CN213402812U - Over-power protection circuit for switching power supply - Google Patents
Over-power protection circuit for switching power supply Download PDFInfo
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- CN213402812U CN213402812U CN202021293561.2U CN202021293561U CN213402812U CN 213402812 U CN213402812 U CN 213402812U CN 202021293561 U CN202021293561 U CN 202021293561U CN 213402812 U CN213402812 U CN 213402812U
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Abstract
The utility model discloses an overpower protection circuit for switching power supply, include: an AC-DC conversion unit converting an input AC voltage into a stable primary side DC voltage; the isolated DC-DC conversion circuit is coupled to the output end of the AC-DC conversion unit, converts the primary side direct current voltage from the AC-DC conversion unit into a secondary side direct current voltage, and works in an intermittent mode when the output power of the switching power supply exceeds the predetermined threshold output power; the current sampling unit is used for sampling the primary side bus current of the isolated DC-DC conversion circuit and providing a feedback electric signal containing the information of the sampled current to the controller; and a controller that performs an over-power protection action to limit output of power from the AC-DC conversion unit to a secondary side of the isolated DC-DC conversion circuit when the metric value of the feedback electrical signal exceeds the threshold metric value. By means of the circuit, reliable over-power protection can be provided at low cost.
Description
Technical Field
The utility model relates to an overpower protection circuit for switching power supply especially relates to the overpower protection circuit of primary side electric current based on isolated form direct current converter.
Background
Over-power protection is one of the functions that power supply products may have. For power products with a fixed output, such as a fixed voltage output power supply, over-power protection can be achieved by output over-current protection. On the other hand, for a current source with a fixed output, overpower protection can be achieved by outputting overvoltage protection. For a variable output range power supply, if the output maximum power is greater than the product of the maximum output current and the maximum output voltage, the over-power protection of the power supply can be achieved by both output over-current protection and output over-voltage protection. Separate over-power protection is not required for these several applications.
However, there is a class of power supplies, such as gel electrophoresis apparatus power supplies, which have very wide voltage output range and current output range due to their specific application, when different gels are connected to the load terminal, both output voltage and output current are variable. For different applications, it can support an output voltage range of up to 2V-300V, a current output range of up to 1mA-3A, and an output power of up to, for example, 380W, as non-limiting examples. In this case, the theoretical maximum output 900W calculated from the maximum voltage and the maximum current exceeds the allowable maximum output 380W, and when both the output voltage and the output current are variable, it is not possible to achieve the purpose of overpower protection by limiting one of them. For example, when overvoltage protection is performed by setting the allowable output voltage to 200V, the current can reach 3A at maximum, and therefore the output power may be as high as 600W, exceeding the allowable maximum output power. Therefore, an additional over-power protection function is required to limit the maximum output power of the power supply.
SUMMERY OF THE UTILITY MODEL
The over-power protection method includes sampling output voltage and output current, inputting the sampled signals to a multiplier circuit to obtain output power, and triggering a limit output executing mechanism to work when the output power exceeds a set power so as to limit the output power. However, this method has the problems of high cost and complex circuit of the multiplier circuit.
In view of the above, it is an object of the present invention to provide an overpower protection circuit capable of adapting to a power supply with a wide dynamic output range and reliably triggering overpower protection at low cost.
One aspect of the present invention is an overpower protection circuit for a switching power supply, including an AC-DC conversion unit, an isolated DC-DC conversion circuit, a current sampling unit, and a controller.
The AC-DC conversion unit may be configured to convert an input alternating current voltage into a stabilized primary side direct current voltage.
The isolated DC-DC conversion circuit may be coupled to an output of the AC-DC conversion unit, configured to convert a primary side direct current voltage from the AC-DC conversion unit into a secondary side direct current voltage, and operate in a discontinuous mode when an output power of the switching power supply exceeds a predetermined threshold output power.
The current sampling unit may be configured to sample a primary side bus current of the isolated DC-DC conversion circuit and provide a feedback electrical signal containing sampled current information to the controller.
The controller may be configured to perform an overpower-protection action to limit power output from the AC-DC conversion unit to the secondary side of the isolated DC-DC conversion circuit when the metric value of the feedback electrical signal exceeds the threshold metric value.
An over-power protection circuit according to an example embodiment of the present invention is particularly suitable for a power supply having a wide voltage output range and a wide current output range, and can reliably provide over-power protection when the maximum output power is allowed to be smaller than the product of the maximum output voltage and the maximum output current. Moreover, since a multiplier is not required, the cost can be significantly reduced and the circuit can be simplified.
