CONVERTER DEVICE

• US 20150002051A1
• Filed: 12/17/2012
• Published: 01/01/2015
• Est. Priority Date: 12/28/2011
• Status: Active Grant

• Current Assignee: OSRAM GmbH (Ams-Osram AG)
• Original Assignee: OSRAM GmbH (Ams-Osram AG)
• Inventors: Angelin, Francesco, De Anna, Paolo
• Granted Patent: US 9,099,920 B2
• Time in Patent Office: Days
• US Class Current: 315/307
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• CPC Class Codes: H05B 45/375 using buck topology

Abstract

A converter, for feeding a load via an inductor, includes a switch to permit or prevent the feeding of current towards inductor, and a current sensor with a resistor coupled to the converter output, adapted to sense the current through said inductor when switch is off. A further switch is provided which is conductive when said switch is turned off; moreover, a drive circuitry is provided which is coupled to current sensor to turn said switch on as a function of the detected current. Drive circuitry is fed by a bootstrap circuit which includes: a bootstrap capacitor to accumulate a feeding charge for drive circuitry and coupled to the converter output and to a bootstrap diode, a coupling capacitor interposed between said further switch and bootstrap diode, as well as a bootstrap resistor interposed between a power supply source and bootstrap diode to charge coupling capacitor therefrom.

Claims

1. A converter for feeding a load via an inductor with a current having a controlled intensity between a maximum level and a minimum level, the converter comprising:

a switch switcheable on and off to permit or prevent, respectively, feeding of current towards said inductor,

a current sensor including a resistor coupled to the converter output and sensitive to the current flowing through said inductor when said switch is off,

a further switch interposed between said switch and said resistor;

said further switch being conductive when said switch is turned off, whereby, with said switch turned off, said resistor coupled to the converter output is traversed by current flowing through said inductor, and

drive circuitry of said switch coupled to said current sensor to turn said switch on as a function if the current detected by said current sensor,

wherein a bootstrap circuit is provided for feeding said drive circuitry, said bootstrap circuit comprising;

a bootstrap capacitor to accumulate a feeding charge for said drive circuitry, wherein said bootstrap capacitor is coupled to the converter output and a bootstrap diode,

a coupling capacitor interposed between said further switch and said bootstrap diode;

a bootstrap resistor interposed between a power supply source and said bootstrap diode to charge said coupling capacitor from said power supply source, whereby, with said switch turned off, said bootstrap diode transfers charge from said coupling capacitor to said bootstrap capacitor and said resistor coupled to the converter output is traversed by the current flowing through said inductor.

2. The converter of claim 1, wherein the following relationship applies for the resistance value of said bootstrap resistor (R_BOOT) and said resistor (R_SHL) coupled to the converter output:

R_BOOT>

>

R_SHL.

3. The converter of claim 1, wherein the following relationship applies for the capacitance values of said coupling capacitor (C_COUP) and said bootstrap capacitor (C_BOOT):

C_COUP>

>

C_BOOT.

4. The converter of claim 1, wherein said further switch conductive when said switch is turned off is a diode.

5. The converter of claim 4, wherein said coupling capacitor is interposed between the anodes of said bootstrap diode and said diode constituting said further switch conductive when said switch is turned off.

6. The converter of claim 1, further comprising:

a first current sensor sensitive to the current flowing through said switch when said switch is on,

said current sensor including a resistor coupled to the converter output as a second current sensor sensitive to the current flowing through said inductor when said switch is off, and wherein;

said drive circuitry is configured to turn said switch off and on upon receiving a first and a second logic signal, respectively, and

comparison circuitry is provided coupled to said first and second current sensors to generate first and second logic signals when, respectively;

the current intensity detected by said first current sensor is offset of a given amount with respect to said maximum level, and

the current intensity detected by said second current sensor is offset of a given amount with respect to said minimum level.

7. The converter of claim 6, wherein said comparison circuitry includes respective level comparators coupled to said first and second current sensors and configured to identify a respective given amount of offset being established between the intensity of the current detected by the current sensor coupled therewith with respect to said maximum level and said minimum level, respectively.

8. The converter of claim 6, wherein said comparison circuitry includes respective level comparators coupled to said first and second current sensors via signal dividers to apply a compensation offset to the current intensity value detected by said first and second current sensors.

9. The converter of claim 8, wherein said comparison circuitry includes level comparators that receive:

on a first input, a signal representative of said maximum level, respectively, of said minimum level, and

on a second input, a signal representative of the current intensity value detected by said first current sensor, respectively, by said second current sensor having a compensation offset applied thereto by a respective signal divider.

10. The converter of claim 6, wherein said comparison circuitry coupled to said first and second current sensors is configured to generate said first and said second logic signals when, respectively:

the current intensity detected by said first current sensor is offset of a given amount and is at a lower level with respect to said maximum level, and

the current intensity detected by said second current sensor is offset of a given amount and is at a higher level with respect to said minimum level.

11. The converter of claim 1, wherein said switch is an electronic switch, such as a mosfet.

12. Use of a converter to drive a load in the form of a light source, such as a LED light source, the converter comprising:

a switch switcheable on and off to permit or prevent, respectively, feeding of current towards said inductor,

a current sensor including a resistor coupled to the converter output and sensitive to the current flowing through said inductor when said switch is off,

a further switch interposed between said switch and said resistor;

said further switch being conductive when said switch is turned off, whereby, with said switch turned off, said resistor coupled to the converter output is traversed by current flowing through said inductor, and

drive circuitry of said switch coupled to said current sensor to turn said switch on as a function if the current detected by said current sensor,

wherein a bootstrap circuit is provided for feeding said drive circuitry, said bootstrap circuit comprising;

a bootstrap capacitor to accumulate a feeding charge for said drive circuitry,

wherein said bootstrap capacitor is coupled to the converter output and a bootstrap diode,

a coupling capacitor interposed between said further switch and said bootstrap diode;

a bootstrap resistor interposed between a power supply source and said bootstrap diode to charge said coupling capacitor from said power supply source, whereby, with said switch turned off, said bootstrap diode transfers charge from said coupling capacitor to said bootstrap capacitor and said resistor coupled to the converter output is traversed by the current flowing through said inductor.