Zetex 310 in MiniMagLED circuit board

[zeeexsixare]

Okay so I'm somewhat competent in circuits, but I've been having problems deciphering all the stuff that goes on in the Zetex circuit.

The thread here: http://www.candlepowerforums.com/vb/showthread.php?t=131784
seems to have used the one resistor available (.05 ohms) and put another one in parallel to make the equivalent resistance of .008 ohms. It doesn't appear to be in series with the Zetex sample circuit diagram in their pdf:

http://www.zetex.com/3.0/pdf/ZXSC310.pdf

So what exactly does the R050 resistor do and how does it work with the transistor? Does this IC perform PWM or CC regulation?

I also remember reading that there's a temperature negative feedback circuit somewhere in this, too. How does that work exactly? Is there an actual sensor in the circuit or does the vLED just drop due to inefficiencies in the driver board?

My goal is to stack a resistor on mine like in the first link above, but I'm not sure what value to use because I'm trying to figure out how the existing resistor fits in the circuit.

I researched the Zetex 310 posts from 3-6 years ago but found lots of bickering and jargon about big lots and inductors cracking and availability and stuff.

My ultimate question here is, does that one resistor directly control the current to the emitter? Thanks.

 

[CM]

The resistor in the Zetex data sheet is a current sense resistor. The circuit senses the voltage across the resistor to determine how long to turn on Q1 to charge the inductor. The IC is "constant current" meaning that it tries to maintain a constant load current. I say "tries" because it does not really do a good job of it and the circuit acts more or less like a voltage multiplier. Look at the runtime graphs of circuits using the Zetex. The output is not flat. This is not necessarily a disadvantage since the circuit is capable of sucking an alkaline cell dry which is desireable in some applications like survival.

I don't recall any temperature feedback in the circuit. In my opinion, it probably doesn't have one since it is designed to be cheap cheap cheap. That's why it is in the M@g. If you want to stack another resistor on top of the existing one, the circuit is not up to the task of driving the load very hard so your efforts may be met with some disappointment. If you really want a good circuit for the M@g, I recommend the ones made by Wayne Yamaguchi which you can buy from www.theledguy.com. He makes some of the best LED drivers out there. Very efficient and capable of driving high power LED's like they were supposed to be driven. In all my time taking lights apart, none can match the simplicity and efficiency of those designs. They're not cheap though but you get what you pay for.

 

[zeeexsixare]

The resistor in the Zetex data sheet is a current sense resistor. The circuit senses the voltage across the resistor to determine how long to turn on Q1 to charge the inductor. The IC is "constant current" meaning that it tries to maintain a constant load current. I say "tries" because it does not really do a good job of it and the circuit acts more or less like a voltage multiplier. Look at the runtime graphs of circuits using the Zetex. The output is not flat. This is not necessarily a disadvantage since the circuit is capable of sucking an alkaline cell dry which is desireable in some applications like survival.

I don't recall any temperature feedback in the circuit. In my opinion, it probably doesn't have one since it is designed to be cheap cheap cheap. That's why it is in the M@g. If you want to stack another resistor on top of the existing one, the circuit is not up to the task of driving the load very hard so your efforts may be met with some disappointment. If you really want a good circuit for the M@g, I recommend the ones made by Wayne Yamaguchi which you can buy from www.theledguy.com. He makes some of the best LED drivers out there. Very efficient and capable of driving high power LED's like they were supposed to be driven. In all my time taking lights apart, none can match the simplicity and efficiency of those designs. They're not cheap though but you get what you pay for.

Okay gotcha. So I was able to check the current at the LED... it's 620mA, and the battery draw is 630mA. This differs from EvilLithiumMan's results with his 2AA. I ruined the dome in the toaster oven trying to loosen the thermal epoxy, so now it won't focus too well, but oh well. The Seoul is on its way.

So generally, if I want to increase the current, I would want to reduce the resistor value (which is .030ohms on my 3AA) down? Is the current drive inversely proportional to the resistor value? I'm not sure how the current sense circuit works.

 

[zeeexsixare]

The resistor in the Zetex data sheet is a current sense resistor. The circuit senses the voltage across the resistor to determine how long to turn on Q1 to charge the inductor. The IC is "constant current" meaning that it tries to maintain a constant load current. I say "tries" because it does not really do a good job of it and the circuit acts more or less like a voltage multiplier. Look at the runtime graphs of circuits using the Zetex. The output is not flat. This is not necessarily a disadvantage since the circuit is capable of sucking an alkaline cell dry which is desireable in some applications like survival.

I don't recall any temperature feedback in the circuit. In my opinion, it probably doesn't have one since it is designed to be cheap cheap cheap. That's why it is in the M@g. If you want to stack another resistor on top of the existing one, the circuit is not up to the task of driving the load very hard so your efforts may be met with some disappointment. If you really want a good circuit for the M@g, I recommend the ones made by Wayne Yamaguchi which you can buy from www.theledguy.com. He makes some of the best LED drivers out there. Very efficient and capable of driving high power LED's like they were supposed to be driven. In all my time taking lights apart, none can match the simplicity and efficiency of those designs. They're not cheap though but you get what you pay for.

Maybe really what I'm looking for is the resistor value that I would need to acheive 1A output. The circuit is 60% there, but I'm really just wondering what I would need to get it all the way there. If you could direct me to appropriate resources on possibly allowing me to teach myself, that would be great too. Thanks for your expertise!

 

[CM]

How did you measure current to the LED?

I'm amazed it can drive 620mA. I would probably leave it there if it is 620mA. The heatsinking on the design is not adequate for anything but around 300-400mA. 1A will just cause the LED to heat up so bad that your output will drop to not much more than what you have at 620mA.

But to answer your question of what resistor value, yes, current is inversely proportional to the resistor value. I don't know what's in there now but to increase it from 620mA to 1000mA means that you must decrease resistor value by about 60%.

 

[zeeexsixare]

How did you measure current to the LED?

I'm amazed it can drive 620mA. I would probably leave it there if it is 620mA. The heatsinking on the design is not adequate for anything but around 300-400mA. 1A will just cause the LED to heat up so bad that your output will drop to not much more than what you have at 620mA.

But to answer your question of what resistor value, yes, current is inversely proportional to the resistor value. I don't know what's in there now but to increase it from 620mA to 1000mA means that you must decrease resistor value by about 60%.

Current was measured by de-epoxying the emitter from the metal pill, flipping the emitter up on its side so that one lead goes straight out the sides, and connecting a small copper wire down where the leads would disappear into the pill. Current was measured between the emitter and the copper wire.

Actually, the 2AA MagLed has a .050 resistor (from EvilLithiumMan's post, linked below), while my 3AA has a .030 resistor. This is nearly exactly the same value that EvilLithiumMan used to get his ~630mA using 2x NiMH cells. He soldered a .1 in parallel with the .050 and got the same current that I'm now getting. I'm wondering if I can extend that and bring the whole shebang to the full 1A. I mean, it's close, and I'm sure I can push it farther. What sort of Bad Things happen when the Zetex is pushed to 1A? What kind of resistor value would be good for getting the driving current up to this kind of level?

http://www.candlepowerforums.com/vb/printthread.php?t=131784

 

[CM]

The Zetex ZXSC300 doesn't bear much of the stress in biasing high. It's the switching transistor that bears the brunt of the current. I do not know what M@g uses but the FMMT617 is rated for a collector current of 3A and Pd of 625mW..