Alternatively, the isolated DC-DC conversion circuit may be an isolated interleaved flyback conversion circuit, including a first transistor, a second transistor, a first transformer and a second transformer, wherein the first transistor and the second transistor are respectively disposed on primary sides of the first transformer and the second transformer, and configured to be alternately turned on, so that a primary side bus current is a pulse current and an excitation current alternately flows on secondary sides of the first transformer and the second transformer. The over-power protection circuit may further include a dc conversion driver coupled to the output of the controller and the first gate of the first transistor and the second gate of the second transistor, configured to provide PWM pulse signals to the first gate and the second gate in opposite phases based on control by the controller.
Under the staggered flyback topology, the phase difference of the driving signals of the first switching tube and the second switching tube is 180 degrees, so that the borne output power is doubled.
Alternatively, the current sampling unit may include: a sampling circuit configured to sample a primary side bus current of the isolated DC-DC conversion circuit; and a preprocessing circuit configured to preprocess the electrical signal output from the sampling circuit and provide the processed electrical signal as a feedback electrical signal to the controller.
By sampling the primary side bus current with the current sampling unit, a trigger point for over-power protection can be determined based on whether a metric value of its feedback electrical signal exceeds a threshold metric value. Compared with the traditional method of performing over-power protection by using the multiplier based on the voltage and the current of the output side, the method has the advantages of obviously reducing the cost and simplifying the circuit.
Optionally, the sampling circuit may include a current transformer, the current transformer may be coupled on a secondary side of the isolated DC-DC conversion circuit, and the preprocessing circuit may include: a rectifier configured to rectify the pulse current output from the current transformer; and a resistance-capacitance network coupled to the output of the rectifier and including at least one resistor and at least one capacitor, the output of the resistance-capacitance network being provided as a feedback electrical signal to the controller.
By varying the turns ratio of the current transformer and/or the resistance value of at least one resistor in the resistor-capacitor network, the amplitude of the signal input to the controller can be adjusted, thereby enabling adjustment of the maximum output power allowed to trigger the over-power protection.
Optionally, the controller may be further configured to stop the over-power protection action after performing the over-power protection action for a predetermined time. The predetermined time may be one or more operating cycles of the controller.
In this way, the circuit of the present disclosure can enable or disable over-power protection during one or more cycles of operation of the controller, with response speeds on the order of milliseconds, which can provide reliable protection for the power supply.
Drawings
The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in this document. Like numerals having different letter suffixes may represent different instances of similar components.
FIG. 1 is a block diagram illustrating an example power supply system 100, according to an embodiment;
fig. 2 is a diagram illustrating an example circuit structure of an example power supply system 200 according to an embodiment;
fig. 3 is a diagram illustrating an example circuit configuration of the current sampling unit 203 according to the embodiment;
fig. 4 is a diagram illustrating another exemplary circuit configuration of the current sampling unit 203 according to the embodiment;
fig. 5 is a diagram illustrating an example circuit configuration of a control portion of the power supply system 200 of fig. 2;
FIG. 6 is a graph illustrating the driving signals G1 and G2 and the bus current I for the first switch tube 204 and the second switch tube 205 in the power supply system 200 of FIG. 2busTiming diagrams of example timings of (1);
FIG. 7 is a waveform diagram illustrating example waveforms of bus current and sampled current signals of the example power system 200 of FIG. 2; and is
FIG. 8 is a graph illustrating a bus current peak value I measured when limiting the allowed maximum output power of an example electrophoresis apparatus according to an embodiment to 380WbusmaxAnd an output voltage VoutA graph of the relationship of (a).
Description of the reference symbols
2AC input; a 4AC-DC conversion unit; 6 an isolated DC-DC conversion circuit; 8, loading; 10 a current sampling unit; 12 a controller; 201 an input filter; 202 an AC-DC conversion unit; 203 current sampling unit; 204 a first switch tube; 205 a second switch tube; 206 a first transformer; 207 a second transformer; a 208 voltage sampler; 209 a controller; 210 a dc conversion driver; 211 a transformer; GND1 front ground; GND2 back end ground; r1 first resistor; r2 second resistor; a C1 first capacitor; a C2 second capacitor; a C3 third capacitor; a D1 first diode; a second diode D2; a third diode D3; d4 fourth diode; d31, D32, D33, D34 rectifier diodes; 2031 current transformer; 2032 a rectifier; 2033 a resistance-capacitance network; a T transformer; g1, G2 drive signals.
Detailed Description
In the following description, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. Meanwhile, in the following description, some or all elements that do not affect the implementation of the present disclosure may be omitted for the convenience of understanding the present disclosure.
