This is only a preview of the May 2009 issue of Silicon Chip. You can view 31 of the 104 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Articles in this series:
Items relevant to "Dead-Accurate 6-Digit GPS-Locked Clock, Pt.1":
Items relevant to "230VAC 10A Full-Wave Motor Speed Controller":
Items relevant to "Precision 10V DC Reference For Checking DMMs":
Items relevant to "Input Attenuator For The Digital Audio Millivoltmeter":
Purchase a printed copy of this issue for $10.00. |
Hig
Fu
Spe
by
JOHN CLARKE
O
will tend to “cog”, caused by erratic firing of the Triac within
ur last Motor Speed Controller, published in Febthe Drill Speed Controller, so that the motor receives interruary 2009, utilised a simple phase-control circuit
mittent bursts of power. An electric motor that is cogging
which works reasonably well with most universal
badly is virtually useless and the only cure is to increase
motors. However, there are some applications where a
the speed setting – and this rather defeats the purpose if
wider and smoother control range is required.
you want to operate at low speed.
One shortcoming of the February 2009 design is that
This new SILICON CHIP Motor Speed Controller overcomes
the maximum speed from the motor when under speed
these drawbacks. The design does not use phase-control
control is significantly reduced. So for an electric drill
circuitry but uses switch-mode power supply techniques
that normally runs at say 3000 rpm, the maximum speed
to produce an outstanding controller for universal brushmight be reduced to around 2200 rpm. This is inevitable
type motors.
with a controller circuit that effectively half-wave-rectifies
By the way, before we go further we should point out
the 230VAC mains waveform to give a maximum output
that virtually all mains-powered power tools and applivoltage of around 160V RMS.
ances use universal motors. These are series wound motors
The second drawback of the February 2009 design has
with brushes.
to do with low speed control. While the circuit does alAnd most power tools will
low your drill or other appliance to run at quite
do a better job if they have a
low speeds, the result
speed control. For example,
leaves much to be Features:
m
electric drills should be
desired. There isn’t
imu
max
to
of motor speed from near zero
slowed down when using
much torque avail- • Full control
larger drill bits as they make
able and the speed • Speed regulation under load
a cleaner cut.
regulation is poor. This
on
rati
ope
or
mot
ed
ooth low-spe
Similarly, it is useful to be
means that if you’re • Sm
to 2300W
able to slow down routers,
operating the drill at a • Rated for universal motors rated up
jigsaws and even circular
low speed and you put
• Over-current protection and limiting
saws when cutting some
a reasonable load on
materials, particularly plasit, its speed will drop • Fuse protection
tics. The same applies to
right away or it may
e
cas
ast
diec
• Rugged earthed
sanding and polishing tools
stall completely.
n filter
and even electric whipper
Worse still, the motor • Interference suppressio
36 Silicon Chip
siliconchip.com.au
gh Performance
230VAC 10A
ull-Wave Motor
eed Controller
This full-range Motor Speed Controller will give smooth
control from near zero to full speed on electric drills,
routers, circular saws, lawn edgers, food mixers – in fact,
any appliances with universal (brush-type) motors.
snipers are less likely to snap their lines when slowed down.
Phase control
Before we continue, we should explain what we mean
by phase control so we can illustrate the benefits of the
new circuitry.
As you know, the mains (AC) voltage closely follows a
sine wave – it starts at zero, rises to a peak, falls back to
zero, then does the same thing in the opposite direction.
This repeats over and over – and does it 50 times each
second (50Hz). A motor connected to the mains uses all
of the energy it can take from each “cycle” and it runs at
its maximum speed.
But what if you were able to stop the motor receiving
energy until, say, half way through each cycle? Obviously,
with less energy available to power it the motor would not
run as fast. If you were able to vary the time during each half
cycle when power was applied, you would have a variable
speed control. This then is the basis of “phase control”
Allow power very early in the cycle and it runs fast.
These waveforms illustrate the operation of a typical phase-controlled SCR. In Fig.1 (left) the SCR is triggered fairly late in
the positive half-cycle, so the motor voltage is just 143V RMS and it runs at a relatively low speed. Compare this with Fig.2,
right, where SCR is triggered earlier in the half-cycle and the RMS value rises to 163V. Hence the motor runs faster.
siliconchip.com.au
May 2009 37
This series of scope screen grabs show the voltage waveforms applied to the motor at progressively higher speed
settings. Fig.3 (above) is the lowest setting with very short
pulses from the IBGT delivering just 92V RMS to the motor.
Fig.4 shows a significantly higher speed setting (167V RMS)
with the IGBT being switched on with longer pulses. Each
time the IGBT turns off it causes a significant voltage spike
due to the back-EMF produced by the motor inductance.
Allow power very late in the cycle and it runs slowly.
The term “phase control” comes about because the timing of the trigger pulses is varied with respect to the phase
of the mains sine wave.
It doesn’t just work with some types of motors – it has
also been the basis of incandescent lamp dimmers and
even heater controls for many decades (it doesn’t work on
most forms of fluorescent nor compact fluorescent bulbs).
The oscilloscope waveform of Fig.1 shows the chopped
waveform from a phase-controlled SCR circuit when a motor is driven at a slow speed.
Fig. 2 shows the waveform from an SCR speed control at
a higher setting. The motor has 163V applied to it while at
the low setting (Fig.1) the motor has 143V applied.
