Understanding Bidirectional Level Shifter for 3.3V to 5V & 5V to 3.3V

  • Thread starter likephysics
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In summary, the provided link is for a bidirectional level shifter that can shift between 3.3V and 5V. It works by using a MOSFET that conducts when the source is at 0V and does not conduct when the source is at 3.3V. This allows the drain to be at 5V when the source is at 3.3V and close to 0V when the source is at 0V. The level shifter also includes a reverse diode to allow for signal transmission from right to left. The reverse diode is built into all discrete MOSFETs and more information can be found at the provided link.
  • #1
likephysics
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I stumbled across this ckt - http://husstechlabs.com/support/tutorials/bi-directional-level-shifter/

It says it's a bidirectional level shifter (3.3 to 5v or 5 to 3.3v)

I can't figure out how it would work when level shifting 5v to 3.3v
When the drain is 5v, the source should be 3.3V
When the drain is 0v, the source should be 0v (how can the drain be 0v)?
 
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  • #2
If the source is at 3.3V, the MOSFET is not conducting, and the drain is at 5V.
If the source is at 0V, the MOSFET is conducting, and the drain is (close to) 0V as well.

Signal transmission goes from left to right.
 
  • #3
mfb said:
If the source is at 3.3V, the MOSFET is not conducting, and the drain is at 5V.
If the source is at 0V, the MOSFET is conducting, and the drain is (close to) 0V as well.

Signal transmission goes from left to right.

mfb, that part I get. But it says bidirectional level shifter. So it has to work from right to left also.
 
  • #4
Hmm... I would expect that the other direction needs a different setup.
A reverse diode (some MOSFETS have that included) can bring the left side to "low" if the right side is at 0V.
 
  • #5
mfb said:
Hmm... I would expect that the other direction needs a different setup.
A reverse diode (some MOSFETS have that included) can bring the left side to "low" if the right side is at 0V.

yup. That's it, its the rev diode.
 
  • #6
All discrete MOSFET has a built-in body diode. And try read this:
http://ics.nxp.com/support/documents/interface/pdf/an97055.pdf
 

1. What is a bidirectional level shifter?

A bidirectional level shifter is a device that allows for the translation of signals between two different voltage levels. It can convert signals from a lower voltage level, such as 3.3V, to a higher voltage level, such as 5V, and vice versa.

2. Why is a bidirectional level shifter important?

A bidirectional level shifter is important because many electronic devices operate at different voltage levels and require a way to communicate with each other. Without a level shifter, these devices would not be able to communicate effectively, leading to compatibility issues and potential damage to the devices.

3. How does a bidirectional level shifter work?

A bidirectional level shifter works by using a combination of MOSFET transistors and voltage dividers to convert the incoming signal from one voltage level to the desired output voltage level. It also ensures that the output signal is properly buffered and does not affect the input signal.

4. What is the difference between unidirectional and bidirectional level shifters?

Unidirectional level shifters can only convert signals in one direction, either from a lower voltage level to a higher one or vice versa. On the other hand, bidirectional level shifters can convert signals in both directions, making them more versatile and suitable for applications where bi-directional communication is required.

5. What are some common applications of bidirectional level shifters?

Bidirectional level shifters are commonly used in electronic devices such as microcontrollers, sensors, and communication modules to enable communication between devices with different voltage levels. They are also used in data transmission systems, battery-powered devices, and many other applications where voltage level conversion is necessary.

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