Best Transistor Circuit to take 2 Square Wave inputs to a single output

Thread Starter

awccook

Joined Sep 17, 2018
4
I am having a dilemma where the physical circuit does not match the theoretical.
Problem: I have two input sources, both are Square Waves, Wave 1: 5V Amplitude (5V offset), f = 1.4 Hz, Phase = 0; Duty = 42.8; Wave 2: 5V Amplitude (5V offset), f = 1.4 Hz, Phase = 45; Duty = 42.8. Based on these two signals, that when either input source is a ground, the overall output is a ground and 10V. On the output node, I have a box that detects the input and when a Ground is sensed, a digital logic 1 is triggered. Conversely, when a the box detects an Open (greater than 8V usually, would like 10V) a digital logic 0 is triggered.

Circuit: (link: http://tinyurl.com/yc3aexhj)
I figured the easiest approach would be to effectively make an AND logic gate, that when either source is Ground, that the output is ground. This portion is working just fine.

The issue I am having is at the output node, the output square wave amplitude is not acting as I expect. Here are two snapshots of the output, #1 without phase shift, #2 with phase shift. Green = Input #1, Yellow = Input #2, Blue = Output. Note, that the green and yellow are identical, just shifted green down to see the waves.

Did I have the right circuit design here? Again, theoretically, I have what I need, but practically, I don't.

danadak

Joined Mar 10, 2018
4,057
Why are you offsetting the second input ? Rather than just feeding
it a ground referenced 5V input ?

And the channel setting on your scope shows only 100 mV / box ?
For the inputs ?

Regards, Dana.

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Alec_t

Joined Sep 17, 2013
12,441
Something like this?

crutschow

Joined Mar 14, 2008
28,458
the output square wave amplitude is not acting as I expect.
I'll bite.
How did you expect it to act?

Thread Starter

awccook

Joined Sep 17, 2018
4
Why are you offsetting the second input ? Rather than just feeding
it a ground referenced 5V input ?

And the channel setting on your scope shows only 100 mV / box ?
For the inputs ?

Regards, Dana.
I had to offset the inputs to get a ground reference, the signal generator that I am using doesn't have the option for a ground reference.

The x-axis are 100ms and y-axis is 5V. I created an offset between input 1 and input 2 to show timing of the inputs.

Thread Starter

awccook

Joined Sep 17, 2018
4
I'll bite.
How did you expect it to act?
I was hoping that if either signal was a ground, that the output would be a ground. Then, when the signals are out of phase, that a ground would still be seen at the output until both source signals are at 10V, then my downstream system will register an Open.

Alec_t

Joined Sep 17, 2013
12,441
.... if either signal was a ground
How can it be if there's a 5V offset?

crutschow

Joined Mar 14, 2008
28,458
I was hoping that if either signal was a ground, that the output would be a ground.
Like this?

Thread Starter

awccook

Joined Sep 17, 2018
4
Yes, that's what I was hoping for, the only difference of what you have to mine is the Resistor into the transistors. In application, the blue wave in the o-scope was the resultant.

crutschow

Joined Mar 14, 2008
28,458
the only difference of what you have to mine is the Resistor into the transistors.
I increased the value of the base resistor so the output voltage when the top transistor is off and the bottom transistor is on is less, due the the bottom base current going through the emitter resistor.

Alec_t

Joined Sep 17, 2013
12,441
The post #8 circuit gives an output of only ~3.6V. Is that enough?

ScottWang

Joined Aug 23, 2012
7,116
The Ve output is depends on the Vb and lower than Vb as Ve = Vb - 0.7V, the Vb will be lower than the Vin(5V), so how can you expect the Ve higher than 5V? (The circuit in the #1)

The circuit below provided around 10mA output, if you want to get more current then you can decrease the Re3, VR1, Rc3, the VR1 was used for adjust to 10V output when you want to get a more accurate close to 10V output. (if you want to get a high current output then the output part should be redesign)

Last edited:

ScottWang

Joined Aug 23, 2012
7,116
The circuit in #12 can't provides the current that I expected, if you just want to get a voltage level then it's ok, the below can be solve the problem for current, the Zd1 will limites the current, if you want to get more current the you can choose the big current for Zd1 and Q3, if you just want to get a voltage level then the 0.5W/1W for the Zd1 is ok.