mbed

How is your mbed powered ? Externally or only through USB ?

With USB it gets a little hot but with Externall it gets so hot I find that the p23 is connected to the GND But MBED works properly Do you think DIP23 of MBED Does not work

How much voltage is the external supply putting out? Not what is the power supply rated at but what actual voltage is it producing with the MBED as a load?

The MBED technical reference lists the maximum voltage connected to VIN as 9V. Most likely the LD33 can handle a higher voltage but without adequate heat sinking it will get too hot if the voltage is too high.

http://mbed.org/handbook/mbed-NXP-LPC1768

I use 9V for VIN ,but LD33 becomes hot recently it is really near burning I tested with Multimeter and I find that the output of LD33 was connected to the GND

That'll do it.

Hi The output of LD33 is connected to the GND Which part should I replace?

You can check the schematic: http://mbed.org/media/uploads/chris/mbed-005.1.pdf

My guess would be C12 (10uF) or maybe the LD33 itself.

Does it run hot even when running standalone ? (not plugged into a breadboard)

The left LD33 has this problem not the right .When I use usb it does not work but with a 9V battery it works and the left LD33 gets so hot and after that the Mbed Interface gets hot Another problem is that the P23 is connected to GND but Mbed works properly I test this when mbed did not connect to power or usb

DIP23 is a PWM output (P2.3 or PWM1.4) and there are no outside components between the LPC and this mbed pin. So if this pin is internally shorted, the LPC is toast I'm afraid. If you programmed it being low and using a multimeter to measure the resistance to GND it will register as a short (ofcourse). When the mbed is not powered it should read higher than 0 ohms, if not this output is defunct.

You said earlier that the output of LD33 is shorted to GND, if that is the LD33 which is powering the mbed then the mbed would never work regardless of being powered from USB or external, if it is the LD33 powering Vout it means there is a short on the output (C12 or external) and the LD33 goes into current limit mode and after becoming too hot into thermal protection mode. So now I am confused... :-)

Ali,

The connection for Vbat on pin 3 is right next to the connection for Vin on pin 2. If Vbat were to make contact with your external 9V power supply (even if briefly/accidentally) or some other transient such as electo-static discharge hit it, that might make the 1768's Vbat pin form an internal short to ground (as well as other possible internal damage). Having the 1768's Vbat pin shorted to ground internally could produce the symptoms you describe. Removing diode D3 (on the LD33's output) may prove diagnostic, and may restore the mbed to operating (but with no RTC).

Fred