Auto-selecting holding current circuit

An auto-selecting holding current circuit applicable to a converter, wherein an input voltage which is input to a primary side of the converter is adjusted by Triode for Alternating Current (TRIAC), the primary side has a bleeder circuit, the TRIAC has a holding-current value, the bleeder circuit makes an input current flowing through the TRIAC greater than or equal to the holding-current value according to a current detector signal and a reference current signal, the current detector signal corresponds to the input current;

• and the auto-selecting holding current circuit comprises:
• a first sensor module (current drop detector), used to detect a current drop time of the current detector signal or a voltage drop time of the input voltage to output a sense signal (Vcd);
• a second sensor module (current range detector), used to receive the current detector signal to output a critical current signal (Vth), wherein the critical current signal is used to judge a current value range of the holding-current value;
• and
• a reference voltage selecting circuit, used to output the reference current signal to the bleeder circuit according to the sense signal and the critical current signal, so that the bleeder circuit maintains the input current greater than or equal to the holding-current value.