Discussion in "8051 Discussion Forum" started by    Kuya_Marc    Apr 1, 2010.
Thu Apr 01 2010, 12:01 PM
#1
I'm using the 7805CT circuit to power my 89CX051 MCU project, but I wish to build the "OverVoltage" circuit that is typically avalable in commercial/industrial products. I know that that 89CX051 MCU can take on up to 6 VDC, but I wish to have a circuit that cuts off at 5.5 VDC.

Case: A cold solder joint in a 7805CT circuit caused High Voltage (11 VDC) to MCU, when supply voltage was 13.5 VDC. The MCU heated up, but still working as a MCU. (I haven't tried erasing & reprogramming it, yet.)

I want this circuit to prevent high voltage from entering the MCU circuit areas, optionally providing a necessary alarm-type notification.

Any ideas?
Thu Apr 01 2010, 12:10 PM
#2
hi,

jus monitor the line current using a shunt resister and connect to comparator with reference and connect the o/p to buzzer

voltage is not the current makes the damages while shorts in mcu
Thu Apr 01 2010, 12:17 PM
#3


hi,

jus monitor the line current using a shunt resister and connect to comparator with reference and connect the o/p to buzzer

voltage is not the current makes the damages while shorts in mcu

pravin_35



So far, I have two (2) dead 89C2051 MCUs caused by over-voltage. I use thermal stickers on my MCU ICs. I've seen both MCU ICs experience enlargening black dots, from heating up too hot. One of them decided to heat up while I was on the toilet... Voltage, measured with DMM, went from 5.00 VDC to 11.67 VDC from a cold-solder joint that heated up nearby the 7805. By the time I cut the power, it was already too late. I have repaired my solder joints since then, but I want to be safe than sorry.
Thu Apr 01 2010, 01:10 PM
#4
i recommend using a zeiner on output side to prevent overvoltage, 7805 is unreliable sometimes, i lost one IC coz of same reason.. or maybe 2.
Thu Apr 01 2010, 06:06 PM
#5


I've seen both MCU ICs experience enlargening black dots, from heating up too hot. One of them decided to heat up while I was on the toilet...

Kuya_Marc


Couldn't you just say you were "away"

Seriously.. the risk of a regulator failing high is so low that it is not worth adding the sort of
backup you would need.

Just make sure you solder the ground pin properly and check for shorted tracks.
Sun Apr 04 2010, 02:11 PM
#6



I've seen both MCU ICs experience enlargening black dots, from heating up too hot. One of them decided to heat up while I was on the toilet...

Kuya_Marc


Couldn't you just say you were "away"

Seriously.. the risk of a regulator failing high is so low that it is not worth adding the sort of
backup you would need.

Just make sure you solder the ground pin properly and check for shorted tracks.

ExperimenterUK



Usually, "away" would signify that I can simply stop what I'm doing to respond to an "alarm" condition... For instance, smoke alarm while eating a meal... I can simply get up and run to it...

My main power supply delivers 13.5 VDC 3 Amps... The 7805 regulator does warm up, but not enough to raise any alarms. But, when V-out went above 9VDC, the regulator gets warmer. When V-out goes to over 11VDC, the regulator gets extremely hot.

I have an idea of building a circuit that operates a "cutoff relay" if or when V-out equals 6VDC+. This particular circuit will still operate while the "cutoff relay" prevents OverVoltage from reaching Vcc of the MCU circuits.

In my past, I remember industrial products that have an overvoltage sensor, and in one case, I had to test the overvoltage sensor at quality control level.

Get Social

Information

Powered by e107 Forum System

Conversation

No messages yet.

Downloads

Comments

Mirza123
Thu Jun 25 2020, 03:46 PM
eunicelove124
Mon Jun 22 2020, 03:03 PM
cerouno
Tue Jun 16 2020, 05:10 PM
Marce
Sat Jun 13 2020, 09:43 PM
Davidthils
Thu May 21 2020, 12:44 PM
Jakeror
Thu May 21 2020, 01:28 AM
motorCar
Wed May 20 2020, 07:05 PM
Vordrync
Wed May 20 2020, 11:52 AM

Online

Guests: 181, Members: 0 ...

most ever online: 182184
(Members: , Guests: 182184) on 06 Aug 2010: 05:37 AM

Members: 38215
Newest member: Mirza123