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I was projecting a simple circuit that, from a digital OUTPUT from an Arduino zero (3.3 V) switch on a BJT that is connected to a relay.
The base of the BJT must have a current of about 5mA or less. Is this configuration enough to run a relay?
I have simulated this circuit and Ic is about 49mA; if I change the relay, Ic increases or it's fixed?
I'm not really good at this thing
simulate this circuit – Schematic created using CircuitLab
if I change the relay, Ic increases or it's fixed?
Different relays will draw different coil currents at their designed operating voltage. Check the datasheet for your relay.
50 mA is a reasonable number for a low power 5 V relay, but pretty low if your relay is rated for more than ~2 A switched current.
To maintain your 5 mA base current limit you might need to either use a Darlington configuration, or change from a BJT to a logic-level MOSFET.
A BJT can be considered a "current amplifier", therefore its gain is of interest. In your case (5mA/50mA) this gain is relatively low
A BJT can be considered a "current amplifier", therefore its gain is of interest. In your case (5mA/50mA) this gain is relatively low. For a given amplification, figure out the required base current. The base circuitry is then quite similar to a resistor-LED-circuit.
Note, that Ic is specific for the used relay (datasheet).