References in the specification to "one embodiment," "an example embodiment," etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.
In some embodiments, the numerical parameters used in the specification and claims are approximations that may vary depending upon the desired properties of the individual embodiments.
The term "coupled" may mean that two or more elements are in direct electrical contact. However, "coupled" may also mean that two or more elements are not in direct electrical contact with each other, but yet still interact with each other, e.g., via a magnetic field.
Moreover, in the figures, the absence of any such connecting element does not imply that no connection, relationship, or association may exist, where a connecting element, such as a solid or dashed line or arrow, is used to illustrate a connection, relationship, or association between two or more other exemplary elements. In other words, some connections, relationships, or associations between elements are not shown in the drawings in order to avoid obscuring the disclosure. In addition, for ease of explanation, a single connected element is used to represent multiple connections, relationships, or associations between elements. For example, where connection elements represent communication of signals, data, or instructions, those skilled in the art will appreciate that such elements may represent one or more signal paths (e.g., buses) as needed to effect the communication.
Overview of Power supply System
Fig. 1 is a block diagram illustrating an example power supply system 100, according to an embodiment.
In fig. 1, the AC (Alternating Current) input 2 may be a mains interface, for example an AC input of 110V or 220V.
The AC-DC (Alternating Current-Direct Current) converting unit 4 is configured to convert an Alternating Current voltage from the AC input 2 into a stable Direct Current voltage, and then input the stable Direct Current voltage to a primary side of an isolated DC-DC (Direct Current-Direct Current) converting circuit 6. In some embodiments, the DC voltage input to the isolated DC-DC converter circuit 6 may be filtered and stepped up and down. For example, the AC-DC conversion unit 4 may convert 220V alternating current into stable 380V direct current. In some embodiments, the AC-DC conversion unit 4 may also perform power factor adjustment on the input alternating current.
The isolated DC-DC conversion circuit 6 isolates input power and output power on both sides of the transformer using an isolated transformer, so that input current cannot directly flow from the primary side to the secondary side of the transformer. Under the control of the controller 12, the isolated DC-DC conversion circuit 6 converts the DC voltage from the AC-DC conversion unit 4 into a desired output DC voltage, and then supplies the output DC voltage to the load 8.
When the output power is high, i.e. higher than the predetermined threshold output power, the isolated DC-DC conversion circuit 6 operates in a Discontinuous Mode (DCM), so that it operates in the Discontinuous Mode when the over-power protection is triggered. Discontinuous mode is discontinuous conduction mode. In the discontinuous mode, before the switch tube is conducted, the energy of the primary winding of the transformer is completely transferred to the secondary side, so that the inductor current always returns to 0. When the output power is low, the isolated DC-DC converter circuit 6 may operate in a Mode other than the discontinuous Mode, for example, a Continuous Mode (CCM). Continuous mode is continuous conduction mode. In continuous mode, the inductor current does not return to 0 during one switching cycle. When the switching tube is opened, current also flows in the coil. It should be noted that the present disclosure does not limit the operation mode at low output power, since no over-power protection is needed at low output power.
The current sampling unit 10 is configured to sample a primary side current of the isolated transformer of the isolated DC-DC conversion circuit 6, and then provide a feedback electrical signal containing information of the sampled current to the controller 12.
The controller 12 is configured to perform an overpower-protection action when a metric (such as voltage, current) value of the feedback electrical signal from the current sampling unit 10 exceeds a threshold metric value. The over-power protection action limits the secondary side output power of the isolated DC-DC conversion circuit 6 by limiting the power input to the primary side of the isolated DC-DC conversion circuit 6. In other words, the over-power protection action limits the output of the power from the AC-DC conversion unit 4 to the secondary side of the isolated DC-DC conversion circuit 6, thereby preventing the output power from further rising. This is because the input power P of the isolated DC-DC converter circuit 6inAnd the output power PoutThe following relationship is satisfied:
Pout＝Pin×η (1)
where η represents the conversion efficiency. Thus enabling to limit the input power PinTo limit the output power Pout。
The controller 12 may perform the overpower-protection action by changing the control signal input to the isolated DC-DC converter circuit 6.
Example Circuit Structure
Fig. 2 is a diagram illustrating an example circuit structure of an example power supply system 200 according to an embodiment. Fig. 3 is a diagram illustrating an example circuit configuration of the current sampling unit 203 according to the embodiment. Fig. 4 is a diagram illustrating another example circuit configuration of the current sampling unit 203 according to the embodiment. Fig. 5 is a diagram illustrating an example circuit configuration of a control portion of the power supply system 200 of fig. 2. FIG. 6 is a graph illustrating the driving signals G1 and G2 and the bus current I for the first switch tube 204 and the second switch tube 205 in the power supply system 200 of FIG. 2busTiming diagram of an example timing sequence of (1). In fig. 2 to 5, arrows schematically show the current direction.
