Types of output transducersTypes of control

Devices for controlOther considerations

ElectronicsControlling Power to Output Transducers

Terry Sturtevant

Wilfrid Laurier University

September 7, 2011

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

Produce “information”Produce “action”

Low power devices

These devices require low power. Low power is typically . 1W .meteroscilloscope

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

Produce “information”Produce “action”

High power devices

These devices require high power. High power is typically & 1W .lightssolenoids

An operational amplifier is a voltage device; it can’t produce morethan a few mW of power.

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

Types of control

on/offlike a switchproportionallike a rheostat or potentiometer

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

Control trade-offs

There are trade-offs involved in choosing a type of control.efficiencyon/off is 100% efficientproportional is less efficientnoiseon/off produces more noiseproportional produces less noise

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

Any device used for control is basically used in a voltagedivider using

the supply voltage,the control device,and the load.

The order of the control element and the load in the voltagedivider has some effects on the circuit operation.

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

Relay

A relay has four types of pins:coilcommonNO; normally open (possibly)NC; normally closed (possibly)

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

Relay OFF

NO

commonNC

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

Since a relay is inductive, all of the precautions for an inductivedevice must be taken.

Vin

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

The relay can be inserted on either side of the load in a voltagedivider.

Vout

VsupplyVin

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

The relay can be inserted on either side of the load in a voltagedivider.

Vout

Vsupply

Vin

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

Transistors

There are several types of transistor; each is a three terminaldevice.The most common types of transistors are BJTs and FETs.Transistors are often used in voltage dividers to act as variableresistors.

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

Metal Oxide Semiconductor Field Effect Transistors

A MOSFET (or Metal Oxide Semiconductor Field EffectTransistor) is a three terminal device.

drainsourcegate

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

FET symbol

drain

sourcegate

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

FET operation

FETS are voltage amplifiers; a small gate voltage controls amuch larger drain/source current.

Actually it’s the voltage between the gate and the source whichmatters.

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

D and E MOSFETs

There are two kinds of MOSFETenhancement mode (E type)As Vgs increases,ID increases.depletion mode (D type)To get ID to zero, a negative Vgs must be applied.

Actually, all MOSFETs operate in enhancement mode. It’s justthat some only operate in that mode. In other words, for someID = 0 even for positive values of Vgs below some threshold.

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

Vsupply

Vo

I ≈ 0 if Vgs . Vgson

Vgs

E (enhancement mode) FET

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

FETS are voltage amplifiers; a small gate-source voltagecontrols a much larger drain/source current.You do not use a gate resistor with an FET!All FETs work in enhancement mode; some also work indepletion mode.

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

Vsupply

Vo = VDS > 0 if Vgs = 0

Vgs = 0gate

D (depletion mode) FET

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

The MOSFET, like the relay, can be placed in either position of avoltage divider. The effects are the same as for the relay.

Vout

Vsupply

Vin

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

The MOSFET, like the relay, can be placed in either position of avoltage divider. The effects are the same as for the relay.

Vout

Vsupply

Vin

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

Bipolar Junction Transistors

A BJT (or Bipolar Junction Transistor) is a three terminal currentdevice.The terminals are

collectoremitterbase

The current from the collector to the emitter is controlled by thecurrent into the base.

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

collector

emitterbase

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

BJT operation

BJTS are current amplifiers; a small base current controls amuch larger collector/emitter current.You should always have a base resistor with a BJT!

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

Vs

Ic ≈ 0 if Vi . 0.7

Vo ≈ Vs if Vi . 0.7Vi . 0.7

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

Like the previous devices, either position in a voltage divider canbe used.

Vout

Vsupply

Vin

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

Like the previous devices, either position in a voltage divider canbe used.

Vout

Vsupply

Vin

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

TRIAC

A TRIAC is a three terminal ac voltage device. The terminals aremain terminal 1main terminal 2gate

A triac will begin to conduct when it receives a voltage pulse onthe gate. It will continue to conduct until the current is zero.

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

gate

MT1

MT2

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

It can operate in two modes.burstdelayed trigger

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

RelayTransistorsMOSFETBJTTRIAC

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

Using TTL gates for control

Using TTL gates for control

“Extra” current from TTLsink instead of source0.4ml vs. 8 ml (LS)

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

Using TTL gates for control

Current sourcing

IOH ≤ 0.4mA

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

Using TTL gates for control

Current sinking

VCC

IOL ≤ 8.0mA

Terry Sturtevant Electronics Controlling Power to Output Transducers

Types of output transducersTypes of control

Devices for controlOther considerations

Using TTL gates for control

Using a TTL gate to sink instead of source allows 20x the current!

Terry Sturtevant Electronics Controlling Power to Output Transducers