CN1144345C - Flyback synchronous rectification DC/DC converter protection device - 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

Flyback synchronous rectification DC/DC converter protection device

The invention relates to the field of power converters, more specifically, to a protection device in a flyback synchronous rectification DC-DC converter that converts high-voltage direct current into low-voltage direct current.

In the existing DC-DC converter, a rectification circuit is usually connected to the AC power grid, and rectification and filtering are performed to obtain a high DC voltage. After passing through the DC-DC converter, the high-voltage direct current can be turned into a low-voltage direct current, which is provided to the load, namely the computer. In this way, a stable voltage can be obtained. Figure 1 shows a simplified structure of a common flyback converter as an example of a common DC-DC converter. Wherein, the main switch Q101 adopts MOSFET, which is connected in series with the primary winding of the main transformer T1. The rectifier diode D101 is connected in series with the secondary winding of T1. In this DC-DC converter, the high-frequency switching action of the main switch Q101 and the detected load terminal voltage (the output voltage detection, isolation, control, etc. are not shown in Figure 1), can be used for the original side of T1 The high DC voltage is converted, and a low DC voltage is obtained on the side of T1, and then a stable voltage is obtained by changing the duty cycle. In this way, a stable power supply can be provided to the load. Among them, the main switch Q101 is controlled by a PWM circuit to perform high-frequency on/off. In other words, the main switch Q101 is controlled by the oscillation signal output from the PWM control circuit. By changing the duty cycle of the output oscillation signal of the PWM control circuit, the duration of Q101 being turned on can be changed, so that even if the input voltage or output load fluctuates, the output voltage Vo can also be kept in a constant range.

However, the DC-DC converter shown in Figure 1 uses rectifier diodes D101, and the loss due to their own voltage drop accounts for about half of the total loss of the DC-DC converter shown (when the output voltage is less than 5V). In recent years, the operating voltages of loads such as data processing devices including computers, that is, the output voltages provided by DC-DC converters to these devices, tend to decrease. For example, going from 5V down to below 3.3V. Therefore, in addition to the energy dissipated, the voltage drop of about 0.7V across these diodes cannot be ignored.

In recent years, a DC-DC converter that does not use a rectifier diode has appeared. The rectifier diode is replaced by a MOSFET (synchronous rectifier), and the main switch is also a MOSFET. In this DC-DC converter, the conduction voltage of the MOS tube Lower, so as to achieve low power loss, high efficiency and small size of the DC-DC converter. In Figure 2, the rectifier diode D101 is replaced by Q202 (MOSFET). In this figure, the main switch Q201 is also a MOSFET, corresponding to the main switch Q101 in FIG. 1 , and the connection method is similar to it. In this DC-DC converter, the rectifier Q202 and the main switch Q201 are turned on/off complementary. Among them, the drive control circuit 1 implements complementary turn-on/turn-off of Q201 and Q202, the signal is transmitted to the negative side through the isolation transformer T202, and then phase-inverted through Q203 and Q204 to obtain complementary drive signals of DRIVER1 and DRIVER2. Since the DC-DC converter shown in Figure 2 does not use a PN junction diode as the rectifier diode D101, both the voltage drop and the dissipated power are reduced. In this way, low power loss, high efficiency and reduced size of the DC-DC converter can be achieved.

Further research on the DC-DC converter shown in Figure 2 shows that the synchronous rectifier maintains conduction for a long time when the DC-DC converter loses input power, load changes or other reasons (such as loss of negative side drive signal) Generally, in severe cases, the problems shown in Figure 3 and Figure 4 will appear.

Figure 3 shows the operation of the DC-DC converter shown in Figure 2 when the input power is lost, the load changes suddenly, and for some reason there is no driving signal provided to DRIVER1 for a long time (referring to more than one working cycle). In the DC-DC converter, when DRIVER1 is at low potential for a long time, after signal transmission and processing, the signal of DRIVER2 is at high potential for a long time, and the synchronous rectifier is in the conduction state for a long time, because the current of the synchronous rectifier is bidirectional Due to the characteristics of the flow, the current in the Q202 synchronous rectifier gradually decreases from the initial forward flow, forming a reverse current that gradually increases in the opposite direction, which will eventually exceed the allowable operating current of the Q202 synchronous rectifier, resulting in damage to the Q202 synchronous rectifier .

