove ads between posts
Old Mar 25, 2012, 09:30 AM
Dave the Rave
dmccormick001's Avatar
Joined Jun 2007
857 Posts
You probably need to post a schematic of your circuit if you want help in designing it.
dmccormick001 is offline Find More Posts by dmccormick001
Reply With Quote
Old Mar 25, 2012, 11:43 AM
Registered User
Joined Sep 2005
9 Posts
Hello,
Here is the schema.
Apologise for a little chaos.

Please take a look for this noise filters (polish site and language):
http://www.tme.eu/pl/katalog/filtry-...ry%3D112930%26

Would those filters work for my application ?

Thanks!
maciejbilu is offline Find More Posts by maciejbilu
Reply With Quote
Old Mar 25, 2012, 03:08 PM
Registered User
bnick2k8's Avatar
Portland, Oregon
Joined Aug 2008
1,530 Posts
Quote:
Originally Posted by dmccormick001 View Post
You probably need to post a schematic of your circuit if you want help in designing it.

Dave...

Hi, Would you maybe take a moment and have a look at a thread I wrote yesterday explaining a wiring problem I and many other guys are experiencing with our P-51D Mustangs where the manufacturer has taken all the servos in each wing and has run them into a 6 lead Ribbon Cable for easy connection and diconnect to and from the flying field... The thread will explain better how these ribbon cables are burning up in some cases as well as many of us losing our electric retracts like I did with mine catching fire on the 2nd retract I made with it here at home...

Sorry for the bother but I'm just trying to find someone who has some electronic expertise who can look at what the manufacturer has done by using a 6 wire Ribbon to put 4 servo signal leads on 4 or the 6 Ribbon wires and then has used the last 2 wires to handle the entire loading of the 5 wing circuits, aileron, flaps, landing gear, gear door, and lighting... We are thinking it is too much and somehow may be related to our Ribbon Cables burning up and our main electric landing gears burning up too...

Here's the link to my thread... See Post 22

http://www.rcgroups.com/forums/showt...1618946&page=2

And also a link showing a burned Ribbon Cable just posted this morning...
See Post 2512...

http://www.rcgroups.com/forums/showt...01476&page=168

Thanks,
bnick
bnick2k8 is offline Find More Posts by bnick2k8
Reply With Quote
Old Mar 25, 2012, 03:28 PM
Registered User
Solihull, England
Joined Jun 2004
936 Posts
Clearly the cables are overloaded due to the current drawn by the servos.

What type of servos? Have you measured the current drawn by the servo? Are the control surfaces stiff putting extra load on the servos?

If you compare standard servo cables with the wires you have I think you will see they are to small.

Peter
Quote:
Originally Posted by bnick2k8 View Post
Dave...

Hi, Would you maybe take a moment and have a look at a thread I wrote yesterday explaining a wiring problem I and many other guys are experiencing with our P-51D Mustangs where the manufacturer has taken all the servos in each wing and has run them into a 6 lead Ribbon Cable for easy connection and diconnect to and from the flying field... The thread will explain better how these ribbon cables are burning up in some cases as well as many of us losing our electric retracts like I did with mine catching fire on the 2nd retract I made with it here at home...

Sorry for the bother but I'm just trying to find someone who has some electronic expertise who can look at what the manufacturer has done by using a 6 wire Ribbon to put 4 servo signal leads on 4 or the 6 Ribbon wires and then has used the last 2 wires to handle the entire loading of the 5 wing circuits, aileron, flaps, landing gear, gear door, and lighting... We are thinking it is too much and somehow may be related to our Ribbon Cables burning up and our main electric landing gears burning up too...

Here's the link to my thread... See Post 22

http://www.rcgroups.com/forums/showt...1618946&page=2

And also a link showing a burned Ribbon Cable just posted this morning...
See Post 2512...

http://www.rcgroups.com/forums/showt...01476&page=168

Thanks,
bnick
Peter Seddon is offline Find More Posts by Peter Seddon
Reply With Quote
Old Mar 25, 2012, 03:30 PM
Registered User
Solihull, England
Joined Jun 2004
936 Posts
Switching systems such as this are as much dependant on circuit design as layout for good low noise performance.

