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 Post subject: Re: Switching PS issues?
PostPosted: August 21st, 2017, 4:04 pm 
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Joined: April 22nd, 2013, 12:58 pm
Posts: 285
Agreed. It's generally better to kill the noise at its source than to try and filter it out after it has radiated either through the air or down an electrical line (signal or power).
A linear PSU for the MacBook would help the problem, but the Tripplite is at least keeping most of the RFI nasties from getting back into your household AC wiring.


DaveR wrote:
It's a noise issue. Your laptop power supply is putting noise into the line. When the LED lamp is plugged into the same side of the Tripplight as your power supply the noise from the PS is going straight into the LED lamp. When you plug the lamp in somewhere else the Tripplight is filtering the noise enough so that it doesn't affect the LED. A ferrite core on the AC line to the PS may help. Pretty on both counts, PS and LED.


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 Post subject: Re: Switching PS issues?
PostPosted: August 21st, 2017, 4:05 pm 
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Joined: March 12th, 2013, 11:12 am
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A 17v linear PS should be fairly simple but with the macbook Pro I think there might be control issues with charging needing to be turned of when battery is fully charged?

Roscoe Primrose wrote:
Just build a linear supply for the laptop ;)


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 Post subject: Re: Switching PS issues?
PostPosted: August 21st, 2017, 4:11 pm 
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Joined: April 22nd, 2013, 12:58 pm
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Yup, way too many control interfaces to reverse engineer, and Apple designs can be devious sometimes......although their hardware is more mainstream these days.

TubeDriver wrote:
A 17v linear PS should be fairly simple but with the macbook Pro I think there might be control issues with charging needing to be turned of when battery is fully charged?

Roscoe Primrose wrote:
Just build a linear supply for the laptop ;)


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 Post subject: Re: Switching PS issues?
PostPosted: August 21st, 2017, 4:42 pm 
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Joined: July 24th, 2015, 4:17 pm
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Location: Parkville, Maryland
Instead of reinventing the wheel how about a shunt capacitor across the LED. It is a DC device and any AC component being introduced to it can be bypassed to ground out of harm's way.

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 Post subject: Re: Switching PS issues?
PostPosted: August 21st, 2017, 6:24 pm 
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Joined: February 28th, 2013, 3:31 pm
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I am surprised that a commercial LED is responding to the line noise. The LEDs you buy in the store have a power supply that converts the constant voltage from the mains line to the constant current the LED needs. Apparently there is insufficient filtering in the CC supply to reject the noise. Cheap construction. I'm also surprised that the power supply for th Apple is not noise suppressed. Any switcher over 50 watts is supposed to have power factor correction but they also usually have noise suppression. I'm guessing cheap construction again. I would try a commercial line filter for the switcher. It would not have to be expensive. They have them on Amazon for as little as $18. If you want to do a little work, ebay has line filters built into an IEC input receptacle for around $4.00. You would have to put it into a box with an output AC socket.

http://www.ebay.com/itm/CW1D-10A-T-Nois ... SwqfNXmW28

Tom


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 Post subject: Re: Switching PS issues?
PostPosted: August 21st, 2017, 6:36 pm 
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Joined: March 12th, 2013, 11:12 am
Posts: 738
This is what the Apple 85w charger looks like inside:

http://www.righto.com/2015/11/macbook-c ... ising.html


tomp wrote:
I am surprised that a commercial LED is responding to the line noise. The LEDs you buy in the store have a power supply that converts the constant voltage from the mains line to the constant current the LED needs. Apparently there is insufficient filtering in the CC supply to reject the noise. Cheap construction. I'm also surprised that the power supply for th Apple is not noise suppressed. Any switcher over 50 watts is supposed to have power factor correction but they also usually have noise suppression. I'm guessing cheap construction again. I would try a commercial line filter for the switcher. It would not have to be expensive. They have them on Amazon for as little as $18. If you want to do a little work, ebay has line filters built into an IEC input receptacle for around $4.00. You would have to put it into a box with an output AC socket.

http://www.ebay.com/itm/CW1D-10A-T-Nois ... SwqfNXmW28

Tom


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 Post subject: Re: Switching PS issues?
PostPosted: August 21st, 2017, 7:05 pm 
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Joined: February 28th, 2013, 3:31 pm
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Interesting that the cheap imitation is a linear supply. Not as efficient but without the switching noise.


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 Post subject: Re: Switching PS issues?
PostPosted: August 21st, 2017, 10:26 pm 
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Joined: July 24th, 2015, 4:17 pm
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Location: Parkville, Maryland
LEDs are simple diodes -- what power supply? You use them with your DC power supply to indicate on-off status. Of course you need an appropriate resistor in series to limit current -- most LEDs are rated for use on anything from 1-1/2-volts to 3-volts DC. The voltage drop from a resistor gets you there. That's why a simple bypass capacitor can shunt the bothersome AC noise to ground.

??? Am I missing something here?

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 Post subject: Re: Switching PS issues?
PostPosted: August 22nd, 2017, 8:51 am 
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LEDs can be run with a DC suply and a simple resistor. In that configuration you get a sort of constant current to the LED. That is not a very efficient way to do it and in addition, any changes in voltage will be reflected as changes in light output. Better LED light sources use a constant current supply that mitigates line voltage changes. Also common today are dimmable LEDs where a circuit inside the lamp looks at the RMS voltage coming into the powersuply from the dimmer and sets an appropriate current to the LED. BTW, The quality of that voltage to current conversion can vary widely depending on the quality of the power supply used.


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 Post subject: Re: Switching PS issues?
PostPosted: August 22nd, 2017, 8:57 am 
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If anyone wants a greater explanation of different light sources and their characteristics, here is a document I created when working on my patent for low cost LED lighting. As with all scientific matters, it is generally out of date by the time it is written but the fundamentals have not changed.


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Future High Efficiency Lighting Trends.pdf [30.05 KiB]
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