CN102005931A - Forward converter - Google Patents
Forward converter Download PDFInfo
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- CN102005931A CN102005931A CN 201010141775 CN201010141775A CN102005931A CN 102005931 A CN102005931 A CN 102005931A CN 201010141775 CN201010141775 CN 201010141775 CN 201010141775 A CN201010141775 A CN 201010141775A CN 102005931 A CN102005931 A CN 102005931A
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Abstract
The invention relates to a forward converter, aiming to expand the duty cycle of a forward converter and ensure the stability thereof. The forward converter comprises a transformer, a switching tube, a rectifying unit, a first RCD (Resistor-Capacitor-Diode) circuit and a second RCD circuit, wherein the switching tube is connected in series with a primary winding of the transformer and connected with both ends of an input voltage, the rectifying unit is connected with a secondary winding of the transformer, the first RCD circuit is connected in parallel with the primary winding of the transformer and absorbs energy generated from switch surge or input voltage saltation, the second RCD circuit is respectively connected in parallel with the primary winding of the transformer and the first RCD circuit and realizes magnetic resetting of the transformer in each duty cycle, and the rectifying unit is one of a half-wave rectifier circuit, a full-wave rectifier circuit and a full-bridge rectifier circuit. The maximum duty cycle of the forward converter can be 63 percent by the design of the first RCD circuit and the second RCD circuit and the lower power consumption and the high reliability of the forward converter are realized by adopting the simple circuit.
Description
Technical field
The present invention relates to the converter technical field, particularly a kind of forward converter.
Background technology
Forward converter generally comprises LCD (Inductance-Capacitance-Diode, inductor-capacitor-diode) forward converter, RCD (Resistance-Capacitance-Diode, resistance-capacitance-diode) forward converter and active clamp converter.The LCD forward converter is simple in structure, but its cost is slightly high, and duty ratio is less than 50%, and the loss of clamp circuit is low; The loss of main switch is big, does not have obvious odds for effectiveness.The RCD forward converter is simple in structure, and is with low cost, and its duty ratio is less than 50%, but the power consumption of its clamp resistance is big, temperature rise; And transformer leakage inductance can cause power consumption to rise, and the voltage stress of switching tube Q1 increases, and efficient is not high.The duty ratio of active clamp converter can reach more than 50%, and efficient is higher, but the cost height, control is complicated, and especially when switching on and shutting down and load saltus step, reliability is lower than RCD and LCD forward converter.
In sum, existing RCD and LCD forward converter are simple in structure, with low cost, but its duty ratio all is not more than 50%.And the active clamp converter is used because of cost and reliability and is restricted.
Summary of the invention
One of goal of the invention of the present invention is the duty ratio that solves forward converter, improves the conversion efficiency of forward converter and a kind of forward converter of proposing.
Forward converter of the present invention comprises transformer, switching tube, rectification unit, a RCD circuit and the 2nd RCD circuit, wherein be connected with the input voltage two ends after switching tube and the former limit of the transformer windings in series, rectification unit is connected with transformer secondary winding, the one RCD circuit is in parallel with the former limit of transformer winding, the energy that produces when absorbing switching surge or input voltage mutation; The 2nd RCD circuit is in parallel with a transformer former limit winding and a RCD circuit respectively, realizes the magnetic reset of transformer in each work period.
Preferably, above-mentioned the 2nd RCD circuit comprises second resistance, second electric capacity and second diode, wherein second diode is with after second resistance is in parallel, again with second capacitances in series, the positive pole of described second diode is connected with an end of the former limit of transformer winding and the drain electrode of described switching tube respectively, the other end and second capacitances in series of the former limit of described transformer winding;
Switching tube is open-minded, and input voltage charges to second electric capacity; Switching tube disconnects, and the static exciter inductance charges to resetting voltage earlier to second electric capacity, discharges then, and through the former limit of transformer winding, transformer is finished magnetic reset to its discharging current by the second resistance reverse flow.
Preferably, an above-mentioned RCD circuit comprises first resistance, first electric capacity and first diode, wherein after first resistance and first capacitances in series, connect with first diode again, the positive pole of first diode is connected with an end of the former limit of transformer winding and the drain electrode of switching tube respectively, the other end of the former limit of transformer winding and first resistance and first capacitances in series.
