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L6203 H-Bridge overcurrent protection

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Exo

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I'm using a L6203 (sgs, **broken link removed** )
to drive a DC motor for a sattelite dish positioning system. Now i want to add overcurrent protection...

The device can handle up to 4A, So i thought of adding a current sensing resistor in series with the supply and measuring the voltage drop,...

But here's the problem, The motor's startup current can be a lot bigger then 4A, so my system would trigger and deactivate the chip every time it starts up, so i need something that would allow a bigger startup current for a short time...

I thought of just disabling the protection for 1 second or so on startup, but then there wouldn't be any protection for the first second if there was a real short circuit and my chip would blow ...

So, does anyone have an idea on how to do this ...
 
There are a number of ways to do it, one (as you suggested) is to disable (or restrict) the over current protection at start up - as long as it's only a very short time it shouldn't damage the chip. It could be as simple as a capacitor on the over current line - which delays the over current signal!.

Another way is a surge limiter, feed the chip through a large resistor, calculated to limit the current to no more than 4A. This prevents the over current triggering, then, after a short delay, short the resistor out - this is commonly done in high power amplifiers with toroidal transformers, the mains transformer is fed from a large resistor which is then shorted out by a triac after a couple of seconds. If you need to limit at DC you could use a transistor, FET, or relay to short it out.
 
How about making the protection in 2 stages?
If the current goes above 5A (the absolute max for the L6203 chip) then it gets shut down immediately...
And then a second stage that shuts down if the current goes above 2A for some time period (motor operating current is +- 1.5A)...

Any comments on this ?
 
You could try a circuit breaker, you probably want a self-resetting one. In fact, there are self resetting ones such as those from Polyfuse which don't have a bunch of moving parts. This is simplest since it should be slow enough to fix your startup problems, sustain the a total shutdown condition for long enough, and reset automatically.

You can use a lower resistance shunt resistor and amplify it with an op amp (or use as a comparator). You could do some filtering to prevent the turnon pulse from shutting it off.
 
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