Re: [neonixie-l] How much voltage do cathode transistors need to be able to handle?

2015-10-23 Thread gregebert 
In my opinion, you want a transistor rated at the full anode-voltage in 
order to ensure reliability. This is probably more critical for MOS 
devices, because of the risk of oxide breakdown.

Basically, when the cathode driver is off, there is only leakage current, 
typically less than 1uA. Therefore, the voltage-drop across the anode 
resistor is about zero. If you consider the nixie to be a resistive device, 
it's voltage-drop will be about zero. Therefore, almost the entire anode 
voltage will appear across the driver. 

For bipolar devices, you might be able to use a Vceo rating less than the 
anode supply-voltage because breakdown isn't destructive as long as the 
current is limited. I suspect that NPN drivers with Vceo less than the 
anode voltage actually begin to breakdown, and as the current increases the 
voltage-drop across the tube & anode resistor will increase; this causes 
the voltage across the NPN to drop. At some point, equilibrium is reached. 
What matters the most is if the leakage current at equilibrium is enough to 
cause visible glowing. Leakage is exponentially temperature-dependent.

I thought about measuring the voltage-drop across an un-ionized nixie with 
a voltmeter, but my DMM's impedance is only 10Meg so I doubt I would get an 
accurate reading. 


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RE: [neonixie-l] How much voltage do cathode transistors need to be able to handle?

2015-10-23 Thread Bill van Dijk 
On re-reading your message, if one digit is lit, the voltage drop over the 
anode resistor can be calculated according to Ohm's law, and determines the 
"real" voltage present at the tube's anode (Ub - Ura). The remaining open 
switching transistors now see the calculated anode voltage minus the internal 
tube voltage drop. This is usually in the order of 70V or so, depending on your 
tubes and supply voltage. That voltage would jump significantly if all digits 
were switched off simultaneously, the condition I described in my first reply 
since there would now be 0V drop over the anode resistor. For that reason tube 
blanking should not be done by opening all cathode transistors unless they can 
handle that voltage.

 

Bill

 

From: neonixie-l@googlegroups.com [mailto:neonixie-l@googlegroups.com] On 
Behalf Of Bill van Dijk
Sent: Friday, October 23, 2015 8:14 AM
To: neonixie-l@googlegroups.com
Subject: RE: [neonixie-l] How much voltage do cathode transistors need to be 
able to handle?

 

According to Mr. Ohm, the voltage drop over a resistor is equal to the 
resistance multiplied by the current. In the off state, the current is 0A, so 
regardless of the value of the anode resistor, the drop over the anode resistor 
is 0V. The switching transistor therefore sees the full voltage minus the 
internal drop in the tube.

 

Bill

 

From: neonixie-l@googlegroups.com [mailto:neonixie-l@googlegroups.com] On 
Behalf Of alex nolan
Sent: Friday, October 23, 2015 3:30 AM
To: neonixie-l
Subject: [neonixie-l] How much voltage do cathode transistors need to be able 
to handle?

 

I'm struggling to get my head around this. But considering the following setup 
for a nixie tube, wouldn't the voltage across the cathode transistor be close 
to 0? Most of the voltage should be dropped across the tube itself, with the 
remained dropped across the current-limiting resistor, right? Does it have to 
do with the transistors keeping the other cathodes open? If so, how do we 
calculate those voltages given the tube is on, just to a different cathode?

 <http://www.mcamafia.de/nixie/images/nix_th01.jpg> 

 

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RE: [neonixie-l] How much voltage do cathode transistors need to be able to handle?

2015-10-23 Thread Bill van Dijk 
According to Mr. Ohm, the voltage drop over a resistor is equal to the 
resistance multiplied by the current. In the off state, the current is 0A, so 
regardless of the value of the anode resistor, the drop over the anode resistor 
is 0V. The switching transistor therefore sees the full voltage minus the 
internal drop in the tube.

 

Bill

 

From: neonixie-l@googlegroups.com [mailto:neonixie-l@googlegroups.com] On 
Behalf Of alex nolan
Sent: Friday, October 23, 2015 3:30 AM
To: neonixie-l
Subject: [neonixie-l] How much voltage do cathode transistors need to be able 
to handle?

