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AH1751 Hall Effect Latch Behavior

Created on: 1 September 2012
Updated on: 6 February 2023

In this article, the AH1751 hall effect latch behavior is explained and demonstrated. The AH1751 is a hall effect latch from Diodes Zetex. It has a single digital output in the form of an open-collector which is able to sink 50mA of current. This allows it to easily drive an LED directly through a current limiting resistor.

This video shows the behavior of the hall effect latch when the magnet from a small loudspeaker is moved near the sensor. An explanation follows.

Initially the hall effect latch switches on when power is applied to the circuit – this is not shown in the video. The hall effect latch was already switched off using a magnet before the video was recorded.

The AH1751 hall effect latch is bipolar. This means that the south pole of the magnet will switch the hall effect latch on and the north pole of the magnet will switch the latch off.

Because this device is a latch, it will remain in the state that it switched to after the magnetic field is removed – e.g. it will remain latched off if the north pole of the magnet is moved close enough to switch it off and then the magnet is removed.

Moving a magnet past the device causes it to latch in one state when the magnet approaches and then in the opposite state when the magnet passes by.

AH1751 Hall Effect Latch Circuit

The circuit used in the video to test the hall effect latch is very simple. Pin 1 of the device is connected to +9V. Pin 2 is connected to GND. A LED is connected to +9V through a 1k resistor onto pin 3 of the AH1751.

AH1751 Hall Effect Latch Pinout

In the datasheet of the AH1751, the pinout diagram for the device in a SIP3 package appears to be drawn with the flat face of the device up. The diagram is in fact for a device with the angled face (the face with the part number printed on it) facing up as shown here:

AH1751 hall effect latch pinout for SIP3 package

Part Numbers

The hall effect latch part number is AH1751-PG-B-A and the RS stock no. is 712-2845.

Note that the AH1751 is now an obsolete component which became obsolete some time after 2012 when this article was first written. The recommended replacement part is AH3774.