CN107070441B - Soft switching circuit of switching power supply - Google Patents
Soft switching circuit of switching power supply Download PDFInfo
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- CN107070441B CN107070441B CN201710178902.8A CN201710178902A CN107070441B CN 107070441 B CN107070441 B CN 107070441B CN 201710178902 A CN201710178902 A CN 201710178902A CN 107070441 B CN107070441 B CN 107070441B
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
- H03K17/56—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices
- H03K17/687—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being field-effect transistors
Abstract
A soft switching circuit of a switching power supply comprises a power sampling circuit, a load current judging circuit and an auxiliary soft switching circuit. The power sampling circuit is connected to the load current size judging circuit, and the load current size is judged by reading the voltage values at the two ends of the power resistor through the sampling circuit. The load current size judging circuit is connected with the auxiliary light-load soft switch realizing circuit, the auxiliary light-load soft switch realizing circuit is started through judging the load current size condition, and the auxiliary system realizes the light-load soft switch state.
Description
Technical Field
The invention relates to the field of power electronics, in particular to a soft switching circuit for solving the problem that a light load is difficult to realize. The soft switching principle is suitable for realizing the full-load range soft switching circuit principle of power circuits such as a switching power supply, a frequency converter, a driver and the like.
Background
With the development of power electronic technology, switching power supplies with high power density and high efficiency are required to be used in many fields. The increase of the switching frequency can reduce the volumes of a transformer, an inductor and a capacitor, and is a trend of improving the power density of the existing switching power supply. However, the increase in switching frequency increases the loss of the switching power supply. In order to reduce the switching loss of the switching power supply and improve the switching frequency, the soft switching technology is developed. The resonant soft switch can provide zero voltage switching and zero current switching for the power device switch.
In order to establish soft-switching conditions for switching without increasing the cycle energy, a number of soft-switching PWM techniques have been developed. They use some form of resonant soft switching process, and after the switching conversion is finished, the normal PWM operation mode is recovered, but its resonant inductor is series-connected in the main circuit, so that its zero switching condition is related to the variation range of power supply voltage and load current, and under the condition of light load it can lose the soft switching condition. Because soft switching can not be realized in a light load state, the power device has large loss and serious heating, and the reliability of the system is reduced. Therefore, realizing soft switching in the full load range is a key problem of the miniaturized high-power density design of the switching power supply.
The common technical means for realizing soft switching under light load comprises that a fixed load is added at the output part, and the light load condition of the system is avoided. Because a lot of fixed loads need to be added, soft switching under a light load state is realized, but in a heavy load state, the fixed loads exist, the system efficiency is reduced, and the heating is increased. And the resonant inductance is increased by various means, the dead time is increased and the like, but the method has complex system parameter optimization and is difficult to realize, and the realization effect of the resonant soft switch in a heavy-load state can be reduced.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the soft switching circuit overcomes the defects of the prior art, realizes soft switching in a system light load state, reduces switching loss, and can avoid influencing the overall efficiency of the system heavy load state.
The technical scheme adopted by the invention is as follows:
a soft switching circuit of a switching power supply comprises a power sampling circuit, a load current judging circuit and an auxiliary soft switching circuit;
the power sampling circuit is connected to an output power loop of the switching power supply and used for collecting load current of the output power loop and sending collected load current signals to the load current judging circuit, the load current judging circuit compares the received load current signals with a preset threshold value to determine whether the output power loop is in a light load state or a heavy load state and sends state signals to the auxiliary soft switching circuit, the auxiliary soft switching circuit judges whether to realize soft switching according to the state signals, if the received load current signals are heavy load state signals, soft switching is not realized in an auxiliary mode, and if the received light load state signals are light load state signals, soft switching of the output power loop is realized through the auxiliary soft switching circuit.
The power sampling circuit comprises a resistor R1 and a capacitor C3;
a resistor R1 and a capacitor C3 are connected in series between the output positive end and the output negative end of the output power loop, and an output positive signal and an output negative signal are led out from two ends of a capacitor C3; a power sampling signal CS is led out between the output negative terminal of the output power loop and the resistor R1.
