CN1144345C - Counter exciting synchronous rectification DC/DC converter protector - Google Patents

Abstract

The present invention relates to a flyback synchronous rectification DC/DC converter protector which comprises a state detection unit 1 and a control circuit 2, wherein the state detection unit 1 can generate signals according to a detected DC-DC converter state; the control circuit 2 can control a synchronous rectifying tube which is connected to the secondary side of a main transformer according to the signals generated by the state detection unit 1; when the DC-DC converter is in an abnormal state, the control circuit 2 can generate control instruction signals to shut off the synchronous rectifying tube so as to cut off a reverse current circuit. The present invention is especially suitable for DC-DC converters adopting a switch controller technique since the present invention can prevent element damage under the condition of secondary side rectifying tube overcurrent caused by abnormal states, power failure or abrupt change of load.

Description

Counter exciting synchronous rectification DC/DC converter protecting apparatus

The present invention relates to the supply convertor field, more particularly, relate to the protective device in a kind of counter exciting synchronous rectification DC-DC converter that high voltage direct current is become low-voltage direct.

Existing DC-DC converter normally inserts a rectification circuit in AC network, carry out rectification and filtering again, to obtain a dc high voltage.Pass through the DC-DC converter again, high voltage direct current just can become low-voltage direct, and offering load is computer.Like this, just stable voltage can have been obtained.Fig. 1 has provided the simplified structure of a common anti exciting converter, with this example as common DC-DC converter.Wherein, main switch Q101 adopts MOSFET, former side's windings in series of it and main transformer T1.Secondary side's windings in series of rectifier diode D101 and T1.In this DC-DC converter, utilize HF switch action and the detected load terminal voltage (not providing in the partial graphs 1 such as output voltage detection, isolation, control) of main switch Q101, can change the former side's of T1 High Level DC Voltage, obtain low dc voltage in the T1 side of paying, by changing duty ratio, just obtained stable voltage again.Like this, just can provide stable power to load.Wherein, main switch Q101 is controlled by a pwm circuit, carries out opening/turn-offing of high frequency.In other words, main switch Q101 is by the oscillator signal control of pwm control circuit output.By changing the duty ratio of pwm control circuit outputting oscillation signal, just can change Q101 and keep the duration of opening, like this, even there are fluctuation in input voltage or output loading, output voltage V o also can remain on a constant scope.

Yet, DC-DC converter using shown in Figure 1 rectifier diode D101 because the loss that they self pressure drop causes accounts for diagram DC-DC converter total losses half (when output voltage during less than 5V) greatly.In recent years, load such as data processing unit comprise the operating voltage of computer, and just the DC-DC converter has the trend of reduction to the output voltage that these devices provide.For example, drop to below the 3.3V from 5V.Therefore, except the energy that dissipates, the pressure drop of about 0.7V also just can not be ignored on these diodes.

A kind of DC-DC converter that does not use rectifier diode has appearred again in recent years, rectifier diode is substituted by MOSFET (synchronous rectifier), main switch also is MOSFET, in this DC-DC converter, the conduction voltage drop of metal-oxide-semiconductor is lower, thereby realizes low-power consumption, high efficiency and the small size of DC-DC converter.In Fig. 2, rectifier diode D101 is substituted by Q202 (MOSFET).Among this figure, main switch Q201 also is MOSFET, and corresponding to the main switch Q101 among Fig. 1, connected mode also similarly.In this DC-DC converter, rectifying tube Q202 and main switch Q201 complementation are opened/are turn-offed.Wherein, Drive and Control Circuit 1 realization Q201, Q202 complementation are opened/are turn-offed, and signal is delivered to marginal through isolating transformer T202, realize paraphase through Q203, Q204 again, obtains the drive signal of DRIVER1 and DRIVER2 complementation.Because DC-DC converter shown in Figure 2 does not use the PN junction diode as rectifier diode D101, the power of voltage drop and dissipation has all reduced.Like this, just can realize low-power consumption, the high efficiency of DC-DC converter and reduce volume.

DC-DC converter shown in Figure 2 is further studied, can find: the DC-DC converter causes synchronous rectifier to keep conducting for a long time in input power down, load changing or other reason (losing as marginal drive signal), under the serious situation, the problem that Fig. 3 and Fig. 4 represent can appear.

