AND8056/D - ON Semiconductor

 Semiconductor Components Industries, LLC, 2001

March, 2001 – Rev. 0 1Publication Order Number:

AND8056/D

Control Solution using Logic,

Analog Switches, and

Discrete Semiconductor

Devices for Reversing a

One-Phase Motor

Alex Lara and Gabriel Gonzalez

Applications Engineers

INTRODUCTION

In the huge variety of the AC motors, one–phase motors

are an excellent option when only single–phase power is

available t o supply electrical ener gy which motors require to

operate. One of the most common single–phase motors is the

split–phase motor which is used in many applications, such

as pumps, bench drills, compressors, vacuum cleaners,

electrical sewing machines, etc.

In some of these applications it is necessary to reverse the

motor which requires two conditions. The first condition is

the removal of power to the motor in order to stop it. The

second condition is to change the electrical connections

between the main and the start windings.

One of the most common methods to reverse a motor is to

use mechanical relays. This would not be a good solution for

an application in which a fast inversion of its rotation is

needed, since it would be necessary to wait about 5 seconds

before being able to change the motor rotation. Otherwise,

it will operate in the same direction due to the open function

of the centrifugal switch which remains closed until the

motor reaches a low speed.

This application note shows a possible solution to control

a 1/3 HP split–phase motor by taking advantage of different

functions performed by some devices ON Semiconductor

offers in its product portfolio. In addition, the circuit

proposed in this application note eliminates the use of the

centrifugal switch, since its function is being replaced by th e

same triacs which are performing the reversing function for

the motor.

DEFINITIONS

Split–Phase Motor

Split–phase motors have two stator windings, a main

winding and a start winding, with their axes displaced 90

electrical degrees in space. The start winding has a higher

resistance–to–reactance ratio than the main winding, so the

two currents are out of phase. Thus, the stator field first

reaches a maximum about the axis of one winding and then

later (about 80 to 85 electrical degrees), reaches a maximum

about the axis of the winding 90 electrical degrees away in

space. The result is a rotating stator field which causes the

motor to start.

At about 75 percent synchronous speed, the start winding

is cut out by a centrifugal switch. The rotational direction of

the motor is determined during its start by the initial fields

arrange which is generated in the stator by the main and start

windings. This means, as result of the connection illustrated

in Figure 1 between both windings (M2–S1 and M1–S2), the

motor will start with a certain rotational direction. If reverse

direction is desired, the connection between both windings

must be changed as follows: M2–S2 and M1–S1. With this

new connection, the fields arrange in the stator will be

changed and, as a result, the rotational direction will be

reversed. The previous statement will work whenever the

connection change is done with the centrifugal switch

closed.

Figure 1 shows a typical representation schematic for a

split–phase motor.

Main

Winding

Start

Winding

S1 S2

Centrifugal

Switch

110 VAC

50/60 Hz

Figure 1.

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APPLICATION NOTE

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Motor Characterization

In order to properly design the power and control circuits,

it is essential to characterize the motor. This means, measure

the maximum peak of inrush and nominal current

conditions, and determine how long these conditions take.

IPK = –63.2 Amp

Inrush current

IPK = 8.8 Amp

Nominal current

T = 88 msec

Figure 2. Plot #1

This plot shows the waveform of the total current flowing

through both windings (Main and Start) during the motor starting

condition. This current must be driven by the triac device

selected for this purpose. The picture was taken when the motor

was not driving any kind of mechanical load.

(Conversion factor: 100 mV = 1 Amp)

IPK = 34.4 Amp

Current flowing

through the start

winding

T = 82 msec

Figure 3. Plot #2

This plot shows the waveform of the current flowing only through

the start winding. This current condition must be driven by triac

devices which will replace the centrifugal switch function. The

picture was taken when the motor was not driving any kind of

mechanical load.

(Conversion factor: 100 mV = 1 Amp)

Based on the previous motor characterizations, the

MAC15N triac device was selected as the main device in the

power circuit. The MAC15N is able to handle up to a 90 A

peak during five, 60 Hz cycles, in a nonrepetitive mode.

Based on this, the MAC15N would be able to drive the total

current demanded by the motor every time it starts to

operate. Based on the same criteria, the MAC9N triac device

was selected to perform the reversing function. The MAC9N

is able to drive up to a 50 A peak during five, 60 Hz cycles;

the inrush current condition only involves a 34.4 A peak of

about 90 msec. In addition, both the MAC15N and the

MAC9N devices were selected due to their high immunity

to noise (snubberless devices). Since the dV/dt capability is

very critical for this kind of application, a short–circuit

condition could occur if a thyristor device is triggered by

noise conditions.

