AVR-Chat

A quick question on the AVX Transguard transient voltage suppressors.  The
specs give a DC and AC working voltage.  The AC value looks like 0.7 x DC
value, so I assume it is an RMS value.   

If so, is it then ok to put a 3.3 V Transguard (DC working V = 3.3 V, AC
working V = 2.3 V) on, say, a 3.3 V level serial stream, even though the
stream could be labeled "AC"?  

Thanks, Steve
 

__________ Information from ESET Smart Security, version of virus signature
database 5762 (20110105) __________

The message was checked by ESET Smart Security.

http://www.eset.com

Steve -

Even though you may consider it AC, what really matters is the extreme  
peaks in normal operation, relative to the "ground" that the transient  
absorber is connected to). Transguards, and their relatives work fine  
with digital signals.

If your signal is between 0V and some V+, you need to choose one with  
the "working voltage" no smaller than V+. That is the largest voltage  
that the device is guaranteed NOT to conduct. As a quick example,  
suppose that you have a signal that swings between 0 and 5V. You would  
probably need to choose one about 5.2V and a breakdown about 7.5V (the  
two limit voltages won't be any closer than about this at 5V).

This demonstrates the "problems" with these devices. First, they are  
not very sharp breakdown and there is a lot of variability in the  
actual breakdown. One that is spec'd at 5.2V and 7.5V is simply  
guaranteed NOT to break down below 5.2V but to break down (at some  
specified forward current) at 7.5V. You can't tell where, between  
these limits, any individual device will do it. This means that (in  
this example) a 5V receiver might have to withstand a short-term  
transient of up to 7.5V during an extreme event. Actually, its not  
quite that bad because you will never have the spec'd 5A (or what ever  
the spec happens to be) in a real circuit.

I tend to use a transient absorber with a PTC "fuse".

If this is a high speed signal, you also need to be very careful about  
device capacitance. Its quite large for these things (often 100s of  
pf). There are, for example, low capacitance ones made especially for  
USB.

This brings us to bipolar vs unipolar. If its a logic signal, you want  
to use a unipolar one. If it is genuinely AC (swinging above and below  
the "ground" that the transient absorber is connected to), then you  
want a bipolar one.

Hope this helps

Jim Wagner
Oregon Research Electronics

On Jan 5, 2011, at 9:14 AM, Steve Hodge wrote:

> A quick question on the AVX Transguard transient voltage  
> suppressors. The
> specs give a DC and AC working voltage. The AC value looks like 0.7  
> x DC
> value, so I assume it is an RMS value.
>
> If so, is it then ok to put a 3.3 V Transguard (DC working V = 3.3  
> V, AC
> working V = 2.3 V) on, say, a 3.3 V level serial stream, even though  
> the
> stream could be labeled "AC"?
>
> Thanks, Steve
>
>
> __________ Information from ESET Smart Security, version of virus  
> signature
> database 5762 (20110105) __________
>
> The message was checked by ESET Smart Security.
>
> http://www.eset.com
>
>
>
> 



[Non-text portions of this message have been removed]

Hi,

Any one can suggest me a programmer for AT89C2051. I am very new into this and i want to program AT89C2051 for temperature display. pls. suggest me circuit also if possible.

Thank you in advance.

Regards,Deepak Patil.deepakpatil23@yahoo.com

--- On Thu, 1/6/11, Jim Wagner <wagnerj@proaxis.com> wrote:

From: Jim Wagner <wagnerj@proaxis.com>
Subject: Re: [AVR-Chat] AVX Transguard
To: AVR-Chat@yahoogroups.com
Date: Thursday, January 6, 2011, 9:44 AM

Steve -

Even though you may consider it AC, what really matters is the extreme  
peaks in normal operation, relative to the "ground" that the transient  
absorber is connected to). Transguards, and their relatives work fine  
with digital signals.

If your signal is between 0V and some V+, you need to choose one with  
the "working voltage" no smaller than V+. That is the largest voltage  
that the device is guaranteed NOT to conduct. As a quick example,  
suppose that you have a signal that swings between 0 and 5V. You would  
probably need to choose one about 5.2V and a breakdown about 7.5V (the  
two limit voltages won't be any closer than about this at 5V).

This demonstrates the "problems" with these devices. First, they are  
not very sharp breakdown and there is a lot of variability in the  
actual breakdown. One that is spec'd at 5.2V and 7.5V is simply  
guaranteed NOT to break down below 5.2V but to break down (at some  
specified forward current) at 7.5V. You can't tell where, between  
these limits, any individual device will do it. This means that (in  
this example) a 5V receiver might have to withstand a short-term  
transient of up to 7.5V during an extreme event. Actually, its not  
quite that bad because you will never have the spec'd 5A (or what ever  
the spec happens to be) in a real circuit.

I tend to use a transient absorber with a PTC "fuse".

If this is a high speed signal, you also need to be very careful about  
device capacitance. Its quite large for these things (often 100s of  
pf). There are, for example, low capacitance ones made especially for  
USB.

This brings us to bipolar vs unipolar. If its a logic signal, you want  
to use a unipolar one. If it is genuinely AC (swinging above and below  
the "ground" that the transient absorber is connected to), then you  
want a bipolar one.

