actuators

USER GUIDE for the study of

ACTUATORS

Made by:

Ramana Krishnan

B.Tech - MPAE

NSIT

Swati Bansal

Btech Computer Science Engg.

Delhi College of Engineering

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This tutorial assumes certain basic knowledge of DC motors. This tutorial should be used

as a reference material and not as a primary source of study. This tutorial attempts to give

the reader a brief peek into the world of actuators…

Speed control of DC motor through PWM

One of the most fundamental problems in robotics is DC motor speed control. The most

common method of speed control is PWM or pulse width modulation. Pulse width

modulation is the process of switching the power to a device on and off at a given

frequency, with varying on and off times. These on and off times are referred to as "duty

cycle". The diagram below shows the waveforms of 10%, 50%, and 90% duty cycle

signals.

As you can see from the diagram, a 10% duty cycle signal is on for 10% of the

wavelength and off for 90%, while a 90% duty cycle signal is on for 90% and off for

10%. These signals are sent to the motor at a high enough frequency that the pulsing has

no effect on the motor. The end result of the PWM process is that the overall power sent

to the motor can be adjusted from off (0% duty cycle) to full on (100% duty cycle) with

good efficiency and stable control.

While many robot builders use a microcontroller to generate the required PWM signals,

the 555 PWM circuit explained here will give the novice robot builder an easy to

construct circuit, and good understanding of pulse width modulation. It is also useful in a

variety of other applications where the PWM setting need only be changed occasionally.


The 555 timer in the PWM circuit is configured as an astable oscillator. This means that

once power is applied, the 555 will oscillate without any external trigger. Before the

technical explanation of the circuit, let's look at the 555 timer IC itself.

A block diagram of the 555 timer:


Pin descriptions for the 555

PIN DESCRIPTION PURPOSE

1 Ground DC Ground

2 Trigger

The trigger pin triggers the beginning of the timing

sequence. When it goes LOW, it causes the output pin

to go HIGH. The trigger is activated when the voltage

falls below 1/3 of +V on pin 8.

3 Output

The output pin is used to drive external circuitry. It

has a "totem pole" configuration, which means that it

can source or sink current. The HIGH output is

usually about 1.7 volts lower than +V when sourcing

current. The output pin can sink up to 200mA of

current. The output pin is driven HIGH when the

trigger pin is taken LOW. The output pin is driven

LOW when the threshold pin is taken HIGH, or the

reset pin is taken LOW.

4 Reset

The reset pin is used to drive the output LOW,

regardless of the state of the circuit. When not used,

the reset pin should be tied to +V.

5 Control Voltage

The control voltage pin allows the input of external

voltages to affect the timing of the 555 chip. When

not used, it should be bypassed to ground through a

0.01uF capacitor.

6 ThresholdThe threshold pin causes the output to be driven LOW

when its voltage rises above 2/3 of +V.

7 Discharge

The discharge pin shorts to ground when the output

pin goes HIGH. This is normally used to discharge the

timing capacitor during oscillation.

8 +V DC Power? Apply +3 to +18VDC here.


The schematic diagram for the 555 PWM Circuit:

The reset pin is connected to +V, so it has no effect on the circuit's operation.

When the circuit powers up, the trigger pin is LOW as capacitor C1 is discharged. This

begins the oscillator cycle, causing the output to go HIGH.

When the output goes HIGH, capacitor C1 begins to charge through the right side of R1

and diode D2. When the voltage on C1 reaches 2/3 of +V, the threshold (pin 6) is

activated, which in turn causes the output (pin 3), and discharge (pin 7) to go LOW.

When the output (pin 3) goes LOW, capacitor C1 starts to discharge through the left side

of R1 and D1. When the voltage on C1 falls below 1/3 of +V, the output (pin 3) and

discharge (pin 7) pins go HIGH, and the cycle repeats.

Pin 5 is not used for external voltage input, so it is bypassed to ground with a 0.01uF

capacitor.

Note the configuration of R1, D1, and D2. Capacitor C1 charges through one side of R1

and discharges through the other side. The sum of the charge and discharge resistance is

always the same; therefore the wavelength of the output signal is constant. Only the duty

cycle varies with R1.

The overall frequency of the PWM signal in this circuit is determined by the values of R1

and C1. In the schematic above, this has been set to 144 Hz.


