A kind of drive circuit of bridge circuit
Technical field
The present invention relates to electronic technology field, in particular, relate to a kind of drive circuit of bridge circuit.
Background technology
In the power electronic product; bridge circuit is widely applied; in the use of bridge circuit; usually can be in Dead Time produce negative voltage being about to open on the driving stage of pipe; and when when having only the chip for driving of positive supply power supply; usually the input pin or the output pin of chip for driving can not bear negative voltage, and this avoids the problem that negative voltage damages with regard to proposing a protection chip.
Fig. 1 shows the brachium pontis and the drive circuit thereof of the bridge circuit that is usually used in the power electronic product, comprising: following pipe (power tube Q2) series connection of going up pipe (power tube Q1) and brachium pontis of brachium pontis, a brachium pontis of formation bridge circuit; The pipe Q1 that goes up of brachium pontis is driven by chip for driving U1, and the following pipe of brachium pontis is driven by chip for driving U2; Wherein, be connected with the forward drive branch road of last pipe in parallel and oppositely turn-off branch road between the grid of the first output OUTA of chip for driving U1 (7 pin of chip for driving U1) and last pipe Q1 (on manage Q1 1 pin); Described forward drive branch road is the forward drive resistance R 3 that is connected between the grid of the first output OUTA of chip for driving U1 and last pipe Q1; Described reverse shutoff branch road comprise series connection resistance R 1 and can only be from the grid of last pipe Q1 anti-phase shutoff diode D1 to the unidirectional conducting of the first output OUTA of chip for driving U2; Corresponding, the first output OUTA of chip for driving U2 (7 pin of chip for driving U2) and the forward drive branch road and reverse shutoff branch road that are connected with following pipe in parallel down between the grid of pipe Q2 (1 pin of pipe Q2 down); Described forward drive branch road is to be connected the first output OUTA of chip for driving U2 and the following forward drive resistance R 4 between the grid of pipe Q2; Described reverse shutoff branch road comprise series connection resistance R 2 and can only be from the grid of managing Q2 down anti-phase shutoff diode D2 to the unidirectional conducting of the first output OUTA of chip for driving U2.
In the Dead Time of the drive circuit of bridge circuit, having negative voltage on the chip for driving of the power tube that is about to conducting produces, thereby make its chip for driving output that negative voltage (5 pin current potentials are higher than 7 pin) be arranged, output waveform when the drive circuit that Fig. 2 shows Fig. 1 is used for the phase whole-bridging circuit chip for driving, wherein, abscissa is the time, ordinate is the voltage that 7 pin produce 5 pin, as seen from the figure, before the inherent output of the Dead Time of the chip for driving high level big negative voltage is arranged, be about-1.6V.This negative voltage is easy to exceed the scope that chip for driving allows, and can damage chip for driving.
Fig. 3 shows the principle that above-mentioned negative voltage produces: the drive circuit with the following pipe Q2 of brachium pontis is an example, capacitor C 1 is the drain electrode of power tube Q2 and the parasitic capacitance between source electrode (being 2 pin, 3 pin of power tube Q2), capacitor C 2 is the grid of power tube Q2 and the parasitic capacitance between drain electrode (being 1 pin, 2 pin of power tube Q2), when pipe Q1 was in conducting state on the brachium pontis, the electric current of inductance L 1 flowed from left to right; If last pipe Q1 turn-offs, in Dead Time subsequently, electric current makes parasitic capacitance C1 discharge into no-voltage at a terrific speed in the inductance L 1, and parasitic capacitance C2 is owing to the reason of resistance R 4 and chip for driving U2 internal resistance, its velocity of discharge is slower than parasitic capacitance C1, the source voltage of pipe Q2 is higher than grid voltage thereby following pipe Q2 occurs down, the second output OUTB (5 pin) voltage of Here it is chip for driving U1 is higher than the basic reason of the first output OUTA (7 pin), cause the first output OUTA (7 pin) that the second output OUTB (5 pin) has been produced negative voltage, and this negative voltage is created in the Dead Time, shown in the waveform of Fig. 2.