Hope this helps

Jim Wagner
Oregon Research Electronics

On Jan 5, 2011, at 9:14 AM, Steve Hodge wrote:

> A quick question on the AVX Transguard transient voltage  
> suppressors. The
> specs give a DC and AC working voltage. The AC value looks like 0.7  
> x DC
> value, so I assume it is an RMS value.
>
> If so, is it then ok to put a 3.3 V Transguard (DC working V = 3.3  
> V, AC
> working V = 2.3 V) on, say, a 3.3 V level serial stream, even though  
> the
> stream could be labeled "AC"?
>
> Thanks, Steve
>
>
> __________ Information from ESET Smart Security, version of virus  
> signature
> database 5762 (20110105) __________
>
> The message was checked by ESET Smart Security.
>
> http://www.eset.com
>
>
>
> 



[Non-text portions of this message have been removed]



------------------------------------

Yahoo! Groups Links






      

[Non-text portions of this message have been removed]

Thanks, Jim.  I had chosen Transguards with a working voltage of 3.3 V
because I use 3.3 V signals (most DC, but a few up to 10-50 KHz).  It sounds
like you saying you would be a bit leery of doing that, and it would it be
better to go with ones with some headroom.  The next available working
voltage seems to be 5.6 V.  Would that be a better choice?

I looked at the AVX staticguard series, which is labeled as "for CMOS", but
in 0603 or larger package sizes the working voltage is "<= 18 V".  Same with
all the USB series.  Is it ok to use these for lower signal levels like 3.3
V?  I assume it must be because USB is 5 V.

Steve

| -----Original Message-----
| From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On
| Behalf Of Jim Wagner
| Sent: Wednesday, January 05, 2011 8:14 PM
| To: AVR-Chat@yahoogroups.com
| Subject: Re: [AVR-Chat] AVX Transguard
| 
| Steve -
| 
| Even though you may consider it AC, what really matters is the extreme
| peaks in normal operation, relative to the "ground" that the transient
| absorber is connected to). Transguards, and their relatives work fine
| with digital signals.
| 
| If your signal is between 0V and some V+, you need to choose one with
| the "working voltage" no smaller than V+. That is the largest voltage
| that the device is guaranteed NOT to conduct. As a quick example,
| suppose that you have a signal that swings between 0 and 5V. You would
| probably need to choose one about 5.2V and a breakdown about 7.5V (the
| two limit voltages won't be any closer than about this at 5V).
| 
| This demonstrates the "problems" with these devices. First, they are
| not very sharp breakdown and there is a lot of variability in the
| actual breakdown. One that is spec'd at 5.2V and 7.5V is simply
| guaranteed NOT to break down below 5.2V but to break down (at some
| specified forward current) at 7.5V. You can't tell where, between
| these limits, any individual device will do it. This means that (in
| this example) a 5V receiver might have to withstand a short-term
| transient of up to 7.5V during an extreme event. Actually, its not
| quite that bad because you will never have the spec'd 5A (or what ever
| the spec happens to be) in a real circuit.
| 
| I tend to use a transient absorber with a PTC "fuse".
| 
| If this is a high speed signal, you also need to be very careful about
| device capacitance. Its quite large for these things (often 100s of
| pf). There are, for example, low capacitance ones made especially for
| USB.
| 
| This brings us to bipolar vs unipolar. If its a logic signal, you want
| to use a unipolar one. If it is genuinely AC (swinging above and below
| the "ground" that the transient absorber is connected to), then you
| want a bipolar one.
| 
| Hope this helps
| 
| Jim Wagner
| Oregon Research Electronics
| 
| On Jan 5, 2011, at 9:14 AM, Steve Hodge wrote:
| 
| > A quick question on the AVX Transguard transient voltage
| > suppressors. The
| > specs give a DC and AC working voltage. The AC value looks like 0.7
| > x DC
| > value, so I assume it is an RMS value.
| >
| > If so, is it then ok to put a 3.3 V Transguard (DC working V = 3.3
| > V, AC
| > working V = 2.3 V) on, say, a 3.3 V level serial stream, even though
| > the
| > stream could be labeled "AC"?
| >
| > Thanks, Steve
| >
| >
| > __________ Information from ESET Smart Security, version of virus
| > signature
| > database 5762 (20110105) __________
| >
| > The message was checked by ESET Smart Security.
| >
| > http://www.eset.com
| >
| >
| >
| >
| 
| 
| 
| [Non-text portions of this message have been removed]
| 
| 
| 
| ------------------------------------
| 
| Yahoo! Groups Links
| 
| 
| 
| 
| __________ Information from ESET Smart Security, version of virus
| signature database 5763 (20110105) __________
| 
| The message was checked by ESET Smart Security.
| 
| http://www.eset.com
| 
| 
| 
| 
| __________ Information from ESET Smart Security, version of virus
| signature database 5763 (20110105) __________
| 
| The message was checked by ESET Smart Security.
| 
| http://www.eset.com
| 
| 
| __________ Information from ESET Smart Security, version of virus
| signature database 5764 (20110106) __________
| 
| The message was checked by ESET Smart Security.
| 
| http://www.eset.com
| 
 

__________ Information from ESET Smart Security, version of virus signature
database 5764 (20110106) __________

The message was checked by ESET Smart Security.

http://www.eset.com

You need to look at the tolerance specs. And, it depends, greatly, on what
the connected electronics will tolerate.

