Hall sensor and BC547

[KevinW]

I found this circuit using 12vdc and considering the Hall Sensor output voltage is equal to operating voltage does the base of the transistor not require a resistor?

 

[alec_t]

Depends on the Hall device characteristics. It may have some current-limiting feature internally.

 

[rjenkinsgb]

Absolutely, yes!

As well as a series resistor to the base, I'd add a base-emitter resistor to ensuire any residual leakage does not cause problems.

 

[Nigel Goodwin]

Depends on the Hall device characteristics. It may have some current-limiting feature internally.

Or it might be yet another crappy non-working circuit out there on the internet

It doesn't even give you a clue as to what the sensor might be.

 

[KevinW]

Thanks for the replies, the sensor is A3144.

Digital Output Hall-effect sensor

• Operating voltage: 4.5V to 28V (typically 5V)
• Output Current: 25mA
• Can be used to detect both the poles of a magnet
• Output voltage is equal to operating voltage
• Operating temperature: -40°C to 85°C
• Turn on and Turn off time is 2uS each
• Inbuilt reverse polarity protection

 

[alec_t]

Output voltage is equal to operating voltage

Actually the A3144 output is open collector, giving a choice of 'operating voltage' and requiring a pull-up resistor.
So the BC547 in the post #1 pic would be redundant if the LED needed less than 25mA.
BTW, the A3144 is obsolete.

 

[KevinW]

A3144 3144E OH3144E Hall Effect Sensor is how it was advertised and they have been shipped so I hope to get them soon.
I slipped a 10k resistor onto the base of the transistor and it seems to be working fine through the transistor without the Hall sensor.
I don't see the need for the transistor when the Hall Sensor is the switch.