CN113746358A - Synchronous rectification switch control circuit - Google Patents
Synchronous rectification switch control circuit Download PDFInfo
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- CN113746358A CN113746358A CN202110936916.8A CN202110936916A CN113746358A CN 113746358 A CN113746358 A CN 113746358A CN 202110936916 A CN202110936916 A CN 202110936916A CN 113746358 A CN113746358 A CN 113746358A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M7/2176—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only comprising a passive stage to generate a rectified sinusoidal voltage and a controlled switching element in series between such stage and the output
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
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Abstract
The invention discloses a synchronous rectification switch control circuit which provides a grid drive signal for a synchronous power MOSFET. The invention comprises a synchronous power MOSFET drain-source voltage slope detection circuit, a start detection circuit, a turn-off detection circuit and a logic control circuit, wherein the output ends of the synchronous power MOSFET drain-source voltage slope detection circuit, the start detection circuit and the turn-off detection circuit are respectively and independently connected with the input end of the logic control circuit, and the output end of the logic control circuit is connected with the grid electrode of the synchronous power MOSFET. The circuit structure adopted by the invention not only realizes the accurate turn-on and turn-off of the synchronous power MOSFET, but also provides a current path for the demagnetization of the transformer when the synchronous power MOSFET is turned on, and prevents the breakdown of the synchronous circuit when the synchronous power MOSFET is turned off. Meanwhile, the invention also prevents the abnormal opening of the synchronous power MOSFET caused by system resonance after the demagnetization of the transformer is finished, thereby ensuring the high efficiency and the high reliability of the work of the synchronous power MOSFET.
Description
Technical Field
A synchronous rectification switch control circuit belongs to the technical field of electronics, and is particularly suitable for being integrated in a synchronous rectification chip.
Background
In a conventional secondary rectifier circuit, as shown in fig. 1, a schottky diode is the first choice for low voltage, high current applications. However, with increasing power, schottky diodes have had limited efficiency improvements in low voltage, high current applications. Particularly, aiming at the increasingly enhanced environmental protection requirements of people, the six-level energy consumption standards successively introduced by the united states and the european union have higher requirements on standby power and working efficiency of power supply products such as power chargers and adapters.
Due to the characteristics of low on-resistance, mature process and the like of the power MOSFET, the synchronous rectification technology is selected to replace a Schottky diode in the secondary rectification circuit, and the tendency of non-blocking is realized.
In the application of low voltage and large current, the synchronous rectification technology has obvious advantages. The power MOSFET has strong current conducting capacity, the voltage drop of the secondary rectification is equal to the voltage drop of the power MOSFET, the on resistance of the power MOSFET is determined, the on resistance of the power MOSFET is low, the conduction loss is small, and the switching loss of the power MOSFET is reduced by the improvement of the control technology.
However, in the synchronous rectification circuit using the driving power MOSFET, the synchronous circuit is a passive operation mode. Therefore, how to accurately control the on and off of the power MOSFET becomes a key factor affecting the operating efficiency and stability of the synchronous rectification system. The power MOSFET is switched on at the moment of demagnetization of the transformer, and is switched off at the moment of demagnetization ending, which is the most ideal condition. However, in practical system applications, how to do this as much as possible becomes a difficult problem for circuit engineers.
Disclosure of Invention
In view of the above, the present invention provides a synchronous rectification switch control circuit, which can realize the precise on and off of a synchronous power MOSFET. When the synchronous power MOSFET is turned on, a current path is provided for demagnetization of the transformer, and when the synchronous power MOSFET is turned off, the synchronous power MOSFET is prevented from being broken down. Meanwhile, the invention can also prevent the abnormal opening of the synchronous power MOSFET caused by the system resonance after the demagnetization of the transformer is finished, thereby ensuring the high efficiency and the high reliability of the work of the synchronous power MOSFET.
The invention discloses a synchronous rectification switch control circuit, which comprises a synchronous power MOSFET drain-source voltage slope detection circuit, a starting detection circuit, a switching-off detection circuit and a logic control circuit;
the output ends of the synchronous power MOSFET drain-source voltage slope detection circuit, the turn-on detection circuit and the turn-off detection circuit are respectively and independently connected with the input end of the logic control circuit, and the output end of the logic control circuit is connected with the grid electrode of the synchronous power MOSFET.
