DC-DC converter, power supply circuit, method for controlling DC-DC converter, and method for controlling power supply circuit

• US 20020126512A1
• Filed: 03/05/2002
• Published: 09/12/2002
• Est. Priority Date: 03/07/2001
• Status: Active Grant

• Current Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Original Assignee: Fujitsu Limited
• Inventors: Nakagawa, Shinichi, Ito, Hidenobu
• Granted Patent: US 6,611,132 B2
• Time in Patent Office: Days
• US Class Current: 363/16
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• CPC Class Codes: H02M 1/0041 Control circuits in which a clock signal is selectively enabled or disabled
• CPC Class Codes: H02M 1/36 Means for starting or stopping converters
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• 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 DC-DC converter for decreasing power consumption and quickly increasing an output voltage. The converter includes a voltage generation circuit, a switching control circuit, a current detection circuit, and a step control circuit. An output transistor performs switching to generate the output voltage of the switching control circuit. The current detection circuit is connected to the voltage generation circuit to detect a load current, which is derived from the output voltage, and to generate a detection signal. A stop control circuit maintains the output transistor in an activated state in accordance with the detection signal and stops the operation of the switching control circuit when the load current is less than or equal to the load current.

Claims

1. A DC-DC converter comprising:

a voltage generation circuit for receiving a power supply voltage and generating an output voltage, wherein the voltage generation circuit includes an output transistor for performing switching to generate the output voltage;

a switching control circuit connected to the voltage generation circuit for controlling the switching of the output transistor;

a current detection circuit connected to the voltage generation circuit for detecting a load current derived from the output voltage of the voltage generation circuit to generate a detection signal; and

a stop control circuit connected to the voltage generation circuit, the switching control circuit, and the current detection circuit for maintaining the output transistor in an activated state and stopping the operation of the switching control circuit in accordance with the detection signal when the load current is less than or equal to a predetermined value.

2. The DC-DC converter according to claim 1, wherein the stop control circuit includes:

a control comparator for comparing the detection signal with a reference voltage to generate a comparison signal;

a gate control circuit connected to the control comparator for maintaining the output transistor in the activated state in accordance with the comparison signal; and

a power supply disconnection circuit connected to the control comparator for disconnecting the switching control circuit from a power supply in accordance with the comparison signal.

3. The DC-DC converter according to claim 2, wherein the switching control circuit includes:

an oscillator for generating a reference signal having a predetermined frequency;

an error detection amplifier for generating an error amplification signal with the output voltage;

a PWM comparator connected to the oscillator and the error detection amplifier for generating a pulse signal in accordance with the reference signal and the error amplification signal;

a PFM control circuit connected to the PWM comparator for generating a switching signal to control the switching of the output transistor in accordance with the pulse signal;

a first current source circuit connected to the error detection amplifier for supplying the error detection amplifier with operational current;

a second current source circuit connected to the oscillator for supplying the oscillator with operational current; and

a third current source circuit connected to the PWM comparator for supplying the PWM comparator with operational current;

wherein the power supply disconnection circuit inactivates the first, second, and third current source circuits in accordance with the comparison signal.

4. A power supply circuit comprising:

a DC-DC converter for receiving a power supply voltage and generating a first output voltage, wherein the DC-DC converter includes;

a voltage generation circuit having a first output transistor, wherein the first output transistor performs switching, and the voltage generating circuit generates the first output voltage in accordance with the switching of the first output transistor; and

a switching control circuit connected to the voltage generation circuit for controlling the switching of the first output transistor;

a voltage regulator connected to the DC-DC converter for generating the second output voltage in accordance with the first output voltage;

a current detection circuit for detecting a load current derived from the second output voltage of the voltage generation circuit to generate a first detection signal in accordance with the detected load current; and

a stop control circuit connected to the voltage generation circuit, the switching control circuit, and the current detection circuit for maintaining the output transistor in an activated state and stopping the operation of the switching control circuit in accordance with the first detection signal when the load current is less than or equal to a predetermined value.

5. The power supply circuit according to claim 4, wherein the voltage regulator includes:

a second output transistor for generating the second output voltage in accordance with the first output voltage; and

wherein the current detection circuit includes;

a current detection transistor connected to the second output transistor for functioning as a current mirror with the second output transistor; and

a conversion resistor connected to the current detection transistor for converting an output current of the current detection transistor to a voltage and generating the first detection signal which has the converted voltage.

