SWITCHING CURRENT CONTROL CIRCUIT, LED DIMMER SYSTEM, AND LED ILLUMINATION DEVICE

• US 20130342122A1
• Filed: 03/05/2012
• Published: 12/26/2013
• Est. Priority Date: 03/07/2011
• Status: Active Grant

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: Sawada, Akinobu
• Granted Patent: US 9,374,083 B2
• Time in Patent Office: Days
• US Class Current: 315/200.R
• CPC Class Codes: H03K 17/51 characterised by the components used H03K17/04 - H03K17/30, H03K17/94 take precedence
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 47/19 via wireless transmission
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

The switching current control circuit includes a switching pulse supply circuit, a comparator circuit, and analog circuit unit, a digital circuit unit, etc. The A/D converter (2) detects a load current in an ON period of a switching pulse as a detected current, and converts it into digital data. The arithmetic control circuit (3) calculates a lower limit of the detected current for providing a timing of switching from OFF to ON of the switching pulse, based on the converted data. Continuation/discontinuous modes are determined whether the lower limit is equal to or greater than 0.

Claims

1. A switching current control circuit for controlling a load current flowing through a predetermined device by switching operation, the switching current control circuit comprising:

a switching pulse supply circuit configured to supply a switching pulse for performing the switching operation;

a comparator circuit configured to detect a load current as a detected current in an ON period of the switching pulse, and to compare the detected current with a peak current value;

an A/D conversion circuit configured to detect a load current in the ON period of the switching pulse as a detected current, and to convert the detected current into digital data; and

an arithmetic control circuit configured to calculate a lower limit of the detected current for providing a timing of switching the switching pulse from OFF to ON based on data of the detected current output from the A/D conversion circuit, wherein

the switching current control circuit determines that it is in a continuous mode when the lower limit of the detected current calculated by the arithmetic control circuit is equal to or greater than 0, and determines that it is in a discontinuous mode when the lower limit of the detected current is a negative value.

2. The switching current control circuit according to claim 1, wherein the lower limit of the detected current is set to be equal to or greater than 0 by increasing the switching pulse frequency, when determining that it is in the discontinuous mode based on the lower limit of the detected current.

3. The switching current control circuit according to claim 2, wherein a value to the switching pulse frequency is returned to an initial setting frequency value, when the lower limit of the detected current becomes equal to or greater than 0 and further exceeds a predetermined value by increasing the switching pulse frequency.

4. The switching current control circuit according to claim 1, wherein the switching pulse frequency is decreased, when determining that it is in the continuous mode based on the lower limit of the detected current, and a length of the ON period of the switching pulse is equal to or lower than a length of a switching noise generating period occurring at the time when the switching pulse is switched from ON to OFF.

5. The switching current control circuit according to claim 1, wherein the A/D conversion circuit performs the A/D conversion of the detected current in the ON period of the switching pulse one after another or performs the A/D conversion of the current values in two points of the detected current.

6. The switching current control circuit according to claim 5, wherein the A/D conversion circuit is composed two sample hold circuits and one A/D converter.

7. The switching current control circuit according to claim 6, wherein operational modes are assigned for every one cycle for three cycles of the switching pulse, and the A/D conversion circuit performs the A/D conversion/output of one value of the current values in two points of the detected current, and samples and holds the another value of the current values, in a first cycle of the three cycles.

8. The switching current control circuit according to claim 7, wherein the A/D conversion circuit performs the A/D conversion/output of the current value sampled and held in the first cycle, in a second cycle of the switching pulse.

9. The switching current control circuit according to claim 7, wherein the A/D conversion circuit performs the A/D conversion of the detected current in the ON period of the switching pulse one after another, in a third cycle of the switching pulse.

10. The switching current control circuit according to claim 1, wherein the switching current control circuit itself is connected to an LED via a switching element and an inductor, and

the switching current control circuit controls so that an average current flowing through the LED becomes constant even when the switching pulse frequency is increased.

