Secondary side control circuit and control method of isolated converter and isolated converter

Abstract

The present invention provides a secondary side control circuit, a control method and an isolated converter of an isolated converter, wherein the secondary side control circuit of the isolated converter includes a state signal acquisition circuit, an optocoupler control circuit and a pulse generating circuit. The state signal acquisition circuit is used to receive the state signal of the secondary side circuit. The optocoupler control circuit is coupled to the state signal acquisition circuit and the optocoupler element respectively, and the optocoupler control circuit is used to output a first control signal according to the state signal, and the first control signal is used to control the optocoupler current flowing through the optocoupler element. The pulse generating circuit is used to control the conduction state of the secondary side rectifier tube or the switch set in parallel with the secondary side rectifier tube according to the state signal, so that when the state signal is abnormal, a shutdown protection signal is sent to the primary side circuit. The present invention can be applied to a switching power supply device to realize output voltage overvoltage protection, output current overcurrent protection and over-temperature protection of the isolated converter, and effectively improve the stability and reliability of the isolated converter.

Description

Technical Field

[0001] The present invention relates to the technical field of switching power supplies, and in particular to a secondary side control circuit and a control method of an isolated converter and an isolated converter. Background Art

[0002] Isolated converters are widely used in the field of switching power supplies due to their strong anti-interference ability, high safety, easy buck-boost conversion, and easy multi-channel output. Isolated converters usually include rectifier circuits, primary circuits, and secondary circuits. Through the precise control of the primary and secondary control circuits, the isolated converter can output safely and stably. However, with the influence of factors such as the continuous working heat of the isolated converter, load changes, and changes in the external environment, the primary and secondary control circuits need to make corresponding control adjustments in time to ensure the normal operation of the isolated converter.

[0003] like Figure 1 As shown, it is a relatively common flyback isolation conversion circuit in the prior art. This scheme adopts the primary side control method to achieve overvoltage protection. The detection of the output voltage is indirectly achieved by detecting the voltage of the auxiliary winding of the transformer. The feedback signal obtained from the auxiliary winding cannot accurately reflect the output voltage in some cases, such as when the dummy load (Dummy Load) is open. In addition, the invention patent application with publication number CN109347066A discloses a secondary side control circuit and its isolated power conversion circuit and overvoltage protection method. This technical scheme puts the overvoltage detection into the secondary side circuit, and triggers the primary side circuit protection state by turning on the secondary side rectifier tube under a specific state, which effectively improves the detection accuracy and reliability of the output voltage overvoltage protection of the isolated power conversion circuit. However, in this scheme, the primary side switch tube and the secondary side rectifier tube are turned on at the same time, which is easy to cause short-circuit damage to the isolated converter.

[0004] Therefore, when the secondary side of the isolated converter is abnormal, it is urgent to solve the problem of effective communication and control of the primary and secondary side signals in order to effectively protect the stable operation of the secondary side circuit. Summary of the invention

[0005] The purpose of the present invention is to propose a secondary side control circuit, a control method and an isolated converter of an isolated converter, which can be applied to a switching power supply device to realize output voltage overvoltage protection, output current overcurrent protection and over-temperature protection of the isolated converter, thereby effectively improving the stability and reliability of the isolated converter.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The present invention discloses a secondary side control circuit of an isolated converter, which comprises:

[0008] A status signal acquisition circuit, used for receiving a status signal of a secondary circuit;

[0009] an optocoupler control circuit, coupled to the state signal acquisition circuit and the optocoupler element, respectively, and configured to output a first control signal according to the state signal, wherein the first control signal is configured to control an optocoupler current flowing through the optocoupler element; and

[0010] A pulse generating circuit is used to control the conduction state of the secondary rectifier tube or a switch set in parallel with the secondary rectifier tube according to the state signal, so that a shutdown protection signal is sent to the primary circuit when the state signal is abnormal.

[0011] As an implementation manner of the present invention, the secondary side control circuit further includes:

[0012] A first demagnetization detection circuit, whose input end is coupled to the secondary rectifier tube and whose output end is coupled to the pulse generating circuit, is used to detect the demagnetization state of the secondary circuit and output a first demagnetization detection signal;

[0013] The pulse generating circuit is used to control the conduction state of the secondary rectifier tube or the switch set in parallel with the secondary rectifier tube according to the state signal and the first demagnetization detection signal, so that a shutdown protection signal is sent to the primary circuit when the state signal is abnormal.

[0014] As an embodiment of the present invention, the secondary side control circuit also includes: a first delay circuit, which is used to output a first delay signal of a valid state when the status signal is abnormal, so as to delay the pulse generating circuit to control the conduction state of the secondary side rectifier tube or the switch set in parallel with the secondary side rectifier tube.

[0015] As an embodiment of the present invention, the secondary side control circuit also includes: a second delay circuit, whose output end is coupled to the optocoupler control circuit, and is used to output a second delay signal of a valid state when the status signal is abnormal, so as to delay the optocoupler control circuit from controlling the optocoupler current.

[0016] The present invention discloses a secondary side control circuit of an isolated converter, which comprises:

[0017] A status signal acquisition circuit, used for receiving a status signal of a secondary circuit;

[0018] A comparison circuit, whose input terminal is coupled to the state signal acquisition circuit, for comparing the state signal with a preset state threshold and outputting a comparison signal;

[0019] An optocoupler control circuit, whose input end is coupled to the comparison circuit and whose output end is coupled to the optocoupler element, is used to output a first control signal according to the comparison signal, wherein the first control signal is used to control the optocoupler current flowing through the optocoupler element; when the status signal is abnormal, the optocoupler current is controlled to turn off the primary switch.

