The present invention discloses a circuit capable of protecting low-voltage devices. The circuit includes: a pin configured to receive a signal of an external device; a control voltage generating circuit configured to generate a first control voltage according to a supply voltage to turn on a protected device when the supply voltage is at a high level, and generate a second control voltage according to a voltage of the pin to turn on the protected device when the supply voltage is at a low level; and the protected device configured to be turned on according to one of the first and the second control voltages and thereby electrically couple the pin with an internal circuit, in which the difference between the voltage of the pin and each of the first and the second control voltages is within a maximum withstanding voltage of the protected device.