 

I'm struggling to get my head around this. But considering the following setup 
for a nixie tube, wouldn't the voltage across the cathode transistor be close 
to 0? Most of the voltage should be dropped across the tube itself, with the 
remained dropped across the current-limiting resistor, right? Does it have to 
do with the transistors keeping the other cathodes open? If so, how do we 
calculate those voltages given the tube is on, just to a different cathode?

  

 

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Re: [neonixie-l] How much voltage do cathode transistors need to be able to handle?

2015-10-23 Thread alex nolan 
Thanks Bill! Is there any way to calculate that internal voltage drop when 
for unpowered cathodes (or when all the cathodes are off)? I don't believe 
I've seen it on any data sheet.

On Friday, October 23, 2015 at 8:29:41 AM UTC-4, Bill v wrote:
>
> On re-reading your message, if one digit is lit, the voltage drop over the 
> anode resistor can be calculated according to Ohm's law, and determines the 
> "real" voltage present at the tube's anode (Ub - Ura). The remaining open 
> switching transistors now see the calculated anode voltage minus the 
> internal tube voltage drop. This is usually in the order of 70V or so, 
> depending on your tubes and supply voltage. That voltage would jump 
> significantly if all digits were switched off simultaneously, the condition 
> I described in my first reply since there would now be 0V drop over the 
> anode resistor. For that reason tube blanking should not be done by opening 
> all cathode transistors unless they can handle that voltage.
>
>  
>
> Bill
>
>  
>
> *From:* neoni...@googlegroups.com  [mailto:
> neoni...@googlegroups.com ] *On Behalf Of *Bill van Dijk
> *Sent:* Friday, October 23, 2015 8:14 AM
> *To:* neoni...@googlegroups.com 
> *Subject:* RE: [neonixie-l] How much voltage do cathode transistors need 
> to be able to handle?
>
>  
>
> According to Mr. Ohm, the voltage drop over a resistor is equal to the 
> resistance multiplied by the current. In the off state, the current is 0A, 
> so regardless of the value of the anode resistor, the drop over the anode 
> resistor is 0V. The switching transistor therefore sees the full voltage 
> minus the internal drop in the tube.
>
>  
>
> Bill
>
>  
>
> *From:* neoni...@googlegroups.com  [
> mailto:n...@googlegroups.com ] *On Behalf Of *alex nolan
> *Sent:* Friday, October 23, 2015 3:30 AM
> *To:* neonixie-l
> *Subject:* [neonixie-l] How much voltage do cathode transistors need to 
> be able to handle?
>
>  
>
> I'm struggling to get my head around this. But considering the following 
> setup for a nixie tube, wouldn't the voltage across the cathode transistor 
> be close to 0? Most of the voltage should be dropped across the tube 
> itself, with the remained dropped across the current-limiting resistor, 
> right? Does it have to do with the transistors keeping the other cathodes 
> open? If so, how do we calculate those voltages given the tube is on, just 
> to a different cathode?
>
> <http://www.mcamafia.de/nixie/images/nix_th01.jpg>
>
>  
>
> -- 
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Re: [neonixie-l] How much voltage do cathode transistors need to be able to handle?

2015-10-23 Thread David Forbes 

Greg,

The Nixie tube is not at all a resistive device. It's like a 150V Zener 
diode. Therefore, your analysis doesn't make sense.


The Nixie tube has the ability to stand off about 70-100V before current 
flows, and then the current is microamperes. You can do this test easily 
with a potentiometer to supply a variable voltage (0-150V) to the tube, 
and a ~10K series resistor tying all cathodes together to the negative 
supply voltage. Measure the voltage across the 10K resistor as you turn 
up the voltage. Ohm's Law will tell you how much current is flowing for 
a given tube voltage.



On 10/23/15 11:00 AM, gregebert wrote:

If you consider the nixie to be a resistive device,
it's voltage-drop will be about zero. Therefore, almost the entire anode
voltage will appear across the driver.




--
David Forbes, Tucson AZ

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Re: [neonixie-l] How much voltage do cathode transistors need to be able to handle?

