Hello everyone,
I am a beginner and I'm trying to understand how a motor works with a transistor.
Here are two configurations allowing the use of a motor with a transistor:
The transistor used is "BC337" and I don't know if the diodes are correctly placed.
Can you tell me what are the pros and cons? What is the most suitable configuration?
I noticed that the transistor got very hot in the second configuration but I don't know why. Do you have an idea?
The top circuit is OK in principle. The bottom is not. You cannot use an NPN transistor as a high side driver in such a circuit.
However, the BC337 is not suitable for most motors, as it not designed for typical start/stall currents, which exceed the 800 mA absolute maximum collector current.
A logic level N-MOSFET would be a better choice.
I was inspired by that:
The motor is linked to the emitter of two NPN transistors. What do you think of this configuration?
The person who drew it obviously does not understand the problem with using an NPN transistor as a high side switch, and is obviously not an engineer.
Also, the BC547 is a FAR worse choice than the BC337 for motors, as it is limited to a paltry 100 mA absolute maximum collector current.
I'll add that web site to my "utter nonsense" list (like most Instructables), and recommend that you do so, as well.
I have found in general it is more cost effective to buy a bridge driver then to design and build one. The upper part T1 and T4 may work as emitter followers but the output will be about 0.7V less then the base voltage which will help them get nice and hot driver voltage (A, B) and base resistor voltages (R1, R3) have not been included.
Thank you for your answers.
My goal is to understand certain concepts which is why I don't buy a bridge driver yet.
I didn't quite understand the last sentence. Were you explaining to me the reason for the transistor overheating in the second configuration?
I still don't understand why the transistor heats up more in the second configuration and why I can't use an NPN transistor as a high side driver in this circuit.
As any textbook on transistor circuit design will explain, the voltage on the transistor emitter can never be higher than (base voltage - 0.7V), which in this case increases the transistor power dissipation. So it heats up.
If you want to actually learn this material, randomly chosen web sites are usually not the best sources of information.
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