# Reverse Polarity of Every Pulse

Discussion in 'The Projects Forum' started by ifiaxxy, Jul 1, 2014.

1. ### ifiaxxy Thread Starter New Member

Jun 5, 2014
10
0
Hi, I am trying to build a circuit similar to what I found here:

I use the solution provided by the following the post and build a circuit:

Here is the actual circuit diagram, everything is the same except I've added op-amps to get an output voltage whose pulse is flipping one after another: http://forum.allaboutcircuits.com/attachment.php?attachmentid=70343&d=1404231329

But when I built it, the circuit does not work!
The current across R_clock in the original diagram (or R3 in mine) did not provide the result shown in the software. Instead, the current behaved like a regular pulse.
The voltage on the left of R_clock (or R3) is about the same as the input signal and that on the right of R_clock (or R3) is about to be zero. My supply voltage is 12V and I have grounded all the unused pins of the flip-flop (cd4013B) and the Schmitt trigger (I use cd40106BCM instead of cd40106B though).
As the circuit is not working, I'm not sure why and I'm hopping someone can help me figure it out.
Thanks everyone!

2. ### crutschow Expert

Mar 14, 2008
16,506
4,440
One thing I noticed is that the opamps are cutting the voltage in half from R1 and R2 due to their input resistance. Try reducing the values of R1 and R2 and increasing the values of R6 and R9 to minimize this effect. R6 and R9 should at least 10 times the value of R1 and R2.

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3. ### ifiaxxy Thread Starter New Member

Jun 5, 2014
10
0
Thanks for the suggestion, the output is more clear
I've change the two resistors into 1K instead of 10K, but the problem is still there. It looks like the voltage is traveling through half of the H bridge but not both sides at the same time.
After I turn on the pulse generator, there is no voltage on the left side of R3 (or R_clock) and voltage similar to input pulse on the right. The voltage between Q and mosfet is constant around 10-12V.
So I guess is the flipflop not working?
Also, I've noticed that the Schmitt Trigger gets pretty hot... It's still working though, but hot

4. ### crutschow Expert

Mar 14, 2008
16,506
4,440
Yes it sounds like the FF is not working. Double check the wiring.

The Schmitt trigger is likely getting hot because you don't have all the unused inputs tied to ground. All unused inputs on CMOS circuits must be tied to ground including those on the FF.

Last edited: Jul 2, 2014
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