Furthermore, the synchronous power MOSFET drain-source voltage slope detection circuit performs preparation action for starting the synchronous power MOSFET, is used for detecting the change slope of the synchronous power MOSFET drain-source voltage, and latches the detected signal;
the starting detection circuit is used for controlling the starting detection of the synchronous power MOSFET;
the turn-off detection circuit is used for controlling turn-off detection of the synchronous power MOSFET;
the logic control circuit carries out logic operation on the received turn-on and turn-off signals and then controls the turn-on and turn-off of the synchronous power MOSFET; if the change slope of the drain-source voltage of the synchronous power MOSFET in the set time is larger than the set threshold, the synchronous power MOSFET is started; and otherwise, if the change slope of the drain-source voltage of the synchronous power MOSFET in the set time is smaller than the set threshold, the synchronous power MOSFET is turned off.
Furthermore, the drain-source voltage slope detection circuit of the synchronous power MOSFET comprises a first comparator, a second comparator, a third comparator, a current source, a PMOS (P-channel metal oxide semiconductor) tube, an NMOS (N-channel metal oxide semiconductor) tube, a capacitor, a first two-input NOR gate, a first inverter, a second inverter and a first RS trigger;
the positive input end of the first comparator is connected with the drain-source voltage of the synchronous power MOSFET, and the negative input end of the first comparator is connected with a first reference voltage; the output end of the first comparator is connected with one input end of the first two-input NOR gate and the input end of the second inverter;
the positive input end of the second comparator is connected with a second reference voltage, and the negative input end of the second comparator is connected with the drain-source voltage of the synchronous power MOSFET; the output end of the second comparator is connected with the other input end of the first two-input NOR gate;
the output end of the first two-input NOR gate is connected with the input end of a first phase inverter, and the output end of the first phase inverter is connected with the grid electrodes of a PMOS tube and an NMOS tube;
the positive end of the current source is connected with a power VCC, and the negative end of the current source is connected with the source electrode of the PMOS tube;
the drain electrode of the PMOS tube is connected with the drain electrode of the NMOS tube and the anode of the capacitor;
the source electrode of the NMOS tube is grounded, and the negative electrode of the capacitor is also grounded;
the positive input end of the third comparator is connected with the positive electrode of the capacitor, the negative input end of the third comparator is connected with a third reference voltage, and the output end of the third comparator is connected with the position end of the first RS trigger;
the reset end of the first RS trigger is connected with the output end of the second phase inverter, and the output end of the first RS trigger is connected with the logic control circuit.
Further, the turn-on detection circuit includes a fourth comparator;
the positive input end of the fourth comparator is connected with the drain-source voltage of the synchronous power MOSFET, and the negative input end of the fourth comparator is connected with a fourth reference voltage; and the output end of the fourth comparator is connected with the logic control circuit.
Further, the turn-off detection circuit includes a fifth comparator;
the positive input end of the fifth comparator is connected with a fifth reference voltage, and the negative input end of the fifth comparator is connected with the drain-source voltage of the synchronous power MOSFET; and the output end of the fifth comparator is connected with the logic control circuit.
Further, the logic control circuit comprises a second two-input NOR gate and a second RS flip-flop.
One end of the second two-input NOR gate is connected with the output end of the first RS trigger RS1, and the other end of the second two-input NOR gate is connected with the output end of the fourth comparator;
the output of the second two-input NOR gate is connected with the setting end of the second RS trigger and used for controlling the start of the synchronous power MOSFET;
the reset end of the second RS trigger is connected with the output end of the fifth comparator and is used for controlling the turn-off of the synchronous power MOSFET;
and the output end of the second RS trigger is used for driving the grid electrode of the synchronous power MOSFET and controlling the on and off of the synchronous power MOSFET.
Further, the first reference voltage is used for setting a starting point of the detection of the drain-source voltage falling slope of the synchronous power MOSFET, and the second reference voltage is used for setting a termination point of the detection of the drain-source voltage falling slope of the synchronous power MOSFET.
