Soft-start circuit
The present invention discloses a soft-start circuit having a reference signal generator, a first current generator, a second current generator, and a soft-start capacitor. The reference signal generator generates a first signal and a second signal. The first current generator generates a first current according to the first signal, and the second current generator generates a second current according to the second signal. The soft-start capacitor is coupled to the first current generator and the second current generator, and charged by a current difference of the first current and the second current to generate a soft-start signal.
1. A soft-start circuit, comprising:
a reference signal generator, for generating a first signal and a second signal;
a first current generator, for generating a first current according to the first signal;
a second current generator, for generating a second current according to the second signal; and
a soft-start capacitor, coupled to the first current generator and the second current generator, for performing an electric charging to generate a soft-start signal according to a current difference of the first current and the second current, wherein the first current generator is a P-type bipolar transistor and the second current generator is an N-type bipolar transistor.
2. The soft-start circuit of claim 1 , further comprising a level shifter circuit coupled to the soft-start capacitor for adjusting a level of the soft-start signal.
3. The soft-start circuit of claim 1 , wherein the reference signal generator is a current mirror.
4. The soft-start circuit of claim 1 , wherein an emitter of the P-type bipolar transistor is coupled to the reference signal generator, and an emitter of the N-type bipolar transistor is coupled to the reference signal generator.
5. The soft-start circuit of claim 4 , wherein the N-type bipolar transistor has a β value greater than that of the P-type bipolar transistor.
6. The soft-start circuit of claim 4 , wherein the N-type bipolar transistor has a temperature coefficient of a β value greater than that of the P-type bipolar transistor.
7. The soft-start circuit of claim 4 , wherein the P-type bipolar transistor has a base current greater than that of the N-type bipolar transistor.