CN103391016A - MOSFET synchronous rectification circuit directly connected in parallel with output capacitor and 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

MOSFET circuit of synchronous rectification and the method direct in parallel with output capacitance

Technical field

The invention belongs to electronic technology field, relate to circuit of synchronous rectification, more particularly, the present invention relates to a kind of for can with output filter capacitor directly low-cost circuit of synchronous rectification in parallel, i.e. MOSFET circuit of synchronous rectification and the method direct in parallel with output capacitance.

Background technology

In the application of low-voltage, high-current alternating current-direct current, the interchange that at first needs a bridge rectifier to input changes direct current into; Change in the process of direct current in interchange, the loss of bridge rectifier is to reduce the main factor of whole system efficiency; Input voltage as common bridge rectifier is 6V, and the voltage drop at bridge rectifier two ends is about 1.5V, namely by the potential loss after bridge rectifier, can reach 25%.In order to reduce the loss, find in research, by using Schottky diode, loss can be reduced by 50% left and right, and the use synchronous rectification bridge with MOSFET as shown in Figure 1, loss further can be reduced (being reduced to almost nil degree), thereby make the efficiency of system greatly improve.

MOSFET synchronous rectification bridge as shown in Figure 1 consists of two P channel mosfets and two N-channel MOS FET, two P channel mosfets of above-described four MOSFET(and two N-channel MOS FET) input and drive by exchanging of MOSFET synchronous rectification bridge.The MOSFET synchronous rectification bridge circuit structure of this class is very simple, and with low cost, and can use in wider input voltage range.

But the output of this type of MOSFET synchronous rectification bridge can not be directly in parallel with output filter capacitor.Specifically, in this type of MOSFET synchronous rectification bridge, the effect of MOSFET is the bidirectional switch valve of the interchange input control of synchronous rectification bridge, rather than is used for the one-way on-off valve of current flowing; Therefore, output filter capacitor can feed back to the reverse input current of synchronous rectification bridge and exchange input or by the MOSFET short circuit; Due to above-described defect, having caused the output of this type of circuit power application must be inductance or resistance; And limited the application of this type of circuit in many occasions.

Summary of the invention

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

In order to solve the problems of the technologies described above, the invention provides a kind of MOSFET circuit of synchronous rectification direct in parallel with output capacitance, comprise the rectification circuit that MOSFET forms; The rectification circuit that described MOSFET forms comprises two one-way on-off valve and two bidirectional switch valves of being used for current flowing.

As to the directly improvement of MOSFET circuit of synchronous rectification in parallel of of the present invention and output capacitance: described one-way on-off valve is by MOSFET and drive circuit A formation; Described drive circuit A comprises MOSFET Sampling network, level comparator and the driver of signal connection successively; Include current source, resistance and voltage-stabiliser tube in described MOSFET Sampling network; The input of MOSFET Sampling network is connected with the voltage input end of the rectification circuit that MOSFET forms, one end of described resistance is connected with the input of MOSFET Sampling network, an other end of described resistance is connected with the output of MOSFET Sampling network, and described current source is connected with resistance at the output of MOSFET Sampling network respectively with voltage-stabiliser tube; Described voltage comparator comprises reference voltage and comparator; Described reference voltage is connected with the electrode input end of comparator; The output of described MOSFET Sampling network is connected with the negative input of comparator; The output of described comparator is connected with the input of driver; The output of described driver is connected with the grid of MOSFET; Described current source produces by external outer meeting resistance on reference voltage.

A kind of and output capacitance be the method for MOSFET circuit of synchronous rectification in parallel directly: the voltage input end of the rectification circuit that MOSFET forms is inputted input voltage vin to the MOSFET Sampling network; Described MOSFET Sampling network output output voltage V _ODescribed output voltage V _OBe input to voltage comparator; Voltage comparator passes through output voltage V _OCompare rear outputs level signals with reference voltage Vref; Described driver is controlled turning on and off of MOSFET according to the level signal of voltage comparator output.