These examples show only the positive half of the
mains waveform being used, as is the normal case with a
phase- controlled SCR circuit. This automatically limits
the amount of power which can be delivered to the motor
– one half cycle is wasted. So this means that in a phasecontrol circuit the range of speed control is severely limited
at the top end.
For the motor to run at full speed, it would need to be
fed with both the positive and negative half-cycles of the
50Hz mains waveform. Normally this is not possible with
an SCR circuit (which is, effectively, a controlled diode
which therefore only conducts in one direction). While it
is possible with a Triac, it is difficult to achieve without
a complex circuit.
Another big problem with conventional phase-controlled
circuits is that the trigger pulse applied to the Triac or SCR
is very short and if this corresponds with the instant when
the brushes hit an open-circuit portion of the commutator, no current will flow and consequently, the motor will
miss out on a whole cycle of the mains waveform. This
problem is more critical at low speed settings and is one of
the reasons for the “cogging” behaviour referred to earlier.
Incidentally, the sparks you see when you look into a
universal (brush-type) motor are mostly caused by brushes
passing through an open-circuit section of the commutator – a typical power drill might have a dozen or more of
these which keep the motor windings separate.
Speed regulation
Fig.7: These waveforms show the interaction of the
triangle waveform and the speed voltage. The triangle
waveform at the top is compared to the speed voltage,
the horizontal voltage intersecting the triangle wave. The
resulting lower trace is the pulse width modulation signal
from the comparator. The comparator output is fed to the
gate driver IC2 and Q2 and Q3 that then drives the IGBT.
38 Silicon Chip
Most phase-controlled SCR speed control circuits incorporate a form of feedback that is designed to maintain the
speed of the motor under load. When the motor is loaded,
the back-EMF (electromotive force) produced by the motor
drops and the circuit compensates by triggering the SCR
earlier in the mains cycle. This helps to drive the motor
at the original speed.
In practice, the back-EMF generated by most series motors when the SCR is not conducting is either very low or
nonexistent. If there is any back-EMF it is produced too
late after the end of each half-cycle to have a worthwhile
effect on the circuit triggering in the next half-cycle.
Pulse-width modulation
As we mentioned, the new SILICON CHIP speed control
siliconchip.com.au
Similarly, Fig.5 shows an even higher speed setting with
now 208V RMS being delivered to the motor by the IGBT.
Motor speed would already be higher than that capable of a
phase-controlled circuit and shows how good this circuit is!
Fig.6: here the IGBT is virtually full-on delivering maximum
voltage to the motor. However, the RMS voltage reads lower,
due to the fact that the spikes which were present in the
earlier waveforms are no longer there to confuse the scope.
circuit uses Pulse Width Modulation (PWM) and a different feedback method for speed regulation that effectively
solves the problems above associated with phase control.
Fig.3 and Fig.4 shows the voltage waveforms applied to
the motor at high and low speed settings. What happens is
that we rectify the mains voltage and then chop it up at a
switching rate of about 1.25kHz using a high-voltage IGBT
(Insulated Gate Bipolar Transistor). For the high-speed
setting the pulses applied to the motor is relatively wide
(Fig.3) while at the low speed setting, the pulses are very
narrow (Fig.4).
There are 12 pulses during each half-cycle, so the motor
receives a more continuous stream of current compared
to when driven via phase control. As a result, the motor
operates very smoothly over the whole of its speed range.
For speed regulation the circuit does not rely upon
back-EMF from the motor. Instead, it monitors the current
through the motor and adjusts the pulse width to maintain
the motor speed. If the current rises, indicating that the
motor is under load, then the pulse width is widened to
maintain motor speed.
FUSE & FILTER
F1, L1, L2
230V
AC IN
Block diagram
Fig.8 shows the basic circuit arrangement. The 230VAC
input waveform is fed through a filter and full-wave rectified. The resulting positive-going waveform is fed to one
side of the motor. The other motor terminal is switched
on and off via IGBT Q1.
Switching of the IGBT is under the control of comparator
IC1b, which compares the speed setting required (as set by
VR1) against a triangle waveform generator. If the speed
voltage is high relative to the triangle waveform, then the
MOTOR
CURRENT
FULL WAVE
RECTIFIER
K
+
A
–
D1
TRIANGLE
GENERATOR
IC1a
COMPARATOR
IC1b
SPEED
CONTROL
MOTOR
C
GATE DRIVER
IC2, Q2, Q3
Q1
G
SNUBBER
E
VR1
OVERCURRENT
Q4
AMPLIFIER
IC3b
A
CURRENT
SENSE
R1
SAMPLE & HOLD
IC4
D2
K
IC3a
REFERENCE
OVER CURRENT
COMPARATOR
siliconchip.com.au
Fig.8: the basic circuit arrangement of the Motor Speed
Controller. The 230VAC input is full-wave rectified and fed
to one side of the motor, while the other motor terminal
is switched on and off via IGBT Q1. A conventional PWM
circuit using IC1, IC2 & IC3, controls Q1.