Once the triacs have been selected based on the motor

characterization, the power schematic diagram can be

generated (Figure 4).

Figure 4 shows the proposed power schematic to perform

the start–stop and reversing functions of the motor. The

MAC15N device switches one of the two terminals of the

110 V, 60 Hz power line. This device basically performs a

function of a start–stop switch. Before it can be triggered by

optocoupler 5, two MAC9N devices should be triggered in

order to connect the main and start windings, to define the

initial rotational direction (motor connections M1–S1 and

M2–S2).

Once the motor has started to operate completely, the

trigger signal supplied to optocouplers 1 and 2 of the two

MAC9N devices must be removed; the start winding would

be disconnected from the power circuit. This replaces the

centrifugal switch function while the main winding would

remain connected to the power line through the MAC15N

triac and, therefore, the motor would continue operating

until a stop or reverse function is chosen.

If a reverse function is selected, the control signal

provided to optocoupler 5 (MAC15N) must immediately be

removed. The motor would be turned off and, at the same

time, the control circuit would activate optocouplers 3 and

4 which would trigger the other two MAC9N triacs to select

different connections between the main and start windings

(motor connections M1–S2 and M2–S1).

This new motor configuration would allow the motor’s

rotation to invert as soon as the main switch (the MAC15N

device) is triggered. This main switch would only trigger

after about 190 msec has elapsed. 190 msec is the minimum

period of time required to start the motor in the opposite

direction when optocouplers 3 and 4 of the MAC9N devices

are triggered. The motor would continue operating until a

stop or reverse function is selected by the user.

The operational sequence of the previously described

power schematic diagram must be commanded by a control

circuit which is described as follows (Figure 8).

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Main

Winding

Start

Winding

S1 S2

110 VAC

50/60 Hz

MOC3041 MOC3041

MOC3041MOC3041MOC3041

MAC15N MAC9N

MAC9N MAC9N

MAC9N

510 Ω510 Ω510 Ω

510 Ω510 Ω

Figure 4. Power Schematic Diagram

Control Circuit

Figure 8 shows the proposed control circuit which

commands the functions involved in the power circuit to

control the start and stop of the motor in either direction.

The control circuit (Figure 8), which is explained as

follows, was developed based on the operational sequence

of the power schematic diagram (Figure 4).

Let’s start from the supposition that the motor is not

operating. Under this condition, the four 2N2222 transistors

illustrated are in the saturation region. None of the triac

devices (MAC15N, MAC9N) are being triggered in this

condition; therefore, neither of the two possible connections

between the main and start windings have been established.

If the left button is pushed on, flip–flop 1 (MC41013B) is

activated and immediately transistor 1 is changed from the

saturation to the cutoff region. Optocouplers 1 and 2 are

activated, triggering two MAC9N triac devices which

establish a connection between the main and the start

windings (M1–S1, M2–S2). This connection will remain

approximately 280 msec (timer conformed by operational

amplifier 1).

At the same time, flip–flop 1 actives a circuit (operational

amplifier 2) which delays (about 190 msec) the triggering of

the MAC15N triac device to allow the connection between

the main and starting windings. There is a period of time

(about 85 msec) during which the MAC15N device and the

two MAC9N devices are being triggered simultaneously

(see Plot #3, Figure 5). In this condition, the motor is able to

start with its rotation in a certain direction and will remain

operating until a stop or reversing function is selected.

If a stop condition is chosen, the control and power

circuits will return to their original conditions (motor

stopped) but if the right button is pushed on, then flip–flop

2 is activated which will command a control sequence

similar to the one explained for the flip–flop 1. However in

this case, the connection between the main and start

windings is changed by the other two MAC9N devices

(M1–S2, M2–S1) to invert the rotation of the motor.

Figure 5. Plot #3

This plot shows trigger signals for the optocouplers during the

initial sequence control:

Ch1 – Pulse control for the MAC9N devices (Start winding)

Ch2 – Pulse control for the MAC15N device (Main switch)

Ch3 – Current waveform (Conversion factor: 0.1 V = 1 Amp)

Delay before triggering the

main switch (MAC15N)

Period of time in which

the MAC9N triacs are

activated

Motor current waveform

Inrush current (82msec)

196 msec

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At the same time flip–flop 2 is being activated, a reset

signal is provided to flip–flop 1, so its Q output activates

one–gate analog switch 1 (MC74VHC1G66). This drains

the capacitor discharge of the RC network of operational

amplifier 2 t o ground, so as a result, transistor 2 returns to its

saturation region and optocoupler 5 is deactivated. Because

of this, the gate signal to MAC15N is removed and the power

to the motor will be removed after about 190 msec (see Plot

#4, Figure 6). 190 msec is the minimum period of time

required to start the motor in the opposite direction when the

MAC15N triac device is again triggered by optocoupler 5.