Further, a current source, a capacitor and a third reference voltage in the synchronous power MOSFET drain-source voltage slope detection circuit commonly set a slope threshold value of the synchronous power MOSFET drain-source voltage drop.
Further, the first RS trigger is used for latching the detected change slope signal of the drain-source voltage of the synchronous power MOSFET.
Further, the fourth reference voltage is used to set a threshold point at which the synchronous power MOSFET is turned on.
Further, the fifth reference voltage is used to set a threshold point at which the synchronous power MOSFET turns off.
Further, if the drain-source voltage falling slope of the synchronous power MOSFET is greater than a set threshold, the logic control circuit transmits a start signal detected by the start detection circuit to a set end of the second RS trigger to start the synchronous power MOSFET;
if the falling slope of the drain-source voltage of the synchronous power MOSFET is smaller than a set threshold, shielding the output of the start detection circuit and keeping the output of the second RS trigger in a state of turning off the synchronous power MOSFET;
and the logic control circuit transmits a turn-off signal of the turn-off detection circuit to the reset end of the second RS trigger to turn off the synchronous power MOSFET.
The circuit structure adopted by the invention not only realizes the accurate turn-on and turn-off of the synchronous power MOSFET, but also provides a current path for the demagnetization of the transformer when the synchronous power MOSFET is turned on, and prevents the breakdown of the synchronous circuit when the synchronous power MOSFET is turned off. Meanwhile, the invention also prevents the abnormal opening of the synchronous power MOSFET caused by system resonance after the demagnetization of the transformer is finished, thereby ensuring the high efficiency and the high reliability of the work of the synchronous power MOSFET.
Drawings
FIG. 1 is a circuit diagram of a conventional Schottky diode used as a rectifying circuit;
FIG. 2 shows a flyback power supply using TdelayAfter the shielding demagnetization is finished, the resonance waveform starts a circuit diagram of the synchronous power MOSFET;
FIG. 3 shows a flyback power supply using TdelayAfter shielding demagnetization is finished, the resonant waveform starts a grid driving waveform diagram of the synchronous power MOSFET;
FIG. 4 is a circuit diagram of the turn-on detection of the synchronous rectification switch according to the present invention;
fig. 5 is a waveform diagram of the gate driving of the synchronous power MOSFET after the present invention is used in the flyback power supply.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the accompanying drawings and specific embodiments.
First, terms of art to which the present invention relates will be explained:
PMOS: a P-channel metal oxide semiconductor FET, a P-channel metal oxide semiconductor field effect transistor;
NMOS, N-channel metal oxide semiconductor FET and N-channel metal oxide semiconductor field effect transistor.
The synchronous rectification switch control circuit provided by the invention judges whether the synchronous power MOSFET is turned on in the current period by detecting the falling slope of the Vds voltage of the synchronous power MOSFET in a set time period.
When a Schottky diode is used as a rectifier device in the prior art, the Schottky diode is conducted in the forward direction when a transformer is demagnetized; after the demagnetization of the transformer is finished, the system is in damping resonance, and the Schottky diode is cut off reversely.
In the application of synchronous rectification, after a power MOSFET is adopted to replace a Schottky diode, the Vds voltage of the power MOSFET is rapidly reduced to negative voltage during demagnetization, and the power MOSFET is started by adopting a set negative voltage threshold (generally about-100 mV); after the power MOSFET is opened, the on-resistance is small, the voltage drop of the power MOSFET is small, the loss is small, and the efficiency of the synchronous circuit is high. With the reduction of demagnetization current, the voltage drop on the power MOSFET is reduced, and when the voltage drop is reduced to a certain degree (generally about-5 mV), the power MOSFET is turned off, and the synchronous rectification in one period is finished, and the next period is entered.
In the actual circuit design, after demagnetization is finished, a power supply system starts to resonate due to parasitic effect, and abnormal opening in a shielding resonant period is needed to prevent a transformer from being broken through and affecting the normal operation of the system.