Preferably, the drain electrode of above-mentioned switching tube is connected with the former limit of transformer winding, and source electrode is connected with the negative input end of input voltage, and base stage is connected with the switching tube drive circuit.
Preferably, above-mentioned switching tube drive circuit is a pwm control circuit.
Preferably, above-mentioned rectification unit is a kind of in half-wave rectifying circuit, full-wave rectifying circuit, the full bridge rectifier.
Forward converter of the present invention makes the duty ratio of this forward converter reach as high as 63%, and adopts simple circuit to realize the low-power consumption of forward converter, high reliability by the design of a RCD circuit and the 2nd RCD circuit.
Description of drawings
Fig. 1 is the electrical block diagram of forward converter in an embodiment of the invention;
Fig. 2 to Fig. 6 is the mode of operation schematic diagram of forward converter among the embodiment of above-mentioned execution mode;
Fig. 7 is the working waveform figure of first electric capacity in the start surge process of forward converter among the embodiment of above-mentioned execution mode, second electric capacity;
Fig. 8 is the working waveform figure of first electric capacity behind the start surge of forward converter among the embodiment of above-mentioned execution mode, second electric capacity;
Fig. 9 is switching tube, first resistance of forward converter among the embodiment of above-mentioned execution mode, the power consumption diagram of second resistance;
Main electric parameters oscillogram when Figure 10 is a forward converter circuit working shown in Figure 1;
Figure 11 is the electrical block diagram of RCD forward converter in the prior art;
Figure 12 is the power consumption diagram of forward converter circuit shown in Figure 11.
The realization of the object of the invention, functional characteristics and advantage will be in conjunction with the embodiments, are described further with reference to accompanying drawing.
Embodiment
Should be appreciated that specific embodiment described herein only in order to explanation the present invention, and be not used in qualification the present invention.
With reference to Fig. 1, the circuit structure of the forward converter of the utility model first embodiment has been proposed.This forward converter comprises transformer TX1, switching tube Q1, a RCD circuit 10, the 2nd RCD circuit 20 and rectification unit 30.Wherein, after switching tube Q1 and the former limit of the transformer TX1 windings in series, be connected with the input voltage vin two ends again.Rectification unit 30 is connected with transformer TX1 secondary winding.The one RCD circuit 10 is in parallel with the former limit of transformer TX1 winding, and the energy that produces when absorbing switching surge or input voltage mutation constitutes the metastable constant pressure source of voltage; The 2nd RCD circuit 20 is in parallel with a transformer TX1 former limit winding and a RCD circuit 10 respectively, realizes the magnetic reset of transformer TX1 in each work period.
An above-mentioned RCD circuit 10 comprises first resistance R 1, first capacitor C 1 and the first diode D1.Wherein, first resistance R 1 is connected with the first diode D1 with after first capacitor C 1 is in parallel again.The positive pole of the first diode D1 is connected with an end of the former limit of transformer winding and the drain electrode of switching tube Q1 respectively.The other end of the former limit of transformer TX1 winding is connected with first resistance R 1 and first capacitor C 1 respectively.The source electrode of switching tube Q1 is connected with the negative input end of input voltage vin, and base stage is connected with the switching tube drive circuit.This switching tube drive circuit is preferably pwm control circuit, and switching tube Q1 can be in conducting or cut-off state according to the pwm control signal that pwm control circuit produces.
In the foregoing description, pwm control circuit can be the pwm control signal of the duty ratio that changes, and by the output voltage of sampling forward converter, and produces dynamic pwm control signal according to the output voltage of converter, to adjust the output of forward converter.
Above-mentioned the 2nd RCD circuit 20 comprises second resistance R 2, second capacitor C 2 and the second diode D2.Wherein, the second diode D2 connects with second capacitor C 2 with after second resistance R 2 is in parallel again.The positive pole of the second diode D2 is connected with an end of the former limit of transformer TX1 winding and the drain electrode of switching tube Q1 respectively.The other end of the former limit of transformer TX1 winding is connected with second capacitor C 2.
In the foregoing description, rectification unit 30 comprises the half-wave rectifying circuit that rectifying tube D3, continued flow tube D4, the 3rd capacitor C 3 and inductance L 2 are formed.This rectification unit 30 also can be full-wave rectifying circuit or full bridge rectifier.
