Explanation Of Ipm Drive Circuit - IVT GS-XP12HR-N Service Manual

GSXP12HRN
4.3. PAM protection circuit
To prevent excessive voltage of PAM output from
damaging the IPM and electrolytic capacitor as well
as the control printed circuit board (PCB), this circuit
monitors the PAM output voltage and turns off the
PAM control signal and PAM drive immediately
when an abnormal voltage output is generated. At
the same time, it shuts off the compressor operation.
The PAM output voltage is distributed to pin (4) of
the comparator (IC8). If this voltage exceeds the ref-
erence voltage at pin (5) of the IC8, the output of the
comparator (IC8) reverses (from H to L) and it is
input to pin (38) of the microcomputer (IC1) to halt
the PAM drive.
The protection voltage level is as follows.
4.3.1 Details of troubleshooting procedure for PAM
1) PAM shutdown due to error
1) When the DC voltage detection circuit sends a signal exceeding the specified voltage to the microcomputer
DC voltage of 350 V or higher (detection circuit input voltage of about 9.2 V or higher) [IC8 pin (4)]
– When an error is detected
• PAM IGBT turns OFF.
• Compressor turns OFF.
• All units shut down completely when the error occurs four times.
2) When the outdoor unit clock waveform differs from the specified value immediately before the PAM IGBT turns ON
When there is no clock waveform input
When a clock signal of other than specified power source frequency (50/60 Hz) is input
– When an error is detected
• PAM IGBT does not turn ON.
• Compressor operates normally.
• Complete shutdown does not occur.
2) PAM error indication
In case of error "1)"
– An error signal is sent to the indoor unit as soon as an error is generated.
• Malfunction No. 14-0 is indicated when the error code is called out by the indoor unit's self-diagnosis function.
– The LED on the outdoor unit flashes 14 times when an error is generated.
• The LED continues flashing in the 14-time cycle even after the compressor stops operating.
• The LED turns off (data is deleted from the memory) when the outdoor unit power is turned off.
In case of error "2)"
– An error signal is sent to the indoor unit as soon as an error is judged.
• Malfunction No. 14-1 is indicated when the error code is called out by the indoor unit's self-diagnosis function.
– The LED on the outdoor unit flashes 14 times when an error is judged.
• The LED on the outdoor unit flashes in normal pattern when the compressor stops operating.
(Compressor OFF or Thermostat OFF from remote control)
* When a user complains that the air conditioner does not provide sufficient cool air or warm air
In addition to conventional error-generating reasons, there is a possibility that the PAM IGBT does not turn ON even if the compressor is operating.
In that case, the DC voltage does not rise even though the compressor is operating, and lowers to the 180-VDC level.
– Check items
• Clock circuit check
• PAM IGBT check
• Fuse (Fu6) open-circuit check

5. Explanation of IPM drive circuit

The IPM for compressor drive is made by Mitsubishi Electric.
The power supply for the IPM drive, the shunt resistance for overcurrent detection, etc., are provided outside the IPM (control PCB).
R2
255K
420V
C9 C10
750uF
R5
300K
R7 R8
23.7K 23.7K
0V
2 – 12
(Overvoltage detection)
15V
R112 R114
15K 1M
5
2
4
IC8
R113
19.1KF
0V
0V
During abnormal voltage output
5V
R115
1.8K
R116
IC1
1K
38