Systems and methods to safely discharge inductors without energy limitations

Abstract

Embodiments of a discharge circuit are disclosed for quickly and safely discharging energy from an inductor load. The discharge circuit comprises a first switch, a second switch and a voltage regulator. The inductor load couples between the first switch and the second switch. During fast demagnetization, a high side switch is tuned off to decouple the load from a voltage source and the second switch is turned on. Voltage on one end of the load is pushed high and maintained at a predetermined level due to the voltage regulator. The predetermined voltage pulls down the current at the inductive load and causes temperature of the discharge circuit going up quickly. Once the temperature reaches a predetermined threshold, a comparing circuit outputs a signal to a driver and eventually pulls down voltage of the inductor load for low-power demagnetization.

Claims

1. A discharge circuit for demagnetizing an inductive load, comprising: a first switch having a first terminal coupled to one end of the inductive load; a voltage regulator coupled between a control terminal of the first switch and the one end of the inductive load, the voltage regulator prevents current passing through when a voltage across the voltage regulator is less than a predetermined value; a second switch coupled to another end of the inductive load, upon being switched on, the second switch grounds the another end of the inductive load such that a voltage at the one end of the inductive load reaches or is above the predetermined value; a first temperature sensor that generates a sensed temperature signal based on a temperature of at least one component of the discharge circuit; a comparing circuit that receives a reference temperature signal representing a predetermined temperature and the sensed temperature signal and generates an output with respect to a comparison between the reference temperature signal and the sensed temperature signal; and a driver that receives the output from the comparing circuit and generates a driver output to the control terminal of the first switch, responsive to the output from the comparing circuit indicating that the temperature of the at least one component of the discharge circuit is above the predetermined temperature, the driver output switches on the first switch and causes the voltage across the voltage regulator below the predetermined value.

2. The discharge circuit of claim 1 wherein the discharge circuit is implemented as a single integrated circuit.

3. The discharge circuit of claim 1 wherein voltage regulator comprises a Zener diode and a series diode coupled in series, the Zener diode has a cathode coupled to the one end of the inductive load, the series diode has opposite polarity to the Zener diode.

4. The discharge circuit of claim 1 wherein the voltage across the voltage regulator is applied between the first terminal and the control terminal of the first switch.

5. The discharge circuit of claim 1 wherein the comparator has hysteresis, when the temperature of at least one component of the discharge circuit decreases below the predetermined temperature by a hysteresis amount, the driver output causes the first switch to be away from a low on-resistance state.

6. The discharge circuit of claim 1 wherein the driver comprises an inverter receiving the output of the comparing circuit, a push-pull driver comprising a P-channel complementary metal-oxide-semiconductor (CMOS) transistor and an N-channel CMOS transistor, and a resistor.

7. The discharge circuit of claim 1 wherein the first switch is an N-type metal-oxide-semiconductor (NMOS) transistor incorporated with a body drain diode with a diode anode connected to a source terminal of the NMOS transistor and a diode cathode connected to a drain terminal of the NMOS transistor.

8. A method for demagnetizing an inductive load, the method comprising: coupling one end of the inductive load to a first terminal of a first switch, a voltage regulator coupled between a control terminal and the first terminal of the first switch, the voltage regulator prevents current passing through when a voltage across the voltage regulator is less than a predetermined value; switching on a second switch, coupled to another end of the inductive load, to ground the another end of the inductive load such that a voltage at the one end of the inductive load is induced to reach or be above the predetermined value; generating, using a temperature sensor placed in proximity of the first switch, a sensed temperature signal indicating a temperature of the first switch; generating, using a comparison circuit, an output based on a comparison between the sensed temperature signal and a reference temperature signal representing a predetermined temperature; and generating, using a driver coupled to the comparison circuit, a driver output to the control terminal of the first switch according to the output from the comparing circuit, responsive to the output from the comparing circuit indicating that the temperature of the first switch is above the predetermined temperature, the driver output switches on the first switch and causes the voltage across the voltage regulator below the predetermined value.

