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參數(shù)資料
| 型號： | DI 300 |
| 廠商： | SIEMENS AG |
| 英文描述： | Phase Switch-off Dimmer(相位轉(zhuǎn)換調(diào)光器) |
| 中文描述： | 相開關(guān)過調(diào)光器（相位轉(zhuǎn)換調(diào)光器） |
| 文件頁數(shù)： | 2/5頁 |
| 文件大小： | 466K |
| 代理商： | DI 300 |
phase switch-off
dimmer
However, as described below,
conventional and electronic transformers
impose different requirements on the
series-connected dimmer.
Phase switch-on dimmers
The principle of phase switch-on is
used to control most conventional
transformers. With this, the voltage is
only applied to the load for a certain
interval of time per mains cycle; see
Figure 2. The average power output, here
50% of full load, is determined by the
length of the time interval. With phase
cut-on, the load initially has no power
after the mains voltage passes through
zero. After an (adjustable) interval of
time has elapsed, a triac built into the
dimmer is triggered, and this switches on
the mains voltage. At the next passage
through zero, the hold current for the
triac is no longer attained, and the power
is switched off. The cycle just described
is repeated after each passage through
zero. Figure 3 shows the principle of the
design of a phase switch-on dimmer.
For the dimmer, conventional
transformers represent an inductive load,
which produces a phase shift between the
voltage and current. Whereas the voltage
has already passed through zero, the
current has not yet fallen to zero.
Conventional phase switch-on dimmers
are not suitable for this type of load,
because the triac is not triggered at the
“correct point” in the current cycle. Any
trigger pulse output by the dimmer
before the current has fallen to zero will
have no effect. So-called half-wave
operation results, which quickly drives
the transformer to saturation, and usually
results in its failure.
Dimming halogen lamps with
conventional transformers thus requires
special phase cut-on dimmers, which
detect a phase shift either by measuring
the current and voltage or by determining
the passages through zero, and
automatically adjust the timing of the
trigger impulse. Examples of dimmers
which satisfy these requirements are the
halogen lamp primary dimmers described
in “ELVjournal” 5/93 or the dimmers in
the ELV radio switching system, FS 10.
Phase switch-off dimmers
For dimming purposes, most
electronic transformers require a so-
called phase switch-off dimmer. Either
the type plate or the instructions for use
will then indicate the device is
“dimmable” or “dimmable using a phase
switch-off dimmer”. Phase switch-off
dimmers can also be used with no
problems to dim normal filament bulbs
and high-voltage halogen lamps.
Fig. 3: The operating
principle of the phase
a triac
In contrast to the phase cut-on
dimmer, a phase cut-off dimmer switches
the mains voltage on immediately at
passage through zero, and then off again
after an (adjustable) time; see Figure 4.
Because a conventional triac cannot be
used to switch off the voltage during a
half-wave, other alternatives must be
explored in order to realize a dimmer of
this type. Figure 5 shows the block
diagram of the ELV phase cut-off
dimmer. The switch used here is a high-
voltage MOS-FET. As a MOS-FET is
only suitable for switching DC, the
mains voltage is first rectified using a
bridge rectifier. A control logic unit, in
this case a microcontroller, determines
the points when the mains voltage passed
through zero and switches the MOS-FET
on at these points. The mains voltage is
thereby applied to the load, here an
electronic transformer. After a set
interval of time has elapsed, the MOS-
FET is switched off, and the load is
deenergized. This cycle is repeated after
each passage through zero by the mains
supply, giving the voltage trace shown in
Figure 4 at the load. The switch shown in
Figure 5 is used for control purposes, e.g.
for switching on and off and for
dimming.
New CoolMOS technology from
Siemens
A completely original generation of
high-voltage MOS-FETs is used in the
new ELV phase cut-off dimmer, i.e. the
Siemens “CoolMOS” range. While the
familiar MOS structure had reached the
limits of its development, and the only
way left to reduce the switch-on
resistance RDS(on), which is the main
determinant of the power dissipation,
would be to maximize the area of silicon,
Siemens’ new “CoolMOS” technology
reduces RDS(on) by a factor of between
5 and 10 for the same chip area. This
greatly reduces the power loss in the
transistor in its on state. “CoolMOS”
technology also sets the standard in terms
Control logic
Fig. 2:
Principle of a
phase switch-
on dimmer
Fig. 4:
Principle of a
main voltage
Voltage at the
load
U
U
main voltage
Voltage at the
load
t
t
t
t
U
U
ELVjournal 5/99
230 V
main voltage
Phase switch-on dimmer
Conventional transformer
Halogen
lamp
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