PGH Datasheet, PDF (5/10 Pages) Nihon Inter Electronics Corporation – 3-phase diode bridge plus thyristor

during all of the on-period. At present, major
switching devices, such as MOSFET and IGBT,
I_T
are driven by voltage, but thyristor is current-
driven device. Please keep in mind this fact when
e
you design gate firing circuit for thyristor.
Gate trigger current
e
Gate
current
Gate current turns on Thyristor
2, Behaviors of Thyristor as a switch — Holding
current, and Latching current
2-1, Holding current
Once thyristor turns on, the on-state is main-
tained as far as anode current is larger than a cer-
tain value. In other words, thyristor turns off
when anode current decreases to a certain value.
The “certain current” is the holding current, and
that of PGH308 (30A 800V) is 70mA typical at
25℃. (Refer to individual datasheet.) Now, let's
see the influence of holding current in an actual
circuit.
Anode current decreases.
Holding current
Thyristor
turns off.
Time
ON
OFF
Holding current
Supposing that pulse trigger current is applied
only once. Thyristor is turned on, however, if the
load is resistive and anode-cathode voltage goes to
zero, anode current altogether decreases to below
holding current. After that, positive voltage
would be applied to anode, however, thyristor
maintains off-state so far as gate current would be
applied again.
2-2. Latching current
Assume that, due to slow rise of anode current,
the current doesn’t reach a certain level before
gate current is terminated, thyristor turns off. It
follows that, after removal of gate current, the
I_T
Thyristor turns off when anode current be-
comes below holding current.
minimum anode current which can maintain on-
state is the latching current. For example, typical
latching current of PGH308 (30A 800V) is 90mA
（25℃).
Pulse gate current
Latching current
Time
Anode current
Thyristor turns off
because of slow rise
of anode current.
time
Latching current
If thyristor cannot be turned on or on-state may
not be able to maintain, increase gate pulse width
or try multiple gate pulses. Both holding current
and latching current are temperature-dependent,
and they become larger at low temperature.
Compared with at 25℃, they are about twice lar-
ger at –40℃.
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