To compute the component values for other frequencies, use the formula:

Frequency = 1.44 / (R1 * C1)

In this circuit, the output pin is used to charge and discharge C1, rather than the discharge

pin. This is done because the output pin has a "totem pole" configuration. It can source

and sink current, while the discharge pin only sinks current. Note that the output and

discharge pins go HIGH and LOW at the same time in the oscillator cycle.

The discharge pin is used to drive the output. In this case, the output is an IRFZ46N

MOSFET. The gate of the MOSFET must be pulled high, as the discharge pin is open

collector only. Being an N channel MOSFET, the IRFZ46N will conduct from drain to

source when the gate pin rises above 4 volts or so. It will stop conducting when the gate

voltage falls below this voltage. The configuration of the output also serves to invert the

signal from the 555 circuit.


H-BRIDGE

1. Motor Supply (+12V / +24V)

2. Logic Supply (+5V)

3. Clockwise (Active Low)

4. Counter-Clockwise (Active Low)

5. Ground

6. Points to be soldered with DC motor

7. Power Transistor

8. Opto-Coupler Device to provide isolation

1 2 4 53

6

7

8


What's all this talk about H-Bridges? How do they work? Well let's see . . .

How do we make a motor turn?

You take a battery; hook the positive side to one side of your DC motor. Then you

connect the negative side of the battery to the other motor lead. The motor spins forward.

If you swap the battery leads the motor spins in reverse.

Ok, that's basic. Now let’s say you want a Micro Controller Unit (MCU) to control the

motor, how would you do it? Well, for starters you get a device that would act like a solid

state switch, a transistor, and hook it up the motor.

NOTE: If you connect up these relay circuits, remember to put a diode across the coil of

the relay. This will keep the spike voltage (back EMF), coming out of the coil of the

relay, from getting into the MCU and damaging it. The anode, which is the arrow side of

the diode, should connect to ground. The bar, which is the Cathode side of the diode,

should connect to the coil where the MCU connects to the relay

If you connect this circuit to a small hobby motor you can control the motor with a

processor (MCU, etc.) Applying a logical one, (+12 Volts in our example) to point A

causes the motor to turn forward. Applying a logical zero, (ground) causes the motor to

stop turning (to coast and stop).

Hook the motor up in this fashion and the circuit turns the motor in reverse when you

apply a logical one (+12Volts) to point B. Apply a logical zero, which is usually a

ground, causes the motor to stop spinning.

If you hook up these circuits you can only get the motor to stop or turn in one direction,

forward for the first circuit or reverse for the second circuit.


Motor Speed

You can also pulse the motor control line, (A or B) on and off. This powers the motor in

short burst and gets varying degrees of torque, which usually translates into variable

motor speed.

But if you want to be able to control the motor in both forward and reverse with a

processor, you will need more circuitry. You will need an H-Bridge. Notice the "H"-

looking configuration in the next graphic. Relays configured in this fashion make an H-

Bridge. The "high side drivers" are the relays that control the positive voltage to the

motor. This is called sourcing current.

The "low side drivers" are the relays that control the negative voltage to sink current to

the motor. "Sinking current" is the term for connecting the circuit to the negative side of

the power supply, which is usually ground.

So, you turn on the upper left and lower right circuits, and power flows through the motor

forward, i.e.: 1 to A, 0 to B, 0 to C, and 1 to D.


Then for reverse you turn on the upper right and lower left circuits and power flows

through the motor in reverse, i.e.: 0 to A, 1 to B, 1 to C, and 0 to D.

CAUTION: You should be careful not to turn on both circuits on one side or the other,

or you have a direct short which will destroy your circuit; Example: A and C or B and D

both high (logical 1).

Semiconductor H-Bridges

We can better control our motor by using transistors or Field Effect Transistors (FETs).

Most of what we have discussed about the relays H-Bridge is true of these circuits. You

don't need diodes that were across the relay coils now. You should use diodes across your

transistors though. See the following diagram showing how they are connected.

These solid state circuits provide power and ground connections to the motor, as did the

relay circuits. The high side drivers need to be current "sources" which is what PNP

transistors and P-channel FETs are good at. The low side drivers need to be current

"sinks" which is what NPN transistors and N-channel FETs are good at.


If you turn on the two upper circuits, the motor resists turning, so you effectively have a

breaking mechanism. The same is true if you turn on both of the lower circuits. This is

because the motor is a generator and when it turns it generates a voltage. If the terminals

of the motor are connected (shorted), then the voltage generated counteracts the motor’s

freedom to turn. It is as if you are applying a similar but opposite voltage to the one

generated by the motor being turned. Vis-à-vis, it acts like a brake.

