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Ice Tube Clock Help
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Please be positive and constructive with your questions and comments.

Re: Ice Tube Clock Help

by jarchie on Sun Mar 16, 2014 4:56 pm

Russell 27 wrote:Every time I think I know something about electricity, or how that works, something else comes along and WHAAAAAAT... Any part made of CMOS construction is static sensitive, seems like almost all modern parts. I've pulled some real blunders and never destroyed a microcontoller or MOSFET that I know of, from ESD, and I'm not fanatical about it.

I agree... It doesn't seem like electrostatic damage alone explains the frequency of the flaky segment problem. My suspicion is that the problem is due to voltage oscillation caused by a dodgy Q3, and the fact that the ZVP3306 PFET included with the kit does not turn fully on would make Q3 more prone to oscillation issues.

The cause of Q3-related oscillation could be normal part-to-part variation where occasionally marginal ZVP3306 PFETs are the problem. Or the cause could be due to minor electrostatic damage. Or the cause might be both or either in different clocks.

Regardless, I suspect that switching to a PFET that turns on fully would prevent the flaky segment problem from cropping up so often.

Russell 27 wrote:I would say that P channel MOSFET's are harder to turn on than N channel, especially in this package size, and circuit voltage. If the tube was switched by an N channel instead, I don't think you would see this problem.

You're probably right, but I also think that a better PFET is another way to prevent the problem. The display and VFD chips should only pull 100 mA, and at that current, the ZVP2110A will reach saturation with a gate-source voltage of only -4. The Ice Tube Clock provides around -4.8, certainly enough for the ZVP2110A, although not quite sufficient for the ZVP3306.
--John <www.jarchie.com/email>

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Re: Ice Tube Clock Help

by Russell 27 on Mon Mar 17, 2014 2:10 pm

When you talk about this suspect voltage oscillation, have you ever put one on the scope?
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Re: Ice Tube Clock Help

by jarchie on Mon Mar 17, 2014 2:55 pm

No, unfortunately I've never seen one of these clocks in person, but another user, Frank_tt, has performed that test.

Frank_tt had the classic flaky segment problem. Voltages at all Q3 pins were normal when the clock was active. The only thing that was amiss was an odd ripple on the output of Q3. Reversing Q3 restored the display but sleep no longer worked--presumably due to conduction through the body diode. Replacing Q3 with a ZVP2110A solved his problem.

By the way, Frank_tt's thread is where I first speculated that oscillation--and not current--is responsible for the flaky segment problem. In the ensuing discussion with Phil, I provide some additional circumstantial evidence from other user's posts. That discussion might be worth a read, if you're interested.
--John <www.jarchie.com/email>

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Joined: Sun Jun 24, 2012 2:16 pm
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Please be positive and constructive with your questions and comments.