What size a resistor one needs for a circuit with a transformer output of 12VDC at 200mA to a relay of 75mA?
All componets are 12VDC and an added circuit that turns on when the other turns off powers a buzzer of 10mA which I don't know the resistor for either so help would be appreciated.
Answer:
If the relay is designed for 12v (which it is), it can be connected directly to the 12v supply and it will take 75mA when activated. No resistor is needed.
This is a trick question!!
Not enough information has been provided for the buzzer part of the question.
V=IR
Voltage = Current * Resistance
That's all I remember from my Electrical Engineering class...
use 200 ohm resistor (12000/75). this Will drive your relay smoothly, and don't forgot to add one Diode in parallel to Relay for blocking the reverse current.
It doesn't matter how much current might be able to come from the transformer. All you care about is the 75mA that the relay needs. You have not said what resistance the relay has. It might not need any additional series resistance to limit its current to 75mA if it is itself at 160 ohms (Ohms law of R=E/I for 12V/.075A).
You mention that the components are all DC but a transformer is an AC device that outputs an AC current. I am assuming that there is also a rectifier (and maybe a filter) to make that AC into DC for the relay.
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Answer:
If the relay is designed for 12v (which it is), it can be connected directly to the 12v supply and it will take 75mA when activated. No resistor is needed.
This is a trick question!!
Not enough information has been provided for the buzzer part of the question.
V=IR
Voltage = Current * Resistance
That's all I remember from my Electrical Engineering class...
use 200 ohm resistor (12000/75). this Will drive your relay smoothly, and don't forgot to add one Diode in parallel to Relay for blocking the reverse current.
It doesn't matter how much current might be able to come from the transformer. All you care about is the 75mA that the relay needs. You have not said what resistance the relay has. It might not need any additional series resistance to limit its current to 75mA if it is itself at 160 ohms (Ohms law of R=E/I for 12V/.075A).
You mention that the components are all DC but a transformer is an AC device that outputs an AC current. I am assuming that there is also a rectifier (and maybe a filter) to make that AC into DC for the relay.
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