Circuit and method for controlling DC-DC converter

Abstract

A DC-DC converter for generating a stable output voltage and being applicable to a transient load fluctuation. The DC-DC converter detects an input current, and compares the input current with a rated current of an external power supply. The DC-DC converter controls a positive charging current that is supplied to a secondary battery in accordance with a consumption current of a load so that the input current does not exceed the rated current. The DC-DC converter further controls a negative charging current that is supplied from the secondary battery to the load when the load requires an input current exceeding the rated current.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

FIG. 1 is a schematic block circuit diagram of a charging circuit (DC-DC converter) in the prior art example;

FIG. 2 is a schematic block circuit diagram of a further charging circuit (DC-DC converter) in the prior art;

FIG. 3 is a schematic block circuit diagram of an electronic device including a DC-DC converter according to a preferred embodiment of the present invention;

FIG. 4 is a schematic block circuit diagram of the DC-DC converter of FIG. 3;

FIG. 5 is a circuit diagram of a switching control circuit shown in FIG. 4; and

FIG. 6 is a schematic block circuit diagram of a DC-DC converter according to a further embodiment of the present invention.

Claims

1. A DC-DC converter for use in an electronic device that receives an input current and includes a load that operates on the input current and a secondary battery, the DC-DC converter comprising: a control circuit which detects the input current, compares the detected input current with a predetermined value, and based on the comparison, controls a positive charging current for charging the secondary battery and a negative charging current supplied from the secondary battery to the load.

2. The DC-DC converter according to claim 1, wherein: the input current is a synthesized current obtained by synthesizing a consumption current of the load with the positive charging current or the negative charging current; andthe control circuit supplies the load with the negative charging current from the secondary battery when the consumption current of the load exceeds the predetermined value and supplies the secondary battery with the positive charging current when the consumption current of the load is less than or equal to the predetermined value.

3. The DC-DC converter according to claim 1, further comprising: a first transistor, connected to the control circuit, for receiving the input current;a second transistor connected to the control circuit and connected in series to the first transistor; anda choke coil, connected between the secondary battery and a node between the first and second transistors;wherein the control circuit activates and inactivates each of the first and second transistors to supply the secondary battery with the positive charging current via the choke coil or supply the load with the negative charging current from the secondary battery via the choke coil.

4. The DC-DC converter according to claim 3, wherein said predetermined value is a first predetermined value or a second predetermined value, which differs from the first predetermined value, the control circuit including: a first detector for detecting the difference between a first reference voltage representing the first predetermined value and a voltage of a signal representing the detected input current to generate a first detection signal;a second detector for detecting the difference between a reference current, which corresponds to a second reference voltage for controlling the positive charging current, and the positive charging current to generate a second detection signal;a third detector for detecting the difference between a third reference voltage, for controlling a charging voltage of the secondary battery, and the charging voltage to generate a third detection signal;a fourth detector for detecting the difference between a fourth reference voltage representing the second predetermined value and a voltage of a signal representing the detected input current to generate a fourth detection signal; anda fifth detector for detecting the difference between a fifth reference voltage, for controlling an output voltage of the DC-DC converter, and the output voltage to generate a fifth detection signal.

5. The DC-DC converter according to claim 4, wherein the control circuit includes: a first converter, connected to the first detector, the second detector, and the third detector, for generating a first pair of control signals each having a pulse width that is in accordance with one of the first detection signal, the second detection signal, and the third detection signal;a second converter, connected to the fourth detector and the fifth detector, for generating a second pair of control signals each having a pulse width that is in accordance with one of the fourth detection signal and the fifth detection signal; anda switching control circuit, connected to the first converter, the second converter, the first transistor, and the second transistor, for activating and inactivating the first and second transistors with either one of the first pair of control signals and the second pair of control signals in accordance with the consumption current of the load.

6. The DC-DC converter according to claim 5, wherein the switching control circuit includes: a state detection circuit, connected to the first converter and the second converter, for detecting an operation state of the DC-DC converter based on the first pair of control signals and the second pair of control signals; anda selection circuit, connected to the state detection circuit, the first transistor, and the second transistor, for selecting either one of the first pair of control signals and the second pair of control signals as a pair of switching control signals provided to the first and second transistors in accordance with the operation state detected by the state detection circuit.

7. The DC-DC converter according to claim 6, wherein the operation state of the DC-DC converter includes: a first operation state in which the first pair of control signals is selected as the pair of switching control signals; anda second operation state in which the second pair of control signals is selected as the pair of switching control signals;wherein the selection circuit receives a charge enablement signal and cancels selection of the first pair of control signals in response to the charge enablement signal when the DC-DC converter is in the first operation state.

8. A control circuit for a DC-DC converter for use in an electronic device that receives an input current and includes a load that operates on the input current and a secondary battery, the control circuit comprising: a current detection device which detects the input current and generates a current detection signal, wherein the control circuit compares the current detection signal with a predetermined value, and based on the comparison, controls a positive charging current for charging the secondary battery and a negative charging current supplied from the secondary battery to the load.

