# Logic Level Converter Bi-Directional LV Fights Bench Power?

**URL:** <https://community.sparkfun.com/t/logic-level-converter-bi-directional-lv-fights-bench-power/66803>\
**Category:** Development Tools\
**Created:** [September 3, 2025, 11:04pm UTC](https://community.sparkfun.com/t/logic-level-converter-bi-directional-lv-fights-bench-power/66803 "2025-09-03T23:04:04Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![mattbvb](https://avatars.discourse-cdn.com/v4/letter/m/7c8e57/32.png) [@mattbvb](https://community.sparkfun.com/u/mattbvb)\
**Post date:** [September 3, 2025, 11:04pm UTC](https://community.sparkfun.com/t/logic-level-converter-bi-directional-lv-fights-bench-power/66803/1 "2025-09-03T23:04:04Z")

</div>

Have been using USB **Pocket AVR Programmer** and **Logic Level Converter - Bi-Directional** to run avrdude on Windows. Target is circuit with ATMega328P operating at 3.3v. This setup seems to work fine (for flashing, fuse bits). However, I noticed when I turned off bench power to the 328P, one of its connected LEDs stayed lit until I powered down the USB. I thought LV was an **input** only as a reference level. Obviously it cannot produce enough current to run a 328P. I wonder if there’s any risk of LV and bench power fighting each other. Should I be adding in a serial diode such that power flows only from the target to LV? The Hookup Guide says nothing about any of this.

---

<div class="post-metadata">

**Author:** ![dilshana](https://avatars.discourse-cdn.com/v4/letter/d/f4b2a3/32.png) [@dilshana](https://community.sparkfun.com/u/dilshana)\
**Post date:** [September 4, 2025, 5:41pm UTC](https://community.sparkfun.com/t/logic-level-converter-bi-directional-lv-fights-bench-power/66803/2 "2025-09-04T17:41:07Z")

</div>

If both supplies are the _same_ voltage and within tolerance (both ~3.3 V), the risk is low but not zero. You can still get currents circulating through protection diodes, MOSFETs, or pull-ups which can cause unexpected behaviour, inaccurate voltage sensing, or stress on components.

---

<div class="post-metadata">

**Author:** ![dilshana](https://avatars.discourse-cdn.com/v4/letter/d/f4b2a3/32.png) [@dilshana](https://community.sparkfun.com/u/dilshana)\
**Post date:** [September 7, 2025, 10:11am UTC](https://community.sparkfun.com/t/logic-level-converter-bi-directional-lv-fights-bench-power/66803/3 "2025-09-07T10:11:19Z")

</div>

The _probability_ of major damage is low if both are regulated 3.3 V supplies within tolerance. However, the _possibility_ of subtle issues or long-term stress is still there. Especially during power-up, power-down, or transient events.

---

<div class="post-metadata">

**Author:** ![mattbvb](https://avatars.discourse-cdn.com/v4/letter/m/7c8e57/32.png) [@mattbvb](https://community.sparkfun.com/u/mattbvb)\
**Post date:** [September 7, 2025, 2:28pm UTC](https://community.sparkfun.com/t/logic-level-converter-bi-directional-lv-fights-bench-power/66803/4 "2025-09-07T14:28:29Z")

</div>

I wasn’t too worried but the hookup guide should have said something about it. Your response implies that adding a protection diode is unnecessary. Thanks.