As to the directly improvement of the method for MOSFET circuit of synchronous rectification in parallel of of the present invention and output capacitance: when input voltage vin greater than voltage-stabiliser tube voltage V _CLAMPThe time, the output voltage V of MOSFET Sampling network _OV _CLAMPWhen input voltage vin less than voltage-stabiliser tube voltage V _CLAMPThe time, the output voltage V of MOSFET Sampling network _O=I _SS* R _DET+ V _DSDescribed V _DSWhile for MOSFET, working in the synchronous rectification state, the electric current I that MOSFET flows through _DSConducting resistance R at MOSFET _DSONOn voltage drop; Described electric current I _DSFor negative value, described voltage drop V _DS＜0.

As to the directly improvement of the method for MOSFET circuit of synchronous rectification in parallel of of the present invention and output capacitance: described output voltage V _OGreater than reference voltage Vref, the comparator output low level; Described reference voltage Vref is greater than output voltage V _O, comparator output high level.

As to the directly improvement of the method for MOSFET circuit of synchronous rectification in parallel of of the present invention and output capacitance: described low level outputs to the grid of MOSFET through driver, make the MOSFET shutoff; Described high level outputs to the grid of MOSFET through driver, make MOSFET keep open-minded.

As to the directly improvement of the method for MOSFET circuit of synchronous rectification in parallel of of the present invention and output capacitance: when MOSFET turn-offed, the body diode of MOSFET was arrived in the electric current change of current of flowing through 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 _DSGreater than voltage-stabiliser tube voltage V _CLAMPThe time, the output voltage V of MOSFET Sampling network _OFor voltage-stabiliser tube voltage V _CLAMP

In existing MOSFET synchronous rectification bridge, be all the one-way on-off valve that is subjected to the bidirectional switch valve of the interchange input control of synchronous rectification bridge rather than is used for current flowing due to the effect of four MOSFET, the output of MOSFET synchronous rectification bridge can not be directly in parallel with output filter capacitor.So in of the present invention and output capacitance directly in MOSFET circuit of synchronous rectification and method in parallel, in four MOSFET, adopted two MOSFET to be controlled structure for the one-way on-off valve of current flowing, as two P channel mosfets textural association that is one-way on-off valve, a P channel mosfet and the textural association that N-channel MOS FET is one-way on-off valve, or two textural associations that N-channel MOS FET is one-way on-off valve; Such textural association makes the MOSFET synchronous rectification bridge can be directly in parallel with output filter capacitor, and the electric capacity of the MOSFET synchronous rectification bridge output of this textural association is not to the path of the reverse input current of synchronous rectification bridge;

That is to say, by four kinds of following a series of MOSFET synchronous rectification bridges that are combined to form can with output filter capacitor directly (output capacitance has not had to the path of the reverse input current of this synchronous rectification bridge) in parallel, four kinds of combinations are as follows:

The first combination (as shown in Figure 4): structure, two N-channel MOS FET that two P channel mosfets are the bidirectional switch valve are the textural association of one-way on-off valve;

The second combination (as shown in Figure 5): structure, two N-channel MOS FET that two P channel mosfets are one-way on-off valve are the textural association of bidirectional switch valve;

The third combination (as shown in Figure 2): P channel mosfet and N-channel MOS FET be one-way on-off valve structure, a P channel mosfet and the textural association that N-channel MOS FET is the bidirectional switch valve;

The 4th kind of combination (as shown in Figure 3): P channel mosfet and N-channel MOS FET be one-way on-off valve structure, a P channel mosfet and the textural association that N-channel MOS FET is the bidirectional switch valve;

In the textural association of obvious above-described bidirectional switch valve, drive circuit is comprised of resistance and voltage-stabiliser tube, and is with low cost; But in the textural association of above-described one-way on-off valve, drive circuit normally consists of extra drive circuit A or corresponding integrated circuit A; And adopt the cost of extra drive circuit A certainly high than the cost of the drive circuit of resistance and voltage-stabiliser tube composition.But in the present invention, owing to having adopted two bidirectional switch valves and two compound modes (concrete four kinds of combinations as previously discussed) that one-way on-off valve combines, both kept the drive circuit that in the bidirectional switch valve, resistance and voltage-stabiliser tube form, having increased again by extra drive circuit A is the one-way on-off valve that basis forms, so reached cost-effective purpose (especially under the wide input voltage application conditions).

