Schottky Diode - Open Circuit

[Sadlercomfort]

Hi Guys,

I'm investigating a faulty infrared remote at work, the remotes seem to be discharging the 9V batteries when not in use.

Now, upon my initial investigation I noticed that the Schottky Diode which protects the circuit from reverse polarity was open circuit. I then confirmed this fault was caused by reverse polarity by using a new remote, which again caused the Schottky Diode to go open circuit.

Now I'm wondering whether the Schottky Diode became 'Resistive' before failing open circuit.. which could explain the discharge rate of the batteries.

I would like to know:
-Is it possible for Diodes to become resistive?
-If so.. Is this the defect im looking for?
-What can cause batteries to discharge quickly when not in use?

Thanks,
Ash

 

[dorke]

"-Is it possible for Diodes to become resistive?"
Yes.it is possible but mostly they would be either short or open.

"-If so.. Is this the defect im looking for?"
Could be,but you should also check the resistance seen by the battery (faulty diode pulled of circuit).

"-What can cause batteries to discharge quickly when not in use?"
Only thing is something loading them.(assuming the battery itself isn't faulty).

 

[Sadlercomfort]

So its unlikely that a faulty 'resistive diode' could be the problem.

What do you mean by checking the resistance seen by the battery? Measuring the resistance across the +/- terminals with the battery pulled? I can test this on a new remote if necessary.


I know the batteries are ok after speaking with the supplier, and testing 50+ of them.. so I know there is something loading the batteries when the remote is not in use.

 

[dorke]

Yes, exactly.

 

[Sadlercomfort]

I'm getting 1MΩ and OL when I test it in reverse polarity.

It seems when I put reverse the polarity of the supply for to long and measure the resistance again, I get OL and 52MΩ when I test it in reverse polarity.

 

[dorke]

The 1M should be high enough,it will create a 9uA(not very low,but low) discharge current.

How long should the battery hold? Is it a rechargeable battery?
How long does it take for the battery to discharge?
Or how long does it take to drop from say 9V to 8V?

Can you please post photos of the remote board.
Are there any electrolytic caps on it?

 

[73's de Edd]

.




Sir Sadlercomfort . . . . . . . . aka Ash


At this point in time and not knowing your brand of unit, BUT knowing that it is utilizing a 9 V battery for power.
Lets find the most important parameters associated with the unit, since verification that batteries are not being the problem.
As per the mock up illustration below most 9 v powered inits have a bit of a pigtail on the battery.
Lets take our DC metering and unplug half of the battery and swing its contact 90 degrees . That will be leaving you easy access
to place one meter probe on each terminal, one on the battery proper and the other one on the 9V plug connectors now free terminal.
That will open its power input circuitry to permit monitoring THE current drain of the unit .
Don't worry about probe polarity, as it will sort itself out on the meters display readout.
Place metering in DC CURRENT MODE. If auto ranging instrumentation, let it seek out for you , if being manual, initially shoot on up
to a very safe 100 ma and work down as needed.

Test a number and you will probably just get a fast single current blip.

Test a vol up or volume down . . . . . ch up or ch down and the unit willl be pulling current as long as the button(s) is/are held down.
Figure your worst cases and log down.
But NOW ! the real thing that we are wanting to know is, with no button activity, what is the quiescent current drain that the unit is taking from the battery for 24 hours a day.?

Feed back those magical numbers to us for evaluation.

Thasssit . . . . . .


Techno Illustration . . . . .
(In not knowing if you might have a "TOP" brand, or yours might just be an el cheapo "Bottom Feeder")

73's de Edd



.

 

[Sadlercomfort]

I can't show you the remote I'm afraid because of a disclosure agreement =[

The remote has only 3 buttons, which draws approximately 30mA when one is pressed. It draws very low current when not pressed... its negligible. Usually the buttons are pressed for 10 seconds a time, with long delays in-between.

The remote is specially made for us.