In most current circuits, as shown in fig. 2, Vds and a turn-on negative voltage (usually about-100 mV) are compared and output, a certain delay time (usually about 100 ns) is set, and then the power MOSFET is turned on again, and the waveform is shown in fig. 3, so that abnormal turn-on of the power MOSFET caused by resonance can be effectively shielded. However, as a result of this approach, the normal turn-on of the power MOSFET is also shielded around 100ns, which virtually reduces the operating efficiency of the system. Moreover, the resonance frequency is different for different circuit systems, and the set delay time (usually about 100 ns) is not compatible with all the systems, so although the method is simple, the defect is obvious.
In order to improve the situation, the invention particularly provides a synchronous rectification switch control circuit which judges whether to turn on a synchronous power MOSFET by detecting the falling slope of the Vds voltage of the synchronous power MOSFET in a set time period, and the specific circuit is shown in FIG. 4.
As shown in fig. 4, the present invention includes a slope detection circuit 10 for the drain-source voltage Vds of the synchronous power MOSFET, a turn-on detection circuit 20, a turn-off detection circuit 30, and a logic output circuit 40. The output ends of the synchronous power MOSFET drain-source voltage slope detection circuit 10, the on detection circuit 20 and the off detection circuit 30 are respectively and independently connected with the input end of the logic control circuit 40, and the output end of the logic control circuit is connected with the grid of the synchronous power MOSFET.
The Vds slope detection circuit 10 performs a preparation operation for turning on the synchronous power MOSFET, detects a Vds change slope of the synchronous power MOSFET, and latches a detected signal. If the Vds of the synchronous power MOSFET changes with a slope larger than a set threshold value within a set time, the synchronous power MOSFET is started; on the contrary, if the change slope of Vds of the synchronous power MOSFET in the set time is smaller than the set threshold, the synchronous power MOSFET is turned off.
The turn-on detection circuit 20 is used to detect whether the synchronous power MOSFET needs to be turned on, and the reference voltage vref4 is used to set a threshold point for turning on the synchronous power MOSFET, which is generally a negative voltage (-100mV or so), indicating that the synchronous power MOSFET needs to be turned on.
The turn-off detection circuit 30 is used for detecting whether the synchronous power MOSFET is turned off, and the reference voltage vref5 is used for setting a threshold point for turning off the synchronous power MOSFET, and the voltage is generally a negative voltage (-about 5 mV) or a zero voltage, which indicates the turn-off requirement of the synchronous power MOSFET.
The logic control circuit 40 is configured to perform a logic operation on the output signals of the Vds slope detection circuit 10, the turn-on detection circuit 20, and the turn-off detection circuit 30, output a drive signal to drive the gate of the synchronous power MOSFET, and control the turn-on and turn-off of the synchronous power MOSFET.
The Vds slope detection circuit 10 comprises a first comparator comp1, a second comparator comp2, a third comparator comp3, a current source Idc, a PMOS transistor PM0, an NMOS transistor NM0, a capacitor C, a first two-input nor gate nor2_1, a first inverter inv1, a second inverter inv2 and a first RS flip-flop RS 1. The positive input end of the first comparator comp1 is connected with Vds, and the negative input end is connected with a reference voltage Vref 1; the output of the first comparator comp1 is connected to one of the inputs of the first two-input nor gate nor2_1 and the input of the second inverter inv 2. The positive input end of the second comparator comp2 is connected with the reference voltage Vref2, and the negative input end is connected with Vds; the output of the second comparator comp2 is connected to the other input of the first two-input nor gate nor2_ 1. The output of the first two-input nor2_1 is connected to the input of the first inverter inv1, and the output of the first inverter inv1 is connected to the gates of the PMOS transistor PM0 and the NMOS transistor NM 0. The positive end of the current source Idc is connected with a power supply VCC, and the negative end of the current source Idc is connected with the source electrode of the PMOS tube PM 0. The drain of the PMOS transistor PM0 is connected to the drain of the NMOS transistor NM0 and the anode of the capacitor C. The source of the NMOS transistor NM0 is grounded, and the cathode of the capacitor C is also grounded. The positive input end of the third comparator comp3 is connected with the positive electrode of the capacitor C, the negative input end is connected with the reference voltage Vref3, and the output end of the third comparator comp3 is connected with the set end S of the first RS flip-flop RS 1. The reset terminal R of the first RS flip-flop RS1 is connected to the output of the second inverter inv2, and the output of the first RS flip-flop RS1 is connected to the logic control circuit 40.
