Patent Publication Number: US-2015069984-A1

Title: Buck converter with overshoot protection

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to power supplies and, particularly, to a buck converter with overshoot protection. 
     2. Description of Related Art 
     Buck converters are used in motherboards. The buck converter mainly includes a main switch, a secondary switch, and an inductance. A high frequency switching mode is applied between the main switch and the secondary switch to make the inductance store or discharge energy to supply a load. 
     The inductance can be saturated and then the inductance equates to a short circuit. A large current can pass through all of the inductance, the main switch, and the secondary switch. Thus, the larger current can damage the inductance and destroy the buck converter. 
     Therefore, it is desirable to provide a buck converter with overshoot protection, which can overcome the limitation described. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The components of the drawing are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments of the present disclosure. 
       The FIGURE is a schematic view of a buck converter with overshoot protection, according to an exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The figure shows an exemplary embodiment of a buck converter  10 . The buck converter  10  is configured with a function of overshoot protection. The buck converter  10  is configured for converting an input voltage  20  into a suitable voltage to apply to a load  30 . 
     The buck converter  10  includes a pulse width modulation unit  11 , a first switch  12 , a second switch  13 , an inverter  14 , an inductance  15 , a capacitor  16 , and a sensor  17 . The inductance  15  and the capacitor  16  operate as a low-pass filter  18 . The sensor  17  is located near the inductance  15  for sensing the status of the inductance  15 . 
     The pulse width modulation unit  11  is connected to the first switch  12 . The second switch  13  is connected to the pulse width modulation unit  11  through the inverter  14 . The pulse width modulation unit  11  controls the first switch  12  and the second switch  13  to allow conduction and to cut off conduction. The input voltage  20  is applied to the load  30  through the low-pass filter  18 . 
     The first switch  12  can be a metal oxide semiconductor field effect transistor (MOSFET) or a bipolar junction transistor (BJT). The second switch  13  can also be a MOSFET or a BJT. In this embodiment, the first switch  12  is a MOSFET and the second switch  13  is a MOSFET. 
     The first switch  12  includes a first gate  121 , a first drain  122 , and a first source  123 . The second switch  13  also includes a second gate  131 , a second drain  132 , and a second source  133 . 
     The first gate  121  of the first switch  12  is directly connected to the pulse width modulation unit  11 . The first drain  122  is connected to the input voltage  20 . The first source  123  is connected to the inductance  15 . The second gate  131  of the second switch  13  is connected to the pulse width modulation unit  11  through the inverter  14 . The second drain  132  is connected to the inductance  15  and the first source  123 . The second source  133  is grounded. 
     In other embodiment, the first gate  121  of the first switch  12  is connected with the pulse width modulation unit  11  through the inverter  14 , but the second gate  131  of the second switch  13  is directly connected to the pulse width modulation unit  11 . 
     A high level signal is applied to the first drain  122  and the first source  123 , so the first switch  12  conducts and the second switch  13  cuts off conduction. The first switch  12  and the inductance  15  form a loop, the inductance  15  stores energy applied from the input voltage  20 . Current through the inductance  15  decreases, and the input voltage  20  is applied to the load  30 . 
     A low level signal is applied to the first gate  121  of the first switch  12  and the first source  123 , so the first switch  12  cuts off conduction. According to Lenz&#39;s law, a counter or back electromotive force is generated in the inductance  15  as the first switch  12  cuts off conduction, thus the second switch  13  is powered on. Under this condition, the inductance  15  discharges energy to the load  30 . 
     The inductance  15  is a magnetic element. If the inductance  15  stores excessive energy, the inductance  15  can be damaged. The worst condition is that the buck converter  10  is also damaged. 
     When the inductance  15  is saturated with current, one or more of a sound, a vibration, and a decrease in current can happen. The sensor  17  near the inductance  15  can sense any one or more of these happenings. When the sensor  17  senses such a happening, the sensor  17  sends a signal to the pulse width modulation unit  11 . The plus width modulation unit  11  controls the first switch  12  to cut off conduction and the second switch  13  to power on. The inductance  15  thus discharges all the contained energy and protection for the inductance  15  is thus achieved. 
     The sensor  17  is selected from the group consisting of an acoustic sensor and a vibration sensor. 
     It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the disclosure or sacrificing all of its material advantages, the examples hereinbefore described merely exemplary embodiments of the disclosure.