Battery Charger

Hi,

Need help with the following problem. What isolation should I use?

ac to dc adapter ( 5v) -----> isolation -------> LTC 4062

LTC Data sheet:

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AC to DC Adapter:

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melissa

Reply to
walravenmelissa
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Hi Melissa

Is it because you want to charge the individual cells?

/Glenn

Reply to
Glenn

If so - do you have other batterypack criterias?

/Glenn

Reply to
Glenn

I am charging a 3.7 V 1200mAh LiIon battery. I want to isolate the AC to DC adapter because of safety issue.

melissa

Reply to
walravenmelissa

The ac to dc adapter should have adequate isolation. Is that not good enough?

/Glenn

Reply to
Glenn

What are you doing that you need more than the several thousands of volts of isolation provided by the charger?

--
Tim Wescott 
Wescott Design Services 
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Reply to
Tim Wescott

The wart looks fine. It's already isolated.

--
John Larkin         Highland Technology, Inc 

jlarkin at highlandtechnology dot com 
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Reply to
John Larkin

I am trying to provide user more protection. The other thing is that its an interesting problem to solve. But I do need some direction here.

melissa

Reply to
walravenmelissa

More than what? There's some common test protocols, and models of human-body load, involved. If you want an UNCOMMON test or model, it'll cost ya.

Easiest way to provide 'user' more protection, of course, is to use connections that the user doesn't come in contact with. My electric toothbrush charges by proximity, not an electrical contact anywhere you can see or touch.

Reply to
whit3rd

snipped-for-privacy@gmail.com brought next idea :

Wots your REAL problem? ;-) Or do you have so little knowledge that you cannot describe your real problem?

There is no relation at all between the 2 data sheets you quote.

One plugs directly into the mains and the other only uses the already isolated supply within an already certified device. :-?

--
John G
Reply to
John G

I was told by a collegue that this is a challenging problem. i took sometime and tired to figure out but could not figure it out. You can take the AC to DC adapter out of the picture and use a +5v power bench power supply.

Reply to
walravenmelissa

Please explain in detail what makes it challenging.

Please explain what level of isolation you are seeking.

Please quote any specifications you must meet.

Reply to
John S

Best would be if the OP describes his real problem then we could maybe offer some ideas.

John S and John G are not the same person even though the agree at this point. lol

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John G
Reply to
John G

Ahh!! but what isolation does the bench supply have ??? (Hint like the wall wart? ).

Reply to
Rheilly Phoull

Hello, Could your colleague specify where the challenge is ? Most wall warts and bench power supplies use the standard step-down transformer->bridge rectifier-> capacitor bank->voltage regulator/overvoltage protection design. So the isolation is there right at the start. Is there anything special - a biomedical device with some special requirements ?

Reply to
dakupoto

** Lose that switching AC adaptor and use one that incorporates an iron transformer - no need for regulation as the IC can take up to 8v input.

Iron transformer adaptors, with Class 2 or Double Insulation, have a long track record of being exceptionally safe - the same cannot be said for most of the switching types pouring out of China.

Another idea is to change the plug on the output cable to a non touchable kind - but it cannot be any connector that is associated with AC power.

You have not indicated whether the imagined " safety issue " originates from the adaptor or the battery side of things ?

... Phil

Reply to
Phil Allison

The wall wart she picked is a switcher. Actually most modern wall warts are switchers these days...for better or worse.

It is certainly possible to add a second DC/DC with isolation, but that is a lot of work for a dubious return on investment. It would most certainly reduce the efficiency.

I suppose if you really didn't trust the wall wart peddlers, you could go AC on the output. Then all the peddler is supplying is a low tech transformer and some sort of short circuit protection element.

Reply to
miso

Hi Melissa

Please read:

The "old" way is to use a 50Hz or 60Hz insulation certified (5000V) transformer. E.g. the transformer could have the primary winding separated from the rest of the windings on the bobbin. Combined with a linear regulator this is normally a very robust solution, that works for decades.

The "new" way is to use a insulation certified (5000V) high frequency transformer in some SMPS circuit. The problem with these is that the designer or component-buyer sometimes use bad capacitors or bad designs (incl. to little filtering) so they to often fails prematurely. The most used way of signalling back from the secondary circuit the primary circuit is to use an optocoupler that can 5000V (most can). The good thing about SMPS is that they can be efficient. Some can even use almost zero power from the grid when not loaded on the secondary side.

Another way is to transfer the power wirelessly. There is ongoing research and development to make this a public reality. The area has of cause been littered with patents.

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Please note that the primary to secondary circuits must also be insulation certified (5000V).

Anything that bridges (e.g. noise suppression capacitors) between primary and secondary circuit must withstand 5000V.

Note that the term isolation transformer (e.g. 110V->110V - or

230V->230V) has a special meaning. They are used by repair technicians:
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October 27, 2012, A dozen USB chargers in the lab: Apple is very good, but not quite the best:

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USB Power Supply/charger Test:

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February 12, 2013, Teardown of a HomePlug Adapter:

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5kV HIGH VOLTAGE DIGITAL INSULATION TESTER WITH SOFTWARE & USB:

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Professional insulation meter with test voltage programmable up to 10kVDC:

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Fluke 1550C Insulation measuring device, 250 V - 5 kV Manufacturers guarantee 3*:

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Comparison table - insulation measuring instruments:

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Back to Basics: Voltage Regulator ICs, Part 1 There are two basic types of regulator ICs, linear and switch-mode. The linear regulator operates in the linear region and is always on, whereas basic the switch-mode type turns on and off and requires a rectifier to produce a dc output voltage.

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Back to Basics: Voltage Regulators, Part 2. In this second part of the Back to Basics series on regulators, we examine buck (step-down) and the boost (step-up) forward and flyback topologies, as well as the SEPIC, hysteretic and multiphase converters.

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Off-Line SMPS Failure Modes PWM Switchers and DC-DC Converters

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Quote: "... This transistor failure is often caused by bad capacitors. It is extremely common to find output filter capacitors that are swollen or leaking electrolytic material. ..."

Badcaps.net - What Causes This:

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How-To Repair a Desktop LCD with Bad Capacitors:

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7 June 2007, Wireless power a reality:

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13 August 2012, Tiny transmitters that cost a penny to print unveiled:
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Institute of Physics (2012, August 9). Wireless power for the price of a penny?. ScienceDaily:
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Dec 12, 2012, Magnetic metamaterials could boost wireless energy transmission:

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DIY: Wireless Battery Charger:

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/Glenn

Reply to
Glenn

On 18/07/13 10.14, Glenn wrote: ...

...

The above links are only for signal transmission - not for power - sorry.

/Glenn

Reply to
Glenn

One more link:

May 19, 2012, Apple iPhone charger teardown: quality in a tiny expensive package:

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/Glenn

Reply to
Glenn

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