9. The method of claim 8 wherein voltage regulator comprises a Zener diode and a series diode coupled in series, the Zener diode has a cathode coupled to the one end of the inductive load, the series diode has opposite polarity to the Zener diode.

10. The method of claim 8 wherein the comparator has hysteresis, responsive to the output from the comparing circuit indicating that the temperature of the first switch is below the predetermined temperature by a hysteresis amount, the driver output causes the first switch to be away from a low on-resistance state.

11. The method of claim 8 wherein responsive to the output from the comparing circuit indicating that the temperature of the first switch is above the predetermined temperature, the driver output is a high level.

12. The method of claim 8 wherein the first switch is turned off initially to enable that the voltage at the one end of the inductive load is induced to reach or be above the predetermined value when the second switch is switch on to ground the one end of the inductive load.

13. The method of claim 8 wherein the first switch is an N-type metal-oxide-semiconductor (NMOS) transistor incorporated with a body drain diode with a diode anode connected to a source terminal of the NMOS transistor and a diode cathode connected to a drain terminal of the NMOS transistor.

14. A method for demagnetizing an inductive load, the method comprising: decoupling, via a high side switch, one end of the inductive load from a voltage source; coupling the one end of the inductive load to a first terminal of a first switch, a voltage regulator coupled between a control terminal and the first terminal of the first switch, the voltage regulator prevents current passing through when a voltage across the voltage regulator is less than a predetermined value, the first switch has a second terminal grounded; switching on a second switch, coupled to another end of the inductive load, to ground the another end of the inductive load and switching off the first switch such that a voltage at the one end of the inductive load reaches or is above the predetermined value to allow current passing through the voltage regulator and pull-up the control terminal of first switch; upon the control terminal of first switch reaching a threshold voltage, forming a current path through the second switch, the inductive load, and the first switch; and responsive to demagnetization of the inductive load transitioning into a safe demagnetization mode, generating, using a driver, a driver output to the control terminal of the first switch to switch on the first switch and cause the voltage across the voltage regulator below the predetermined value.

15. The method of claim 14 wherein voltage regulator comprises a Zener diode and a series diode coupled in series, the Zener diode has a cathode coupled to the one end of the inductive load, the series diode has opposite polarity to the Zener diode.

16. The method of claim 14 wherein transitioning into the safe demagnetization mode comprising steps of: generating, using a temperature sensor placed in proximity of the first switch, a sensed temperature signal indicating a temperature of the first switch; generating, using a comparison circuit, an output based on a comparison between the from the sensed temperature signal and a reference temperature signal representing a predetermined temperature; and responsive to the output from the comparing circuit indicating that the temperature of the first switch is above the predetermined temperature, transitioning into the safe demagnetization mode.

17. The method of claim 16 wherein in the safe demagnetization mode, the voltage at the one end of the inductive load is less than the predetermined value.

18. The method of claim 14 wherein the first switch is an N-type metal-oxide-semiconductor (NMOS) transistor incorporated with a body drain diode with a diode anode connected to a source terminal of the NMOS transistor and a diode cathode connected to a drain terminal of the NMOS transistor.

19. The method of claim 14 wherein the first switch is an N-type metal-oxide-semiconductor (NMOS) transistor, the threshold voltage is the minimum gate-to-source voltage needed to create a conducting current path between a source terminal and a drain terminal of the NMOS transistor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Reference will be made to exemplary embodiments of the present invention that are illustrated in the accompanying figures. Those figures are intended to be illustrative, rather than limiting. Although the present invention is generally described in the context of those embodiments, it is not intended by so doing to limit the scope of the present invention to the particular features of the embodiments depicted and described.

(2) FIG. 1A depicts an electrical schematic and functional block diagram of a prior art discharge circuit comprising separate clamp and switch devices for an inductor.

(3) FIG. 1B depicts a current-voltage function of the clamp of the prior art discharge circuit.

(4) FIG. 2 depicts an exemplary block diagram with a clamp and a switch integrated as one device according to various embodiments of the invention.

