CN103391016B - MOSFET synchronous rectification circuit directly connected in parallel with output capacitor and synchronous rectification method - Google Patents

Abstract

The invention discloses an MOSFET (Metal Oxide Semiconductor Field Effect Transistor) synchronous rectification circuit directly connected in parallel with an output capacitor. The MOSFET synchronous rectification circuit comprises a rectification circuit part comprising MOSFETs, wherein the rectification circuit part comprising the MOSFETs comprises two one-way switch valves and two two-way switch valves used for current flowing; the one-way switch valves comprises the MOSFETs and driving circuits A; the driving circuits A comprise MOSFET detection networks; the MOSFET detection networks comprise current sources; input ends of the MOSFET detection networks are connected with voltage input ends; one end of each resistor is connected with each input end of each MOSFET detection network; the other end of each resistor is connected with each output end of each MOSFET detection network; the current sources and voltage stabilizing tubes are connected with the resistors; voltage comparators comprise reference voltage; the reference voltage is connected with anode input ends of the comparators; the output ends of the MOSFET detection networks are connected with cathode input ends of the comparators; output ends of the comparators are connected with input ends of drivers; the drivers are connected with grid electrodes of the MOSFETs; and the current sources are generated by externally connecting external resistors with the reference voltage.

Description

The MOSFET circuit of synchronous rectification directly in parallel with output capacitance and synchronous rectification method

Technical field

The invention belongs to electronic technology field, it is related to circuit of synchronous rectification, it is more particularly related to one kind is used for Inexpensive circuit of synchronous rectification that can be directly in parallel with output filter capacitor, MOSFET that is, directly in parallel with output capacitance is synchronous Rectification circuit and method.

Background technology

It is necessary first to the exchange of input is changed into directly by a bridge rectifier in the application of low-voltage, high-current alternating current-direct current Stream；During exchange is changed into direct current, the loss of bridge rectifier is to reduce whole system efficiency major factor；As usual The input voltage of bridge rectifier is 6V, and the voltage drop at bridge rectifier two ends is about 1.5V, that is, pass through bridge rectifier Potential loss afterwards can reach 25%.In order to reduce loss, find in research, by using Schottky diode, can be by Loss reduces by 50% about, and using the synchronous rectification bridge with MOSFET as shown in Figure 1, then can drop loss further Low (being reduced to almost nil degree), so that the efficiency of system greatly improves.

MOSFET synchronous rectification bridge as shown in Figure 1 is made up of two P-channel MOSFET and two N-channel MOS FET, with Upper described four MOSFET (two P-channel MOSFET and two N-channel MOS FET) are by the exchange of MOSFET synchronous rectification bridge Input drives.This kind of MOSFET synchronous rectification bridge circuit structure very simple, and with low cost, and can be in relatively wide input Use in voltage range.

But the output of such MOSFET synchronous rectification bridge can not be directly in parallel with output filter capacitor.Specifically, exist In such MOSFET synchronous rectification bridge, the effect of MOSFET is the two-way switch valve of the exchange input control of synchronous rectification bridge, and It is not intended to the one-way on-off valve of electric current flowing；Therefore, output filter capacitor can return to the reverse input current of synchronous rectification bridge It is fed to exchange input or by MOSFET short circuit；Due to above-described defect, the output that result in such circuit power application must Must be inductance or resistance；And limit the application in many occasions for such circuit.

Content of the invention

The technical problem to be solved in the present invention is to provide a kind of MOSFET synchronous rectification electricity directly in parallel with output capacitance Road and method.

In order to solve above-mentioned technical problem, the present invention provides a kind of MOSFET synchronous rectification directly in parallel with output capacitance Circuit, including the rectification circuit including MOSFET composition；The rectification circuit that described MOSFET is constituted includes two for electric current The one-way on-off valve of flowing and two two-way switch valves.

Improvement as the MOSFET circuit of synchronous rectification directly in parallel with output capacitance to the present invention：Described unidirectional open Close valve and pass through MOSFET and drive circuit A composition；Described drive circuit A include MOSFET detection network that signal successively connects, Level comparator and driver；Described MOSFET detection network includes current source, resistance and stabilivolt；MOSFET detects network The voltage input end of the rectification circuit that input is constituted with MOSFET is connected, and network is detected with MOSFET in one end of described resistance Input be connected, the other end of described resistance and MOSFET detect that the outfan of network is connected, described current source and The outfan that stabilivolt detects network in MOSFET respectively is connected with resistance；Described voltage comparator includes reference voltage and ratio Compared with device；Described reference voltage is connected with the electrode input end of comparator；Described MOSFET detects the outfan of network and compares The negative input of device is connected；The outfan of described comparator is connected with the input of driver；Described driver defeated Go out end to be connected with the grid of MOSFET；Described current source passes through external outer meeting resistance on reference voltage and produces.

