What Is a Level Shifter?
A level shifter (logic level converter) is a circuit that safely connects two devices operating at different logic voltage levels.
Why Is It Needed?
Modern chips run at 3.3 V or 1.8 V, older devices at 5 V. Feeding a 5 V signal directly into a 3.3 V input can damage the chip. A level shifter converts the signal to the level both sides understand.
Unidirectional and Bidirectional
Some converters work in only one direction (e.g. 5V→3.3V). For bidirectional lines like I2C, bidirectional converters (usually MOSFET-based) that work in both directions are used.
| Type | Use |
|---|---|
| Resistive divider | Simple, step-down only |
| MOSFET-based | Bidirectional (I2C) |
| Dedicated IC | Fast, multi-channel |
Speed Matters
Simple resistive methods corrupt high-speed signals. On fast interfaces like SPI, dedicated level-shifter ICs that minimize the delay are preferred.
Where Is It Used?
Connecting a 3.3 V MCU to a 5 V sensor/module, SD-card interfaces, bridging old and new chips and mixed-voltage systems.
Common Mistakes
- Direction error: using a unidirectional converter on a bidirectional line.
- Speed limit: a resistive divider falls short on a fast signal.
- Reference voltage: the correct supply must be connected for both sides.
Frequently Asked Questions
Is a resistor divider enough?+
Which one for I2C?+
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