Method and apparatus for simplifying the control of a switch

• US 20060238224A1
• Filed: 06/23/2006
• Published: 10/26/2006
• Est. Priority Date: 09/30/2003
• Status: Active Grant

• Current Assignee: Balu Balakrishnan
• Original Assignee: Balu Balakrishnan
• Inventors: Balakrishnan, Balu
• Granted Patent: US 7,466,170 B2
• Time in Patent Office: Days
• US Class Current: 327/108
• CPC Class Codes: H02M 3/33571 Half-bridge at primary side of an isolation transformer
• CPC Class Codes: H02M 3/33592 having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
• CPC Class Codes: H03K 17/0822 in field-effect transistor switches
• CPC Class Codes: H03K 17/6871 the output circuit comprising more than one controlled field-effect transistor
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A technique for simplifying the control of a switch is presented. In one embodiment, a method of controlling a switch as a function of the voltage across the switch is presented. In one embodiment a method of controlling a switch as a function of the slope of the voltage across the switch is present. In one embodiment a switching is switched on for an on time period that is substantially fixed in response to a voltage across the switch while the switch is off. In one embodiment a switch is switched on for an on time period that is substantially fixed in response to the slope of the voltage across the switch while the switch is off.

Claims

1. A circuit, comprising:

switching means coupled to a load for applying a voltage of a first polarity across the load during a first on time period and applying a voltage of the opposite polarity during a second on time period; and

sensing means coupled to the load for sensing the voltage across the load for a first sense period during the first on period and for a second sense period during the second on period, wherein the switching means is controlled to maintain a magnitude of the voltage across the load during the first on period substantially equal to the voltage across the load during the second on period.

2. The circuit of claim 1 wherein the sensing means is adapted to generate a sense signal for a duration of the first and second sense periods.

3. The circuit of claim 2 wherein a magnitude of the sense signal is adapted to be adjusted according to a magnitude of the voltage across the load during the first and second sense periods.

4. The circuit of claim 3 wherein the sensing means comprises a capacitor and current charging means coupled to the capacitor for charging and discharging the capacitor.

5. The circuit of claim 4 wherein the current charging means is adapted to adjust a current for charging and discharging the capacitor in response to the magnitude of the voltage across the load during the first and second sense periods.