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Rheostat vs Bridge Rectifier


electronerd122

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I am trying to figure out the difference between a rheostat and a bridge rectifier. I tried Wikipedia, a bunch of resources and even a few videos, such as this one (url deleted) but I’m still not 100% sure about the difference. Can somebody here tell me like I’m 5 what the difference is.

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A rheostat is a variable resistor.  It controls how much current is delivered to a load.  The adjustment is made by moving a slider along to change resistance. A simple example is like this:

Rheostat-Circuit-Diagram.jpg

Light dimmers are an example, as is the heat adjustment knob for an electric range top burner.

A bridge rectifier uses diodes, which are arranged in in a manner to convert alternating current (current that alternates its direction flow rapidly) to direct current ( current the flows only in one direction.

A diagram would look like this:

bridge-rectifier-construction.png

D1-D4 are diodes. They act like one-way valves for electricity, letting it flow one way through them and stopping it from flowing the other. The arrangement of the diodes is such that no matter what direction the current in flowing from the source, it only flows one direction through RL.

If the source current is in one direction it passes from point A through D1 to point D then to the left through RL to point C, through D3 to point B, and then back to the source

When the source current reverses direction, it flows from point B through D4 to point D, then to the left through RL to point C, Then through D2 point A before returning to the source.

So, no matter what the direction the current flows from the source it flows through RL from right to left.

If it helps, think of the wires as streets and the ones with diodes are one-way streets,  It doesn't matter whether a car enters through A or B, it has to travel from right to left through RL.

Thus rheostats control the amount of current, and bridge rectifiers control the direction of current.

 

 

 

 

 

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40 minutes ago, Janus said:

Light dimmers are an example, as is the heat adjustment knob for an electric range top burner.

Generally an excellent explanation, +1,

but your examples need updating somewhat.

Both these examples were used in 1930's electrical equipment but have long since been abandoned as wasteful of power and potentially dangerous as they result in the excessive generation of heat.

https://electronics.stackexchange.com/questions/252352/setting-heat-on-electric-stove

 

On 1/24/2021 at 5:49 PM, electronerd122 said:

I am trying to figure out the difference between a rheostat and a bridge rectifier. I tried Wikipedia, a bunch of resources and even a few videos, such as this one (url deleted) but I’m still not 100% sure about the difference. Can somebody here tell me like I’m 5 what the difference is.

Electronerd, are you sure you meant a bridge rectifier ?

There are many sorts of bridges, but a simple bridge rectifier is not directly comparable to a rheostat.

A bridge is a particular sort of circuit configuration containing four circuit components arranged in a 'diamond pattern.

Some bridges are used for power control. This application would be comparable to using a rheostat for this purpose, but much more efficient.

Such a bridge would be called a 'controlled bridge rectifier' and contain at least one, probably two or four silicon controlled rectifiers (SCR) or TRIACs

 
Quote

Wiki

triode for alternating current
 
A TRIAC (triode for alternating current; also bidirectional triode thyristor or bilateral triode thyristor) is a three terminal electronic component that conducts current in either direction when triggered.

 

If you have been reading about bridges for power control are you sure you don't mean this sort of bridge rectifier ?

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1 hour ago, studiot said:

Generally an excellent explanation, +1,

but your examples need updating somewhat.

Both these examples were used in 1930's electrical equipment but have long since been abandoned as wasteful of power and potentially dangerous as they result in the excessive generation of heat.

https://electronics.stackexchange.com/questions/252352/setting-heat-on-electric-stove

 

Electronerd, are you sure you meant a bridge rectifier ?

There are many sorts of bridges, but a simple bridge rectifier is not directly comparable to a rheostat.

A bridge is a particular sort of circuit configuration containing four circuit components arranged in a 'diamond pattern.

Some bridges are used for power control. This application would be comparable to using a rheostat for this purpose, but much more efficient.

Such a bridge would be called a 'controlled bridge rectifier' and contain at least one, probably two or four silicon controlled rectifiers (SCR) or TRIACs

 

 

If you have been reading about bridges for power control are you sure you don't mean this sort of bridge rectifier ?

I was also wondering if he meant a Wheatstone bridge, which uses a similar arrangement with resistors.

And yes, rheostats are old-school, and energy wasters ( they also don't play well with compact florescent lights, which is why if you had an home with the old rheostat type light-dimmer switches, you wouldn't want to use CFLs with them).  Some of the newer dimmer circuits use SCRs ( Silicon Controlled Rectifiers) circuits, which use duty cycle to control power to the load.

And solid state power supplies often replace the old step-down transformer, bridge-rectifier, filter, voltage regulator power supplies.

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