Fig. 3 has provided DC-DC converter shown in Figure 2 at input power down, load changing and form long-time no drive signal for a certain reason and offer the ruuning situation of DRIVER1 when (referring to above the more than one work period).In the DC-DC converter, when DRIVER1 is electronegative potential for a long time, transmission and processing through signal, the signal that obtains DRIVER2 is long high potential, the conducting state that synchronous rectifier is in for a long time, because the characteristic of synchronous rectification tube current two-way flow, make the electric current in the Q202 synchronous rectifier reduce gradually from initial forward flow, form the reverse current that rightabout increases gradually, finally can surpass the operating current that the Q202 synchronous rectifier allows, cause the Q202 synchronous rectifier to damage.

It is normal at drive signal DRIVER1 that Fig. 4 has provided DC-DC converter shown in Figure 2, (as the damage of R201, C202, T202, C203) for a certain reason causes DRIVER2 to be in the ruuning situation of high potential when (referring to surpass the more than one work period) for a long time.Because the signal of DRIVER1 can not be delivered to marginal, make that the signal of DRIVER2 is long high potential, the conducting state that synchronous rectifier is in for a long time, because the characteristic of synchronous rectification tube current two-way flow, make the electric current in the Q202 synchronous rectifier reduce gradually from initial forward flow, form the reverse current that rightabout increases gradually, finally can surpass the operating current that the Q202 synchronous rectifier allows, cause the Q202 synchronous rectifier to damage.

The object of the present invention is to provide a kind of protective device of DC-DC converter, under the situation of or circuit internal fault unusual, can prevent that the MOSFET of synchronous rectifier from damaging because of overcurrent in drive signal.

The object of the present invention is achieved like this, construct a kind of counter exciting synchronous rectification DC/DC converter protecting apparatus, be arranged in counter exciting synchronous rectification DC/DC converter, described converter comprises driving loop and major loop, described major loop comprises main transformer (T201) and synchronous rectifier (Q202), described driving loop comprises the Drive and Control Circuit that drives described synchronous rectifier (Q202), it is characterized in that, also comprise the control circuit (2) that is used to detect the state detection unit (1) in described converter major loop or driving loop and is used to produce the control command signal of turn-offing described synchronous rectifier; The input of described control circuit (2) connects the output of described state detection unit (1), and the output of described control circuit (2) links to each other with described Drive and Control Circuit input.

According to a kind of counter exciting synchronous rectification DC provided by the invention/DC converter protecting apparatus, it is characterized in that the former limit of described main transformer winding connects the DC input by main switch MOSFET, described main switch is by a pulse-width modulation PMW unit controls.

According to counter exciting synchronous rectification DC provided by the invention/DC converter protecting apparatus, it is characterized in that described control circuit comprises an electronics controlled switch, its control end is connected the output of described state detection unit.

According to counter exciting synchronous rectification DC provided by the invention/DC converter protecting apparatus, it is characterized in that described control circuit adopts the P channel MOS tube.

According to counter exciting synchronous rectification DC provided by the invention/DC converter protecting apparatus; it is characterized in that; described Drive and Control Circuit comprises: teaser transformer (T202), the input of described state detection unit (1) links to each other with the earth-free output of above-mentioned teaser transformer (T202).

According to counter exciting synchronous rectification DC provided by the invention/DC converter protecting apparatus, it is characterized in that the input of described state detection unit (1) links to each other with the output of the same name of the former limit of main transformer (T201) positive voltage input.

According to counter exciting synchronous rectification DC provided by the invention/DC converter protecting apparatus; it is characterized in that; described control circuit adopts the PNP triode; when described state detection unit detects in the regular hour less than signal; manage the B that links to each other with Q206 so; the current potential that E is ordered will be index law to be reduced; when this current potential is reduced to the threshold potential of Q205 pipe unlatching; the Q205 pipe works in conducting state; with Q203; the grid potential of Q204 is drawn high high potential; synchronous rectifier Q202 grid potential step-down; cut off the reverse current loop, prevent to damage synchronous rectifier Q202 owing to increase reverse current gradually.