In fig. 2, AC denotes a mains interface, corresponding to the AC input 2 in fig. 1, for example an AC supply input of 110V or 220V. The ac supply input may be filtered via an input filter 201. The input filter 201 is used to rectify and filter the input ac power.
The filtered alternating current is input to the AC-DC conversion unit 202. The AC-DC conversion unit 202 converts the alternating current signal into a primary side direct current signal with a stabilized voltage. In some embodiments, the AC-DC conversion unit 202 may perform a buck-boost process on the AC signal. The AC-DC conversion unit 202 may further adjust the Power Factor of the AC signal, and may be, for example, a Power Factor Correction (PFC) circuit. The direct current signal output from the AC-DC conversion unit 202 is converted to have a desired output voltage V by the isolated DC-DC conversion circuit 220outThe dc signal of (1).
In this embodiment, the isolated DC-DC conversion circuit 220 adopts an interleaved flyback topology. Specifically, as shown by the dashed-line box in fig. 2, the example isolated DC-DC conversion circuit 220 includes a first switching tube 204, a second switching tube 205, a first transformer 206, a second transformer 207, a first diode D1, a second diode D2, a third diode D3, and a fourth diode D4. A first end of the primary winding of the first transformer 206 is connected to the output end of the AC-DC conversion unit 202, and a second end of the primary winding of the first transformer 206 is connected to the drain of the first switching tube 204. The source of the first switch tube 204 is connected to the front end ground GND1, and the drain of the first switch tube 204 is connected to the anode of the first diode D1. The cathode of the first diode D1 is connected to the output terminal of the AC-DC conversion unit 202 through a first resistor R1. The first resistor R1 is connected in parallel with a first capacitor C1. A first end of the primary winding of the second transformer 207 is connected to the output end of the AC-DC converting unit 202, and a second end of the primary winding of the second transformer 207 is connected to the drain of the second switching tube 205. The source of the second switch tube 205 is connected to the front end ground GND1, and the drain of the second switch tube 205 is connected to the anode of the second diode D2. The cathode of the second diode D2 is connected to the output terminal of the AC-DC converting unit 202 through a second resistor R2. The second resistor R2 is connected in parallel with a second capacitor C2. The gate of the first switching tube 204 and the gate of the second switching tube 205 are respectively used for receiving two paths of PWM pulse signals with opposite phases from the dc conversion driver 210 via the transformer 211. A first terminal of the secondary winding of the first transformer 206 is connected to the anode of the third diode D3, and a second terminal of the secondary winding of the first transformer 206 is connected to the back-end ground GND 2. A first terminal of the secondary winding of the second transformer 207 is connected to the back-end ground GND2, and a second terminal of the secondary winding of the second transformer 207 is connected to the cathode of the fourth diode D4. The cathode of the third diode D3 and the anode of the fourth diode D4 serve as output terminals of the isolated DC-DC converter circuit 220. A third capacitor C3 is also connected between the output terminal and the back end ground GND 2.
The voltage sampler 208 is used for sampling the output voltage V of the isolated DC-DC conversion circuit 220outSampling is performed. The controller 209 is configured to provide a control signal to the dc conversion driver 210 based on the control signal from the voltage sampler 208. The dc conversion driver 210 controls the conduction of the first switch tube 204 and the second switch tube 205 based on the control signal to achieve the purpose of dc conversion and obtain the required output voltage Vout。
In the power supply system, according to the principle of interleaved flyback, the first transformer 206 and the second transformer 207 operate in time division into a charging period and a discharging period, and the charging period is controlled by the first switch tube 204 and the second switch tube 205 respectively. During the period when the corresponding first switching tube 204 (second switching tube 205) is turned on, the direct current from the AC-DC conversion unit 202 charges the first transformer 206 (second transformer 207) with magnetic energy. During the time that the first switch tube 204 (the second switch tube 205) is turned off, the magnetic energy stored in the first transformer 206 (the second transformer 207) discharges current to the output circuit (the load). The conduction and the closing of the first switch tube 204 and the second switch tube 205 are controlled by the duty ratio of a PWM (Pulse Width Modulation) signal, and the output is higher the larger the duty ratio is. Because the phase difference of the driving signals of the first switch tube 204 and the second switch tube 205 is 180 degrees, the output power which can be carried is doubled.
