CN1985431A

CN1985431A - Method and apparatus for driving a power MOS device as a synchronous rectifier

Info

Publication number: CN1985431A
Application number: CN 200380102332
Authority: CN
Inventors: B·C·那达; X·德富如特斯; A·墨瑞尔
Original assignee: International Rectifier Corp USA
Current assignee: Infineon Technologies Americas Corp
Priority date: 2002-10-11
Filing date: 2003-10-14
Publication date: 2007-06-20

Abstract

A synchronous rectifier comprising a MOSFET device, and a gate driver for driving the gate of the MOSFET device, the MOSFET device comprising first and second MOSFET transistors coupled with their drain-source paths in parallel to receive an alternating current waveform for rectification by the drain- source paths of the MOSFET transistors, the first transistor having a low Rdson and the second transistor having a high Rdson whereby the apparent Rdson of the MOSFET device is increased when the current through the MOSFET device is below a threshold thereby enabling zero crossing detection.

Description

Be used to drive method and apparatus as the power MOS (Metal Oxide Semiconductor) device of synchronous rectifier

Cross reference to related application

The application's requirement was submitted on October 11st, 2002, exercise question is the U.S. Provisional Application S.N.60/418 of " Improved Methodto Drive a Power MOS Device As a Synchronous Rectifier ", 417 rights and interests and priority are incorporated its whole disclosed contents into the application by reference at this.

Technical field

The present invention relates to be used for the method and apparatus of driving power semiconductor device, relate in particular to the method and apparatus that is used to drive as the power MOS (Metal Oxide Semiconductor) device of synchronous rectifier.

Background technology

Be subjected to the driving that increases day by day for the demand of raising the efficiency, and that it is become is feasible owing to the validity of ultralow Rdson (conducting resistance) power MOSFET, in low pressure applications, replace PN or Schottky rectifier diode to catch on MOSFET.A typical example is a motor vehicle alternator.By replacing diode rectifier bridge (it descends above two volts) with the MOSFET that suitably drives, people can improve 10% to 15% to total alternative electric generation engine efficiency.Fig. 1 has shown so a kind of prior art systems, and it uses MOSFET to replace diode.

For a kind of like this designer of system, one of problem is to find the mode of a kind of FET of driving, and it imitates the performance of diode, but does not have the limitation of diode.

An object of the present invention is to provide the mode that drives rectification MOSFET, it is not subjected to the limitation of prior art.

Fig. 2 comprises Fig. 2 A to 2C, has shown the mode of the synchronous rectifier MOSFET shown in a kind of known execution graph 1.

Fig. 2 A has shown the principle of this circuit, and it has shown a MOSFET; Fig. 2 B has shown the Id that shows with the chart static state operation than Vds; Fig. 2 C has shown the waveform of the circuit of Fig. 2 A.

When Vds is timing, the body diode of FET20 is back-biased, and MOSFET closes.The working point is the section 3 of Fig. 2 B.If an AC waveform is loaded on this device, the working point will finally reach the point 1 of Fig. 2 B, and Vds=-Von there satisfies condition.As a result, the output of Schmidt trigger 10 will be increased, and power MOSFET 20 is connected.The section 4 of Fig. 2 B is shifted in the working point.Final AC waveform just becomes, and the working point reaches a little 2.Vds＞the Voff that satisfies condition, and the Schmidt trigger will cut out power MOSFET.

The practical application of sort circuit is difficult to realize, because in the very big environment of common noise, must control threshold value tightly, needs low-down offset comparator.In a typical case uses,, the MOSFET of 1 milliohm will be used for the electric current about 100A.The result is that 1 millivolt skew will produce undesirable 1A negative current at point 2 places.The designer that has its source in of this problem attempts to reproduce a current over-zero by the voltage that one of sensing has device two ends of almost nil dead resistance and detects.

Therefore, the purpose of this invention is to provide a kind of improved circuit and method that is used to operate as the power MOS (Metal Oxide Semiconductor) device of synchronous rectifier.

Summary of the invention

According to the present invention, the MOS device comes work as synchronous rectifier, and and if only if electric current when low, the apparent of power MOS (Metal Oxide Semiconductor) device (apparent) Rdson increases artificially, causes zero cross detection to become simple.According to an embodiment, power MOSFET is a Darlington, and it is made up of a small transistor and the megacryst pipe with low Rdson with high Rdson.

In another embodiment, the grid of an operational amplifier driven MOS FET, this operational amplifier has an offset reference voltage at input end, causes the relation curve of drain electrode-source current and drain electrode-source voltage to have a threshold value, and it allows current over-zero to detect.