Figure 4 shows that the DC-DC converter shown in Figure 2 is normal when the drive signal DRIVER1 is normal. For some reason (such as damage to R201, C202, T202, and C203), DRIVER2 is at a high potential for a long time (referring to more than one operating cycle). Since the signal of DRIVER1 cannot be transmitted to the negative side, the signal of DRIVER2 is at a high potential for a long time, and the synchronous rectifier is in the conduction state for a long time. Due to the bidirectional flow characteristics of the synchronous rectifier current, the current in the Q202 synchronous rectifier The initial positive flow gradually decreases, forming a reverse current that gradually increases in the opposite direction, which will eventually exceed the allowable operating current of the Q202 synchronous rectifier, resulting in damage to the Q202 synchronous rectifier.

The purpose of the present invention is to provide a protection device for a DC-DC converter, which can prevent the MOSFET of the synchronous rectifier from being damaged due to overcurrent in the case of an abnormal drive signal or an internal fault in the circuit.

The purpose of the present invention is achieved by constructing a protection device for a flyback synchronous rectification DC/DC converter, which is arranged in a flyback synchronous rectification DC/DC converter, the converter includes a drive circuit and a main circuit, and the The main circuit includes a main transformer (T201) and a synchronous rectifier (Q202), the drive circuit includes a drive control circuit for driving the synchronous rectifier (Q202), and it is characterized in that it also includes a circuit for detecting the main circuit of the converter. Or the state detection unit (1) of the drive circuit and the control circuit (2) used to generate the control instruction signal for turning off the synchronous rectifier; the input end of the control circuit (2) is connected to the state detection unit (1 ), the output end of the control circuit (2) is connected to the input end of the drive control circuit.

A flyback synchronous rectification DC/DC converter protection device according to the present invention is characterized in that the primary winding of the main transformer is connected to the DC input terminal through a main switch MOSFET, and the main switch is composed of a pulse width modulation PWM unit control.

The flyback synchronous rectification DC/DC converter protection device according to the present invention is characterized in that the control circuit includes an electronically controlled switch, the control terminal of which is connected to the output terminal of the state detection unit.

According to the protection device of the flyback synchronous rectification DC/DC converter provided by the present invention, the feature is that the control circuit adopts a P-channel MOS transistor.

According to the flyback synchronous rectification DC/DC converter protection device provided by the present invention, it is characterized in that the drive control circuit includes: an auxiliary transformer (T202), the input terminal of the state detection unit (1) and the above-mentioned auxiliary transformer (T202) ungrounded output connected.

The protective device for flyback synchronous rectification DC/DC converter provided by the present invention is characterized in that the input terminal of the state detection unit (1) is connected to the output terminal with the same name as the primary side positive voltage input terminal of the main transformer (T201).

According to the flyback synchronous rectification DC/DC converter protection device provided by the present invention, it is characterized in that the control circuit uses a PNP transistor, and when the state detection unit cannot detect a signal within a certain period of time, it is connected to the Q206 tube The potentials of points B and E will decrease exponentially. When the potential drops to the threshold potential of the Q205 tube, the Q205 tube will work in the conduction state, and the gate potentials of Q203 and Q204 will be pulled up to a high potential, synchronously The gate potential of the rectifier tube Q202 becomes lower, and the reverse current loop is cut off to prevent the synchronous rectifier tube Q202 from being damaged due to the gradually increasing reverse current.

According to the flyback synchronous rectification DC/DC converter protection device provided by the present invention, it is characterized in that the control circuit uses a comparator, and if the state detection unit detects no signal within a certain period of time, it is connected to the comparator input negative The potential of points B and E connected to the terminal will decrease exponentially. When the potential drops to the valve potential of the comparator, the comparator outputs a high potential, and the gate potential of Q203 and Q204 is pulled up to high through the D203 tube. Potential, the gate potential of the synchronous rectifier Q202 becomes lower, Q202 is turned off, and the reverse current loop is cut off to prevent the synchronous rectifier Q202 from being damaged due to the gradually increasing reverse current.

Implementing the flyback synchronous rectification DC/DC converter protection device of the present invention effectively prevents the MOSFET of the synchronous rectifier from being damaged due to overcurrent in the case of an abnormal drive signal or an internal circuit fault, and improves the reliability of the module .

