Zener Diode purchasing help

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Ouchyfoot
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Zener Diode purchasing help

I’d like to try some Zener diode mods on Qlite and other 4.2V drivers so I can run 8.4V, but get confused with the specs when searching for the proper diode. Which Zener Diode would be the optimum one to purchase? If I had some specs, or a model code, it would help me a lot.

Also, a link for the proper resistor to go with it would be an aid.

Pavithra_uk
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normally zener diodes has zener voltage & power rating. 0.25w/0.5w & 1W power available everywhere.

LinusHofmann
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Just had a quick check on ebay since I don’t know any US/Canadian based retailers.

This is the zener I use. The 4.3v rating is the most important and 0.5w rating should be plenty. Higher wattage versions just mean a bigger overall package.

Ebay 4.3v 0.5w Zener

Resistors

This 200Ohm smd resistor is what I use. They’re very small but this is the perfect size to replace the diode on the driver board.

RMM
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Here is what I have used in all of my mods, I bought them from Mouser but I am sure you can find something similar locally:

CRCW0805200RFKEB
1/8watt 200ohms 1%
0805 Thick Film Resistor

MMSZ5229B
4.3V 0.5W Zener
SOD-123 Package

There are many other sizes / specifications that you could make work, the resistor doesn't need to be an 0805 size, and I've even seen a few guys use some pretty big diodes (with similar specs).  These sit right in place/on top of the existing components, look good, and are easy to place.

Also, order a few extra resistors if you do go with the 0805 size.  I have lost a few and once they're out of your sight... good luck finding them!

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comfychair
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The zener/resistor mod doesn't turn it into a 2 cell/8.4v driver, it turns it into a driver for a ~6v LED (which just happens to require higher input voltage). It won't work with 2 cells and a single XML/XPG.

Ouchyfoot
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I guess I mostly want it for MT-G2. There are just so many differently rated ones, I wanted to check in with you guys first so I got the correct one.

Gj
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comfychair
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The voltage across the zener will vary depending on your choice of resistor... I ignore the markings and measure them. Whatever the voltmeter reads is what will be supplied to the MCU.

http://75.65.123.78/Dsc06513.jpg

Beer

EDIT: That's two 4.2v batteries, a resistor, a zener diode, and a voltmeter. This is only the test circuit to figure out the voltage across an unknown zener diode, or to find out exactly what it will do with your particular resistor.

TheGloriousTachikoma
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So, I need a little help understanding how this mod works. The Zeiner diode, if I understand it correctly, limits the voltage that flows across it, yes? According to comfy’s diagram the Zeiner is in parallel to the emitter, so does that mean that the diode is a relief gate of sorts? And the mod is not about the extra voltage harming the components of the driver? And does the addition of the resistor decrease the efficiency of the driver?

comfychair
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The zener/resistor are ONLY in the power supply to run the MCU, it's nothing to do with the LED or the load side of the 7135s. The only connection between the MCU and the 7135s is the PWM/Vdd line, and they share a common ground, and just happen to be mounted to the same PCB. BAT+ is run straight to LED+, the power for the MCU just taps into it where the original diode attaches beside the red LED+ wire.

 

Find MCU pin 8, follow the trace down, see the via in the fork in the road? That via goes through to the capacitor on the other side.

See the three vias right above the 'BAT+' label? That comes through from the pad on the other side where the spring is soldered on, it's connected to the battery positive pole any time there's a battery in the light. So follow the trace to the right from the three vias, there's the pad for the original diode, and then the pad for LED+. So LED+ is also connected to BAT+ at all times.

http://75.65.123.78/Dsc06369.jpg

 

http://75.65.123.78/NANJG105Cmod.jpg

In the above pic, find D1 and C1 and MCU pin 8. That's the only part of the diagram involved in the zener/resistor mod. Resistor replaces D1, zener goes from anywhere in the red part and then to ground. It can be placed anywhere as long as it's between pin 8 and ground (see next pic).

http://75.65.123.78/Dsc06506.jpg

It can even attach straight onto the MCU pin directly. It's all electrically the same.

http://75.65.123.78/driver.jpg

 

The zener dumps any voltage above its rating (approximately...), and the resistor limits the current that goes through the zener to ground to keep the zener from burning up. And by limiting the voltage input to the MCU, that also limits the voltage the MCU will output on pin 6 to the 7135s.