Need to prove that the equivalent capacity Cr among Fig. 1 is that the Coss electric capacity of switching tube Q1, the rectifying tube D3 of transformer TX1 secondary reflex to the electric capacity on former limit and the summation of transformer TX1 parasitic capacitance.The resistance of first resistance R 1 is much larger than the resistance of second resistance R 2, and the appearance value of first capacitor C 1 is much larger than the appearance value of second capacitor C 2.
With regard to a switch periods, the operation principle of forward converter shown in Figure 1 is analyzed below, its work wave is with reference to Figure 10:
(1), the former limit of transformer TX1 is to secondary transmission of power (its equivalent circuit Fig. 2)
During the forward converter start, t
0Constantly, switching tube Q1 conducting.On the one hand, transformer TX1 bears input voltage vin in former limit, and the input current Iin on the former limit of transformer TX1 increases gradually, and this input current Iin is that transformer TX1 secondary winding current is converted the electric current I p on former limit and the exciting current Im sum that transformer TX1 iron core produces; On the other hand, input voltage vin make that the voltage of second capacitor C 2 is last negative just down, and the burning voltage at these second capacitor C, 2 two ends equals input voltage vin to 2 chargings of second capacitor C.Simultaneously, the rectifying tube D3 conducting of transformer TX1 secondary, continued flow tube D4 ends.The former limit of transformer TX1 produces output voltage V out to the secondary transmission of power.
As seen from Figure 7, before the switching tube Q1 conducting, the voltage V-C1 at first capacitor C, 1 two ends is stabilized on the clamp voltage 300V always.After the switching tube Q1 conducting, the voltage V-C2 at second capacitor C, 2 two ends rises gradually along with the voltage Vds at switching tube Q1 two ends and tends towards stability, and the magnitude of voltage at first capacitor C, 2 two ends is lower than the magnitude of voltage at switching tube Q1 two ends.
(2) transformer imput current Iin is equivalent capacity Cr charging (its equivalent circuit Fig. 3)
t
1Constantly, switching tube Q1 disconnects, and the input current Iin on the former limit of transformer TX1 is equivalent capacity Cr charging, and the voltage Vds at switching tube Q1 two ends sharply rises.At this moment, the electric current I p that transformer TX1 secondary winding current is converted former limit is constant, and exciting current Im continues to increase, and reduces gradually but increase speed.
(3) transformer secondary afterflow (its equivalent circuit Fig. 4)
t
1To t
2Constantly, equivalent capacity Cr, C1 and C2 charging tend towards stability, and promptly the voltage Vds at switching tube Q1 two ends reaches maximum, and the electric current I p that transformer TX1 secondary winding current is converted former limit also drops to zero gradually.Simultaneously, the rectifying tube D3 of transformer TX1 secondary ends, and continued flow tube D4 conducting is the afterflow of transformer TX1 secondary circuit.
The former limit of transformer TX1 exciting current Im is first capacitor C 1,2 chargings (its equivalent circuit Fig. 5) of second capacitor C
The voltage Vds at switching tube Q1 two ends has reached the conducting voltage of the first diode D1, the second diode D2, the first diode D1, the second diode D2 conducting, and then the exciting current Im on the former limit of transformer TX1 then is first capacitor C 1,2 chargings of second capacitor C.
The appearance value of first capacitor C 1 is much larger than the appearance value of first capacitor C 2, and the resistance of first resistance R 1 is much larger than the resistance of second resistance R 2.So in switching surge process or input voltage mutation process, the energy that a RCD circuit 10 absorbs is more than the energy that the 2nd RCD circuit 20 absorbs.
The exciting current Im that the former limit of transformer TX1 winding produces gives first capacitor C 1 charging through the first diode D1, the voltage at capacitor C 1 two ends of winning is tended towards stability gradually, and the voltage of the former limit of transformer TX1 this moment winding is clamped at the voltage V-C1 at first capacitor C, 1 two ends.By shown in Figure 8, the clamp voltage at these first capacitor C, 1 two ends is about 300V.
Simultaneously, former limit exciting current Im gives second capacitor C 2 chargings through the second diode D2, and after zero point reverse charging to resetting voltage.As shown in Figure 8, when the Q1 conducting, the voltage direction at these second capacitor C, 2 two ends is opposite with the voltage direction at first capacitor C, 1 two ends, and promptly voltage direction is last just bearing down, and the input voltage vin that equals to bear, and is about-420V.