[0020] As an embodiment of the present invention, the optocoupler control circuit includes a third switch and a third switch control circuit; the third switch is coupled to the optocoupler element, and the third switch control circuit is used to control the conduction state of the third switch according to the state signal, thereby controlling the size of the optocoupler current.

[0021] As an implementation manner of the present invention, the optocoupler control circuit further includes a current limiting resistor coupled to the third switch.

[0022] The present invention discloses a secondary side control circuit of a DCM isolated converter, which comprises:

[0023] A status signal acquisition circuit, used for receiving a status signal of a secondary circuit;

[0024] a first demagnetization detection circuit, whose input end is coupled to the secondary rectifier tube, for detecting the demagnetization state of the secondary circuit and outputting a first demagnetization detection signal; and

[0025] A pulse generating circuit, whose input end is respectively coupled to the status signal acquisition circuit and the first demagnetization detection circuit, is used to control the conduction state of the secondary rectifier tube or the switch set in parallel with the secondary rectifier tube according to the status signal and the first demagnetization detection signal, so that a shutdown protection signal is sent to the primary circuit when the status signal is abnormal.

[0026] As an implementation manner of the present invention, the secondary side control circuit further includes:

[0027] A synchronous rectification control circuit, configured to output a synchronous rectification control signal; and

[0028] An OR gate has a first input terminal coupled to the pulse generating circuit, a second input terminal coupled to the synchronous rectification control circuit, and an output terminal coupled to the control terminal of the secondary side rectifier tube.

[0029] As an implementation manner of the present invention, the secondary side control circuit further includes: a secondary side rectifier tube, and the secondary side rectifier tube is a switch type transistor.

[0030] The present invention discloses an isolated converter, which comprises a primary circuit and a secondary circuit. The primary circuit receives an input voltage and comprises a primary winding and a primary switch. The secondary circuit comprises a secondary winding, a secondary rectifier tube and the secondary control circuit as described above. The secondary winding and the primary winding are coupled to form a transformer.

[0031] As an embodiment of the present invention, the primary circuit also includes: a second demagnetization detection circuit, whose input end is coupled to the first end or the auxiliary winding of the primary switch, and whose output end is coupled to the control end of the primary switch, for obtaining a shutdown protection signal issued by the secondary circuit to control the conduction state of the primary switch.

[0032] As an implementation manner of the present invention, the primary circuit further includes:

[0033] an identification circuit, whose input end is coupled to the second degaussing detection circuit, and is used to output an identification signal according to a second degaussing detection signal output by the second degaussing detection circuit; when the state signal is abnormal, the identification circuit outputs an identification signal of a valid state according to the second degaussing detection signal; and

[0034] A primary switch control circuit, whose input end is coupled to the identification circuit and whose output end is coupled to the control end of the primary switch, is used to control the conduction state of the primary switch according to the identification signal; when the identification circuit outputs an identification signal of a valid state, the primary switch control circuit controls the primary switch to be turned off.

[0035] The present invention discloses a control method for protecting an isolated converter circuit, which comprises:

[0036] Receive a status signal of a secondary circuit;

[0037] Outputting a first control signal according to the state signal, the first control signal being used to control the optocoupler current flowing through the optocoupler element; when the state signal is abnormal, the first control signal controls to increase the optocoupler current; and

[0038] The conduction state of the secondary rectifier tube or the switch set in parallel with the secondary rectifier tube is controlled according to the state signal, so that a shutdown protection signal is sent to the primary circuit when the state signal is abnormal.

[0039] As an implementation manner of the present invention, the process of controlling the conduction state of the secondary rectifier tube or the switch set in parallel with the secondary rectifier tube according to the state signal specifically includes:

[0040] Detecting the demagnetization state of the secondary circuit to output a first demagnetization detection signal;

[0041] According to the state signal and the first demagnetization detection signal, the conduction state of the secondary rectifier tube or the switch set in parallel with the secondary rectifier tube is controlled so that a shutdown protection signal is sent to the primary circuit when the state signal is abnormal.

[0042] As an implementation manner of the present invention, the process of outputting the first control signal according to the state signal is specifically: outputting the first control signal with a delay according to the state signal and the second delay signal.

[0043] The present invention discloses a control method for circuit protection of a DCM isolated converter, which comprises:

[0044] Receive a status signal of a secondary circuit;

[0045] detecting the demagnetization state of the secondary circuit to output a first demagnetization detection signal; and

[0046] The conduction state of the secondary rectifier tube or the switch set in parallel with the secondary rectifier tube is controlled according to the state signal and the first demagnetization detection signal, so that a shutdown protection signal is sent to the primary circuit when the state signal is abnormal.

[0047] The present invention discloses a control method for protecting an isolated converter circuit, which comprises:

[0048] Receive a status signal of a secondary circuit;

[0049] Comparing the state signal with a preset state threshold and outputting a comparison signal;

[0050] A first control signal is outputted according to the comparison signal, wherein the first control signal is used to control the optocoupler current flowing through the optocoupler element; when the state signal is abnormal, the first control signal controls to increase the optocoupler current.