The 7135s are shielded from the higher input voltage because the MTG2 'eats' double the voltage a single XML does. You put 8.4 volts in, the MTG2 eats 6.2 volts, leaving only a measly 2.2 volts for the 7135s to deal with. This would NOT work with 8.4 volts in, and a 3 volt LED - the poor little 7135s would freak out and be very unhappy if you asked them to get rid of an unwanted 5 volts.

TheGloriousTachikoma
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I see, so it’s kind of tricking the controller like a piggyback fuel computer does to the ECU in a [modified] car, it gives the controller the voltage/current it needs to operate and the 7135’s are commanded to operate as normal, they’re just dealing with more energy going through them.

Also, thanks for that pic of the 105 board, it really helps illustrate how these things work. Not quite as much to them as I had thought. Makes me wonder about other drivers too. Smile

comfychair
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Well if we're gonna do car analogies, the zener works like a return-style fuel pressure regulator (but instead of returning the fuel back to the tank, it dumps it out on the ground). Smile

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So what specific voltage value should be the Zener diode for 2×18350, MT-G & 7135 board?

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Ouchyfoot
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What if you had two 3v XML in series?

Also, I’ve been wondering if the battery + wire could go directly from the battery to the emitter, bypassing the board entirely, as long as the – LED wire links back to the board.

LinusHofmann
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Ouchyfoot wrote:
Also, I’ve been wondering if the battery + wire could go directly from the battery to the emitter, bypassing the board entirely, as long as the – LED wire links back to the board.

Yes that’s basically already happening on the standard driver setup. The + spring pad on the back of the board goes straight through and connects directly to the led + wire with only a feed off to power the MCU. You can bypass the board completely and just run a bigger + wire directly to the emitters for less resistance losses, just remember to also tap off a small wire to power the MCU somewhere Smile

Ouchyfoot
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RMM wrote:

Here is what I have used in all of my mods, I bought them from Mouser but I am sure you can find something similar locally:

CRCW0805200RFKEB
1/8watt 200ohms 1%
0805 Thick Film Resistor

MMSZ5229B
4.3V 0.5W Zener
SOD-123 Package


Thanks RMM. Those were the type of diodes I was looking for. I’ve never ordered from Mouser because of the $20 shipping charge, but I went to checkout just to double check, and it gives another $8 USPS Global Priority option.
I guess I should look around at any other products they have while I’m ordering.
TheGloriousTachikoma
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comfychair wrote:

Well if we’re gonna do car analogies, the zener works like a return-style fuel pressure regulator (but instead of returning the fuel back to the tank, it dumps it out on the ground). Smile

Wait…so the driver just discards 25% of the power it sucks off the batteries? A 75% efficient driver, or is that on top of the inefficiency the 105C is known for at MT-G2 amperage? Because that’s implying that even a full doubling of chips won’t drive a MT-G2 to its full potential.

comfychair
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No... power supplied to the zener has to go through the resistor. It's nothing to do with the high-power load side of the circuit that runs the LED. MCU power supply only. Not the LED. Miniscule amount of current through the ~200 ohm resistor.And even then, only the voltage above the zener's rating flows away to ground. The rest is retained in the pipe.

After all, a 1/4 watt zener survives just fine. How can it drain the batteries or affect efficiency in any significant way?

nofearek9
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one question i can do the zener mode to any “7135×8” driver ? do i have to program the mcu ?

RMM
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nofearek9 wrote:
one question i can do the zener mode to any "7135x8" driver ? do i have to program the mcu ?

No programming needed, the MCU doesn't know the difference.  You lose driver voltage reading, but even with simple programming you can't bring that back because a circuit tweak is needed.  

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nofearek9
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i c thanks .