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edited Jan 7, 2021 at 11:48

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I am designing a simple H bridge circuit for use with the Atmega8 microcontroller. The DC motor moves this application a lot and generates 140ma140 mA current spikes (DC motor locked) or 60ma60 mA with normal workload.

The working voltage ranges from 10V10 to 16V16 V, I will use the transistors BD441 / BD442 (2A2 A of DC current at 20V20 V and 4A4 A DC at 10V10 V) were the most robust that will fit in my circuit.

Q1 to Q5 will be BD441 / 442, some questions:

Q5 through R8 (shunt) limits the current (I will leave 200ma peak), it makes sense to use this transistor to limit the inductive current peaks or I could just limit the current through the base of the transistors? What would be the problem of operating the base current transistor to operate in a linear region up to 200ma200 mA?
Q6 will be a small npn, together with a 20V20 V zener it makes Q5 cut and stops driving in cases of over voltage. I've seen this DC motor being operated by a transistor with 45 Vce without fail, I wanted more robustness in the circuit, does it make sense to use it or not?
Use small resistors (0R33, 0R66 etc.) in the DC motor terminals help protect the circuit against very short surge currents that the oscilloscope cannot see or does my 4 ohm rshunt resistor solve this already?

I am designing a simple H bridge circuit for use with the Atmega8 microcontroller. The DC motor moves this application a lot and generates 140ma current spikes (DC motor locked) or 60ma with normal workload.

The working voltage ranges from 10V to 16V, I will use the transistors BD441 / BD442 (2A of DC current at 20V and 4A DC at 10V) were the most robust that will fit in my circuit.

Q1 to Q5 will be BD441 / 442, some questions:

Q5 through R8 (shunt) limits the current (I will leave 200ma peak), it makes sense to use this transistor to limit the inductive current peaks or I could just limit the current through the base of the transistors? What would be the problem of operating the base current transistor to operate in a linear region up to 200ma?
Q6 will be a small npn, together with a 20V zener it makes Q5 cut and stops driving in cases of over voltage. I've seen this DC motor being operated by a transistor with 45 Vce without fail, I wanted more robustness in the circuit, does it make sense to use it or not?
Use small resistors (0R33, 0R66 etc.) in the DC motor terminals help protect the circuit against very short surge currents that the oscilloscope cannot see or does my 4 ohm rshunt resistor solve this already?

I am designing a simple H bridge circuit for use with the Atmega8 microcontroller. The DC motor moves this application a lot and generates 140 mA current spikes (DC motor locked) or 60 mA with normal workload.

The working voltage ranges from 10 to 16 V, I will use the transistors BD441 / BD442 (2 A of DC current at 20 V and 4 A DC at 10 V) were the most robust that will fit in my circuit.

Q1 to Q5 will be BD441 / 442, some questions:

Q5 through R8 (shunt) limits the current (I will leave 200ma peak), it makes sense to use this transistor to limit the inductive current peaks or I could just limit the current through the base of the transistors? What would be the problem of operating the base current transistor to operate in a linear region up to 200 mA?
Q6 will be a small npn, together with a 20 V zener it makes Q5 cut and stops driving in cases of over voltage. I've seen this DC motor being operated by a transistor with 45 Vce without fail, I wanted more robustness in the circuit, does it make sense to use it or not?
Use small resistors (0R33, 0R66 etc.) in the DC motor terminals help protect the circuit against very short surge currents that the oscilloscope cannot see or does my 4 ohm rshunt resistor solve this already?

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asked Jan 7, 2021 at 10:17

Marcelo Augusto

H-Bridge current limiting

The working voltage ranges from 10V to 16V, I will use the transistors BD441 / BD442 (2A of DC current at 20V and 4A DC at 10V) were the most robust that will fit in my circuit.

Q1 to Q5 will be BD441 / 442, some questions:

Q5 through R8 (shunt) limits the current (I will leave 200ma peak), it makes sense to use this transistor to limit the inductive current peaks or I could just limit the current through the base of the transistors? What would be the problem of operating the base current transistor to operate in a linear region up to 200ma?
Q6 will be a small npn, together with a 20V zener it makes Q5 cut and stops driving in cases of over voltage. I've seen this DC motor being operated by a transistor with 45 Vce without fail, I wanted more robustness in the circuit, does it make sense to use it or not?
Use small resistors (0R33, 0R66 etc.) in the DC motor terminals help protect the circuit against very short surge currents that the oscilloscope cannot see or does my 4 ohm rshunt resistor solve this already?