(5) FIG. 3 depicts an electrical schematic of a discharge circuit with clamp and switch integration according to various embodiments of the invention.

(6) FIG. 4 depicts an on-phase operation of the discharge circuit with clamp and switch integration according to various embodiments of the invention.

(7) FIG. 5 depicts a fast demagnetization operation of the discharge circuit with clamp and switch integration according to various embodiments of the invention.

(8) FIG. 6 depicts a safe demagnetization operation of the discharge circuit with clamp and switch integration according to various embodiments of the invention.

(9) FIG. 7 depicts an exemplary driver circuit for driving a switch of the discharge circuit according to various embodiments of the invention.

(10) One skilled in the art will recognize that various implementations and embodiments of the invention may be practiced in accordance with the specification. All of these implementations and embodiments are intended to be included within the scope of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(11) In the following description, for purposes of explanation, specific details are set forth in order to provide an understanding of the invention. It will be apparent, however, to one skilled in the art that the invention can be practiced without these details. Furthermore, one skilled in the art will recognize that embodiments of the present invention, described below, may be implemented in a variety of ways, such as a process, an apparatus, a system, a device, or a method on a tangible computer-readable medium.

(12) Components, or modules, shown in diagrams are illustrative of exemplary embodiments of the invention and are meant to avoid obscuring the invention. It shall also be understood that throughout this discussion that components may be described as separate functional units, which may comprise sub-units, but those skilled in the art will recognize that various components, or portions thereof, may be divided into separate components or may be integrated together, including integrated within a single system or component. It should be noted that functions or operations discussed herein may be implemented as components. Components may be implemented in software, hardware, or a combination thereof.

(13) Furthermore, connections between components or systems within the figures are not intended to be limited to direct connections. Rather, data between these components may be modified, re-formatted, or otherwise changed by intermediary components. Also, additional or fewer connections may be used. It shall also be noted that the terms “coupled,” “connected,” or “communicatively coupled” shall be understood to include direct connections, indirect connections through one or more intermediary devices, and wireless connections.

(14) Reference in the specification to “one embodiment,” “preferred embodiment,” “an embodiment,” or “embodiments” means that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention and may be in more than one embodiment. Also, the appearances of the above-noted phrases in various places in the specification are not necessarily all referring to the same embodiment or embodiments.

(15) The use of certain terms in various places in the specification is for illustration and should not be construed as limiting. A service, function, or resource is not limited to a single service, function, or resource; usage of these terms may refer to a grouping of related services, functions, or resources, which may be distributed or aggregated. The terms “include,” “including,” “comprise,” and “comprising” shall be understood to be open terms and any lists the follow are examples and not meant to be limited to the listed items.

(16) Furthermore, one skilled in the art shall recognize that: (1) certain steps may optionally be performed; (2) steps may not be limited to the specific order set forth herein; (3) certain steps may be performed in different orders; and (4) certain steps may be done concurrently.

(17) FIG. 1A depicts an electrical schematic and functional block diagram of a prior art discharge circuit 100 comprising separate clamp 110 and safe demagnetization switch 120 for an inductive load 140. The safe demagnetization switch 120 enables a low-power path only when the die temperature (T.sub.CLAMP monitored by a temperature sensor 115) has reached a predetermined level during an inductor demagnetization process. A comparing circuit 130 compares the die temperature T.sub.CLAMP to a signal T.sub.PROTECTION presenting the predetermined temperature level and outputs a signal, when T.sub.CLAMP is larger than T.sub.PROTECTION, to close the safe demagnetization switch 120 for low-power demagnetization.

(18) FIG. 1B depicts a current-voltage function of the clamp of the art discharge circuit. The clamp current/voltage characteristics are shown as a function of |V.sub.REF−V.sub.OUT|. The clamp circuit starts providing current |I.sub.OUT| when the difference |V.sub.REF−V.sub.OUT| increases above the clamp voltage. In one or more embodiments, the clamp voltage is 50V, although other values may also be used. The clamp and the switch may be made by the same transistors. During the clamp phase (or a high power demagnetization phase), the voltage drops mainly across the clamp, thus the power is dissipated mainly by clamp 110.