More specifically, the AC input is rectified into a stable direct current voltage after passing through the input filter 201 and the AC-DC conversion unit 202. In the isolated DC-DC converter circuit 220, the first switch tube 204 and the second switch tube 205 are alternately conducted. When the first switch tube 204 is turned on, the second switch tube 205 is turned off, and the bus current IbusThe primary winding of the first transformer 206 starts to store energy via the primary winding of the first transformer 206, the first switching tube 204 and back to the AC-DC converting unit 202. When the second switch tube 205 is turned on, the first switch tube 204 is already turned off, and the bus current IbussThe magnetic energy stored in the first transformer 206 is discharged through the third diode D3 while the energy stored in the first transformer 207 is stored by the second transformer 207 primary winding and the second switch 205 returning to the AC-DC converting unit 202. Then, the first switch tube 204 is turned on again, the second switch tube 205 is turned off, the first transformer 206 stores energy, and the second transformer 207 discharges energy through the secondary winding and via the fourth diode D4.
The first diode D1, the second diode D2, the first resistor R1, the second resistor R2, the first capacitor C1, and the second capacitor C2 are absorption circuits of the first switch tube 204 and the second switch tube 205, respectively, and are used for absorbing spike voltages generated by leakage inductances of the first transformer 206 and the second transformer 207 to reduce voltage stress of the first switch tube 204 and the second switch tube 205.
The isolated DC-DC converter circuit 6 is designed to operate in discontinuous mode when the output power is high, i.e. above a predetermined threshold output power.
The current sampling unit 203 samples the bus current I of the primary side of the isolated DC-DC conversion circuit 220busSamples are taken and a feedback electrical signal containing the sampled current information is then provided to the controller 209. The current sampling unit 203 may include a sampling circuit and a preprocessing circuit. The sampling circuit is used for the bus current IbusSampling is performed. The preprocessing circuit is used for processing the signal collected by the sampling circuit, obtaining the peak information of the sampled signal and providing the peak information to the controller 209 as a feedback electrical signal. For example, the preprocessing circuit may rectify the pulse signal collected by the sampling circuit into a direct current signal. In some embodiments, the pre-processing circuit may further remove glitches and ringing signals in the dc signal. The pre-processing circuit may also adjust the amplitude of the dc signal to accommodate the input range of the controller 209.
In the example embodiment of the current sampling unit 203 shown in fig. 3, the current sampling unit 203 includes a current transformer 2031 as a sampling unit and a rectifier 2032 as a preprocessing unit. The current transformer 2031 is coupled to the secondary side of the isolated DC-DC converter circuit 220, and couples the bus current I on the primary side via the transformer TbusSampling is performed. The rectifier 2032 includes, for example, a rectifier bridge made up of four rectifier diodes D31, D32, D33, and D44. The sampled pulse signal is rectified into a dc signal by the rectifier 2032, and the amplitude thereof corresponds to the peak value of the pulse signal. The rectified DC signal is used as feedback electric signal IsampleIs provided to the controller 209.
In another example embodiment of the current transformer 203 shown in fig. 4, the preprocessing circuit of the current sampling unit 203 further includes a resistive-capacitive network 2033. The RC network 2033 comprises at least one capacitor and at least one resistor for removing glitches and ringing signals in the DC signal while simultaneously feeding the feedback electrical signal I to the controller 209sampleE.g. a voltage value.
The implementation of the current sampling unit 203 is not limited to the above embodiments, and for example, the current sensor may be used to directly couple the bus to the primary side of the isolated DC-DC conversion circuit 220Stream IbusThe measurement is performed and the measurement result is provided to the controller 209. Any circuit capable of achieving the above-mentioned objectives may be employed by those skilled in the art.
As shown in fig. 5, the feedback electrical signal I from the current sampling unit 203sampleTo the input of the controller 209. The controller 209 is configured to provide corresponding control signals to the dc-conversion driver 210 based on the voltage sampling signals from the voltage sampler 208. The dc conversion driver 210 supplies driving signals G1 and G2 to the gates of the first transformer 206 and the second transformer 207 based on the control signal. In the embodiment of fig. 5, dc conversion driver 210 provides drive signals G1 and G2 via transformer 211.
In addition, the controller 209 feeds back the electrical signal IsampleWhen the metric (such as voltage, current) value of (a) exceeds the threshold metric value, an over-power protection action is performed to limit the output of power from the AC-DC conversion unit 202 to the secondary side of the isolated DC-DC conversion circuit 220.