[0051] As an embodiment of the present invention, the control method of the isolated converter circuit protection further includes:

[0052] Detecting the demagnetization state of the secondary circuit to output a second demagnetization detection signal;

[0053] outputting an identification signal according to the second demagnetization detection signal; when the state signal is abnormal, outputting an identification signal of a valid state according to the second demagnetization detection signal; and

[0054] The conduction state of the primary switch is controlled according to the identification signal; when the identification signal is in a valid state, the primary switch is controlled to be turned off.

[0055] Compared with the prior art, the beneficial effect of the present invention is that the present invention proposes a secondary side control circuit, a control method and an isolated converter of an isolated converter. In the application of an isolated converter with an optocoupler, when the state signal of the secondary circuit is abnormal, the primary switch is turned off for a short time by controlling the current flowing through the optocoupler element to protect the circuit. When the state signal of the secondary circuit is seriously abnormal, such as short-time shutdown is not enough to protect the circuit, at this time, during the stage of short-time shutdown of the primary switch, the secondary control circuit controls the conduction state of the secondary rectifier tube or the switch set in parallel with the secondary rectifier tube, thereby sending a shutdown protection signal to the primary circuit, so that the primary circuit can maintain a reasonable shutdown time, thereby achieving effective shutdown protection. In the application of a DCM isolated converter without an optocoupler, when the state signal of the secondary circuit is abnormal, after the secondary demagnetization is completed through the first demagnetization detection circuit, the secondary control circuit sends a shutdown protection signal to the primary circuit within the oscillation interval, so that the primary circuit can maintain a reasonable shutdown time. The present invention can be applied to a switching power supply device to realize circuit protection such as output voltage overvoltage protection, output current overcurrent protection and over-temperature protection of an isolated converter, thereby effectively improving the stability and reliability of the isolated converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 A schematic diagram of the circuit structure of an isolated converter overvoltage protection in the prior art;

[0057] Figure 2 A schematic diagram of the circuit structure of an isolated converter circuit according to an embodiment of the present invention;

[0058] Figure 3 A schematic diagram of a circuit structure of an optocoupler isolation converter circuit according to an embodiment of the present invention;

[0059] Figure 4 A schematic diagram of waveforms of signals in an isolated conversion circuit according to an embodiment of the present invention;

[0060] Figure 5 A schematic diagram of waveforms of signals in an isolated conversion circuit according to an embodiment of the present invention;

[0061] Figure 6 FIG. 4 is a waveform diagram of a signal in an isolated conversion circuit according to an embodiment of the present invention. DETAILED DESCRIPTION

[0062] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0063] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0064] The description of this section is only for several typical embodiments, and the present invention is not limited to the scope of the embodiments. The same or similar prior art means and some technical features in the embodiments are mutually replaced within the scope of the present invention. The "coupling" or connection in the specification includes both direct connection and indirect connection, such as connection through some active devices, passive devices or electrically conductive media. "Multiple" refers to two or more.

[0065] An embodiment of the present invention discloses a secondary side control circuit of an isolated converter, which includes: a state signal acquisition circuit, an optocoupler control circuit and a pulse generating circuit. The state signal acquisition circuit is used to receive a state signal of the secondary side circuit. The state signal can be any one or a combination of state parameters of the secondary side circuit such as output voltage, output current and chip temperature. In one embodiment of the present invention, the state signal is the output voltage; in another embodiment of the present invention, the state signal is the output voltage and the chip temperature. The optocoupler control circuit is coupled to the state signal acquisition circuit and the optocoupler element respectively, and the optocoupler control circuit is used to output a first control signal according to the state signal, and the first control signal is used to control the optocoupler current flowing through the optocoupler element. In one embodiment of the present invention, when the state signal is within a normal range, the optocoupler control circuit outputs a first control signal of an invalid state; when the state signal is abnormal (i.e., beyond the normal range), the optocoupler control circuit outputs a first control signal of a valid state. The first control signal of the valid state can control to increase the optocoupler current flowing through the optocoupler element. When the optocoupler current increases, the corresponding primary side circuit turns off the primary side switch and can maintain the off state for a short time. The pulse generating circuit is used to control the conduction state of the secondary rectifier tube according to the state signal, so that when the state signal is abnormal, the secondary circuit sends a shutdown protection signal to the primary circuit. In another embodiment of the present invention, the pulse generating circuit is used to control the conduction state of the setting switch connected in parallel with the secondary rectifier tube according to the state signal, so that when the state signal is abnormal, the secondary circuit sends a shutdown protection signal to the primary circuit. When the state signal is abnormal, the pulse generating circuit controls the conduction state of the secondary rectifier tube or the setting switch connected in parallel with the secondary rectifier tube when the primary circuit is turned off for a short time, so that the shutdown protection signal can be sent to the primary circuit. In one embodiment of the present invention, when the state signal is abnormal, the pulse generating circuit sends a driving signal of several pulses to the secondary rectifier tube to make the secondary rectifier tube conduct and turn off accordingly, so that the primary circuit can know the shutdown protection signal.

[0066] Because the off state of the primary switch is maintained for a short time (generally in the millisecond level) when the current of the optocoupler increases, when the state signal of the secondary circuit is abnormal, such as when the output voltage is overvoltage or the chip is overheated, the short-term shutdown of the primary circuit is not enough to protect the circuit. The pulse generating circuit controls the conduction state of the secondary rectifier tube or the switch set in parallel with the secondary rectifier tube, and then the transformer principle is used to make the primary circuit receive the shutdown protection signal, so that the primary circuit can maintain a reasonable shutdown time (for example, seconds), thereby effectively protecting the normal operation of the isolated converter.

