Page 59 - Rashid, Power Electronics Handbook

J. Hudgins et al.
4444 J. Hudgins et al.
cathode 3.6.4 Optically Triggered Thyristors
Optically gated thyristors have traditionally been used in
power utility applications where series stacks of devices are
n + necessary to achieve the high voltages required. Isolation
between gate drive circuits for circuits such as static VAR
compensators and high-voltage dc to ac inverters have driven
b uried gate (p ) +
the development of this class of devices. One of the most
recent devices can block 6 kV forward and reverse, conduct
n - 2.5 kA average current, and maintains a di=dt capability of 300
A=ms, and a dn=dt capability of 3000 V=ms, with a required
trigger power of 10 mW. An integrated light-triggered and
light-quenched static induction thyristor has been produced
that can block 1.2 kV and conduct up to 20 A (at a forward
drop of 2.5 V). This device is an integration of a normally off,
buried-gate static induction photothyristor and a normally off,
p-channel Darlington surface-gate static induction photo-
n + transistor. The optical trigger and quenching power required
is <5 and 0.2 mW, respectively.
p +

3.6.5 Bidirectional Control Thyristor

The Bidirectional control thyristor (BCT) is an integrated
anode
assembly of two antiparallel thyristors on one Si wafer. The
FIGURE 3.21 Cross section of a static induction thyristor (SITh) or intended application for this switch is in VAR compensators,
®eld-controlled thyristor (FCT). static switches, soft starters, and motor drives. These devices
are rated at up to 6.5 kV blocking. Cross talk between the two
halves has been minimized. A cross section of the BCT is
structure have been demonstrated that can block 2 kV and shown in Fig. 3.22. Note that each surface has a cathode and
conduct 200 A, with claims of up to 3.5-kV blocking and an anode (opposite devices). The small gate-cathode periphery
200-A conduction. Buried gate devices that block 2.5 kV necessarily restricts the BCT to low-frequency applications
and conduct 300 A have also been fabricated. because of its di=dt limit.

Thyristor half Separation Thyristor half
B region A

Gate A
Anode B

Cathode A

Shallow p-b ase
Deep p-b ase
V (t) n-b ase V (t)
A
B

Deep p-b ase
Shallow p-b ase

Cathode B Anode A
Gate B
(not visib le)
FIGURE 3.22 Cross section of a bidirectional control thyristor (BCT).