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depending on post 1 and 3
what this configuration equations ? while the desired output current is emitter current using for relay-on because the current from mcu insufficient
The relay coil should be connected from the collector of the transistor to +5V and a reverse connected diode should be parallel to the relay coil to quench its inductive high voltage spike. Then the transistor should have its emitter connected to 0V and have a series base resistor calculated for a current that is 1/10th the collector current.
but i connect relay to the emitter and it work very well !
hFE of a transistor is the current gain or amplification factor of a transistor.
hFE (which is also referred to as β) is the factor by which the base current is amplified which is fed into the transistor.
A transistor works by feeding a base current into the base of the transistor. The base current is then amplified by hFE to yield its amplified current. The formula is below:
IC= hFEIB=βIB
So if 1mA is fed into the base of a transistor and it has a hFE of 100, the collector current will be 100mA.
Every transistor has its own unique hFE. The hFE is normally seen to be a constant value, normally around 10 to 500, but it may change slightly with temperature and with changes in collector-to-emitter voltage.
Check the transistor's datasheet for the hFE value in its specifications.
The relay coil should be connected from the collector of the transistor to +5V and a reverse connected diode should be parallel to the relay coil to quench its inductive high voltage spike. Then the transistor should have its emitter connected to 0V and have a series base resistor calculated for a current that is 1/10th the collector current.