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  • Author Author: mcb1
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5W Load Schematic

For the Beyond the Phone challenge I have been waiting for my kit to arrive.

 

After some Customs and UPS delivery delays, it arrived.

 

One concern I had was that since the kit was dispatched from the USA, the power plug and voltage may not suit our angled pins and 230v AC.

imagerather than the what we usehttp://nz.element14.com/productimages/farnell/standard/2254795-40.jpg

 

 

So as I feared the kit includes the wrong pings, but the voltage is 110/230 so it will fit with a travel adaptor

http://media2.dicksmith.co.nz/media/catalog/product/cache/3/small_image/150x/9df78eab33525d08d6e5fb8d27136e95/m/7/m7_dsnz_m7308_v0_4105.jpg which I thought we had ... but I can't find it if we do have one laying around.

 

 

Option 2

I checked and I did have some other 5v USB outlets that claim to be 1.2A but in reality the voltage tends to fall to the lower end of an acceptable USB voltage.

 

Placing the Receiver onto the unit, D5 flashes but not much else.

A bit of digging around in the Tx spec sheet suggests it flashes when transfer is occurring (I would hate to use that output as the Buzzer as the chip data suggests)

 

The Rx or part of the load gets warm, but no pretty red LED's.

 

Since there are 4 parts to this kit, establishing where the problem lays is a process that needs to be done.

Its no different to sorting out whats wrong with your car ... narrow it down an bit and you have a better chance of fixing it.

 

POWER

Its always a good idea to see if you have power.

TI have placed labelled test points on the kit that you can get a meter onto  ....well done.

The meter verified there was 5v which dropped to 4.8 or so, but when D5 flashed (ie when the load came on) so that's not the issue.

 

Jumpers

Try to establish what jumpers should be where is a little hard.

The images are not quite big enough to be very clear, and the smallish image shows where the jumpers should be if the LED load isn't in place .... but does the load board emulate this.?

 

Document http://www.ti.com/lit/ug/sluua44a/sluua44a.pdf gives the settings which showed JP6 needed to be shifted to the Fixed position, as per the image copied from the User guide

http://www.we-online.de/web/en/index.php/show/media/07_electronic_components/produkte_3/wireless_power/Wireless_Power_Kit_Solution.pdf

 

 

   hard to see but is in the middle of the board and should be on the two lower pins.

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Looking at the Load board three of the zero ohm resistors have been removed (R2, R3, and R6) and the flux residue suggests this is post production.

The remainders emulate the jumper settings shown (as if the LED board wasn't used) and these match the spec sheet.

 

The TX board has placeholders labelled JP1 and JP2 BUT these aren't jumpers they are connections for Temp sensor and Ext LED.

This annoys me since the receiver uses JP for jumpers and plain J for connectors, yet the Tx board uses both for connectors ...

Both items find themselves used as a pair so it stands to reason to use the same terminology.  ..... more documentation checking required Mr TI.

 

Voltages

Some of the TI documents for this kit and receiver refer to using 19v going into the TX.

Clearly the cut and paste failed to pick it up, as the transmitter markings show 5v, and some of the other documents also state 5v ....so Mr TI, you might need to review your documentation and stop confusing the buyers.

 

Having established that its 5v In and 5v OUT to the load, the next check was am I getting that.

A quick check with a meter showed that 5v give or take some fluctuations was being generated at the output of the receiver unit with the load attached, but still no red leds.

 

LED Load Board

I tried searching for some information on the board PMP8603 Rev A, but alas I failed.

I got a nice picture which detailed some of the parts used, and that's about it.

 

The board has a very nice inductor and some connectors and leds.

Checking the Leds showed they all work or illuminate, and feeding 5v into the Vin and Gnd resulted in nothing.

 

Looking at the underside and comparing the picture

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My board seems to have C3 populated, which is in parallel with C2.

 

There are 4 groups of 11 LEDs in series and from the spec sheet, the Fb (voltage) is 1.9v meaning that 5v wont light them up.

The chip has to boost the voltage to around more than 20v before passing thru a 798 ohm resistor.

 

I could only measure 7.6v out of U1 (the marking is SF98) which I can't find any information for.

I assume its a booster converter and certainly is wired that way.

 

So until I can identify the boost IC and replace it, my LED's won't light.

 

 

Verification

If anyone would care to check the jumper settings, and the voltage being delivered to the load board, I'd be grateful.

If Wurth could provide the schematic that would also be useful.