Peter
Quote:
Originally Posted by maciejbilu View Post
Hello,
There was few posts about that. But in these kind of subjects every project is individual problem to fix.

I'm trying to design a stabilized 5V on LM2576 (52kHz) for my lightning system.
max input 21V
max Iout 0,5A
based on ATmega8 switching on the darlington driver ULN2803 ports. Ports goes from driver to LEDs.
LM2576 works with inductor 470uH. Input Capacitors are tantal (tried 100uF to 680uF). Output capacitors are tanatal and electrolit (tried from 100uF to 3300uF - electrolits are LOW ESR JAMICON).
On the input wire I add small axial choke 0,33uH to minimize V ripple.

And I still get terrible noise (on the battery side). The noise on oscilloscope looks like around 40mVpp. But the servos rage when the Tx stands more than 1m (with antenna collapsed). Rx was connected to regulator linear BEC, regulator share the same battery as my module. So my conclusion: the noise is from V ripple from wire system.
It seams like the problem is while the LED are blinking. The current goes instantly from 300mA to 500mA sometimes.

I get a little help from Mr.RC-CAM to add ceramic capacitors 0,001 - 0,1uF.
And more to add common mode Toroid. But which one? On what frequencies or what uH should it have?

RC system is 35Mhz. Did not try on 2,4GHz, but if on 35Mhz will be ok, than on 2,4Ghz as well.

I would be very gratefull for your help!
Thanks
Maciek.
Poland/Europe
Peter Seddon is offline Find More Posts by Peter Seddon
Reply With Quote
Old Mar 25, 2012, 08:06 PM
Registered User
bnick2k8's Avatar
Portland, Oregon
Joined Aug 2008
1,530 Posts
Quote:
Originally Posted by Peter Seddon View Post
Clearly the cables are overloaded due to the current drawn by the servos.

What type of servos? Have you measured the current drawn by the servo? Are the control surfaces stiff putting extra load on the servos?

If you compare standard servo cables with the wires you have I think you will see they are to small.

Peter
Peter...

Thanks and no we haven't measured the load yet... The aileron and flap servos are 25 gram, the Gear door servo is a 9 gram, and the E-Retract main gear as I remember are 200mAh at stall, and 5mah at idle... I can't speak for the Light circuit drain...

All of this is laid upon 2 wires in that 6 wire Ribbon Cable and the remaining 4 wires are the signal leads for the gear and 3 servos...

I'm really thinking this is a problem... Several us are going to traditional Y splitters and extenders...
bnick
bnick2k8 is offline Find More Posts by bnick2k8
Reply With Quote
Old Mar 26, 2012, 07:30 AM
Registered User
Adelaide, SA
Joined Sep 2009
48 Posts
@Maciek - you have placed a choke in series with your input. This is fine, but it must be BEFORE the input capacitor, not after it. The input capacitor must connect directly to the LM2576. You have placed your choke between the input capacitor and the rest of the Buck converter - this is not permitted.

The LM2576 datasheet gives clear instructions about single point earthing, this is generally good advice and should be followed. A ground plane will also usually work. As Peter has pointed out, switching power supplies are very layout dependent.

In a Buck converter there are two current loops that should have their areas minimised:
1. Ground - input capacitor - upper switch - inductor - output capacitor - ground.
2. Ground - catch diode - inductor - output capacitor - ground.

Trace these paths out on your board and make sure they form nice small loops, and contain no skinny tracks. Minimising loop area will minimise radiated emissions.

Cheers,
Andrew.
Andrew Dunlop is offline Find More Posts by Andrew Dunlop
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Question Hornet OSD Problems - Voltage/mAh Display and Overheating heath.collmer FPV Talk 6 Jul 26, 2012 08:19 AM
Discussion Voltage ripple firehawkzach Castle Creations 6 Apr 19, 2012 09:27 PM
Discussion kkmulticontroller 5 volt power source tkorocky Multirotor Talk 3 Mar 15, 2012 12:17 PM
Discussion GensAce Ripple Voltage cause ESC Death? " ToxicBanana Batteries and Chargers 57 Mar 10, 2012 11:55 AM