May 2009 39
40 Silicon Chip
siliconchip.com.au
N
SC
33k
12
VR1
1k
8.2k
–
SPEED
10k
LIN
~
10
9
8
IC1b
1M
A
K
6
7
10k
1
22k
7
IC3: LM358
K
FEEDBACK
GAIN
VR2
1M
A
4
IC3b
100k
B
6
10k
5
9
325V
15
IC2e
12
IC2b
4
IC2d
IC4
4066B
4
5
A
K
100nF
7
14
3
G
1nF
10k
R1
D1
STTH3012W
+15V
ZD2
15V
1W
10
10 F
C
E
E
C
SAMPLE & HOLD
100nF
100nF
10
100k
10k
Q3
BC327
B
B
Q2
BC337
GATE DRIVE
8 IC2f
1
1M
270
0.394V
10k
14
11
CURRENT
6 AMPLIFIER
5
3
2
1nF
(15.8A
LIMIT)
Q4
BC547
IC3a
OVER-CURRENT
D2
COMPARATOR
8
1N4148
E
C
7
IC2c
+15V
MOV1
275V
0V
OVER CURRENT
DETECTOR
220pF
470 F
16V
4.7k
100nF
250VAC
X2
PWM COMPARATOR
470
10 F
1k
ZD1
15V
1W
K
D3
1N4004
A
IC1: LM319
IC2: 4050
+15V
4.7k
5W
4.7k
5W
+
10A/230V MOTOR SPEED CONTROLLER
ALL COMPONENTS AND WIRING IN THIS
CIRCUIT OPERATE AT MAINS POTENTIAL.
DO NOT OPERATE WITH CASE OPEN –
ACCIDENTAL CONTACT COULD BE FATAL!
SAFETY WARNING!
100nF
4.7k
L2
L1
~
BR1 35A/600V
Fig.9: the circuit uses a 50A 1200V avalanche-protected IGBT (insulated gate bipolar
transistor) as the switching element to the load. It is switched at 1.2kHz so that there
are about 12 on and off cycles for each half-cycle of the 50Hz 230VAC mains supply.
2009
3
IC1a
11
470k
1W
TRIANGLE GENERATOR
5
4
100k
10nF
250VAC
X2
CASE
F1 10A
100k
18nF
100k
IEC MALE
INPUT
CONNECTOR
E
A
230V AC
INPUT
E
N
G
A
STTH3012W
C
C
K
K
A
K
ZD1, ZD2
A
1N4148
A
1N4004
E
FGA25N120ANTDTU
K
E
B
BC327, BC337, BC547
X2
CASE
E
470
1W
Q1
FGA25N120
ANTDTU 47nF
IGBT 250VAC
A
CURRENT
SENSE
0.025
5W
C
A
K
230V AC
OUTPUT
3-PIN SOCKET
comparator will produce wide pulses at its output. Conversely, a lower speed voltage will reduce the pulse width.
This operation can be seen in the scope waveforms of
Fig.7. The triangle waveform at the top is compared to
the speed voltage, the horizontal voltage intersecting the
triangle wave. The resulting lower trace is the pulse-widthmodulation signal from the comparator. The comparator
output is fed to the gate driver (IC2 and transistors Q2 and
Q3) that then drives the high voltage IGBT (Ql).
Diode D1 is a fast-recovery type to conduct the motor
current when Q1 is switched off. The snubber across Q1
prevents excessive voltage excursions across it.
Resistor R1 monitors the current flow through the motor when Q1 is on and the resulting voltage generated is
sampled using switch IC4. This sampling occurs whenever
Q1 is on.
Excessive current drawn by the motor is detected by
siliconchip.com.au
transistor Q4, used as an over-current detector to switch
off the IGBT gate drive if current exceeds about 48A.
IC3b amplifies the voltage from R1 and applies it to the
speed pot. This operates such that an increase in motor
current, as the motor is loaded and slows down, leads to
an increase in the output from IC3b. This in turn increases
the speed setting from VR1, resulting in an increase in the
voltage applied to the motor.
IC3a also monitors the voltage produced from R1 via IC4
and compares it against a reference voltage. If the voltage
from R1 exceeds the reference threshold, IC3a’s output
goes low and reduces the speed pot voltage via diode D2.
This reduces the voltage applied to the motor and provides
current limiting. Current limit is set at 15.8A.
Circuit description
The circuit for the Motor Speed Controller is shown in
May 2009 41
Q1
FGA25N120ANTDTU
D1
STTH3012W
: N OITUA C
ST NE N OP M O C LLA
TA OLF SK CART D NA
E GATL OV S NIA M TA A
ZD2
15V
47nF
250VAC X2
470 1W
10
N
A
R1
F1 10A
100nF
250VAC X2
1nF
10nF
250VAC X2
10 F
10k
Q2
470k 1W
Q3
4.7k 5W
10k
4.7k 5W
100nF
22k
10 F
470 F
ZD1
1M
4.7k
10k
270
10k
100k
4.7k
1k
IC2 4050B
1k
220pF
100k
100nF
(-)
~
1M
100k
470
L1
L2
VR2
Q4
+
IC3
LM358
18nF 100nF
D3
4004
4148
29050101
D E EP S R O T O M
RELL ORT N O C
MOV1
~
100k
1nF
10k
100k
N
IC4 4066B
0.025
100nF
15V
Fig.10: the complete
component overlay
for the Full-Wave
Speed Controller.
Be very careful not
to mix up the diodes
and zeners – they
often look very
similar. It’s also a
good idea to use IC
sockets, just in case!