To be nice to your transistors, you should add diodes to catch the back voltage that is

generated by the motor's coil when the power is switched on and off. This flyback

voltage can be many times higher than the supply voltage! If you don't use diodes, you

could burn out your transistors.


Transistors, being a semiconductor device, will have some resistance, which causes them

to get hot when conducting much current. This is called not being able to sink or source

very much power, i.e.: Not able to provide much current from ground or from plus

voltage.

Mosfets are much more efficient; they can provide much more current and not get as hot.

They usually have the flyback diodes built in so you don't need the diodes anymore. This

helps guard against flyback voltage frying your MCU.

To use Mosfets in an H-Bridge, you need P-Channel Mosfets on top because they can

"source" power and N-Channel Mosfets on the bottom because then can "sink" power. N-

Channel Mosfets are much cheaper than P-Channel Mosfets, but N-Channel Mosfets used

to source power require about 7 volts more than the supply voltage, to turn on. As a

result, some people manage to use N-Channel Mosfets, on top of the H-Bridge, by using

cleaver circuits to overcome the breakdown voltage.

It is important that the four quadrants of the H-Bridge circuits be turned on and off

properly. When there is a path between the positive and groundside of the H-Bridge,

other than through the motor, a condition exists called "shoot through". This is basically a

direct short of the power supply and can cause semiconductors to become ballistic, in

circuits with large currents flowing. There are H-bridge chips available that are much

easier, and safer, to use than designing your own H-Bridge circuit.

H-Bridge Devices

The L 293 has 2 H-Bridges, can provide about 1 amp to each and occasional peak loads

to 2 amps. Motors typically controlled with this controller are near the size of a 35 mm

film plastic canister.

The L298 has 2 h-bridges on board, can handle 1amp and peak current draws to about

3amps. You often see motors between the size of 35 mm film plastic canister and a coke

can, driven by this type H-Bridge. The LMD18200 has one h-bridge on board, can handle

about 2 or 3 amps and can handle a peak of about 6 amps. This H-Bridge chip can usually

handle an average motor about the size of a coke. There are several more commercially

designed H-Bridge chips as well.


Sample Program

Sample Program for the working of 2 DC Motors using H-Bridges

M1R EQU P0.0 ; Motor 1 Reverse

M1F EQU P0.1 ; Motor 1 Forward

M2F EQU P0.2 ; Motor 2 Forward

M2R EQU P0.3 ; Motor 2 Reverse

FM EQU P1.0 ; Forward Motion

BM EQU P1.1 ; Backward Motion

LM EQU P1.2 ; Left Motion

RM EQU P1.3 ; Right Motion

ORG 00H

AJMP MAIN

ORG 30H

MAIN: SETB M1F

SETB M1R

SETB M2F

SETB M2R

JNB FM, FMR

JNB BM, BMR

JNB LM, LMR

JNB RM, RMR

AJMP MAIN

FMR: ; Forward Motion Routine

CLR M1F

CLR M2F

SETB M1R

SETB M2R

AJMP MAIN

BMR: ; Backward Motion Routine

CLR M1R

CLR M2R

SETB M1F

SETB M2F

AJMP MAIN

LMR: ; Left Motion Routine

CLR M1R

CLR M2F

SETB M1F

SETB M2R

AJMP MAIN

RMR: ; Right Motion Routine

CLR M1F

CLR M2R

SETB M1R

SETB M2F

AJMP MAIN

Discussion

The above example shows the implementation of a simple ‘Differential Mechanism’

using two DC Motors.

DC MOTOR

1

DC MOTOR

2

BASE

Figure 1 – Forward Motion

Figure 2 – Right Motion

DC MOTOR

2

BASE

DC MOTOR

1


In the above figures, a simplified differential motor mechanism has been shown. Figure 1

shows the mechanism involved in Forward motion. Basically, in this both the shafts

rotate in the same direction (looking from the left, anti-clockwise). For backward motion,

just the direction of both the shafts is reversed (looking from the left, clockwise) and the

rest remains same.

Figure 2 shows the direction of rotation for the 2 motor shafts for taking a right turn. In

this, the motor on the right moves such that it makes a backward rotation (clockwise,

looking from left) while the motor on the left continues to rotate in the forward direction.

This makes the vehicle turn in the right. A similar effect can be achieved by stopping the

right motor, although that would be a bit unreliable and more importantly slow.