[0067] like Figure 2 As shown, one embodiment of the present invention discloses a secondary side control circuit of an isolated converter and an isolated converter, wherein the isolated converter includes a primary side circuit 10, a secondary side circuit 20 and an optocoupler element 30. A first end of the optocoupler element 30 is coupled to the secondary side circuit 20, and a second end of the optocoupler element 30 is coupled to the primary side circuit 10. In another embodiment of the present invention, the isolated converter may not include an optocoupler element. Figure 2 As shown, the primary circuit 10 receives an input voltage, and the primary circuit 10 includes a primary winding, a primary switch S1, and a primary control circuit 11. The secondary circuit 20 includes a secondary winding, a secondary rectifier S2, and a secondary control circuit 21. The primary switch S1 may be included in or not included in the primary control circuit 11, and the secondary rectifier S2 may be included in or not included in the secondary control circuit 21. In one embodiment of the present invention, the secondary rectifier S2 is a diode. In another embodiment of the present invention, the secondary rectifier S2 is a switch transistor, such as a metal oxide semiconductor field effect transistor (MOSFET) or a junction field effect transistor (JFET). The secondary control circuit 21 is used to control the conduction state of the secondary rectifier S2 according to the state signal of the secondary circuit 20, and the secondary winding and the primary winding are coupled to form a transformer.

[0068] like Figure 2As shown, in one embodiment of the present invention, the secondary control circuit 21 includes a state signal acquisition circuit 211, an optocoupler control circuit 212 and a pulse generating circuit 213. The input end of the state signal acquisition circuit 211 receives the state signal of the secondary circuit 20, and the output end of the state signal acquisition circuit 211 is coupled to the optocoupler control circuit 212 and the pulse generating circuit 213 respectively. When the state signal is abnormal, the optocoupler control circuit 212 outputs a first control signal of a valid state, and the first control signal controls to increase the optocoupler current flowing through the optocoupler element 30. The primary circuit 10 receives the output signal of the optocoupler element 30, and the primary circuit 10 controls the primary switch S1 to remain in an off state for a short time. In the short-term off stage of the primary switch S1, the pulse generating circuit 213 controls the conduction state of the secondary rectifier tube S2, thereby sending a turn-off protection signal to the primary circuit 10. Through the transformer principle, the primary circuit 10 obtains the turn-off protection signal sent by the secondary circuit 20, and the primary circuit 10 controls the primary switch S1 to perform turn-off protection. Therefore, in the isolated conversion circuit, even if an abnormality occurs in the secondary circuit, the present invention can timely and effectively control the primary circuit to shut down, thereby effectively protecting the stable operation of the isolated conversion circuit.

[0069] One embodiment of the present invention discloses a secondary control circuit, which also includes a first demagnetization detection circuit, wherein the input end of the first demagnetization detection circuit is coupled to the cathode end or the drain end of the secondary rectifier tube, and the output end of the first demagnetization detection circuit is coupled to the pulse generation circuit, and the first demagnetization detection circuit is used to detect the demagnetization state of the secondary circuit and output a first demagnetization detection signal. The pulse generation circuit is used to control the conduction state of the secondary rectifier tube or the setting switch connected in parallel with the secondary rectifier tube according to the state signal and the first demagnetization detection signal. When the state signal is abnormal, the first demagnetization detection signal indicates that the secondary circuit has been demagnetized, and the pulse generation circuit controls the conduction state of the secondary rectifier tube or the setting switch connected in parallel with the secondary rectifier tube.

[0070] An embodiment of the present invention discloses a secondary control circuit, which also includes a first delay circuit, which is used to output a first delay signal of a valid state when the state signal is abnormal, so as to delay the pulse generating circuit to control the conduction state of the secondary rectifier tube or the setting switch connected in parallel with the secondary rectifier tube, so as to ensure that when the secondary rectifier tube or the setting switch connected in parallel with the secondary rectifier tube is controlled, the demagnetization of the secondary circuit has been completed.

[0071] An embodiment of the present invention discloses a secondary side control circuit, which also includes a second delay circuit. The output end of the first delay circuit is coupled to the optocoupler control circuit, and is used to output a second delay signal of a valid state when the state signal is abnormal, so as to delay the optocoupler control circuit to control the optocoupler current, so as to prevent false triggering of protection and improve the stability of the control circuit operation.

[0072] An embodiment of the present invention discloses a secondary side control circuit, wherein the optocoupler control circuit further includes a current limiting resistor Rlimit coupled to the third switch S3, and the current limiting resistor Rlimit is used to prevent the third switch S3 from being damaged by excessive discharge current, thereby protecting the third switch.

[0073] like Figure 3 As shown, an embodiment of the present invention discloses an isolated converter, which includes a primary circuit and a secondary circuit. The primary circuit includes a primary winding, a primary switch S1 and a primary control circuit, and the secondary circuit includes a secondary winding, a switch transistor S2 and a secondary control circuit. The primary control circuit may include a DEM pin, an FB pin, a GND pin, a CS pin, a GATE pin and a VDD pin. Among them, the DEM pin is a demagnetization detection pin, the FB pin is a voltage feedback pin, the GND pin is a common ground, the CS pin is a current feedback pin, and the VDD pin is a power supply pin. The primary control circuit is coupled to the primary switch S1 through the GATE pin, and the primary control circuit is used to control the conduction state of the primary switch S1. The primary switch S1 can be set in the primary control circuit or outside the primary control circuit. The input end of the secondary control circuit 210 receives the state signal of the secondary circuit 20, and the output end of the secondary control circuit 210 is coupled to the switch transistor S2. The secondary side control circuit 210 includes a state signal acquisition circuit, an optocoupler control circuit and a pulse generation circuit.

