Project may need transistor circuits

[ahe]

Hi everyone,

I'm currently working on a project and part of this project may need transistor circuits in it. As I'm totally new to transistors and circuits I would greatly appreciate any help offered.

I was wondering if it is possible to program/create transistors to perform certain tasks. Specifically, would the transistor circuit be able to alternate signals (currents) to two objects (e.g.lights) at high speeds (1/10th a second switching times). Also, what is the expected lifespan of transistors and are they expensive?

Thanks for your contributions!

Cheers

 

[I_am_learning]

You usually don't create or program transistors, you buy various kinds, arrange and wire them to perform certain tasks.
Transistor circuit are capable of doing most clever of things. Perhaps, also what you want.
1/10 th a second switching isn't considered a High speed in electronics. Rather it is a very slow speed.
Transistor are generally very reliable, if you don't push them to limits. Don't worry about their life span.
Their price highly depends upon their type. But, I am in the thought that, all the kinds you will probably need will be considered quite cheap.

 

[berkeman]

Hi everyone,

I'm currently working on a project and part of this project may need transistor circuits in it. As I'm totally new to transistors and circuits I would greatly appreciate any help offered.

I was wondering if it is possible to program/create transistors to perform certain tasks. Specifically, would the transistor circuit be able to alternate signals (currents) to two objects (e.g.lights) at high speeds (1/10th a second switching times). Also, what is the expected lifespan of transistors and are they expensive?

Thanks for your contributions!

Cheers

I googled transistor circuits tutorial, and got lots of good hits. Here is the hit list:

http://www.google.com/search?source...L_enUS301US302&q=transistor+circuits+tutorial

.

 

[ahe]

hey guys, thanks for the advice! :) that's helping me get my head around this!

 

[Bob S]

Here in thumbnail is a two-transistor multi-vibrator circuit with two flashing LEDs. Each LED flashes about four times a second. The transistors cost less than $1.00 each at RadioShack or similar stores. This simulation is now running on a 3 volt battery. The LED simulation model is unrealistic, so the two 100-ohm resistors may have to be reduced, or the battery may have to be boosted up to 4.5 volts.

Bob S

 

[ahe]

Hey Bob,

Thanks for drawing up that schematic. I was wondering if it is possible to alternate the LEDs lighting up (currently, they light up simultaneously?)

Also, how can I calculate the power required (used and remaining) for a circuit such as this? For example it is shown that a 3V battery is used to light the LEDs but how can I calculate any voltage going out?

Cheers

 

[Bob S]

Hi ahe-

You have some good questions.

1) Only one transistor is on at a time, so the two LEDs alternate back and forth..

2) You can calculate the current in each transistor as follows. In the waveform in the thumbnail, the voltage across the 100-ohm resistors is 2.4 volts - 0.1 volts = 2.3 volts when the transistor is ON. So 2.3 volts/100 ohms = 23 milliamps. So the power is .023 amps x 3 volts = 69 milliwatts.

3) By the way, an old 5-volt cell phone charger would be an excellent battery substitute. The waveform shown is the npn transistor collector. You can probably easily drive 1000 ohms to ground from it. If you want to drive a low impedance, use a voltage follower on Vout1 (Q1 collector).

4) The period of the waveform is about 0.25 seconds (4 Hz). This is determined by the two capacitors C1 and C2, and the two resistors R3 and R4. C1*R3 = 20uF x 10,000 ohms = 0.2 seconds. N the simulation, I changed C1 and C2 to 2nF, the battery to 5 volts (and C3 to 1nF), and the period went down to 25 microseconds (40 kHz). The rise and fall times are less than 1 microsecond.

5) The values of R3 and R4 should not be more than 100 times R1 and R2, due to the gain of the two transistors.

6) The transistors will last indefinitely. The capacitors will cost between $1.00 and $2.00 each. If possible, avoid electrolytics.

I hope this helps. Let me know if you want me to try other values of resistors, capacitors, battery, etc.

Bob S