Load Driving Device, and Lighting Apparatus and Liquid Crystal Display Device Using the Same

• US 20100220049A1
• Filed: 03/24/2010
• Published: 09/02/2010
• Est. Priority Date: 07/07/2003
• Status: Active Grant

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: MURAKAMI, Sadakazu
• Granted Patent: US 8,519,680 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G05F 1/46 wherein the variable actually regulated by the final control device is dc G05F1/625 takes precedence
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 3/155 using semiconductor devices only
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• CPC Class Codes: H05B 45/347 Dynamic headroom control [DHC]
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines
• CPC Class Codes: H05B 47/10 Controlling the light source

Abstract

A load driving device disclosed in the specification includes a power supply circuit for supplying to a load an output voltage converted from an input voltage, a detection voltage generation circuit for generating a detection voltage which varies depending on a magnitude of a voltage drop which across the load, and a control circuit for controlling the power supply circuit so that it performs output feedback control of the output voltage, on the basis of the detection voltage.

Claims

1. A load driving device, comprising:

a power supply circuit for supplying to a load an output voltage converted from an input voltage;

a detection voltage generation circuit for generating a detection voltage which varies depending on a magnitude of a voltage drop across the load; and

a control circuit for controlling the power supply circuit so that output feedback control of the output voltage is performed based on the detection voltage.

2. The load driving device according to claim 1, wherein

the control circuit includes:

an error amplifier for generating an error voltage corresponding to a difference between the detection voltage to be inputted to an inverting input terminal and a predetermined reference voltage to be inputted into a noninverting input terminal, and

wherein the control circuit generates a control signal of the power supply circuit so that the error voltage is reduced.

3. The load driving device according to claim 1, wherein

the power supply circuit supplies the output voltage to multiple of loads,

the detection voltage generation circuit generates multiple detection voltages, each corresponding to the multiple of loads, and

the control circuit generates a control signal of the power supply circuits so as to equalize the detected voltage corresponding to a load with a largest voltage drop and the predetermined reference voltage.

4. The load driving device according to claim 3, wherein the control circuit includes multiple error amplifiers which generate multiple error voltages based on the multiple detection voltages and the multiple reference voltages, each of the multiple detection voltages and the reference voltages are to be inputted to each of the multiple error amplifiers one by one;

and

a control signal generation circuit for generating a control signal of the power supply circuit, on the basis of an error voltage generated corresponding to the load with the largest voltage drop, among the multiple error voltages.

5. The load driving device according to claim 1, wherein

the detection voltage generation circuit includes:

a resistance to be connected in series with the load from one end of which the detection voltage is derived.

6. The load driving device according to claim 5, wherein

the detection voltage generation circuit further includes:

a switch for blocking between the load and the resistance in case of abnormality of the power supply circuit.

7. The load driving device according to claim 1, wherein

the detection voltage generation circuit includes:

a pnp type or a p-channel type transistor with an emitter or a source connected to one end of the load;

a first resistance with one end connected to a collector or a drain of the transistor;

a second resistance connected between one end of the load and a base or a gate of the transistor; and

an operational amplifier for controlling a voltage to be given to the base or the gate of the transistor so as to equalize the detected voltage at one end of the first resistance and the predetermined reference voltage.

8. The load driving device according to claim 3, further comprising:

a selector for selecting and outputting a detection voltage generated corresponding to the load with the largest voltage drop among the multiple detection voltages.

9. The load driving device according to claim 3, further comprising:

a drive current control unit for shifting each on period and supplying drive currents to the loads so as to prevent simultaneous driving of the loads of at least one channel and the loads of the remaining channels.

10. The load driving device according to claim 9, wherein

the drive current control unit performs not only pulse-width modulation control of the drive currents, but also current value control of the drive currents.

11. The load driving device according to claim 10, wherein

the drive current control unit performs only the pulse-width modulation of the drive currents unless on duty of the drive currents has reached a predetermined upper limit value, and performs current value control of the drive currents as well as the pulse-width modulation of the drive currents if the on duty of the drive currents has reached the predetermined upper limit value.

12. The load driving device according to claim 9, wherein

the drive current control unit performs supply control of the drive currents so that there is a predetermined simultaneous off time after loads of one channel are turned off till loads of other channels are turned on.

13. The load driving device according to claim 1, wherein

the power supply circuit is any one of the following types:

step-down voltage type which lowers the input voltage to generate the output voltage;

step-up voltage type which boosts the input voltage to generate the output voltage;

inverting type which inverts plus and minus of the input voltage to generate the output voltage;

step-up/down voltage type which boosts or lowers the input voltage to generate the output voltage;

or

transformer type which generates the output voltage from the input voltage according to the winding ratio.

14. The load driving device according to claim 1, wherein

the detection voltage generation circuit includes:

a constant-current source being connected in series with the load and flowing constant current that can be adjusted, and

the control circuit generates a control signal of the power supply circuit so that a voltage of a connecting point of the load and the constant-current source becomes a constant voltage.

15. The load driving device according to claim 14, wherein

the constant-current source includes:

a constant-current circuit of variable current type;

an input side transistor for a current mirror connected in series with the constant-current circuit; and

an output side transistor for a current mirror to which a same control input as the input transistor for the current mirror is given,

wherein the constant current that can be adjusted is supplied to the output side transistor for the current mirror flows.

16. The load driving device according to claim 15, wherein

the constant voltage is higher than a saturated voltage of the output side transistor for the current mirror.

17. The load driving device according to claim 16, wherein

the power supply circuit includes:

a coil;

a switch for switching current conducting to the coil; and

a rectifying/smoothing circuit for rectifying/smoothing a voltage which appears at one end of the coil, to generate the output voltage.

18. A lighting apparatus, comprising

at least one load the operating point of which is determined by a flowing current;

and

a load driving device for driving the load, wherein

the load driving device includes;

a power supply circuit for supplying to the load an output voltage converted from an input voltage;

a detection voltage generation circuit for generating a detection voltage whose voltage level varies depending on a magnitude of a voltage drop across the load; and

a control circuit for controlling the power supply circuit so that it performs output feedback control of the output voltage, on the basis of the detection voltage.

19. The lighting apparatus according to claim 18, wherein

the load is a group of light-emitting diodes including at least one light-emitting diode.

20. A liquid crystal display device comprising the lighting apparatus according to claim 19.