CN105186844A - Protective circuit for preventing power tube from being opened wrongly - Google Patents

Abstract

The invention belongs to the technical field of power supplies, and relates to a protective circuit for preventing a power tube from being opened wrongly. The protective circuit disclosed by the invention mainly comprises a switching node detection module and a discharging module; the switching node detection module is composed of a first PMOS (P-channel Metal Oxide Semiconductor) tube MP1, a second PMOS tube MP2, a first NMOS (N-channel Metal Oxide Semiconductor) tube MN1, a second NMOS tube MN2, a third NMOS tube MN3, a fourth NMOS tube MN4, a first resistor R1 and a second resistor R2; and the discharging module is composed of a first voltage-withstanding NMOS tube MNS1, a second voltage-withstanding NMOS tube MNS2 and a third voltage-withstanding NMOS tube MNS3. The protective circuit disclosed by the invention has the benefits that: the voltage rising slope of a switching node can be rapidly detected in a power tube driving circuit after a main switching tube is opened and corresponding protection operations are then performed; instantaneous rapid discharge is carried out, so that the voltage rising slope of the switching node can be retarded; and furthermore, the switching node quits a protective mechanism in time after the voltage of the switching node rises is inhibited.

Description

A kind of protective circuit opened for preventing power tube from opening by mistake

Technical field

The invention belongs to power technique fields, relating to a kind of protective circuit opened for preventing power tube from opening by mistake.

Background technology

In field of switch power at present in numerous electronic application, operating frequency is more and more higher, although bring the size lightweight of chip like this, and the complexity in the circuit design simultaneously also improved and required precision.

When circuit work frequency is very high, even if be provided with suitable Dead Time, when the moment that main switch is opened, produce larger dV/dt at switching node, to such an extent as to rectifying tube also may be opened.This is that this will bring larger loss because the gate-drain parasitic capacitances generation couple current of rectifying tube causes break-through.Therefore at high working frequencies, the switching loss that there is power MOS pipe replaces the problem of conduction loss.

Summary of the invention

To be solved by this invention, being exactly for the problems referred to above, proposing a kind of protective circuit opened for preventing power tube from opening by mistake.

For achieving the above object, the present invention adopts following technical scheme:

Opening by mistake the protective circuit opened for preventing power tube, it is characterized in that, comprise switching node detection module and discharge module; Described switching node detection module is made up of the first PMOS MP1, the second PMOS MP2, the first NMOS tube MN1, the second NMOS tube MN2, the 3rd NMOS tube MN3, the 4th NMOS tube MN4, the first resistance R1 and the second resistance R2; The drain electrode of the 4th NMOS tube MN4 connects switching signal, its grid and source ground; The grid of the first NMOS tube MN1 is by connecing switching signal after the first resistance R1, its source electrode and grounded drain; Source electrode and the drain electrode of the first PMOS MP1 connect switching signal, and its grid connects the grid of the grid of the first NMOS tube MN1, the grid of the second NMOS tube MN2, the grid of the second PMOS MP2 and the 3rd NMOS tube MN3; The source electrode of the second NMOS tube MN2, drain and gate interconnection; The source electrode of the second PMOS MP2 connects switching signal, and its drain electrode connects the drain electrode of the 3rd NMOS tube MN3; The tie point that second PMOS MP2 drain electrode and the 3rd NMOS tube MN3 drain is by ground connection after the second resistance R2; Second PMOS MP2 drain electrode, the 3rd NMOS tube MN3 drain electrode and the tie point of the second resistance R2 are the output of switching node detection module;

Described discharge module is made up of the first withstand voltage NMOS tube MNS1, the second withstand voltage NMOS tube MNS2 and the 3rd withstand voltage NMOS tube MNS3; The drain electrode of the grid of the first withstand voltage NMOS tube MNS1, the grid of the second withstand voltage NMOS tube MNS2 and the 3rd withstand voltage NMOS tube MNS3 connects the output of switching node detection module; The drain electrode of the first withstand voltage NMOS tube MNS1 connects bootstrap power supply, its source ground; The drain electrode of the second withstand voltage NMOS tube MNS2 connects switching signal, its source ground; The grid of the 3rd withstand voltage NMOS tube MNS3 and source ground.

Further, described first PMOS MP1, the second PMOS MP2, the 3rd NMOS tube MN3 and the 4th NMOS tube MN4 are single-ended pressure resistant type; Described first NMOS tube MN1 and the second NMOS tube MN2 is both-end pressure resistant type.

