RD014-RGUIDE-01
2018-03-15
Rev. 1
4
/
19
© 2018
Toshiba Electronic Devices & Storage Corporation
Example of an application to an inverter
* Toshiba offers the TLP5214A photocoupler suitable for use as an IGBT gate driver.
For details of the TLP5214A →
2. Major features of the TLP7820
Common-mode transient immunity (CMTI)
Common-mode noise is a type of electrical noise that overlaps on both signal and GND lines in
the same direction. A photocoupler is used to optically transmit a signal between two isolated
circuits with independent power supplies, however even in this case, a common-mode noise is
generated by changes in the voltage of either one of the power supplies (for example, input a
noise from outside).
A common-mode noise generates a displacement current to flow through
the internal coupling capacitance between the primary (input) and secondary (output) sides of
a photocoupler and if a displacement current excees a given level into coupling capacitor, the
photocoupler has malfunction, then resulting in faulty system operation.
A displacement current generated by transient common-mode noise could cause bit errors in
an isolation amplifier, in the worst-case, it leads to a short-circuit failure of an IGBT. There fore
it is important for stable system operations to tolerate common-mode noise.
CMTI indicates the
ability of an isolation amplifier to tolerate high-slew-rate transient voltage induced across GND
lines. An isolation amplifier with a high CMTI provides high immunity to common-mode noise
and is suit applications requiring electrical isolation.