9. The control circuit according to claim 8, wherein: the input current is a synthesized current obtained by synthesizing a consumption current of the load with the positive charging current or the negative charging current; andthe control circuit supplies the load with the negative charging current from the secondary battery when the consumption current of the load exceeds the predetermined value and supplies the secondary battery with the positive charging current when the consumption current of the load is less than or equal to the predetermined value.

10. The control circuit according to claim 8, wherein the DC-DC converter includes: a first transistor, connected to the control circuit, for receiving the input current;a second transistor connected to the control circuit and connected in series to the first transistor; anda choke coil, connected between the secondary battery and a node between the first and second transistors;wherein the control circuit activates and inactivates each of the first and second transistors to supply the secondary battery with the positive charging current via the choke coil or supply the load with the negative charging current from the secondary battery via the choke coil.

11. The control circuit according to claim 10, wherein said predetermined value is a first predetermined value or a second predetermined value, which differs from the first predetermined value, the control circuit further comprising: a first detector for detecting the difference between a first reference voltage representing the first predetermined value and a voltage of a signal representing the detected input current to generate a first detection signal;a second detector for detecting the difference between a reference current, which corresponds to a second reference voltage for controlling the positive charging current, and the positive charging current to generate a second detection signal;a third detector for detecting the difference between a third reference voltage, for controlling a charging voltage of the secondary battery, and the charging voltage to generate a third detection signal;a fourth detector for detecting the difference between a fourth reference voltage representing the second predetermined value and a voltage of a signal representing the detected input current to generate a fourth detection signal; anda fifth detector for detecting the difference between a fifth reference voltage, for controlling an output voltage of the DC-DC converter, and the output voltage to generate a fifth detection signal.

12. The control circuit according to claim 11, further comprising: a first converter, connected to the first detector, the second detector, and the third detector, for generating a first pair of control signals each having a pulse width that is in accordance with one of the first detection signal, the second detection signal, and the third detection signal;a second converter, connected to the fourth detector and the fifth detector, for generating a second pair of control signals each having a pulse width that is in accordance with one of the fourth detection signal and the fifth detection signal; anda switching control circuit, connected to the first converter, the second converter, the first transistor, and the second transistor, for activating and inactivating the first and second transistors with either one of the first pair of control signals and the second pair of control signals in accordance with the consumption current of the load.

13. The control circuit according to claim 12, wherein the switching control circuit includes: a state detection circuit, connected to the first converter and the second converter, for detecting an operation state of the DC-DC converter based on the first pair of control signals and the second pair of control signals; anda selection circuit, connected to the state detection circuit, the first transistor, and the second transistor, for selecting either one of the first pair of control signals and the second pair of control signals as a pair of switching control signals provided to the first and second transistors in accordance with the operation state detected by the state detection circuit.

14. The control circuit according to claim 13, wherein the operation state of the DC-DC converter includes: a first operation state in which the first pair of control signals is selected as the pair of switching control signals; anda second operation state in which the second pair of control signals is selected as the pair of switching control signals;wherein the selection circuit receives a charge enablement signal and cancels selection of the first pair of control signals in response to the charge enablement signal when the DC-DC converter is in the first operation state.

15. An electronic device for receiving an input current, the electronic device comprising: a DC-DC converter which generates a charging current from the input current;a load that operates on the input current;a secondary battery charged by the charging current, the DC-DC converter including:a control circuit for detecting the input current, comparing the detected input current with a predetermined value, and based on the comparison, controlling a positive charging current for charging the secondary battery and a negative charging current supplied from the secondary battery to the load.

16. The electronic device according to claim 15, wherein: the input current is a synthesized current obtained by synthesizing a consumption current of the load with the positive charging current or the negative charging current; andthe control circuit supplies the load with the negative charging current from the secondary battery when the consumption current of the load exceeds the predetermined value and supplies the secondary battery with the positive charging current when the consumption current of the load is less than or equal to the predetermined value.

17. The electronic device according to claim 15, wherein the DC-DC converter includes: a first transistor, connected to the control circuit, for receiving the input current;a second transistor connected to the control circuit and connected in series to the first transistor; anda choke coil, connected between the secondary battery and a node between the first and second transistors;wherein the control circuit activates and inactivates each of the first and second transistors to supply the secondary battery with the positive charging current via the choke coil or supply the load with the negative charging current from the secondary battery via the choke coil.

18. The electronic device according to claim 17, wherein said predetermined value is a first predetermined value or a second predetermined value, which differs from the first predetermined value, the control circuit including: a first detector for detecting the difference between a first reference voltage representing the first predetermined value and a voltage of a signal representing the detected input current to generate a first detection signal;a second detector for detecting the difference between a reference current corresponding to a second reference voltage for controlling the positive charging current and the positive charging current to generate a second detection signal;a third detector for detecting the difference between a third reference voltage, for controlling a charging voltage of the secondary battery, and the charging voltage to generate a third detection signal;a fourth detector for detecting the difference between a fourth reference voltage representing the second predetermined value and a voltage of a signal representing the detected input current to generate a fourth detection signal; anda fifth detector for detecting the difference between a fifth reference voltage, for controlling an output voltage of the DC-DC converter, and the output voltage to generate a fifth detection signal.