Below, in conjunction with accompanying drawing and embodiment, further illustrate the feature of the present invention, in the accompanying drawing:

Figure 1 shows a simplified structure of a common flyback converter as an example of a prior art DC-DC converter;

Figure 2 is a schematic diagram of the principle of a DC-DC converter obtained by replacing the rectifier diode in Figure 1 with a MOSFET;

Fig. 3 is a graphical representation of the operation of the DC-DC converter shown in Fig. 2 when the input power is off and the load changes suddenly;

Fig. 4 is a graphical representation of the operation of the DC-DC converter shown in Fig. 2 when an internal component fails;

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

Fig. 6 is an embodiment of implementing the control circuit of the present invention by using a P-channel MOS transistor;

Fig. 7 is another embodiment of implementing the control circuit of the present invention by using a P-channel MOS transistor;

Figure 8 shows the relevant waveforms of the protection circuit and main circuit in Figure 6 and Figure 7 when the DC-DC corresponds to the situation in Figure 3 .

Figure 9 shows the relevant waveforms of the protection circuit and main circuit in Figure 6 and Figure 7 when the DC-DC converter corresponds to the situation in Figure 4 .

Fig. 10 is a schematic diagram of the principle of realizing the control circuit with a PNP transistor;

Fig. 11 is a schematic diagram of the principle of implementing a control circuit with a comparator.

As shown in Figure 5, the DC-DC converter protection device of the present invention includes a state detection unit 1 that generates a control command signal according to the state of the DC-DC converter and a control circuit that controls the synchronous rectifier according to the control command signal 2. When it is detected that the DC-DC converter is in an abnormal state, a control command signal is generated to turn off the synchronous rectifier (Q202) and cut off the reverse current loop, so as to ensure that the synchronous rectifier is not damaged. In the case of a large output current, on the one hand, it protects the synchronous rectifier from being damaged, and on the other hand, it can prevent the main switch (Q201) on the primary side from being damaged. Wherein, the detection signal can be obtained from different positions of the driving circuit or the main circuit, as shown in Fig. 6 and Fig. 7 for details.

6 and 7 are two specific embodiments of implementing a control circuit by using a P-channel MOS transistor according to the principle of the present invention shown in FIG. 5 . Among them, the detection signal in Figure 6 is obtained from the drive circuit (detection signal point A), the detection signal in Figure 7 is obtained from the main circuit (detection signal point D); the signal is obtained from the drive circuit, the signal at point A is the same as the drive signal DRIVER1 It is synchronous. After processing by the detection circuit composed of D202, C204, R205, and R206, the signal B related to the state of the signal DRIVER1 (corresponding to Figure 6) is obtained, and the relationship is as follows:

set up:

τ ₀ =(R ₂₀₅ //R ₂₀₆ )C ₂₀₄

τ ₁ =R ₂₀₅ C ₂₀₄

τ ₂ =R ₂₀₆ C ₂₀₄

T is the working cycle of the switching power supply, and T _on is the high level time in one cycle

D is the duty cycle, $\mathrm{D.}=\frac{T_{\mathrm{on}}}{T}$

t ⁱ is the time from when the drive signal (DRIVER1) is high level to the fault (less than one cycle)

As shown in Figure 8

V ² is the highest voltage value output by the detection circuit during normal operation

V ¹ is the lowest voltage value output by the detection circuit during normal operation

V ^B is the voltage value output by the detection circuit immediately before the abnormal operation

V ⁱ is the voltage value when the detection circuit inputs a high potential

V ^o is the voltage value output by the detection circuit after abnormal operation

^* All time quantities start from PWM output high level in one switching cycle as zero

Then, after the circuit works stably, the detection circuit outputs the highest voltage value and the lowest voltage value:

${\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="V"\; filenames="C0011723200161.png,C0011723200181.png"\; state="\{\{state\}\}">V</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 206</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 205</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 206</span>}}}\frac{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; D.</span>}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}\mathrm{<span\; class="notranslate">\; T</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; D.</span>}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; T</span>}}}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}$