I just looked up the AVX parts, and they are spec'd a bit differently from
some of the others. The 3.3V parts are rated for a 5.0V +/-20% breakdown.
That means anywhere from 4.0V to 6.0V. with a "clamping" voltage of 12V at
1A.

If you look at the V-I chart in the spec sheet, it shows that the 3.3V
ones have a forward current of (about) 100ua at 3.3V, 1ma at 5V, 10ma at
about 6V, 100ma at maybe 7V, and 1A at around 8V.

So, they are NOT really "open" at 3.3V and not really breaking down at 5V.
So, your other circuitry had better be able to handle more than 6V!

The thing you will be relying on is that ESD has a pretty large source
impedance (some K ohms for human body model) and a source capacitance of
some 1000s of pf. Thus, the ability to source high currents is very
limited. This is what saves the circuit, in the end.

Jim

> Thanks, Jim.  I had chosen Transguards with a working voltage of 3.3 V
> because I use 3.3 V signals (most DC, but a few up to 10-50 KHz).  It
> sounds
> like you saying you would be a bit leery of doing that, and it would it be
> better to go with ones with some headroom.  The next available working
> voltage seems to be 5.6 V.  Would that be a better choice?
>
> I looked at the AVX staticguard series, which is labeled as "for CMOS",
> but
> in 0603 or larger package sizes the working voltage is "<= 18 V".  Same
> with
> all the USB series.  Is it ok to use these for lower signal levels like
> 3.3
> V?  I assume it must be because USB is 5 V.
>
> Steve
>
> | -----Original Message-----
> | From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On
> | Behalf Of Jim Wagner
> | Sent: Wednesday, January 05, 2011 8:14 PM
> | To: AVR-Chat@yahoogroups.com
> | Subject: Re: [AVR-Chat] AVX Transguard
> |
> | Steve -
> |
> | Even though you may consider it AC, what really matters is the extreme
> | peaks in normal operation, relative to the "ground" that the transient
> | absorber is connected to). Transguards, and their relatives work fine
> | with digital signals.
> |
> | If your signal is between 0V and some V+, you need to choose one with
> | the "working voltage" no smaller than V+. That is the largest voltage
> | that the device is guaranteed NOT to conduct. As a quick example,
> | suppose that you have a signal that swings between 0 and 5V. You would
> | probably need to choose one about 5.2V and a breakdown about 7.5V (the
> | two limit voltages won't be any closer than about this at 5V).
> |
> | This demonstrates the "problems" with these devices. First, they are
> | not very sharp breakdown and there is a lot of variability in the
> | actual breakdown. One that is spec'd at 5.2V and 7.5V is simply
> | guaranteed NOT to break down below 5.2V but to break down (at some
> | specified forward current) at 7.5V. You can't tell where, between
> | these limits, any individual device will do it. This means that (in
> | this example) a 5V receiver might have to withstand a short-term
> | transient of up to 7.5V during an extreme event. Actually, its not
> | quite that bad because you will never have the spec'd 5A (or what ever
> | the spec happens to be) in a real circuit.
> |
> | I tend to use a transient absorber with a PTC "fuse".
> |
> | If this is a high speed signal, you also need to be very careful about
> | device capacitance. Its quite large for these things (often 100s of
> | pf). There are, for example, low capacitance ones made especially for
> | USB.
> |
> | This brings us to bipolar vs unipolar. If its a logic signal, you want
> | to use a unipolar one. If it is genuinely AC (swinging above and below
> | the "ground" that the transient absorber is connected to), then you
> | want a bipolar one.
> |
> | Hope this helps
> |
> | Jim Wagner
> | Oregon Research Electronics
> |
> | On Jan 5, 2011, at 9:14 AM, Steve Hodge wrote:
> |
> | > A quick question on the AVX Transguard transient voltage
> | > suppressors. The
> | > specs give a DC and AC working voltage. The AC value looks like 0.7
> | > x DC
> | > value, so I assume it is an RMS value.
> | >
> | > If so, is it then ok to put a 3.3 V Transguard (DC working V = 3.3
> | > V, AC
> | > working V = 2.3 V) on, say, a 3.3 V level serial stream, even though
> | > the
> | > stream could be labeled "AC"?
> | >
> | > Thanks, Steve
> | >
> | >
> | > __________ Information from ESET Smart Security, version of virus
> | > signature
> | > database 5762 (20110105) __________
> | >
> | > The message was checked by ESET Smart Security.
> | >
> | > http://www.eset.com
> | >
> | >
> | >
> | >
> |
> |
> |
> | [Non-text portions of this message have been removed]
> |
> |
> |
> | ------------------------------------
> |
> | Yahoo! Groups Links
> |
> |
> |
> |
> | __________ Information from ESET Smart Security, version of virus
> | signature database 5763 (20110105) __________
> |
> | The message was checked by ESET Smart Security.
> |
> | http://www.eset.com
> |
> |
> |
> |
> | __________ Information from ESET Smart Security, version of virus
> | signature database 5763 (20110105) __________
> |
> | The message was checked by ESET Smart Security.
> |
> | http://www.eset.com
> |
> |
> | __________ Information from ESET Smart Security, version of virus
> | signature database 5764 (20110106) __________
> |
> | The message was checked by ESET Smart Security.
> |
> | http://www.eset.com
> |
>
>
> __________ Information from ESET Smart Security, version of virus
> signature
> database 5764 (20110106) __________
>
> The message was checked by ESET Smart Security.
>
> http://www.eset.com
>
>
>

