IndustrialDriveDataDrive Board & Diagnostic Database
Auxiliary SMPS and logic-supply diagnostic boundary

VFD Control Power Supply Stage

Generic no-display and weak-display record for drives where the keypad, CPU, fan relay, gate-driver supply and feedback circuits depend on auxiliary low-voltage rails derived from the DC bus or an auxiliary input.

Record facts

Visible symptomNo display, flashing display, relay clicking, fan twitching or intermittent boot
Typical rails24 V, 15 V, 5 V or local isolated supplies depending on design
Common boundaryStartup resistor, SMPS controller, electrolytic capacitor, optocoupler feedback or load short
Do not confuseA dead keypad is not always a failed keypad

Service notes

  • Check line and DC-link evidence before treating the keypad as the root cause.
  • A shorted downstream load can pull down an otherwise repairable supply.
  • Old electrolytic capacitors and contaminated boards are common contributors in stored or harsh-environment drives.
  • Use this record as a triage map, not a live probing instruction.

Related technical records

NO DISPLAY
VFD keypad dark or control power missing

The drive has line power present but the keypad stays dark, flashes briefly, clicks repeatedly or never reaches a ready state.

Open →Circuit
VFD input rectifier, precharge and DC-link path

Routes incoming three-phase supply through protection, rectification, precharge and DC-link storage before the inverter stage is allowed to run.

Open →Circuit
VFD auxiliary SMPS and control-power path

Maps the auxiliary supply route that powers the CPU, keypad, I/O, relay logic, fan control and often isolated driver supplies.

Open →Workflow
VFD no-display control-power workflow

Drive line power is present, but the keypad is dark, flashing or repeatedly restarting.

Open →Workflow
VFD precharge and DC-link workflow

Drive reports undervoltage/precharge fault, blows input fuses or shows no-display symptoms with uncertain DC-link charging.

Open →