DX 7135 boards - Can reverse polarity diode be removed to increase 18650 performance?

[Wiggle]

Hello,
I notice that the 7135 boards I have from DX have a reverse polarity protection diode (D1) present. Can it be removed to increase the amount of time the 18650 can provide regulation with these boards? I understand there is a risk if I install a cell backwards but I'd rather have more regulation if I could.

 

[kramer5150]

Yes. You eliminate the voltage drop through the diode so the 7135 "looks" directly at the 18650. How significant of an improvement this is... I am not certain. I personally can not visibly see an improvement, especially since I do not deplete my 18650 cells low enough to where it would be apparent.

I tin some solid copper wire and just flow the solder to all the diode points. I have done 5-6 7135 boards with this treatment and have not suffered any ill-effects.

 

[CKOD]

How significant of an improvement this is... I am not certain. I personally can not visibly see an improvement, especially since I do not deplete my 18650 cells low enough to where it would be apparent.

Depending on the diode(s) it could be anywere from .7 to .2 volt improvement, as for a tangible improvment, that'd be a big-ol cup of "It varies" because li-ion has such a flat discharge curve, with high quality cells with a very flat discharge curve, and a Vf thats low, it could stay in regulation until youre at the end of charge, and removing the diode could net you only minutes or even seconds of in-regulation time.

With cheap cells which have a not so flat discharge curve, and a cheap diode with ~.7 v lost, and a LED with a high Vf, if could make a large difference.

Not exactly helpful, but its just a few minutes with a soldering iron, try it out, if it works better, sweet, if not, put it back, or dont...

 

[ama230]

The purpose of a diode is to prevent any reverse voltage or current. Thus, when these are dealing with an ic chip or transistor(s) they will protect a voltage spike or load from a switch's on & off. This is just a precautionary tool to help a load be carefully regulated. If you are driving something with a heavy load the current will want to flow backwards towards the supply(if near depletion) or light source, which ever has the lower potential.

Think of a regulator valve on a drip system for small irrigation. Of course the system will take full pressure a few time but down the road you are sacrificing safety and longevity of the device. Again its a dx driver and they are a dime a dozen. Its all about if you want to take the risk and have to replace the board or components down the road. Its a good excuse to keep upgrading or buying stuff.:devil:

Hope this helps...
Eric

 

[jtsgalaxy]

The purpose of a diode is to prevent any reverse voltage or current. Thus, when these are dealing with an ic chip or transistor(s) they will protect a voltage spike or load from a switch's on & off. This is just a precautionary tool to help a load be carefully regulated. If you are driving something with a heavy load the current will want to flow backwards towards the supply(if near depletion) or light source, which ever has the lower potential.

Think of a regulator valve on a drip system for small irrigation. Of course the system will take full pressure a few time but down the road you are sacrificing safety and longevity of the device. Again its a dx driver and they are a dime a dozen. Its all about if you want to take the risk and have to replace the board or components down the road. Its a good excuse to keep upgrading or buying stuff.:devil:

Hope this helps...
Eric

Eric is right, the doide is to prevent the current flow back from the load to the input only so removing it doesn't help of the performance gain. Actually this 7135 broad does not has the reverse polarity protection.

 

[HKJ]

Hello,
I notice that the 7135 boards I have from DX have a reverse polarity protection diode (D1) present. Can it be removed to increase the amount of time the 18650 can provide regulation with these boards? I understand there is a risk if I install a cell backwards but I'd rather have more regulation if I could.

No, the diode is not in the current path.

 

[Wiggle]

It looks like it connects between the positive battery connection and the rest of the circuit?

Edit: There must be another trace on the bottom I don't see, the diode is connected in parallel to shunt reverse voltages as you guys claimed.

 

[HKJ]

It looks like it connects between the positive battery connection and the rest of the circuit?

A diode before the control circuit will not affect performance, only secure the circuit. The diode has to be in the current path to the led, before it will reduce performance.

 

[Wiggle]

But if the diode is in series before the 7135s, it reduces the amount of voltage overhead these ICs have over the Vf of the LED at drive level thereby reducing the amount of time they can hold regulation. That's assuming its in series with the 7135s though which I'm not clear on, do you mean only the ATMEL chip is protected by the diode?

 

[HKJ]

But if the diode is in series before the 7135s, it reduces the amount of voltage overhead these ICs have over the Vf of the LED at drive level thereby reducing the amount of time they can hold regulation. That's assuming its in series with the 7135s though which I'm not clear on, do you mean only the ATMEL chip is protected by the diode?

The 7135 has 3 pins: gnd, control and led.

The led pin is usual connected directly to the led, without any diode in between. Because the led (Light Emitting Diode) also works as a diode, no separate diode is needed to the led pin.

The control pin is connected to the processor and the diode is connected from battery + to processor +.


Note: The above is a guess, I have not followed the traces on the board in the picture.

 

[Wiggle]

Gotcha, so the diode is not part of the 7135 connection. This makes much more sense because I measured the diodes forward voltage to be .56V. Taking a loaded li-ion cell down .56V on top of the other little losses in there would produce a voltage well below Vf for any reasonable drive level on the XR-E that I have hooked up.