Terminal voltage control circuit for light emitting diode (LED) string and led illumination device

A terminal voltage control circuit for a light emitting diode (LED) string electrically coupled between a high voltage terminal and a low voltage terminal. The terminal voltage control circuit includes a capacitor, an inductor, a diode, a switch and a detection circuit. A first terminal and a second terminal of the capacitor respectively are electrically coupled to the low voltage terminal and a preset voltage. A first terminal of the inductor is electrically coupled to the low voltage terminal. A positive terminal and a negative terminal of the diode are respectively electrically coupled to a second terminal of the inductor and the high voltage terminal. A first terminal and a second terminal of the switch are respectively electrically coupled to the second terminal of the inductor and the preset voltage. The detection circuit detects a voltage on the low voltage terminal, and when the detected voltage on the low voltage terminal is higher than a reference voltage the detection circuit controls the switch to