I got into the stage where we're suppose to build some sort of protection system so we can plug-in outsourced power supply and prevent the arduino uno from frying. The FET, if you pick a decent one will also not drop any appreciable voltage when activated so the 200mV accounted for in the above equations should be ignored and a resistance of about 36.5\$\Omega\$ should be chosen.I just started studying Arduino and I'm watching a online course. However, I'd be tempted to use an N channel MOSFET and you can avoid the heavy current drive into the base. I believe the Arduino can supply this current but check as I'm no expert on it.
PN2222 TRANSISTOR THRESHOLD SERIES
Again, the datasheet will give you more detail, but many of the parameters (like \$\beta\$ or \$h_\$ = 34.5\$\Omega\$.Ĭhoose standard values of resistance that add up 34.5\$\Omega\$ but observe that the power disippation will be \$I^2R=0.1^2\times 34.5=0.345W\$ĭriving the base from the MCU is relatively straightforward - use a series resistor of about 220\$\Omega\$ - this will put about 20mA into the base and ensure the transistor is fairly well switched-on.
When you want to drive the transistor into saturation (as you do here), make the base current 1/15th of the collector current.
Simulate this circuit – Schematic created using CircuitLab There's a rule of thumb for a BJT used as a common-emitter switch, like this: By ignoring it, you slightly reduce the current in the LED, which is erring on the side of caution, so isn't necessarily a bad thing.Īnd I'm also trying to figure out the math used to calculate the required milliamps that have to flow through the base of the transistor in order to fully turn it on (but not waste extra electricity). What I would like to do, is use a transistor (pn2222) to limit the amount of current sent to a circuit, say limit to 45 ma at 5 volts. \$0.2V\$ also isn't very significant to most circuits, so you can just ignore it. The PN2222A, also known as the PN2222, is a general-purpose transistor best suited to applications that don’t require high stress on the component. The datasheet will give you more accurate values, under a range of operating conditions. I typically go for a forced beta of 1/2 the minimum hfe so assuming a minimum hfe of 100 for a 2N2222: 4mA/5080uA. PN2222 General Purpose Transistor, Package: TO-92 (TO-226), Pins3. The PN2222A is equivalent to the 2N2222A, and the names are often used. If a CMOS output is used to drive the transistor, then R2 is not needed because the CMOS output can pull the base to ground. But there are two important features that distinguish both. The 2N2222A transistor is very much similar to the commonly used NPN transistor BC547. The value of Beta for most standard NPN transistors can be found in the manufactures data sheets but generally range between 50 200. Depending on the datasheet, it is characterized as a transistor or an amplifier, but it can perform both of those functions. 2N2907(PNP), 2N3904(PNP), 2N3906 (PNP), BC637, S9014, BC148, 2N4403, MPS2222, PN2222, KN2222, KTN2222. The values of Beta vary from about 20 for high current power transistors to well over 1000 for high frequency low power type bipolar transistors. \$0.2V\$ is a reasonable estimate for most BJTs in saturation. The PN2222A, also known as the PN2222, is a general-purpose transistor best suited to applications that don’t require high stress on the component. This will not operate to limit or restrict the Groups liability for death.
PN2222 TRANSISTOR THRESHOLD HOW TO
What I don't understand is the math for how to figure out the exact voltage drop of the transistor between the collector and emitter. NPN Silicon Planar Switching Transistors.
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