From following detailed, other target of the present invention, feature and advantage will become clearly.

Description of drawings

With reference to accompanying drawing, in being described in detail later, will the present invention be described in more detail, wherein:

Fig. 1 has schematically shown the execution mode of the synchronous rectifier of a known output that is used for the rectification alternating current generator;

Fig. 2 comprises Fig. 2 A, 2B and 2C, has shown that known being used to drives the execution mode of the MOSFET of this synchronous rectifier, a chart that is used for the electric current I d of synchronous rectifier than Vds; With one show Id, Vds, Vgs chart than the time;

Fig. 3 has shown according to a circuit of the present invention;

Fig. 4 comprises Fig. 4 A and 4B, has shown the waveform of Fig. 3;

Fig. 5 comprises Fig. 5 A, 5B and 5C, has shown further execution mode, comprises that Vds is than the chart of Id and Id, Vds, the Vgs waveform than the function of time;

Fig. 6 is a circuit diagram, and it has shown according to close loop maneuver of the present invention; With

Fig. 7 is a schematic diagram in a circuit according to the invention.

Embodiment

Referring now to accompanying drawing, the present invention is described in more detail.Fig. 3 has shown an enforcement circuit of the present invention.The operation of the circuit that shows among Fig. 3 is as follows: the power MOSFET transistor 200 according to Fig. 3 comprises the first device 200A and the second gadget 200B.The grid of the one Schmidt trigger 100A driving element 200A, the grid of the 2nd Schmidt trigger 100B driving element 200B.If an AC waveform is loaded into the drain electrode-source path of the device that is used for rectification, the working point will finally reach the point 1 shown in Fig. 4 A, and Vds=-Von1 there satisfies condition.As a result, the output of Schmidt trigger will be increased, and MOSFET200B will connect.If the electric current increase is enough to reach the point 5 of Fig. 4 A, main power MOSFET 200A also will connect.Cause the point 6 that reaches Fig. 4 A when electric current reduces, main power MOSFET 200A gets back to closed condition.Finally, the AC waveform will just become, and the working point will reach the point 2 of Fig. 4 A.Vds＞the Voff that satisfies condition, and the Schmidt trigger will cut out power MOSFET (MOSFET200B becomes disconnection) fully.The reverse current at point 2 places is Voff/Rdson1, rather than as Voff/Rdson of the prior art.By suitably selecting FETM and M1, can improve reverse current significantly, perhaps can select the voltage of higher thresholds.In many application, can place M and M1 concurrently to carry out several transistors.

Fig. 5 A has shown another embodiment, and the transistorized grid of driving power in a closed-loop path wherein causes near zero, and the Id/Vds curve has been showed a threshold value, and it makes and is easy to detect zero current cross and almost without any skew.In this embodiment, operational amplifier 300 driven MOS FET200.When the voltage on the Vds of Fig. 5 A (section 3) becomes when negative, shown in section 2, (see Fig. 5 B), Vgs begins to increase with conservation condition Vds=Vf1.Finally, operational amplifier will be saturated in zone 1, and power MOSFET will be connected fully.The Vds at power MOSFET two ends will increase once more along with the electric current in the section 1.When electric current reduces and Vds when falling back Vf1 once more, operational amplifier will keep Vds to be in Vf1 equaling 0 up to Vgs, and Vds will increase once more thereafter, shown in section 3.With a big offset comparator cheapness, that implement easily, can carry out zero current detection easily now.

Referring now to Fig. 6, show a Vds voltage control loop 60.Control loop 60 driven MOS FET62 and cause its simulation ideal diode.Control loop 60 has been described a common servo loop, and it has a summator 66, an optional correcting circuit 67 and a booster element 68.Summing junction 66 places+and-homophase and the paraphase input of sign expression operational amplifier 300 (Fig. 5 A).Correcting circuit 67 is frequency compensation network, and according to the classical system control theory, its operation is to obtain a suitable balance between dynamic response, stability and permanent error.Correcting circuit 67 is chosen wantonly, because the operational amplifier model is available, utilizes closed-loop control to merge employed internal compensation usually.

