Resettable fuses are not appropriate over current protection devices for H-Bridge motor drives. The LMD18200T has a current sense source output that gives you 377uA/A of output (pin #8). Look at the application note on the national web site and it tells you exactly how to use this pin (in the typical applications section). You can use the voltage drop across a resistor connected between pin 8 and ground to feed to a differential amp followed by a comparator. The comparator output can then be used to shutdown the bridge at the desired current level. Keep in mind that the current sense output ignores freewheeling currents. The LMD18200 does have an over current shut down at 3A and if your motors can tolerate 3A through their windings at stall then you do not need current protection at less than this level. Madhu ----- Original Message ----- From: "Siva Kumar.M" To: Sent: Thursday, March 28, 2002 12:39 AM Subject: Overload protection-reg. > Hai all > My application is DC motor speed control. For this I am using the > motor driver LM18200T. This gives higher driving capacity with lesser power > dessipated. The motor operating votage is 24V and max. current allowed is > 1A. > Now it requires overload protection. I want to control the current less > than 1A. I have used some of polyfuses(rachem RXE135, siemens - PTC > thermister(part number -C975)). This device starts acting when current > limit exceeds. This continues to be in high resistance state eventough the > current limit is partially reduced. > In this regards, I would like to have following solutions: > 1. We are unable to use PTC, because it requires switch OFF the unit and > switch ON to recovery. To avoid the same I am looking for some hardware > alternate solution (like Oveload protection IC etc..). > 2. Fast acting polyfuse or thermister to avoid switching ON/OFF the unit. > If you have come across any, please suggest. > Looking forward your suggestions for the above.. > Rgds, > JOHN XAVIER > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads