Transistor drive circuit, constant voltage circuit, and method thereof using a plurality of error amplifying circuits to effectively drive a power transistor

• US 20070069819A1
• Filed: 09/20/2006
• Published: 03/29/2007
• Est. Priority Date: 09/21/2005
• Status: Active Grant

• Current Assignee: RICOH Electronic Devices Co., Ltd. (Nisshinbo Holdings Incorporated)
• Original Assignee: Ricoh Company Limited
• Inventors: Hayashi, Katsuhiro, Yoshii, Kohji
• Granted Patent: US 7,541,787 B2
• Time in Patent Office: Days
• US Class Current: 330/297
• CPC Class Codes: G05F 1/56 using semiconductor devices in series with the load as final control devices G05F1/461 takes precedence

Abstract

A transistor drive circuit, a constant voltage circuit, and a method thereof provided with a reference voltage generator, a power voltage detector, and a plurality of error amplifying circuits. The plurality of error amplifying circuits have different operational characteristics. One of the error amplifying circuits is selectively activated in response to a control signal in accordance with an operational mode selected. A reference voltage produced by the reference voltage generator or a divided voltage produced by the power voltage detector is also changed in response to the control signal suitably for each one of the plurality of error amplifying circuits which is selectively activated so as to control the power voltage generated by a power transistor to output a constant power voltage.

Claims

1. A transistor drive circuit which drives a power transistor to output a power voltage from an output terminal and to control the power voltage to have a predefined voltage value, the circuit comprising:

a reference voltage generator configured to generate a reference voltage;

a power voltage detector configured to detect the power voltage output from the output terminal and to generate a divided voltage in proportion to the power voltage; and

a plurality of error amplifying circuits each configured to be activated in response to a control signal input thereto to control an operation of the power transistor in a way such as to substantially equalize the divided voltage with the reference voltage, the plurality of error amplifying circuits having different operational characteristics,

wherein the power voltage detector is further configured to suitably change a proportionality constant of the divided voltage for each one of the plurality of error amplifying circuits which is selectively activated so as to control the power voltage generated by the power transistor to have the predefined power voltage.

2. The transistor drive circuit of claim 1, wherein the power voltage detector is further configured to change a proportionality constant of the divided voltage in response to the control signal input to the error amplifying circuits.

3. The transistor drive circuit of claim 2, wherein the power voltage detector includes

a first resistance connected to the output Terminal;

a second resistance connected in series with the first resistance and configured to form a first series circuit with the first resistance;

a third resistance connected in series with the first and second resistances;

a fourth resistance connected in series with the first, second, and third resistances and a ground, and configured to form a second series circuit with the third resistance;

a first fuse connected in parallel to the second resistance;

a first switch connected in parallel to the second resistance;

a second fuse connected in parallel to the fourth resistance; and

a second switch connected in parallel to the fourth resistance

wherein the second, third, and fourth resistances are variable with a trimmer,

wherein the first and second series circuits have a connection point from which the divided voltage is output, and

wherein each of the first and second switches performs a switching operation to change the proportionality constant of the divided voltage in accordance with the control signal input to the plurality of error amplifying circuits.

4. A transistor drive circuit which drives a power transistor to output a power voltage from an output terminal and to control the power voltage to have a predefined voltage value, the circuit comprising:

a reference voltage generator configured to generate a reference voltage;

a power voltage detector configured to detect the power voltage output front the output terminal and to generate a divided voltage in proportion to the power voltage; and

a plurality of error amplifying circuits each configured to be activated in response to a control signal input thereto to control an operation of the power transistor in a way such as to substantially equalize the divided voltage with the reference voltage, the plurality of error amplifying circuits having different operational characteristics,

wherein the reference voltage generator is further configured to suitably change a voltage value of the divided voltage for each one of the plurality of error amplifying circuits which is selectively activated so as to control the power voltage generated by the power transistor to have the predefined power voltage.

5. The transistor drive circuit of claim 4, wherein the reference voltage generator is further configured to change a voltage value of The reference voltage in accordance with the control signal input to the plurality of error amplifying circuits.

6. The transistor drive circuit of claim 5, wherein the reference voltage generator includes

a constant voltage generator configured to generate a constant voltage;

a first resistance connected with a point to which the constant voltage is supplied;

a second resistance connected in series with the first resistance and configured to form a first series circuit with the first resistance;

a third resistance connected in series with the first and second resistances;

a fourth resistance connected in series with the first, second, and third resistances and a ground, and configured to form a second series circuit with the third resistance;

a first fuse connected in parallel to the first resistance;

a first switch connected in parallel to the first resistance;

a second fuse connected in parallel to the third resistance; and

a second switch connected in parallel to the third resistance,

wherein the first, third, and fourth resistances are variable with a trimmer,

wherein the first and second series circuits have a connection point from which the reference voltage is output, and

wherein each of the first and second switches performs a switching operation to change a voltage value of the divided voltage in accordance with the control signal input to the plurality of error amplifying circuits.

7. A transistor drive circuit which drives a power transistor to output a power voltage from an output terminal and to control the power voltage to have a predefined voltage value, the circuit comprising:

a reference voltage generator configured to generate a reference voltage;

a power voltage detector configured to detect the power voltage output from the output terminal and to generate a divided voltage in proportion to the power voltage; and

a plurality of error amplifying circuits each configured to be activated in response to a control signal input thereto to control an operation of the power transistor in a way such as to substantially equalize the divided voltage with the reference voltage, the plurality of error amplifying circuits having different operational characteristics,

wherein the reference voltage generator is further configured to suitably change a voltage value of the reference voltage for each one of the plurality of error amplifying circuits which is selectively activated so as to control the power voltage generated by the power transistor to have the predefined power voltage.

8. The transistor drive circuit of claim 7, wherein the plurality of error amplifying circuits includes

a first error amplifying circuit configured to be controlled in accordance with, the control signal input thereto to control the power transistor in a way-such that the divided voltage is equalized with the reference voltage, and

a second error amplifying circuit configured to be controlled in accordance with the control signal input thereto to control the power transistor in a way such that the divided voltage is equalized with the reference voltage, the second error amplifying circuit having a smaller current consumption than the first error amplifying circuit,

wherein one of the first and second error amplifying circuits is selectively activated in accordance with the control signal input thereto.

9. The transistor drive circuit of claim 8, further comprising:

a third switch connected between an output terminal of the first error amplifying circuit and a control electrode of the power transistor, having a control electrode to receive the control signal, and configured to control a transmission of an output voltage from the first error amplifying circuit to the power transistor in accordance with the control signal.

10. The transistor drive circuit of claim 9, further comprising:

a fourth switch connected between an output terminal of the second error amplifying circuit and the control electrode of the power transistor, having a control electrode to receive the control signals and configured to control a transmission of an output voltage from the second error amplifying circuit to the power transistor in accordance with the control signal.

11. The transistor drive circuit of claim 7, wherein the reference voltage generator, the output voltage detector, and the plurality of error amplifying circuits are integrated into one integrated circuit chip.

12. A method of driving a power transistor which controls a current output from an input terminal to an output terminal in accordance with a signal input to a control electrode thereof, the method comprising the steps of:

providing a plurality of error amplifying circuits having different operational characteristics;

activating one of the plurality of error amplifying circuits in response to a control signal input thereto to control an operation of the power transistor such that a voltage at the output terminal becomes a predefined power voltage;

producing a reference voltage to the plurality of error amplifying circuits;

generating a divided voltage in proportion to the voltage at the output terminal by using a proportionality constant in accordance wit operational characteristics of each one of the plurality of error amplifying circuits; and

controlling the operation of the power transistor to substantially equalize the divided voltage with the reference voltage.

13. A method of driving a power transistor which controls a current output from an input terminal to an output terminal in accordance with a signal input to a control electrode thereof, the method comprising the steps of:

providing a plurality of error amplifying circuits having different operational characteristics;

activating one of the plurality of error amplifying circuits ill response to a control signal input thereto to control an operation of the power transistor such that a voltage at the output terminal becomes a predefined power voltage;

producing a reference voltage for one of the plurality of error amplifying circuits which is selectively activated in accordance with the operational characteristics thereof;

generating a divided voltage in proportion to the voltage at the output terminal by using a proportionality constant; and

controlling the operation of the power transistor to substantially equalize the divided voltage with the reference voltage.

14. A method of driving a power transistor which controls a current output from an input terminal to an output terminal in accordance with a signal input to a control electrode thereof, the method comprising the steps of;

providing a plurality of error amplifying circuits having different operational characteristics;

activating one of the plurality of error amplifying circuits in response to a control signal input thereto to control an operation of the power transistor such that a voltage at the output terminal becomes a predefined power voltage;

producing a reference voltage for each one of the plurality of error amplifying circuits in accordance with the operational characteristics thereof;

generating a divided voltage in proportion to the voltage at the output terminal by using a proportionality constant; and

controlling the operation of the power transistor to substantially equalize the divided voltage with the reference voltage.

15. A constant voltage circuit, comprising:

a power transistor configured to output a power voltage from an output terminal and to control the power voltage to have a predefined voltage value;

a reference voltage generator configured to generate a reference voltage;

a power voltage detector configured to detect the power voltage output from the output terminal and to generate a divided voltage in proportion to the power voltage, and

a plurality of error amplifying circuits each configured to be activated in response to a control signal input thereto to control an operation of the power transistor in a way such as to substantially equalize the divided voltage with the reference voltage, the plurality of error amplifying circuits having different operational characteristics,

wherein the power voltage detector is further configured to suitably change a proportionality constant of the divided voltage for each one of the plurality of error amplifying circuits which is selectively activated so as to control the power voltage generated by the power transistor to have the predefined lower voltage.

16. The constant voltage circuit of claim 15, wherein the power voltage detector is further configured to change a proportionality constant of the divided voltage in response to the control signal input to the error amplifying circuits.

17. A constant voltage circuit, comprising:

a power transistor configured to output a power voltage from an output terminal and to control the power voltage to have a predefined voltage value;

a reference voltage generator configured to generate a reference voltage;

a power voltage detector configured to detect the power voltage output from the output terminal and to generate a divided voltage in proportion to the power voltage; and

a plurality of error amplifying circuits each configured to be activated in response to a control signal input thereto to control an operation of the power transistor in a way such as to substantially equalize the divided voltage with the reference voltage, the plurality of error amplifying circuits having different operational characteristics,

wherein the reference voltage generator is further configured to suitably change a voltage value of the divided voltage for each one of the plurality of error amplifying circuits which is selectively activated so as to control the power voltage generated by the power transistor to have the predefined power voltage.

18. The constant voltage circuit of claim 17, wherein the reference voltage generator is further configured to change a voltage value of the reference voltage in accordance with the control signal input to the plurality of error amplifying circuits.

19. A constant voltage circuit, comprising;

a power transistor configured to output a power voltage from an output terminal and to control the power voltage to have a predefined voltage value;

a reference voltage generator configured to generate a reference voltage;

a power voltage detector configured to detect the power voltage output from the output terminal and to generate a divided voltage in proportion To the power voltage; and

a plurality of error amplifying circuits each configured to be activated in response to a control signal input thereto to control an operation of the power transistor in a way such as to substantially equalize the divided voltage with the reference voltage, the plurality of error amplifying circuits having different operational characteristics,

wherein the reference voltage generator is further configured to suitably change a voltage value of the reference voltage for each one of the plurality of error amplifying circuits which is selectively activated so as to control the power voltage generated by the power transistor to have the predefined power voltage.

20. The constant voltage circuit of claim 19, wherein the plurality of error amplifying circuits includes

a first error amplifying circuit configured to be controlled in accordance with die control signal input thereto to control the power transistor in a way such that the divided voltage is equalized with the reference voltage, and

a second error amplifying circuit configured to be controlled in accordance with the control signal input thereto to control the power transistor in a way such that the divided voltage is equalized with the reference voltage, the second error amplifying circuit having a smaller current consumption than the first error amplifying circuit,

wherein one of the first and second error amplifying circuits is selectively activated in accordance with the control signal input thereto.

21. The constant voltage circuit of claim 20, further comprising:

a third switch connected between an output terminal of the first error amplifying circuit and a control electrode of the power transistor, having a control electrode to receive the control signal, and configured To control a transmission of an output voltage from the first error amplifying circuit to the power transistor in accordance with the control signal.

22. The constant voltage circuit of claim 21, further comprising:

a fourth switch connected between an output terminal of the second error amplifying circuit and the control electrode of the power transistor, having a control electrode to receive the control signal, and configured to control a transmission of an output voltage from the first error amplifying circuit to the power transistor in accordance with the control signal.

23. The constant voltage circuit of claim 19, wherein the power transistor, the reference voltage generator, the output voltage detector, and the plurality of error amplifying circuits are integrated into one integrated circuit chip.