A Left turn can be achieved similar to a right turn, except that instead of right motor

making backward rotation, the left motor makes the backward rotation while the right

motor makes the forward rotation.


STEPPER MOTOR

Stepper Motors work under a very similar principle to DC motors, except they have

many coils instead of just one. So to operate a stepper motor, one must activate these

different coils in particular patterns to generate motor rotation. So stepper motors need to

be sent patterned commands to rotate. These commands are sent (by a microcontroller) as

high and low logic over several lines, and must be pulsed in a particular order and

combination. Steppers are often used because each 'step,' separated by a set step angle,

can be counted and used for feedback control. For example, a 10 degree step angle

stepper motor would require 36 commands to rotate 360 degrees. However external

torque can force movement to a different step, invalidating feedback. Therefore external

torque must never exceed the holding torque of a stepper.

Notes on Stepper Motors:

Stepper motors can be easily found in any 3.5" disk drive or from junk market. They

require special stepper motor controllers (i.e. SLA7024M, STK6713BMK4). They have a

set resolution; higher resolutions mean higher accuracy but lower holding torque. If

torque applied to stepper is greater than holding torque, stepper will lose accurate

position measurements

Voltage:

Polarized (current cannot be reversed) typically from 5-12V, but can range to extremes in

special application motors. Higher voltages generally mean more torque, but they also

require more power. Steppers can run above or below rated voltage (to meet other design

requirements) most efficient at rated voltage.

Current:

When buying a motor, consider Stall Current, Holding Current and Operating Current

(maximum and minimum).

Stall Current - The current that a stepper motor requires when powered but held so that

it does not rotate.

Stepper Motor Internal diagram


Holding Current - The current that a stepper motor requires when powered but not

signaled to rotate.

Operating Current - The current drawn when a stepper motor experiences zero

resistance torque.

It is best to determine current curves relating voltage, current, and required torque for

optimization. When a stepper motor experiences a change in torque (such as motor

reversal), expect short-lived current spikes. Current spikes can be up to 2x the stall

current, and can fry control circuitry if unprotected. Use diodes to prevent reverse current

into your circuitry. Check power ratings of your circuitry and use heat sinks if needed.

Power (Voltage x Current)

Running motors close to Stall Current often, or reversing current frequently under high

torque, can cause motors to melt Heat Sink.

Torque

When buying a stepper motor, consider Stall Torque and Operating Torque (maximum

and minimum).

Stall Torque - The torque a stepper motor requires when powered but held so that it does

not rotate.

Holding Torque - The torque a stepper motor requires when powered but not signaled to

rotate.

Operating Torque - The torque a stepper motor can apply when experiencing zero

resistance torque. Changing the voltage will change the torque.

Velocity

Motors run most efficient at the highest possible speeds. Gearing a motor allows the

stepper motor to run fast, yet have a slower output speed with much higher torque.

Remember that torque determines acceleration, so a fast robot with poor acceleration is

really a slow robot. If uncertain, favor torque over velocity. Stepper motors are slower

than DC motors.

Efficiency

Stepper motors are most efficient at rated voltage. They are less efficient than DC motors

due to non-continuous stepping. Use gearing (opt to buy stepper motors with built-in

gearing or gear heads) for higher efficiency.

Control Methods

Stepper Motors require a special stepper controller (driver) to prevent loss of torque. It

has a more precise control than a DC motor.


How does a stepper motor work?

A stepper motor can work on one of three possible ways:

1. Single Coil Mode

2. Double Coil Mode

3. Half Step Mode

We consider a motor with 4 coils

1. Coil A

2. Coil B

3. Coil C

4. Coil D

Single Coil Mode

In single coil mode, one coil is energized at a time. The corresponding pattern as to be

implemented in the program is given alongside, assuming active low (active when the

particular bit is set to 0).

Double Coil Mode

In double coil mode, two coils are energized at a time. The pattern for it is again shown

alongside.


A B

D C

A B

D C

A B

D C

A B

D C

0111 1011 11101101

A B

D C

A B

D C

A B

D C

A B

D C

0011 1001 01101100

Half Step Mode

In half step mode, an alteration of single coil mode and double coil mode is used. A

single coil is energized first, then two coils are energized, then again one coil and so on.


A B

D C

A B

D C

A B

D C

A B

D C

A B

D C

A B

D C

A B

D C

A B

D C

0110 1110 11011100

0111 0011 10011011

As we had discussed earlier, stepper motors require a driver circuit. The following is the circuit

diagram for one using the IC – STK6713BMK4.

