Active solid-state devices (e.g. – transistors – solid-state diode – Regenerative type switching device – Having only two terminals and no control electrode – e.g.,...
Reexamination Certificate
2003-04-09
2004-08-24
Prenty, Mark V. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Regenerative type switching device
Having only two terminals and no control electrode , e.g.,...
C257S146000, C257S603000, C438S133000
Reexamination Certificate
active
06781161
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates in general to semiconductor devices, and more particularly to non-gated thyristor devices.
BACKGROUND OF THE INVENTION
Silicon controlled rectifiers (SCRs) and triacs are part of the gated thyristor family that are fabricated as respective four-layer and five-layer devices that can function to control AC circuits, such as light controls, dimmer circuits, power pulse circuits, voltage references in AC power circuits, motor control circuits, etc. Many of these AC circuits are controlled by triggering the gated thyristor devices at desired phase angles of the AC voltage. Rather than triggering these gated thyristor devices directly from the AC power, such gated thyristor devices are more efficiently triggered by two-terminal thyristor devices, known sometimes as diacs, sidacs or silicon trigger switches (STS). Diacs and sidacs are commercially available from Teccor Electronics of Irving, Tex.
A conventional phase angle control circuit
10
used as a light dimmer is shown in
FIG. 1
a.
An AC source
12
of power, such as 110 VAC, is coupled to a triac
14
which is in series with an incandescent light bulb
16
. The triac
14
can be triggered into conduction at various magnitudes of the AC voltage, e.g., at different phase angles, to thereby control the intensity of the light emitted by the light bulb
16
. The triggering of the triac
14
to control the intensity of the light is carried out by the use of an RC network which includes a potentiometer
18
and a capacitor
20
, together with a diac
22
. The diac
22
has a negative resistance characteristic that makes it well suited for use in triggering gated thyristors. The breakover voltage (V
B0
) for many diacs used in 110 VAC applications is in the range of about 27-70 volts. The potentiometer
18
is adjustable for varying the intensity of the light emitted from the light bulb
16
. As the resistance (that is in series with the capacitor
20
) increases, there is an increased delay into each AC cycle before the diac
22
triggers the triac
14
into conduction. Once triggered into conduction, the triac
14
conducts AC current to the light bulb
16
for the remainder of the AC cycle. The shorter the duration of the AC cycle in which the triac
14
conducts, the dimmer the light becomes.
FIG. 1
b
illustrates a circuit configuration using sidacs
19
a
and
19
b
with respective telephone lines
21
a
and
21
b
to provide overvoltage protection thereto. Indeed, sidacs can be used to provide overvoltage protection functions, clamping functions and many other similar functions in numerous other types of circuits. Sidacs are available with breakover voltages in the range of about 6 volts to about 330 volts. The first sidac
19
a
is connected between ground and a telephone line tip conductor
21
a
to provide overvoltage protection thereto. Similarly, the second sidac
19
b
is connected between ground and the telephone line ring conductor
21
b
to provide overvoltage protection thereto. Various other configurations of sidacs and associated components can be coupled in a network between the telephone line conductors
21
a
and
21
b
to provide overvoltage protection functions. When a voltage carried by the telephone line conductor exceeds the breakover voltage of the sidac, the sidac is driven into conduction to thereby clamp the telephone line conductor to a low voltage level. A negative resistance characteristic of the sidac provides a low voltage drop across the two terminals thereof, thereby lowering the power developed by the sidac during conduction of the overvoltage energy.
The diac
22
and sidacs
19
a
and
19
b
are two-terminal thyristor devices that have a voltage/current characteristic generally shown in FIG.
2
. When a voltage of a magnitude between the positive breakover voltage+V
B0
and the negative breakover voltage−V
B0
is applied across the two-terminal thyristor device, such device remains in a non-conductive state. The breakover voltage of a two-terminal thyristor can be exceeded by overvoltages, AC-derived signals, or many other types of signals. Once the breakover voltage is reached, the two-terminal thyristor device conducts and enters into its negative resistance region
26
. Here, the voltage across the device is less than the breakover voltage. This feature can be used as an advantage in many applications.
The importance of the negative resistance region
26
is that the voltage across the two-terminal thyristor device decreases for increasing current through the device. The phenomenon of avalanche current flow through the two-terminal thyristor device causes the negative resistance characteristic
26
. The power developed by the device is less, thus allowing the device to be made smaller in size. With a lower on-state voltage across the two-terminal device, a pulse of current can be provided to more efficiently trigger a triac or other device into conduction.
With conventional two-terminal thyristor devices, the voltage across the device typically decreases about two volts once it fully enters its negative resistance region
26
. The dynamic resistance of the device in the negative resistance region
26
determines the extent by which the voltage across the two-terminal thyristor device decreases once the breakover voltage is exceeded. With a larger negative resistance, there is a larger difference in the voltage drop across the two-terminal thyristor device at breakover and after breakover.
In the light dimmer application of
FIG. 1
a
, after the diac
22
enters the negative resistance region
26
a
or
26
b,
the sudden decrease in voltage across the diac
22
causes an additional voltage (about two volts) to be placed on the gate
24
of the triac
14
. The diac circuit
23
thus produces a current pulse to quickly turn on the triac
14
so that the triac gate current does not languish through its turn-on transition. Less power is thus developed across the triac
14
itself. Once the triac
14
is driven into conduction by the diac circuit
23
, the AC power for the remaining portion of the AC cycle drives the light bulb
16
. Once the AC voltage passes through a zero crossing and the holding current of the triac
14
is no longer sustained, the triac
14
stops conducting current and remains in an off-state until triggered again in the next AC cycle by the current pulse from the diac circuit
23
.
The design considerations of a diac, sidac or STS generally require that they be full wave, i.e., bidirectional devices, so that operation occurs during both the positive and negative cycles of the AC voltage. Moreover, the voltage/current characteristics should be symmetrical for both positive and negative trigger currents. This means that the positive and negative breakover voltages should be substantially the same magnitude. While more difficult to achieve, the break back or negative resistance characteristic
26
should exhibit a low dynamic resistance characteristic to provide a correspondingly larger current pulse to the gated thyristor to be triggered. When utilized for clamping functions, the negative resistance characteristic of the two-terminal thyristor device reduces the voltage across the device during conduction, thereby reducing the power dissipation requirements of the device.
A two-terminal thyristor device constructed according to the prior art is shown in FIG.
3
. Two-terminal thyristor devices are generally three-layer devices, including a p-type midregion
30
and heavily doped n-type regions
32
and
34
diffused into opposite sides of a semiconductor wafer
36
. The concentration of the n-type impurities is related to the magnitude of the breakover voltage of the two-terminal thyristor device. The wafer
36
is masked, and then etched through the top and bottom n-type regions
32
and
34
, down into the p-type midregion
30
. The mask defines the boundaries of each chip of the wafer
36
. The etching process thins the wafer
36
around each chip. Two of the many chips formed on the wafer
36
ar
Turner, Jr. Elmer L.
Wang Yong-Fa Alan
Chauza & Handley LLP
Chauza, Esq. Roger N.
Prenty Mark V.
Teccor Electronics, LP
LandOfFree
Non-gated thyristor device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Non-gated thyristor device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Non-gated thyristor device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3357628