IC1 LM319
1M
33k
CON1
8.2k
1RV
Fig. 7. It comprises four ICs, three low current transistors,
output when changing levels.
several diodes, resistors and capacitors plus the high voltThe pin 7 output of IC1b drives buffers IC2c and IC2d.
age IGBT, Q1.
IC2c drives three paralleled buffers, IC2b, IC2e & IC2f. These
IC1a is a comparator that forms the triangle waveform
in turn drive emitter-followers Q2 and Q3 to provide a high
generator. It is wired as an oscillator where the 18nF cacurrent drive capability to charge and discharge the gate
pacitor at pin 5 is charged and discharged via the 33kΩ
of the high voltage IGBT Ql. The gate of Q1 is protected
resistor connected to the output at pin 12. The triangle or
from excessive drive voltage using with ZD2, a 15V zener
ramp waveform across the capacitor has an amplitude of
diode. The high voltage can be impressed on the gate via
about 5V peak-to-peak.
capacitance between the gate and collector when the IGBT
Comparator IC1b compares the triangle waveform at
switches off.
pin 10 with the speed voltage at pin 9, as set by VR1. VR1
Several circuit features combine to ensure that the IGBT
is part of a voltage divider with a 1kΩ resistor connecting
can safely switch high levels of current through the moto the +15V rail and an 8.2kΩ resistor to 0V. The speed
tor load.
voltage from VR1 is filtered with
First, there is a snubber
a 10μF capacitor to prevent any
network comprising a 470Ω
Warning!
sudden changes in level and
resistor and 47nF capacitor
this voltage is monitored by the
connected in series across the
d controller
(1) The entire circuit of this motor spee
inverting input (pin 9) of IC1b via
IGBT’s source and drain. Seclly lethal. Do not
floats at 230VAC – and is potentia
a 1kΩ resistor.
ond, there is the fast recovery
g.
doin
t you are
build it unless you know exactly wha
The 1MΩ resistor between pin
diode D1. Third, there is a
IT
LE
WHI
UIT
DO NOT TOUCH ANY PART OF THE CIRC
9 and the pin 7 output provides
275VAC metal oxide varistor
and do not operate
IS PLUGGED INTO A MAINS OUTLET
positive feedback to give a small
(MOV) connected across the
without its lid on.
the circuit outside its metal case or
amount of hysteresis in the comoutput of the bridge rectifier.
parator action. This is to prevent
These measures combine to
ors
mot
ction
(2) This circuit is not suitable for indu
oscillation of the comparator
damp any spike voltages that
– see text.
or shaded pole motors used in fans
42 Silicon Chip
siliconchip.com.au
Parts List – Full Wave Universal Motor Speed Controller
1 PC board, code 10105092, 112 x 142mm
1 metal diecast case, 171 x 121 x 55mm
1 front panel label, 168 x 118mm
1 powdered iron core, 28 x 14 x 11mm (L1,L2)
1 single switched mains power outlet
1 10A IEC mains lead
1 IEC male chassis connector with mounting holes
1 3-way PC-mount screw terminal block with 5.08mm
spacing (CON1)
8 6.35mm PC-mount male spade connectors with
5.08mm pin spacing
8 6.35mm insulated female spade quick connectors
with 4-6mm wire diameter entry
2 5.3mm ID insulated quick connect crimp eyelets with
4-6mm wire diameter entry
1 knob
1 16-pin DIP IC socket
2 14-pin DIP IC sockets
1 8-pin DIP IC socket
2 3AG PC-mount fuse clips
1 10A 3AG fast blow fuse (F1)
2 M4 x 10mm screws (Earth connections)
2 M4 x 15mm screws (GPO Mounting)
1 M4 x 20mm countersunk screw (BR1 mounting)
5 M4 nuts
2 M4 star washers
2 M3 x 12mm countersunk screws (for IEC Connector)
2 M3 x 15mm screws (for Q1 and D1)
4 M3 nuts
3 3/16” x 6mm screws (PC board to case)
4 stick-on rubber feet
8 100mm cable ties
2 TO-3P Silicone insulating washers
1 300mm length of blue 10A mains wire
1 300mm length of brown 10A mains wire
1 300mm length of green/yellow 10A mains wire
1 100mm length of 0.8mm tinned copper wire
1 1.1m length of 1mm enamelled copper wire
1 45mm length of black 5mm heatshrink tubing
1 45mm length of red 5mm heatshrink tubing
1 15mm length of green 5mm heatshrink tubing
would otherwise occur every time the IGBT switched off.
Current monitoring
R1 is a used to monitor the current flow through the
motor and IGBT, Q1. Transistor Q4 directly monitors the
current via a voltage divider comprising two 10kΩ resistors in series. At about 48A there is about 1.2V across R1
and the base of Q4 is at 0.6V. The transistor conducts and
pulls the IC1b comparator output low to disconnect drive to
the IGBT. Thus Q4 provides for transient current limiting.
Voltage developed across R1 is also fed through a low
pass filter consisting of a 10kΩ resistor and 1nF capacitor to one side of IC4, a 4066 analog switch. This is the
sample-and-hold circuit and IC4 is switched on to sample
the voltage across R1 each time the IGBT is switched on.