Driver for Stepper Motor


C1

+12V

+5V

+

_

JP2 JP1

IC – STK6713BMK4

1 3 5 8 10 12 14 162 4 7 11 13 156 9

C3

100pF

C4

0.1µF R1

2KΩ

R2

1KΩ

C2

+

_

13 11 9 7 3 156 4 212 10 8

Connector

D C B A

GND

A B C D

The following is the circuitry for another driver of a stepper motor using transistors

without the use of the ICs.

A

+

-

DCB


Sample Program to run two stepper motors on two separate Ports

BM EQU P1.0 ; Back Motion

FM EQU P1.1 ; Front Motion

RM EQU P1.2 ; Right Motion

LM EQU P1.3 ; Left Motion

SM1 EQU P0 ; Stepper Motor 1

SM2 EQU P2 ; Stepper Motor 2

ORG 00H

MOV SM1, #1110 1110B

MOV SM2, #1110 1110B

MAIN: SETB FM

SETB BM

SETB LM

SETB RM

JNB FM, FMF

JNB BM, BMF

JNB LM, LMF

JNB RM, RMF

AJMP MAIN

FMF: MOV A, SM1 ; Forward Motion Function

RL A

MOV SM1, A

ACALL DELAY

MOV A, SM2

RL A

MOV SM2, A

ACALL DELAY

AJMP MAIN

BMF: MOV A, SM1 ; Backward Motion Function

RR A

MOV SM1, A

ACALL DELAY

MOV A, SM2

RR A

MOV SM2, A

ACALL DELAY

AJMP MAIN

LMF: MOV A, SM1 ; Left Motion Function

RR A

MOV SM1, A

ACALL DELAY

MOV A, SM2

RL A

MOV SM2, A

ACALL DELAY


AJMP MAIN

RMF: MOV A, SM1 ; Right Motion Function

RL A

MOV SM1, A

ACALL DELAY

MOV A, SM2

RR A

MOV SM2, A

ACALL DELAY

AJMP MAIN

DELAY: MOV R7, #255

D1: MOV R6, #255

D: DJNZ R6, D

DJNZ R7, D1

RET

Sample Program to run two stepper motors on a single Port

M1FW EQU P3.0 ; Switch for Motor1 Forward

M1BW EQU P3.1 ; Switch for Motor1 Backward

M2FW EQU P3.2 ; Switch for Motor2 Forward

M2BW EQU P3.3 ; Switch for Motor2 Backward

PORT EQU P0 ; Port to attach the 2 Stepper Motors

FRONT EQU P3.4 ; Switch for Forward motion of

BACK EQU P3.5 ; Switch for Backward motion of machine

LEFT EQU P3.6 ; Switch for Left motion of machine

RIGHT EQU P3.7 ; Switch for Right motion of machine

ORG 00H

AJMP START

ORG 030H

START: JNB M1FW, GO1

JNB M1BW, GO2

JNB M2FW, GO3

JNB M2BW, GO4

JNB FRONT, GOFR

JNB BACK, GOBA

JNB LEFT, GOLE

JNB RIGHT, GORI

ACALL DELAY

AJMP START

GO1: MOV R3, #4 ; Motor 1 Forward Motion function

MOV A, #01111111B

LOOP1: MOV PORT, A


ACALL DELAY

RR A

DJNZ R3, LOOP1

JNB M1FW, GO1

AJMP START

GO2: MOV R3, #4 ; Motor 1 Backward Motion function

MOV A, #11101111B

LOOP2: MOV PORT, A

ACALL DELAY

RL A

DJNZ R3, LOOP2

JNB M2FW, GO2

AJMP START

GO3: MOV R3, #4 ; Motor 2 Forward Motion function

MOV A, #11110111B

LOOP3: MOV PORT, A

ACALL DELAY

RR A

DJNZ R3, LOOP3

JNB M2FW, GO3

AJMP START

GO4: MOV R3, #4 ; Motor 2 Backward Motion function

MOV A, #11111110B

LOOP4: MOV PORT, A

ACALL DELAY

RL A

DJNZ R3, LOOP4

JNB M2BW, GO4

AJMP START

GOFR: MOV A, #01110111B ; Forward Motion function using both motors

LOOP11: RR A

MOV PORT, A

ACALL DELAY

JNB FRONT, LOOP11

AJMP START

GOBA: MOV A, #01110111B ; Backward Motion function using both motors

LOOP22: RL A

MOV PORT, A

ACALL DELAY

JNB BACK, LOOP22

AJMP START

GOLE: MOV R3, #4 ; Left Motion function using both motors

MOV R4, #01111111B

MOV R5, #11111110B

LOOP33: MOV A, R4

RL A

MOV R4, A

MOV A, R5

RR A

MOV R5, A



ANL A, R4

MOV PORT, A

ACALL DELAY

DJNZ R3, LOOP33

JNB LEFT, GOLE

AJMP START

GORI: MOV R3, #4 ; Right Motion function using both motors

MOV R4, #11110111B

MOV R5, #11101111B

LOOP44: MOV A, R4

RL A

MOV R4, A

MOV A, R5

RR A

MOV R5, A

ANL A, R4

MOV PORT, A

ACALL DELAY

DJNZ R3, LOOP44

JNB RIGHT, GORI

AJMP START

DELAY: MOV R7, #255

D: MOV R6, #255

D1: DJNZ R6, D1

DJNZ R7, D

RET


AC MOTORS

Unlike DC motors, which work using a single constant current, AC motors run under

three-phase current. To have three-phase power on a robot, you either need a big

bulky/expensive DC-AC converter, or you must tether it to a wall socket. You probably

won't use AC motors unless your robot is stationary, such as a robot arm or robot pancake