Hmmm.   It's beginning to sound like a crap-shoot.    The device I'm
specifically looking at protecting is an AVR uC, its I/O lines specifically.
How would you do it, if I may ask?   The environment is a boat one,
basically an automobile one (engines, pumps, motors) with the added features
of local radar, VHF and HF radio transmissions, as well as wireless computer
and instrument transmissions.  Lightning too.   Shielded cables are a given,
as is spike suppression on inductive loads.   Thanks, Steve

From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
Of wagnerj@proaxis.com
Sent: Thursday, January 06, 2011 8:36 AM
To: AVR-Chat@yahoogroups.com
Subject: RE: [AVR-Chat] AVX Transguard

 

  

You need to look at the tolerance specs. And, it depends, greatly, on what
the connected electronics will tolerate.

I just looked up the AVX parts, and they are spec'd a bit differently from
some of the others. The 3.3V parts are rated for a 5.0V +/-20% breakdown.
That means anywhere from 4.0V to 6.0V. with a "clamping" voltage of 12V at
1A.

If you look at the V-I chart in the spec sheet, it shows that the 3.3V
ones have a forward current of (about) 100ua at 3.3V, 1ma at 5V, 10ma at
about 6V, 100ma at maybe 7V, and 1A at around 8V.

So, they are NOT really "open" at 3.3V and not really breaking down at 5V.
So, your other circuitry had better be able to handle more than 6V!

The thing you will be relying on is that ESD has a pretty large source
impedance (some K ohms for human body model) and a source capacitance of
some 1000s of pf. Thus, the ability to source high currents is very
limited. This is what saves the circuit, in the end.

Jim




://www.eset.com



[Non-text portions of this message have been removed]

Diodes?
 
> To: AVR-Chat@yahoogroups.com
> From: steve@terrafirma.us
> Date: Thu, 6 Jan 2011 09:10:34 -0800
> Subject: RE: [AVR-Chat] AVX Transguard
> 
> Hmmm. It's beginning to sound like a crap-shoot. The device I'm
> specifically looking at protecting is an AVR uC, its I/O lines specifically.
> How would you do it, if I may ask? The environment is a boat one,
> basically an automobile one (engines, pumps, motors) with the added features
> of local radar, VHF and HF radio transmissions, as well as wireless computer
> and instrument transmissions. Lightning too. Shielded cables are a given,
> as is spike suppression on inductive loads. Thanks, Steve
> 
> 
> 
... 		 	   		  

[Non-text portions of this message have been removed]

If data rates will allow, simply add a resistor between the AVR port and
the transient protector. I think (but may be wrong) that communication
with Atmel has established a limit of 0.1ma forward current in the
internal over-voltage protection diodes inside an AVR. Thus, if the
transient protector will practically limit the input voltage to 7.5V, then
a series resistor of (7.5V-5V)/0.1ma = 25K would be appropriate; I would
use 27K or 33K.

The thing to watch out for is rise/fall time at the port pin. A typical
CMOS input has 5-7pf. Lets assume 5pf for the small geometry recent
generation chips. So, in combination with 27K, the time constant would be
around 140ns and the rise/fall time would be about 300ns. So, as long as
the data rate on any protected input is less than 1bit/300ns, you would be
OK.

The transient protector is still important in your environment, especially
with the possibility of lightning. It will limit the input voltage to
something under 12V instead of 100s of volts.

Jim

> Hmmm.   It's beginning to sound like a crap-shoot.    The device I'm
> specifically looking at protecting is an AVR uC, its I/O lines
> specifically.
> How would you do it, if I may ask?   The environment is a boat one,
> basically an automobile one (engines, pumps, motors) with the added
> features
> of local radar, VHF and HF radio transmissions, as well as wireless
> computer
> and instrument transmissions.  Lightning too.   Shielded cables are a
> given,
> as is spike suppression on inductive loads.   Thanks, Steve
>
>
>
> From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
> Of wagnerj@proaxis.com
> Sent: Thursday, January 06, 2011 8:36 AM
> To: AVR-Chat@yahoogroups.com
> Subject: RE: [AVR-Chat] AVX Transguard
>
>
>
>
>
> You need to look at the tolerance specs. And, it depends, greatly, on what
> the connected electronics will tolerate.
>
> I just looked up the AVX parts, and they are spec'd a bit differently from
> some of the others. The 3.3V parts are rated for a 5.0V +/-20% breakdown.
> That means anywhere from 4.0V to 6.0V. with a "clamping" voltage of 12V at
> 1A.
>
> If you look at the V-I chart in the spec sheet, it shows that the 3.3V
> ones have a forward current of (about) 100ua at 3.3V, 1ma at 5V, 10ma at
> about 6V, 100ma at maybe 7V, and 1A at around 8V.
>
> So, they are NOT really "open" at 3.3V and not really breaking down at 5V.
> So, your other circuitry had better be able to handle more than 6V!
>
> The thing you will be relying on is that ESD has a pretty large source
> impedance (some K ohms for human body model) and a source capacitance of
> some 1000s of pf. Thus, the ability to source high currents is very
> limited. This is what saves the circuit, in the end.
>
> Jim
>
>
>
>
> ://www.eset.com
>
>
>
> [Non-text portions of this message have been removed]
>
>

Got it.  Thanks.   But just to make sure I truly get it, in your equation
"(7.5V-5V)/0.1ma", "7.5V" is the breakdown voltage and "5V" is the working
voltage?   In my case, with 3.3 V Transguards and Vcc = 3.3 V, the equation
would be (5.0-3.3)/0.1 = 17K?  