IC4’s gate signal comes from comparator IC1b and is buffered by IC2d. The sampled signal from R1 is stored using
siliconchip.com.au
1 45mm length of white 3mm heatshrink tubing
Semiconductors
1 LM319 dual comparator (IC1)
1 4050 hex CMOS buffers (IC2)
1 LM358 dual op amp (IC3)
1 4066 quad CMOS analog switch (lC4)
1 BC337 NPN transistor (Q2)
1 BC327 PNP transistor (Q3)
1 BC547 NPN transistor (Q4)
1 FGA25N120ANTDTU NPN 50A 1200V TO-3P IGBT
(Q1) (Farnell cat 149-8965)
1 STTH3012W 30A 1200V TO-247 ultrafast recovery
diode (D1) (STMicroelectronics)
1 1N4148 signal diode (D2)
1 1N4004 1A 400V diode (D3)
2 15V 1W zener diodes (ZD1,ZD2)
1 35A 600V bridge rectifier (BR1)
1 S14K275 275VAC metal oxide Varistor (MOV1)
Capacitors
1 470μF 16VW PC electrolytic
2 10μF 16VW PC electrolytic
1 100nF 250VAC X2 class MKT polyester
4 100nF 63V MKT polyester
1 47nF 250VAC X2 class MKT polyester
1 18nF 63V MKT polyester
1 10nF 250VAC X2 class MKT polyester
2 1nF 63V MKT polyester
1 220pF ceramic
Resistors (0.25W, 1%)
2 1MΩ
1 470kΩ 1W
5 100kΩ
1 33kΩ
1 22kΩ
5 10kΩ
1 8.2kΩ
2 4.7kΩ
2 4.7kΩ 5W
2 1kΩ
1 470Ω 1W
1 470Ω
1 270Ω
1 10Ω
1 low ohm shunt resistor 0.025Ω, 1%, 5W (OAR5 –
R025F1) (TT Electronics)
1 10kΩ 25mm linear potentiometer (VR1)
1 1MΩ horizontal trimpot (VR2) (Code 105)
the 100nF capacitor and discharged over a 100ms period
with a 1MΩ resistor.
The sampled voltage from IC4 is fed to two op amps,
IC3a & IC3b. IC3b amplifies the voltage by about 100 when
VR1 is set to maximum and 3.2 when set to minimum. IC3b
acts to vary the DC level fed to comparator IC1b from VR1
and thereby compensates for speed variations in the motor.
IC3a acts as a comparator, comparing the sampled voltage
from R1 with a 394mV reference voltage at its pin 3. If the
current through R1 rises above 15.76A, the voltage across
the resistor equals the 394mV reference and the output of
IC3a goes low and pulls pin 9 of IC1b low via diode D2 and
a 470Ω resistor. This has the effect of greatly reducing the
motor drive voltage and so it limits the current.
Power for the circuit is derived directly from the 230VAC
mains. Fuse F1 protects against shorts while the 10nF
capacitor in conjunction with L1 & L2 prevents switching
May 2009 43
INSULATING PAD
Fig.11: the complete wiring diagram of the Motor Speed Controller. Follow
this wiring exactly – including the earthing detail. It is very important that
the case and lid be separately earthed, as shown here. Note also that all
parts of the circuit, including the terminals of VR1, float at 230VAC.
Inset at right is the mounting arrangement for both D1 and Q1, which mount
on the inside of the case with insulating washers. Their legs must be kinked
outwards slightly so they sit flush on the case wall.
M3 NUT
Q1 (IGBT)
& DIODE D1
KINK IN LEGS
PC BOARD
15mm
x M3
SCREW
CASE
INSULATING
WASHERS
Q1
FGA25N120ANTD
D1
STTH3012W
CASE EARTHING:
M4 x 10mm SCREW WITH
EYELET CONNECTOR,
LOCKWASHER & NUT
! N OITUA C
ST NE N OP M O C LLA
SK CART DRA O B CP D NA
LAIT NET OP S NIA M TA TA OLF
15V
A
N
A
M3 SCREW
& NUT
IEC MAINS
INPUT SOCKET
N
19050101
D E EP S R O T O M
RELL ORT N O C
+
4148
CABLE
TIE
CABLE
TIES
L1
M3 SCREW
& NUT
CABLE
TIE
CABLE
TIE
L2
CAUTION!
ALL COMPONENTS
AND PC BOARD
TRACKS FLOAT
AT MAINS VOLTAGE
(-)
CON1
~
~
1RV
L1: 12 TURNS
–
~
~
+
BR1
(MOUNTED ON
SIDE OF CASE)
CABLE TIES
LID EARTHING:
M4 x 10mm SCREW WITH
EYELET CONNECTOR,
LOCKWASHER & NUT
CABLE TIES
VR1
HEATSHRINK
SLEEVING
(LID OF CASE)
L1 & L2 BOTH WOUND
USING 1mm ENAMELLED
COPPER WIRE ON 28 x 14 x 11mm
IRON POWDERED TOROID
44 Silicon Chip
A
L2: 12 TURNS
Fig.12 (inset left):
winding details
for the input filter
choke. Note that
L1 and L2 are
wound so that their
flux cancels in the
toroid core.
