Hi all,
While I'm searching for the answer for my question, I found the post thread by title named as "What is use of R41 (base to emitter) resistor in Transistor Relay Circuit ?".
But, one of the post in the thread stated that, first need to be calculated the leakage current of the transistor. Again, I don't know how to calculate the leakage current. However, MisterBill2 posted the text by saying what are the thinks need to be calculated to find out the leakage current.
The text from MisterBill2:
https://forum.allaboutcircuits.com/...-resistor-in-transistor-relay-circuit.149416/
[OK, the process for determining that resistor starts elsewhere. As already mentioned, first the required collector current to operate the relay with a worst case transistor saturation voltage must be known. That will require reading the specification sheet.
Next, the base current to bring the switching transistor into saturation, for a minimum gain transistor must be calculated.
Once the required base current is known, the value of R3, the base current limiting resistor can be selected, allowing for both the base-to emitter voltage to vary with temperature, and allowing some current through R41 (R4??). The value of R4 is then selected to pull the base of the transistor below the cutoff voltage even at the maximum leakage current of the opto-isolator plus the off-state base leakage of the transistor.
Of course an adequate margin must be used to allow for tolerance variations of the resistor values. Then an appropriate standard value for the resistor is selected. This is why most engineers just pick values based on experience and common practice.]
In my case, I don't have any relay in my circuit. Just I'm learning how to calculate the Rbe resistor?. I'm not understand that much from the text, but, I have tried my way please could you also help me.
I have just assumed and consider that 1A current (Ic) is the required and 5V (Vbe), such that I have calculated the Rb.
According to datasheet (from page 5), 50mA (Ib) current is required to turn on the transistor to pass 1A current from collector to emitter.
Rb = (Vbe - Vbe(on)) / Ib => (5-1.050) / 50m => 79 ohms ( according to datasheet Vbe(on) = 1.050V)
From here on-wards not understand what I have to do to calculate the leakage current of the transistor. Please could you help me?.
Thank you, all.
While I'm searching for the answer for my question, I found the post thread by title named as "What is use of R41 (base to emitter) resistor in Transistor Relay Circuit ?".
But, one of the post in the thread stated that, first need to be calculated the leakage current of the transistor. Again, I don't know how to calculate the leakage current. However, MisterBill2 posted the text by saying what are the thinks need to be calculated to find out the leakage current.
The text from MisterBill2:
https://forum.allaboutcircuits.com/...-resistor-in-transistor-relay-circuit.149416/
[OK, the process for determining that resistor starts elsewhere. As already mentioned, first the required collector current to operate the relay with a worst case transistor saturation voltage must be known. That will require reading the specification sheet.
Next, the base current to bring the switching transistor into saturation, for a minimum gain transistor must be calculated.
Once the required base current is known, the value of R3, the base current limiting resistor can be selected, allowing for both the base-to emitter voltage to vary with temperature, and allowing some current through R41 (R4??). The value of R4 is then selected to pull the base of the transistor below the cutoff voltage even at the maximum leakage current of the opto-isolator plus the off-state base leakage of the transistor.
Of course an adequate margin must be used to allow for tolerance variations of the resistor values. Then an appropriate standard value for the resistor is selected. This is why most engineers just pick values based on experience and common practice.]
In my case, I don't have any relay in my circuit. Just I'm learning how to calculate the Rbe resistor?. I'm not understand that much from the text, but, I have tried my way please could you also help me.
- Max. case Collector-Emitter Saturation Voltage (Vce) - 305mV (according to ZXTN25060BZ datasheet)
- Max. Collector current (Ic) - 5A (according to ZXTN25060BZ datasheet)
- Min. DC current gain (hFE) - 20 (according to ZXTN25060BZ datasheet)
I have just assumed and consider that 1A current (Ic) is the required and 5V (Vbe), such that I have calculated the Rb.
According to datasheet (from page 5), 50mA (Ib) current is required to turn on the transistor to pass 1A current from collector to emitter.
Rb = (Vbe - Vbe(on)) / Ib => (5-1.050) / 50m => 79 ohms ( according to datasheet Vbe(on) = 1.050V)
From here on-wards not understand what I have to do to calculate the leakage current of the transistor. Please could you help me?.
Thank you, all.