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I need a CMOS (preferably dual) level-triggered mono-stable multi-vibrator that runs at least 12V (better at 15~18VDC), perhaps in the CD4000 family. Everything I have found is edge-triggered only or is in the TTL families which won't operate at the voltages I need. Even an edge-triggered with set pin (instead of reset pin) will do as long as it stays in the pulse while the set pin is held active. The circuit must be continuously retriggered by holding the set pin active. The problem with edge-triggered here is that, if the trigger value never returns back to its idle state, the pulse will complete and no edge will come to retrigger it. A power transistor will turn back on and will go up in smoke. This is for a circuit to protect against shorts.

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  • \$\begingroup\$ Can you post a schematic of the circuitry you want to protect? \$\endgroup\$ – EM Fields Jan 9 '15 at 16:52
  • \$\begingroup\$ NOR gate controls whether T0 is on or off. All 3 inputs must be low in order for Ctl0 to go high. R30=current sensing resistor, U10A=comparator. When too much current going through T0 then voltage will be higher than ref. Output of comparator will go high which triggers one-shot U11A. While Pulse0 is being generated, T0 will be off. The pulse is 1ms. Should be enough to cool off circuit and allow "try" again. Nets externally connected to load are 12V and Gnd0. T0 used to pull pwr thru load by shorting its Gnd pin to supply shown as a ground symbol bottom left. Don't know how to post picture. \$\endgroup\$ – Paul McKneely Jul 27 '15 at 20:36
  • \$\begingroup\$ Zeros are shown on this website to look too much like lower case 'o's. So in my explanation above, Pulse0 (PulseZero) looks like Pulseo. This is very misleading. \$\endgroup\$ – Paul McKneely Jul 27 '15 at 20:39
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The CD4538 (now CD14538) or the CD4047? Here's a digikey link with some serious filters.

Or maybe a Cmos 555?

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  • \$\begingroup\$ Have already looked at CD4047 and CD1438 which only have edge-triggering. Already using a 2-input CMOS OR gate to combine the PWM signal with the pulse from a CD14538 to inhibit power on. Have solved problem another way by replacing 2-input OR Gate with a 3-input OR Gate and added the trigger clock signal to the 3rd input on the OR gate. Now the output of the OR Gate will only go low if all three conditions are met. This was a fairly simple solution since I was already using a 2-input OR gate but I lose one gate from the device because of the additional pins. Just have to use more packages. \$\endgroup\$ – Paul McKneely Jan 9 '15 at 17:42
  • \$\begingroup\$ I like Digikey but I am trying to fill my whole order using Mouser since I am in Texas and they have no minimum order. The 555 was tempting but I need to repeat the circuit 20 times and the 555 requires so many extra components that it would be getting too complicated. I wanted to increase integration to minimize board space as well as complexity of assembly. Thanks for the input. \$\endgroup\$ – Paul McKneely Jan 9 '15 at 17:52
  • \$\begingroup\$ @PaulMcKneely Digi-Key dropped their $25 minimum order requirement a few years ago, probably in response to Mouser. \$\endgroup\$ – tcrosley Feb 8 '15 at 18:09

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