I am using watchdog timer which have adjustable window BUT ITS RESET delay is fixed.This reset pin is active high during normal operation and during fault condition its gives 200ms low pulse. So how can I drive power supply using this reset pulse?

  • \$\begingroup\$ What is current limit an RC=T value \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 13 '18 at 0:59
  • \$\begingroup\$ I am new to electronics I just want to reset power supply using this reset pulse given by external hardware Watchdog timer but I dont know how to increase its pulse width ?Is there any solution to increase its pulse width? I have to stretch this asserted reset pulse to 10 second from 200ms? I heard about Monostable multivibrator or any better approach for this ? \$\endgroup\$ – ARYA1992 Jul 13 '18 at 1:26
  • \$\begingroup\$ You can trigger a one shot multivibrator to stretch the 200ms pulse. \$\endgroup\$ – Spehro Pefhany Jul 13 '18 at 1:30
  • \$\begingroup\$ 10s seems like a fault condition from overtemp \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 13 '18 at 1:35

As you already presumed, you can use a monostable multivibrator to extend your pulse, for example using a 555 timer. If you enter "555 timer monostable" this is the first image that pops up:

monostable 555 timer circuit

(Image source)

Just connect your watchdog timer output instead of R2 and the switch and connect a transistor (with base resistor) to drive the relay on the OUT pin.
Select R1 and C1 so t is 10 seconds according to the formula in the picture.

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  • \$\begingroup\$ Thank you for adding the image source, I see it has a lot of valuable information about 555 timer circuits. \$\endgroup\$ – Marco Zollinger Jul 13 '18 at 13:19

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