maker. Unless you want the pancake maker to also walk your dog or something . . . But

here they are anyway:

Voltage:

• Polarized (current cannot be reversed)

• Typically from 120-240V AC, usually to match mains power

• Higher voltages generally mean more torque, but also require more power

• Rarely used on mobile robots due to power requirements

• NOTE: A universal motor has brushes like a DC motor, but will operate on AC or

DC

Current

• When buying a motor, consider stall and operating current (max and minimum)

• Stall Current - The current a motor requires when powered but held so that it does

not rotate

• Operating Current - The current draw when a motor experiences zero resistance

torque

• It is best to determine current curves relating voltage, current, and required torque for

optimization

• When a motor experiences a change in torque (such as motor reversal) expect short

lived current spikes

• Current spikes can be up to 2x the stall current, and can fry control circuitry if

unprotected

• Use diodes to prevent reverse current to your circuitry

• Check power ratings of your circuitry and use heat sinks if needed


Power (Root-Mean Squared Voltage x Current)

• Running motors close to stall current often, or reversing current often under high

torque, can cause motors to melt

• Heat sink motors if not avoidable

Torque

• When buying a motor, consider stall and operating torque (max and minimum)

• Stall Torque - The torque a motor requires when powered but held so that it does not

rotate

• Operating Torque - The torque a motor can apply when experiencing zero resistance

torque

Velocity

• Motors run most efficient at the highest possible speeds

• Gearing a motor allows the motor to run fast, yet have a slower output speed with

much higher torque

• Remember that torque determines acceleration, so a fast robot with poor acceleration

is really a slow robot

• If uncertain, favor torque over velocity

Efficiency

• More efficient than DC motors

• Typically most efficient at rated voltage and frequency

• Use gearing (opt to buy motors with built-in gearing or gear heads)

Control Methods

• Modifying the AC frequency can alter speed and torque

• Encoder - device which counts rotations of wheel or motor-shaft to determine

velocity for a control feedback loop

• Tachometer - device which measures current draw of motor to control output torque

This circuit will allow you to control the speed of an AC motor.

The bridge rectifier produces DC voltage from the 120VAC line.

A portion on this current passes through the 10K-ohm pot.

The circuit comprised of the 10k pot rated at 3W+, the two 100 ohm resistors and the

50µf capacitors delivers gate drive of the SCR.


The diode D1 protects the circuit from reverse voltage spikes.

The ratings of the bridge rectifier and the SCR should be 25 amps and PIV 600 volts.

The diode D1 should be rated for 2 amps with PIV of 600 volts.

The circuit can handle a load up to 10 amps. The SCR should be very well heat sinked.

DISCLAIMER

This is to remind that we do not hold responsibility for any damage (directly, indirectly, consequentially, specially or

incidentally) arising to the user by use of this document or any part of it. ‘PLC Institute of Electronics’ does not claim

any liability for damages arising from using the document in any form. Under no circumstances, ‘PLC Institute of

Electronics’ will be liable to the reader, third party, any other person or organisation for any damages (monetary or

physical) whatsoever.

Further, we claim no perfection and the material may have certain faults/shortcomings/factual mistakes. Any mistake

may be notified and the institute will be obliged.


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