108 of 282 M-SV-001-EN Rev. G
For Closed-Top Soft Starts, the Mains AC voltage is passed through fast-acting fuses to two (2) onboard
transformers that reduce the primary voltage to a secondary 15VAC. One transformer powers the Soft
Start itself. The second powers the DC-DC converter after DC bus voltage levels reach the minimum
level. Both transformers pass the secondary voltage through separate Nano fuses.
In addition to monitoring the HV DC bus, the Closed-Top Soft Start carries the fuse that both protects
the high-power-side electronics from the service side and passes HV DC to the DC-DC Converter.
For Open-Top Soft Starts, the Mains AC voltage is passed through positive temperature coefficient
(PTC) resettable fuses to a passive diode rectifier which feeds power to an onboard isolated DC-DC
converter during the initial startup stage. After DC bus voltage is built up, it starts powering the DC-DC
converter. Both PTCs in the AC input path and blocking diodes in DC input path protect the high-
power-side electronics from the low-power control side.
In addition to monitoring AC mains voltage and the HV DC bus, the Open-Top Soft Start also provides
an onboard temperature sensor, varistors, and EMI filters for system protection.
All DC voltages from the Soft Start are with respect to the positive DC bus, not the compressor
ground. Refer to "Figure 4-98 Closed-Top Soft Start Connections" and "Table 4-23 Closed-Top Soft Start
Connection Identification" for the Soft Start connector locations and identifications.
4.15.1 Soft Start Connections
Figure 4-98 Closed-Top Soft Start Connections
Table 4-23 Closed-Top Soft Start Connection Identification
No. Component
1 J9: Soft Start Temperature Sensor connector
2 J5: Thermostatic Fan Control connector
3 J7: DC-DC Trigger Signal connector
4 J1: High Voltage AC/DC connector
5 J8: SCR Gate Signal connector
4
3
1
2
5
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