[0074] In one embodiment of the present invention, the optocoupler control circuit includes a third switch S3 and a third switch control circuit. The third switch S3 is coupled to the optocoupler element, and the third switch control circuit is used to control the conduction state of the third switch S3 according to the state signal, thereby controlling the magnitude of the optocoupler current. Figure 3-5 It can be seen that when the status signal is abnormal, such as the chip or the secondary circuit triggering the over-temperature protection OTP (such as Figure 4 When the OTP signal of the optocoupler control circuit is at a high level and the OTP signal is an over-temperature protection signal, the third switch control circuit in the optocoupler control circuit controls the third switch S3 to turn on, and the optocoupler current Ioc flowing through the optocoupler element will increase. Correspondingly, the voltage of the FB pin in the primary control circuit will decrease, and the primary control circuit will stop sending the primary switch drive signal Gate in the valid state, and the primary circuit will turn off the primary switch S1. At this time, the output voltage Vo will gradually decrease, and the temperature of the chip or the secondary circuit will gradually decrease. The primary circuit will then immediately power off and restart, and the effect of reducing the temperature of the chip or the secondary circuit is relatively limited. When the chip temperature is far beyond the upper limit, the chip temperature will not be enough to drop to the normal range.

[0075] Therefore, in another embodiment of the present invention, after the primary circuit turns off the primary switch S3 and the secondary circuit is demagnetized, the secondary control circuit 210 controls the conduction state of the switch transistor S2, thereby sending a shutdown protection signal to the primary circuit. Figure 5 As shown, the pulse generating circuit controls the conduction state of the switch transistor S2 by outputting the switch signal SR Gate. Among them, after the primary circuit turns off the primary switch S3, a certain delay time delay can be set, and then the switch signal SR Gate is sent. Through the transformer principle, for example, the second demagnetization detection signal DEM2 is obtained through demagnetization detection, and the primary circuit obtains the shutdown protection signal sent by the secondary circuit. The primary circuit 10 controls the primary switch S1 to perform shutdown protection (Shut down). The shutdown protection time length is sufficient to reduce the chip temperature to a normal range. After the shutdown protection, the primary circuit restarts and continues to control the conduction state of the primary switch. Among them, by controlling the conduction state of the secondary rectifier or the switch set in parallel with the secondary rectifier, the secondary circuit sends a shutdown protection signal to the primary circuit, which can be understood as: the secondary circuit controls the conduction state of the secondary rectifier or the switch set in parallel with the secondary rectifier, such as sending a switching signal SR Gate of several pulses to the switching transistor S2 in the secondary circuit. Through the transformer principle, the primary circuit can obtain the corresponding second demagnetization detection signal. According to the communication protocol between the primary and secondary sides, when the detected signal corresponds to the circuit shutdown protection signal in the communication protocol, the primary circuit performs shutdown protection for a reasonable duration.

[0076] In one embodiment of the present invention, through the transformer principle, the circuit implementation of the primary circuit obtaining the shutdown protection signal sent by the secondary circuit is specifically as follows: the primary circuit also includes a second demagnetization detection circuit. The input end of the second demagnetization detection circuit is coupled to the first end of the primary switch, the second end of the primary switch is coupled to the ground, the output end of the second demagnetization detection circuit is coupled to the control end of the primary switch, and the second demagnetization detection circuit is used to obtain the shutdown protection signal sent by the secondary circuit to control the conduction state of the primary switch. In one embodiment of the present invention, when the primary switch is a switching transistor MOSFET, the input end of the second demagnetization detection circuit is coupled to the drain of the primary switch, that is, the first end of the primary switch is the drain. In another embodiment of the present invention, the input end of the second demagnetization detection circuit is coupled to the auxiliary winding, and the output end of the second demagnetization detection circuit is coupled to the control end of the primary switch. Figure 3 As shown, the second demagnetization detection circuit is coupled to the auxiliary winding. Through the transformer principle, the demagnetization signal of the secondary circuit is transmitted to the auxiliary winding, and then transmitted to the primary control circuit through the voltage divider resistor. Therefore, the primary circuit obtains the shutdown protection signal issued by the secondary circuit through the second demagnetization detection signal DEM2.

[0077] One embodiment of the present invention discloses a secondary control circuit of a DCM isolated converter, which includes a status signal acquisition circuit, a first demagnetization detection circuit and a pulse generating circuit. The status signal acquisition circuit is used to receive the status signal of the secondary circuit. The input end of the first demagnetization detection circuit is coupled to the cathode end or the drain end of the secondary rectifier tube, and the output end of the first demagnetization detection circuit is coupled to the pulse generating circuit. The first demagnetization detection circuit is used to detect the demagnetization state of the secondary circuit and output a first demagnetization detection signal. The input end of the pulse generating circuit is coupled to the status signal acquisition circuit, and the pulse generating circuit is used to control the conduction state of the secondary rectifier tube or the switch set in parallel with the secondary rectifier tube according to the status signal and the first demagnetization detection signal, so that when the status signal is abnormal, a shutdown protection signal is sent to the primary circuit. The DCM isolated converter may not include an optocoupler element. Figure 6 As shown, when the over-temperature protection signal OTP is at a low level, it indicates that the chip temperature parameter is within the normal range; when the over-temperature protection signal OTP is at a high level, it indicates that the chip temperature parameter is abnormal. After the secondary circuit is demagnetized (as can be seen from the first demagnetization detection signal DEM1), the primary circuit can obtain the shutdown protection signal sent by the secondary circuit through the second demagnetization detection signal DEM2 by sending several pulses of the switch signal SR Gate to the secondary rectifier tube, thereby turning off the primary switch to ensure the normal operation of the isolated converter. Among them, after the primary circuit turns off the primary switch, a certain delay time delay can be set, and then the switch signal SR Gate is sent.