The load current judging circuit includes: capacitors C1, C2, resistors R2, R3, R4 and an operational amplifier V3;
an output negative signal of the power sampling circuit is connected to an input negative terminal of an operational amplifier V3 through a resistor R2, a power sampling signal CS is connected to an input positive terminal of the operational amplifier V3 through a resistor R3, a capacitor C1 is connected to two ends of a resistor R2 in parallel, the input negative terminal of the operational amplifier V3 is also connected to a VCC power supply through a resistor R4, and the resistors R2 and R4 divide the voltage of the VCC power supply to realize the setting of a preset threshold;
the positive input terminal of the operational amplifier V3 is also connected with the negative output signal of the power sampling circuit through a capacitor C2, and the output signal of the operational amplifier V3 is the control level signal and is sent to the auxiliary soft switching circuit.
The control level signal is a state signal representing whether the output power loop is in a light load state or a heavy load state.
The auxiliary soft switching circuit includes: resistors R5-R10, a triode V1 and an MOS transistor V2;
the control level signal output by the load current judging circuit is connected to the base electrode of the triode V1 through a resistor R5, meanwhile, the emitter electrode of the triode V1 is connected to the output negative signal of the power sampling circuit, and the resistor R7 is connected between the base electrode and the emitter electrode of the triode V1 in parallel;
the collector of the triode V1 is connected with a VCC power supply through a resistor R6, meanwhile, the collector of the triode V1 is also connected with the grid of an MOS tube V2, the source of the MOS tube V2 is connected with the output negative signal of the power sampling circuit, and a resistor R8 is connected between the source and the grid of the MOS tube V2 in parallel; the drain electrode of the MOS transistor V2 is connected to the output positive signal of the power sampling circuit through resistors R9 and R10 which are connected in parallel.
Resistors R9 and R10 are power resistors. The resistor R1 is a power sampling resistor.
Compared with the prior art, the invention has the beneficial effects that:
(1) the invention provides a soft switching circuit which solves the problem that a soft switching circuit is difficult to realize under light load, and the soft switching circuit can not realize the soft switching circuit under light load by detecting the light load state of a resistance system in a mode of connecting fixed loads in parallel at the output of the system, thereby realizing the soft switching in the full load range of the whole system and improving the reliability of a heating power device.
(2) The invention reads the loaded state of the system power loop through the power sampling circuit and the load current size judging circuit, designs the system light load range and judges whether the system is in the light load condition or not through the judgment of the margin value setting in the load current size judging circuit. The flexible control of the circuit to the system is realized, the structure is simple, and the practicability is strong.
(3) According to the invention, the output load current of the system is judged, so that the system automatically cuts off the fixed load loop at the output side under the heavy load condition, the fixed load can not work, the problem of low efficiency under the heavy load condition of the system due to the existence of the fixed load is solved, the heat productivity is reduced, and the overall reliability is improved.
Drawings
FIG. 1 is an overall block diagram of the soft switching circuit of the present invention;
FIG. 2 is a schematic diagram of a power sampling circuit of the system of the present invention;
FIG. 3 is a schematic diagram of a circuit for determining the magnitude of the load current of the system according to the present invention;
FIG. 4 is a schematic diagram of an implementation circuit of the auxiliary light-load soft switch of the present invention;
Detailed Description
The present invention will be described with reference to the accompanying drawings.
As shown in fig. 1, the present invention provides a soft switching circuit of a switching power supply, which includes a power sampling circuit, a load current determining circuit, and an auxiliary soft switching circuit, and solves the problem that some soft switching circuits cannot realize soft switching in a light load state. The power sampling circuit is connected to an output power loop of the switching power supply and used for collecting load current of the output power loop and sending collected load current signals to the load current judging circuit, the load current judging circuit compares the received load current signals with a preset threshold value to determine whether the output power loop is in a light load state or a heavy load state and sends state signals to the auxiliary soft switching circuit, the auxiliary soft switching circuit judges whether to realize soft switching according to the state signals, if the received load current signals are heavy load state signals, soft switching is not realized in an auxiliary mode, and if the received light load state signals are light load state signals, soft switching of the output power loop is realized through the auxiliary soft switching circuit.
The invention realizes the soft switching of the power circuit of the auxiliary switching power supply in a light load state, avoids influencing the overall efficiency of the switching power supply in a heavy load state, realizes the soft switching of the whole system in a full load range and improves the reliability of a heating power device. And the structure is simple and the practicability is strong.
As shown in fig. 2, the power sampling circuit includes a resistor R1 and a capacitor C3; the resistor R1 is a power sampling resistor.
