Relay Driver using Bipolar Transistor
Bipolar transistor may be a part that works primarily based on the presence or absence of flow within the foot triggers the bottom. within the relay driver applications, the transistor works as a switch that at the time did not settle for the current triggers, then the transistor are within the position of the cut-off and doesn't conduct current, Ic = 0. And when the bottom receives the flow triggers, then the transistor can turn out to be a state of saturation and delivers current. the subsequent may be a sensible circuit of relay drivers that are reliable for use in microcontroller projects.
The circuit on the left may be a common collector or emitter follower and has the advantage of one less half since a resistor isn't required in series with the transistor base. but the voltage across the relay coil are 2 diode drops but the provision voltage, or regarding eleven volts for a twelve.5 volt input.
The common emitter configuration on the proper offers the advantage of the total supply voltage across the load for most of the delay time, that makes the relay pull-in and drop-out voltages less of a priority however requires an extra resistor in series with transistor base. The common emitter (circuit on the right) is that the better circuit since the series base resistor can be selected to get the required delay time whereas the capacitor should be selected for the common collector (or an additional resistor utilized in parallel with the capacitor).
The time delay for the common emitter are approximately 3 time constants or 3*R*C. The capacitor/resistor values can be discovered from the relay coil current and transistor gain. for example a 120 ohm relay coil can draw one hundred mA at twelve volts and assumming a transistor gain of 30, the bottom current are 100/30 = 3 mA. The voltage across the resistor are the provision voltage minus 2 diode drops or 12-1.4 = 10.6. The resistor price are the voltage/current = 10.6/0.003 = 3533 or regarding 3.6K. The capacitor price for a fifteen second delay are 15/3R = 1327 uF. we can use a regular 1000 uF capacitor and increase the resistor proportionally to induce fifteen seconds.
The circuit on the left may be a common collector or emitter follower and has the advantage of one less half since a resistor isn't required in series with the transistor base. but the voltage across the relay coil are 2 diode drops but the provision voltage, or regarding eleven volts for a twelve.5 volt input.
The common emitter configuration on the proper offers the advantage of the total supply voltage across the load for most of the delay time, that makes the relay pull-in and drop-out voltages less of a priority however requires an extra resistor in series with transistor base. The common emitter (circuit on the right) is that the better circuit since the series base resistor can be selected to get the required delay time whereas the capacitor should be selected for the common collector (or an additional resistor utilized in parallel with the capacitor).
The time delay for the common emitter are approximately 3 time constants or 3*R*C. The capacitor/resistor values can be discovered from the relay coil current and transistor gain. for example a 120 ohm relay coil can draw one hundred mA at twelve volts and assumming a transistor gain of 30, the bottom current are 100/30 = 3 mA. The voltage across the resistor are the provision voltage minus 2 diode drops or 12-1.4 = 10.6. The resistor price are the voltage/current = 10.6/0.003 = 3533 or regarding 3.6K. The capacitor price for a fifteen second delay are 15/3R = 1327 uF. we can use a regular 1000 uF capacitor and increase the resistor proportionally to induce fifteen seconds.
