Triacs and SCRs
Speed controller for power tools
Triacs and SCRs
Inductive DC load on AC mains
Triacs and SCRs
Lamp dimmer
Triacs and SCRs
Universal Motor Speed Controller
Most handheld power tools such as drills, routers, jigsaws
and sanders incorporate a speed controller in their
trigger switch.The popular solution is a half-wave phase
controller incorporating a Silicon Controlled Rectifier
(thyristor) with a high ITRM (repetitive surge) capability.
This simple, compact and efficient circuit offers variable
speed control with the best speed stability under a widely
varying motor load. It also withstands the high, repetitive
inrush currents experienced during multiple start/stop
sequences and motor stall. Another demand placed on
components by this application is high ambient
temperatures, often combined with limited space and
little provision for heatsinking. Our portfolio includes
compact and rugged devices such as the BTH151S-650R
SCR, specifically designed to satisfy all these conditions.
• Compact surface mount package (DPAK)
• Load current I
= 12 A
• High repetitive surge guarantee
• I
= 60 A @ 10 ms, 100 kilocycles
• High surge capability (I
= 110 A @ 10 ms)
Occasions arise where a DC load must be powered from
AC mains via a bridge rectifier. Examples include DC
permanent magnet motors as used in small hand-held
tools & kitchen appliances, DC solenoid valves as used in
home and industry, etc.The motors will most likely be
speed-controlled by means of a triac phase control
circuit.The solenoids also are often triac-controlled, with
the triac used as a solid-state switch to apply full power
only. In both cases, the load current is extremely non-
linear and can more closely resemble a square wave than
a sine wave.This produces very high commutating current
/dt) for the triac. Most triacs will fail to commutate
under such conditions and will experience uncontrolled
conduction of one or more half cycles after removal of
the gate drive.The problem gets rapidly worse with
increasing temperature. Such commutation failure can be
avoided by using Hi-Com (three quadrant) triacs
exclusively. If the least sensitive options are chosen
(B series with IGT = 50 mA), guaranteed reliable
operation is possible without the need for commutation
aids like snubbers or series dI
/dt limiting inductors.
• Hi-Com (three quadrant) triacs require no
commutation aids such as snubbers and dI
limiting inductors
• Simplest possible circuits
• Best reliability
• Most reliable operation at high temperatures
Suitable Products
• Three quadrant triacs
- 1A
BTA201 range
- 4A
BTA204 range
- 8A
BTA208 range
Lamp dimmers must be very compact and generate little
waste heat as they are usually housed in the extremely
restricted space of a wall switch box. A triac phase
control circuit can meet these requirements. Lamp
brightness is varied by varying the amount of time in each
mains half cycle that the lamp is connected to the supply.
This conduction time is governed by how fast the 47 nF
capacitor charges up, which in turn is controlled by the
setting of the 1 MΩ potentiometer. Because the load is
resistive, it offers no smoothing or filtering of the current
waveform, so harmonic distortion remains high.Therefore
it is necessary to include the 2.5 mH inductor to
attenuate the harmonic currents, in addition to the 47 nF
RFI filter capacitor.
• Simple circuit
• Very compact
• Efficient - low heat generation
• Cost effective for cost-critical applications
• Applicable to any lamp power - e.g. 40 to 1000 W -
simply select the appropriate triac current rating*
* Severe current de-rating is routinely applied due to the
extremely limited heatsinking and the very high potential
inrush current of cold filaments or failing lamps
Suitable Products
• Four quadrant triacs
- 4A
BT136 series
- 8A
BT137 series
- 12A BT138 series
- 16A BT139 series
- 25A BTA140 series
• Diac
- BR100/03
Universal motors are commonly used in industrial and
commercial applications, as well as many appliances found
in the home, where high-speed, low-cost and ease of
speed control are a requirement.Typical applications
include mixers, washers, power tools, laboratory
equipment, sewing machines and vacuum cleaners. Motor
speed is easily controlled by varying the average voltage
applied to it.This can be achieved very simply by use of
the phase control circuit. A Phase Controller varies the
amount of time in each mains half-cycle that voltage is
applied to the load, according to the setting of the 1 MΩ
potentiometer.The inductance of the motor provides
some smoothing and filtering of the load current, while
the 220 nF capacitor provides additional filtering of RF
• Simple circuit
• Three quadrant triac requires no Snubber
• Cost effective
• Efficient - low heat generation
• Applicable to any motor power - e.g. 100 W mixer or
2.2 kW heavy duty vacuum cleaner - simply select the
appropriate triac current rating*
* Half current derating has been applied to allow for
inrush and overload currents and to allow for non-ideal
heatsinking in hot environments.
Suitable Products
• Three quadrant triacs
- 4A
BTA204-B series
- 8A
BTA208-B series
- 12A BTA212-B series
- 16A BTA216-B series
- 25A BTA225-B series
• Diac
- BR100/03
Suitable Products
- 12 A BTH151S-650R (DPAK) – leaded option
(TO220) available on request
• Diac
- BR100/03 (SOD27)
- 12A
- 16A
- 25A
BTA212 range
BTA216 range
BTA225 range
Max load
200 W
400 W
600 W
800 W
1250 W
• Diodes
- Any low frequency diode from Philips’ General
Purpose Rectifier range.
Max load
550 W
1100 W
1600 W
2200 W
3400 W
Circuit Diagram
Circuit Diagram
47 kΩ
Circuit Diagram
RFI filter components
2.5 mH
Circuit Diagram
switch closes
for full speed
load current
(three quadrant)
230 V
50 Hz
100 nF
(250 V) AC
class X2
230 V
(50 Hz) supply
40 W - 400 W
10 kΩ
230 V
(50 Hz)
1 MΩ
220 nF
(250 V AC) preset
class X2
10 kΩ
1 MΩ preset sets min.
motor speed
1 MΩ potentiometer is
user-adjustable for
adjusting motor speed
between the min. set
point and maximum.
1 MΩ
Three quadrant triac
(IGT = 50mA)
470 kΩ
47 nF
(63 V)
High dIcom/dt
AC mains
220 nF
(250 V AC)
class X2
1 MΩ
47 nF
(63 V)
Four quadrant
blocking voltage
DC load
100 nF
(63 V)
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