${\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="V"\; filenames="C0011723200181.png"\; state="\{\{state\}\}">V</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="V"\; filenames="C0011723200161.png,C0011723200181.png"\; state="\{\{state\}\}">V</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; D.</span>}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}\mathrm{<span\; class="notranslate">\; T</span>}}$

Immediately before the abnormal operation, the output voltage value of the detection circuit is:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 206</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 205</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 206</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="V"\; filenames="C0011723200181.png"\; state="\{\{state\}\}">V</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; .</span>}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}}$

0≤t _i <DT immediately before abnormal operation, the output voltage value of the detection circuit is:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 206</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 205</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 206</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="V"\; filenames="C0011723200181.png"\; state="\{\{state\}\}">V</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; .</span>}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}}$

0≤t _i <DT

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="V"\; filenames="C0011723200161.png,C0011723200181.png"\; state="\{\{state\}\}">V</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; .</span>}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; DT</span>}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}}$

DT≤t _i <T

After working abnormally, the output voltage value of the detection circuit is:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}<span\; class="notranslate">\; .</span>}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}}$

t≥t _i

Figure 7 shows that the detection signal is obtained from the main circuit, the DRIVER1 signal is transmitted through Q201 and T201, and the signal obtained at point D is synchronized with it. The signal is processed by the detection circuit composed of D202, C204, R205 and R206, and the state of DRIVER1 is obtained. The related signal E (corresponding to Fig. 7) has the same relationship as above.

Figure 8 shows that the DC-DC converter has no drive signal DRIVER1 for a long time (referring to more than one working cycle) or the DC-DC converter is normal when the drive signal DRIVER1 is normal when the input power is off, the load changes suddenly, and for some reason Certain circuit reasons (such as damage to R201, C202, T202, and C203) cause DRIVER2 to be at high potential for a long time (referring to more than one working cycle), the relevant waveforms of the protection circuit and the main circuit in Figure 6 and Figure 7, Its relational formula is the same as above.

It can be seen that if the detection circuit fails to detect a signal within a certain period of time, the potentials of points B and E connected to the Q205 tube will decrease exponentially. C refers to the potential), the Q205 tube works in the conduction state, the gate potential of Q203 and Q204 is pulled up to a high potential, the gate potential of the synchronous rectifier tube Q202 becomes low, and Q202 is turned off, as shown in the figure, the reverse feedback is cut off To the current loop, to prevent damage to the synchronous rectifier tube Q202 due to gradual reverse current.

Figure 9 shows that when the drive signal DRIVER1 of the DC-DC converter is normal, due to some reason (such as the damage of R201, C202, T202, and C203, DRIVER2 is at a high potential for a long time (referring to more than one working cycle), the figure 6 and Figure 7 are related waveforms of the protection circuit and the main circuit.

Figure 10 is a control circuit implemented with a PNP transistor. If the detection circuit fails to detect a signal within a certain period of time, the potentials of points B and E connected to the Q206 tube will decrease exponentially. When the potential drops to the valve opened by the Q206 tube When the electric potential is high (the potential indicated by C in Figures 8 and 9), the Q206 tube works in the conduction state, and the gate potentials of Q203 and Q204 are pulled up to a high potential, and the gate potential of the synchronous rectifier tube Q202 becomes low, as shown in Figure 8 As shown in and 9, the reverse current loop is cut off to prevent the synchronous rectifier tube Q202 from being damaged due to the gradually increasing reverse current.

Figure 11 is a control circuit implemented with a comparator. If the detection circuit cannot detect a signal within a certain period of time, the potentials of points B and E connected to the negative input of the comparator will decrease exponentially. When the potential decreases to the comparator When the valve potential of the action (the potential of C in Figure 8 and Figure 9) is reached, the comparator outputs a high potential, and through the D203 tube, the gate potential of Q203 and Q204 is pulled up to a high potential, and the gate potential of the synchronous rectifier tube Q202 becomes Low, Q202 is turned off, as shown in Figure 4. Cut off the reverse current loop to prevent the synchronous rectifier tube Q202 from being damaged due to the gradual increase of the reverse current.

The DC-DC converter protection device of the present invention can effectively protect the synchronous rectifier from being damaged under abnormal conditions. The most effective protection of synchronous rectifiers improves the reliability of the module. This scheme has been verified by simulation and will be applied in the AG15 series modules to improve work efficiency and enhance 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.

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