Transistor module and its associated semiconductor module

Abstract

A transistor module including a first transistor and a second transistor for start up control is provided. Wherein the first end of the first transistor is coupled to the first end of the second transistor, the second end of the first transistor is coupled to the control end of the second transistor, and the second end of the second transistor provides a start up current for a control circuit.

I/We claim: 
     
         1 . A transistor module comprising:
 a start up circuit for providing a start up current for a control circuit; and   a power transistor controlled by the control circuit;   wherein the transistor module having:
 a first terminal coupled to a first end of the power transistor; 
 a second terminal coupled to a second end of the power transistor; 
 a third terminal coupled to a control end of the power transistor; and 
 a fourth terminal coupled externally to a first terminal of the control circuit;
 and wherein: 
 at start up stage, an input current having a first current value flows into the first terminal, and a current having the first current value flows out of the fourth terminal to the first terminal of the control circuit for providing a start up current for the control circuit; and 
 at operation stage, no current flows through the fourth terminal. 
 
   
     
     
         2 . The transistor module of  claim 1 , wherein when the voltage difference between the fourth terminal and the second terminal is lower than a first threshold, the resistance between the first terminal and the fourth terminal is lower than a third value, and when the voltage difference between the fourth terminal and the second terminal is higher than a second threshold, the resistance between the first terminal and the fourth terminal is higher than a fourth value, wherein the first threshold is lower than the second threshold, and the third value is lower than the fourth value. 
     
     
         3 . The transistor module of  claim 1 , wherein:
 at start up stage, the voltage at the third terminal of the transistor module is lower than a third threshold; and   at operation stage, the voltage at the third terminal of the transistor module is higher than a fourth threshold for at least part of time, wherein the fourth threshold is higher than the third threshold.   
     
     
         4 . The transistor module of  claim 1 , having and only having four terminals of a drain terminal, a source terminal, a control terminal and a start up terminal for providing a start up current respectively. 
     
     
         5 . The transistor module of  claim 1 , further having a sensing terminal, wherein the sensing terminal is coupled to a third terminal of the control circuit, and at operation stage, the voltage at the sensing terminal is proportional to the current flowing out of the second terminal, and the transistor module has and only has five terminals of a drain terminal, a source terminal, a control terminal, a start up terminal and the sensing terminal respectively. 
     
     
         6 . A semiconductor module, comprising:
 a start up circuit configured to provide a start up current for a control circuit, the start up circuit comprising a depletion mode transistor; and   a power transistor comprising an enhancement mode transistor controlled by the control circuit, wherein the gate of the depletion mode transistor is coupled to the source of the enhancement mode transistor and the source of the depletion mode transistor is configured to provide the start up current.   
     
     
         7 . The semiconductor module of  claim 6 , having two terminals coupled to a first terminal and a second terminal of the control circuit respectively, wherein the first terminal of the control circuit receives the start up current and the second terminal of the control circuit is configured to control the power transistor. 
     
     
         8 . The semiconductor module of  claim 6 , is used in a power converter. 
     
     
         9 . The semiconductor module of  claim 8 , wherein the power converter further comprises:
 the control circuit coupled to the semiconductor module;   a primary side winding coupled to the semiconductor module;   a secondary side winding coupled to a secondary side rectifier configured to provide an output voltage of the power converter;   an auxiliary winding; and   a capacitor coupled between the auxiliary winding and a third terminal of the control circuit, wherein at start up stage, the semiconductor module is configured to provide the start up current and charge the capacitor; and at operation stage, the capacitor is charged by the auxiliary winding.