A kind of method of the MOSFET circuit of synchronous rectification directly in parallel with output capacitance：The rectification circuit that MOSFET is constituted Voltage input end to MOSFET detect network inputs input voltage vin；Described MOSFET detection network output output voltage V_O； Described output voltage V_OIt is input to voltage comparator；Voltage comparator passes through output voltage V_OIt is compared with reference voltage Vref Outputs level signals afterwards；Described driver controls turning on and off of MOSFET according to the level signal that voltage comparator exports.

Improvement as the method for the MOSFET circuit of synchronous rectification directly in parallel with output capacitance to the present invention：When defeated Enter voltage Vin and be more than voltage stabilizing tube voltage V_CLAMPWhen, MOSFET detects the output voltage V of network_OIt is V_CLAMP；Work as input voltage vin Less than voltage stabilizing tube voltage V_CLAMPWhen, MOSFET detects the output voltage V of network_O=I_SS×R_DET+V_DS；Described V_DSFor MOSFET work When making in synchronous rectification state, the electric current I that MOSFET is flow through_DSConducting resistance R in MOSFET_DSONOn voltage drop；Described Electric current I_DSFor negative value, described voltage drop V_DS<0.

Improvement as the method for the MOSFET circuit of synchronous rectification directly in parallel with output capacitance to the present invention：Described Output voltage V_OMore than reference voltage Vref, comparator exports low level；Described reference voltage Vref is more than output voltage V_O, than Export high level compared with device.

Improvement as the method for the MOSFET circuit of synchronous rectification directly in parallel with output capacitance to the present invention：Described Low level exports the grid of MOSFET so that MOSFET turns off through driver；Described high level exports through driver The grid of MOSFET is so that MOSFET keeps open-minded.

Improvement as the method for the MOSFET circuit of synchronous rectification directly in parallel with output capacitance to the present invention：When When MOSFET turns off, flow through the body diode of the current commutation of MOSFET to MOSFET；The electricity of the body diode of described MOSFET When stream is zero, the voltage drop V of MOSFET_DSIncrease；The voltage drop V of described MOSFET_DSMore than voltage stabilizing tube voltage V_CLAMPWhen, MOSFET detects the output voltage V of network_OFor voltage stabilizing tube voltage V_CLAMP.

In existing MOSFET synchronous rectification bridge, because the effect of four MOSFET is all to be exchanged by synchronous rectification bridge Two-way switch valve rather than the one-way on-off valve for electric current flowing that input controls, the output of MOSFET synchronous rectification bridge can not Directly in parallel with output filter capacitor.So in the present invention MOSFET circuit of synchronous rectification directly in parallel with output capacitance and In method, in four MOSFET, employ the structure that two MOSFET are controlled the one-way on-off valve for electric current flowing, If two P-channel MOSFET are the structural grouping of one-way on-off valve, a P-channel MOSFET and a N-channel MOS FET are single To the structural grouping of switch valve, or two N-channel MOS FET are the structural grouping of one-way on-off valve；Such structural grouping makes MOSFET synchronous rectification bridge can be directly in parallel with output filter capacitor, the MOSFET synchronous rectification bridge output of this structural grouping Electric capacity is not to the path of the reverse input current of synchronous rectification bridge；That is, by four kinds of following combinations are formed one being MOSFET synchronous rectification bridge can directly in parallel with output filter capacitor (output capacitance be without reverse to this synchronous rectification bridge for row The path of input current), four kinds of combinations are as follows：

The first combines (as shown in Figure 4)：Two P-channel MOSFET are the structure of two-way switch valve, two N-channel MOSFET is the structural grouping of one-way on-off valve；

Second combines (as shown in Figure 5)：Two P-channel MOSFET are the structure of one-way on-off valve, two N-channel MOSFET is the structural grouping of two-way switch valve；

The third combines (as shown in Figure 2)：An one P-channel MOSFET and N-channel MOS FET is one-way on-off valve Structure, a P-channel MOSFET and N-channel MOS FET be the structural grouping of two-way switch valve；