Beneficial effect of the present invention is; in power tube drive circuit; can detect and make corresponding protection act to the rate of rise of node voltage fast after main switch is opened; the repid discharge carrying out moment slows down the voltage rise slope of switching node; and after node voltage rising is inhibited, exit protection mechanism in time.The extra power consumption produced when can effectively reduce driving power pipe in this way, improves operating frequency and the efficiency of chip entirety, simultaneously by simple adjustment, may be used for the power MOS pipe under kinds of processes, has more wide in range applicability.

Accompanying drawing explanation

Fig. 1 is driving circuit structure schematic diagram;

Fig. 2 is that the present invention is for principle schematic after drive circuit in Fig. 1;

Fig. 3 is workflow schematic diagram of the present invention;

Fig. 4 is that the present invention detects the electrical block diagram of protection for switching node;

Fig. 5 is the circuit diagram of breaker in middle nodal test module of the present invention.

Embodiment

Below in conjunction with accompanying drawing, describe technical scheme of the present invention in detail:

The present invention is a kind of protective circuit be applicable in power tube drive circuit mainly; the structure of drive circuit as shown in Figure 1, comprises high-end tubes PowerNMOS1 (hereinafter referred to as upper pipe) and low side pipe PowerNMOS2 (hereinafter referred to as lower pipe) and their respective drive circuits.And TG and BG is the gate drive signal of high-end tubes and low side pipe respectively.SW is switching node, and BST connects bootstrap capacitor by the bootstrap voltage mode that produces after charging (can with reference to the relevant data of boostrap circuit and document) in outside with SW.Instantly pipe upper pipe unlatching after closing, now SW terminal potential can increase sharply, BST current potential also can rise rapidly simultaneously, if SW node voltage increases too fast, produce larger dV/dt, produce charging current CgddV/dt by the gate leakage capacitance Cgd of lower pipe as shown in Figure 2, one part of current flows to parasitic gate inductance L G to pull down resistor RG, and another part charges to grid source electric capacity Cgs.If this strand of electric current is enough large, produce voltage at RG.When this voltage is close or when exceeding lower pipe threshold, lower pipe will be opened even completely in weak conducting, causes the break-through of pipe up and down, produces larger power consumption and even damage circuit.

Based on the wide usage of circuit of the present invention itself, adopt the dVSW/dt of limit switch node SW end and carry out the method for discharge stream over the ground when this voltage rise is too fast.Specific works flow process as shown in Figure 3, first the climbing speed of SW to earth potential AGND (hereinafter referred to as AGND) voltage is detected in real time, if exceed certain value, SW and BST is discharged over the ground simultaneously, so both can ensure the voltage difference between bootstrap power supply, also can slow down the voltage rise slope of SW end.

As shown in Figure 4, when SW voltage rise is too fast, carry out the real-time detection to SW by detection module, a relatively high detection signal T1 can be exported.This signal Direct driver pressure pipe MNS1 and MNS2 carry out to BST and SW to discharge.Because boostrap circuit can be booted SW and BST to very high current potential; so adopt withstand voltage metal-oxide-semiconductor as the metal-oxide-semiconductor detected in the circuit of SW voltage and discharge stream circuit; MNS3 is used for protection two discharge stream pipe MNS1 and MNS2 with diode type of attachment, prevents the gate source voltage of two discharge stream pipes excessive.Effectively avoid producing larger dV/dt when upper pipe is opened at SW end by above-mentioned measure.

As shown in Figure 5, be SW detection module practical circuit diagram, T1 is the output signal of this module.This module is mainly used for detecting the change in voltage of SW to earth potential AGND, i.e. dVSW/dt, when SW voltage VSW produces an instantaneous rising relative to earth potential AGND, by the RC charge path that R1 and CMN1 in circuit is formed, to CMN1 charging, wherein CMN1 is the mos capacitance be made up of both-end pressure pipe MN1.

Obtain according to RC circuit characteristic

$R1C_{MN1}\frac{{\mathrm{dV}}_{MN1}}{dt}+V_{MN1}=V_{SW}$

Wherein R1 is the resistance value of resistance R1 in Fig. 5, and CMN1 is the mos capacitance value that MN1 is formed; VMN1, VSW are respectively the voltage of MN1 grid voltage and SW.When SW voltage has the voltage of instantaneous relative rising, VSW is similar to the linear increase voltage that a slope is larger, then has