In some embodiments, the over-power protection action may be to stop providing the driving signals G1 and G2 to the first switch tube 204 and the second switch tube 205, so that the first switch tube 204 and the second switch tube 205 are no longer conductive, and therefore the AC-DC conversion unit 202 cannot output power to the secondary side of the isolated DC-DC conversion circuit 220. In another embodiment, the over-power protection action may be to reduce the duty ratio of the driving signals G1 and G2 for providing the first switch tube 204 and the second switch tube 205, so as to reduce the input power P of the isolated DC-DC converter circuit 220in。
The over-power protection action may be stopped after a certain period of time has elapsed. For example, the controller 209 may terminate the over-power protection action after performing the over-power protection action for one or more operating cycles thereof, and will re-apply the feedback electrical signal I from the current sampling unit 203sampleThe metric value of (a) is compared to a threshold metric value to determine whether an over-power protection action needs to be performed. If the electric signal I is fed backsampleMay be restored to a normal operating state if the measured value of (b) is below the threshold measured value, and may be converted to dc based on the voltage sampling signal from the voltage sampler 208The driver 210 provides a corresponding control signal. In this way, the power supply system 200 can enable or disable over-power protection during one or more cycles of operation of the controller 209, with response speeds on the order of milliseconds, which can provide reliable protection for the power supply.
By way of non-limiting example, the controller 209 may be, for example, an Application Specific Integrated Circuit (ASIC), a programmable logic array, a programmable logic controller, a microcontroller, a microprocessor, a Digital Signal Processor (DSP), or any other suitable control circuit.
In the above description, the primary side and the secondary side are with respect to the first transformer 206 and the second transformer 207 of the isolated DC-DC conversion circuit 220. The primary side is the side of the front end ground GND1 for receiving input power from the AC-DC conversion unit, and the secondary side is the side of the rear end ground GND2 for supplying output power to the load.
Triggering of over-power protection
According to the method, alternating current is converted into direct current with stable voltage by the AC-DC conversion unit, and direct current conversion is performed by the isolated DC-DC conversion circuit. The current sampling unit samples the bus current of the primary side of the isolated DC-DC conversion circuit. When the metric value of the sampled current exceeds the threshold metric value, an overpower-protection action is performed. Since the AC-DC conversion unit provides stable voltage output, the input power can be limited by limiting the current of the primary side, so that the output power is limited, and the purpose of over-power protection is achieved.
In the exemplary embodiment of FIG. 1, the input power P in equation (1)inCan be calculated as follows:
Pin＝Vin×Iin (2)
in the formula (2), VinAn input voltage on the primary side of the isolated DC-DC conversion circuit 6 is shown, and its value is fixed to an output voltage of the AC-DC conversion unit 4, for example, 380V. I isinIs the input current on the primary side.
The output power P can be obtained by combining the formula (1)outComprises the following steps:
Pout＝Vin×Iin×η (3)
due to the input voltage VinIs a stable value provided by the AC-DC conversion unit 4, and thus the maximum output power PoutmaxComprises the following steps:
Poutmax＝Vin×Iinmax×η (4)
in the above formula (4), IinmaxRepresenting the peak value of the primary side input current. Therefore, by limiting the primary side maximum current IinmaxCapable of limiting maximum output power Poutmax。
It should be noted that the conversion efficiency η varies at different output powers. For example, at an output power of 350W, η may be around 84%. Therefore, the influence of the conversion efficiency needs to be considered when setting the threshold value metric.
Discussed further below in connection with the example power system 200 of fig. 2. When the power supply system 200 shown in fig. 2 operates normally, as shown in fig. 6, the driving signals G1 and G2 are alternately at a high level, so that the first switch tube 204 and the second switch tube 205 are alternately turned on. As a result, the first transformer 206 and the second transformer 207 alternately pass the excitation current. At this time, a primary side input current IinI.e. the bus current Ibus. As shown in fig. 6, the bus current IbusIs a pulsed current. Further, in fig. 6, the power supply system 200 operates in the discontinuous mode, with the bus current IbusReturning to a value of 0 at each switching cycle.
In the example of fig. 2, the first switchThe amplitudes and pulse widths of the driving signals G1 and G2 of the tube 204 and the second switching tube 205 may be the same, and the phases are different by 180 degrees, so that the working timings of the first transformer 206 and the second transformer 207 are different by 180 degrees, and the alternate output is realized. Bus current IbusGradually increasing when the G1 and G2 outputs are high and rapidly transitioning to 0 when the G1 and G2 outputs are low, and thus are pulsed signals.
