CN203011996U - Limit peak value current detection circuit of switch power supply - Google Patents

Abstract

The utility model provides a limit peak value current detection circuit of a switch power supply comprising a reference current source, an output end of which is grounded by a first resistor; a voltage comparator, a positive input end of which is connected with an output end of the reference current source; a power MOSFET transistor, a control end of which is connected with an output end of the voltage comparator; and a detection MOSFET transistor, a control end of which is connected with an output end of the voltage comparator. An output end of the power MOSFET transistor is directly grounded. An output end of the detection MOSFET transistor is connected with a negative input end of the voltage comparator, and is grounded by a second resistor. An input end of the detection MOSFET transistor is connected with an input end of the power MOSFET transistor, and the reference current source is provided with a positive temperature coefficient. The ratio of the first resistor and the second resistor is not related to the temperature, and the ratio of the conduction resistor of the detection MOSFET transistor and the conduction resistor of the power MOSFET transistor is not related to the temperature. The limit peak value current detection circuit is advantageous in that the temperature compensation of the limit peak value current detection can be realized, the costs can be reduced, and the power consumption loss can be reduced.

Description

The maximum peak value current detection circuit of Switching Power Supply

Technical field

The utility model relates to switch power technology, relates in particular to a kind of maximum peak value current detection circuit with Switching Power Supply of temperature compensation ability.

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 the 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 and interface variation, an important factor factor that wherein needs in external condition to consider is exactly " temperature ".Because built-in chip type mosfet transistor, therefore when peak point current was large, chip power-consumption can increase, and then chip temperature can rise, if be triggered to the maximum peak value electric current under high temperature can directly cause working as machine, so temperature is the key factor that affects 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, wherein the maximum peak value electric current I of the built-in mosfet transistor 12 of integrated circuit (IC) chip _SResistance to earth R with inner check point _SRelevant, the relation that is equated by two input terminal voltages of comparer 11 is I as can be known _FR _F=I _SR _S, namely

I wherein _FThe input current of the positive input terminal of expression comparer 11, R _FThat represent is input current I _FResistance value to ground.For guaranteeing the maximum peak value electric current I _STemperature independent, only need to consider

Ratio invariableness and I _FTemperature independent these two conditions, and R _FAnd R _SNormally the integrated resistance of chip internal, can guarantee Ratio invariableness with dielectric material of the same race, also is easy to guarantee in addition I in integrated circuit technique _FTemperature independent.

But above-mentioned prior art has three defectives, the one, and due to R _SResistance is usually very little, and R _FResistance is usually very large again, generally speaking, can't not only do the large resistance of resistance but also do the little resistance of resistance with dielectric material of the same race, otherwise chip cost can be very high; The 2nd, the mosfet transistor 12 resistance in series R of chip internal _SWhen causing peak point current large, loss is very large; The 3rd, chip internal integrated resistor R _S, resistance R _SOn power consumption directly cause the temperature aggravation of rising.

The utility model content

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

For solving the problems of the technologies described above, the utility model 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 connects the negative input end of described voltage comparator 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 the 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 an embodiment of the present utility model, described detection mosfet transistor and power MOSFET are all N-types.

Compared with prior art, the utlity model has following advantage:

In the maximum peak value current detection circuit of the utility model embodiment, the direct ground connection of the output terminal of power MOSFET, detect the control end of mosfet transistor and the control end of power MOSFET and all be connected to the output terminal of voltage comparator, and the output terminal that detects mosfet transistor connects the negative input end of voltage comparator and via the second resistance eutral grounding.Because the direct ground connection of output terminal of detecting mosfet transistor is detected the output terminal of mosfet transistor via the second resistance eutral grounding, can guarantee with lower cost the Ratio invariableness of the first resistance and the second resistance, and the power attenuation of having avoided the output terminal resistance in series of power MOSFET to cause.

Description of drawings

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 maximum peak value current detection circuit of the Switching Power Supply of the utility model embodiment.

Embodiment

The utility model is described in further detail below in conjunction with specific embodiments and the drawings, but should not limit protection domain of the present utility model 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, the second resistance R _SEN

Wherein, reference current source I _FOutput terminal via the first resistance R _FGround connection, the reference current of its generation is designated as I _F, the first resistance R _FResistance value be designated as R _FThe 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 that detects mosfet transistor 302, 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 that detects mosfet transistor 302, the direct ground connection of the output terminal of power MOSFET 303, and the maximum peak value electric current of the power MOSFET 303 of flowing through is designated as I _SDetect the output terminal of mosfet transistor 302 via the second resistance R _SENGround connection, the electric current that detects mosfet transistor 302 of flowing through is designated as the detection electric current I _SENWherein, 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 _FAn 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 terminals; The negative input end of voltage comparator 301 connects the second resistance R _SENAn end, the second resistance R _SENOther end ground connection, the second resistance R _SENWith the detection electric current I _FProduce the voltage of voltage comparator 301 negative input ends.The negative input end of voltage comparator 301 also connects the source that detects mosfet transistor 302 simultaneously.The output terminal of voltage comparator 301 connects the grid that detects mosfet transistor 302 and power MOSFET 303.The drain terminal that detects mosfet transistor 302 connects the drain terminal of power MOSFET 303, the source ground connection of power MOSFET 303.As a nonrestrictive example, detecting mosfet transistor 302 and power MOSFET 303 is all N-type.

As a preferred embodiment, reference current source I _FHas positive temperature coefficient (PTC), the first resistance R _FWith the second resistance R _SENResistance value ratio temperature independent, the ratio of conducting resistance that detects mosfet transistor 302 and power MOSFET 303 is temperature independent.

In the present embodiment, when the positive input terminal of voltage comparator 301 equates with negative input end, realize the shutoff of power MOSFET 303, the electric current of the power MOSFET 303 of flowing through this moment is the maximum peak value electric current I _SSo obtain:

I _FR _F=I _SENR _SEN。

In addition, because the drain terminal that detects mosfet transistor 302 and the drain terminal of power MOSFET link together, as can be known:

I _SEN(R _SEN+ R _P)=I _SR _S, R wherein _PFor detecting the conducting resistance of mosfet transistor 302, R _SConducting resistance for power MOSFET 303.

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

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

Ask local derviation to get 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 _SBe positive temperature characterisitic, and

The 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 satisfy

It is the maximum peak value electric current I _STemperature independent.

The utility model discloses the compensation schemes of the maximum peak value current detecting of built-in mosfet transistor in Switching Power Supply, and describe embodiment of the present utility model and effect with reference to the accompanying drawings.What should be understood that is: above-described embodiment is just to exemplary explanation of the present utility model; rather than to restriction of the present utility model; any utility model that does not exceed in the utility model connotation scope is created; include but not limited to the local structure of circuit change, to the replacement of type or the model of components and parts; and the replacement of other unsubstantialities or modification, within all falling into the utility model protection domain.

Claims (2)

1. the maximum peak value current detection circuit of a Switching Power Supply comprises:

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 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 connects the negative input end of described voltage comparator 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 the 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.

Images