1.6.9. Chopper Overcurrent Protection
Chopper overcurrent protection reduces the risk of damage to the power conversion stages during large load transients or device failures by continuously monitoring the chopper stage current. The protection scheme is based on an expected chopper current rating that defines normal operation.
The rated chopper current (I2) is defined as the chopper current when the product is operating at nominal line voltage and delivering rated output power. The chopper overcurrent trip threshold (I1) is set to 150% of I2. For additional context on the current-fed input architecture, see Principle of Operation. The value of I2 is measured and set at the factory and varies based on line input configuration and the internal main power transformer.
The timing parameters are defined as follows:
t0 - Time at which the measured chopper current first exceeds I1
t1 - Excessive current safety window (1 ms)
t2 - Hard fault window (2 s)
As shown in Fig. 1.11, brief current excursions above I1 that occur within the excessive current safety window (t0 to t1) do not result in current foldback. In this case, the product continues to regulate normally.
As shown in Fig. 1.12, current excursions above I1 that exceed the current safety window (t0 to t1) result in a chopper foldback. In this scenario, the output voltage Vo and output current Io fold back and fall off to zero. The product will automatically restart its chopper, allowing the output voltage and current to recover to their previous operating levels before reaching t2.
If the chopper current exceeds I1 three times between t0 and t2, the product enters a chopper overcurrent hard fault and disables the output. Once this fault occurs, the product must be power-cycled before normal operation can resume, as illustrated in Fig. 1.13. In this condition, the system should be inspected for issues such as an abnormal load or a power supply problem. The hard fault is indicated on the Operating Status Display display as a Statuses hard fault with a corresponding Status Messages entry.
The MagnaDC power supply continuously monitors the chopper stage current to protect the power conversion hardware. If the measured current exceeds the chopper overcurrent threshold and violates the defined timing criteria, the product enters a hard fault state and disables the output.
When a chopper overcurrent hard fault occurs:
Verify that the load does not exceed the product rated specifications.
Inspect cabling and connections for shorts, intermittent faults, or improper wiring.
After correcting the root cause, power-cycle the product to clear the fault.
Refer to Status Messages for the associated hard fault status message.