OUTLET MOUNTING
BOLTS AND NUTS
(M3 x 10mm)
E
3-PIN
OUTLET
N
siliconchip.com.au
A close-up photo of the input (IEC socket) wiring, fuse,
choke and bridge rectifier. All mains leads are terminated
in quick-connect terminals.
Similarly, a close-up of the IGBT (right) and fast recovery
diode (left). These devices do not require an insulating bush
but definitely do need an insulating washer, as seen here.
artefacts from the IGBT and motor being radiated back to
the mains wiring.
BR1 is a bridge rectifier with a 600V 35A rating. The
bridge provides the circuit with the positive full-wave rectified mains voltage and this is lightly filtered using a 100nF
250VAC capacitor. Power for the low voltage circuitry is
derived via two series 4.7kΩ 5W resistors, diode D3 and
the 15V zener diode ZD1. A 470uF capacitor across the 15V
zener smooths the DC while diode D3 prevents the capacitor from discharging when the mains voltage falls to below
15V every half cycle. The result is a regulated 15V supply.
quite hot to the touch.
When inserting diode D2 and D3 and zener diodes ZD1
and ZD2, take care with their orientation and be sure to place
each type in its correct place. D1 is installed later.
We used IC sockets for the ICs. Be sure to install these the
correct way around with the notch facing the direction shown
on the overlay. Transistors Q2-Q4 can now be inserted, again
taking care to place each in its correct position.
Capacitors can be installed next. The accompanying
capacitor table shows the various codes that are used to
indicate the capacitance values of the polyester capacitors.
The electrolytic capacitors must be oriented with the correct polarity.
L1 & L2 are windings wound on a single powdered iron
toroidal core as shown in Fig.12. Each winding is wound
using 12 turns of 1mm enamelled copper wire with the
shown direction.
While the exact number of turns is not critical, it is important that both windings have the same number of turns
and that they are wound in the directions as shown. The
wire ends can be soldered to the PC board after they have
been stripped of insulation using some fine abrasive paper,
or a sharp hobby knife. After soldering, secure the toroid to
the PC board with two plastic cable ties. These wrap around
the core and through holes in the PC board. (It is important
not to secure the toroid with lengths of wire; these could
make a shorted turn around the toroid).
Fuse F1 is mounted in fuse clips that are installed into
the PC board as shown. Clip the fuse into the clips first (lugs
Construction
The Motor Speed Controller is constructed on a PC board
coded 10105092 and measuring 112 x 142mm. It is housed
in a diecast case measuring 171 x 121 x 55mm. The PC board
has cut-outs to match the shape of the case.
Begin construction by checking the PC board. There should
not be any shorts or breaks between tracks. If there are any
problems, repair these as necessary.
Similarly, if the cutouts in the sides of the PC board have
not been shaped, they should be cut and filed before any
components are assembled.
A large semicircular cutout is required on both the long
sides of the board. Also you will need to round off the corners of the board. Make sure the PC board fits into the case
before starting assembly.
Following the overlay diagram shown in Fig.10, begin by
inserting and solde ring in the wire links and then the resistors, using the accompanying table for
Resistor Colour Codes
the colour codes. The two 5W resistors
should be inserted so that they stand a
No. Value
4-Band Code(1%)
5-Band Code (1%)
millimetre above the PC board to allow
2 1MΩ
brown black green brown
brown black black yellow brown
cooling. When the Drill Speed Control1 470kΩ yellow violet yellow brown
yellow violet black orange brown
ler is operating, each resistor will be
5 100kΩ brown black yellow brown
brown black black orange brown
dissipating about 2.7W so would run
1 33kΩ
orange orange orange brown
orange orange black red brown
1 22kΩ
red red orange brown
red red black red brown
Capacitor Codes
5 10kΩ
brown black orange brown
brown black black red brown
Value
μF
IEC
EIA
value
code
code
1 8.2kΩ grey red red brown
grey red black brown brown
100nF 0.1μF
100n
104
2 4.7kΩ yellow violet red brown
yellow violet black brown brown
47nF .047μF
47n
473
2 1kΩ
brown black red brown
brown black black brown brown
18nF .018μF
18n
183
2 470Ω
yellow violet brown brown
yellow violet black black brown
10nF
.01μF
10n
103
1
270Ω
red
violet
brown
brown
red violet black black brown
1nF
.001μF
1n0
102
1 10Ω
brown black black brown
brown black black gold brown
220pF NA
220p
221
1
1
1
1
1
1
1
1
1
1
1
1
siliconchip.com.au
May 2009 45
What Motors Can Be Controlled?
We’ve noted elsewhere in this article that the vast majority of
power tools and appliances use so-called universal motors. These
are series wound motors with brushes. But how do you make sure
that your power tool or appliance is a universal motor and not an
induction motor? As we also said before, induction motors must
not be used with this speed controller.
One clue is that most universal motors are quite noisy compared
to induction motors. However, this is only a guide – it’s certainly
not foolproof.
In many power tools you can easily identify that the motor has
brushes and a commutator – you see sparking from the brushes
and that settles the matter. But if you can’t see the brushes, you
can also get a clue from the nameplate or the instruction booklet.
OK, so how do you identify an induction motor? Most induction
to the outer ends of the fuse) then insert them into the PC
board and solder in position – this hopefully ensures that
you don’t solder them in the wrong way around.
