Challenges in TIP122

Using Arduino General Electronics
1

Hello.
I'm a new learner in microcontrollers, but I have a basic understanding of electronics. I want to switch between two independent 3S battery packs (11.1V - 12.6V) to power the rest of the system, alternating them when fully charged.

I've created a circuit to switch with:

  • ESP32 DevKit v4, which will provide the signal to open and close the circuit.
  • TIP122, a transistor that will act as a switch.
  • LED, simulating the battery pack.

I simulated the circuit in an app, and it worked perfectly.

Screenshot_2023-10-11-14-33-31-850_com.proto.circuitsimulator-edit
Screenshot_2023-10-11-14-33-31-850_com.proto.circuitsimulator-edit1080×1160 95.7 KB

In the image above, you can see all the components I used.

The problem arises when I try to implement it practically. The LED doesn't behave as expected. Here's a video showing what happens.

The code in the video is a simple Blink.

** Note: I found it strange that even when I change the GPIO pin without altering the code, the LED lights up. As far as I know, GPIO pins should default to the INPUT state.
As far as I know, the amount of current available between the emitter and collector is proportional to the amount of current at the transistor's base. I measured the current, and the result was in the µA range, which I found strange. So, I decided to test it by adding a 220-ohm resistor directly to the same GPIO. The result was approximately 15mA, as expected. **

2

I am not gonna,watch videos.
But is your tip122 connected correctly?
BCE

1 Like
3

Without a doubt. It's connected correctly. Base, collector, and emitter, respectively.
Base connected to GPIO33;
Collector connected to the negative side of the load;
Emitter connected to the GND of the external power supply and the ESP32.

I'm sorry, but why not to watch the video? The goal is to show what actually happens.

IMG_20231013_020322
IMG_20231013_0203221920×1440 209 KB

IMG_20231013_020341
IMG_20231013_0203411920×1440 160 KB

Note: I changed to pin 32

4

Must say your setup looks really neat.
But I cannot check it from a video. A picture would be better.

1 Like
5

Done. I edited previous reply with the images

6

What happens if you turn the led around?
Your 220 ohm resistors look differently.
From the picture it is really hard to see the difference between red brown and black...
220 should be red red black black brown or red red brown gold (I guess you do not have ones with silver bands...).

7

It's actually a different one, 270 ohms. I was testing other configurations when I sent the photo.
Now it's correct. However, it's still in the same situation.
After switching, the LED is completely off, unlike the previous way where it was very dimly lit.

IMG_20231013_024451
IMG_20231013_0244511920×2560 117 KB

8

270ohm should be fine as well.

How does the led burn when you put the base resistor at 3v3 (disconnect from gpio!)?

9

The Emitter is on the right , looks like the LED is connected there.
You must connect the Batt neg there.
LED in the middle.

image
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10

I do not believe a TIP122 can have Vce much less than 1V when saturated. Vce of 30,65mV is unrealistic.

A TIP is 1950s technology. Why not use an IRLZ44 or IRL540?

11

Your LED is not wired as in the diagram.

The LED and Resistor is connected across the Emitter and Collector , when the Transistor is off the cct draws current through the LED.

12

I have voltage regulators in my project. I converted 12V to 3.3V using another power source. I connected the 3.3V regulator's output to the base of the TIP, but this time, there's no light signal.

It's connected correctly. The positive terminal of the external source is directly connected to the resistor that is in series with the positive terminal of the LED. The negative terminal of the LED is connected to the Collector. Meanwhile, the negative terminal of the source is connected to the Emitter of the TIP.
Check this imagem

When the transistor is off, how does the LED consume power, considering that it's necessary to bias the transistor and power the base to enable conduction from the emitter to the collector?

13

The led is flickering in the video which is rather odd.
Post the code that is running on the ESP32.
Also take the end of the orange wire which is currently connected to GPIO32 and touch it on 3.3v to see if the led lights correctly.

1 Like
14

Ok that narrows things down.
Is your tip 122 ok?

15

What is those 2 thick black wires .. jumper wire ?

16 
#define ledPin 32

void setup() {
    pinMode(ledPin, OUTPUT);
}

void loop() {
    digitalWrite(ledPin, HIGH);
    delay(1000);
    digitalWrite(ledPin, LOW);
    delay(1000);
}

I had tried with another external 12V source with a voltage regulator for 3.3V, and still got the same result. However, I haven't tested it with the 3.3V pin. I'll try it as soon as I get off work.

So... Because of these occasions, I was unsure if it's really in good condition.
I checked it with a multimeter in continuity (diode) mode:

  • Positive probe on the Base and the other probe on the Collector. It showed continuity with a voltage drop of 0.5V.
  • Positive probe on the Base and the other probe on the Emitter. It showed continuity with a voltage drop of 0.6V~0.7V.
  • Positive probe on the Collector and the other probe on the Emitter. The result was an open circuit, it didn't conduct.
  • Positive probe on the Emitter and the other on the Collector. It conducted with a voltage drop of 1.9V.

It's the positive and negative wires of the external 12V power source. The wire on the right (near the LED) is the positive pole. The wire on the left (near the TIP122) is the negative pole.

17

OK. I think we can safely rule out a coding error and GPIO 32 on a normal ESP32 development board has no restrictions.

18

Have you got another one that you can neadure and compare?
I would have expected Vbe approx. 1.3V...

19

At the moment, I only have this one. But I've already ordered three more of these. They should arrive today

20

Even with a new TIP122, the problem is the same