19. The electronic device according to claim 18, wherein the control circuit includes: a first converter, connected to the first detector, the second detector, and the third detector, for generating a first pair of control signals each having a pulse width that is in accordance with one of the first detection signal, the second detection signal, and the third detection signal;a second converter, connected to the fourth detector and the fifth detector, for generating a second pair of control signals each having a pulse width that is in accordance with one of the fourth detection signal and the fifth detection signal; anda switching control circuit, connected to the first converter, the second converter, the first transistor, and the second transistor, for activating and inactivating the first and second transistors with either one of the first pair of control signals and the second pair of control signals in accordance with the consumption current of the load.

20. The electronic device according to claim 19, wherein the switching control circuit includes: a state detection circuit, connected to the first converter and the second converter, for detecting an operation state of the DC-DC converter based on the first pair of control signals and the second pair of control signals; anda selection circuit, connected to the state detection circuit, the first transistor, and the second transistor, for selecting either one of the first pair of control signals and the second pair of control signals as a pair of switching control signals provided to the first and second transistors in accordance with the operation state detected by the state detection circuit.

21. The electronic device according to claim 20, wherein the operation state of the DC-DC converter includes: a first operation state in which the first pair of control signals is selected as the pair of switching control signals; anda second operation state in which the second pair of control signals is selected as the pair of switching control signals;wherein the selection circuit receives a charge enablement signal and cancels selection of the first pair of control signals in response to the charge enablement signal when the DC-DC converter is in the first operation state.

22. A method for controlling a DC-DC converter for use in an electronic device that receives an input current and includes a load that operates on the input current and a secondary battery, the method comprising: detecting the input current to generate a current detection signal;comparing the current detection signal with a predetermined value to generate a signal indicating the comparison; andcontrolling, based on the signal indicating the comparison, a positive charging current for charging the secondary battery and a negative charging current supplied from the secondary battery to the load.

23. The method according to claim 22, wherein: the input current is a synthesized current obtained by synthesizing a consumption current of the load with the positive charging current or the negative charging current; andsaid controlling includes supplying the load with the negative charging current from the secondary battery when the consumption current of the load exceeds the predetermined value and supplying the secondary battery with the positive charging current when the consumption current of the load is less than or equal to the predetermined value.

24. The method according to claim 22, wherein: the DC-DC converter includes: a first transistor, connected to the control circuit, for receiving the input current;a second transistor connected to the control circuit and connected in series to the first transistor; anda choke coil, connected between the secondary battery and a node between the first and second transistors; andsaid controlling includes: activating and inactivating each of the first and second transistors to supply the secondary battery with the positive charging current via the choke coil; andactivating and inactivating each of the first and second transistors to supply the load with the negative charging current from the secondary battery via the choke coil.

25. The method according to claim 24, wherein: said predetermined value is a first predetermined value or a second predetermined value, which differs from the first predetermined value;said comparing includes: detecting the difference between a first reference voltage representing the first predetermined value and a voltage of the current detection signal to generate a first detection signal; anddetecting the difference between a fourth reference voltage representing the second predetermined value and a voltage of the current detection signal to generate a fourth detection signal;said controlling includes: detecting the difference between a reference current corresponding to a second reference voltage for controlling the positive charging current and the positive charging current to generate a second detection signal;detecting the difference between a third reference voltage, for controlling a charging voltage of the secondary battery, and the charging voltage to generate a third detection signal; anddetecting the difference between a fifth reference voltage, for controlling an output voltage of the DC-DC converter, and the output voltage to generate a fifth detection signal.

26. The method according to claim 25, wherein said controlling includes: generating a first pair of control signals each having a pulse width that is in accordance with one of the first detection signal, the second detection signal, and the third detection signal;generating a second pair of control signals each having a pulse width that is in accordance with one of the fourth detection signal and the fifth detection signal; andactivating and inactivating the first and second transistors with either one of the first pair of control signals and the second pair of control signals in accordance with the consumption current of the load.

27. The method according to claim 26, wherein said activating and inactivating the first and second transistors includes: detecting an operation state of the DC-DC converter based on the first pair of control signals and the second pair of control signals; andselecting either one of the first pair of control signals and the second pair of control signals as a pair of switching control signals provided to the first and second transistors in accordance with the operation state detected by the state detection circuit.

28. The method according to claim 27, wherein the operation state of the DC-DC converter includes: a first operation state in which the first pair of control signals is selected as the pair of switching control signals; anda second operation state in which the second pair of control signals is selected as the pair of switching control signals;wherein the DC-DC converter receives a charge enablement signal, and said selecting includes canceling selection of the first pair of control signals in response to the charge enablement signal when the DC-DC converter is in the first operation state.