Low Amperage Variable Voltage Input to Control High Amperage?
Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=146065
Printed Date: May 03, 2024 at 5:51 PM
Topic: Low Amperage Variable Voltage Input to Control High Amperage?
Posted By: subdermal
Subject: Low Amperage Variable Voltage Input to Control High Amperage?
Date Posted: March 08, 2020 at 12:12 PM
Hello:
I am trying to add on additional lighting features into my car (350z), which has a dimming circuit controlled by the vehicle's BCM. I would love to tap directly in parallel to the wiring circuit that dims the lighting already, but I'm concerned with overloading the circuit and blowing the BCM or a fuse, as I cannot find the max load that illumination circuit would be able to handle.
I would like to find a relay module that allows a low amp draw variable DCV input from ~0-15v and could control voltage output from another 12v circuit in the car (tapped directly from IGN 12v+), outputting the equivalent voltage as the input, but without the worry of amperage draw.
Does anyone know of such a module?
Replies:
Posted By: subdermal
Date Posted: March 08, 2020 at 2:46 PM
Essentially, here is what I am trying to do:
Posted By: geepherder
Date Posted: March 09, 2020 at 6:44 AM
You could use an op amp capable of high current. I'm no electrical engineer, so I don't have a circuit for you, but here's some good reading:
https://electronics.stackexchange.com/questions/70884/voltage-regulator-ic-with-external-reference/70906#70906------------- My ex once told me I have a perfect face for radio.
Posted By: eguru
Date Posted: March 09, 2020 at 7:58 AM
A P-Channel MOSFET is all you would need (along with 2 resistors). The appropriate device would depend on how much current you want to draw.
Posted By: subdermal
Date Posted: March 09, 2020 at 11:07 PM
Thanks guys. I like the OPA549T for the purpose. Looks like I can configure it to accomplish what I'm looking for.
Posted By: eguru
Date Posted: March 10, 2020 at 11:16 PM
The OPAMP is a poor choice for your application for many reasons.
It can't accept input voltage greater than V+ minus 2.3V.
It can't output more than V+ minus 2.7V
A good heatsink is required.
An FQP27P06 MOSFET with a 20K resistor between the Gate and +12V and a 1K resistor between the Gate and your control signal would work.
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