Main switch

disconnected

Motor’s current waveform

During 82 msec both windings

are working simultaneously

Period of time in which

the MAC9N triacs are

activated

Figure 6. Plot #4

This plot shows the sequence of trigger signals for the

optocouplers when the motor is reversed:

Ch1 – Pulse control for the MAC9N devices (Reverse function)

Ch2 – Pulse control for the MAC15N device (Main switch)

Ch3 – Current waveform (Conversion factor: 0.1 V = 1 Amp)

The first prototype of this control circuit was designed

without contemplating the OR gates and the analog

switches. It was observed that this prototype was neither a

secure, nor a reliable circuit because without the OR gates

(MC74VHC1G32), the flip–flop devices could be activated

simultaneously. Due to this, the four MAC9N devices would

be triggered at the same time causing a short–circuit

condition in the power circuit. This why we decided to

consider two, one–gate OR devices in our control circuit.

They act as an electrical padlock which avoids the

possibility of simultaneous activation of the four triacs.

The analog switch devices (MC74VHC1G66) optimize

the reversing function for the motor since they avoid an

unnecessary start of the motor when it is reversed (see

Plot #5). This undesirable start is caused by the capacitor

discharge of the RC network connected in the operational

amplifiers. Since the capacitor remains charged, it causes a

short activation of the main switch. This is why the analog

switches were included in the control circuit.

Waveform current of an

undesirable motor’s starting

Period of time in which

the MAC9N triacs are

activated

This delay in the triggering signal for the main

switch (MAC15N) causes an unnecessary

motor start

Figure 7. Plot #5

This plot shows the sequence of trigger signals for the

optocouplers when the motor is reversed (prototype without

analog switches):

Ch1 – Pulse control for the MAC9N devices (Start winding)

Ch2 – Pulse control signal for the Main switch (MAC15N).

Ch3 – Current waveform (Conversion factor: 0.1 V = 1 Amp)

In conclusion, it has been shown and explained through

this application note, a different alternative to control and

reverse a split–phase 1/3 HP motor; replacing the function

of the centrifugal switch with triac devices which improve

the time in which the motor can be reversed.

Through a typical circuit using mechanical relays, it

would be necessary to wait until the centrifugal switch opens

which could take about 5 seconds (depending on the load

and the power of the motor). While through this electronic

option the motor could be reversed almost immediately;it is

necessary to wait no more than 300 milliseconds.

In addition, the present note illustrates a different

application for the analog switch devices. They are used to

drain the capacitor discharge to ground. The one–gate OR

devices protect the circuit against a possible short condition

that may be caused by trying to operate the motor in either

direction at the same time, which is commonly done by

users.

It is important to mention that the devices for power

management purposes (MAC15N and MAC9N) were

selected, based on the motor characterization. If it is

desirable t o follow this kind of solid–state solution to control

a bigger motor, the motor must be characterized in order to

select the most proper triac devices, and the delays times that

the motor will require to operate under its normal conditions.

It is very important to mount the triac onto a proper heatsink

to avoid overheating conditions; otherwise, they would not

operate properly. Also, extreme environmental

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temperatures could effect the proper functionality of the

electronic circuit. If it is necessary to operate under extreme

environmental temperatures, it would be necessary to

characterize its operation at those temperature levels;

however, i t is a fact that this solid–state solution can operate

in an environmental temperature range between 15C to

40C.

MC14013B

1 kΩ1 kΩ1 kΩ

MC74VHC1G32

TL084 –

TL084 +

–

MC74VHC1G66

–TL084

MC74VHC1G66

TL084

–

2N2222

MOC3041

MUR120

2N2222

MUR120 MUR120

1.2 kΩ

0.27 Ω

10 kΩ

10 µF+5 VDC 10 µF

1.2 kΩ

0.51 k

1.0 kΩ1.0 kΩ

0.27 Ω

+5 VDC +5 VDC

+5 VDC+5 VDC

+5 VDC +5 VDC

22 kΩ

10 µF+5 VDC

10 µF

10 kΩ

2N2222

39 Ω39 Ω

+5 VDC

LED (MOTOR ON/OFF)

MOC3041

+5 VDC +5 VDC +5 VDC

Left Right Stop

MC74VHC1G32

+5 VDC

100 Ω22 kΩ

MUR120

1.0 kΩ

MUR120 MUR120

2N2222

+5 VDC

100 Ω

1.2 kΩ

0.51 k

+5 VDC

Figure 8. Control Circuit

MC14013B

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Notes

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Notes

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