Motores

Main Applications and Selection
of Gate Driver Optocouplers
Application Note 1335
Introduction
IGBTs are now commonly used as switching components
in both inverter and converter circuits, which are used in
power control and motor drive applications. A typical
power control and motor drive system shown in Figure
1 requires isolation between the high voltage devices
(IGBT/MOSFET) and thelow voltage devices (microcontroller). In addition to meeting the severe
requirements for the isolation function, Avago
Technologies optocouplers provide customized
functionality such as direct gate drive for IGBTs or
power MOSFETs. This application note focuses on the
use of Avago Technologies Gate Drive Optocouplers.

Advantages of Using Optocouplers as Gate Drivers for
IGBT/MOSFET
•Low system solution cost
• High reliability and long life
• Variable speed / frequency capability
• Ease and simplicity of design
• Small size and footprint area
• Low power dissipation
• Safe optical isolation (galvanic isolation)
• Regulatory and safety agency approvals

+HV
GATE
DRIVE

GATE
DRIVE

U+

V+

GATE
DRIVE

CURRENT
SENSE

W+
A

3-PHASE
OUTPUT
VOLTAGESENSE

GATE
DRIVE

GATE
DRIVE

U-

C

V-

GATE
DRIVE
WB
CURRENT
SENSE

-HV
U+, U-, V+, V-,
W+, W-

A, B, C
ANALOG
ISOLATION

MICROCONTROLLER

Figure 1. Isolation Circuits for Power Control – System Overview

MOTOR SPEED POSITION

Block Diagrams of Main Applications of Gate Drive Optocouplers

GATE
DRIVER

GATE
DRIVER

GATE
DRIVER

M

GATE
DRIVERGATE
DRIVER

GATE
DRIVER

Figure 2. VVVF Inverter (PWM)

GATE
DRIVER

GATE
DRIVER

GATE
DRIVER

GATE
DRIVER

M

GATE
DRIVER

GATE
DRIVER

GATE
DRIVER

GATE
DRIVER

GATE
DRIVER

GATE
DRIVER

GATE
DRIVER

GATE
DRIVER

GATE
DRIVER

Figure 3. VVVF Inverter (PAM)

Figure 4. CVCF Inverter (UPS)

2

GATE
DRIVER

GATE
DRIVER

GATE
DRIVERGATE
DRIVER

Figure 5. Low Power CVCF Inverter (UPS)

GATE
DRIVER

GATE
DRIVER

M

GATE
DRIVER

GATE
DRIVER

GATE
DRIVER

Figure 6. DC Servo

M
M

GATE
DRIVER

Figure 7. Switched Reluctance Drive

3

LOAD
IRON POT

M

DC

+
–
GATE
DRIVER

GATE
DRIVER

Figure 8. DC Chopper

Figure 9. Induction Cooker

GATE
DRIVER
LOAD
IRON POT

GATE
DRIVERFigure 10. Series Resonant Induction Cooker

GATE
DRIVER

GATE
DRIVER

Figure 11. Welder

4

GATE
DRIVER

GATE
DRIVER

Calculation of Minimum Output
Current (IOL) to Drive IGBT / MOSFET
The key requirement for any
IGBT/MOSFET gate drive
optocoupler is for it to supply the
Minimum Output Current (IOL)
needed to switch the IGBT/
MOSFET to the low-impedance
state. Acommon
misunderstanding in selecting a
gate drive optocoupler is looking
at the Maximum Peak Output
Currents [ IOH(PEAK) / IOL(PEAK) ]
in the Absolute Maximum Rating
Section of the data sheet. Though
Maximum Peak Output Currents
are no less important, they are
meant to define the maximum
permissible operational condition
that could result in the
destruction of the device if
exceeded.To determine the suitability of a
gate drive optocoupler, it is
necessary to look at the Minimum
Output Currents (IOH / IOL) of the
gate drive optocoupler in the
Electrical Specifications Section
of the data sheet. Particularly
important, the IOL needs to be
specified at the condition when
VO is low, that is when the gate
drive optocoupler is at the
charging state. This is becauseunder this condition the load
draws the highest output current.
Avago specifies IOL at
VO = VCC – 10 V. Similarly for IOH,
it is important to specify at the
condition when VO is high, that is
when the gate drive optocoupler
is discharging. Avago specifies
IOH at VO = VEE + 10 V.
This Minimum Output Current
(IOL) required to switch IGBT /
MOSFET to the low-impedance
state could be easily...