A resistor R1 and a capacitor C3 are connected in series between the output positive end and the output negative end of an output power loop in the switching power supply, and output positive signals and output negative signals are led out from two ends of a capacitor C3; a power sampling signal CS is led out between the output negative terminal of the output power loop and the resistor R1. The resistor R1 is a power sampling resistor, has the characteristics of small resistance, small parasitic inductance and the like, ensures that the power resistor does not influence the overall efficiency of the switching power supply system, and has low power loss when large current flows. The stability of collecting the voltage at two ends of the R1 is guaranteed through the C3 capacitor, so that the data reliability is guaranteed, and the rear-end judgment and control circuit misoperation is prevented from being influenced.
As shown in fig. 3, the load current determination circuit includes: capacitors C1, C2, resistors R2, R3, R4 and an operational amplifier V3;
an output negative signal of the power sampling circuit is connected to an input negative end of an operational amplifier V3 through a resistor R2, an input negative end of an operational amplifier V3 reads voltage values at two ends of an output power loop R1, an input power sampling signal CS is connected to an input positive end of the operational amplifier V3 through a resistor R3, a capacitor C1 is connected to two ends of the resistor R2 in parallel, the input negative end of the operational amplifier V3 is also connected to a VCC power supply through a resistor R4, the resistors R2 and R4 divide the voltage of the VCC power supply, setting of a preset threshold is achieved, a load current light load and heavy load judgment threshold is determined, stability of signal acquisition at the input negative end of the operational amplifier V3 is guaranteed through the capacitor C1, and an interference signal is filtered out to prevent false operation; the positive input end of the operational amplifier V3 is also connected with the negative output signal of the power sampling circuit through a capacitor C2, the stability of signal acquisition of the positive input end of the operational amplifier V3 is guaranteed through a capacitor C2, and the false action caused by the filtering of interference signals is avoided. The output signal of the operational amplifier V3 is the control level signal and is sent to the auxiliary soft switch circuit.
The control level signal is a state signal representing whether the output power loop is in a light load state or a heavy load state.
As shown in fig. 4, the auxiliary soft switching circuit includes: resistors R5-R10, a triode V1 and an MOS transistor V2; the control level signal output by the load current judging circuit is connected to the base electrode of the triode V1 through a resistor R5, meanwhile, the emitter electrode of the triode V1 is connected to the output negative signal of the power sampling circuit, and the resistor R7 is connected between the base electrode and the emitter electrode of the triode V1 in parallel; the switch reliability can be ensured by setting the margin of the turn-on voltage of the triode V1 according to the resistance values of the resistor R5 and the resistor R7. The collector of the triode V1 is connected with a VCC power supply through a resistor R6, and the current of the collector of the triode V1 is limited through R6. Meanwhile, the collector of the triode V1 is also connected to the gate of the MOS transistor V2, the source of the MOS transistor V2 is connected to the output negative signal of the power sampling circuit, the resistor R8 is connected in parallel between the source and the gate of the MOS transistor V2, the resistor R6 and the resistor R8 divide the voltage of a VCC power supply to set the highest opening voltage of the gate of the MOS transistor V2, and the voltage of the source and the gate of the MOS transistor V2 is quickly discharged through the resistor R8; the drain electrode of the MOS transistor V2 is connected to the output positive signal of the power sampling circuit through resistors R9 and R10 which are connected in parallel. The resistors R9 and R10 are power resistors, and when the power circuit is in a light load state, the resistors R9 and R10 are connected in parallel between the output positive terminal and the output negative terminal of the output power circuit, so that the light load state of the power circuit is avoided.
Example (b):
according to one embodiment provided by the invention, a power acquisition resistor with the resistance value of 100m omega is selected as R1, a cement lead resistor with the power of 5W is selected as R9 and R10, a 0.1K resistor is selected as R2, a 30K resistor is selected as R4, an NPN type triode is selected as V1, an NMOS (N-channel metal oxide semiconductor) tube with low conduction internal resistance is selected as V2, and LM2904 is selected as V3.
The power acquisition resistor R1 can be replaced by a current transformer and related peripheral devices, and when the current flowing through the main power loop is large, the acquired R1 voltage signal in the power sampling circuit can be amplified and then sent to the load current judgment circuit.
The invention has simple circuit, safety, reliability, convenient operation and low cost, is not only suitable for solving the problem that the soft switching circuit is not easy to realize under light load, but also can be used in other wide fields.
Those skilled in the art will appreciate that those matters not described in detail in the present specification are well known in the art.
