Tagged Questions

2
votes
2answers
96 views

Using a transistor to add to max current output from a opamp?

I thought I understood transistors but now I'm confused again. I have a basic opamp circuit to amplify the input of a electret microphone. The output of the opamp will vary within 1-4V. Now I want ...
2
votes
2answers
126 views

Is this switch circuit correct?

This is a follow-up question to How high is "high impedance" on this chip (CD74HC125E) I finally decided to use a pn2222 transistor to act as a switch that activates the transmitter. The ...
2
votes
1answer
73 views

transistor loop to limit the current

I am trying to implement the DALI TX/RX circuit below. The description says: The other transistor (T2) is controlled by the current flowing through the resistor (R1). If a DALI slave unit is ...
3
votes
2answers
128 views

arduino pulse to transistor power maximum

Hello I want to get a confirmation that what I am doing is not going to fry my Arduino Mega. The sketch I am using to send a pulse out on pin 8 to a 2n3055 that is switching 12 volts is this: ...
3
votes
1answer
105 views

Transistor varies with Temperature

My questions pertains to the \$ \beta\$ value of a transistor. On page 162 of this book, it says that \$ \beta\$ increases as temperature of the transistor increases. But it doesn't explain why. Can ...
3
votes
3answers
390 views

Problems with Transistor TIP122

I was testing some things on my protoboard to learn a little about transistors. I made this: The batteries are two AA 1.5V in series. The resistor is a 1Kohm. The transistor in a TIP122 npn ...
5
votes
3answers
343 views

Purpose of these two transistors

Hi does anybody know what's the purpose of the Q1 and Q2 transistors, sounds to me like they are constant current sources. Am I wrong? Could somebody explain me the purpose of those Q1 and Q2 ...
7
votes
1answer
182 views

Current flow priorities in PSU / PSU review

Being an electronics hobbyist, I'm having quite a challenge to design a PSU, which must run both on batteries (during the night time) as well as on Solar energy (daytime). The device is intend to run ...
3
votes
2answers
1k views

Arduino/Atmega with TIP120/121/122 transistors: base current question

I am learning about transistors, and can't seem to find the answer to a few questions which are stumping me. I will be referring to the TIP120/121/122 Darlington Transistor. As I understand ...
2
votes
3answers
306 views

safety margin in transistor base current

In this answer poster calculates a safety factor of 10 for the minimum base current in a transistor used as a switch. Seems like a lot to me, and for higher collector currents this may mean that a ...
3
votes
2answers
293 views

BJT in Active/Linear mode — How can it still conduct current?

So I've read quite a few books on how BJT's work and all of them seem to gloss over how a BJT in the linear mode with the base/emitter junction forward biased and ...
4
votes
1answer
205 views

Understanding a transistor configuration

I started watching this video series on a DIY lab power supply by Dave @ EEVBlog. On his video he's analyzing mostly simple constant current circuit. However, at the top of the circuit there's two ...
2
votes
1answer
1k views

Transistor current limiter, microcontroller controlled?

I've come across a few transistor current limiter schematics, similar to this one: However, I am not entirely sure how I could implement microcontroller functionality to control this. I think ...
-2
votes
1answer
962 views

How does transistor amplify current? [duplicate]

Possible Duplicate: I don't care how a transistor works, how do I get one to work? Basic questions about transistor amplification I have heard transistors are used in many electronic ...
5
votes
2answers
367 views

Transistor in saturation mode?

I was wondering why do we so often want out transistor to work in saturation mode? Ie. For a MOS Current Steering Circuit we want our transistors to operate in the saturation region....
0
votes
3answers
1k views

how to drive 5x5 IR LEDs with 100 mA, using Arduino

I am trying to do my first Arduino project, and I would like to drive a 5x5 matrix of IR leds. I would only like to have one switched on at a time. I understand that in an array I can do it with 5 ...
8
votes
3answers
1k views

Need help operating a transistor

I have a relay operated by an NPN transistor that needs some voltage applied to the base. I'm working with an arduino and if I give it a digital port, all's well. The circuit looks like this one: ...