Hi,
I have a question about high negative voltage on osilloscope. I am trying to start and stop control DC motor with TIP122 transistor by signaling D3 pin on ESP-C3-13 kit. There's no problem when I set HIGH D3 pin and scope displays ~12V without any noise. Things getting weird when I set LOW D3 pin. When I set D3 to LOW, scope show -67 V with unstable graph.
I checked FFT graph and found out many noise inside the signal, but it is an easy circuit and shouldn't have kind of noise. If I face with noise I should see same problem at FFT graph on +12V too. Am I correct?
So, can anybody make a comment why I am facing -67 V with unstable graph when I set D3 pin to LOW?
As an additional information, multimeter measure 0 voltage level whereas I see that high negative voltage level on scope when D3 is LOW.
Please note that scope probes attached to motor pins. Even if I drop motor from circuit, I face with same problem.
Please find scheme and scope outputs.
-67V with large scale:
-67V with FFT (FFT graph is red):
12v stable:
Thank you for your helps,
Orkun Gedik
High negative voltage on scope
High negative voltage on scope
Last edited by ogedik on Thu Aug 24, 2023 2:59 pm, edited 2 times in total.
Re: High negative voltage on scope
ogedik wrote: ↑Thu Aug 24, 2023 2:17 pm
Schema is here: Hi,
I have a question about high negative voltage on osilloscope. I am trying to start and stop control DC motor with TIP122 transistor by signaling D3 pin on ESP-C3-13 kit. There's no problem when I set HIGH D3 pin and scope displays ~12V without any noise. Things getting weird when I set LOW D3 pin. When I set D3 to LOW, scope show -67 V with unstable graph.
I checked FFT graph and found out many noise inside the signal, but it is an easy circuit and shouldn't have kind of noise. If I face with noise I should see same problem at FFT graph on +12V too. Am I correct?
So, can anybody make a comment why I am facing -67 V with unstable graph when I set D3 pin to LOW?
As an additional information, multimeter measure 0 voltage level whereas I see that high negative voltage level on scope when D3 is LOW.
Please find scheme and scope outputs.
-67V with large scale:
IMG_1308.jpg
-67V with FFT (FFT graph is red):
IMG_1312.jpg
12v stable:
IMG_1310.jpg
Thank you for your helps,
Orkun Gedik
-
- Posts: 94
- Joined: Tue Sep 07, 2021 12:07 pm
Re: High negative voltage on scope
check the Q1 part number. Double check the pinout.
The scope ground must be connected to the circuit ground (not a motor pin.)
https://electronics.stackexchange.com/q ... transistor hints the 10K resistor might be too big.
Scope probe to the base on Q1:
It's been a long time, but I think it has to be high (5V) to turn it on and low (gnd) to turn it off.
Scope probe to the collector:
if Q1 is on, the collector should be near ground, not 12V.
if Q1 is off and the motor provides a path to 12V, the collector should be near 12V.
if there is no motor installed, I think you might expect to see noise when Q1 is off.
The scope ground must be connected to the circuit ground (not a motor pin.)
https://electronics.stackexchange.com/q ... transistor hints the 10K resistor might be too big.
Scope probe to the base on Q1:
It's been a long time, but I think it has to be high (5V) to turn it on and low (gnd) to turn it off.
Scope probe to the collector:
if Q1 is on, the collector should be near ground, not 12V.
if Q1 is off and the motor provides a path to 12V, the collector should be near 12V.
if there is no motor installed, I think you might expect to see noise when Q1 is off.
Craige
Re: High negative voltage on scope
Hi Craige,Craige Hales wrote: ↑Fri Aug 25, 2023 12:23 amcheck the Q1 part number. Double check the pinout.
The scope ground must be connected to the circuit ground (not a motor pin.)
https://electronics.stackexchange.com/q ... transistor hints the 10K resistor might be too big.
Scope probe to the base on Q1:
It's been a long time, but I think it has to be high (5V) to turn it on and low (gnd) to turn it off.
Scope probe to the collector:
if Q1 is on, the collector should be near ground, not 12V.
if Q1 is off and the motor provides a path to 12V, the collector should be near 12V.
if there is no motor installed, I think you might expect to see noise when Q1 is off.
Thank you for your precious information. Very informative for my learning path.
Best regards,
Orkun Gedik
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