In order to solve the problem that negative voltage produces, current programme often adopts in the drive circuit of each power tube the mode that increases a catching diode, and as shown in Figure 4: clamped respectively between the first output OUTA of chip for driving U1, U2 and the second output OUTB have catching diode D7, a D8.Still following pipe Q2 is an example, produce principle analysis as can be known by previous negative voltage, the source voltage of Q2 is higher than grid voltage, this voltage has been added in the series loop of catching diode D8 and forward drive resistance R 4, because the conducting of catching diode D8, make the second output OUTB (5 pin), the first output OUTA (7 pin) voltage of chip for driving U2 equal catching diode D8 conduction voltage drop, the conduction voltage drop of common diode is about 0.7V.The maximum normal 0.3V that is of negative voltage that the output of (as IR21814---chip for driving such as UC4424) can bear because chip for driving, existing negative voltage will be obtained and 0.3V can not be surpassed, the second output OUTB (5 pin) that is chip for driving U2 can not surpass 0.3V to the first output OUTA (7 pin) voltage, the negative voltage 0.3V that the conduction voltage drop of catching diode D7, the D8 of this increase of will looking for novelty can bear less than chip, diode is difficult to choose like this.And if diode D7, D8 use conducting voltage is about the general-purpose diode of 0.7V, the negative voltage that negative pressure still can be born greater than chip behind its voltage clamping, promptly the clamped effect of negative voltage is bad.
Summary of the invention
For overcoming above-mentioned defective, technical problem to be solved by this invention provides a kind of drive circuit that alleviates the negative voltage of generation in the Dead Time to the bridge circuit of chip for driving infringement.
The objective of the invention is to be achieved through the following technical solutions:
A kind of drive circuit of bridge circuit, be used for driving the power tube of described bridge circuit, comprise chip for driving, be connected with forward drive branch road in parallel between first output of described chip for driving and the grid of power tube and oppositely turn-off branch road, second output of chip for driving links to each other with the source electrode of power tube; Wherein: described drive circuit also comprises first catching diode and second catching diode, and the described first catching diode forward is connected in parallel between the source electrode and grid of described power tube; In the forward drive branch road, the described second catching diode forward is connected between the grid of first output of chip for driving and power tube.
In the voltage range that the difference of the conduction voltage drop of described first catching diode and second catching diode can be born between second output of first output of chip for driving and chip for driving.The difference of the conduction voltage drop of described first catching diode and second catching diode is in 0.3V.
Described first catching diode and second catching diode are the diode of same model.Use the diode of same model, its conduction voltage drop is identical, then to the elimination better effects if of the negative voltage between the chip for driving output.Experiment showed, that this mode can be so that the voltage difference between the first output OUTA of chip for driving and the second output OUTB be almost nil.
The present invention since in parallel between the source electrode of power tube Q2 and grid can only be from the first catching diode D6 of source electrode to the unidirectional conducting of grid; Series connection can only be from the first output OUTA of the chip for driving U2 second catching diode D4 to the unidirectional conducting of grid of power tube Q2 in the forward drive branch road, at the first catching diode D6, chip for driving U2, in the loop that the second catching diode D4 and forward drive resistance R 4 form, the second catching diode D4 and the first catching diode D6 is in conducting state and conduction voltage drop is equal substantially, the conduction voltage drop that two newly-increased catching diodes form is cancelled out each other substantially, the second catching diode D4 and the first catching diode D6 make when can use the bigger diode of conduction voltage drop commonly used, satisfy the requirement of chip negative voltage, make negative electricity pressure energy that chip for driving bears easily less than permissible value, the interior negative voltage that produces of Dead Time that has alleviated the drive circuit of bridge circuit damages chip for driving, has improved the reliability of drive circuit.
Description of drawings
Fig. 1 is the brachium pontis of existing original bridge circuit and the circuit diagram of drive circuit thereof;
Fig. 2 is the output waveform that drive circuit shown in Figure 1 is used for the phase whole-bridging circuit chip for driving;
Fig. 3 is the schematic diagram that the chip for driving output of drive circuit shown in Figure 1 produces negative voltage;
Fig. 4 is the circuit diagram that common solution chip for driving output produces the scheme of negative voltage;
Fig. 5 is a kind of circuit diagram that solves the scheme of chip for driving output generation negative voltage of the embodiment of the invention.
Embodiment
The invention will be further described below in conjunction with accompanying drawing and preferred embodiment.