[0078] An embodiment of the present invention discloses a secondary side control circuit of an isolated converter, which includes a state signal acquisition circuit, a comparison circuit and an optocoupler control circuit. The state signal acquisition circuit is used to receive the state signal of the secondary side circuit. The input end of the comparison circuit is coupled to the state signal acquisition circuit; the comparison circuit is used to compare the state signal with a preset state threshold and output a comparison signal. The input end of the optocoupler control circuit is coupled to the comparison circuit, the output end of the optocoupler control circuit is coupled to an optocoupler element, and the optocoupler control circuit is used to output a first control signal according to the comparison signal, and the first control signal is used to control the optocoupler current flowing through the optocoupler element. Exemplarily, when the state signal exceeds the preset state threshold range, a comparison signal indicating that the state signal is abnormal is output, and the comparison signal can be a high level signal or a low level signal. The optocoupler control circuit outputs the first control signal according to the comparison signal, and when the state signal is abnormal, the optocoupler control circuit controls to increase the optocoupler current. When the state signal of the secondary side circuit is abnormal, the primary side switch is turned off for a short time by controlling the current flowing through the optocoupler element, so as to protect the isolated converter circuit.

[0079] An embodiment of the present invention discloses a secondary side control circuit, which also includes a synchronous rectification control circuit and an OR gate. The synchronous rectification control circuit is used to output a synchronous rectification control signal. The first input end of the OR gate is coupled to the pulse generating circuit, the second input end of the OR gate is coupled to the synchronous rectification control circuit, and the output end of the OR gate is coupled to the control end of the secondary side rectifier tube.

[0080] An embodiment of the present invention discloses a secondary-side control circuit, which further includes a secondary-side rectifier tube, and the secondary-side rectifier tube is a switch-type transistor.

[0081] One embodiment of the present invention discloses an isolated converter, wherein the primary circuit further includes an identification circuit and a primary switch control circuit. The input end of the identification circuit is coupled to the second demagnetization detection circuit, and the identification circuit is used to output an identification signal according to the second demagnetization detection signal output by the second demagnetization detection circuit; when the state signal is abnormal, the identification circuit outputs an identification signal of a valid state according to the second demagnetization detection signal. The input end of the primary switch control circuit is coupled to the identification circuit, and the output end of the primary switch control circuit is coupled to the control end of the primary switch, and the primary switch control circuit is used to control the conduction state of the primary switch according to the identification signal; when the identification circuit outputs an identification signal of a valid state, the primary switch control circuit controls the primary switch to be turned off.

[0082] An embodiment of the present invention discloses a control method for protecting an isolated converter circuit, which includes:

[0083] Step S1, receiving a status signal of a secondary circuit;

[0084] Step S2, outputting a first control signal according to the state signal, wherein the first control signal is used to control the optocoupler current flowing through the optocoupler element; when the state signal is abnormal, the first control signal controls to increase the optocoupler current; and

[0085] Step S3: controlling the conduction state of the secondary rectifier tube or a switch connected in parallel with the secondary rectifier tube according to the state signal, so that a shutdown protection signal is sent to the primary circuit when the state signal is abnormal.

[0086] An embodiment of the present invention discloses a control method for protecting an isolated converter circuit. The process of controlling the conduction state of a secondary rectifier tube or a switch connected in parallel with the secondary rectifier tube according to a state signal specifically includes:

[0087] Step S31, detecting the demagnetization state of the secondary circuit to output a first demagnetization detection signal;

[0088] Step S32: According to the state signal and the first demagnetization detection signal, control the conduction state of the secondary rectifier tube or the switch set in parallel with the secondary rectifier tube, so that when the state signal is abnormal, a shutdown protection signal is sent to the primary circuit.

[0089] An embodiment of the present invention discloses a control method for protecting an isolated converter circuit. The process of outputting a first control signal according to the state signal is specifically: outputting the first control signal with a delay according to the state signal and a second delay signal.

[0090] An embodiment of the present invention discloses a control method for circuit protection of a DCM isolated converter, which includes:

[0091] Step S1, receiving a status signal of a secondary circuit;

[0092] Step S2, detecting the demagnetization state of the secondary circuit to output a first demagnetization detection signal; and

[0093] Step S3: controlling the conduction state of the secondary rectifier tube or the switch set in parallel with the secondary rectifier tube according to the state signal and the first demagnetization detection signal, so that a shutdown protection signal is sent to the primary circuit when the state signal is abnormal.