According to counter exciting synchronous rectification DC provided by the invention/DC converter protecting apparatus; it is characterized in that; described control circuit adopts comparator; if described state detection unit detects in the regular hour less than signal; the B that links to each other with comparator input negative terminal; the current potential that E is ordered will be index law to be reduced; when this current potential is reduced to the valve current potential of comparator action; comparator output high potential; through the D203 pipe; with Q203; the grid potential of Q204 is drawn high high potential, synchronous rectifier Q202 grid potential step-down, and Q202 turn-offs; cut off the reverse current loop, prevent to damage synchronous rectifier Q202 owing to increase reverse current gradually.

Implement counter exciting synchronous rectification DC of the present invention/DC converter protecting apparatus, realized preventing that effectively the MOSFET of synchronous rectifier from damaging because of overcurrent under the situation of or circuit internal fault unusual, improved the reliability of module in drive signal.

Below, in conjunction with the accompanying drawings and embodiments, further specify characteristics of the present invention, in the accompanying drawing:

Fig. 1 has provided the simplified structure of a common anti exciting converter, with this example as prior art DC-DC converter;

Fig. 2 is the principle schematic that replaces the DC-DC converter that rectifier diode obtains among Fig. 1 with MOSFET;

Fig. 3 is the ruuning situation pictorial diagram of DC-DC converter shown in Figure 2 when input power down, load changing;

Fig. 4 is the ruuning situation pictorial diagram of DC-DC converter shown in Figure 2 when the inner member fault;

Fig. 5 is the schematic diagram of DC-DC converter protective device of the present invention;

Fig. 6 adopts the P channel MOS tube to realize an embodiment of control circuit of the present invention;

Fig. 7 adopts the P channel MOS tube to realize another embodiment of control circuit of the present invention;

Fig. 8 provides DC-DC when corresponding diagram 3 situations, the waveform correlation of Fig. 6 and Fig. 7 protective circuit and major loop.

Fig. 9 provides the DC-DC converter when corresponding diagram 4 situations, the waveform correlation of Fig. 6 and Fig. 7 protective circuit and major loop.

Figure 10 is the principle schematic that realizes control circuit with the PNP triode;

Figure 11 is the principle schematic that realizes control circuit with comparator.

As shown in Figure 5; DC-DC converter protecting apparatus of the present invention; comprise state detection unit 1 and a control circuit 2 of adopting a state to produce control command signal according to control command signal control synchronous rectifier according to the DC-DC converter; producing control command signal when detecting the DC-DC converter and be in abnormality turn-offs synchronous rectifier (Q202); cut off the reverse current loop, thereby guarantee that synchronous rectifier is not damaged.Under the big situation of output current, protect synchronous rectifier not to be damaged on the one hand, can prevent that on the other hand former limit main switch (Q201) from damaging.Wherein, detection signal can be obtained from driving loop or the different position of major loop, specifically sees Fig. 6 and Fig. 7.

Fig. 6, the 7th, the employing P channel MOS tube that proposes according to principle of the present invention shown in Figure 5 is realized two specific embodiments of control circuit.Wherein, the detection signal among Fig. 6 is obtained (detection signal point A) from driving the loop, and the detection signal among Fig. 7 is obtained (detection signal point D) from major loop; Signal is obtained from driving the loop, and signal that A is ordered and drive signal DRIVER1 are synchronous, pass through the processing of the testing circuit of being made up of D202, C204, R205, R206, obtain the signal B (corresponding diagram 6) relevant with signal DRIVER1 state, and its relational expression is:

Set:

τ ₀＝(R ₂₀₅//R ₂₀₆)C ₂₀₄

τ ₁＝R ₂₀₅C ₂₀₄

τ ₂＝R ₂₀₆C ₂₀₄

T is the work period of Switching Power Supply, T _OnBe high level time in one-period

D is a duty ratio, $D=\frac{T_{\mathrm{on}}}{T}$

t ⁱTime (less than one-period) when beginning to fault for high level for drive signal (DRIVER1)

Show as Fig. 8

V ²During for operate as normal, the maximum voltage value of testing circuit output