As described above, when the output power is higher than the predetermined threshold output power, the isolated DC-DC conversion circuit 6 operates in the discontinuous mode. At this time, the bus current I during the conduction of the first switching tube 204 and the second switching tube 205busPeak value of (1)busmaxAccording to the following formula:
in the above formula (3), VbusThe bus voltage, that is, the primary side input voltage of the isolated DC-DC converter circuit 6 is a stable value. T isonThe conduction time of the first switch tube 204 and the second switch tube 205.
When the isolated DC-DC conversion circuit 6 of the flyback topology works in the discontinuous mode, the conduction time TonCan be calculated as follows:
in the above formula (4), IoutIs the output current of the power supply system 200, which is a function of the output load and the output voltage VoutMay vary. Lp is the source side inductance of the output transformers (first transformer 206 and second transformer 207). VfThe conduction voltage drop of the rectifier diodes D31, D32, D33 and D34 in the rectifier 2032 is about 0.7V for commonly used silicon transistors. f is the frequency of the drive signals G1 and G2.
Output power PoutCan be calculated as follows:
Pout＝Vout*Iout (5)
further, let constant k be as follows:
the on-time T can be obtained by substituting the formula (5) and the formula (6) for the formula (4)onAnd the output power PoutThe relationship of (1) is:
substituting the formula (7) into the formula (3) to obtain a bus current peak value IbusmaxAnd the output power PoutThe relationship between them is as follows:
from the equation (8), the output power P isoutSame but output current IoutIn different cases, the voltage drop V is reduced by the conduction of the rectifier diodefExistence of bus current peak value IbusmaxVariations will also occur.
Taking the case of electrophoresis apparatus as an example, assume that the output voltage range covers 2V-300V and the output current range covers 1 mA-3A. Then over-power protection may occur at the output voltage VoutIn the range of 150V to 300V. At this time, the isolated DC-DC conversion circuit 6 operates in the discontinuous mode. FIG. 8 is a graph illustrating the bus current peak I measured when limiting the maximum allowable output power of the example electrophoresis apparatus to 380WbusmaxAnd an output voltage VoutA graph of the relationship of (a). As shown in fig. 8, the peak value of the bus current IbusmaxThe conduction voltage drop V caused by the rectifier diodes D31, D32, D33 and D34fIs changed. However, the amount of change is less than 0.12%, which is negligible. Thus, at the output voltage VoutDuring the course of the change, as long as the output power P isoutKeeping the bus current peak value I unchangedbusmaxRemain almost unchanged. Equation (8) can therefore be rewritten as:
from the above equation (9), in the discontinuous mode, the peak value I of the bus currentbusmaxAnd the output power PoutIs proportional to the square root of the bus current peak value IbusmaxTo trigger the theoretical basis of over-power protection. Thus, the peak value of the bus current I shown in the formula (9) is usedbusmaxAnd the output power PoutIn conjunction with the bus current IbusAnd a feedback electric signal IsampleThe unique corresponding relation between the two signals can be realized by feeding back the electric signal IsampleKnowing the current output power PoutSo as to be able to be based on the feedback electrical signal IsampleTo determine whether to trigger over-power protection.
As a non-limiting example, the threshold output power may be set to 200W, and the allowed maximum output power that triggers over-power protection may be set to 380W, for example. When the output power PoutAbove 200W, the power supply system operates in discontinuous mode. When the output power PoutFurther increases and reaches 380W, for example, as shown in FIGS. 4 and 5, at I of the controller 209limThe terminal receives a sampled voltage signal of, for example, 1.2V, due to the feedback electrical signal IsampleReaches the threshold voltage value (1.2V), thus triggering the over-power protection so that the output power does not rise further.
The feedback electrical signal I received by the controller 209 from the current sampling unit 203sampleIs to the bus current IbusObtained by sampling and preprocessing, and the bus current IbusHave a corresponding relationship. Changing the set value of the threshold voltage value (1.2V) can change the allowed maximum output power. Of course, it can also be based on the feedback electrical signal IsampleTrigger the over-power protection by changing the set value of the threshold current valueTo change the maximum output power allowed. In addition, parameters of the current sampling unit 203 may also be changed without changing the threshold metric value, including but not limited to the turn ratio of the current transformer 2031, the resistance values of the resistors in the resistive-capacitive network 2033, and the like.
The present disclosure provides a stable input voltage using the AC-DC conversion unit 4, the isolated DC-DC conversion circuit 6 is designed to operate in an intermittent mode in a high power state, and a primary side, i.e., an input side current of the isolated DC-DC conversion circuit is sampled using a proportional relationship between a peak value of the input (primary) side current (i.e., a bus current) and a square root of an output power in the intermittent mode, to obtain an electrical feedback signal. Since the electrical feedback signal has a correspondence with the peak value of the primary side bus current, it is possible to determine whether to perform the overpower protection by determining whether the metric value of the electrical feedback signal exceeds the threshold metric value. Therefore, it is not necessary to sample the output side voltage and the output side current and calculate the output power by using a multiplier, the cost is remarkably reduced, and the circuit structure is simplified.