(19) The separation of the clamp and the safe demagnetization switch may bring some issues, including higher cost associated with separate IC packages, challenges for applications with size limitations, communication interference between the ICs, etc. Therefore, it would be desirable to integrate the clamp and the safe demagnetization switch together in one IC, or as a single element, as shown in FIG. 2, for compact circuit layout, lower cost, and/or improved adaptability for certain applications. In FIG. 2, a clamp, a switch and a temperature sensor are all integrated in one IC package to act as a clamp for fast (or high power) demagnetization of an inductive load L when the temperature of the IC package is lower than the predetermined temperature, or act as a switch for safe (or low power) demagnetization of the inductive load L when the temperature of the IC package is higher than the predetermined temperature.

(20) FIG. 3 depicts an electrical schematic of a discharge circuit 300 with clamp and switch integration to discharge an inductive load according to various embodiments of the invention. The discharge circuit 300 comprises a first discharge switch M.sub.LS1 320 including a first terminal, a second terminal and a control terminal, and a second discharge switch M.sub.LS2 324 including a first terminal, a second terminal and a control terminal. In one or more embodiments, the first discharge switch M.sub.LS1 320 is an N-type MOS transistor incorporated with a body drain diode 322 with the diode anode connected to the source terminal of the transistor and the diode cathode connected to the drain terminal of the transistor. The second discharge switch M.sub.LS2 324 is an N-type MOS transistor incorporated with a body drain diode 326 with the diode anode connected to the source terminal of the transistor and the diode cathode connected to the drain terminal of the transistor.

(21) In one or more embodiments, the inductive load 315 couples to a voltage source V.sub.DD 305 via a high side switch M.sub.HS 310 including a first terminal, a second terminal and a control terminal. The first terminal of the high side switch M.sub.HS 310 couples to the voltage supply V.sub.DD, which may be at a voltage level of 30V. The second terminal of the high side switch M.sub.HS couples to both a first end of an inductive load 315 at a node 316 (OUT) and to the first terminal of the second discharge switch M.sub.LS2. A second terminal of the second discharge switch M.sub.LS2 is grounded. The second end 317 of the load couples to the first terminal of the first discharge switch M.sub.LS1 320. A voltage regulator 318 couples between the second end 317 and the control gate of the first discharge switch M.sub.LS1 320. The voltage regulator 318 behaves as an open circuit or does not allow current passing through it when the voltage across it is below a predetermined value and allows current passing through when the voltage reaches or is above the predetermined value.

(22) In one or more embodiment, the voltage regulator 318 comprises a Zener diode 330 and a series diode 332 with opposite polarity to the Zener diode 330. The Zener diode 330 has a cathode coupled to the second end 317 of the load. The series diode 332 has a cathode coupled to the control terminal of the first discharge switch M.sub.LS1 320. By coupling the cathode of the Zener diode 330 with the load, induced voltage result from current change at the load may be more accurately reflected at the cathode of the Zener diode 330 to the inductive load 315 with minimum distortion or delay compared to alternative implementations with intermediate component(s) between the Zener diode and the load. The second terminal of the first discharge switch M.sub.LS1 320 is grounded.

(23) In one or more embodiment, a temperature sensor 334 is placed in proximity of the first discharge switch M.sub.LS1 320 to sense a temperature of the first discharge switch M.sub.LS1 320. A comparing circuit 340 receives a reference temperature signal T.sub.PROTECTION at a negative input and a sensed temperature signal T.sub.MLS1 from the temperature sensor 340 at a positive input. In one or more embodiments, the comparing circuit 340 uses hysteresis. An output 342 of the comparing circuit 340 is fed to a driver circuit 350. The driver circuit 350 couples to the control gate of the first discharge switch M.sub.LS1 320 for ON/OFF control of the first discharge switch M.sub.LS1.

