Concerning the need for an anti-swamp resistor(s)

  • Thread starter Scott McKie
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In summary, .1R/5W resistors, known as "anti-swamp" resistors, are necessary in a multi-parallel legged current booster schematic using an LM317 variable voltage regulator, in order to balance the current and prevent overheating or failure. This is not required in a single parallel legged current booster schematic using the same LM317, unless it is being used in an audio amplifier configuration. The resistors help to keep the currents and temperatures similar by compensating for the negative temperature coefficient of power BJTs.
  • #1
Scott McKie
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Why are .1R/5W resistors, known as "anti-swamp" resistors, required in a multi-parallel legged current booster schematic using an LM317 variable voltage regulator schematic when no resistor is shown on a single parallel legged current booster schematic using the same LM317? variable voltage regulator? This is not to be used in a audio amplifier configuration.
 
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  • #2
Scott McKie said:
Why are .1R/5W resistors, known as "anti-swamp" resistors, required in a multi-parallel legged current booster schematic using an LM317 variable voltage regulator schematic when no resistor is shown on a single parallel legged current booster schematic using the same LM317? variable voltage regulator? This is not to be used in a audio amplifier configuration.

Link to schematic...? :smile:
 
  • #3
Hello Berkeman,
I am do not see any schematic (reference your reply) to link to. Can you please send me directions on where and how to do so.
Thanks,
Scott McKie
 
  • #4
Scott McKie said:
Hello Berkeman,
I am do not see any schematic (reference your reply) to link to. Can you please send me directions on where and how to do so.
Thanks,
Scott McKie

Where did you see the circuit? Can you scan it and upload it? Or worst case, take a picture of it with your cellphone and upload the picture? I'm not familiar with the term "swamp resistor", so I'm not sure what to do a Google Images search for...
 
  • #5
The resistors balance the current from the multiple supplies. If one supply provides more current then it may get hotter and the temperature coefficient may increase the current further, leading to failure. It will be swamped.

The VBE of power BJTs has a negative temperature coefficient. A series 0R1 is sufficient to keep the currents and temperatures similar.
 
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Likes berkeman

What is an anti-swamp resistor?

An anti-swamp resistor is a type of resistor that is specifically designed to resist the effects of moisture and humidity in a swampy or wet environment. It is used to protect electronic devices and circuits from damage caused by these conditions.

Why is an anti-swamp resistor needed?

In swampy or wet environments, the high levels of moisture and humidity can cause corrosion and short circuits in electronic devices. An anti-swamp resistor helps to prevent this damage and ensure the proper functioning of the devices.

How does an anti-swamp resistor work?

An anti-swamp resistor is typically made of materials that are resistant to corrosion and moisture, such as carbon or metal film. It is also coated with a protective layer to further prevent moisture from reaching the resistor. This combination of materials and coatings allows the resistor to function properly in wet or humid conditions.

Where are anti-swamp resistors commonly used?

Anti-swamp resistors are commonly used in outdoor electronics, such as those found in military equipment, agricultural machinery, and outdoor lighting. They are also used in industries where high levels of moisture and humidity are present, such as marine or oil and gas industries.

Are there different types of anti-swamp resistors?

Yes, there are different types of anti-swamp resistors available, such as thick film resistors, thin film resistors, and metal film resistors. The type of resistor used will depend on the specific application and the level of moisture resistance required.

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