The embodiments of the present invention have been described above in detail. It will be appreciated that various embodiments and modifications of the invention may be made without departing from the broader spirit and scope of the invention. Many modifications and variations may be made in light of the above teaching by those of ordinary skill in the art without undue experimentation. Therefore, the technical solutions that can be obtained by the present invention through logic analysis, reasoning or limited experiments based on the prior art shall all fall within the scope of protection defined by the claims of the present invention.
Claims (11)
1. An over-power protection circuit for a switching power supply, comprising:
an AC-DC conversion unit configured to convert an input alternating-current voltage into a stabilized primary-side direct-current voltage;
an isolated DC-DC conversion circuit coupled to an output of the AC-DC conversion unit, configured to convert a primary side direct current voltage from the AC-DC conversion unit into a secondary side direct current voltage, and to operate in a discontinuous mode when an output power of the switching power supply exceeds a predetermined threshold output power;
a current sampling unit configured to sample a primary side bus current of the isolated DC-DC conversion circuit and provide a feedback electrical signal containing sampled current information to a controller; and
the controller is configured to perform an over-power protection action to limit power output from the AC-DC conversion unit to the secondary side of the isolated DC-DC conversion circuit when the metric value of the feedback electrical signal exceeds a threshold metric value.
2. The over-power protection circuit according to claim 1, wherein the isolated DC-DC conversion circuit is an isolated interleaved flyback conversion circuit including a first transistor, a second transistor, a first transformer and a second transformer, wherein the first transistor and the second transistor are respectively disposed on primary sides of the first transformer and the second transformer, configured to be alternately turned on so that the primary-side bus current is a pulse current and an excitation current alternately flows on secondary sides of the first transformer and the second transformer,
the over-power protection circuit further includes a dc conversion driver coupled to an output of the controller and to the first gate of the first transistor and the second gate of the second transistor, configured to provide PWM pulse signals of opposite phases to the first gate and the second gate based on control of the controller.
3. The over-power protection circuit of claim 2, wherein the current sampling unit comprises:
a sampling circuit configured to sample the primary side bus current of the isolated DC-DC conversion circuit; and
a pre-processing circuit configured to pre-process the electrical signal output from the sampling circuit and provide the processed electrical signal as the feedback electrical signal to the controller.
4. The over-power protection circuit of claim 3,
the sampling circuit includes a current transformer coupled on a secondary side of the isolated DC-DC conversion circuit, and
the pre-processing circuit includes a rectifier configured to rectify the pulse current output from the current transformer and to provide the rectified current as the feedback electrical signal to the controller.
5. The over-power protection circuit of claim 3,
the sampling circuit includes a current transformer coupled on a secondary side of the isolated DC-DC conversion circuit, and
the preprocessing circuit includes:
a rectifier configured to rectify a pulse current output from the current transformer; and
a resistor-capacitor network coupled to the output of the rectifier and including at least one resistor and at least one capacitor, the output of the resistor-capacitor network being provided to the controller as the feedback electrical signal.
6. The over-power protection circuit of claim 2, wherein the over-power protection action comprises ceasing to provide the PWM pulse signal to the first gate and the second gate to cease power from the AC-DC conversion unit from being output to the secondary side of the isolated DC-DC conversion circuit.
7. The over-power protection circuit of claim 2, wherein the over-power protection action comprises reducing a duty cycle of a PWM pulse signal provided to the first gate and the second gate.
8. The over-power protection circuit of any of claims 1-7, wherein the controller is further configured to stop the over-power protection action after performing the over-power protection action for a predetermined time.
9. The over-power protection circuit of claim 8, wherein the predetermined time is one or more cycles of operation of the controller.
10. The overpower-protection circuit of any one of claims 1 to 7, wherein the switching power supply is for an electrophoresis apparatus.
11. The over-power protection circuit of claim 10, wherein the allowed maximum output power of the switching power supply is less than the product of its maximum output voltage and maximum output current and greater than the threshold output power.
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| CN113996252A (en) * | 2021-10-28 | 2022-02-01 | 西安交通大学 | Activation system for PVC gel activation |
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| CN113996252A (en) * | 2021-10-28 | 2022-02-01 | 西安交通大学 | Activation system for PVC gel activation |
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