#Pnp transistor base emitter collector how to
#Pnp transistor base emitter collector trial
#Pnp transistor base emitter collector plus

So yes, a lower value pull-down might be safer with nuclear devices. Even a tiny 2uA leakage current could light your 2mA LED (2uA x hFE = 800uA is visible). at RESET)Īny CMOS pin is very sensitive to noise when it is an i/p. The reason for the 10k base-emitter resistor is to ensure that your transistor does not turn on when the PORT is configured as an i/p. Your simple general purpose 2.100mA type of transistor switch will be fine with a 10k base resistor. you need to calculate the base current, and check data sheets.

You need a protective diode across the relay coil. (5) can be done the same for small currents. (2),(3) are easily done with a small NPN transistor with the load between 5V and collector. This is why you were asked what you want to switch on and off. In my experience I have always had to use a lower resistor, such as 220ohms on the base saturate the transistor sufficiently to drive things such as small 5V motors and relays etc. Rhoaste wrote: Someone also mentioned here that a 10K resistor between base and AVR for general applications.

Good for buffering say audio signals generated from AVR.

the emitter voltage follows the base voltage. The collector-emitter voltage is about 0.2V when transistor is fully on, so in a 5V system your load gets about 4.8V at high currents.Īnother nice feature of the transistor is that the base-emitter voltage is about 0.7V, so if you put the load on emitter and drive the base with AVR, the load can never have more than 4.3V over it in 5V system, i.e. Normally 4k7 would be good there but people may put some safety factor there and just put a 1k base resistor. So a 100mA motor on collector needs 1mA of base current. As a rule of thumb you can approximate a regular small-signal transistor to have a current gain of about 100. Transistors can be thought as current amplifiers. For digital control you almost always put the load on collector and ground the emitter if you have a NPN transistor. Well it depends are you trying to drive digital things on/off like leds, motors and relays or drive analog things like speakers etc. What, these things are not in electronics books these days? Someone also mentioned here that a 10K resistor between base and AVR for general applications.

#Pnp transistor base emitter collector trial

I have been working with trial and error and dependent on google really.

#Pnp transistor base emitter collector how to

My question is one for my own general understanding on how to connect the load to the transistor (via the emitter or collector) so I can take these reasons into account in my designs. I'm not referring to any specific application that I am currently building. Part 12 discusses ways of driving a PNP transistor when the load must be driven with a higher voltage than the microcontroller.I'm sorry, but I'm still a bit lost really. The microcontroller would likely be damaged in this situation.

#Pnp transistor base emitter collector plus

Worse yet, the microcontroller output pin will be seeing more than 5V, which greatly exceeds the usual limitation of the microcontroller supply voltage plus 0.3V. Unless the transistor has exceptionally low gain, it will be turned on even though with the output pin high it should be turned off. Assume the output pin is high, at 5V, and the base resistor is 1000 ohms. Consider the following.: Suppose the load voltage is +12V and the microcontroller is running at 5 volts. Normally it is best to use the same voltage to drive the load that is used to power the microcontroller. One additional thing you need to be careful with PNP high side switches is the voltage used to drive the load. Part 12 - Switching Higher Voltage Loads with PNP Transistors Part 8 - Using PNP Transistors as High Side Switches Part 7 - Using Transistors to Switch Higher Power Loads