4th kind of combination (as shown in Figure 3)：An one P-channel MOSFET and N-channel MOS FET is one-way on-off valve Structure, a P-channel MOSFET and N-channel MOS FET be the structural grouping of two-way switch valve；

Obviously in the structural grouping of above-described two-way switch valve, drive circuit is made up of resistance and stabilivolt, becomes This is cheap；But in the structural grouping of above-described one-way on-off valve, drive circuit typically by extra drive circuit A or Corresponding integrated circuit A is constituted；And adopt the cost affirmative ratio resistance of extra drive circuit A and the driving electricity of stabilivolt composition The cost on road will height.But in the present invention, due to employing two two-way switch valves and two one-way on-off valve combine Compound mode (specifically four kinds of combinations as described above), had both remained the driving of resistance and stabilivolt composition in two-way switch valve Circuit, increased by the one-way on-off valve forming based on extra drive circuit A, so having reached cost-effective mesh again (especially under wide input voltage application conditions).

Brief description

Below in conjunction with the accompanying drawings the specific embodiment of the present invention is described in further detail.

Fig. 1 is the structural representation of existing MOSFET synchronous rectification bridge；

Fig. 2 is a kind of MOSFET circuit of synchronous rectification structural representation directly in parallel with output capacitance of the present invention；

Fig. 3 is MOSFET circuit of synchronous rectification another structural representation directly in parallel with output capacitance of the present invention Figure；

Fig. 4 is a kind of MOSFET circuit of synchronous rectification directly in parallel with output capacitance still further structural representation of the present invention Figure；

Fig. 5 be the present invention the MOSFET circuit of synchronous rectification directly in parallel with output capacitance again still further a kind of structure show It is intended to；

Fig. 6 present invention is used for the structural representation of the drive circuit A of one-way on-off valve of electric current flowing；

Fig. 7 present invention is used for the input of the MOSFET detection network 100 of the drive circuit A of one-way on-off valve of electric current flowing V_INOutput V_OGraph of a relation；

Fig. 8 is the concrete structure schematic diagram of the drive circuit A of the one-way on-off valve that the present invention is used for electric current flowing.

Specific embodiment

Fig. 1～Fig. 8 gives a kind of MOSFET circuit of synchronous rectification directly in parallel with output capacitance and method.

By the research discovery to MOSFET synchronous rectification bridge, in MOSFET synchronous rectification bridge (as shown in Figure 1), because Four MOSFET are that to be exchanged, by synchronous rectification bridge, two-way switch valve that input controls (rather than unidirectional for electric current flowing Switch valve), so the output of MOSFET synchronous rectification bridge can not be directly in parallel with output filter capacitor.

But when two MOSFET in four MOSFET are controlled the one-way on-off valve for electric current flowing, MOSFET synchronous rectification bridge just can be directly in parallel with output filter capacitor, because (i.e. four, this MOSFET synchronous rectification bridge Two MOSFET in MOSFET are controlled the one-way on-off valve for electric current flowing) output capacitance not to this The path of the reverse input current of MOSFET synchronous rectification bridge.

Embodiment 1, a kind of MOSFET circuit of synchronous rectification directly in parallel with output capacitance, whole including MOSFET composition Current circuit；The rectification circuit constituting in MOSFET includes two one-way on-off valve for electric current flowing and two two-way switch Valve.

Above-described one-way on-off valve is passed through MOSFET and drive circuit A and is constituted；Drive circuit A includes signal successively and connects MOSFET detection network (100), level comparator (200) and the driver (300) connecing；MOSFET detection network (100) includes Current source, resistance and stabilivolt；MOSFET detects that the voltage of the rectification circuit that the input of network (100) is constituted with MOSFET is defeated Enter end to be connected, one end of resistance and MOSFET detect that the input of network (100) is connected, the other end of resistance with MOSFET detects that the outfan of network (100) is connected, and current source and stabilivolt detect the defeated of network (100) in MOSFET respectively Go out end to be connected with resistance；Voltage comparator (200) includes reference voltage and comparator；Reference voltage is defeated with the positive pole of comparator Enter end to be connected；MOSFET detects that the outfan of network (100) is connected with the negative input of comparator；The output of comparator End is connected with the input of driver (300)；The outfan of described driver (300) is connected with the grid of MOSFET；Electricity Stream source is passed through external outer meeting resistance on reference voltage and is produced.