The feature that the operation of closed-loop control 60 provides is approximately-20 millivolts the voltage drop that keeps power MOSFET 62 two ends.Control loop 60 is promptly used the grid of closed loop feedback driven MOS FET62 according to principle operation, to keep the Vds voltage constant about-20 millivolts of benchmark 64.When Vds is timing, MOSFET62 closes, and the operation by control loop 60, and when Vds becomes when negative, MOSFET62 connects fully.Control loop 60 is simple close-loop feedback control systems, and it provides a linear Feedback Control.According to the control that control loop 60 provides, the operation of MOSFET62 obtains synchronous rectification, and wherein MOSFET62 occurs as an ideal diode with smooth operation.Control loop 60 provides the operation of MOSFET62, causes as MOSFET62 and limits (Fig. 5 B) when operation at a reversed image, and MOSFET62 has a homophase Vds/Vgs gain.It is level and smooth and stable that the parameter of MOSFET62 is changeed, and causes and greatly reduced the EMI interference, thereby provide tangible operation to strengthen.When the Vds voltage drop surpassed the value of benchmark 64, control loop 60 guaranteed that MOSFET62 remains on complete on-state.

Referring now to Fig. 7, a schematic diagram is shown generically circuit 70 according to an embodiment of the invention.Circuit of synchronous rectification 70 is provided for MOSFET75,77 Vds voltage control based on a little negative voltage benchmark 71.The closed-loop control that circuit 70 provides preferably has a linear gain, and provides a suitable Closed loop Control to guarantee MOSFET75, ideal diode of 77 simulations.MOSFET75,77 is shown as operation repetitive, but can merge into an independent MOS device, for example, has an independent grid control.

In the severe rugged environment that is subjected to high EMI or noise jamming, can revise the circuit of illustrating among Fig. 7, to have improved dv/dt vulnerability to jamming.For example, can provide a Vgs comparator, when grid voltage is lower than the MOSFET threshold value,

grid

74,76 be foreshortened to source electrode 78,79.The fixed voltage value that the Vgs comparator is lower than MOSFET75,77 threshold voltage with the value of Vgs and one relatively.When the electric current among the MOSFET75,77 near zero the time, closed-loop control is tended to move

grid

74,76 to zero, equals desired value because closed-loop control is attempted Vds voltage remained on.The Vgs comparator produces the logical signal that an indication Vgs has low voltage value.This logical signal as a safety value, with by connecting the low impedance path between

grid

74,76 and the

source electrode

78,79, is avoided in noisy environment MOSFET75,77 wrong conducting (false conduction).

Because circuit 70 is simple and compact, carry out the employed element of this Closed loop Control and can open in 75,77 minutes with power MOSFET, or directly be embedded in MOSFET75, in 77 as their part of controlled function.For example, circuit 70 can be integrated in the element that comprises power MOSFET 75 and/or 77.By a closed-loop control is provided, the present invention has eliminated vibration, and this vibration may cause owing to unsteadiness or the inconsistency in the Vds voltage threshold, for example, can be caused by manufacturing tolerance.Therefore, even in check MOSFET has different threshold values or owing to change in the component tolerances operation, closed-loop control also can be eliminated according to the operation in the synchronous rectifier of embodiments of the invention operation and change.By better closed-loop characteristic is provided, it is more level and smooth that Vds becomes, thereby improved element EMI performance.

Although described the present invention, yet to those skilled in the art, much other change and modification and other application will become clearly with reference to specific embodiment wherein.Therefore, the present invention should specificly from here openly not limit, and should be limited to the appended claims.

Claims

1. synchronous rectifier comprises:

A MOSFET device; With

A gate drivers, be used to drive the grid of this MOSFET device, this MOSFET device comprises first and second mosfet transistors that couple, drain electrode-the source path of first and second mosfet transistors is parallel to receive the ac power waveform that is used for rectification with the drain electrode-source path by mosfet transistor, the first transistor has a low on-resistance, transistor seconds has a high conducting resistance, by this, when the electric current that flows through this MOSFET device is lower than a threshold value, the apparent conducting resistance of this MOSFET device increases, thereby realizes zero passage detection.

2. synchronous rectifier as claimed in claim 1, wherein this gate drivers comprises a Schmidt trigger, this Schmidt trigger output is couple to the grid of MOSFET device, and the input of Schmidt trigger is couple to the two ends of drain electrode-source path of MOSFET.

3. synchronous rectifier as claimed in claim 2, wherein this Schmidt trigger comprises two Schmidt triggers, a first transistor that is used to have low on-resistance, another is used to have the transistor seconds of high conducting resistance.

4. synchronous rectifier as claimed in claim 2, wherein the input of this Schmidt trigger is couple to the two ends of the drain electrode-source voltage of MOSFET device.