Description of drawings

Below in conjunction with accompanying drawing, 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 the MOSFET circuit of synchronous rectification a kind of structural representation direct in parallel with output capacitance of the present invention;

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

Fig. 4 is directly MOSFET circuit of synchronous rectification in parallel another structural representation again of of the present invention and output capacitance;

Fig. 5 is directly MOSFET circuit of synchronous rectification in parallel another structural representation more again of of the present invention and output capacitance;

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

Fig. 7 the present invention is for the input V of the MOSFET Sampling network 100 of the drive circuit A of the one-way on-off valve of current flowing _INOutput V _OGraph of a relation;

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

Embodiment

Fig. 1 ~ Fig. 8 has provided a kind of MOSFET circuit of synchronous rectification and the method direct in parallel with output capacitance.

Find by the research to MOSFET synchronous rectification bridge, in MOSFET synchronous rectification bridge (as shown in Figure 1), because four MOSFET are the bidirectional switch valve that is subjected to the interchange input control of the synchronous rectification bridge one-way on-off valve of current flowing (rather than be used for), 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 one-way on-off valve for current flowing, MOSFET synchronous rectification bridge just can be directly in parallel with output filter capacitor, and the output capacitance of (namely two MOSFET in four MOSFET are controlled the one-way on-off valve for current flowing) is not to the path of the reverse input current of this MOSFET synchronous rectification bridge because this MOSFET synchronous rectification bridge.

Embodiment 1, a kind of MOSFET circuit of synchronous rectification direct in parallel with output capacitance, comprise the rectification circuit that MOSFET forms; The rectification circuit that forms at MOSFET comprises two one-way on-off valve and two bidirectional switch valves that are used for current flowing.

Above-described one-way on-off valve forms by MOSFET and drive circuit A; Drive circuit A comprises MOSFET Sampling network 100, level comparator 200 and the driver 300 of signal connection successively; Include current source, resistance and voltage-stabiliser tube in MOSFET Sampling network 100; The input of MOSFET Sampling network 100 is connected with the voltage input end of the rectification circuit that MOSFET forms, one end of resistance is connected with the input of MOSFET Sampling network 100, an other end of resistance is connected with the output of MOSFET Sampling network 100, and current source is connected with resistance at the output of MOSFET Sampling network 100 respectively with voltage-stabiliser tube; Voltage comparator 200 comprises reference voltage and comparator; Reference voltage is connected with the electrode input end of comparator; The output of MOSFET Sampling network 100 is connected with the negative input of comparator; The output of comparator is connected with the input of driver 300; The output of described driver 300 is connected with the grid of MOSFET; Current source produces by external outer meeting resistance on reference voltage.

In the actual process of using, realize the single-way switch valve action of current flowing by turning on and off corresponding MOSFET; Completed by following step and turn on and off corresponding MOSFET:

1, the voltage input end of the rectification circuit of MOSFET formation is to MOSFET Sampling network 100 input input voltage vin;

2, MOSFET Sampling network 100 output output voltage V _O

3, level comparator 200 is by the output voltage V of MOSFET Sampling network 100 outputs _OCompare with reference voltage, according to the corresponding level signal of result output relatively;

4, the level signal driven MOS FET of drive circuit 300 by level comparator 200 output turns on and off.