The turn-on detection circuit 20 includes a fourth comparator comp 4. The positive input of the fourth comparator comp4 is connected to Vds and the negative input is connected to the reference voltage Vref 4. The output of the fourth comparator comp4 is connected to the logic control circuit 40.
The shutdown detection circuit 30 includes a fifth comparator comp 5. The positive input end of the fifth comparator comp5 is connected with the reference voltage Vref5, and the negative input end is connected with Vds; the output of the fifth comparator comp5 is connected to the logic control circuit 40.
The logic control circuit 40 comprises a second two-input nor gate 2_2 and a second RS flip-flop RS 2. One end of the second two-input nor2_2 is connected to the output of the Vds slope detection circuit 10, i.e. the output of the first RS flip-flop RS1, and the other end is connected to the output of the fourth comparator comp 4. The output of the second two-input nor2_2 is connected to the set terminal S of the second RS flip-flop RS2 for controlling the turn-on of the synchronous power MOSFET. The reset terminal R of the second RS flip-flop RS2 is connected to the output of the fifth comparator comp5 for controlling the turn-off of the synchronous power MOSFET. The output of the second RS2 flip-flop is used to drive the gate of the synchronous power MOSFET, controlling the on and off of the synchronous power MOSFET.
And judging whether the synchronous power MOSFET is turned on in the current period by detecting the falling slope of the drain-source voltage Vds of the synchronous power MOSFET.
The Vds slope detection circuit 10 prepares for the synchronous power MOSFET to turn on, and provides a period of time for detecting the Vds voltage falling slope. Where Vref1 sets the starting point for Vds voltage droop slope detection and Vref2 sets the end point for Vds voltage droop slope detection, where Vref1 must be higher than Vref 2. The Vds slope detection circuit 10 sets a slope threshold of the Vds voltage drop of the synchronous power MOSFET in common through the current source Ids, the capacitor C, and the reference voltage Vref 3.
The first RS flip-flop RS1 is used to latch the detected Vds change slope signal. If the drop slope of Vds is fast, the voltage of the capacitor C does not exceed the reference voltage Vref3 in the period of time from the drop of Vds from Vref1 to Vref2, and the output of the first RS flip-flop is latched low; if the drop slope of Vds is slow, the voltage on the capacitor C exceeds the reference voltage Vref3 during the period from the time when Vds drops from Vref1 to Vref2, and the first RS flip-flop is latched high. In addition, the first comparator comp1 is used as the reset terminal of the first RS flip-flop RS1 to ensure that each switching cycle can be detected.
If the Vds drop slope is fast, the normal requirement of the synchronous power MOSFET is judged, a starting signal detected by the starting detection circuit 20 can be transmitted to a setting end S of the second RS trigger, and the synchronous power MOSFET is started; if Vds is slowly decreased, it is determined that the synchronous power MOSFET is in an abnormal condition, the transmission of the turn-on signal detected by the turn-on detection circuit 20 is prohibited, that is, the output of the turn-on detection circuit 20 is shielded, and the output of the second RS flip-flop RS2 is maintained in a state where the synchronous power MOSFET is turned off.
Meanwhile, the logic control circuit 40 also transmits a turn-off signal of the turn-off detection circuit 30 to the reset terminal R of the second RS flip-flop, turning off the synchronous power MOSFET.
Specifically, fig. 5 shows a waveform diagram of the operation of the circuit according to the present invention. When the transformer is demagnetized, the Vds voltage of the power MOSFET is rapidly reduced to negative voltage, and can be reduced by several volts within 10ns generally. And when the transformer is demagnetized and resonated, the falling slope of Vds is much slower. The invention utilizes the characteristic and adopts a mode of detecting the slope to judge whether the drop of the Vds is demagnetization or resonance after demagnetization. Vds decreases from Vref1 to Vref2 for a maximum time of
The timing is started when Vds is lower than Vref1, and the timing is ended when Vds is lower than Vref 2. If the voltage on the capacitor C is lower than Vref3 in the period T, the drop of Vds is considered to be caused by demagnetization, the output of the first RS trigger RS1 is latched low, and the power MOSFET is opened when the Vds is lower than Vref 4; otherwise, if the voltage on the capacitor C is higher than Vref3 in the period of T, then the Vd is considered to beThe drop in s is caused by the resonance after demagnetization and the output of the first RS flip-flop RS1 is set high and the power MOSFET will not turn on even if Vds then falls below Vref 4.
