Transistor BC337 with problems using like a switch

Hardware
1

I everyone. This is m first post.

I'm tring to use a transistor bc337 like a switch beetween a 12V battery and a circuit. the base of the transistor is connect to a esp32 wroom gpio pin, using a resistence of the base of 1.5K. The collector is connect to the VIN- pin of a regulator LM2596, and the emisor of the transistor is connect to the negative terminal of the batteries pack. The positive terminal of the batteries is connect to the VIN+ pin of a regulator LM2596. When I connect the esp32 wroom to the circuit, with the GPIO pin un LOW, the transistor activate
immediately.

When I test the voltaje in the GPIO pin with the esp32 wroom disconnected I'd a voltaje of -8V aprox, and a voltaje of -10V in the emissor.
image
Any idea? I'm new working with transistors.
Thanks a lot

2

Please post a schematic. A PCB layout doesn't reveal very much.

1 Like
3

Hi.
A schematic speaks a thousand words.........

1 Like
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image
image693×509 7.98 KB

There is the schematic

5

That schematic image is of too low resolution to be readable. Any chance of a better image please? Is the PCB layout track side or component side up?

I had a look at the datasheet for the LM2596 and don't see a VIN- (or -VIN) pin so I'm not sure whether you are referring to +VIN or something else?

6

Please complete the schematic by connecting the wires. That is just the unfinished component pin list that the CAD program makes automatically.

It's almost useless for analyzing the circuit.

7

Hi, I want to help here.
Better to provide a schematics, not a PCB layout ("we do not trace back how you have wired").

I tried to understand your text description. Confusing is:
"The collector is connect to the VIN- pin of a regulator LM2596".
What does it mean? You have grounded the collector? How could it work?

Here my schematics you want to have at the end (for my understanding).
Just check how C (collector), E (emitter) are connected.
For a NPN transistor - very common to use as a digital MCU driver:

  • the B (base) is driven by an MCU GPIO pin: correct: have a resistor there

  • the E (emitter) is the common ground: all negative poles go to same ground plane

  • the C (collector) takes ("switches") the load current: it is still positive, e.g. positive out after voltage regulator. Make sure, the current is limited (not to burn transistor).

But a C (collector) on an NPN transistor connected to GND (VIN-) - cannot work.
For a PNP transistor it would be correct - but you have chosen BC337 as NPN.
You can do a similar logic with a PNP (but the schematics and even the logic changes).

Here, how the (your) schematic should look like:

PNP_transistor
PNP_transistor1504×979 72.1 KB

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