(24) During fast demagnetization, a clamp may be formed by the first discharge switch M.sub.LS1, the Zener diode, and the temperature sensor. During safe demagnetization, the safe demagnetization switch is implemented by the first discharge switch M.sub.LS1 and the second discharge switch M.sub.LS2. Details of the fast demagnetization and safe demagnetization are described with respect to FIG. 5 and FIG. 6 respectively.

(25) Referring now to FIG. 4 for an on-phase operation of the discharge circuit 300 according to various embodiments of the invention, the second discharge switch M.sub.LS2 is initially turned off, the high side switch M.sub.HS and the first discharge switch M.sub.LS1 are turned on to enable a current (e.g., 1 A) through the inductive load 315. Little power is dissipated inside the die due to the low on-resistance of M.sub.LS1 (e.g., R.sub.MLS1=0.1Ω), a state when the switch M.sub.LS1 is switched on by a high output (e.g., 5V) at the control gate as shown in FIG. 4. In one or more embodiments, during the ON phase, the first discharge switch M.sub.LS1 is actively turned on through the driver independently from the comparator 340. In one or more embodiments, the high side switch M.sub.HS may be a P- or N-type transistor controlled with pulse width modulation (PWM) in junction with the second discharge switch M.sub.LS2.

(26) Referring now to FIG. 5, during a fast demagnetization operation of the discharge circuit 300, the high side switch M.sub.HS 310 is tuned off and the second discharge switch M.sub.LS2 324 is turned on. The first discharge switch M.sub.LS1 320 is turned off initially in the beginning of the fast demagnetization. The current at the inductive load is assumed as 1 A when the demagnetization starts. Since the inductor current cannot be stopped while it is flowing, with the initial 1 A current and current flow through the second discharge switch M.sub.LS2 324, the node OUT 316 (first end of the load) has a potential pulled from around 30V as shown in FIG. 4 to −0.1V (assuming R.sub.MLS2=0.1Ω, V.sub.OUT=0−0.1Ω×1 A=−0.1V).

(27) However, with the decreasing tendency of the current flow, the inductive load generates an inductive potential across the load. Since the potential of the first end 316 is fixed at −0.1V after the second discharge switch M.sub.LS2 324 switched on, the potential on the second end 317 is pushed high immediately. Once the potential at the second end 317 is beyond a predetermined level of the voltage regulator 318 (e.g., a sum of the breakdown voltage or Zener voltage of the Zener diode 330, voltage drop on diode 332, and the voltage VGS of the transistor 320), the Zener diode 330 starts to conduct current, which flows through diode 332 and in turns pulls-up the gate of first discharge switch M.sub.LS1 320. Once the gate-source voltage of the first discharge switch M.sub.LS1 320 reaches the threshold voltage of the FET (e.g., 1.5V), the first discharge switch M.sub.LS1 320 starts to conduct current I.sub.LOAD, thus stopping voltage at the second end 317 from raising further. The threshold voltage of the FET is the minimum gate-to-source voltage VGS needed to create a conducting current path between the source and drain terminals of the FET. A current path 360 is therefore formed through the second discharge switch M.sub.LS2 324, the inductive load 315, and the first discharge switch M.sub.LS1 320.

(28) The potential at the second end 317 is maintained at the predetermined level, which may be determined by the choosing desired Zener diode, series diode and transistor. Furthermore, the diode 322 incorporated with the first discharge switch M.sub.LS1 320 has its anode coupled to the second end 317. Such an arrangement also ensures that the potential at the second end 317 is maintained at the predetermined level during the fast demagnetization. For the embodiment shown in FIG. 4, the Zener voltage of the Zener diode is 50V. Assuming a gate-source voltage 1.5V required to have 1 A flowing through the switch M.sub.LS1 and a 0.5V forward bias voltage for the diode 332, the predetermined level is set at 52V. Such a 52V voltage applied on the second end 317 pulls down the current at the inductive load quickly and thus fast demagnetization is achieved.