[0094] An embodiment of the present invention discloses a control method for protecting an isolated converter circuit, which includes:

[0095] Step S1, receiving a status signal of a secondary circuit;

[0096] Step S2, outputting a first control signal according to the state signal, wherein the first control signal is used to control the optocoupler current flowing through the optocoupler element;

[0097] Step S3, controlling the conduction state of the secondary rectifier tube or a switch connected in parallel with the secondary rectifier tube according to the state signal, so that a shutdown protection signal is sent to the primary circuit when the state signal is abnormal;

[0098] Step S4, detecting the demagnetization state of the secondary circuit to output a second demagnetization detection signal;

[0099] Step S5, outputting an identification signal according to the second demagnetization detection signal; when the state signal is abnormal, outputting an identification signal of a valid state according to the second demagnetization detection signal; and

[0100] Step S6, controlling the on state of the primary switch according to the identification signal; when the identification signal is in a valid state, controlling the primary switch to be turned off.

[0101] An embodiment of the present invention discloses a control method for circuit protection of a DCM isolated converter, which includes:

[0102] Step S1, receiving a status signal of a secondary circuit;

[0103] Step S2, detecting the demagnetization state of the secondary circuit to output a first demagnetization detection signal;

[0104] Step S3, controlling the conduction state of the secondary rectifier tube or the switch set in parallel with the secondary rectifier tube according to the state signal and the first demagnetization detection signal, so that when the state signal is abnormal, a shutdown protection signal is sent to the primary circuit;

[0105] Step S4, detecting the demagnetization state of the secondary circuit to output a second demagnetization detection signal;

[0106] Step S5, outputting an identification signal according to the second demagnetization detection signal; when the state signal is abnormal, outputting an identification signal of a valid state according to the second demagnetization detection signal; and

[0107] Step S6, controlling the on state of the primary switch according to the identification signal; when the identification signal is in a valid state, controlling the primary switch to be turned off.

[0108] The present invention can be applied to switching power supply equipment to realize circuit protection such as output voltage overvoltage protection, output current overcurrent protection, undervoltage protection and overtemperature protection of the isolated converter, thereby effectively improving the stability and reliability of the isolated converter.

[0109] The description and application of the present invention here are illustrative and are not intended to limit the scope of the present invention to the above-described embodiments. The deformation and changes of the embodiments disclosed here are possible, and the replacement of the embodiments and the various components equivalent to those of ordinary skill in the art are well known. It should be clear to those skilled in the art that the present invention can be realized in other forms, structures, arrangements, proportions, and with other components, materials and parts without departing from the spirit or essential characteristics of the present invention. Other deformations and changes can be made to the embodiments disclosed here without departing from the scope and spirit of the present invention.

Claims

1. A secondary side control circuit of an isolated converter, characterized in that: include: A status signal acquisition circuit, used for receiving a status signal of a secondary circuit; an optocoupler control circuit, coupled to the state signal acquisition circuit and the optocoupler element respectively, and used to output a first control signal according to the state signal, wherein the first control signal is used to control the optocoupler current flowing through the optocoupler element; a first end of the optocoupler element is used to couple to a secondary circuit, and a second end of the optocoupler element is used to couple to a primary circuit; as well as A pulse generating circuit is used to control the conduction state of the secondary rectifier tube or a switch set in parallel with the secondary rectifier tube according to the state signal, so that a shutdown protection signal is sent to the primary circuit when the state signal is abnormal.

2. The secondary side control circuit according to claim 1, characterized in that: Also includes: A first demagnetization detection circuit, whose input end is coupled to the secondary rectifier tube and whose output end is coupled to the pulse generating circuit, is used to detect the demagnetization state of the secondary circuit and output a first demagnetization detection signal; The pulse generating circuit is used to control the conduction state of the secondary rectifier tube or the switch set in parallel with the secondary rectifier tube according to the state signal and the first demagnetization detection signal, so that a shutdown protection signal is sent to the primary circuit when the state signal is abnormal.

3. The secondary side control circuit according to claim 1, characterized in that: Also includes: The first delay circuit is used to output a first delay signal of a valid state when the state signal is abnormal, so as to delay the pulse generating circuit to control the conduction state of the secondary rectifier tube or the setting switch connected in parallel with the secondary rectifier tube.

4. The secondary side control circuit according to claim 3, characterized in that: Also includes: The second delay circuit has an output end coupled to the optocoupler control circuit and is used to output a second delay signal of a valid state when the state signal is abnormal, so as to delay the optocoupler control circuit from controlling the optocoupler current.

5. A secondary side control circuit of an isolated converter, characterized in that: include: A status signal acquisition circuit, used for receiving a status signal of a secondary circuit; A comparison circuit, whose input terminal is coupled to the state signal acquisition circuit, for comparing the state signal with a preset state threshold and outputting a comparison signal; an optocoupler control circuit, whose input end is coupled to the comparison circuit and whose output end is coupled to the optocoupler element, and is used to output a first control signal according to the comparison signal, wherein the first control signal is used to control the optocoupler current flowing through the optocoupler element; When the state signal is abnormal, the optocoupler current is controlled to turn off the primary switch; the first end of the optocoupler element is used to couple to the secondary circuit, and the second end of the optocoupler element is used to couple to the primary circuit.

6. The secondary side control circuit according to claim 1 or 5, characterized in that: The optocoupler control circuit includes a third switch and a third switch control circuit; the third switch is coupled to the optocoupler element, and the third switch control circuit is used to control the conduction state of the third switch according to the state signal, thereby controlling the magnitude of the optocoupler current.

7. The secondary side control circuit according to claim 6, characterized in that: The optocoupler control circuit also includes a current limiting resistor coupled to the third switch.