Solder in the eight 6.4mm PC-mount spade connectors to
the PC board for the mains wiring connections, along with
the 3-way screw terminal connector for the potentiometer
connecting wires.
D1 and Q1 are the last components to be soldered to the
PC board. Solder them in so their metal flanges are towards
the edge of the PC board and their full-length leads extending about lmm below the PC board.
motors used in domestic appliances will be 2-pole or 4-pole and
always operate at a fixed speed which is typically 2850 rpm for
a 2-pole or 1440 rpm for a 4-pole unit. The speed will be on the
nameplate. Bench grinders typically use 2-pole induction motors.
Note that this speed controller must NOT be used with power
tools, etc, which already have a speed controller built into the
trigger.
One final point: if you are using this controller with a high power
tool such as a large circular saw or 2HP router, it will not give the
same kick when starting.
Because of the current limiting, the motor will take a few seconds to come up to full speed. Normally though, if you want to
use the appliance at full speed, it is better not to use the Speed
Controller at all.
All that is left are bridge BR1, diode D1 and IGBT Q1, all
of which mount on the inside walls of the case when the
PC board is in place.
Mounting the hardware
First of all, mark out the hole position for the IEC connector and earth screw in the end wall of the case. The IEC
connector mounts in the horizontal centre, about 6mm down
from the top.
As you can see in our photographs, about 1mm of the
top of the end-wall channel is left when the hole is made.
Another view of the completed motor speed controller, very close to same size. The front panel artwork is printed
overleaf, or it can be downloaded from siliconchip.com.au.
46 Silicon Chip
siliconchip.com.au
The IEC hole is made by drilling a series of small holes
around the perimeter of the desired shape, knocking out the
piece and filing to shape.
Insert the PC board into the case and mark the mounting
hole positions for diode D1, IGBT Q1 and bridge rectifier BR1.
Note that the leads for D1 and Q1 must be kinked outward
slightly so that the metal flange of each device is parallel to
and in contact with the side of the case.
Drill out the holes for these three components Holes are
also required in the lid for the GPO, VR1 and the earth terminal. All holes must be deburred on the inside of the cas
e with a countersinking tool or larger drill to round off the
sharp edge of the hole and in the case of D1 and Ql, prevent
punch-through of the insulating washers.
Attach the PC board to the case with the 3/16” screws. Note
that we do not use a screw in the corner where BR1 mounts.
BR1 effectively holds the PC board in place here. Secure D1
and Q1 to the case with a screw, nut and insulating washer.
The arrangement for this is shown in the inset in Fig.11.
After mounting D1 and Q1, check that the metal tabs of
the devices are isolated from the case by measuring the resistance with a multimeter. The meter should show a very
high resistance measurement between the case and any of
the diode and IGBT leads.
The complete wiring diagram is shown in Fig.11. The
earthing details of the case are most important since the
IGBT, fast recovery diode D1 and potentiometer, VR1, are
all at mains potential yet are attached to the case. If the
insulating washers or the insulation of the potentiometer
were to break down, the case would be live (ie, at 230VAC)
if it was not properly earthed.
For the same reason, the case lid must also be separately
earthed, also as shown in Fig.11.
The bridge rectifier (BR1) is secured to the case with a
4mm screw and nut. It does not require an insulating washer
between its body and the case.
All mains wiring must be done using 10A mains-rated
(ie 250V) wire. Wiring for the potentiometer must also be
mains rated but it does not need to be 10A rated. The IEC
connector must be wired using the correct wire colours
with brown for the Active, blue for the Neutral and green/
yellow striped wire for the Earth. Use quick-connectors
for the mains wiring connection to the PC board connectors. Wires to the IEC connector need to be insulated with
Troubleshooting the Motor Speed Controller
If the speed controller does not work when you apply power,
it’s time to do some troubleshooting.
First, a reminder: all of the circuit is connected to the 230V
AC mains supply and is potentially lethal. This includes the
tabs of Dl and Ql, the terminals of potentiometer VRl – in fact,
all other parts. Do not touch any part of the circuit when it is
plugged into a mains outlet. Always remove the plug from
the mains outlet before touching or working on any part
of the circuit.
If the live circuit must be worked on, it must be operated
via a 1:1 mains isolation transformer. We’re only saying that
because it is safer but we’d still prefer you didn’t do it.
Before going any further, give you PC board another thorough check (using a magnifying glass?). Kit suppliers tell us
that at least 99% of problems are due to wrong or swapped
components, right components in the wrong way around and,
of course, the “biggie”: poor soldering (or even completely
missed solder joints).
If you are 110% sure your Speed Controller isn’t suffering
from any of these maladies, it’s time to get more technical!
Fortunately, there is a safe way to check most of the circuit
and that is to operate it from a low voltage (12V) DC supply.
Naturally, before you remove the lid you would have already
disconnected the 230V mains lead (don’t just turn it off, unplug it!). The supply is connected with the positive connecting
to the anode of diode D3 and the negative connecting to the
anode of ZD1 (the anodes are the ends opposite the striped
end on the diode body).
Before you connect the supply, measure it to make sure it
is not exceeding 14V – if it does, you’re liable to blow up the
15V zener diode.
With power applied, a multimeter connected with the negative lead to the negative supply can be used to test voltages.