2015-10-23 Thread taylorjpt 
http://www.tayloredge.com/storefront/SmartNixie/DataSheets/Datasheet_SmartNixie.pdf

If you look at Fig20 of the above data sheet, it shows the voltage on the "6" 
cathode transistor while the tube cycles continuously from "0" to "9".  As you 
can see, the voltage on the transistor is not a single voltage but depends on 
its relationship to the other cathodes in the tube.  

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RE: [neonixie-l] How much voltage do cathode transistors need to be able to handle?

2015-10-23 Thread Bill van Dijk 
As you can see, no shortage of confusing answers and opinions. I thought 
science long ago abandoned the opinion or Socrates approach: -if one reasons 
long enough, the truth will reveal itself- long ago in favor of the empirical 
options. David Forbes is correct that the nixie behaves more like a zener, and 
cold cathode tubes (what a nixie essentially is) were often used as voltage 
stabilizers in the old tube era for exactly that property. 

 

I am somewhat at a loss to what you are trying to accomplish. The voltage value 
you are looking for varies, and at best you may establish a range for your 
tubes. It may vary from 70 up to as much as 100V. If you are looking for a 
transistor to use, I'd recommend the MPSA42 for low side switch, and an MPSA92 
for the high side if you wish to implement tube blanking. They are cheap, 
plentiful, and available in through hole as well as SMD. They have never failed 
me on any nixie tube so far. Check E-Pay for pricing if you are not in a rush.

 

Hope that helps

 

Bill

 

From: neonixie-l@googlegroups.com [mailto:neonixie-l@googlegroups.com] On 
Behalf Of alex nolan
Sent: Friday, October 23, 2015 9:09 AM
To: neonixie-l
Subject: Re: [neonixie-l] How much voltage do cathode transistors need to be 
able to handle?

 

Thanks Bill! Is there any way to calculate that internal voltage drop when for 
unpowered cathodes (or when all the cathodes are off)? I don't believe I've 
seen it on any data sheet.

On Friday, October 23, 2015 at 8:29:41 AM UTC-4, Bill v wrote:

On re-reading your message, if one digit is lit, the voltage drop over the 
anode resistor can be calculated according to Ohm's law, and determines the 
"real" voltage present at the tube's anode (Ub - Ura). The remaining open 
switching transistors now see the calculated anode voltage minus the internal 
tube voltage drop. This is usually in the order of 70V or so, depending on your 
tubes and supply voltage. That voltage would jump significantly if all digits 
were switched off simultaneously, the condition I described in my first reply 
since there would now be 0V drop over the anode resistor. For that reason tube 
blanking should not be done by opening all cathode transistors unless they can 
handle that voltage.

 

Bill

 

From: neoni...@googlegroups.com   
[mailto:neoni...@googlegroups.com  ] On Behalf Of Bill van Dijk
Sent: Friday, October 23, 2015 8:14 AM
To: neoni...@googlegroups.com  
Subject: RE: [neonixie-l] How much voltage do cathode transistors need to be 
able to handle?

 

According to Mr. Ohm, the voltage drop over a resistor is equal to the 
resistance multiplied by the current. In the off state, the current is 0A, so 
regardless of the value of the anode resistor, the drop over the anode resistor 
is 0V. The switching transistor therefore sees the full voltage minus the 
internal drop in the tube.

 

Bill

 

From: neoni...@googlegroups.com   [mailto:n...@googlegroups.com 
 ] On Behalf Of alex nolan
Sent: Friday, October 23, 2015 3:30 AM
To: neonixie-l
Subject: [neonixie-l] How much voltage do cathode transistors need to be able 
to handle?

 

I'm struggling to get my head around this. But considering the following setup 
for a nixie tube, wouldn't the voltage across the cathode transistor be close 
to 0? Most of the voltage should be dropped across the tube itself, with the 
remained dropped across the current-limiting resistor, right? Does it have to 
do with the transistors keeping the other cathodes open? If so, how do we 
calculate those voltages given the tube is on, just to a different cathode?

 <http://www.mcamafia.de/nixie/images/nix_th01.jpg> 

 

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