How to Amplify a 2.5 mA Pulse to Drive a Latching Relay?

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Discussion Overview

The discussion centers around the amplification of a 2.5 mA pulse to drive a latching relay. Participants explore methods for achieving this amplification, particularly through the use of transistors, and discuss circuit protection considerations.

Discussion Character

  • Technical explanation, Experimental/applied

Main Points Raised

  • John initiates the discussion by expressing a need to amplify a 2.5 mA pulse to operate a latching relay, indicating a lack of familiarity with the amplification process.
  • One participant provides a circuit diagram for a relay driver, noting the importance of a diode for protecting the transistor from high voltage induced by the relay coil.
  • Another participant suggests using a Darlington transistor, specifically the TIP120, for applications where the relay current exceeds 50 milliamps, and mentions the need for a 10k resistor from the data input to ground.
  • John acknowledges the suggestions and indicates plans to acquire the necessary parts for the project.

Areas of Agreement / Disagreement

Participants present various approaches to amplifying the pulse, but no consensus is reached on a single method or circuit design. The discussion remains open to further contributions and refinements.

Contextual Notes

There are assumptions regarding the relay specifications and the exact requirements for the amplification that are not fully detailed. The discussion does not resolve the optimal configuration for the transistor or the relay driver circuit.

jbord39
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Hey. I am trying to use a single quick pulse of about 2.5 mA to run a latching relay. I know that this signal needs to be amplified (probably with a transistor) but am unfamiliar on how to do this.

Thanks for the help,

John
 
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Here is a relay driver. The diode in this circuit is used to protect the transistor from high voltage that is being induced by the relay coil.


http://www.vlearnvshare.com/home/images/articles/NPN-DRIVER1.GIF
 
Last edited by a moderator:
If the relay current is over 50 milliamps, you should use a Darlington transistor, such as the TIP120 (available at Radioshack) or equivalent. See datasheet

http://www.learn-c.com/tip120.pdf

The current gain at saturation is ~250. You should also have a 10k resistor from the data input to ground.

Bob S
 
Thanks for the help. I'm going to get the parts today so I'll let you know.
 

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