6. The power supply circuit according to claim 4, wherein the stop control circuit includes:

a control comparator for comparing the detection signal with a reference voltage to generate a comparison signal;

a gate control circuit connected to the control comparator for maintaining the first output transistor in an activated state in accordance with the comparison signal; and

a power supply disconnection circuit connected to the control comparator for disconnecting the switching control circuit from a power supply in accordance with the comparison signal.

7. The power supply circuit according to claim 6, wherein the switching control circuit includes:

an oscillator for generating a reference signal having a predetermined frequency;

an error detection amplifier for generating an error amplification signal with the first output voltage;

a PWM comparator connected to the oscillator and the error detection amplifier for generating a pulse signal in accordance with the reference signal and the error amplification signal;

a PFM control circuit connected to the PWM comparator for generating a switching signal to control the switching of the first output transistor in accordance with the pulse signal;

a first current source circuit connected to the error detection amplifier for supplying the error detection amplifier with operational current;

a second current source circuit connected to the oscillator for supplying the oscillator with operational current; and

a third current source circuit connected to the PWM comparator for supplying the PWM comparator with operational current;

wherein the power supply disconnection circuit inactivates the first, second, and third current source circuits in accordance with the comparison signal.

8. The power supply circuit according to claim 7, wherein the PFM control circuit shifts states in accordance with the first detection signal, wherein the PFM control circuit shifts between a state in which the PFM control circuit changes a switching frequency of the first output transistor and a state in which the PFM control circuit PWM controls the first output transistor in response to a PWM output signal of the PWM comparator.

9. The power supply circuit according to claim 8, wherein the voltage regulator includes the current detection circuit.

10. The power supply circuit according to claim 4, wherein the voltage regulator inactivates the second output transistor in response to a control signal.

11. The power supply circuit according to claim 10, wherein the switching control circuit includes an auxiliary transistor that functions in parallel to the first output transistor in response to the control signal.

12. The power supply circuit according to claim 11, wherein the switching control circuit further includes:

an output voltage detection circuit for generating a second detection signal when the first output voltage is less than or equal to a predetermined value; and

a gate control circuit connected to the output voltage detection circuit for inactivating the first output transistor in accordance with the second detection signal;

wherein the auxiliary transistor is activated in accordance with the second detection signal to generate the first output voltage when the first output transistor is inactivated.

13. The power supply circuit according to claim 11, wherein the switching control circuit is formed on a single semiconductor substrate, and the auxiliary transistor has an ON resistance that is greater than that of the first output transistor.

15. The method according to claim 14, wherein the switching control circuit includes a switching unit for generating a switching signal to switch the output transistor and a current source circuit for supplying the switching unit with current;

and

wherein the stopping step includes inactivating the current source circuit.

17. The method according to claim 16, wherein the switching control circuit includes a switching unit for generating a switching signal to switch the output transistor and a current source circuit for supplying the switching unit with current;

and

wherein the stopping step includes inactivating the current source circuit.

14. A method for controlling a DC-DC converter, wherein the DC-DC converter includes an output transistor for performing switching to generate an output voltage and a switching control circuit connected to the voltage generation circuit for controlling the switching of the output transistor, the method comprising the steps of:

supplying a load with a load current derived from the output voltage of the output transistor;

detecting the load current;

determining whether the load current is less than or equal to a predetermined value;

maintaining the output transistor in an activated state when the load current is determined as being less than or equal to the predetermined value; and

stopping the operation of the switching control circuit when the load current is determined as being less than or equal to the predetermined value.

16. A method for controlling a power supply circuit, wherein the power supply circuit includes a DC-DC converter having an output transistor for performing switching to generate a first output voltage and a switching control circuit for controlling the switching of the output transistor, and a voltage regulator connected to the DC-DC converter for generating a second output voltage in accordance with the first output voltage, the method comprising the steps of:

supplying a load with a load current derived from the second output voltage;

detecting the load current;

determining whether the load current is less than or equal to a predetermined value;

maintaining the output transistor in an activated state when the load current is determined as being less than or equal to the predetermined value; and

stopping the operation of the switching control circuit when the load current is determined as being less than or equal to the predetermined value.