5. synchronous rectifier, comprise: a power MOS (Metal Oxide Semiconductor) device and an amplifier that drives the grid of this power MOS (Metal Oxide Semiconductor) device, this amplifier has second input that is couple to the drain electrode or one the first input end in the source electrode of this power MOS (Metal Oxide Semiconductor) device and is couple to reference voltage, this reference voltage is couple between the drain electrode of second input and this power MOS (Metal Oxide Semiconductor) device or in the source electrode another, by this, when the drain electrode-source voltage at MOSFET two ends during near reference voltage, amplifier will drain-and source voltage remains on reference voltage and is approximately equal to zero up to grid-source voltage, thereby can realize that zero current cross detects by enough offset comparators.

6. a driving comprises as the method for the MOSFET of synchronous rectifier:

When the electric current of drain electrode-source path of the MOSFET that flows through was lower than a threshold level, the apparent that increases MOSFET drained to source on-state resistance (Rdson), thereby realized zero passage detection.

7. method as claimed in claim 6 further comprises: two MOSFET that drain electrode-source path is parallel are provided, and a MOSFET has high conducting resistance, and another has low on-resistance.

8. method as claimed in claim 7, further comprise: the voltage at the drain electrode of sense MOSFET-source path two ends, at first connect MOSFET, and when the electric current increase is opened threshold level above one, connect MOSFET with low on-resistance with high conducting resistance.

9. method as claimed in claim 8 further comprises: is lower than one when closing threshold level when electric current reduces, disconnects MOSFET with low on-resistance, and thereafter when electric current further reduces, the MOSFET that disconnection has high conducting resistance.

10. method as claimed in claim 9, wherein opening threshold level is different with closing threshold level.

11. method as claimed in claim 6, wherein drain electrode-source voltage is fully constant to be similar to zero up to grid-source voltage to keep by an offset voltage is provided, and increases apparent drain electrode-source on-state resistance when being lower than the current level of described threshold level.

12. a method that is used to drive as the power MOSFET of synchronous rectifier comprises:

Couple the first and second parallel MOSFET devices of drain electrode-source path, to receive the ac power waveform that is used for rectification by this drain electrode-source path, the one MOSFET has a low on-resistance, the 2nd MOSFET has a high conducting resistance, by this, when the electric current that flows through this MOSFET is lower than a threshold value, thereby the apparent conducting resistance of these two parallel MOSFET increases the realization zero passage detection.

13. method as claimed in claim 12, further comprise: the input that couples the Schmidt trigger, wherein the output of this trigger is couple to the grid of MOSFET, and the drain electrode-source voltage at sense MOSFET two ends switches on and off first and second MOSFET to determine when.

14. method as claimed in claim 13 comprises two Schmidt triggers are provided, a MOSFET who is used to have low on-resistance, and another is used to have the 2nd MOSFET of high conducting resistance.

15. method that is used to drive the synchronous rectifier that comprises power MOS (Metal Oxide Semiconductor) device, method comprises: the amplifier that the grid of a driving power MOS device is provided, this amplifier has second input that is couple to the drain electrode or one the first input end in the source electrode of this power MOS (Metal Oxide Semiconductor) device and is couple to reference voltage, this reference voltage is couple between the drain electrode of second input and this power MOS (Metal Oxide Semiconductor) device or in the source electrode another, when the drain electrode-source voltage at MOSFET two ends during near reference voltage, to drain-source voltage remains on the reference voltage place and is approximately equal to zero up to grid-source voltage, thus the enough offset comparators of energy realize that current over-zero detects.

16. a synchronous rectifier comprises:

A MOSFET device that is used to provide the rectification operation;

One is couple to the drain electrode of this MOSFET device and at least one the feedback signal in the source electrode;

A control circuit, described control circuit are couple to described feedback signal and a grid control signal operationally are provided;

This grid control signal is loaded into a grid of this MOSFET device, and operationally keeps the rectification operation; With

A reference voltage that is couple to control circuit, this control circuit is used for closed-loop control is worked, by this ideal diode of MOSFET device imitation.

17. synchronous rectifier as claimed in claim 16, wherein said control circuit and reference voltage are integrated in the common elements that has a MOSFET device.

18. one kind is used to control MOSFET Vds voltage method, comprises:

Obtain a voltage reference, this voltage reference works to providing to the control signal of MOSFET;

Operate a closed-loop control that combines with described reference voltage so that described control signal is offered MOSFET;

With the described closed-loop control that a feedback offers, the Vds voltage of controlling MOSFET by this is to simulate an ideal diode based on a MOSFET parameter.

19. method as claimed in claim 18 further comprises with described closed-loop control a linear gain is provided.

20. method as claimed in claim 18, further comprise reduce with the Vds voltage threshold in the relevant sensitivity of variation.