Hello.
I'm working on a performance automotive ignition project for uni, that will be situated in the engine bay, so will be subject to some heat. The IC's the product uses have built in thermal protection that kicks in when they reach 94°C.
The initial design called for this thermal protection to be used as the main protection for the device, but its effect is so immediate that the IC's cool to below 94°C very quickly, and the device re-activates. The protection scheme manifests itself during real world testing as an erratic misfire in the engine... Misfires can be a real PITA to track down, so we really dont want to make a device that could potentially introduce one!
After doing some googling and what-not, I'm wondering if it might be possible to create a thermal protection circuit from a PTC resetable fuse in thermal contact with the case of the device?
The IC's we're using have an enable pin, than lets the device run with this pin grounded, but turns the IC's off if it is tied high, or left floating.
The idea i had was to run a known current through the PTC fuse, which has been chosen to trip at this known current, and a specific temperature. When this trips, the enable pin will be floating the and device will turn off.
The case of the device is basically one large heatsink, so it would take some time for this to cool down and the fuse to reset.
The worry i have is that all the PTC fuses I've looked at have a fairly large section between normal current handling mode, where their resistance is known and fairly low, and the tripped mode, where their resistance is high. During this mode, they can apparently be un-tripped, or tripped...
Any of you smart chaps out there have and ideas? Whats the 'typical' way to go about thermal protection like this? The ideal result would be for the device to shut down for a good 30 seconds or so, as that would make tracking the problem down very easy for the end user.
Cheers .
I'm working on a performance automotive ignition project for uni, that will be situated in the engine bay, so will be subject to some heat. The IC's the product uses have built in thermal protection that kicks in when they reach 94°C.
The initial design called for this thermal protection to be used as the main protection for the device, but its effect is so immediate that the IC's cool to below 94°C very quickly, and the device re-activates. The protection scheme manifests itself during real world testing as an erratic misfire in the engine... Misfires can be a real PITA to track down, so we really dont want to make a device that could potentially introduce one!
After doing some googling and what-not, I'm wondering if it might be possible to create a thermal protection circuit from a PTC resetable fuse in thermal contact with the case of the device?
The IC's we're using have an enable pin, than lets the device run with this pin grounded, but turns the IC's off if it is tied high, or left floating.
The idea i had was to run a known current through the PTC fuse, which has been chosen to trip at this known current, and a specific temperature. When this trips, the enable pin will be floating the and device will turn off.
The case of the device is basically one large heatsink, so it would take some time for this to cool down and the fuse to reset.
The worry i have is that all the PTC fuses I've looked at have a fairly large section between normal current handling mode, where their resistance is known and fairly low, and the tripped mode, where their resistance is high. During this mode, they can apparently be un-tripped, or tripped...
Any of you smart chaps out there have and ideas? Whats the 'typical' way to go about thermal protection like this? The ideal result would be for the device to shut down for a good 30 seconds or so, as that would make tracking the problem down very easy for the end user.
Cheers .