Transistor Circuit Templates

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NPN transistor circuit template

currentmeter

0

currentmeter

0

voltmeter

0

+

+

+

+

+0

voltmeter

n

n

p pn junctions

This transistor is in conduction

collector

base

emitter

currentmeter

0

+0

voltmeter

n

ppn junction

This diode is forward biased

anode

cathode

1 pn junction

2 pn junctions

voltmeter

0

+

+

+

+

n

n

p pn junctions

resistance varies as resistor knob is turned.

emitterIf the input signal and the output signal are “grounded” at the same potential the circuit is know as a common-emitter circuit.

output signal

This transistor is connected in a common-emitter circuit

dvWhen gets high enough, the light will turn on.

input signal

dIf v gets higher, the light will become brighter.

NPN transistor circuit template

vdgoes up as the

variable resistance value goes up.

Voltage here, ,

knob is turned so light goes on.

knob is turned more so light gets brighter.

voltmeter

0

n

n

p

E

This transistor is connected in a common-emitter circuit

Variable Resistor

R1

R2

+

-

v1 = R

vR

1+

Rv

R1

vdgoes up as the

variable resistance value goes up.

Voltage here, ,

vtv

t[ ]

vd = v

t - v1

dvWhen gets high enough, the light will turn on.

output signal

input signal

Many sensors are designed to provide a variable resistance output signal.

NPN transistor circuit template

voltmeter

0

n

n

p

E

This transistor is connected in a common-emitter circuit

R1

+

-

vt

=

time

the voltage across these two terminals

vin

At low voltage value, light is OFF.

high value

Low value

At high voltage value, light is ON.

output signal

input signal

vin

Example of a digital circuit - a buffer

NPN transistor circuit template

voltmeter

0

n

n

p

E

This transistor is connected in a common-emitter circuit

R1

+

-

vt

time

At low voltage value, light is ON.

high value

Low value

At high voltage value, light is OFF.

Example of a digital circuit - an inverter

vin

NPN transistor circuit template

the voltage is applied across these two terminals

vin

voltmeter

0

n

n

p

E

This transistor is connected in a common-emitter circuit

R1

+

-

vt

time

high value

Low value

high voltage value

Example of a digital circuit - Flip-flop Output

vinlow voltage value

NPN transistor circuit template

vin

the voltage is applied across these two terminals

voltmeter

0

n

n

p

E

This transistor is connected in a common-emitter circuit

R1

+

-

vt

time

high value

Low value

high voltage value

Example of a digital circuit - Flip-flop Output

vinlow voltage value

NPN transistor circuit template

vin

the voltage is applied across these two terminals

voltmeter

0

n

n

p

E

This transistor is connected in a common-emitter circuit

R1

+

-

vt

Example of a linear output circuit

vin

NPN transistor circuit template

R3

R2

There is a voltage at the orange node because of the voltage divider circuit element highlighted in blue.

Voltage divider output set so transistor is just barely conducting.

This light get brighter as input signal is linearly increased.

This light get dimmer as input signal is linearly increased.

This input signal is varied linearly to brighten/dim the lights.

R3

vt[ ]

R3

R2+

vd = v

t -

vd

n

0

currentmeter

Rsensor

Template for monitor circuit

V+Reference voltage often not used.

vbe

p

E

n

Vref

Rpull up

Output circuit to monitor resistive sensor

Template for FCE circuit

Output circuit to activate relay

to the FCE power circuit

NPN transistor circuit template

0

currentmeterV

+

Rsensor

Vref

RPull up v

be n

p

E

n

+

NPN transistor circuit template

Template for FCE circuit

Output circuit to activate relay

to the FCE power circuit

V+

Rsensor

Vref

RPull up v

be n

p

E

n

+

single pole

Single polesingle throw contact set

single throw

NPN transistor circuit template

V+

Vref

R Pull up

+

circuit for PSH to activate relay

FCE power supply

FCE motor

pressure

U-Betch-um

Pressure sensor

Our guarantee is guaranteed

Sensor is now presenting a high resistance to the transistor base circuit.

vbe

n

p

E

nVbe is low, transistor is OFF

Rsensor

motor running

NPN transistor circuit template

V+

Rsensor

Vref

R Pull up

FCE power supply

FCE motor

goes up

+

Vbe is low, transistor is OFF

n

p

E

n

pressure

Vbe is high, transistor is ON v

be

motor runningnot

running

no current is flowing in emitter-collector circuit

current is flowing in emitter-collector circuit

currentmeter

0

N.O.push button