 

From a practical point of view, what is the significance of the "clamping
voltage"?

 

Clearly the Transguards are just fine for 50 KHz signals.

 

Steve

From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
Of wagnerj@proaxis.com
Sent: Thursday, January 06, 2011 10:08 AM
To: AVR-Chat@yahoogroups.com
Subject: RE: [AVR-Chat] AVX Transguard

 

  

If data rates will allow, simply add a resistor between the AVR port and
the transient protector. I think (but may be wrong) that communication
with Atmel has established a limit of 0.1ma forward current in the
internal over-voltage protection diodes inside an AVR. Thus, if the
transient protector will practically limit the input voltage to 7.5V, then
a series resistor of (7.5V-5V)/0.1ma = 25K would be appropriate; I would
use 27K or 33K.

The thing to watch out for is rise/fall time at the port pin. A typical
CMOS input has 5-7pf. Lets assume 5pf for the small geometry recent
generation chips. So, in combination with 27K, the time constant would be
around 140ns and the rise/fall time would be about 300ns. So, as long as
the data rate on any protected input is less than 1bit/300ns, you would be
OK.

The transient protector is still important in your environment, especially
with the possibility of lightning. It will limit the input voltage to
something under 12V instead of 100s of volts.

Jim






[Non-text portions of this message have been removed]

You need to limit the current going into the clamping diode IN the AVR.
So, under over-volt conditions, one end of the resistor is at the AVR's
Vcc and the other is at the transient protector's "clamping voltage".  I
simply chose 5V as an example of a system Vcc value.

Hmm, I slipped a decimal point in my example. I would choose 7.5V as the
clamping voltage and 3.3V as your system Vcc if that is how it operates.
That means a drop 4.2V and a minimum resistor value of 42K (I'd choose
47K).

Even with this larger resistor value, 50KHz will be just fine.

Jim

> Got it.  Thanks.   But just to make sure I truly get it, in your equation
> "(7.5V-5V)/0.1ma", "7.5V" is the breakdown voltage and "5V" is the working
> voltage?   In my case, with 3.3 V Transguards and Vcc = 3.3 V, the
> equation
> would be (5.0-3.3)/0.1 = 17K?
>
>
>
> From a practical point of view, what is the significance of the "clamping
> voltage"?
>
>
>
> Clearly the Transguards are just fine for 50 KHz signals.
>
>
>
> Steve
>
>
>
> From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
> Of wagnerj@proaxis.com
> Sent: Thursday, January 06, 2011 10:08 AM
> To: AVR-Chat@yahoogroups.com
> Subject: RE: [AVR-Chat] AVX Transguard
>
>
>
>
>
> If data rates will allow, simply add a resistor between the AVR port and
> the transient protector. I think (but may be wrong) that communication
> with Atmel has established a limit of 0.1ma forward current in the
> internal over-voltage protection diodes inside an AVR. Thus, if the
> transient protector will practically limit the input voltage to 7.5V, then
> a series resistor of (7.5V-5V)/0.1ma = 25K would be appropriate; I would
> use 27K or 33K.
>
> The thing to watch out for is rise/fall time at the port pin. A typical
> CMOS input has 5-7pf. Lets assume 5pf for the small geometry recent
> generation chips. So, in combination with 27K, the time constant would be
> around 140ns and the rise/fall time would be about 300ns. So, as long as
> the data rate on any protected input is less than 1bit/300ns, you would be
> OK.
>
> The transient protector is still important in your environment, especially
> with the possibility of lightning. It will limit the input voltage to
> something under 12V instead of 100s of volts.
>
> Jim
>
>
>
>
>
>
> [Non-text portions of this message have been removed]
>
>

I missed the part about radios, radar, etc. So, in addition to  
transient protectors, liberal use of lossy ferrites (beads, etc) are  
strongly called for.

There really is no one technology that will handle the full spectrum  
of ESD, lighting, general conducted EMI, and RF through microwave. I  
am sure that I'm not the only one on the list who has been through  
this commercially. Its NOT a trivial task and its particularly  
difficult to do with confidence in the absence of testing. Lacking  
that, you are going to have to rely on your own interpretation of  
other's experiences and hope that you understand what is offered.

