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logic level converter/Why you need one/02. What a converter does
Why you need one · 02 of 11

What a converter does

Two supplies in, the same signal out at a different height, in either direction. That is the whole job, and seeing its shape once makes every wiring question in this book easy.

Updated 2026-09-113 min readlogic level converter

Two sides, two supplies

Every board in both boxes has two sides. The A side is powered at 3.3 V and connects to your 3.3 V board. The B side is powered at 5 V and connects to the 5 V part. Those two supplies are how the converter knows what HIGH means on each side.

Same bits, two heights, either direction
3.3 V side talking
Who is talking
HIGH on the A side
3.3 V
HIGH on the B side
5 V
Direction pins to set
0
The pattern survives; only the height changes. A converter does not read your data or care what it means. It copies each HIGH and LOW across, lifting a 3.3 V HIGH to 5 V on the way.

No direction pin

A HIGH that goes in on A comes out as a HIGH on B, and the other way round. Whichever side pulls the wire first is the one being copied. That is what lets an I²C sensor answer on the same wire the board used to ask the question.

The 2-channel converter board at an angle: black with gold pads, two small three-legged transistors and four tiny resistors, A1, LV, GND and A2 printed down one edge and B1, HV, GND and B2 down the other.
The smallest board in the 27-pack. A1 and A2 on one edge, B1 and B2 on the other, and the power pins between them.

What it does not do

  • It does not power anything. LV and HV tell the converter the two voltages. The 5 V part still needs its own 5 V.
  • It does not drive loads. An LED, a relay or a motor needs far more current than a converter channel gives. Converters carry signals.
  • It does not change your data. It copies each HIGH and LOW across. It does not know what they mean, which is why one board works for any protocol it is fast enough for.

When it does not work

I powered my 5 V part through HV and it will not turn on

HV is an input, not an output. The converter uses it to learn what 5 V is and draws almost nothing from it. Feed the 5 V part from a real 5 V supply — often the same wire that goes to HV.

An LED on a converter output is dim, or does nothing

The channels are for signals, not loads. On a MOSFET board a HIGH arrives through a 10 kΩ resistor, which is half a milliamp at 5 V — far too little for an LED. Drive LEDs, relays and motors from their own driver, and use the converter only for the signal that tells the driver what to do.

My signal only ever goes one way. Is a two-way converter wrong for it?

No. A bidirectional channel carries a one-way signal perfectly well — it simply never gets asked to go the other way. Every board in both boxes is fine for this.

Alongside this page
The reference: all five boards and their specs
Where this goes next

Three sizes of one circuit, two chips on one footprint, and one rule that holds for all of them.

The five boards →

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