V ¹During for operate as normal, the minimum voltage value of testing circuit output

V ^BBe moment before the operation irregularity, the magnitude of voltage of testing circuit output

V ⁱMagnitude of voltage during for testing circuit input high potential

V ^oBehind operation irregularity, the magnitude of voltage of testing circuit output

^*All time quantums all are that to begin with PWM output high level in the switch periods be zero point

Then, after circuit working was stable, testing circuit output maximum voltage value and minimum voltage value were:

${\mathrm{<figure-callout\; id="2"\; label="V"\; filenames="C0011723200161.png,C0011723200181.png"\; state="\{\{state\}\}">V</figure-callout>}}_2=\frac{R_{206}}{R_{205}+R_{206}}\frac{1-e^{-\frac{D}{{\mathrm{\&tau;}}_0}T}}{1-e^{-(\frac{1}{{\mathrm{\&tau;}}_2}-\frac{D}{{\mathrm{\&tau;}}_1})T}}{V}_i$

${\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="C0011723200181.png"\; state="\{\{state\}\}">V</figure-callout>}}_1={\mathrm{<figure-callout\; id="2"\; label="V"\; filenames="C0011723200161.png,C0011723200181.png"\; state="\{\{state\}\}">V</figure-callout>}}_2\&CenterDot;e^{-\frac{1-D}{{\mathrm{\&tau;}}_2}T}$

Moment before the operation irregularity, the magnitude of voltage of testing circuit output is:

$V_B=V_i\frac{R_{206}}{R_{205}+R_{206}}(1-e^{-\frac{t_i}{{\mathrm{\&tau;}}_0}})+{\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="C0011723200181.png"\; state="\{\{state\}\}">V</figure-callout>}}_{1.}{e}^{-\frac{t_i}{{\mathrm{\&tau;}}_0}}$

0≤t _iMoment before the＜DT operation irregularity, the magnitude of voltage of testing circuit output is:

$V_B=V_i\frac{R_{206}}{R_{205}+R_{206}}(1-e^{-\frac{t_i}{{\mathrm{\&tau;}}_0}})+{\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="C0011723200181.png"\; state="\{\{state\}\}">V</figure-callout>}}_{1.}{e}^{-\frac{t_i}{{\mathrm{\&tau;}}_0}}$

0≤t _i＜DT

$V_B={\mathrm{<figure-callout\; id="2"\; label="V"\; filenames="C0011723200161.png,C0011723200181.png"\; state="\{\{state\}\}">V</figure-callout>}}_{2.}{e}^{-\frac{t_i-\mathrm{DT}}{{\mathrm{\&tau;}}_2}}$

DT≤t _i＜T

Behind the operation irregularity, the magnitude of voltage of testing circuit output is:

$V_o=V_{B.}{e}^{-\frac{t-t_i}{{\mathrm{\&tau;}}_2}}$

t≥t _i

Fig. 7 illustrates detection signal and obtains from major loop, the DRIVER1 signal is through the transmission of Q201, T201, synchronous with it this signal of signal that obtains at the D point passes through the processing of being made of testing circuit D202, C204, R205, R206, obtain the signal E (corresponding diagram 7) relevant with the DRIVER1 state, its relational expression is the same.

Fig. 8 provide the DC-DC converter at input power down, load changing and form long-time no drive signal DRIVER1 (finger) for a certain reason above the more than one work period or the DC-DC converter normal at drive signal DRIVER1; owing to certain circuit reason (as the damage of R201, C202, T202, C203) own; cause DRIVER2 to be in high potential for a long time when (referring to surpass the more than one work period); the waveform correlation of Fig. 6 and Fig. 7 protective circuit and major loop, its relational expression is the same.

As can be seen, if testing circuit detects in the regular hour less than signal, the B that links to each other with the Q205 pipe, the current potential that E is ordered will be index law and reduce, when this current potential is reduced to the threshold potential (current potential that C refers among this figure) of Q205 pipe unlatching, the Q205 pipe works in conducting state, the grid potential of Q203, Q204 is drawn high high potential, synchronous rectifier Q202 grid potential step-down, Q202 turn-offs, as shown in the figure, cut off the reverse current loop, prevent since gradually reverse current damage synchronous rectifier Q202.

