Diode Selection for Automotive Circuit

0:34

Chat History

Project

Clarifying pull-down resistor connection.

Using Knowledge Base Tool.

Confirming resistor connection.

Based on Flux knowledge-base guidance on pull-up/pull-down networks, you absolutely should tie the pull-down resistor between the OR-ed output node (the common cathode) and Ground. In your case:

The cathodes of the two BAV170-Q diodes join to form the OR-ing node.
Place a pull-down resistor from that node directly to ground to sink any reverse leakage current.
A value in the 100 kΩ to 1 MΩ range is typical to hold the node at 0 V without significantly loading the forward-driven input.

211 days

acolborn

So to clarify in this set up, if one anode received 12V and the other did not, you would have 12V at the cathode (minus whatever forward voltage from the diode) but no voltage or current would come back through the other diode because of the lower impedance path of the resistor?

211 days

flux

0:31

Chat History

Project

Clarifying diode behavior.

Clarifying diode function.

Yes—that’s exactly right. Here’s what happens in your OR-ing network with a pull-down resistor:

When one anode drives 12 V, its BAV170-Q conducts and clamps the common cathode to about 12 V − Vf (≈11.3 V).
The pull-down resistor (e.g. a 100 kΩ resistor) from that cathode node to Ground provides a much lower-impedance path than the nanoamp-level reverse leakage of the other diode.
The second diode’s anode is reverse-biased, so only a tiny leakage current flows toward the cathode, and that leakage is sunk immediately by the resistor. As a result, the non-driven anode stays effectively at 0 V (apart from any microvolt-level leakage).

This ensures no appreciable voltage or current is “fed back” through the idle diode.

Select pull-down resistor

Choose OR-ing diode

Rename output net

Add output capacitor

Layout guidelines

211 days

Ready.

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