CN103033669B - Limit peak point current-sensing circuit of switching power supply - Google Patents

Abstract

The invention provides a limit peak point current-sensing circuit of a switching power supply. The limit peak point current-sensing circuit of the switching power supply comprises a reference current source, a voltage comparator, a power metal-oxide-semiconductor field effect transistor (MOSFET), and a detection MOSFET, wherein an output end of the reference current source is connected with the ground through a first resistor, a positive input end of the voltage comparator is connected with the output end of the reference current source, a control end of the power MOSFET is connected with the an output end of the voltage comparator, an output end of the power MOSFET is directly connected with the ground, a control end of the detection MOSFET is connected with the output end of the voltage comparator, an output end of the detection MOSFET is connected with a negative input end of the voltage comparator and is connected with the ground through a second resistor, and an input end of the detection MOSFET is connected with the input end of the power MOSFET. Besides, the reference current source has a positive temperature coefficient. The ratio of the first resistor and the second resistor is irrelevant with temperatures, and the ratio of the break-over resistance of power MOSFET and the break-over resistance of the detection MOSFET is irrelevant with the temperatures. The limit peak point current-sensing circuit of the switching power supply can achieve that limit peak point current-sensing temperatures are made up, and is beneficial for lowering cost and decreasing power consumption.

Description

The maximum peak value current detection circuit of Switching Power Supply

Technical field

The present invention relates to switch power technology, particularly relate to a kind of maximum peak value current detection circuit with the Switching Power Supply of temperature compensation capability.

Background technology

In the Switching Power Supply of built-in mosfet transistor, peak current detection is the key point of Switching Power Supply always.The degree of accuracy of peak current detection point directly has influence on output power, and then the degree of accuracy of maximum peak value current detecting point directly has influence on limited output power size.Therefore in field of switch power, for accomplishing the consistance of limited output power, wish that maximum peak value current detecting point can be consistent under the condition of external condition with interface variation, wherein in external condition, need the important factor factor considered to be exactly " temperature ".Because built-in chip type mosfet transistor, therefore when peak point current is large time, chip power-consumption can increase, and then chip temperature can rise, if the maximum peak value electric current under being triggered to high temperature, can directly cause working as machine, so temperature is the key factor affecting maximum peak value current detecting point.

Fig. 1 shows the maximum peak value current detection circuit 10 of a kind of Switching Power Supply of the prior art, the maximum peak value electric current I of the mosfet transistor 12 that wherein integrated circuit (IC) chip is built-in _swith the resistance to earth R of inner check point _srelevant, the relation known I equal by two input terminal voltages of comparer 11 _fr _f=I _sr _s, namely wherein I _frepresent the input current of the positive input terminal of comparer 11, R _fthat represent is input current I _fto the resistance value on ground.For ensureing maximum peak value electric current I _stemperature independent, only need to consider ratio invariableness and I _fthese two conditions temperature independent, and R _fand R _sthe resistance that normally chip internal is integrated, can ensure Ratio invariableness with same media material, is also easy in addition ensure I in integrated circuit technique _ftemperature independent.

But above-mentioned prior art has three defects, and one is due to R _sresistance is usually very little, and R _fresistance is usually very large again, generally speaking, not only cannot do the large resistance of resistance but also do the little resistance of resistance, otherwise chip cost can be very high with same media material; Two is mosfet transistor 12 resistance in series R of chip internal _swhen causing peak point current large, loss is very large; Three is chip internal integrated resistor R _s, resistance R _son power consumption directly cause temperature rise aggravation.

Summary of the invention

The technical problem to be solved in the present invention is to provide a kind of maximum peak value current detection circuit of Switching Power Supply, can realize the temperature compensation to maximum peak value current detecting.

