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I have a little project i'm working on.. At the moment I would like to limit current in a voltage 12v-200v DC system to 4 Ampres like a 'fuse' does but not blow like one. How would I start, is there any designs or device I could buy?
What do you mean by "does not blow like one?". Be specific...really specific.
If you are just talking about limiting the current to 4A rather than disconnecting it, keep in mind that voltage will have to be reduced to accomplish this. If this is not acceptable, then your task is impossible. If it is, what you do is get an your microcontroller (or whatever smarts is controlling the PWM on an H-bridge) and equip it with a current sensor (ie. hall effect current sensor, or a current shunt resistor with a current sense amplifier IC if needed), and program it to reduce the PWM duty cycle to keep the current at a certain level if it exceeds this level.
So, no, you can't buy one. Make a series-connected device that does this (like a TVS diode, but for current) and you'll be rich.
There is a such thing as a current limiting diode. I've never used one though, and apparently they're limited to 15ma. This PDF describes using one with a BJT to increase the current.
You may be able to use a "hot swap" contoller IC. These ICs basically take an input rail and connect it to a load in a controlled manner using a pass device (typically a MOSFET). Many of them utilize current sense resistors for over-current protection. I doubt, however, that you will find a hot swap controller capable of up to 200V DC as many of them are meant for servers/telecom equipment and such for insertion into a live backplane.
Look up some datasheets, though - it may give you an idea on how to do it discretely.
Boncuk understands me correctly. The project is for a DC motor from a treadmill for a electric kart project. I need to power it and intrestingly I still have the circuit for the treadmill, maybe the original MOSFET chips too.
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