Claims (5)
1. A soft switching circuit of a switching power supply, characterized in that: the power sampling circuit comprises a power sampling circuit, a load current judging circuit and an auxiliary soft switching circuit;
the power sampling circuit is connected to an output power loop of the switching power supply and used for collecting load current of the output power loop and sending a collected load current signal to the load current judging circuit, the load current judging circuit compares the received load current signal with a preset threshold value so as to determine whether the output power loop is in a light load state or a heavy load state and sends a state signal to the auxiliary soft switching circuit, the auxiliary soft switching circuit judges whether to realize soft switching according to the state signal, if the received load current signal is a heavy load state signal, soft switching is not realized in an auxiliary mode, and if the received light load state signal is a light load state signal, soft switching of the output power loop is realized through the auxiliary soft switching circuit;
the power sampling circuit comprises a resistor R1 and a capacitor C3;
a resistor R1 and a capacitor C3 are connected in series between the output positive end and the output negative end of the output power loop, and an output positive signal and an output negative signal are led out from two ends of a capacitor C3; a power sampling signal CS is led out between the output negative end of the output power loop and the resistor R1;
the load current judging circuit includes: capacitors C1, C2, resistors R2, R3, R4 and an operational amplifier V3;
an output negative signal of the power sampling circuit is connected to an input negative terminal of an operational amplifier V3 through a resistor R2, a power sampling signal CS is connected to an input positive terminal of the operational amplifier V3 through a resistor R3, a capacitor C1 is connected to two ends of a resistor R2 in parallel, the input negative terminal of the operational amplifier V3 is also connected to a VCC power supply through a resistor R4, and the resistors R2 and R4 divide the voltage of the VCC power supply to realize the setting of a preset threshold;
the positive input terminal of the operational amplifier V3 is also connected with the negative output signal of the power sampling circuit through a capacitor C2, and the output signal of the operational amplifier V3 is the control level signal and is sent to the auxiliary soft switching circuit.
2. The soft switching circuit of a switching power supply according to claim 1, wherein: the control level signal is a state signal representing whether the output power loop is in a light load state or a heavy load state.
3. The soft switching circuit of a switching power supply according to claim 1, wherein: the auxiliary soft switching circuit includes: resistors R5-R10, a triode V1 and an MOS transistor V2;
the control level signal output by the load current judging circuit is connected to the base electrode of the triode V1 through a resistor R5, meanwhile, the emitter electrode of the triode V1 is connected to the output negative signal of the power sampling circuit, and the resistor R7 is connected between the base electrode and the emitter electrode of the triode V1 in parallel;
the collector of the triode V1 is connected with a VCC power supply through a resistor R6, meanwhile, the collector of the triode V1 is also connected with the grid of an MOS tube V2, the source of the MOS tube V2 is connected with the output negative signal of the power sampling circuit, and a resistor R8 is connected between the source and the grid of the MOS tube V2 in parallel; the drain electrode of the MOS transistor V2 is connected to the output positive signal of the power sampling circuit through resistors R9 and R10 which are connected in parallel.
4. The soft switching circuit of a switching power supply according to claim 3, wherein: resistors R9 and R10 are power resistors.
5. The soft switching circuit of a switching power supply according to claim 1, wherein: the resistor R1 is a power sampling resistor.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
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| CN201710178902.8A CN107070441B (en) | 2017-03-23 | 2017-03-23 | Soft switching circuit of switching power supply |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201710178902.8A CN107070441B (en) | 2017-03-23 | 2017-03-23 | Soft switching circuit of switching power supply |
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| CN107070441A CN107070441A (en) | 2017-08-18 |
| CN107070441B true CN107070441B (en) | 2020-09-18 |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN108933520A (en) * | 2018-07-19 | 2018-12-04 | 启攀微电子（上海）有限公司 | A kind of super low-power consumption DCDC Switching Power Supply |
| CN112821726B (en) * | 2021-01-19 | 2022-03-29 | 张亚尔 | Switching power supply circuit and method |
| CN113252970B (en) * | 2021-04-23 | 2022-11-18 | 长城电源技术有限公司 | Load detection circuit and power supply system |
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| CN203596603U (en) * | 2013-12-10 | 2014-05-14 | 北京易世恒电子技术有限责任公司 | Power supply control circuit |
| CN105871213B (en) * | 2015-01-21 | 2020-02-21 | 南京航空航天大学 | Control method and device in non-contact electric energy transmission system |
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