V _SW＝kt

Wherein k is the VSW rate of rise, substitutes into above formula and obtains

$R1C_{MN1}\frac{{\mathrm{dV}}_{MN1}}{dt}+V_{MN1}=kt$

Above formula obtains after arranging

$\frac{{\mathrm{dV}}_{MN1}}{dt}+\frac{1}{R1C_{MN1}}{V}_{MN1}=\frac{1}{R1C_{MN1}}kt$

The solution differential equation above obtains

$V_{MN1}\left(t\right)=e^{-\∫\frac{1}{R1C_{{\mathrm{MN}}_1}}dt}\[\∫\frac{1}{R1C_{MN1}}kt\·e^{\∫\frac{1}{R1C_{MN1}}dt}dt+K\]$ (wherein K is constant)

Abbreviation above formula obtains

$V_{MN1}\left(t\right)=e^{-\frac{1}{R1C_{MN1}}t}\[{\mathrm{kte}}^{\frac{1}{R1C_{MN1}}t}-kR1C_{MN1}{e}^{\frac{1}{R1C_{MN1}}t}+K\]$

Namely

$V_{MN1}\left(t\right)=kt-kR1C_{MN1}+{\mathrm{Ke}}^{-\frac{1}{R1C_{MN1}}t}$

During assumed initial state t=0, VMN1 (0)=V0, due to when main switch is not opened, V0 ≈ 0V then has

K＝kR1C _MN1

$V_{MN1}\left(t\right)=kt-kR1C_{MN1}+\left(kR1C_{MN1}\right)e^{-\frac{1}{R1C_{MN1}}t}$

The drain terminal of MP2 and MN3 is as the output T1 of this detection module, and when SW rises, because mos capacitance grid terminal voltage can not be suddenlyd change, VMN1 is lower than VSW, and by suitably regulating R1CMN1, can obtain when SW voltage rise is too fast, VMN1 is a relatively low level.A relative high level signal T1 is exported after MP2 with MN3 is reverse.Wherein MN2 connects with diode form, is used as protection and prevents MN3 gate source voltage excessive.MP1 drain-source connects SW end, and grid termination MN1 grid is used for filtering the noise spike of switching node SW.R1 has the initialized effect of detection module.MN4 drain terminal meets SW, and grid source Substrate ground current potential is used for being ESD.

Claims (2)

1. the protective circuit opened for preventing power tube from opening by mistake, is characterized in that, comprises switching node detection module and discharge module; Described switching node detection module is made up of the first PMOS MP1, the second PMOS MP2, the first NMOS tube MN1, the second NMOS tube MN2, the 3rd NMOS tube MN3, the 4th NMOS tube MN4, the first resistance R1 and the second resistance R2; The drain electrode of the 4th NMOS tube MN4 connects switching signal, its grid and source ground; The grid of the first NMOS tube MN1 is by connecing switching signal after the first resistance R1, its source electrode and grounded drain; Source electrode and the drain electrode of the first PMOS MP1 connect switching signal, and its grid connects the grid of the grid of the first NMOS tube MN1, the grid of the second NMOS tube MN2, the grid of the second PMOS MP2 and the 3rd NMOS tube MN3; The source electrode of the second NMOS tube MN2, drain and gate interconnection; The source electrode of the second PMOS MP2 connects switching signal, and its drain electrode connects the drain electrode of the 3rd NMOS tube MN3; The tie point that second PMOS MP2 drain electrode and the 3rd NMOS tube MN3 drain is by ground connection after the second resistance R2; Second PMOS MP2 drain electrode, the 3rd NMOS tube MN3 drain electrode and the tie point of the second resistance R2 are the output of switching node detection module;

Described discharge module is made up of the first withstand voltage NMOS tube MNS1, the second withstand voltage NMOS tube MNS2 and the 3rd withstand voltage NMOS tube MNS3; The drain electrode of the grid of the first withstand voltage NMOS tube MNS1, the grid of the second withstand voltage NMOS tube MNS2 and the 3rd withstand voltage NMOS tube MNS3 connects the output of switching node detection module; The drain electrode of the first withstand voltage NMOS tube MNS1 connects bootstrap power supply, its source ground; The drain electrode of the second withstand voltage NMOS tube MNS2 connects switching signal, its source ground; The grid of the 3rd withstand voltage NMOS tube MNS3 and source ground.

2. a kind of protective circuit opened for preventing power tube from opening by mistake according to claim 1, is characterized in that, described first PMOS MP1, the second PMOS MP2, the 3rd NMOS tube MN3 and the 4th NMOS tube MN4 are single-ended pressure resistant type; Described first NMOS tube MN1 and the second NMOS tube MN2 is both-end pressure resistant type.