HCPL-3120-500E Datasheet, PDF (18/25 Pages) AVAGO TECHNOLOGIES LIMITED – 2.5 Amp Output Current IGBT Gate Drive Optocoupler

Applications Information
Eliminating Negative IGBT Gate Drive (Discussion applies
to HCPL-3120, HCPL-J312, and HCNW3120)
To keep the IGBT firmly off, the HCPL-3120 has a very
low maximum V_OL specification of 0.5 V. The HCPL-3120
realizes this very low V_OL by using a DMOS transistor
with 1 Ω (typical) on resistance in its pull down circuit.
When the HCPL-3120 is in the low state, the IGBT gate
is shorted to the emitter by Rg + 1 Ω. Minimizing Rg
and the lead inductance from the HCPL-3120 to the
IGBT gate and emitter (possibly by mounting the HCPL-
3120 on a small PC board directly above the IGBT) can
eliminate the need for negative IGBT gate drive in many
applica­tions as shown in Figure 25. Care should be taken
with such a PC board design to avoid routing the IGBT
collector or emitter traces close to the HCPL-3120 input
as this can result in unwanted coupling of transient
signals into the HCPL-3120 and degrade performance. (If
the IGBT drain must be routed near the HCPL-3120 input,
then the LED should be reverse-biased when in the off
state, to prevent the transient signals coupled from the
IGBT drain from turning on the HCPL‑3120.)
+5 V
1
270 Ω
2
CONTROL
INPUT
3
74XXX
OPEN
4
COLLECTOR
HCPL-3120
8
0.1 µF
7
6
+ ^{VCC = 18 V}
–
Rg
Q1
5
Q2
Figure 25. Recommended LED drive and application circuit.
HCPL-3120 fig 25
+ HVDC
3-PHASE
AC
- HVDC
18