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

As shown in Figure 4, two drive circuit A connect in publicly mode.As shown in Figure 8, with hereinafter, resistance is resistance R to drive circuit A _DETReference voltage is reference voltage Vref; Current source is current source I _SSOuter meeting resistance is outer meeting resistance R _SS

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

1, obtain the output voltage V of MOSFET Sampling network 100 _O:

1.1, the voltage input end of the rectification circuit that forms of MOSFET is to resistance R _DETThe input input voltage vin;

1.2, when input voltage vin greater than voltage-stabiliser tube voltage V _CLAMPThe time, the output voltage V of MOSFET Sampling network 100 _O=V _CLAMP

When input voltage vin less than voltage-stabiliser tube voltage V _CLAMPThe time, the output voltage V of MOSFET Sampling network 100 _O=I _SS* R _DET+ V _DS, as shown in Figure 8; And when MOSFET works in the synchronous rectification state, V _DSIt is the electric current I that MOSFET flows through _DSConducting resistance R at MOSFET _DSONOn voltage drop V _DSDue to I _DSNegative value, so V _DS＜0; Current source I _SSBy reference to the external outer meeting resistance R of voltage Vref _SSProduce.

2, select the output level of level comparator 200:

Output voltage V when MOSFET Sampling network 100 _ODuring less than the reference voltage Vref of level comparator 200, level comparator 200 output high level;

Output voltage V when MOSFET Sampling network 100 _ODuring greater than the reference voltage Vref of level comparator 200, level comparator 200 output low levels.

3, determine that MOSFET turns on and off:

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

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

When above-described MOSFET opens, the electric current I that flows through along with MOSFET _DSReduce the output voltage V of MOSFET Sampling network 100 _OIncrease; Output voltage V when MOSFET Sampling network 100 _OWhile being increased to gradually the reference voltage Vref greater than level comparator 200, level comparator 200 is output low level.

When above-described MOSFET turn-offs, flow through the body diode of the electric current nature change of current 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 greater than voltage-stabiliser tube voltage V _CLAMPThe time, the output voltage V of MOSFET Sampling network 100 _OFor voltage-stabiliser tube voltage V _CLAMPAlong with the voltage drop of MOSFET further increases, the voltage drop of MOSFET is through resistance R _DETBe loaded into voltage-stabiliser tube, the output voltage V of MOSFET Sampling network 100 _OBe still voltage-stabiliser tube voltage V _CLAMP

In the drive circuit A of this implementation column, by cost, be only that minimum resistance bears extraneous MOSFET high tension voltage.Resistance R _DETSize and current source I _SSAnd reference voltage Vref is relevant.

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

Vref≤I _SS·R _DET-I _D·R _DSON (1)

$R_{\mathrm{DET}}\≥\frac{\mathrm{Vref}}{I_{\mathrm{SS}}}+\frac{I_D}{I_{\mathrm{SS}}}\·R_{\mathrm{DSON}}\≥\frac{\mathrm{Vref}}{I_{\mathrm{SS}}}---\left(2\right)$

Maximum MOSFET voltage drop is V _DSM, when MOSFET turn-offs, resistance R _DETMaximum current I _DET:

$I_{\mathrm{DET}}\≤\frac{V_{\mathrm{DSM}}}{R_{\mathrm{DET}}}\≤\frac{V_{\mathrm{DSM}}}{\mathrm{Vref}}\·I_{\mathrm{SS}}---\left(3\right)$

R _DETMaximum power dissipation be P _DET:

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

In the scheme of this implementation column, current source I _SSBy reference to the external outer meeting resistance R of voltage Vref _SSProduce; Precision problem is that the precision by reference voltage Vref adds resistance R _DETWith outer meeting resistance R _SSPrecision, add the overall gain k precision that voltage turns electric current and current mirror and form.Usually resistance (is resistance R _DETWith outer meeting resistance R _SS) select 1% precision, the precision that voltage turns the overall gain k of electric current and current mirror is 2%.If the precision of reference voltage Vref is 2%, the conducting voltage V of MOSFET _DSONAccuracy of detection can reach 6%.

