I am working up a design for a thermal protection system for some LED lighting.
The lights are RGBW DMX controlled lights, when all 4 colors are on full, the thing overheats, but normally all 4 channels are never turned on. The dimmers are off-the-shelf so I cannot modify them.
An open circuit DMX input picks up stray voltages which can be easily interpreted as an "everything on full" signal, so I need to implement a hardware solution.
There are three LED boards, so the idea is to have 3 small 2-wire sensor boards connected to a common bus (wired OR) that nominally draw 200uA, but when the temp goes over 60 degrees C, they draw 10 mA, which then shuts down the LED common supply via some yet-to-be-designed circuit
The sensor should have 5 degrees of hysterisis to prevent the thing from flashing all crazy around the trip point.
Attached is a rough sketch of an idea, based on an analog temp sensor and a TL431 as a reference and comparator.
The PNP is supposed to provide 100 mV of hysteresis, but I think it needs to be a PFET not a bipolar.
The whole thing runs on 24 VDC about 2A max.
Any ideas how this could be simpler?
The lights are RGBW DMX controlled lights, when all 4 colors are on full, the thing overheats, but normally all 4 channels are never turned on. The dimmers are off-the-shelf so I cannot modify them.
An open circuit DMX input picks up stray voltages which can be easily interpreted as an "everything on full" signal, so I need to implement a hardware solution.
There are three LED boards, so the idea is to have 3 small 2-wire sensor boards connected to a common bus (wired OR) that nominally draw 200uA, but when the temp goes over 60 degrees C, they draw 10 mA, which then shuts down the LED common supply via some yet-to-be-designed circuit
The sensor should have 5 degrees of hysterisis to prevent the thing from flashing all crazy around the trip point.
Attached is a rough sketch of an idea, based on an analog temp sensor and a TL431 as a reference and comparator.
The PNP is supposed to provide 100 mV of hysteresis, but I think it needs to be a PFET not a bipolar.
The whole thing runs on 24 VDC about 2A max.
Any ideas how this could be simpler?
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