Triacs and SCRs
Improved speed control of small
universal motors
Description
A universal motor’s speed drops off rapidly when it is
loaded. This effect is emphasized further if the motor is
undersized or subject to intermittent overload, typical in
mixers, sewing machines and power tools. A half wave
phase control circuit - one that uses a Silicon Controlled
Rectifier (SCR) instead of a triac - enables improved
compensation by the motor for changes in load and
therefore helps maintain a more constant speed for a
given power setting. In some applications a bypass switch
is included to connect the motor directly to the mains
supply for full speed. However, the difference in motor
speed between 180º (half wave) conduction and 360º (full
wave) conduction is often not great. A degree of RFI
filtering is provided by the motor inductance and the 100
nF capacitor. An SCR capable of withstanding high
repetitive surge current will be required for arduous
applications such as professional, heavy duty power tools.
Benefits
• Simple, compact circuit
• Cost effective
• Efficient - low heat generation
• Better speed maintenance as load varies
Suitable Products
• SCRs
- 8A BT300 series
- 12A BT151series
- 20A BT152 series
• Diac
- BR100/03
Triacs and SCRs
Reversible induction motor
Rectifiers and Zeners
Ultrafast diodes for high frequency
applications
Rectifiers and Zeners
High frequency diode bridge
Description
Industrial applications such as roller shutter doors and
conveyors, and domestic appliances including tumble
dryers and top-loading washing machines often employ
reversible induction motors. Many controllers for these
motors use two triacs to connect two motor terminals
alternately to the supply. To avoid uncontrolled discharge
of the motor capacitor through both triacs it is essential
that their operation is mutually exclusive.
This requires high quality Hi-Com (High Commutation)
triacs with excellent immunity to false triggering. In
addition, due to the voltage boosting that occurs across
the undriven motor winding (voltage step-up by
‘autotransformer effect’), high voltage triacs must be
specified. Using the recommended triacs in the circuit
shown below ensures reliable operation without the need
for snubbers or gate capacitors.
Benefits
• Three Quadrant triacs require
no
snubbers
• Increased reliability from simpler circuit
• Microcontroller / triac combination does not require
driver IC
• Best reliability due to high voltage triacs
Suitable Products
• Triacs (8 A, 1000 V)
- BTA208B-1000C
- BTA208X-1000C
• Microcontroller: 87LPC764
• Transistor: BC557
• Diode: 1N4148
Description
In fast switching applications where low conduction losses
are important, Philips BYV29 (9 A / 600 V) ultrafast diodes
gave the lowest total power loss in a component test
which measured several parameters. In the first circuit the
diodes were used as a boost diode in a 600 W PFC
circuit with a ZVS (zero voltage switching) circuit to limit
power loss in the PFC switch.The second test involved a
full diode bridge in a 1500 W isolation stage. Additionally
forward voltage was measured at two different
temperatures and the reverse recovery time at two
different switch conditions.
Compared against four other ultrafast diodes, the tests
showed that the BYV29 has the lowest body
temperature, the lowest forward voltage and an
intermediate reverse recovery time.
For higher power converters the 20 A BYV34 and 30 A
BYV44 diodes are recommended.
Benefits
• Highly efficient solution
• Extra reliability from low operating temperature
• Up to 150 kHz switching
• Surface mount and leaded packages
Suitable Products
• BYV29-500
• BYV29-600
Description
Taking a 400 V / 1600 W isolation stage used in a solar
energy inverter, the high frequency diode bridge in this
application consists of four ultrafast recovery diodes
(BYV29B-500/600).
A full-bridge inverter consisting of four 600 V MOSFETs
converts the DC input voltage to AC, with a frequency as
high as 150 kHz to reduce the size of the 1:1
transformer.
With a full diode bridge, the secondary AC voltage is
rectified to 400 V DC.The high frequency needs ultrafast
recovery diodes and, as conduction losses play a major
role, the forward voltage must be as low as possible. As
the maximum reverse voltage is equal to the maximum
DC voltage, for safe operation this application requires
500 V or 600 V diodes. Philips ultrafast recovery diodes
with optimized forward voltages are available from 500 V
to 800 V.
Benefits
• Ultrafast switching up to 150 kHz in given application
• Optimized to reduce conduction losses
• High temperature operation at maximum rated reverse
voltage
• Soft recovery characteristics reduce EMI
• Surface mount and leaded packages
Suitable Products
• BYV29
• BYV29X
• BYV29B
• BYT79
• BYR29
• BYR29X
Circuit Diagram
ZVS
circuit
Circuit Diagram
Circuit Diagram
1)
600W/100kHz PFC
L
100
BC557
Circuit Diagram
400 V DC
47 kΩ
1000 V
Hi-com triacs
(I
GT
= 35 mA)
switch closes
for full speed
5V
BZX79C5V6
100
230 V
(50 Hz)
supply
100 nF
(250 V AC)
class X2
mains supply
470 kΩ
47 nF
(63 V)
33
Diac
LPC
MICRO
CONTROLLER
1N4148
motor running
capacitor
BC557
BYV29B-500/600
400 V DC
SCR
0V
R-C
mains
dropper
reversible
induction motor
bra540
bra656
1N4148
M
MSE156
N
2)
1500W/130kHz Isolation stage
56
57
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