METHOD AND APPARATUS FOR DETECTING DEMAGNETIZING TIME OF MAGNETIC DEVICE

• US 20080043503A1
• Filed: 08/15/2006
• Published: 02/21/2008
• Est. Priority Date: 08/15/2006
• Status: Active Grant

• Current Assignee: Fairchild Semiconductor Corporation (ON Semiconductor Corporation)
• Original Assignee: System General Corporation (ON Semiconductor Corporation)
• Inventors: Yang, Ta-yung
• Granted Patent: US 7,471,523 B2
• Time in Patent Office: Days
• US Class Current: 363/97
• CPC Class Codes: G01R 33/1215 Measuring magnetisation; Particular magnetometers therefor G01R33/14 takes precedence; electrodynamic magnetometers G01R33/028
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence

Abstract

A detection circuit for detecting the demagnetizing time of a magnetic device is provided. An input circuit is coupled to the magnetic device for detecting a magnetizing voltage and a demagnetizing voltage of the magnetic device. A control circuit is coupled to the input circuit for generating a demagnetizing-time signal in response to the magnetizing voltage, the demagnetizing voltage, and a magnetizing time. The magnetizing time is correlated to the enable period of the magnetizing voltage. The demagnetizing time of the magnetic device is represented by the demagnetizing-time signal.

Claims

1. A detection circuit for detecting the discharge time of a magnetic device, comprising:

an input circuit coupled to the magnetic device to detect a first voltage and a second voltage of the magnetic device for generating a first signal, a second signal, and a charge-time signal in response to the first voltage and the second voltage, wherein the first voltage is applied to the magnetic device for charging the magnetic device, and the second voltage is applied on the magnetic device during the discharging of the magnetic device; and

a control circuit coupled to the input circuit to generate a discharge-time signal in response to the first signal, the second signal, and the charge-time signal,

wherein the first signal is correlated to the first voltage, the second signal is correlated to the second voltage, the charge-time signal is correlated to the enable period of the first voltage, and the period of the discharge-time signal represents the discharge time of the magnetic device.

2. The detection circuit for detecting the discharge time of the magnetic device as claimed in claim 1, wherein the period of the discharge-time signal is increased in response to the increase of the first voltage, the period of the discharge-time signal is decreased in response to the decrease of the period of the charge-time signal, and the period of the discharge-time signal is decreased in response to the increase of the second voltage.

3. The detection circuit for detecting the discharge time of the magnetic device as claimed in claim 1, wherein the input circuit comprising:

a first resistive device coupled to detect the first voltage for generating a first current;

a first circuit coupled to the first resistive device to generate the first signal and the charge-time signal in response to the first current; and

a second circuit coupled for detecting the second voltage to produce a second current,

wherein the second signal is generated in response to the second current.

4. The detection circuit for detecting the discharge time of the magnetic device as claimed in claim 1, wherein the control circuit, comprising:

a capacitor;

a first switch coupled in between the first signal and the capacitor;

a second switch coupled in between the second signal and the capacitor;

a comparator coupled to the capacitor to generate a switch signal once the voltage of the capacitor is higher than a reference voltage; and

an output circuit coupled to generate the discharge-time signal in response to the switch signal and the disabling of the charge-time signal,

wherein the first switch is turned on in response to the enabling of the charge-time signal, the second switch is turned on in response to the enabling of the discharge-time signal, the first signal is used for charging the capacitor, and the second signal is utilized for discharging the capacitor.

5. A detection circuit to detect the demagnetizing time of a magnetic device, comprising:

an input circuit coupled to the magnetic device for detecting a magnetizing voltage and a demagnetizing voltage of the magnetic device; and

a control circuit coupled to the input circuit for generating a demagnetizing-time signal in response to the magnetizing voltage, the demagnetizing voltage, and a magnetizing time, wherein the magnetizing time is correlated to the enable period of the magnetizing voltage, and the demagnetizing-time signal represents the demagnetizing time of the magnetic device.

6. The detection circuit to detect the demagnetizing time of the magnetic device as claimed in claim 5, wherein the period of the demagnetizing-time signal is increased in response to the increase of the magnetizing voltage, the period of the demagnetizing-time signal is decreased in response to the decrease of the magnetizing time, and the period of the demagnetizing-time signal is decreased in response to the increase of the demagnetizing voltage.

7. The detection circuit to detect the demagnetizing time of the magnetic device as claimed in claim 5, wherein the input circuit, comprising:

a first circuit coupled to the magnetizing voltage for generating a first signal and a magnetizing-time signal in response to the magnetizing voltage, wherein the magnetizing-time signal represents the magnetizing time; and

a second circuit coupled to the demagnetizing voltage for producing a second signal.

8. The detection circuit to detect the demagnetizing time of the magnetic device as claimed in claim 5, wherein the control circuit, comprising:

a capacitor;

a first switch coupled in between the first signal and the capacitor;

a second switch coupled in between the second signal and the capacitor;

a comparator coupled to the capacitor for generating a switch signal once the voltage of the capacitor is higher than a reference voltage; and

an output circuit generating the demagnetizing-time signal in response to the switch signal and the disabling of the magnetizing-time signal,

wherein the first switch is enabled in response to the enabling of the magnetizing-time signal, the second switch is enabled in response to the enabling of the demagnetizing-time signal, the first signal is used for charging the capacitor, and the second signal is utilized for discharging the capacitor.

9. An apparatus for detecting demagnetizing time of a magnetic device, comprising:

a voltage source;

a first switch connected to the voltage source;

a transformer, having a primary winding and a secondary winding with a first node and a second node,

wherein the primary winding is connected to the first switch;

a detection circuit for detecting the demagnetizing time of the transformer, having a first voltage node, a second voltage node, and a ground node, wherein the first voltage node is connected to the first node of the secondary winding, the second voltage node is connected to the second node of the secondary winding, the ground node is connected to the ground, and the detection circuit further comprising;

an input circuit;

a control circuit coupled to the input circuit;

a diode connected to the first node of the secondary winding and the ground; and

an output load connected to the second node of the secondary winding and the ground.

10. The apparatus according to claim 9, wherein the input circuit is coupled to receive a first voltage and a second voltage for obtaining a discharge time signal to generate a charge time signal, a first signal, and a second signal in response to the first voltage and the second voltage.

11. The apparatus according to claim 10, wherein the control circuit is coupled to receive the charge time signal, the first signal, and the second signal for generating a discharge time signal in response to the charge time signal, the first signal, and the second signal.

12. An apparatus for detecting demagnetizing time of a magnetic device, comprising:

a detection circuit, having a first voltage node, a second voltage node, and a ground node, wherein the first voltage node is connected to the first node of the magnetic device, the second voltage node is connected to the second node of the magnetic device, and the ground node is connected to the ground and the detection circuit further comprising an input circuit and a control circuit; and

an output circuit connected to the second node of the magnetic device and the ground.

13. The apparatus according to claim 12, wherein the first node of the magnetic device is charged with a voltage, and the second node of the magnetic device is discharged with a voltage.

14. The apparatus according to claim 12, wherein the input circuit coupled to receive a first voltage and a second voltage for generating a charge time signal, a first signal, and a second signal in response to the first voltage and the second voltage.

15. The apparatus according to claim 14, wherein the control circuit coupled to receive the charge time signal, the first signal, and the second signal for generating a discharge time signal in response to the charge time signal, the first signal, and the second signal.