Jim Wagner
Oregon Research Electronics

On Jan 6, 2011, at 9:15 AM, Cat C wrote:

>
> Diodes?
>
> > To: AVR-Chat@yahoogroups.com
> > From: steve@terrafirma.us
> > Date: Thu, 6 Jan 2011 09:10:34 -0800
> > Subject: RE: [AVR-Chat] AVX Transguard
> >
> > Hmmm. It's beginning to sound like a crap-shoot. The device I'm
> > specifically looking at protecting is an AVR uC, its I/O lines  
> specifically.
> > How would you do it, if I may ask? The environment is a boat one,
> > basically an automobile one (engines, pumps, motors) with the  
> added features
> > of local radar, VHF and HF radio transmissions, as well as  
> wireless computer
> > and instrument transmissions. Lightning too. Shielded cables are a  
> given,
> > as is spike suppression on inductive loads. Thanks, Steve
> >
> >
> >
> ..
>
> [Non-text portions of this message have been removed]
>
>
> 



[Non-text portions of this message have been removed]

Thanks, Jim.  You have been a good help.  I do have a bunch of RF ferrite
chokes that I put here and there.  They didn't do anything to solve the SSB
radio turning on the horn (!), but a shielded cable did.  

The tip about there being no one solution helps actually.  I guess I was
looking for that, and you've made it clear that's impossible.

So I'm going to do more or less what you suggested and use the 3.3 V
Transguards with a series resistor, at least on low frequency signal uC
ports.  However, I'm still struggling with the numbers.  

Poking around a bit on AVRFreaks seems to indicate the internal protection
diodes can handle up to 1 mA rather than the 0.1 mA you quoted.  Is that
what you meant by your "I think" caveat?   Taking this figure and the
clamping voltage of 12 V for the 3.3 V working voltage Transguards, I
compute (12-3.3)/1 = 8.7 K for the series resistor.  Actually, I suppose one
could substitute 3.8 V, the abs. max. voltage the port can take, and reduce
this to 8.2 K.  At any rate, being a bit conservative, choose 10 K.  Do
these numbers make sense?

For a max. frequency, the particular Transguard I chose (and happen to have
100 or so lying around) has a whopping high capacitance of 5000 pF.  If I
continue to use these, I compute a max. usable frequency of about 10 KHz.
Do you concur?  This would be ok for many signals I have.

However, I do have some higher frequency signals.  I looked at the
UltraGuard series, which are for "high speed clock...application".  But the
lowest capacitance for, say, a 5 V one, is only 175 pF, not a heck of an
improvement by the above numbers.  Plus there is no breakdown or clamping
voltage in the data sheet.  So I continue to be confused.  Do these work
differently or something?

Steve

| -----Original Message-----
| From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On
| Behalf Of Jim Wagner
| Sent: Friday, January 07, 2011 9:21 PM
| To: AVR-Chat@yahoogroups.com
| Subject: Re: [AVR-Chat] AVX Transguard
| 
| I missed the part about radios, radar, etc. So, in addition to
| transient protectors, liberal use of lossy ferrites (beads, etc) are
| strongly called for.
| 
| There really is no one technology that will handle the full spectrum
| of ESD, lighting, general conducted EMI, and RF through microwave. I
| am sure that I'm not the only one on the list who has been through
| this commercially. Its NOT a trivial task and its particularly
| difficult to do with confidence in the absence of testing. Lacking
| that, you are going to have to rely on your own interpretation of
| other's experiences and hope that you understand what is offered.
| 
| Jim Wagner
| Oregon Research Electronics
| 
| On Jan 6, 2011, at 9:15 AM, Cat C wrote:
| 
 

__________ Information from ESET Smart Security, version of virus signature
database 5769 (20110108) __________

The message was checked by ESET Smart Security.

http://www.eset.com
 
 

__________ Information from ESET Smart Security, version of virus signature
database 5769 (20110108) __________

The message was checked by ESET Smart Security.

http://www.eset.com

Yes, that was the "I think" caveat. That suggests being able to use  
smaller limiting resistors.

The high capacitance CAN be a challenge. Sometimes, it will actually  
help. Whether it hurts or helps depends on the "source resistance" of  
the signal source. Logic is typically 80-200 ohms (tending to be a bit  
larger with Vcc of 3.3V compared to 5V). It is THAT resistance, in  
combination with the transient protector capacitance, that sets the  
rise and fall times. If the signal source is the AVR and is "talking"  
through a series current limit resistor such as what we have been  
talking about, you need to add that resistor value to the 100 ohms or  
so output resistance to determine as rise time estimate.

I took a look at the AVX spec sheets. particularly,

//www.avx.com/docs/masterpubs/transgrd.pdf

There, I get the impression that they all have, pretty much, the same  
I-V characteristics.

HF-SSB can be particularly problematic. The high transmitter power,  
the close proximity of the antenna to other wiring, and the fact that  
the frequency CAN be in the range that the micro will respond to,  
makes it difficult. Further, the "real" problem is often signal  
rectification. To solve that, you just have to keep the signal small  
in your circuitry. That often involves shielding, as you have  
observed, good filters, good connections between board ground and  
shields. On particularly problematic lines, you may have to add a  
multi-section L-C lowpass filter to get the levels low enough.