Firstly, check that there is 11.4V on pin 1 of IC2 and pin 11 of
IC1. IC3 should have 11.4V on pin 8. Similarly pin 14 of IC4
should also have 11.4V.
Voltage on the wiper of VR1 should be adjustable from
siliconchip.com.au
4.86V to 10.79V or similar by rotating the potentiometer to its
full extremes. The same voltage range should be seen at pin
9 of IC1a.
Pin 7 of IC3a should be close to 0V. Pin 1 of IC3b should
be at about 9V or more.
With the meter still set to read DC volts, the triangle wave
can be measured and should provide approximately a half
supply reading, in this case about 5V. If your meter can read
a AC volts at 1kHz, then the meter can be set to read ACV. The
reading will be around 1.5ACV.
Similarly, when the multimeter is set to read DC volts the
pulse width drive can be checked. On the output of IC1a at pin
7, the DC volts should be adjustable from 0V to close to 11V
when VR1 is altered from minimum to maximum. The same
voltage range should be available at the pin 4, pin 12 and pin
15 output of IC2. A slightly lower voltage range will be available
on the gate of Q1.
If the gate voltage remains at 0V, then suspect a damaged
IGBT, a shorted ZD2 or open circuit 10Ω resistor.
Measuring the resistance between IGBT pins is a simple
way to check it. If there is a short circuit between collector and
emitter, or if the gate is shorted to the emitter, then the IGBT
is faulty.
Diode (D1) operation can be checked using the diode test
on your multimeter. In any case there should not be a short
circuit measured between anode and cathode.
Be sure to remove the 12V supply and replace the lid before
reconnecting to the mains.
Incidentally, do not try to monitor the waveforms with an
oscilloscope unless you know exactly what you are doing.
Ideally it needs with a scope with true differential inputs or a
mains isolation transformer. The waveforms in Fig.7 can only
be measured using a low-voltage DC supply, as detailed above.
You must not connect the earth terminal of a scope
probe to any part of the circuit.
If you do, you are likely to cause severe damage to the circuit
and possibly to the scope as well!
May 2009 47
heatshrink tubing covering all exposed metal.
For the earthing, solder two earth wires from the IEC
connector with one terminating to the earth eyelet and the
other running to the power outlet earth terminal. Another
green/yellow earth wire runs between the earth connection
on the power outlet and the earth eyelet on the lid. The earth
eyelets are secured with M4 screws, a star washer and nut.
Wire up the potentiometer, again using 250VAC rated
wire. The reason for voltage rating this is to ensure that in
the worst-case scenario and a mains-voltage-carrying wire
lets go inside the case (eg, it unsolders due to heat), a bare
end contact with one of the pot wires will not allow mains
to “punch through” lesser-rated wire insulation.
Finally, hold the wiring in place using cable ties as
shown – also to minimize the possibility of loose wires
contacting something they shouldn’t.
Note that the Active and Neutral wires running to the
GPO socket should not be allowed to lie near to the potentiometer wiring. Instead have these wires lie on the Q1
side of R1 when the lid is closed. Failure to observe this
wiring arrangement may cause the controller to power the
motor with sudden bursts of speed.
This is to minimise the possibility of the high voltage
switching signal on the Neutral wire being induced into
the potentiometer wiring.
Testing
Before you power up the circuit, insert the ICs into their
respective sockets, taking care with their orientation. Set
SILICON
CHIP
trimpot VR2 to its mid-position – this setting should give
good performance with most motors.
Now, check all of your wiring very carefully against the
overlay and wiring diagram. Also check that the case and
lid are connected to the earth pin of the power socket.
If you are satisfied that all is as it should be, screw the
lid onto the case.
Do not be tempted to operate the Drill Speed Controller
without the lid in place AND screwed in position – it’s
not worth the risk.
The easiest way to test the circuit operation is to connect
a load such as an electric drill. Apply power and check
that you can vary the drill speed with VR1. Some motors
may require adjustment of VR2 for best speed regulation,
which must be done on a trial-and-error basis. Disconnect
power from the mains wall outlet (or unplug the IEC connector) before removing the lid, adjust VR2 very slightly
and replace the lid.
In practice, if VR2 is adjusted too far clockwise, the
motor will tend to be overcompensated when loaded and
will actually speed up. It may even hunt back and forth
between a fast and slow speed. If this happens, readjust
VR2 anticlockwise for best results.
If you are using a drill for example, at fairly low speed,
the motor should not slow down by much as you put a
reasonable load on it.
At the risk of sounding repetitive, remove the plug from
the mains outlet before making any changes to VR2 and
replace the lid before reconnecting power.
SC
POWER OUTLET MOUNTING HOLES
www.siliconchip.com.au
4mm
230V
INPUT
4mm
CUTOUT FOR POWER OUTLET
(60 x 40mm)
GREY: POWER OUTLET POSITION
230V 10A
FULL WAVE
MOTOR SPEED
CONTROLLER
Fig.13 : same-size artwork for the front panel. A photocopy
of this can also be used as a drilling/cutting template.
48 Silicon Chip
10mm
x
SPEED
For universal (brush-type)
(brush-type)
motors up to 10A/2300W
nameplate rating
3
Do NOT use on induction
or shaded-pole motors
x: 3mm pot locating hole drilled from lid underside
– does not need to go all the way through lid.
siliconchip.com.au
|