The one-way on-off valve of electric current flowing in actually used process, is realized by turning on and off corresponding MOSFET Effect；And turn on and off corresponding MOSFET and completed by the steps：

1st, the voltage input end of the rectification circuit that MOSFET is constituted detects network 100 input input voltage vin to MOSFET；

2nd, MOSFET detection network 100 output output voltage V_O；

3rd, level comparator 200 detects the output voltage V of network 100 output by MOSFET_OCompared with reference voltage Relatively, corresponding level signal is exported according to result of the comparison；

4th, drive circuit 300 drives turning on and off of MOSFET by the level signal that level comparator 200 exports.

Below in conjunction with the accompanying drawings the 4 and Fig. 8 MOSFET circuit of synchronous rectification directly in parallel with output capacitance to the present invention and Method is described in further detail.

As shown in figure 4, two drive circuit A are to connect in the way of publicly.Drive circuit A is as shown in figure 8, following Wen Zhong, resistance is resistance R_DET；Reference voltage is reference voltage Vref；Current source is current source I_SS；Outer meeting resistance is Outer meeting resistance R_SS.

The output of level comparator 200 exports through driver 300, to control MOSFET to turn on and off.

1st, obtain the output voltage V that MOSFET detects network 100_O：

1.1st, the voltage input end of the rectification circuit that MOSFET is constituted is to resistance R_DETInput input voltage vin；

1.2nd, when input voltage vin is more than voltage stabilizing tube voltage V_CLAMPWhen, MOSFET detects the output voltage V of network 100_O= V_CLAMP；

When input voltage vin is less than voltage stabilizing tube voltage V_CLAMPWhen, MOSFET detects the output voltage V of network 100_O=I_SS× R_DET+V_DS, as shown in Figure 8；And when MOSFET works in synchronous rectification state, V_DSIt is the electric current I that MOSFET is flow through_DS? Conducting resistance R of MOSFET_DSONOn voltage drop V_DS；Due to I_DSIt is negative value, so V_DS<0；Current source I_SSBy reference to voltage Vref external outer meeting resistance R_SSProduce.

2nd, select the output level of level comparator 200：

When MOSFET detects the output voltage V of network 100_OLess than level comparator 200 reference voltage Vref when, level Comparator 200 exports high level；

When MOSFET detects the output voltage V of network 100_OMore than level comparator 200 reference voltage Vref when, level Comparator 200 exports low level.

3rd, determine that MOSFET turns on and off：

When level comparator 200 output high level, high level exports through driver 300 to keep MOSFET open-minded；

When level comparator 200 output low level, low level makes MOSFET turn off through driver 300 output.

When above-described MOSFET opens, the electric current I that flow through with MOSFET_DSReduce, MOSFET detects network 100 Output voltage V_OIncrease；When MOSFET detects the output voltage V of network 100_OProgressively increase to more than level comparator 200 During reference voltage Vref, level comparator 200 exports low level.

When above-described MOSFET turns off, flow through the body diode of the electric current nature commutation of MOSFET to MOSFET.And When the electric current of the body diode of MOSFET is zero, the voltage drop V of MOSFET_DSIncrease；When the voltage drop of MOSFET is more than voltage stabilizing Tube voltage V_CLAMPWhen, MOSFET detects the output voltage V of network 100_OFor voltage stabilizing tube voltage V_CLAMP.Voltage drop with MOSFET Increase further, the voltage drop of MOSFET is through resistance R_DETIt is loaded into stabilivolt, MOSFET detects the output voltage V of network 100_O It is still voltage stabilizing tube voltage V_CLAMP.

In the drive circuit A of this enforcement row, it is the MOSFET high-tension electricity that minimum resistance to bear the external world only by cost Pressure.Resistance R_DETSize and current source I_SSAnd reference voltage Vref is related.

As shown in figure 8, the operation condition of level comparator 200 is as follows：

Vref≤I_SS·R_DET-I_D·R_DSON

$R_{DET}\&GreaterEqual;\frac{Vref}{I_{SS}}+\frac{I_D}{I_{SS}}\&CenterDot;R_{DSON}\&GreaterEqual;\frac{Vref}{I_{SS}}---\left(2\right)$

Maximum MOSFET voltage drop is V_DSM, when MOSFET turns off, resistance R_DETMaximum current I_DET：

$I_{DET}\&le;\frac{V_{DSM}}{R_{DET}}\&le;\frac{V_{DSM}}{V_{ref}}\&CenterDot;I_{SS}---\left(3\right)$

R_DETMaximum power dissipation be P_DET:

