# Transistor wiring question?

I've searched for two days to determine how to wire a transistor... there's a lot of info about engineering and math and physics... I don't want to return to college. I have a 9v dc source and an NPN transistor, where do I apply the (+) and (-) leads of my supply to the transistor and where do I apply the leads of my multimeter to measure the output? Do I need to introduce other components? (I think I understand the collector, base, emitter relationship).

The plan is to use the transistor to *increase* current? (I know there are lots of laws and theories that might suggest that I worded this wrong but help me out... you know what I mean).

Relevance

** With the focus on obtaining an increase in current from the

input to the output, (amplification), perform the following tasks.

From basics, bipolar transistor Base current controls

Collector current. No base current, then no collector current,

full stop.

Each individual transistor increases the base current by a

factor known as the current gain,

ß (Beta), or hFE ( a hybrid parameter).

This gain can be as high as 600 for high gain low power transistors.

But can be as low as 3 for high frequency, high power transistors.

However typical gains for everyday low power transistors

have current gains around 150 to 300.

.

Using a common small signal NPN transistor, a simple

setup to demonsrate this would be to connect

measure DC CURRENT. If a manual range change meter

is used, set for a few hundred mA full scale.

Connect the (-) meter lead to the Collector.

Connect the Emitter to the Power Supply (-).

.

Now any current, somewhere <1mA, which we can

arrange to flow in the Base to Emitter will be amplified.

This is what we are trying to arrange to show transistor

current gain operation.

.

Connect a 100kΩ fixed resistor in series with a variable

resistor, of approximate 250kΩ. (If you have a 2nd meter,

set it to 1mA Full Scale, if not autoranging. Connect this

in series with the two resistors. This will display Base

current Ib at the same time as the other meter is displaying

Ic).

.

Connect one end of the above series circuit to the (+) supply,

and the other end to the transistor Base. If an analog meter

needle kicks the wrong way, reverse the meter leads.

.

Switch ON the power supply.

While adjusting the variable resistor, observe and note a few

meter reading pairs, Each Ib has a corresponding Ic.

Provided the transistor is not saturated or heating up,

there should be a reasonable linear relationship between

the two currents. Current Gain = Ic /Ib.

Example; For Ic = 45mA, and Ib = 0.15ma( =150µA ),

then Current Gain = Ic / Ib = 45 x 10^-3 / 0.15 X10^-3 = 300

.

This shows that the base input current is amplified 300 times

and appears as output collector current. Job done.

.

A very low control current <1mA , can produce much higher

currents, sufficient to drive, relay coils, solid state power devices like SCRs, indicator lamps, and with another stage of current amplification, small motors.

.

• Login to reply the answers
• How you wire the transistor up depends on what you want to do with it. 'Increasing current' is too vague (increasing the current through what?).

However, in any case, the + side of your supply needs to be connected on the collector side (not necessarily directly on the collector) of the transistor and the - goes on the emitter side (again, not directly on the emitter), the signal you want to amplify goes on the base. If you connect both the + and - supply leads directly to the collector/emitter and a signal on the base, you'll quickly burn up you transistor, there needs to be some other components in the circuit (for example, resistors or LEDs or something).

Exactly how you connect it up depends on what you're doing with it though (wiring it up as a switch is a lot different from wiring it up as an amplifier for example).

Where you measure the output again depends on the circuit, because it depends on what 'output' you're looking for (the output of one circuit configuration could be the input of another circuit configuration for example).

• Login to reply the answers
• You may have heard the expression "trying to run before you can walk". I think that's what you are trying to do.

You MUST read up about them, and get at least a fundamental understanding of they work.

Take a look here http://homepage.ntlworld.com/g.knott/index9.htm

There must be many other sites which will be of help.

• Login to reply the answers
• Login to reply the answers