Finally, it is also to be noted that, what more than enumerate is only a specific embodiment of the present invention.Obviously, the invention is not restricted to above embodiment, many distortion can also be arranged.All distortion that those of ordinary skill in the art can directly derive or associate from content disclosed by the invention, all should think protection scope of the present invention.

Claims (7)

1. the MOSFET circuit of synchronous rectification direct in parallel with output capacitance, comprise the rectification circuit that MOSFET forms; It is characterized in that: the rectification circuit that described MOSFET forms comprises two one-way on-off valve and two bidirectional switch valves of being used for current flowing.

2. the direct MOSFET circuit of synchronous rectification in parallel of according to claim 1 and output capacitance, it is characterized in that: described one-way on-off valve is by MOSFET and drive circuit A formation;

Described drive circuit A comprises MOSFET Sampling network (100), level comparator (200) and the driver (300) of signal connection successively;

Include current source, resistance and voltage-stabiliser tube in described MOSFET Sampling network (100);

The input of MOSFET Sampling network (100) is connected with the voltage input end of the rectification circuit that MOSFET forms, one end of described resistance is connected with the input of MOSFET Sampling network (100), an other end of described resistance is connected with the output of MOSFET Sampling network (100), and described current source is connected with resistance at the output of MOSFET Sampling network (100) respectively with voltage-stabiliser tube;

Described voltage comparator (200) comprises reference voltage and comparator; Described reference voltage is connected with the electrode input end of comparator; The output of described MOSFET Sampling network (100) is connected with the negative input of comparator;

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

Described current source produces by external outer meeting resistance on reference voltage.

One kind with the direct method of MOSFET circuit of synchronous rectification in parallel of output capacitance, it is characterized in that: the voltage input end of the rectification circuit that MOSFET forms is inputted input voltage vin to MOSFET Sampling network (100);

Described MOSFET Sampling network (100) output output voltage V _O

Described output voltage V _OBe input to voltage comparator (200);

Voltage comparator (200) passes through output voltage V _OCompare rear outputs level signals with reference voltage Vref;

Described driver (300) is controlled turning on and off of MOSFET according to the level signal of voltage comparator (200) output.

4. the direct method of MOSFET circuit of synchronous rectification in parallel of according to claim 3 and output capacitance is characterized in that: when input voltage vin greater than voltage-stabiliser tube voltage V _CLAMPThe time, the output voltage V of MOSFET Sampling network (100) _OV _CLAMP

When input voltage vin less than voltage-stabiliser tube voltage V _CLAMPThe time, the output voltage V of MOSFET Sampling network (100) _O=I _SS* R _DET+ V _DS

Described V _DSWhile for MOSFET, working in the synchronous rectification state, the electric current I that MOSFET flows through _DSConducting resistance R at MOSFET _DSONOn voltage drop;

Described electric current I _DSFor negative value, described voltage drop V _DS＜0.

5. the direct method of MOSFET circuit of synchronous rectification in parallel of according to claim 4 and output capacitance, is characterized in that: described output voltage V _OGreater than reference voltage Vref, the comparator output low level; Described reference voltage Vref is greater than output voltage V _O, comparator output high level.

6. the direct method of MOSFET circuit of synchronous rectification in parallel of according to claim 5 and output capacitance, it is characterized in that: described low level outputs to the grid of MOSFET through driver (300), makes the MOSFET shutoff; Described high level outputs to the grid of MOSFET through driver (300), make MOSFET keep open-minded.

7. the direct method of MOSFET circuit of synchronous rectification in parallel of according to claim 6 and output capacitance, it is characterized in that: when MOSFET turn-offed, the body diode of MOSFET was arrived in the electric current change of current of flowing through 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 _DSGreater than voltage-stabiliser tube voltage V _CLAMPThe time, the output voltage V of MOSFET Sampling network (100) _OFor voltage-stabiliser tube voltage V _CLAMP

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