(29) At the same time, given the 52V voltage on the first terminal of the first discharge switch M.sub.LS1 320 and the 1 A initial current, the initial power dissipation for the first discharge switch M.sub.LS1 320 is P.sub.MLS1=52V×1 A=52 W. Such high power dissipation causes the temperature of M.sub.LS1 320 going up quickly.

(30) In one or more embodiment, the temperature of M.sub.LS1320 is monitored by a temperature sensor integrated within the same IC package for the discharge circuit and placed in proximity of the first discharge switch M.sub.LS1 320. Once the temperature of the first discharge switch M.sub.LS1 reaches T.sub.PROTECTION, operation of the discharge circuit transitions to the safe demagnetization mode.

(31) FIG. 6 depicts a safe demagnetization operation of the electrical schematic of the discharge circuit with clamp and switch integration according to various embodiments of the invention. The comparing circuit 340 receives a reference temperature signal T.sub.PROTECTION at a negative input and a sensed temperature signal T.sub.MLS1 from the temperature sensor 340 at a positive input. In one or more embodiments, the comparing circuit 340 uses hysteresis. Upon the measured temperature T.sub.MLS1 reaches T.sub.PROTECTION, the comparing circuit 340 generates an output 342 to the driver circuit 350. In one or more embodiments, the output 342 is a high output when the measured temperature T.sub.MLS1 reaches T.sub.PROTECTION. Upon receiving the high output 342, the driver circuit 350 pushes the control gate of the first discharge switch M.sub.LS1 320 to a high level (e.g., 5V), which causes the voltage across the Zener diode 330 below its Zener voltage (e.g., 50V) and therefore pulls down the voltage level at the first terminal of the first discharge switch M.sub.LS1 320 to a level (e.g., 0.1V) much less than the predetermined level of 52V. During the safe demagnetization, a current path 370 is still through the second discharge switch M.sub.LS2 324, the inductive load 315, and the first discharge switch M.sub.LS1 320, but at a less value since the current in the inductive load has been pulled down during the fast demagnetization. The amount of current drop depends on how large the inductor is and how long the fast demagnetization lasts before the temperature rises to the threshold temperature. Given the decreased current through the switch M.sub.LS1 320 and a much reduced voltage level at the second end 317, power dissipation for the switch M.sub.LS1 320 during the safe demagnetization is significantly less, therefore, the temperature of the switch M.sub.LS1 320 decreases.

(32) In one or more embodiments, the comparing circuit 340 uses hysteresis. Once the temperature of the switch M.sub.LS1 320 decreases below T.sub.PROTECTION by a hysteresis amount, comparing circuit 340 outputs a low signal to cause the switch M.sub.LS1 320 away from a low on-resistance (e.g., 0.1Ω) state, and thus the discharge circuit returns to the fast demagnetization.

(33) FIG. 7 depicts an exemplary driver circuit for driving a switch of the discharge circuit according to various embodiments of the invention. The exemplary drive 350 comprises an inverter 354, a push-pull driver 356 having a P-channel and an N-channel complementary metal-oxide-semiconductor (CMOS) transistors, and a resistor 358 coupled in series. When the measured temperature T.sub.MLS1<T.sub.PROTECTION, the driver input 342 (from the comparing circuit 340) is low and the driver output 352 from the driver circuit 350 is low. During fast demagnetization, although the output of the push-pull driver is low, the gate of the switch M.sub.LS1 is pulled up by the Zener diode and maintained at the desired voltage (e.g., 1.5V) due to the existence of the resistor 358. When the measured temperature T.sub.MLS1>T.sub.PROTECTION, the INPUT 342 from the comparing circuit 340 becomes high and the OUTPUT 352 from the driver circuit 350 transits to high also.

(34) It will be appreciated to those skilled in the art that the preceding examples and embodiments are exemplary and not limiting to the scope of the present disclosure. It is intended that all permutations, enhancements, equivalents, combinations, and improvements thereto that are apparent to those skilled in the art upon a reading of the specification and a study of the drawings are included within the true spirit and scope of the present disclosure. It shall also be noted that elements of any claims may be arranged differently including having multiple dependencies, configurations, and combinations.