Jim
On Jan 8, 2011, at 10:56 AM, Steve Hodge wrote:

> Thanks, Jim. You have been a good help. I do have a bunch of RF  
> ferrite
> chokes that I put here and there. They didn't do anything to solve  
> the SSB
> radio turning on the horn (!), but a shielded cable did.
>
> The tip about there being no one solution helps actually. I guess I  
> was
> looking for that, and you've made it clear that's impossible.
>
> So I'm going to do more or less what you suggested and use the 3.3 V
> Transguards with a series resistor, at least on low frequency signal  
> uC
> ports. However, I'm still struggling with the numbers.
>
> Poking around a bit on AVRFreaks seems to indicate the internal  
> protection
> diodes can handle up to 1 mA rather than the 0.1 mA you quoted. Is  
> that
> what you meant by your "I think" caveat? Taking this figure and the
> clamping voltage of 12 V for the 3.3 V working voltage Transguards, I
> compute (12-3.3)/1 = 8.7 K for the series resistor. Actually, I  
> suppose one
> could substitute 3.8 V, the abs. max. voltage the port can take, and  
> reduce
> this to 8.2 K. At any rate, being a bit conservative, choose 10 K. Do
> these numbers make sense?
>
> For a max. frequency, the particular Transguard I chose (and happen  
> to have
> 100 or so lying around) has a whopping high capacitance of 5000 pF.  
> If I
> continue to use these, I compute a max. usable frequency of about 10  
> KHz.
> Do you concur? This would be ok for many signals I have.
>
> However, I do have some higher frequency signals. I looked at the
> UltraGuard series, which are for "high speed clock...application".  
> But the
> lowest capacitance for, say, a 5 V one, is only 175 pF, not a heck  
> of an
> improvement by the above numbers. Plus there is no breakdown or  
> clamping
> voltage in the data sheet. So I continue to be confused. Do these work
> differently or something?
>
> Steve
>
> | -----Original Message-----
> | From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On
> | Behalf Of Jim Wagner
> | Sent: Friday, January 07, 2011 9:21 PM
> | To: AVR-Chat@yahoogroups.com
> | Subject: Re: [AVR-Chat] AVX Transguard
> |
> | I missed the part about radios, radar, etc. So, in addition to
> | transient protectors, liberal use of lossy ferrites (beads, etc) are
> | strongly called for.
> |
> | There really is no one technology that will handle the full spectrum
> | of ESD, lighting, general conducted EMI, and RF through microwave. I
> | am sure that I'm not the only one on the list who has been through
> | this commercially. Its NOT a trivial task and its particularly
> | difficult to do with confidence in the absence of testing. Lacking
> | that, you are going to have to rely on your own interpretation of
> | other's experiences and hope that you understand what is offered.
> |
> | Jim Wagner
> | Oregon Research Electronics
> |
> | On Jan 6, 2011, at 9:15 AM, Cat C wrote:
> |
>
>
> __________ Information from ESET Smart Security, version of virus  
> signature
> database 5769 (20110108) __________
>
> The message was checked by ESET Smart Security.
>
> http://www.eset.com
>
>
>
> __________ Information from ESET Smart Security, version of virus  
> signature
> database 5769 (20110108) __________
>
> The message was checked by ESET Smart Security.
>
> http://www.eset.com
>
>
>
> 



[Non-text portions of this message have been removed]

> From: Steve Hodge
> 
> Hmmm.   It's beginning to sound like a crap-shoot.    The device I'm
> specifically looking at protecting is an AVR uC, its I/O lines specifically.
> How would you do it, if I may ask?   The environment is a boat one,
> basically an automobile one (engines, pumps, motors) with the added features
> of local radar, VHF and HF radio transmissions, as well as wireless computer
> and instrument transmissions.  Lightning too.   Shielded cables are a given,
> as is spike suppression on inductive loads.

Hi Steve,

Preface: This is my first use of transorbs and my knowledge has come from this list,
the Electronics_101 list, the datasheets, as well as Internet reading and, as to
picking exact parts, to some extent using the time-honored flip-of-a-coin :-)

My application involves long cable runs outdoors and is subject to a lot of
(Florida) lightning.  Here is what I have had in the field on two prototype boards
successfully for over a year:

Nominal 12vdc Power input from a power supply over 1,000 feet away (in order from
input to regulator):
	- 5x10 mm, 250ma fast blow glass cartridge fuse 
	- LittelFuse SA15A Transorb to GND (Mouser# 576-SA15A)

Analog inputs connected to 100's of feet of aluminum rail, nominal signal voltage
0-5vdc (in order from input to regulator):
	- 5x10 mm, 100ma fast blow glass cartridge fuse
	- LittelFuse SAC7.0 Transorb to GND (Mouser# 576-SAC7.0) and
		5k resistor to unregulated V+ (rail bias)
	- in series with a 100k resistor (limit current to ADC pin and part of R/C
w/cap below)
	- .1 mfd cap to GND (to somewhat filter noise, I'm only interested 
		in fairly slow DC change - akin to sensing a switch)

The fuse protects the Transorb from major hits.  IIRC the transorbs can take a
"surge current" of 70A - significant, but that's for a very short time.

This has served me well on the prototype boards.  I had several cases when one or
more of the fuses blew due to nearby lightning strikes.

On one occasion the system appears to have taken a direct, or nearly direct
lightning strike.  One board was heavily blackened on the back (trace side) with
several vaporized traces.  The other board had one or two vaporized traces.  

