CN202075331U - Current detecting circuit - Google Patents

Abstract

The utility model relates to a current detecting circuit comprising a pulse width modulation chip, an output inductor or transformer, resistors R1, R3, R4and R6, field-effect tubes Q1 and Q2, a triode Q3 and a diode D1. The drain electrodes of the field-effect tubes Q1 and Q2 are both electrically connected with the output inductor or transformer; the base electrode of the triode Q3 is electrically connected with the output inductor or transformer through the resistor R6; one ends of the resistors R1 and R3 are respectively and electrically connected with the output end of the pulse width modulation chip, and the other ends of the resistors R1 and R3 are respectively connected to the grid electrodes of the field-effect tubes Q1 and Q2; the diode D1 is bridged at two ends of the resistor R3; the resistor R4 is connected between the source electrode of the field-effect tube Q2 and the collector electrode of the triode Q3; and the collector electrode of the triode Q3 is electrically connected with the input end of the pulse width modulation chip. The circuit provided by the utility model realizes current detection of a switch power supply by using fewer elements and has the advantages of simple structure, low cost, small occupied space of the total circuit, low circuit loss, and accuracy in detection.

Description

A kind of current detection circuit

Technical field

The utility model relates to Switching Power Supply, is specifically related to a kind of current detection circuit of Switching Power Supply.

Background technology

The implementation method of now common on the market current detection circuit mainly contains two classes: the resistance detection summation current transformer detects.When side circuit designed, the special method of resistance detection that adopts when designing high-power, high-current circuit was unsatisfactory, because in high-power, the high-current circuit, it is serious and cause loss to increase to detect resistance heating, can reach several watts even tens watts; And be difficult to find hundreds of milliohm or the so little resistance of tens milliohms.Current transformer detects the bandwidth that has broad when keeping good waveforms, also provide electrical isolation, and it is also little to detect the little loss of electric current, detects resistance and can select big slightly value for use, as the resistance in ten or twenty Europe, but current transformer detects the cost height and takes up room big.

The utility model content

At the deficiencies in the prior art, the purpose of this utility model is intended to provide a kind of current detection circuit, reduces circuit loss, reducing cost and reducing takes up room.

For achieving the above object, the utility model adopts following technical scheme:

A kind of current detection circuit, comprise pulse width modulating chip, outputting inductance or transformer, resistance R 1, resistance R 3, resistance R 4, resistance R 6, field effect transistor Q1, field effect transistor Q2, triode Q3, diode D1, the drain electrode of the drain electrode of described field effect transistor Q1 and field effect transistor Q2 all electrically connects with outputting inductance or transformer, the base stage of described triode Q3 electrically connects through resistance R 6 and outputting inductance or transformer, one end of resistance R 1 and resistance R 3 all electrically connects with the output terminal of pulse width modulating chip, the other end is connected to the grid of field effect transistor Q1 and the grid of field effect transistor Q2 respectively, diode D1 cross-over connection is in the two ends of resistance R 3, resistance R 4 is connected between the collector of the source electrode of field effect transistor Q2 and triode Q3, and the current detecting input end of the collector of triode Q3 and pulse width modulating chip electrically connects.

For guaranteeing field effect transistor Q1 than the first conducting of field effect transistor Q2, the resistance of described resistance R 3 is greater than the resistance of resistance R 1.

As improvement, the utility model circuit also comprises a filter capacitor C1, the end ground connection of described filter capacitor C1, and the other end is connected between the collector of resistance R 4 and triode Q3, and filter capacitor C1 can reduce the noise in the circuit.

As further improvement, the utility model circuit also comprises one of following or combination in any:

One first noise reduction resistance R 2,2 cross-over connections of the described first noise reduction resistance R are between the source electrode and grid of field effect transistor Q1;

One second noise reduction resistance R 5, the described second noise reduction resistance R, 5 one end ground connection, the other end is connected between the source electrode of resistance R 4 and field effect transistor Q2;

One the 3rd noise reduction resistance R 7,7 cross-over connections of described the 3rd noise reduction resistance R are between the base stage and emitter of triode Q3.The first noise reduction resistance R 2, the second noise reduction resistance R 5, the 3rd noise reduction resistance R 7 act as the noise that reduces in the circuit, can be used alone or in combination in current detection circuit.

A kind of current detection circuit that the utility model is set forth, compared with prior art, its beneficial effect is: only use the minority components and parts can realize the current detecting of Switching Power Supply, simple in structure, cost is low, the space that takies way circuit is little, and do not undertaken by detecting resistance, circuit loss is little, detects accurately.

Description of drawings

Accompanying drawing 1 is the circuit theory diagrams of a kind of current detection circuit of the utility model.

Embodiment

Below, in conjunction with the accompanying drawings and embodiment, a kind of current detection circuit of the present utility model is described further, so that clearerly understand the utility model technological thought required for protection.