(4) t
2To t
3Constantly, transformer magnetic reset (its equivalent circuit Fig. 6)
The discharging current of second capacitor C 2 oppositely through the former limit of transformer TX1 winding, makes this transformer TX1 can be operated in the 1-3 quadrant by second resistance R 2, and realizes the magnetic reset of transformer TX1.
(5) t
3To t
4Constantly, when the voltage Vds at second capacitor C 2 switching tube Q1 two ends after overdischarge equals Vin or during a little less than Vin, transformer TX1 finishes magnetic reset, switching tube Q1 conducting afterwards enters next switch periods.
By above-mentioned analysis, this transformer TX1 can be operated in the 1-3 quadrant, and the shutoff voltage of this switching tube Q1 is no-voltage, and turning-on voltage is an input voltage vin or a little less than Vin, thereby makes the voltage stress of switching tube Q1 be equal to or slightly lower than input voltage vin.When switching surge or overvoltage, a RCD circuit 10 can absorb lot of energy, avoids damaging to guarantee the electronic component in the circuit.20 in the 2nd RCD circuit has further been realized the magnetic reset of transformer by forward and reverse charge and discharge process of second capacitor C 2.And the 2nd RCD circuit can also dynamically be adjusted the clamp voltage of two RCD circuit according to the change of input voltage vin and duty ratio.
With reference to Fig. 9, second resistance R 2 is only lossy when switching tube Q1 opens as can be known, and average is 1.62W.First resistance R 1 is all lossy when switching tube Q1 turns on and off, and average is 3.2W.Loss when the loss when switching tube Q1 opens is turn-offed is big, and its loss average is 2.58W.Therefore, the gross power of the switching tube Q1 in the present embodiment, first resistance R 1 and second resistance R 2 is 7.4W.
With reference to Figure 11, Figure 12, under equal conditions, the total power consumption of forward converter shown in Figure 11 is 10.44W, manys 4.26W than the total power consumption of forward converter in the present embodiment.Wherein, the loss average of first resistance R 1 is 7.23W, and the loss the when loss when switching tube Q1 opens is turn-offed is little, and its loss average is 3.24W.
In sum, forward converter of the present invention has following advantage with respect to forward converter of the prior art:
1, can enlarge duty ratio: the duty ratio of the switching tube Q1 in this forward converter can increase, and can reach 63%;
2, prolong output holding time, reduced the voltage stress of switching tube Q1, prolonged the useful life of switching tube Q1;
3, efficient height, power consumption is little: the power consumption that the RCD of forward converter of the prior art and switching tube Q1 produce is higher by 57% than the power consumption of two RCD of forward converter of the present invention and switching tube Q1 generation;
4, circuit is simple, and is with low cost.
The above only is the preferred embodiments of the present invention; be not so limit claim of the present invention; every equivalent structure or equivalent flow process conversion that utilizes specification of the present invention and accompanying drawing content to be done; or directly or indirectly be used in other relevant technical fields, all in like manner be included in the scope of patent protection of the present invention.
Claims (6)
1. forward converter, it is characterized in that, comprise transformer, switching tube, rectification unit, a RCD circuit and the 2nd RCD circuit, wherein be connected with the input voltage two ends after switching tube and the former limit of the transformer windings in series, rectification unit is connected with transformer secondary winding, the one RCD circuit is in parallel with the former limit of transformer winding, the energy that produces when absorbing switching surge or input voltage mutation; The 2nd RCD circuit is in parallel with a transformer former limit winding and a RCD circuit respectively, realizes the magnetic reset of transformer in each work period.
2. forward converter as claimed in claim 1, it is characterized in that, described the 2nd RCD circuit comprises second resistance, second electric capacity and second diode, wherein second diode is with after second resistance is in parallel, again with second capacitances in series, the positive pole of described second diode is connected with an end of the former limit of transformer winding and the drain electrode of described switching tube respectively, the other end and second capacitances in series of the former limit of described transformer winding;
Switching tube is open-minded, and input voltage charges to second electric capacity; Switching tube disconnects, and the static exciter inductance charges to resetting voltage earlier to second electric capacity, discharges then, and through the former limit of transformer winding, transformer is finished magnetic reset to its discharging current by the second resistance reverse flow.
