I'm presuming that an MOV (varistor) can be described with an equation
defining resistance versus voltage?

But I can't locate a site that gives such an equation.

Suggestions?

Thanks!

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

Jim Thompson wrote:
I'm presuming that an MOV (varistor) can be described with an equation
defining resistance versus voltage?

But I can't locate a site that gives such an equation.

Suggestions?

Thanks!

...Jim Thompson

It probably isn't single-valued, so you might need a subcircuit with a
few flip flops in it.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058

email: hobbs (atsign) electrooptical (period) net
http://electrooptical.net

On 04/28/2011 11:22 AM, Jim Thompson wrote:
I'm presuming that an MOV (varistor) can be described with an equation
defining resistance versus voltage?

But I can't locate a site that gives such an equation.

Suggestions?

Try different search terms? I'll bet that physicists don't think
"resistance vs. voltage". I'll bet they think "current vs. voltage".
So maybe search on "current in metal oxide varistors"?

What does Wikipedia say?

I'll bet that when you finally get down to the nitty-gritty, you'll
discover that there's a bazillion different effects, and for any given
MOV you just have to do a best fit to measured data. But I'm a skeptic.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

On Thu, 28 Apr 2011 14:26:25 -0400, Phil Hobbs
wrote:

Jim Thompson wrote:
I'm presuming that an MOV (varistor) can be described with an equation
defining resistance versus voltage?

But I can't locate a site that gives such an equation.

Suggestions?

Thanks!

...Jim Thompson

It probably isn't single-valued, so you might need a subcircuit with a
few flip flops in it.

Cheers

Phil Hobbs

It snaps back? I've modeled BVceo snap back without flip-flops, so,
if I can get a definitive equation (or curve), I can likely model it.

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Remember: Once you go over the hill, you pick up speed

On Thu, 28 Apr 2011 11:22:03 -0700, Jim Thompson
wrote:

I'm presuming that an MOV (varistor) can be described with an equation
defining resistance versus voltage?

But I can't locate a site that gives such an equation.

Suggestions?

Thanks!

...Jim Thompson

Here's one:-

http://www.orcad.com/documents/commu...pice/tn28.aspx

Basically just a voltage dependent resistance plus some parasitics-
they don't really have hysteresis.

On 04/28/2011 11:35 AM, Tim Wescott wrote:
On 04/28/2011 11:22 AM, Jim Thompson wrote:
I'm presuming that an MOV (varistor) can be described with an equation
defining resistance versus voltage?

But I can't locate a site that gives such an equation.

Suggestions?

Try different search terms? I'll bet that physicists don't think
"resistance vs. voltage". I'll bet they think "current vs. voltage". So
maybe search on "current in metal oxide varistors"?

What does Wikipedia say?

I'll bet that when you finally get down to the nitty-gritty, you'll
discover that there's a bazillion different effects, and for any given
MOV you just have to do a best fit to measured data. But I'm a skeptic.

Actually, Wikipedia has some curves, which pretty much back up my
hypothesis that it depends on the material. Think "lots of back to back
diodes in series-parallel", and you get an idea of the behavior.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

On Thu, 28 Apr 2011 14:45:31 -0400, Spehro Pefhany
wrote:

On Thu, 28 Apr 2011 11:22:03 -0700, Jim Thompson
wrote:

I'm presuming that an MOV (varistor) can be described with an equation
defining resistance versus voltage?

But I can't locate a site that gives such an equation.

Suggestions?

Thanks!

...Jim Thompson

Here's one:-

http://www.orcad.com/documents/commu...pice/tn28.aspx

Basically just a voltage dependent resistance plus some parasitics-
they don't really have hysteresis.


Thanks! Should have known... Brian Hirasuna was one of PSpice's best
support engineers, along with Charlie Edmondson (and Mohi :-)... they
actually know simulators _and_ circuits!

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Remember: Once you go over the hill, you pick up speed

On Thu, 28 Apr 2011 11:39:26 -0700, Jim Thompson
wrote:

On Thu, 28 Apr 2011 14:26:25 -0400, Phil Hobbs
wrote:

Jim Thompson wrote:
I'm presuming that an MOV (varistor) can be described with an equation
defining resistance versus voltage?

But I can't locate a site that gives such an equation.

Suggestions?

Thanks!

...Jim Thompson

It probably isn't single-valued, so you might need a subcircuit with a
few flip flops in it.

Cheers

Phil Hobbs

It snaps back? I've modeled BVceo snap back without flip-flops, so,
if I can get a definitive equation (or curve), I can likely model it.

...Jim Thompson

IIRC the V-I curves look a lot like those of neon lamps. There are some
similarities in the physical processes.

On Thu, 28 Apr 2011 11:39:26 -0700, Jim Thompson
wrote:

On Thu, 28 Apr 2011 14:26:25 -0400, Phil Hobbs
wrote:

Jim Thompson wrote:
I'm presuming that an MOV (varistor) can be described with an equation
defining resistance versus voltage?

But I can't locate a site that gives such an equation.

Suggestions?

Thanks!

...Jim Thompson

It probably isn't single-valued, so you might need a subcircuit with a
few flip flops in it.

Cheers

Phil Hobbs

It snaps back? I've modeled BVceo snap back without flip-flops, so,
if I can get a definitive equation (or curve), I can likely model it.

...Jim Thompson

IIRC the V-I curves look a lot like those of neon lamps. There are some
similarities in the physical processes.

Jim Thompson wrote:

I'm presuming that an MOV (varistor) can be described with an equation
defining resistance versus voltage?

But I can't locate a site that gives such an equation.

Anyone who uses an MOV after the invention of the Transzorb is an idiot.
http://www.vishay.com/diodes/protection-tvs-esd/

Hope This Helps!
Rich