For solving the problems of the technologies described above, the invention provides a kind of maximum peak value current detection circuit of Switching Power Supply, comprising:

Reference current source, its output terminal is via the first resistance eutral grounding;

Voltage comparator, its positive input terminal connects the output terminal of described reference current source;

Power MOSFET, its control end connects the output terminal of described voltage comparator;

Wherein, the direct ground connection of the output terminal of described power MOSFET; Described maximum peak value current detection circuit also comprises:

Detect mosfet transistor, its control end connects the output terminal of described voltage comparator, its output terminal connect described voltage comparator negative input end and via the second resistance eutral grounding, its input end connects the input end of described power MOSFET, wherein said reference current source has positive temperature coefficient (PTC), the ratio of described first resistance and the second resistance is temperature independent, and the ratio of the conducting resistance of described detection mosfet transistor and power MOSFET is temperature independent.

According to one embodiment of present invention, described detection mosfet transistor and power MOSFET are all N-types.

Compared with prior art, the present invention has the following advantages:

In the maximum peak value current detection circuit of the embodiment of the present invention, the direct ground connection of output terminal of power MOSFET, detect the output terminal that the control end of mosfet transistor and the control end of power MOSFET are all connected to voltage comparator, and the output terminal detecting mosfet transistor connect voltage comparator negative input end and via the second resistance eutral grounding.The output terminal of mosfet transistor is detected via the second resistance eutral grounding owing to detecting the direct ground connection of output terminal of mosfet transistor, the Ratio invariableness of the first resistance and the second resistance can be ensured with lower cost, and the power attenuation that the output terminal resistance in series that it also avoid power MOSFET causes.

Accompanying drawing explanation

Fig. 1 is the electrical block diagram of the maximum peak value current detection circuit of a kind of Switching Power Supply of the prior art;

Fig. 2 is the electrical block diagram of the maximum peak value current detection circuit of the Switching Power Supply of the embodiment of the present invention.

Embodiment

Below in conjunction with specific embodiments and the drawings, the invention will be further described, but should not limit the scope of the invention with this.

With reference to figure 2, the maximum peak value current detection circuit 100 of the Switching Power Supply of the present embodiment comprises: reference current source I _f, the first resistance R _f, voltage comparator 301, power MOSFET 303, detect mosfet transistor 302, second resistance R _sEN.

Wherein, reference current source I _foutput terminal via the first resistance R _fground connection, its reference current produced is designated as I _f, the first resistance R _fresistance value be designated as R _f; The positive input terminal of voltage comparator 301 connects reference current source I _foutput terminal, the negative input end of voltage comparator 301 connects the output terminal detecting mosfet transistor 302, and the output terminal of voltage comparator 301 connects power MOSFET 303 and detects the control end of mosfet transistor 302; The input end of power MOSFET 303 is connected with the input end detecting mosfet transistor 302, and the direct ground connection of output terminal of power MOSFET 303, the maximum peak value electric current flowing through power MOSFET 303 is designated as I _s; Detect the output terminal of mosfet transistor 302 via the second resistance R _sENground connection, flows through the electric current detecting mosfet transistor 302 and is designated as detection electric current I _sEN.Wherein, the voltage signal of the positive input terminal of voltage comparator 301 is by reference current source I _fproduce; The voltage signal of the negative input end of voltage comparator 301 is by detecting electric current I _sENwith the second resistance R _sENresistance value R _sENproduct produce.

More specifically, the positive input terminal of described voltage comparator 301 connects the first resistance R _fone end, the first resistance R _fother end ground connection, the first resistance R _fwith reference current I _fproduce the voltage of voltage comparator 301 positive input terminal; The negative input end of voltage comparator 301 connects the second resistance R _sENone end, the second resistance R _sENother end ground connection, the second resistance R _sENwith detection electric current I _fproduce the voltage of voltage comparator 301 negative input end.The negative input end of voltage comparator 301 also connects the source detecting mosfet transistor 302 simultaneously.The output terminal of voltage comparator 301 connects the grid detecting mosfet transistor 302 and power MOSFET 303.The drain terminal detecting mosfet transistor 302 connects the drain terminal of power MOSFET 303, the source ground connection of power MOSFET 303.As a nonrestrictive example, detection mosfet transistor 302 and power MOSFET 303 are all N-types.