$P_{DET}=I_{DET}\&CenterDot;V_{DSM}=\frac{{V^2}_{DSM}}{Vref}\&CenterDot;I_{SS}---\left(4\right).$

In the scheme of this enforcement row, current source I_SSBy reference to voltage Vref external outer meeting resistance R_SSProduce；Precision problem It is that resistance R is added by the precision of reference voltage Vref_DETWith outer meeting resistance R_SSPrecision, along with voltage turns electric current and current mirror Overall gain k precision composition.Generally resistance (i.e. resistance R_DETWith outer meeting resistance R_SS) select 1% precision, voltage turns electric current and electricity The precision of overall gain k of stream mirror is 2%.If the precision of reference voltage Vref is conducting voltage V of 2%, MOSFET_DSONInspection Survey precision and can reach 6%.

Last in addition it is also necessary to it is noted that listed above be only the present invention a specific embodiment.Obviously, the present invention It is not limited to above example, can also have many deformation.Those of ordinary skill in the art can be straight from present disclosure Connect all deformation derived or associate, be all considered as protection scope of the present invention.

Claims (2)

1. the MOSFET circuit of synchronous rectification directly in parallel with output capacitance, the rectification circuit constituting including MOSFET；Its feature It is：The rectification circuit that described MOSFET is constituted includes two one-way on-off valve for electric current flowing and two two-way switch Valve；

Described one-way on-off valve is passed through MOSFET and drive circuit A and is constituted；

Described drive circuit A includes MOSFET detection network (100), level comparator (200) and the driving that signal connects successively Device (300)；Described MOSFET detection network (100) includes current source, resistance and stabilivolt；

MOSFET detects that the voltage input end of the rectification circuit that the input of network (100) is constituted with MOSFET is connected, described The input that network (100) is detected with MOSFET in one end of resistance is connected, and the other end of described resistance is detected with MOSFET The outfan of network (100) is connected, described current source and stabilivolt detect in MOSFET respectively the outfan of network (100) with Resistance is connected；

Described voltage comparator (200) includes reference voltage and comparator；Described reference voltage and the electrode input end of comparator It is connected；Described MOSFET detects that the outfan of network (100) is connected with the negative input of comparator；

The outfan of described comparator is connected with the input of driver (300)；The outfan of described driver (300) with The grid of MOSFET is connected；

Described current source passes through external outer meeting resistance on reference voltage and produces.

2. a kind of using MOSFET circuit of synchronous rectification as claimed in claim 1 directly in parallel with output capacitance carry out same Step method for rectifying, is characterized in that：The voltage input end of the rectification circuit that MOSFET is constituted is to MOSFET detection network (100) input Input voltage vin；

Described MOSFET detection network (100) output output voltage V_O；

Described output voltage V_OIt is input to voltage comparator (200)；

Voltage comparator (200) passes through output voltage V_OIt is compared rear outputs level signals with reference voltage Vref；

Described driver (300) controls turning on and off of MOSFET according to the level signal that voltage comparator (200) exports；

When input voltage vin is more than voltage stabilizing tube voltage V_CLAMPWhen, MOSFET detects the output voltage V of network (100)_OIt is V_CLAMP；

When input voltage vin is less than voltage stabilizing tube voltage V_CLAMPWhen, MOSFET detects the output voltage V of network (100)_O=I_SS× R_DET+V_DS；

Described I_SSFor the current value of current source, described R_DETFor the resistance value of resistance, described V_DSWork in synchronous rectification for MOSFET During state, the electric current I that MOSFET is flow through_DSConducting resistance R in MOSFET_DSONOn voltage drop；

Described electric current I_DSFor negative value, described voltage drop V_DS<0；

Described output voltage V_OMore than reference voltage Vref, comparator exports low level；Described reference voltage Vref is more than output electricity Pressure V_O, comparator output high level；

Described low level exports the grid of MOSFET so that MOSFET turns off through driver (300)；Described high level is through driving Device (300) exports the grid of MOSFET so that MOSFET keeps open-minded；

When MOSFET turns off, flow through the body diode of the current commutation of MOSFET to MOSFET；

When the electric current of the body diode of described MOSFET is zero, the voltage drop V of MOSFET_DSIncrease；

The voltage drop V of described MOSFET_DSMore than voltage stabilizing tube voltage V_CLAMPWhen, MOSFET detects the output voltage V of network (100)_O For voltage stabilizing tube voltage V_CLAMP.