 

Mark

 

edit 05 Apr 2014.

I have obtained a travel adapter and tried using the supplied power pack, with the same results (ie no LED's) and voltages in the 6.5-7 v instead of the 20 odd volts.

Hendrik has kindly provided the link to the converter chip.

My board has an extra capacitor at C3 which shouldn't cause an issue as its on the output, however a schematic would prove very useful.

Parents

  • So I traced the board, and found that it follows the default schematic of the LMR64010. The feedback voltage divider has some different resistors (its R7+R8,160k+10k, named R1+R2 in the DS). On the output, there are four lines of 11 LEDs each, from Vout to GND. The lines are connected via a 79 ohm resistor (R9-R12) (though I measure them as 640 ohm, which is way to high), which drops about 1.5V.

  • in reply to hlipka

    Hendrik

    Thanks for that. (ordering now)

    I did measure the resistors and assumed they read 790 ohm, but measure around the 640 ohm mark.

     

    I will fire up the scope because the diode could be leaky, which may result in the reduced output voltage.

     

    mark

  • in reply to mcb1

    The resistors are marked as '79R', so I think they are 79 ohm. If they really are 790 or 640, it would mean that the LEDs are driven with maybe 2 mA or so. I think this is too low. But without schematic we cannot tell image

  • in reply to hlipka

    OK, I did something I should have done before: measuring the LED board current consumption. Its 147 mA at 5 V, so 0.735W. This means the LEDs are driven at about 8 mA or so (depending on their actual efficiency). Voltage on the resistors is about 4V (depending on which one I measure) - that would be a resistance of 500 ohm. So probably the measurement is right, and the LEDs get driven by just 6 mA.

  • in reply to hlipka

    Damn

    You beat me to reply...

     

     

    According to the links on this page.

    http://www.we-online.com/web/en/electronic_components/produkte_pb/demoboards/wireless_power/wireless_power_we.php?formblock=1141949#1141949

    The leds have this characteristic

    image

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    The previous calculation showed the leds have approx 1.81-1.83 volts drop across each led.

    Looking at the curve and assuming its not linear then 6mA could work.

     

    It appears that the converter produces around 25v, with 4 v dropped in the series resistor leaving 21 v ish for the forward drop on the leds.

     

    The power of 0.735w in and about 0.6w out is 81% efficiency which is also within the range expected. (the graph is for 20v out)

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    So all we need is for Wurth to confirm our findings in the form of a schematic for the LED Board.

     

    This testing suggests that the LED board isn't a decent load for the 5w unit and needs a large resistor slapped onto the input terminals ....

     

    Thanks for your help

    Mark

Comment
  • in reply to hlipka

    Damn

    You beat me to reply...

     

     

    According to the links on this page.

    http://www.we-online.com/web/en/electronic_components/produkte_pb/demoboards/wireless_power/wireless_power_we.php?formblock=1141949#1141949

    The leds have this characteristic

    image

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    The previous calculation showed the leds have approx 1.81-1.83 volts drop across each led.

    Looking at the curve and assuming its not linear then 6mA could work.

     

    It appears that the converter produces around 25v, with 4 v dropped in the series resistor leaving 21 v ish for the forward drop on the leds.

     

    The power of 0.735w in and about 0.6w out is 81% efficiency which is also within the range expected. (the graph is for 20v out)

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    So all we need is for Wurth to confirm our findings in the form of a schematic for the LED Board.

     

    This testing suggests that the LED board isn't a decent load for the 5w unit and needs a large resistor slapped onto the input terminals ....

     

    Thanks for your help

    Mark

Children
  • in reply to mcb1

    Update.

    Some of the values we observed didn't match the measurements.

    I have been able to confirm that the problem is how we read them, and I'm blaming the extremely small markings ....image

     

    I did use a bench supply of 5v for the testing, but have also confirmed the Rx output is 5v.

    It would appear that some switching is taking part, since the output is approx 7 volts. (it should be 24v)

     

    R7 is marked 1873 and measures about 175K ohms in circuit, R8 is marked O1C and measures 9.7K ohms.

    The 4 LED series resistors are marked 79A and measure 640 Ohms.

     

    This chart gives the Markings v Values and lines up with the values measured. (I've bookmarked this because smd is here to stay)

    01S

     

    The diode is marked B4Z which translates to a MBR0540 (40v schottky)

     

    As Hendrik said earlier, the circuit is identical in layout to the datasheet for the LMR64010.

     

     

    Mark