Schottky Diode Bi-Directional Logic Level Conversion

Schottky Diode Bi-Directional Logic Level Conversion

When connecting 3.3V devices and 5V devices voltage level conversion is required. The following circuit will allow this to be done bi-directionally using only a schottky diode and resistor. A schottky diode is used because it's forward voltage drop is less than a normal diode (~ 0.3V)

The diode protects the 3.3V side of the circuit from the higher 5V side by being reverse biased.

When the low voltage side is sending

  • 0V from the low voltage side gives 0V at the high voltage side
  • 3.3V from the low voltage side gives ~3V at the high voltage side due to the voltage drop across the diode which should be enough for a logic level high on mosts microcontrollers

When the high voltage side is sending

  • 0V from the high voltage side forward biases the diode through the pullup resistor and gives ~0.3V at the low voltage side which should register as a logic low on mosts microcontrollers.
  • 5V from the high voltage side reverse biases the diode. The low voltage side remains at 3.3V from the pullup resistor.

Limitations
This circuit is NOT suitable for I2C or SPI communication as the 3.3V (low) side cannot pull down the 5V (high) side.

This is a useful circuit for straighforward logic level conversion so long as the 5V high side of the circuit can accept the limitations of a logic level of 3V for high. This is easily within the logic level parameters of most microcontrollers.

If a full 5V logic level is required or for I2C and SPI consider the MOSFET Logic Level Conversion circuit

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