Accompanying drawing 1 is the circuit theory diagrams of a kind of current detection circuit of the utility model.As shown in Figure 1, a kind of current detection circuit, comprise pulse width modulating chip, outputting inductance or transformer, resistance R 1, resistance R 3, resistance R 4, resistance R 6, field effect transistor Q1, field effect transistor Q2, triode Q3, diode D1, the drain electrode of the drain electrode of field effect transistor Q1 and field effect transistor Q2 all electrically connects with outputting inductance or transformer, the base stage of triode Q3 electrically connects through resistance R 6 and outputting inductance or transformer, one end of resistance R 1 and resistance R 3 all electrically connects with the output terminal of pulse width modulating chip, the other end is connected to the grid of field effect transistor Q1 and the grid of field effect transistor Q2 respectively, diode D1 cross-over connection is in the two ends of resistance R 3, resistance R 4 is connected between the collector of the source electrode of field effect transistor Q2 and triode Q3, and the detection input end of the collector of triode Q3 and pulse width modulating chip electrically connects.

For reducing the noise in the circuit, the utility model circuit also comprises a filter capacitor C1, the end ground connection of described filter capacitor C1, and the other end is connected between the collector of resistance R 4 and triode Q3.

The utility model circuit also comprises one of following or combination in any: one first noise reduction resistance R 2, and 2 cross-over connections of the described first noise reduction resistance R are between the source electrode and grid of field effect transistor Q1; One second noise reduction resistance R 5, the described second noise reduction resistance R, 5 one end ground connection, the other end is connected between the source electrode of resistance R 4 and field effect transistor Q2; One the 3rd noise reduction resistance R 7,7 cross-over connections of described the 3rd noise reduction resistance R are between the base stage and emitter of triode Q3.The first noise reduction resistance R 2, the second noise reduction resistance R 5, the 3rd noise reduction resistance R 7 act as the noise that reduces in the circuit, can be used alone or in combination in current detection circuit.In the utility model preferred embodiment, take being used in combination of three, more effectively reduced the noise in the circuit, improved accuracy of detection.

The concrete principle of work of current detection circuit is: what the PWM pin of pulse width modulating chip was exported is pulse width modulating signal, when PWM pin output high level, because the value of resistance R 3 can guarantee like this that much larger than resistance R 1 field effect transistor Q1 is than the first conducting of field effect transistor Q2; After the field effect transistor Q1 conducting, outputting inductance or transformer just have flow through drain electrode-source electrode of field effect transistor Q1 of electric current, and this electric current forms voltage drop on the conducting resistance of field effect transistor Q1; The current detecting input end CS pin of width modulation circuit is just delivered to drain electrode-source voltage drop of field effect transistor Q1 in the conducting of field effect transistor Q2 subsequently by resistance R 4, because drain electrode-source voltage drop of field effect transistor Q1 is very low, can't drive triode Q3 by resistance R 6, so triode Q3 ends, drain electrode-source voltage drop of assurance field effect transistor Q1 is not subjected to the influence of triode Q3.

When PWM pin output low level, diode D1 forward conduction, make field effect transistor Q2 the gate charge snap-out release and by, thereby stop to detect by drain electrode-source current among the field effect transistor Q1, subsequently when resistance R 1 has discharged the gate charge of field effect transistor Q1, field effect transistor Q1 by, the drain electrode of field effect transistor Q1 becomes noble potential, drive triode Q3 conducting by resistance R 6, triode Q3 conducting makes the electric charge on the capacitor C 1 be released to zero, for the current detecting (when being PWM pin output high level) of following one-period is got ready.

For a person skilled in the art, can make other various corresponding changes and distortion, and these all changes and distortion should belong within the protection domain of the utility model claim all according to technical scheme described above and design.

Claims (4)

1. current detection circuit, comprise pulse width modulating chip, outputting inductance or transformer, it is characterized in that, also comprise resistance R 1, resistance R 3, resistance R 4, resistance R 6, field effect transistor Q1, field effect transistor Q2, triode Q3, diode D1, the drain electrode of the drain electrode of described field effect transistor Q1 and field effect transistor Q2 all electrically connects with outputting inductance or transformer, the base stage of described triode Q3 electrically connects through resistance R 6 and outputting inductance or transformer, one end of resistance R 1 and resistance R 3 all electrically connects with the output terminal of pulse width modulating chip, the other end is connected to the grid of field effect transistor Q1 and the grid of field effect transistor Q2 respectively, diode D1 cross-over connection is in the two ends of resistance R 3, resistance R 4 is connected between the collector of the source electrode of field effect transistor Q2 and triode Q3, and the current detecting input end of the collector of triode Q3 and pulse width modulating chip electrically connects.

2. current detection circuit as claimed in claim 1 is characterized in that the resistance of described resistance R 3 is greater than the resistance of resistance R 1.

3. current detection circuit as claimed in claim 2 is characterized in that, also comprises a filter capacitor C1, the end ground connection of described filter capacitor C1, and the other end is connected between the collector of resistance R 4 and triode Q3.

4. as each described current detection circuit of claim 1 ~ 3, it is characterized in that, also comprise one of following or combination in any:

One first noise reduction resistance R 2,2 cross-over connections of the described first noise reduction resistance R are between the source electrode and grid of field effect transistor Q1;

One second noise reduction resistance R 5, the described second noise reduction resistance R, 5 one end ground connection, the other end is connected between the source electrode of resistance R 4 and field effect transistor Q2;

One the 3rd noise reduction resistance R 7,7 cross-over connections of described the 3rd noise reduction resistance R are between the base stage and emitter of triode Q3.