BUCK CONVERTER AND CONTROL METHOD THEREFOR

• US 20150188425A1
• Filed: 04/17/2014
• Published: 07/02/2015
• Est. Priority Date: 12/27/2013
• Status: Active Grant

• Current Assignee: Anpec Electronics Corporation
• Original Assignee: Anpec Electronics Corporation
• Inventors: CHANG, HSIANG-CHUNG, LIU, DONG-YI, CHEN, YU-YU
• Granted Patent: US 9,350,241 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• CPC Class Codes: H02M 3/158 including plural semiconductor devices as final control devices for a single load
• CPC Class Codes: H02M 3/1588 comprising at least one synchronous rectifier element H02M3/1582, H02M3/1584 take precedence
• CPC Class Codes: H03K 17/063 in field-effect transistor switches
• 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

The present disclosure provides a pair of NMOSFET switches connected in series, an output filter, a control circuit, a boot-strap capacitor and a disabling circuit. A high-side MOSFET switch is coupled to an input voltage. A low-side MOSFET switch is coupled to a ground. The high-side MOSFET switch and the low-side MOSFET switch have complementary duty cycles. The output filter is coupled to the NMOSFET switches to provide an output voltage. The boot-strap capacitor is coupled to the source of the high-side MOSFET switch. The voltage crossing the boot-trap capacitor is for making the gate voltage of the high-side MOSFET switch to be higher than the input voltage. The disabling circuit senses the voltage crossing the boot-strap capacitor, and generates a control signal to control the control circuit for continuously turning off the high-side MOSFET switch when the voltage crossing the boot-strap capacitor is less than a threshold voltage.

Claims

1. A buck converter, stepping-down an input voltage to an output voltage, comprising:

a high-side N-type MOSFET switch, the drain electrode of the high-side N-type MOSFET switch coupled to the input voltage;

a low-side N-type MOSFET switch, the drain electrode of the low-side N-type MOSFET switch coupled to the source electrode of the high-side N-type MOSFET switch, the source electrode of the low-side N-type MOSFET switch coupled to a ground, wherein the high-side N-type MOSFET switch and the low-side N-type MOSFET switch have complementary duty cycles;

an output filter, coupled to the source electrode of the high-side N-type MOSFET switch and the drain electrode of the low-side N-type MOSFET switch, providing the output voltage;

a control circuit, controlling the high-side N-type MOSFET switch and the low-side N-type MOSFET switch;

a boot-strap capacitor, a first terminal of the boot-strap capacitor coupled to a regulating voltage, a second terminal of the boot-strap capacitor coupled to the source electrode of the high-side N-type MOSFET switch, the boot-strap capacitor being charged by the regulating voltage, the voltage of the first terminal of the boot-strap capacitor being provided to the control circuit for generating a gate driving signal controlling the high-side N-type MOSFET switch, wherein the voltage of the gate driving signal is larger than the input voltage; and

a disabling circuit, coupling to the boot-strap capacitor and the control circuit, the disabling circuit sensing the voltage across the boot-strap capacitor, and generating a control signal to control the control circuit for continuously turning off the high-side N-type MOSFET switch when the voltage crossing the boot-strap capacitor is less than a threshold voltage.

2. The buck converter according to claim 1, wherein the disabling circuit comprises:

a determining unit, coupled to the boot-strap capacitor, determining whether the voltage across the boot-strap capacitor is less than the threshold voltage and generating the control signal accordingly; and

a discharge unit, coupled to the boot-strap capacitor and the determining unit, wherein the discharge unit discharges the boot-strap capacitor to make the voltage across the boot-strap capacitor be zero according to the control signal when the voltage across the boot-strap capacitor is less than the threshold voltage.

3. The buck converter according to claim 2, wherein the determining unit comprises:

a comparator, comparing the voltage across the boot-strap capacitor with the threshold voltage for generating the control signal.

4. The buck converter according to claim 2, wherein the discharge unit comprises:

a discharge switch, coupled to a first terminal and a second terminal of the boot-strap capacitor; and

a discharge control circuit, coupled to a control terminal of the discharge switch, controlling the discharge switch to discharge the boot-strap capacitor according to the control signal.

5. The buck converter according to claim 1, wherein the disabling circuit comprises:

a determining unit, coupled to the boot-strap capacitor, determining whether the voltage across the boot-strap capacitor is less than the threshold voltage and generating the control signal accordingly; and

a logic control unit, coupled to the determining unit, wherein the logic control unit controls the control circuit to disable the high-side N-type MOSFET switch when the voltage across the boot-strap capacitor is less than the threshold voltage.

6. The buck converter according to claim 5, wherein the determining comprises:

a comparator, comparing the voltage across the boot-strap capacitor with the threshold voltage for generating the control signal.

7. The buck converter according to claim 1, wherein the control circuit comprises:

a feedback circuit, receiving the output voltage, generating a feedback voltage according to the output voltage;

a feedback comparator, coupled to the feedback circuit, comparing the feedback voltage and a reference voltage for generating a comparing signal; and

a gate driving circuit, coupled to the feedback comparator, the gate electrode of the high-side N-type MOSFET switch and the gate electrode of the low-side N-type MOSFET switch, controlling the high-side N-type MOSFET switch and the low-side N-type MOSFET switch according to the comparing signal.

8. The buck converter according to claim 1, wherein the output filter comprises:

an inductor, a first terminal of the inductor coupled to the source electrode of the high-side N-type MOSFET switch and the drain electrode of the low-side N-type MOSFET switch, a second terminal of the inductor providing the output voltage; and

a capacitor, a first terminal of the capacitor coupled to the second terminal of the inductor, a second terminal of the capacitor coupled to the ground.

9. A control method for a buck converter, for controlling a high-side N-type MOSFET switch of the buck converter, the buck converter comprising the high-side N-type MOSFET switch coupling to an input voltage and a low-side N-type MOSFET switch coupling to a ground, the control method comprising:

coupling a boot-strap capacitor between a regulating voltage and the source electrode of the high-side N-type MOSFET switch, wherein the source electrode of the high-side N-type MOSFET switch is coupled to the drain electrode of the low-side N-type MOSFET switch;

turning-on the low-side N-type MOSFET switch, so as to make the regulating voltage charge the boot-strap capacitor through a path comprising the low-side N-type MOSFET switch;

utilizing a gate driving signal to drive the high-side N-type MOSFET switch, wherein the voltage level of the gate driving signal is corresponding to the voltage across the boot-strap capacitor;

sensing the voltage across the boot-strap capacitor; and

turning-off the high-side N-type MOSFET switch continuously when the voltage across the boot-strap capacitor is less than a threshold voltage.

10. The control method according to claim 9, wherein the step of turning-off the high-side N-type MOSFET switch continuously when the voltage across the boot-strap capacitor is less than a threshold voltage further comprises discharging the boot-strap capacitor for making the voltage across the boot-strap capacitor be zero.

11. The control method according to claim 9, wherein the step of turning-off the high-side N-type MOSFET switch continuously when the voltage across the boot-strap capacitor is less than a threshold voltage further comprises disabling the high-side N-type MOSFET switch.