Resistor capacitance

[Paul Stamler]

Hi folks:

Which has the lowest stray capacitance, given the same value and wattage
rating: a carbon comp, carbon film or metal film resistor?

Peace,
Paul

[Phil Allison]

"Paul Stamler"
>
> Which has the lowest stray capacitance, given the same value and wattage
> rating: a carbon comp, carbon film or metal film resistor?
>


** Carbon comp resistors have the best high frequency characteristics,
maintaining value up to the VHF range - they are widely used in RF
circuits for that reason. Since there is no spiralling of the resistance
material, as with the other types, they have only simple, bulk inductive and
capacitive parameters.

Why do you ask ?



............ Phil

[Phil Allison]

"Paul Stamler"
>
> Which has the lowest stray capacitance, given the same value and wattage
> rating: a carbon comp, carbon film or metal film resistor?
>


** Carbon comp resistors have the best high frequency characteristics,
maintaining value up to the VHF range - they are widely used in RF
circuits for that reason. Since there is no spiralling of the resistance
material, as with the other types, they have only simple, bulk inductive and
capacitive parameters.

Why do you ask ?



............ Phil

[Paul Stamler]

"Phil Allison" > wrote in message
...
>
> "Paul Stamler"
> >
> > Which has the lowest stray capacitance, given the same value and wattage
> > rating: a carbon comp, carbon film or metal film resistor?
> >
>
>
> ** Carbon comp resistors have the best high frequency characteristics,
> maintaining value up to the VHF range - they are widely used in RF
> circuits for that reason. Since there is no spiralling of the resistance
> material, as with the other types, they have only simple, bulk inductive
and
> capacitive parameters.
>
> Why do you ask ?

Looking for a resistor which will pipe as little RFI into later stages as
possible. It won't handle audio, just current-limiting a safety diode.

Peace,
Paul

[Paul Stamler]

"Phil Allison" > wrote in message
...
>
> "Paul Stamler"
> >
> > Which has the lowest stray capacitance, given the same value and wattage
> > rating: a carbon comp, carbon film or metal film resistor?
> >
>
>
> ** Carbon comp resistors have the best high frequency characteristics,
> maintaining value up to the VHF range - they are widely used in RF
> circuits for that reason. Since there is no spiralling of the resistance
> material, as with the other types, they have only simple, bulk inductive
and
> capacitive parameters.
>
> Why do you ask ?

Looking for a resistor which will pipe as little RFI into later stages as
possible. It won't handle audio, just current-limiting a safety diode.

Peace,
Paul

[Phil Allison]

"Paul Stamler"
> >
> > ** Carbon comp resistors have the best high frequency characteristics,
> > maintaining value up to the VHF range - they are widely used in RF
> > circuits for that reason. Since there is no spiralling of the
resistance
> > material, as with the other types, they have only simple, bulk inductive
> and
> > capacitive parameters.
> >
> > Why do you ask ?
>
> Looking for a resistor which will pipe as little RFI into later stages as
> possible. It won't handle audio, just current-limiting a safety diode.
>
>


** If you want a resistor to suppress RF coupling then why not use a wire
wound one lots of lovely inductance !!

You failed to mention the value and size of of the resistor - it matters a
lot when considering capacitive and inductive effects. A 50 ohm 1/2 watt
carbon comp resistor may be good ( ie still a 50 ohm resistor) to 100
z - but a 50 kohms one is good only to a few hundred kHz.




............. Phil

[Phil Allison]

"Paul Stamler"
> >
> > ** Carbon comp resistors have the best high frequency characteristics,
> > maintaining value up to the VHF range - they are widely used in RF
> > circuits for that reason. Since there is no spiralling of the
resistance
> > material, as with the other types, they have only simple, bulk inductive
> and
> > capacitive parameters.
> >
> > Why do you ask ?
>
> Looking for a resistor which will pipe as little RFI into later stages as
> possible. It won't handle audio, just current-limiting a safety diode.
>
>


** If you want a resistor to suppress RF coupling then why not use a wire
wound one lots of lovely inductance !!

You failed to mention the value and size of of the resistor - it matters a
lot when considering capacitive and inductive effects. A 50 ohm 1/2 watt
carbon comp resistor may be good ( ie still a 50 ohm resistor) to 100
z - but a 50 kohms one is good only to a few hundred kHz.