As shown in Figure 5: the brachium pontis of bridge circuit is composed in series by the following pipe (power tube Q2) of going up pipe (power tube Q1) and brachium pontis of brachium pontis; Wherein, the pipe Q1 that goes up of brachium pontis is driven by chip for driving U1, and the following pipe of brachium pontis is driven by chip for driving U2; Wherein, be connected with the forward drive branch road of last pipe in parallel and oppositely turn-off branch road between the grid of the first output OUTA of chip for driving U1 (7 pin of chip for driving U1) and last pipe Q1 (on manage Q1 1 pin); Described forward drive branch road is the forward drive resistance R 3 that is connected between the grid of the first output OUTA of chip for driving U1 and last pipe Q1; Described reverse shutoff branch road comprise series connection resistance R 1 and can only be from the grid of last pipe Q1 anti-phase shutoff diode D1 to the unidirectional conducting of the first output OUTA of chip for driving U2; Being parallel with between the source electrode of described power tube Q1 and the grid can only be from the catching diode D5 of source electrode to the unidirectional conducting of grid; Being in series with in the described forward drive branch road can only be from the first output OUTA of the chip for driving U1 catching diode D3 to the unidirectional conducting of grid of power tube Q1.Corresponding, the first output OUTA of chip for driving U2 (7 pin of chip for driving U2) and the forward drive branch road and reverse shutoff branch road that are connected with following pipe in parallel down between the grid of pipe Q2 (1 pin of pipe Q2 down); Described forward drive branch road is to be connected the first output OUTA of chip for driving U2 and the following forward drive resistance R 4 between the grid of pipe Q2; Described reverse shutoff branch road comprise series connection resistance R 2 and can only be from the grid of managing Q2 down anti-phase shutoff diode D2 to the unidirectional conducting of the first output OUTA of chip for driving U2; Being parallel with between the source electrode of described power tube Q2 and the grid can only be from the first catching diode D6 of source electrode to the unidirectional conducting of grid; Being in series with in the described forward drive branch road can only be from the first output OUTA of the chip for driving U2 second catching diode D4 to the unidirectional conducting of grid of power tube Q2.
Compare with ifq circuit figure shown in Figure 1, the present invention has increased catching diode D3 and catching diode D5 two diodes at the drive circuit of power tube Q1, and wherein, described catching diode D3 and catching diode D5 are the diode of same model.The drive circuit of power tube Q2 has increased by the second catching diode D4 and the first catching diode D6, two diodes, and wherein, the described first catching diode D6 and the second catching diode D4 are the diode of same model.
Still the drive circuit with the following pipe Q2 of brachium pontis is an example, manage down when having negative pressure to produce between the source electrode (3 pin) of Q2 and the grid (1 pin), the source electrode of power tube Q2 (3 pin) to grid (1 pin) owing to there is the first catching diode D6 clamped, the first catching diode D6 can adopt common diode, its conduction voltage drop is about 0.7V, then with the source electrode (3 pin) of Q2 to the voltage clamping between the grid (1 pin) at about 0.7V.In the loop that the first catching diode D6, chip for driving U2, the second catching diode D4 and forward drive resistance R 4 form, the second catching diode D4 and the first catching diode D6 is in conducting state and conduction voltage drop is equal substantially, the conduction voltage drop that two newly-increased catching diodes form is cancelled out each other substantially, the negative voltage that is added on the output (7 pin are to 5 pin) of chip for driving is littler, this just make be added in chip for driving U2 two outputs---5 pin equal zero substantially to the voltage between 7 pin, just eliminated the negative voltage that is added on the chip for driving substantially.
It is for the negative voltage that produces between the chip for driving output almost completely being offset that catching diode D3 and catching diode D5 and the second catching diode D4 and the first catching diode D6 use the diode of same model.Certainly, first newly-increased catching diode D6 and the conduction voltage drop of the second catching diode D4 needn't be subjected to must be less than the restriction of the negative value that chip for driving allowed, get final product in the voltage range that the difference that only need to require its conduction voltage drop for the model of the first catching diode D6 and the second catching diode D4 can be born between the second output OUTB of the first output OUTA of chip for driving U2 and chip for driving U2, only need be controlled at the difference of conduction voltage drop in the 0.3V and can adapt to normally used chip for driving usually.
The restriction of the negative voltage that second newly-increased catching diode D4 and the conduction voltage drop of the first catching diode D6 can bear less than chip, do not need its conduction voltage drop less than 0.3V, get final product in the voltage range that the difference that only needs its conduction voltage drop can be born between the second output OUTB of the first output OUTA of chip for driving U2 and chip for driving U2, this just can use very common diode, and needn't use the very low diode of special conduction voltage drop, just can satisfy the requirement of chip negative voltage easily, make negative electricity pressure energy that chip for driving bears easily less than permissible value (0.3V), improved the reliability of drive circuit.
Above content be in conjunction with concrete preferred implementation to further describing that the present invention did, can not assert that concrete enforcement of the present invention is confined to these explanations.For the general technical staff of the technical field of the invention, without departing from the inventive concept of the premise, can also make some simple deduction or replace, all should be considered as belonging to protection scope of the present invention.