In the equivalent way,
i.e. the maximum slope that identifies either demagnetization or resonance for Vds, this slope can also be expressed as
The circuit structure adopted by the invention not only realizes the accurate turn-on and turn-off of the synchronous power MOSFET, but also provides a current path for the demagnetization of the transformer when the synchronous power MOSFET is turned on, and prevents the breakdown of the synchronous circuit when the synchronous power MOSFET is turned off. Meanwhile, the invention also prevents the abnormal opening of the synchronous power MOSFET caused by system resonance after the demagnetization of the transformer is finished, thereby ensuring the high efficiency and the high reliability of the work of the synchronous power MOSFET.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (10)
1. A synchronous rectification switch control circuit is characterized by comprising a synchronous power MOSFET drain-source voltage slope detection circuit, a turn-on detection circuit, a turn-off detection circuit and a logic control circuit;
the output ends of the synchronous power MOSFET drain-source voltage slope detection circuit, the turn-on detection circuit and the turn-off detection circuit are respectively and independently connected with the input end of the logic control circuit, and the output end of the logic control circuit is connected with the grid electrode of the synchronous power MOSFET.
2. A synchronous rectification switch control circuit as claimed in claim 1,
the synchronous power MOSFET drain-source voltage slope detection circuit performs preparation action for starting the synchronous power MOSFET, is used for detecting the change slope of the synchronous power MOSFET drain-source voltage and latches the detected signal;
the starting detection circuit is used for controlling the starting detection of the synchronous power MOSFET;
the turn-off detection circuit is used for controlling turn-off detection of the synchronous power MOSFET;
the logic control circuit carries out logic operation on the received turn-on and turn-off signals and then controls the turn-on and turn-off of the synchronous power MOSFET; if the change slope of the drain-source voltage of the synchronous power MOSFET in the set time is larger than the set threshold, the synchronous power MOSFET is started; and if the change slope of the drain-source voltage of the synchronous power MOSFET in the set time is smaller than the set threshold, the synchronous power MOSFET is turned off.
3. A synchronous rectification switch control circuit as claimed in claim 1 or2,
the drain-source voltage slope detection circuit of the synchronous power MOSFET comprises a first comparator, a second comparator, a third comparator, a current source, a PMOS (P-channel metal oxide semiconductor) tube, an NMOS (N-channel metal oxide semiconductor) tube, a capacitor, a first two-input NOR gate, a first inverter, a second inverter and a first RS trigger;
the positive input end of the first comparator is connected with the drain-source voltage of the synchronous power MOSFET, and the negative input end of the first comparator is connected with a first reference voltage; the output end of the first comparator is connected with one input end of the first two-input NOR gate and the input end of the second inverter;
the positive input end of the second comparator is connected with a second reference voltage, and the negative input end of the second comparator is connected with the drain-source voltage of the synchronous power MOSFET; the output end of the second comparator is connected with the other input end of the first two-input NOR gate;
the output end of the first two-input NOR gate is connected with the input end of a first phase inverter, and the output end of the first phase inverter is connected with the grid electrodes of a PMOS tube and an NMOS tube;
the positive end of the current source is connected with a power VCC, and the negative end of the current source is connected with the source electrode of the PMOS tube;
the drain electrode of the PMOS tube is connected with the drain electrode of the NMOS tube and the anode of the capacitor;
the source electrode of the NMOS tube is grounded, and the negative electrode of the capacitor is also grounded;
the positive input end of the third comparator is connected with the positive electrode of the capacitor, the negative input end of the third comparator is connected with a third reference voltage, and the output end of the third comparator is connected with the position end of the first RS trigger;
the reset end of the first RS trigger is connected with the output end of the second phase inverter, and the output end of the first RS trigger is connected with the logic control circuit.