............. Phil

[Phil Allison]

"Phil Allison" >

> A 50 ohm 1/2 watt carbon comp resistor may be good ( ie still a 50 ohm
resistor) to 100
> z - but a 50 kohms one is good only to a few hundred kHz.


** Damn OE snipping my posts again !

The above should read "....... to 100 MHz - "




............... Phil

[Phil Allison]

"Phil Allison" >

> A 50 ohm 1/2 watt carbon comp resistor may be good ( ie still a 50 ohm
resistor) to 100
> z - but a 50 kohms one is good only to a few hundred kHz.


** Damn OE snipping my posts again !

The above should read "....... to 100 MHz - "




............... Phil

[nuke]

<< Hi folks:

Which has the lowest stray capacitance, given the same value and wattage
rating: a carbon comp, carbon film or metal film resistor?

Peace,
Paul >><BR><BR>


The expensive ones, of course!

;-)


--
Dr. Nuketopia
Sorry, no e-Mail.
Spam forgeries have resulted in thousands of faked bounces to my address.

[nuke]

<< Hi folks:

Which has the lowest stray capacitance, given the same value and wattage
rating: a carbon comp, carbon film or metal film resistor?

Peace,
Paul >><BR><BR>


The expensive ones, of course!

;-)


--
Dr. Nuketopia
Sorry, no e-Mail.
Spam forgeries have resulted in thousands of faked bounces to my address.

[Ben Bradley]

On Fri, 04 Jun 2004 06:37:56 GMT, "Paul Stamler"
> wrote:

>Looking for a resistor which will pipe as little RFI into later stages as
>possible. It won't handle audio, just current-limiting a safety diode.

How about putting N resistors in series, each of value
Desired_Resistance/N? This would lower capacitance by (almost) 1/N,
and get to the point where layout capacitance would become (more)
significant.

>Peace,
>Paul
>

-----
http://mindspring.com/~benbradley

[Ben Bradley]

On Fri, 04 Jun 2004 06:37:56 GMT, "Paul Stamler"
> wrote:

>Looking for a resistor which will pipe as little RFI into later stages as
>possible. It won't handle audio, just current-limiting a safety diode.

How about putting N resistors in series, each of value
Desired_Resistance/N? This would lower capacitance by (almost) 1/N,
and get to the point where layout capacitance would become (more)
significant.

>Peace,
>Paul
>

-----
http://mindspring.com/~benbradley

[Paul Stamler]

"Phil Allison" > wrote in message
...
>
> "Paul Stamler"
> > Looking for a resistor which will pipe as little RFI into later stages
as
> > possible. It won't handle audio, just current-limiting a safety diode.
> >
>
> ** If you want a resistor to suppress RF coupling then why not use a
wire
> wound one lots of lovely inductance !!

The thought has occurred to me. They tend to be bigger, though, and space is
at a premium.

> You failed to mention the value and size of of the resistor - it matters a
> lot when considering capacitive and inductive effects. A 50 ohm 1/2 watt
> carbon comp resistor may be good ( ie still a 50 ohm resistor) to 100
> z - but a 50 kohms one is good only to a few hundred kHz.

22 ohms, probably 1/4W or 1/2W.

Peace,
Paul

[Paul Stamler]

"Phil Allison" > wrote in message
...
>
> "Paul Stamler"
> > Looking for a resistor which will pipe as little RFI into later stages
as
> > possible. It won't handle audio, just current-limiting a safety diode.
> >
>
> ** If you want a resistor to suppress RF coupling then why not use a
wire
> wound one lots of lovely inductance !!