8. A secondary side control circuit of a DCM isolated converter, characterized in that: include: A status signal acquisition circuit, used for receiving a status signal of a secondary circuit; A first demagnetization detection circuit, whose input end is coupled to the secondary rectifier tube, is used to detect the demagnetization state of the secondary circuit and output a first demagnetization detection signal; as well as A pulse generating circuit, whose input end is respectively coupled to the status signal acquisition circuit and the first demagnetization detection circuit, is used to control the conduction state of the secondary rectifier tube or the switch set in parallel with the secondary rectifier tube according to the status signal and the first demagnetization detection signal, so that a shutdown protection signal is sent to the primary circuit when the status signal is abnormal.

9. The secondary side control circuit according to any one of claims 1-5 and 7-8, characterized in that: Also includes: A synchronous rectification control circuit, used for outputting a synchronous rectification control signal; as well as An OR gate has a first input terminal coupled to the pulse generating circuit, a second input terminal coupled to the synchronous rectification control circuit, and an output terminal coupled to the control terminal of the secondary side rectifier tube.

10. The secondary side control circuit according to claim 6, characterized in that: Also includes: A synchronous rectification control circuit, used for outputting a synchronous rectification control signal; and an OR gate, a first input terminal of which is coupled to the pulse generating circuit, a second input terminal of which is coupled to the synchronous rectification control circuit, and an output terminal of which is coupled to the control terminal of the secondary side rectifier tube.

11. The secondary side control circuit according to any one of claims 1-5 and 7-8, characterized in that: It also includes a secondary rectifier tube, which is a switch type transistor.

12. The secondary side control circuit according to claim 6, characterized in that: It also includes a secondary rectifier tube, which is a switch type transistor.

13. An isolated converter, characterized in that: The isolated converter includes a primary circuit and a secondary circuit. The primary circuit receives an input voltage and includes a primary winding and a primary switch. The secondary circuit includes a secondary winding, a secondary rectifier and a secondary control circuit as described in any one of claims 1 to 8. The secondary winding and the primary winding are coupled to form a transformer.

14. The isolated converter according to claim 13, characterized in that: The primary circuit further comprises: The second demagnetization detection circuit has an input end coupled to the first end or the auxiliary winding of the primary switch and an output end coupled to the control end of the primary switch, and is used to obtain a shutdown protection signal issued by the secondary circuit to control the conduction state of the primary switch.

15. The isolated converter according to claim 14, characterized in that: The primary circuit further comprises: an identification circuit, whose input end is coupled to the second degaussing detection circuit, and is used to output an identification signal according to a second degaussing detection signal output by the second degaussing detection circuit; when the state signal is abnormal, the identification circuit outputs an identification signal of a valid state according to the second degaussing detection signal; and A primary switch control circuit, whose input end is coupled to the identification circuit and whose output end is coupled to the control end of the primary switch, is used to control the conduction state of the primary switch according to the identification signal; when the identification circuit outputs an identification signal of a valid state, the primary switch control circuit controls the primary switch to be turned off.

16. A control method for protecting an isolated converter circuit, wherein a first end of an optocoupler element is coupled to a secondary circuit, and a second end of the optocoupler element is coupled to a primary circuit, wherein: The control method comprises: Receive a status signal of a secondary circuit; Outputting a first control signal according to the state signal, the first control signal being used to control the optocoupler current flowing through the optocoupler element; when the state signal is abnormal, the first control signal controls to increase the optocoupler current; and The conduction state of the secondary rectifier tube or the switch set in parallel with the secondary rectifier tube is controlled according to the state signal, so that a shutdown protection signal is sent to the primary circuit when the state signal is abnormal.

17. The control method according to claim 16, characterized in that: The process of controlling the conduction state of the secondary rectifier tube or the switch connected in parallel with the secondary rectifier tube according to the state signal specifically includes: Detecting the demagnetization state of the secondary circuit to output a first demagnetization detection signal; According to the state signal and the first demagnetization detection signal, the conduction state of the secondary rectifier tube or the switch set in parallel with the secondary rectifier tube is controlled so that a shutdown protection signal is sent to the primary circuit when the state signal is abnormal.

18. The control method according to claim 16, characterized in that: The process of outputting the first control signal according to the state signal is specifically: outputting the first control signal with a delay according to the state signal and the second delay signal.

19. A control method for DCM isolated converter circuit protection, characterized in that: include: Receive a status signal of a secondary circuit; Detecting the demagnetization state of the secondary circuit to output a first demagnetization detection signal; as well as The conduction state of the secondary rectifier tube or the switch set in parallel with the secondary rectifier tube is controlled according to the state signal and the first demagnetization detection signal, so that a shutdown protection signal is sent to the primary circuit when the state signal is abnormal.

20. A control method for protecting an isolated converter circuit, wherein a first end of an optocoupler element is coupled to a secondary circuit, and a second end of the optocoupler element is coupled to a primary circuit, wherein: The control method comprises: Receive a status signal of a secondary circuit; Comparing the state signal with a preset state threshold and outputting a comparison signal; A first control signal is outputted according to the comparison signal, wherein the first control signal is used to control the optocoupler current flowing through the optocoupler element; when the state signal is abnormal, the first control signal controls to increase the optocoupler current.

21. The control method according to any one of claims 16 to 20, characterized in that: Also includes: Detecting the demagnetization state of the secondary circuit to output a second demagnetization detection signal; outputting an identification signal according to the second demagnetization detection signal; When the state signal is abnormal, outputting an identification signal of a valid state according to the second demagnetization detection signal; as well as The conduction state of the primary switch is controlled according to the identification signal; when the identification signal is in a valid state, the primary switch is controlled to be turned off.

Images