As a preferred embodiment, reference current source I _fthere is positive temperature coefficient (PTC), the first resistance R _fwith the second resistance R _sENresistance value ratio temperature independent, the ratio detecting the conducting resistance of mosfet transistor 302 and power MOSFET 303 is temperature independent.

In the present embodiment, when the positive input terminal of voltage comparator 301 is equal with negative input end, realize the shutoff of power MOSFET 303, the electric current now flowing through power MOSFET 303 is maximum peak value electric current I _s.So obtain:

I _FR _F=I _SENR _SEN。

In addition, because the detection drain terminal of mosfet transistor 302 and the drain terminal of power MOSFET link together, known:

I _sEN(R _sEN+ R _p)=I _sr _s, wherein R _pfor detecting the conducting resistance of mosfet transistor 302, R _sfor the conducting resistance of power MOSFET 303.

Can obtain maximum peak value electric current according to above two equatioies is:

$I_S=I_F\·\frac{R_F}{R_{\mathrm{SEN}}}\·(\frac{R_P}{R_S}+\frac{R_{\mathrm{SEN}}}{R_S}).$

Local derviation is asked to obtain to temperature:

$\frac{\∂I_S}{\∂T}=\frac{R_F}{R_{\mathrm{SEN}}}\·[(\frac{R_P}{R_S}+\frac{R_{\mathrm{SEN}}}{R_S})\frac{\∂I_F}{\∂T}+\frac{I_F}{R_S}(\frac{\∂R_{\mathrm{SEN}}}{\∂T}-\frac{R_{\mathrm{SEN}}}{R_S}\frac{\∂R_S}{\∂T})].$

For existing integrated circuit processing technique, the conducting resistance R of power MOSFET 303 _sin positive temperature characterisitic, and second resistance R of IC interior _sENnegative temperature coefficient, or zero-temperature coefficient, or have than the first resistance R _slittle many positive temperature coefficient (PTC)s, therefore $\frac{\&PartialD;R_{\mathrm{SEN}}}{\&PartialD;T}-\frac{R_{\mathrm{SEN}}}{R_S}\frac{\&PartialD;R_S}{\&PartialD;T}<0,$ As long as make

$\frac{\&PartialD;I_F}{\&PartialD;T}=\frac{I_F}{R_S}(\frac{R_{\mathrm{SEN}}}{R_S}\frac{\&PartialD;R_S}{\&PartialD;T}-\frac{\&PartialD;R_{\mathrm{SEN}}}{\&PartialD;T})/(\frac{R_P}{R_S}+\frac{R_{\mathrm{SEN}}}{R_S})>0,$

Can meet i.e. maximum peak value electric current I _stemperature independent.

The invention discloses the compensation schemes of the maximum peak value current detecting of built-in mosfet transistor in Switching Power Supply, and describe the specific embodiment of the present invention and effect with reference to the accompanying drawings.It is understood that above-described embodiment is just to exemplary explanation of the present invention; instead of limitation of the present invention; any innovation and creation do not exceeded in spirit of the present invention; include but not limited to the change of the local structure to circuit, to the type of components and parts or the replacement of model; and the replacement of other unsubstantialities or amendment, all fall within scope.

Claims (2)

1. a maximum peak value current detection circuit for Switching Power Supply, comprising:

Reference current source, its output terminal is via the first resistance eutral grounding;

Voltage comparator, its positive input terminal connects the output terminal of described reference current source;

Power MOSFET, its control end connects the output terminal of described voltage comparator;

It is characterized in that, the direct ground connection of output terminal of described power MOSFET; Described maximum peak value current detection circuit also comprises:

Detect mosfet transistor, its control end connects the output terminal of described voltage comparator, its output terminal connect described voltage comparator negative input end and via the second resistance eutral grounding, its input end connects the input end of described power MOSFET, wherein said reference current source has positive temperature coefficient (PTC), the ratio of described first resistance and the second resistance is temperature independent, and the ratio of the conducting resistance of described detection mosfet transistor and power MOSFET is temperature independent.

2. maximum peak value current detection circuit according to claim 1, is characterized in that, described detection mosfet transistor and power MOSFET are all N-types.