A voltage converting circuit has an output terminal for supplying an output current at an output voltage to a load. In response to a transient of the load, a current sinking circuit allows a current source to provide a sink current flowing from the output terminal of the voltage converting circuit into a ground potential. The sink current is finite and stable. When the output voltage decreases below a threshold voltage, the current sinking circuit allows the current source to keep providing the finite and stable sink current for an extension time, causing the output voltage to decrease from the threshold voltage to a regulated value.