Specifications

28
Dec. 20
Mitsubishi IPM-series Application Note
(5) Notice of using photo coupler
The photo coupler can isolate the primary side and secondary side. But, this is not correct at the high
frequency. Because, photo coupler have a parasitic capacity between primary side and secondary side. When
high dv/dt is impressed, the pulse electric current flows from the primary side to the secondary side via the
parasitic capacity of photo coupler. This current sometimes turn on the photo coupler.
Therefore, it is important to design a circuit so that the LED will not turn on erroneously by this dv/dt.
When the input signal is OFF, make sure the circuit that the LED of primary side of photo coupler is with
low-impedance.
IPM
OFF
dv/dt current
Parasitic capacity
The LED is ON and
outputs extraordinary ON signal.
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Fig.9.5 The example of the circuit which isn't good
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IPM
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Fig.9.6. The example of the circuit to recommend
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The recommended circuit doesn't make malfunction (LED of primary side of photo coupler is ON) because the
dv/dt current can not turn ON the LED of primary side of photo coupler.
Please consult the application-note of the photo coupler for the detailed instruction of the circuit around the
photo coupler.
Using IPM