It is normal at drive signal DRIVER1 that Fig. 9 provides the DC-DC converter; for a certain reason (as the damage of R201, C202, T202, C203; cause DRIVER2 to be in high potential for a long time when (referring to surpass the more than one work period), the waveform correlation of Fig. 6 and Fig. 7 protective circuit and major loop.

Figure 10 realizes control circuit with the PNP triode, if testing circuit detects in the regular hour less than signal, the B that links to each other with the Q206 pipe, the current potential that E is ordered will be index law and reduce, when this current potential is reduced to the threshold potential (current potential that C refers among Fig. 8 and 9) of Q206 pipe unlatching, the Q206 pipe works in conducting state, the grid potential of Q203, Q204 is drawn high high potential, synchronous rectifier Q202 grid potential step-down, shown in Fig. 8 and 9, cut off the reverse current loop and prevent to damage synchronous rectifier Q202 owing to increase reverse current gradually.

Figure 11 realizes control circuit with comparator, if testing circuit detects in the regular hour less than signal, the B that links to each other with comparator input negative terminal, the current potential that E is ordered will be index law and reduce, when this current potential was reduced to the valve current potential (current potential that C refers among Fig. 8 and Fig. 9) of comparator action, comparator output high potential was through the D203 pipe, the grid potential of Q203, Q204 is drawn high high potential, synchronous rectifier Q202 grid potential step-down, Q202 turn-offs, as shown in Figure 4.Cut off the reverse current loop, prevent to damage synchronous rectifier Q202 owing to increasing reverse current gradually.

DC-DC converter protecting apparatus of the present invention is to protect the damage of synchronous rectifier under abnormal conditions effectively.Protect synchronous rectifier most effectively, improved the reliability of module, this scheme through the emulation demonstration, will be applied in the AG15 series module, improve operating efficiency, strengthen reliability.

Claims (8)

1, a kind of counter exciting synchronous rectification DC/DC converter protecting apparatus, be arranged in counter exciting synchronous rectification DC/DC converter, described converter comprises driving loop and major loop, described major loop comprises main transformer (T201) and synchronous rectifier (Q202), described driving loop comprises the Drive and Control Circuit that drives described synchronous rectifier (Q202), it is characterized in that, also comprise the control circuit (2) that is used to detect the state detection unit (1) in described converter major loop or driving loop and is used to produce the control command signal of turn-offing described synchronous rectifier; The input of described control circuit (2) connects the output of described state detection unit (1), and the output of described control circuit (2) links to each other with described Drive and Control Circuit input.

According to the described counter exciting synchronous rectification DC of claim 1/DC converter protecting apparatus, it is characterized in that 2, the former limit of described main transformer winding connects the DC input by main switch MOSFET, described main switch MOSFET is controlled by a pwm unit.

According to the described counter exciting synchronous rectification DC of claim 1/DC converter protecting apparatus, it is characterized in that 3, described control circuit (2) comprises an electronic switch (Q205), its control end is connected the output of described state detection unit.

According to the described counter exciting synchronous rectification DC of claim 1/DC converter protecting apparatus, it is characterized in that 4, described control circuit (2) adopts the P channel MOS tube.

5, according to the described counter exciting synchronous rectification DC of claim 1/DC converter protecting apparatus; it is characterized in that; described Drive and Control Circuit comprises: teaser transformer (T202), the input of described state detection unit (1) links to each other with the earth-free output of above-mentioned teaser transformer (T202).

According to the described counter exciting synchronous rectification DC of claim 1/DC converter protecting apparatus, it is characterized in that 6, the input of described state detection unit (1) links to each other with the output of the same name of the former limit of main transformer (T201) positive voltage input.

According to the described counter exciting synchronous rectification DC of claim 1/DC converter protecting apparatus, it is characterized in that 7, described control circuit (2) is a triode, its base stage connects the output of described state detection unit.

According to the described counter exciting synchronous rectification DC of claim 1/DC converter protecting apparatus, it is characterized in that 8, described control circuit (2) is a comparator, an one input connects described state detection unit output, its another input termination reference voltage.

Images