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I know it has been long time since video is up, but I have two questions. In this connection we are applying 5V to the base and it needs only 0.7 V, is it too much? Another one probably not related, I understand that connecting resistor in series limits current but connecting it in parallel reduces voltage, is that correct? Thanks in advance
The base will keep the voltage across it close to no more than about 0.7 volts as long as the current is limited. The rest of the voltage goes across whatever else is in series with it. A parallel resistor has the same voltage across it as whatever it is parallel with. If it is a low resistance though, then it is more likely to have less voltage across it than what a higher value resistor would have. So it all depends.
as a beginner this has helped me a lot in understanding transistors. i've been struggling with a truck alarm design operated by a mkr nb 1500 3.3v microcontroller. the part i'm trying to figure out right now is how to make a 12v alarm siren go off. the alarm siren is powered from my 12v car battery so i figured i could use a solid state relay to power that but the one i purchased won't close the relay until it gets 5v instead of 3.3v.(false advertisement i guess) so i'm thinking my workaround could be to use the 2n2222a transistor, which i already have in my kit. connect the 5v from the mkr board to the collector which will also be connected to the SSR +. connect the 3.3v digital output pin to the base. and connect the emitter to ground and the negative of the SSR. my question for you. how high of a resistance would you use on the inline base resistor and the other one to ground, being a 3.3v microcontroller with a desire to keep power usage to a minimum? would 10kohm inline and 100kohm to ground be optimal? and should that 100kohm resistor go to ground between the arduino output and the inline 10kohm resistor to prevent the transistor from being activated before the output pin gets a logic low? and any other comments on my design are greatly appreciated. i know i could just use a mosfet but i don't really understand them and i can't find one that would work with a 3.3v microcontroller. and on a side note since you seem to really understand your electrical engineering well i have one more question.(sorry i keep going) i'm also connecting this alarm to a 12v wire which gets +12v when any of the doors are opened. since i would like to read this as a digital input, what would be a good voltage divider to keep from frying my microcontroller?
I don't do anything with vehicles, so wont have the best answer. You will lose voltage if you have the load on the emitter side of a Bipolar Junction Transistor. When used as switches, the load is on the collector side. The emitter goes directly to ground when an NPN BJT is used as a switch. I don't know what resistors would be needed. Could build a prototype circuit with the highest value(s) you think will work and go down from there If need be. Good luck!
Okay I am gonna swap mine around to look like yours; R2 is 220Ω just like you have it which I got from Mouser; I got the LED to light without the 2N2222; Base is *P* so you are loading it from the *{+}* on the rails; I missed something; *NPN* makes the base P-doped? Thus it seems to me we would saturate it from the negative rail;
Yup, base is P type material for NPN. Emitter is N type material, so when base is more positive than emitter by about 0.7V, it will conduct, which also lets current conduct from collector to emitter.
@@Electronzap I thought about it and derive my "more simpler" explanation → Charge carriers and like usual there is some struggling but I did get the LED to light using how you showed it; I also watched some work where 4 meters were used to show forward voltage drop and other that I am sure you are very familiar with; I am trying to implement 2222 drivers for a power MOSFET with the intent being the power device handles an 0.83 Nominal forward current that is likely near 1 amp actual so the 0.83 is going to be near RMS for solenoid coils as most use A/C I plan to get a good FWB at least 3 to 5 times over-rated to the load and run the contractor coils on DC; I have the contractor on the bench and is very heavy compared to the actual load ○○○ much of this I have accomplished but very much hung on inverting to get the 2222 to switch with Hysteresis using the thermistor that is in that kit;
@@Electronzap I obtained an NTE2313 since it was only $2.13 and figured I could burn one up at that price learning then use it on something else if I do not break it; It is only *2 Amp* _label rating_ and looks to be an HV device; This wont meet my spec of 3 to 5 times over-rated; This *HAS* to operate un-attended; I plan to cover with fine-mesh screen - fail containment › as that can be done where install location is ~ my experimenter kit looks to be the same as yours and I much much prefer to keep my ATmega328 free for an actual Real Time Operating monitor for this and other ideas; That is much simpler to me; One of those would be wrap some wire around a single phase load that pulls 13.83 Amps A/C measured as I need to monitor when the contacts are down on that device which is a common 18-gallon water heater then monitoring outside air temp would help in utilization of the audrino RTOS; Critical juncture now is getting Hysteresis for driving what I guess will end up being an NTE2337: 15-A Collector Current 7-Amp Base Current Collector Power Dissipation - 2 Watts Load current Collector to chassis is planned at 1 Amp so this is 15-x overrating? This was pulled by my supplier as very common and price supplier wants gets within can-do range;
Hi , New at this , love your vids. When I measure the emitter (hope I got that right) to ground with an Led (2.2 v) and only a 3v I get a 49ma. Perhaps a clue that I do not understand is that it stays at 49ma no matter what the protecting resistor on the Led is, 465 to 10K. Any idea what to test ??
Thanks! The emitter passes the current of both the collector and base so I am guessing that 49mA is about how much current is going through the base. Base current should be a lot lower than collector.
@@Electronzap Yes I am using the 10k resistor so from that to the control (middle) it is .20ma . Wait, I totally screwed this up. I had the Led on the same leg as the switch when the switch was turned on . I am not sure what this did. Correcting the mistake I now get 2.74ma from emitter to ground with Led in circuit. So what was my circuit doing ? Besides pulling way too much current. Not sure why Led did not burn out??
LEDs can withstand higher currents than 20mA especially at low voltages. It may not be as bright as it used to be anymore and might not last as long now.