21. An LED dimmer system comprising the switching current control circuit according to claim 1, the LED dimmer system performing dimming of an LED, the LED dimmer system comprising:

a bridge type full wave rectifying circuit connected to one end side of an AC power supply;

a triac dimmer connected to other end side of the AC power supply;

a bleeder resistor connected to an output side of the triac dimmer; and

a bleeder control unit configured to control a current flowing through the bleeder resistor.

22. The LED dimmer system according to claim 21, the bleeder control unit controls to supply a predetermined holding current for holding ON state to the triac dimmer via the bleeder resistor.

23. The LED dimmer system according to claim 21 further comprising

a control resistor connected to the bleeder resistor via a switching element;

and

a monitor resistor connected to the control resistor and the bridge type full wave rectifying circuit, wherein

the bleeder control unit performs on/off control of the switching element in accordance with a value of a current flowing through the monitor resistor.

24. The LED dimmer system according to claim 1, wherein a current flowing through the bleeder resistor is controlled to be 20-50 mA.

25. The LED dimmer system according to claim 1 further comprising a switching unit for switching a first dimming mode for performing phase dimming using the triac dimmer, a second dimming mode for performing pulse width modulation dimming, and a third dimming mode for performing linear dimming using a variable resistor.

26. An LED illumination device comprising the LED dimmer system according to claim 21.

27. The LED illumination device according to claim 26 composed as a bulb type LED illumination device or a ceiling light type LED illumination device.

11. A switching current control circuit for controlling a load current flowing through a predetermined device by switching operation, the switching current control circuit comprising:

a switching pulse supply circuit configured to supply a switching pulse for performing the switching operation;

a comparator circuit configured to detect a load current as a detected current in an ON period of the switching pulse, and to compare the detected current with a peak current value; and

a peak current calculation circuit configured to calculate a linear increasing rate of the detected current in the ON period of the switching pulse, to calculate a maximum current value at the time of assuming that the detected current is increased until end of the ON period of switching operation using the increasing rate, and to use the maximum current value as the peak current value, wherein

the switching pulse is switched to an OFF period based on an output signal of the comparator circuit when the detected current exceeds the peak current value calculated by the peak current calculation circuit.

12. The switching current control circuit according to claim 11, wherein the linear increasing rate of the detected current is calculated by detecting current values of two points of the detected current in the ON period of the switching pulse, and calculating inclination of a straight line on the two points.

13. The switching current control circuit according to claim 11, wherein setting up a fixed lower limit with respect to the load current in order to switch the switching pulse from the OFF period to the ON period.

14. The switching current control circuit according to claim 12 further comprising an A/D conversion circuit configured to perform an A/D conversion of the current value in two points of the detected current in the ON period of the switching pulse.

15. The switching current control circuit according to claim 13, wherein the A/D conversion circuit is composed two sample hold circuits and one A/D converter.

16. The switching current control circuit according to claim 15, wherein operational modes are assigned for every one cycle of the switching pulse, and the switching current control circuit operates with three cycles, a sample mode by the A/D conversion circuit, an A/D conversion mode by the A/D conversion circuit, and a compute mode by the A/D conversion circuit and the peak current calculation circuit.

17. The switching current control circuit according to claim 16, wherein, the A/D conversion circuit performs the A/D conversion/output of one value of the current values in two points of the detected current, and samples and holds the another value of the current values, in the sample mode.

18. The switching current control circuit according to claim 16, wherein the A/D conversion circuit performs the A/D conversion/output of the current value sampled and held in the sample mode, in the A/D conversion mode.

19. The switching current control circuit according to claim 11 further comprising a D/A conversion circuit configured to perform a D/A conversion of the peak current value output from the peak current calculation circuit, and to output the converted peak current value to the comparator circuit.

20. The switching current control circuit according to claim 19, wherein the D/A conversion circuit is composed of a DAC decoder and an R-2R ladder D/A converter.