Casualties:
	- Several lost traces
	- Most of the fuses were blown
	- A couple of Transorbs failed (shorted - which is good because it still
protects the rest of the circuit) 
	- One processor (PDIP ATMega16) was blown (oddly enough, it was on the board
with the least visible damaged)

A total of about $8 in parts and some wire to replace the blown traces and the
boards were back in service.

Considering the severity of the strike I was very happy with the results.

The big thing I learned from this was "pay attention to signal routing on the
board".  I expected that, when the fuse blew it would isolate the circuit enough
(due to the, now large, physical separation of the ends of the fuse) from high
voltage excursions, but, I forgot to pay attention to what was going on on the back
of the board.

From what I can tell, it looks like everything went as planned: the fuses (and a
couple of transorbs) sacrificed themselves to protect others - but - the (now
isolated) input passed close to other traces which allowed the (now released to
rise) spike voltage to jump across and attack the rest of the board.

Lesson:  Be sure that the input is separated from everything else by a physical
separation at least as large as created when the fuse blows!

I have no illusions of being able to protect the boards from direct strikes but this
seems to be working for me.

I have looked at the possibility of using the solid-state resettable fuses (I forget
the name for them at the moment) but rejected them because a) they don't provide the
desirable physical separation when blown, and b) I don't know if they are fast
enough to protect the transorb.

Note that I selected the smallest fuse I had on hand that would support the nominal
currents involved.  One thing I have to look into is some testing to pick a fuse
that is large enough to allow the transorb to take as much of a hit as possible
without failing (to having to replace unnecessarily blown fuses in cases where the
transorb could have absorbed the surge) but not so large that the transorbs fail.  

To do this one has to 'assume' (watch out, there's that word again ...) an expected
surge profile (short high voltage, long high current, etc.).  I'm just planning on
charging a large cap to maybe 1-2Kv and discharging it into the input (maybe via a
low value resistor, have to look at that).  I'll keep increasing the fuse size until
something fails and then decrease it by, let's say, 20% for a safety margin.

BTW:  I have an old defibrillator.  I wonder if that would make a good test source
:-)

I hope this is useful.
 
Cheers,

Chuck Hackett
"Good judgment comes from experience, experience comes from bad judgment"
7.5" gauge Union Pacific Northern (4-8-4) 844 http://www.whitetrout.net/Chuck

Jim, a quick question.  It's probably a dumb one, but I'm getting a bit
paranoid that I could be missing something.  I assume the leakage current
only occurs when the line is high, or more correctly, above ground (ignoring
transient events).  If so any active-low line that is pulled high when not
asserted (say using the internal pull-up in the uC) would be incurring this
leakage current when "idle".  Is that correct?  

The Transguard series has a pretty high leakage current, 100 uA.  So with,
say, 50 lines pulled high, all with a Transguard, this adds up to 5 mA, way
more than what the AVR itself will consume on average!   It's beginning to
look like another "gotcha" to me and I should really switch to lower leakage
current ones like the Staticguards at 10 uA.

Thanks, Steve

| -----Original Message-----
| From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On
| Behalf Of Jim Wagner
| Sent: Saturday, January 08, 2011 11:57 AM
| To: AVR-Chat@yahoogroups.com
| Subject: Re: [AVR-Chat] AVX Transguard
| 
| Yes, that was the "I think" caveat. That suggests being able to use
| smaller limiting resistors.
| 
| The high capacitance CAN be a challenge. Sometimes, it will actually
 

__________ Information from ESET Smart Security, version of virus signature
database 5775 (20110110) __________

The message was checked by ESET Smart Security.

http://www.eset.com

Steve -

I would hardly call it paranoia. That is exactly how I would interpret it.

One thing to watch out for with lower leakage devices. The spread between
the hold-off voltage (working voltage) and the breakdown voltage MAY be
greater which could translate into a larger series resistor between the
transient protector and the micro. Not saying that this IS the case, just
check it before running down that path. Also check device capacitances.
Easy to overlook.

Jim

> Jim, a quick question.  It's probably a dumb one, but I'm getting a bit
> paranoid that I could be missing something.  I assume the leakage current
> only occurs when the line is high, or more correctly, above ground
> (ignoring
> transient events).  If so any active-low line that is pulled high when not
> asserted (say using the internal pull-up in the uC) would be incurring
> this
> leakage current when "idle".  Is that correct?
>
> The Transguard series has a pretty high leakage current, 100 uA.  So with,
> say, 50 lines pulled high, all with a Transguard, this adds up to 5 mA,
> way
> more than what the AVR itself will consume on average!   It's beginning to
> look like another "gotcha" to me and I should really switch to lower
> leakage
> current ones like the Staticguards at 10 uA.
>
> Thanks, Steve
>
> | -----Original Message-----
> | From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On
> | Behalf Of Jim Wagner
> | Sent: Saturday, January 08, 2011 11:57 AM
> | To: AVR-Chat@yahoogroups.com
> | Subject: Re: [AVR-Chat] AVX Transguard
> |
> | Yes, that was the "I think" caveat. That suggests being able to use
> | smaller limiting resistors.
> |
> | The high capacitance CAN be a challenge. Sometimes, it will actually
>
>
> __________ Information from ESET Smart Security, version of virus
> signature
> database 5775 (20110110) __________
>
> The message was checked by ESET Smart Security.
>
> http://www.eset.com
>
>
>