Hi, I’m working on an Arduino project and have computed all the type/values for the needed discreet components, but am struggling with one. I’ve attached a Spice diagram of this piece of the circuit:
I need to drive a door strike that has the following characteristics:
Operating Voltage = 12
Current Draw = 750 mA
RL (calculated) = 16 ohm
I plan to use a transistor and while a 2N2222 is rated at 1 amp, my understanding is that you should not drive a transistor beyond 2/3 of its max current. Therefore, I selected a BD135 which has a max IC of 1.5 amps. From its datasheet:
Vbe = 1 V
Vce = 2 V
hFE = 250
Using the calculator at http://www.petervis.com/GCSE_Design...ator/transistor_base_resistor_calculator.html
I calculate an Rb of 533Ω, the closest I have on hand is a 510Ω or 680Ω.
Sorry for the long background, now my questions:
1) Is the BD135 a reasonable choice for the transistor? If not, what is a better choice?
2) Is my Rb calculation correct?
3) Assuming it is correct, do I use the 510Ω or 680Ω resistor and why?
4) In transistor circuits I often see a second resistor connecting the emitter to the base (R2 in the Spice diagram). Is this needed and if so why and what value?
5) Since the door strike is an inductive load I believe I need a flyback diode – do I have D1 (in the spice diagram) in the correct bias/location?
6) If I used a higher rated transistor, like a TIP120 (5 amps) would it run cooler?
7) Since the strike is 12V would it be smarter to isolate it from the Arduino with a optocoupler or relay?
Thanks in advance,
Tom
I need to drive a door strike that has the following characteristics:
Operating Voltage = 12
Current Draw = 750 mA
RL (calculated) = 16 ohm
I plan to use a transistor and while a 2N2222 is rated at 1 amp, my understanding is that you should not drive a transistor beyond 2/3 of its max current. Therefore, I selected a BD135 which has a max IC of 1.5 amps. From its datasheet:
Vbe = 1 V
Vce = 2 V
hFE = 250
Using the calculator at http://www.petervis.com/GCSE_Design...ator/transistor_base_resistor_calculator.html
I calculate an Rb of 533Ω, the closest I have on hand is a 510Ω or 680Ω.
Sorry for the long background, now my questions:
1) Is the BD135 a reasonable choice for the transistor? If not, what is a better choice?
2) Is my Rb calculation correct?
3) Assuming it is correct, do I use the 510Ω or 680Ω resistor and why?
4) In transistor circuits I often see a second resistor connecting the emitter to the base (R2 in the Spice diagram). Is this needed and if so why and what value?
5) Since the door strike is an inductive load I believe I need a flyback diode – do I have D1 (in the spice diagram) in the correct bias/location?
6) If I used a higher rated transistor, like a TIP120 (5 amps) would it run cooler?
7) Since the strike is 12V would it be smarter to isolate it from the Arduino with a optocoupler or relay?
Thanks in advance,
Tom
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