hi
im currently designing a transistor switching circuit for a 5VDC relay to switch an output of 240 VAC. There's no speed switching required. just on/off=)
The coil of my relay is 63 ohms requiring 79.4mA of current to turn it on as per datasheet.
As this is a switching circuit controlled by a MCU pin, I tend to make use of the saturation region so that Vce becomes almost completely zero (full drop across coil) thus resulting in almost no power dissipation across the transistor. (Is this assumption correct?) Apart from low power consumption, and acheiving the desired bias points, is there any other areas which I have overlooked in designing a switching transistor circuit?
In my college lab, there are 2n2222 transistors which I found are commonly used for switching and other small signal amplifiers like bc107 etc..
does purely using a 2n2222 have an advantage over the small signal amplifiers ? I know both will achieve the job of switching as I've tried but I want to know the distinctions or should I say strong points of using each respective one?
I also noticed that on the 2n2222 datasheet, the DC gain @ approx Ic=80mA as I require is not explicitly shown but only shown for values of Ic @ 10mA and other nice round numbers that start with 1. There also seems to be no graph unlike the BC547 transistors which show Ic versus gain. How should I extrapolate from the given values? All I can do for now is obtain the gain at the required current through orcad simulations.
thanks alot
im currently designing a transistor switching circuit for a 5VDC relay to switch an output of 240 VAC. There's no speed switching required. just on/off=)
The coil of my relay is 63 ohms requiring 79.4mA of current to turn it on as per datasheet.
As this is a switching circuit controlled by a MCU pin, I tend to make use of the saturation region so that Vce becomes almost completely zero (full drop across coil) thus resulting in almost no power dissipation across the transistor. (Is this assumption correct?) Apart from low power consumption, and acheiving the desired bias points, is there any other areas which I have overlooked in designing a switching transistor circuit?
In my college lab, there are 2n2222 transistors which I found are commonly used for switching and other small signal amplifiers like bc107 etc..
does purely using a 2n2222 have an advantage over the small signal amplifiers ? I know both will achieve the job of switching as I've tried but I want to know the distinctions or should I say strong points of using each respective one?
I also noticed that on the 2n2222 datasheet, the DC gain @ approx Ic=80mA as I require is not explicitly shown but only shown for values of Ic @ 10mA and other nice round numbers that start with 1. There also seems to be no graph unlike the BC547 transistors which show Ic versus gain. How should I extrapolate from the given values? All I can do for now is obtain the gain at the required current through orcad simulations.
thanks alot