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3 Phase Sequence Detector W/O Microcontroller

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New Member
Hello guys. So, I found a circuit online which I am trying to replicate in real life however, there is always a 1 as the output. There is no switching as should be the case. When the lines switch another LED should light to indicate phase sequence change. Comments appreciated, thanks.



Active Member
A 7400N cannot source much current, maybe 1mA. It can sink up to about 16-20mA. The way the schematic is drawn, the pin 11 driving LED2 will always be drawn low by LED2, as that pin cannot source enough current to drive the LED. Thus, it seems pin 11 will always be low (less than 0.8V??)
This circuit, even if it worked, would be toggling at 60Hz (or faster) since it seems to be simply comparing the 3 phases of a 3 phase 60Hz signal. Also missing in your schematic is the +5V supply for the 7400 IC. Where does that come from, the +12V supply?


Well-Known Member
Most Helpful Member
Q1 needs a base resistor! The way you have it the 7400 can not pull down below VDD1- 0.7 volts.
The 7400 needs a 5V supply.

Think about this


New Member
sagor1 well i had the source and ground for the nand gate, however the way the spice program was set they going as inputs to the nand gate so i removed them from the schematic.
ronsimpson thank you for the comments. the nand gate has a supply at pin 14 and ground at 7, however as i told sagor1 the spice program takes them as inputs which is another problem,but i would apply that in real life applications
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