Switch mode converter that allows 100% duty cycle on gate driver

• US 6,812,782 B2
• Filed: 10/25/2002
• Issued: 11/02/2004
• Est. Priority Date: 10/25/2002
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Grant, David A.
• Primary Examiner(s): Riley, Shawn
• Application Number:
  US10/280,743
• Publication Number:
  US 20040080963A1
• Time in Patent Office: 739 Days
• Field of Search: 323/283, 323/282, 323/288, 327/589
• US Class Current: 327/589
• CPC Class Codes: H02M 1/08 Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
• CPC Class Codes: H02M 3/1588 comprising at least one synchronous rectifier element H02M3/1582, H02M3/1584 take precedence
• 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 switch mode converter uses the bootstrap capacitor 30 to operate all the way to 100% duty cycle by adding only a very small amount of low-area extra circuitry. The additional circuitry includes a charge pump 40 and a duty cycle detect device 42. When the duty cycle detect device 42 detects that the converter is attempting to operate in 100% duty cycle, the charge pump 40 provides additional charge to the bootstrap capacitor 30 to ensure that the 100% duty cycle is maintained.

Claims

1. A switch mode converter circuit comprising:

a high side transistor;

a low side transistor coupled to the high side transistor;

an inductor having a first end coupled to a node between the high side transistor and the low side transistor and a second end coupled to an output node;

a boot capacitor having a first end coupled to the first end of the inductor;

a high side driver coupled to a control node of the high side transistor;

a first diode coupled between a second end of the boot capacitor and an input voltage node;

a charge pump for providing additional charge to the boot capacitor when a duty cycle of the switch mode converter circuit is one hundred percent;

wherein the charge pump is coupled to the control node of the high side transistor;

wherein a first switch is coupled between the charge pump and the control node of the high side transistor; and

wherein a second switch is coupled between the high side driver and the control node of the high side transistor.

2. The circuit of claim 1 further comprising a duty cycle detect device for controlling the first switch and the second switch.

3. A switch mode converter circuit comprising:

a high side transistor;

a low side transistor coupled to the high side transistor;

an inductor having a first end coupled to a node between the high side transistor and the low side transistor and a second end coupled to an output node;

a boot capacitor having a first end coupled to the first end of the inductor;

a high side driver coupled to a control node of the high side transistor;

a first diode coupled between a second end of the boot capacitor and an input voltage node;

a charge pump for providing additional charge to the boot capacitor when a duty cycle of the switch mode converter circuit is one hundred percent;

wherein the charge pump is coupled to the second end of the boot capacitor; and

a second diode coupled between the charge pump and the second end of the boot capacitor.

4. The circuit of claim 3 wherein the second end of the boot capacitor is coupled to a first supply voltage node of the high side driver.

5. The circuit of claim 4 wherein a second supply voltage node of the high side driver is coupled to the node between the high side transistor and the low side transistor.

6. The circuit of claim 3 further comprising a duty cycle detect device for determining when the duty cycle in one hundred percent.