3. forward converter as claimed in claim 2, it is characterized in that, a described RCD circuit comprises first resistance, first electric capacity and first diode, wherein after first resistance and first capacitances in series, connect with first diode again, the positive pole of described first diode is connected with an end of the former limit of transformer winding and the drain electrode of described switching tube respectively, the other end of the former limit of described transformer winding respectively with first resistance and first capacitances in series.
4. as each described forward converter in the claim 1 to 3, it is characterized in that the drain electrode of described switching tube is connected with the former limit of transformer winding, source electrode is connected with the negative input end of input voltage, and base stage is connected with the switching tube drive circuit.
5. forward converter as claimed in claim 4 is characterized in that, described switching tube drive circuit is a pwm control circuit.
6. as each described forward converter in the claim 1 to 3, it is characterized in that described rectification unit is a kind of in half-wave rectifying circuit, full-wave rectifying circuit, the full bridge rectifier.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN 201010141775 CN102005931B (en) | 2010-04-08 | 2010-04-08 | Forward converter |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN 201010141775 CN102005931B (en) | 2010-04-08 | 2010-04-08 | Forward converter |
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| CN102005931A true CN102005931A (en) | 2011-04-06 |
| CN102005931B CN102005931B (en) | 2013-07-17 |
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| CN 201010141775 Active CN102005931B (en) | 2010-04-08 | 2010-04-08 | Forward converter |
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103117656A (en) * | 2013-02-23 | 2013-05-22 | 杭州乐图光电科技有限公司 | Voltage surge standing protection circuit and switching power supply with same |
| CN104009643A (en) * | 2014-05-06 | 2014-08-27 | 苏州汇川技术有限公司 | Flyback switching power supply of low voltage stress absorption circuit |
| CN104144300A (en) * | 2014-08-21 | 2014-11-12 | 青岛蓝图文化传播有限公司市南分公司 | Light compensating method for dual-mode mobile phone camera |
| CN104159045A (en) * | 2014-08-21 | 2014-11-19 | 青岛蓝图文化传播有限公司市南分公司 | Mobile phone camera with dual-mode light compensation |
| CN104242656A (en) * | 2013-06-17 | 2014-12-24 | Abb研究有限公司 | Adaptive rcd snubber and method for switching converter |
| CN104301589A (en) * | 2014-08-15 | 2015-01-21 | 青岛蓝图文化传播有限公司市南分公司 | Multi-camera mobile phone camera |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2004248479A (en) * | 2003-02-17 | 2004-09-02 | Toshiba Corp | Three-level converter |
| CN201656781U (en) * | 2010-04-08 | 2010-11-24 | 深圳市航嘉驰源电气股份有限公司 | Forward converter |
-
2010
- 2010-04-08 CN CN 201010141775 patent/CN102005931B/en active Active
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2004248479A (en) * | 2003-02-17 | 2004-09-02 | Toshiba Corp | Three-level converter |
| CN201656781U (en) * | 2010-04-08 | 2010-11-24 | 深圳市航嘉驰源电气股份有限公司 | Forward converter |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103117656A (en) * | 2013-02-23 | 2013-05-22 | 杭州乐图光电科技有限公司 | Voltage surge standing protection circuit and switching power supply with same |
| CN103117656B (en) * | 2013-02-23 | 2015-05-20 | 杭州乐图光电科技有限公司 | Voltage surge standing protection circuit and switching power supply with same |
| CN104242656A (en) * | 2013-06-17 | 2014-12-24 | Abb研究有限公司 | Adaptive rcd snubber and method for switching converter |
| CN104009643A (en) * | 2014-05-06 | 2014-08-27 | 苏州汇川技术有限公司 | Flyback switching power supply of low voltage stress absorption circuit |
| CN104301589A (en) * | 2014-08-15 | 2015-01-21 | 青岛蓝图文化传播有限公司市南分公司 | Multi-camera mobile phone camera |
| CN104144300A (en) * | 2014-08-21 | 2014-11-12 | 青岛蓝图文化传播有限公司市南分公司 | Light compensating method for dual-mode mobile phone camera |
| CN104159045A (en) * | 2014-08-21 | 2014-11-19 | 青岛蓝图文化传播有限公司市南分公司 | Mobile phone camera with dual-mode light compensation |
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| CN102005931B (en) | 2013-07-17 |
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