4. A synchronous rectification switch control circuit as claimed in claim 1 or2, wherein said turn-on detection circuit comprises a fourth comparator;
the positive input end of the fourth comparator is connected with the drain-source voltage of the synchronous power MOSFET, the negative input end of the fourth comparator is connected with a fourth reference voltage, and the fourth reference voltage is used for setting a threshold point for starting the synchronous power MOSFET; and the output end of the fourth comparator is connected with the logic control circuit.
5. A synchronous rectification switch control circuit as claimed in claim 1 or2, wherein said turn-off detection circuit includes a fifth comparator;
the positive input end of the fifth comparator is connected with a fifth reference voltage, the negative input end of the fifth comparator is connected with the drain-source voltage of the synchronous power MOSFET, and the fifth reference voltage is used for setting the turn-off threshold point of the synchronous power MOSFET; and the output end of the fifth comparator is connected with the logic control circuit.
6. The synchronous rectification switch control circuit according to claim 1 or2, wherein the logic control circuit comprises a second two-input nor gate and a second RS flip-flop;
one end of the second two-input NOR gate is connected with the output end of the first RS trigger RS1, and the other end of the second two-input NOR gate is connected with the output end of the fourth comparator;
the output of the second two-input NOR gate is connected with the setting end of the second RS trigger and used for controlling the start of the synchronous power MOSFET;
the reset end of the second RS trigger is connected with the output end of the fifth comparator and is used for controlling the turn-off of the synchronous power MOSFET;
and the output end of the second RS trigger is used for driving the grid electrode of the synchronous power MOSFET and controlling the on and off of the synchronous power MOSFET.
7. A synchronous rectification switch control circuit as claimed in claim 3,
the first reference voltage is used for setting a starting point of the detection of the drain-source voltage falling slope of the synchronous power MOSFET, and the second reference voltage is used for setting a termination point of the detection of the drain-source voltage falling slope of the synchronous power MOSFET.
8. A synchronous rectification switch control circuit as claimed in claim 3,
and a current source, a capacitor and a third reference voltage in the synchronous power MOSFET drain-source voltage slope detection circuit commonly set a slope threshold value of the synchronous power MOSFET drain-source voltage drop.
9. The synchronous rectification switch control circuit as claimed in claim 3, wherein the first RS flip-flop is configured to latch the detected slope signal of the drain-source voltage of the synchronous power MOSFET.
10. A synchronous rectification switch control circuit as claimed in claim 6,
if the drain-source voltage falling slope of the synchronous power MOSFET is larger than a set threshold, the logic control circuit transmits a starting signal detected by the starting detection circuit to a set end of the second RS trigger, and the synchronous power MOSFET is started;
if the falling slope of the drain-source voltage of the synchronous power MOSFET is smaller than a set threshold, shielding the output of the start detection circuit and keeping the output of the second RS trigger in a state of turning off the synchronous power MOSFET;
and the logic control circuit transmits a turn-off signal of the turn-off detection circuit to the reset end of the second RS trigger to turn off the synchronous power MOSFET.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
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| CN202110936916.8A CN113746358A (en) | 2021-08-16 | 2021-08-16 | Synchronous rectification switch control circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202110936916.8A CN113746358A (en) | 2021-08-16 | 2021-08-16 | Synchronous rectification switch control circuit |
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Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106941321A (en) * | 2017-03-22 | 2017-07-11 | 深圳市稳先微电子有限公司 | A kind of control circuit of synchronous rectifier |
| CN108258923A (en) * | 2017-12-12 | 2018-07-06 | 深圳市芯茂微电子有限公司 | A kind of synchronous rectification driving circuit of voltage decrease speed judgement |
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Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106941321A (en) * | 2017-03-22 | 2017-07-11 | 深圳市稳先微电子有限公司 | A kind of control circuit of synchronous rectifier |
| CN108258923A (en) * | 2017-12-12 | 2018-07-06 | 深圳市芯茂微电子有限公司 | A kind of synchronous rectification driving circuit of voltage decrease speed judgement |
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