Voltage Controlled Switch
Printed From: the12volt.comForum Name: Lights, Neon, LEDs, HIDs
Forum Discription: Under Car Lighting, Strobe Lights, Fog Lights, Headlights, HIDs, DRL, Tail Lights, Brake Lights, Dashboard Lights, WigWag, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=139492
Printed Date: May 07, 2025 at 6:06 AM
Topic: Voltage Controlled Switch
Posted By: jrichard82
Subject: Voltage Controlled Switch
Date Posted: September 29, 2015 at 10:21 AM
The problem I'm trying to solve: I have a vehicle that has 3 wires for the tail/brake light. When the vehicle is on there is 12v+ between the red and black wires and there is 7v+ between the red and Orange wires. When you hit the brakes the 7v+ between the red and orange wires steps up to 10v+.
So I need to create a circuit that will turn on a set of LED lights when the voltage goes above 9 volts. Currently, my circuit consists of a voltage divider (changing 12v down to 9v), an LM324N OPAMP and an FQI50N06 MOSFET (Schematic shows IRF540). For some reason, on the OPAMP, when there is no input, the output is on, when the non-inverting input is higher than the inverting input the output is on and when the inverting input is higher than the non inverting input the output is off. So in my mind, this circuit is working, except when there is no input, the the output should be off. Please see the attached schematic:
So I need to create a circuit that will turn on a set of LED lights when the voltage goes above 9 volts. Currently, my circuit consists of a voltage divider (changing 12v down to 9v), an LM324N OPAMP and an FQI50N06 MOSFET (Schematic shows IRF540). For some reason, on the OPAMP, when there is no input, the output is on, when the non-inverting input is higher than the inverting input the output is on and when the inverting input is higher than the non inverting input the output is off. So in my mind, this circuit is working, except when there is no input, the the output should be off. Please see the attached schematic:
Replies:
Posted By: tonanzith
Date Posted: October 10, 2015 at 10:17 PM
Posted By: jrichard82
Date Posted: October 12, 2015 at 8:31 AM