The thought has occurred to me. They tend to be bigger, though, and space is
at a premium.

> You failed to mention the value and size of of the resistor - it matters a
> lot when considering capacitive and inductive effects. A 50 ohm 1/2 watt
> carbon comp resistor may be good ( ie still a 50 ohm resistor) to 100
> z - but a 50 kohms one is good only to a few hundred kHz.

22 ohms, probably 1/4W or 1/2W.

Peace,
Paul

[Scott Dorsey]

In article >,
Paul Stamler > wrote:
>"Phil Allison" > wrote in message
...
>>
>> "Paul Stamler"
>> > Looking for a resistor which will pipe as little RFI into later stages
>as
>> > possible. It won't handle audio, just current-limiting a safety diode.
>> >
>>
>> ** If you want a resistor to suppress RF coupling then why not use a
>wire
>> wound one lots of lovely inductance !!
>
>The thought has occurred to me. They tend to be bigger, though, and space is
>at a premium.
>
>> You failed to mention the value and size of of the resistor - it matters a
>> lot when considering capacitive and inductive effects. A 50 ohm 1/2 watt
>> carbon comp resistor may be good ( ie still a 50 ohm resistor) to 100
>> z - but a 50 kohms one is good only to a few hundred kHz.
>
>22 ohms, probably 1/4W or 1/2W.

Smallest wirewound in the Digikey book is 1W, and physical size is
appropriate for that. IRC can do 1/2W ones, but that's not appropriate
for a DIY project because they want to do quantities.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

In article >,
Paul Stamler > wrote:
>"Phil Allison" > wrote in message
...
>>
>> "Paul Stamler"
>> > Looking for a resistor which will pipe as little RFI into later stages
>as
>> > possible. It won't handle audio, just current-limiting a safety diode.
>> >
>>
>> ** If you want a resistor to suppress RF coupling then why not use a
>wire
>> wound one lots of lovely inductance !!
>
>The thought has occurred to me. They tend to be bigger, though, and space is
>at a premium.
>
>> You failed to mention the value and size of of the resistor - it matters a
>> lot when considering capacitive and inductive effects. A 50 ohm 1/2 watt
>> carbon comp resistor may be good ( ie still a 50 ohm resistor) to 100
>> z - but a 50 kohms one is good only to a few hundred kHz.
>
>22 ohms, probably 1/4W or 1/2W.

Smallest wirewound in the Digikey book is 1W, and physical size is
appropriate for that. IRC can do 1/2W ones, but that's not appropriate
for a DIY project because they want to do quantities.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[normanstrong]

"Ben Bradley" > wrote in message
...
> On Fri, 04 Jun 2004 06:37:56 GMT, "Paul Stamler"
> > wrote:
>
> >Looking for a resistor which will pipe as little RFI into later
stages as
> >possible. It won't handle audio, just current-limiting a safety
diode.
>
> How about putting N resistors in series, each of value
> Desired_Resistance/N? This would lower capacitance by (almost) 1/N,
> and get to the point where layout capacitance would become (more)
> significant.

Be careful, or you'll find yourself building a bridged-T circuit,
which is much worse than a simple pole or zero.

Norm Strong

[normanstrong]

"Ben Bradley" > wrote in message
...
> On Fri, 04 Jun 2004 06:37:56 GMT, "Paul Stamler"
> > wrote:
>
> >Looking for a resistor which will pipe as little RFI into later
stages as
> >possible. It won't handle audio, just current-limiting a safety
diode.
>
> How about putting N resistors in series, each of value
> Desired_Resistance/N? This would lower capacitance by (almost) 1/N,
> and get to the point where layout capacitance would become (more)
> significant.

Be careful, or you'll find yourself building a bridged-T circuit,
which is much worse than a simple pole or zero.

Norm Strong