CN219812075U - Circuit structure capable of improving PWM pulse width - Google Patents
Circuit structure capable of improving PWM pulse width Download PDFInfo
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- CN219812075U CN219812075U CN202320834048.7U CN202320834048U CN219812075U CN 219812075 U CN219812075 U CN 219812075U CN 202320834048 U CN202320834048 U CN 202320834048U CN 219812075 U CN219812075 U CN 219812075U
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- 239000003990 capacitor Substances 0.000 claims abstract description 88
- 238000001514 detection method Methods 0.000 description 7
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 2
- 229910052732 germanium Inorganic materials 0.000 description 2
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 description 2
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Abstract
The utility model relates to a circuit structure capable of improving PWM pulse width, which comprises a fixed frequency driving chip, a first switching tube, a flyback power supply transformer, a charging resistor unit, a charging capacitor unit, a first resistor, a first capacitor and a fifth resistor, wherein the fixed frequency driving chip is connected with the first switching tube; the OUT pin of the fixed frequency driving chip is connected with the third end of the first switching tube, a charging resistor unit is connected between the Vref pin and the RT/CT pin of the fixed frequency driving chip, and a charging capacitor unit is connected between the RT/CT pin and the GND pin of the fixed frequency driving chip; one end of the first resistor is grounded, the other end of the first resistor is connected with the second end of the first switch tube and the first end of the fifth resistor respectively, and one end of the first capacitor is grounded, and the other end of the first capacitor is connected with the second end of the fifth resistor; the second end of the fifth resistor is connected with the charging capacitor unit or the charging resistor unit; the utility model solves the problem of insufficient driving voltage caused by too narrow pulse width of the PWM IC under the high-voltage light load of the flyback power supply.
Description
Technical Field
The utility model relates to the technical field of power conversion, in particular to a circuit structure capable of improving PWM pulse width.
Background
The high-voltage light load of the constant-frequency PWM IC type flyback auxiliary power supply can meet the following problems:
the pulse width Ton output by the PWM IC is too narrow, and the amplitude of the driving voltage waveform obtained by the MOS gate cannot reach the designed voltage value; and when the control loop is overlapped, MOS driving waveforms are lost, so that output voltage fluctuation is larger.
The duty of the flyback SPS is determined at a certain input voltage and output power, and in this case, if the on-time of the MOS is increased, the problem that the amplitude of the gate driving voltage is not high under light load is solved, and only the only way is to reduce the switching frequency at present. For some PWM ICs with a settable switching frequency, the PWM frequency is usually determined by the charging time of the CT capacitor, and the CT discharge is fast as a result of the transistor being turned on in a controlled saturation.
Therefore, how to actively reduce the switching frequency of the flyback auxiliary power supply of the constant-frequency PWM IC and solve the problem of insufficient driving voltage caused by the too narrow pulse width of the PWM IC under the high-voltage light load of the flyback power supply is needed to be solved.
Disclosure of Invention
The utility model aims to provide a circuit structure capable of improving PWM pulse width so as to actively reduce the switching frequency of a flyback auxiliary power supply of a constant-frequency PWM IC and solve the problem of insufficient driving voltage caused by the too narrow pulse width of the PWM IC under the high-voltage light load of the flyback power supply.
The aim of the utility model can be achieved by the following technical scheme:
a circuit structure capable of improving PWM pulse width comprises a constant frequency driving chip, a first switching tube, a flyback power transformer, a charging resistor unit, a charging capacitor unit, a first resistor, a first capacitor and a fifth resistor;
the OUT pin of the fixed frequency driving chip is connected with the third end of the first switching tube, a charging resistor unit is connected between the Vref pin and the RT/CT pin of the fixed frequency driving chip, and a charging capacitor unit is connected between the RT/CT pin and the GND pin of the fixed frequency driving chip;
the first end of the first switch tube is connected with one end of a primary side of the flyback power transformer, one end of the first resistor is grounded, the other end of the first resistor is respectively connected with the second end of the first switch tube and the first end of the fifth resistor, and one end of the first capacitor is grounded, and the other end of the first capacitor is connected with the second end of the fifth resistor; the second end of the fifth resistor is connected with the charging capacitor unit or the charging resistor unit;
the first switching tube is a MOS tube, the first end of the first switching tube is a drain electrode, the second end of the first switching tube is a source electrode, and the third end of the first switching tube is a grid electrode.
Optionally, the charging resistor unit includes a resistor RT, and the charging capacitor unit includes a capacitor CT and a second capacitor;
two ends of the resistor RT are respectively connected with an RT/CT pin and a Vref pin of the constant frequency driving chip;
and two ends of the capacitor CT are respectively connected with the RT/CT pin and the GND pin of the constant frequency driving chip, and two ends of the second capacitor are respectively connected with the RT/CT pin of the constant frequency driving chip and the second end of the fifth resistor.
Optionally, the charging resistor unit includes a resistor RT, a sixth resistor and a second switching tube, and the charging capacitor unit includes a capacitor CT;
the two ends of the resistor RT are respectively connected with an RT/CT pin and a Vref pin of the constant frequency driving chip, the first end of the second switching tube is connected to the RT/CT pin, the second end of the second switching tube is grounded, one end of the sixth resistor is connected with the third end of the second switching tube, and the other end of the sixth resistor is connected with the second end of the fifth resistor;
two ends of the capacitor CT are respectively connected with an RT/CT pin and a GND pin of the constant frequency driving chip;
the second switching tube is a triode, the first end of the second switching tube is an emitter, the second end of the second switching tube is a collector, and the third end of the second switching tube is a base.
Optionally, the charging resistance unit includes a resistor RT and a seventh resistor, and the charging capacitance unit includes a capacitor CT;
two ends of the resistor RT are respectively connected with an RT/CT pin and a Vref pin of the constant frequency driving chip, one end of the seventh resistor is connected with the RT/CT pin of the constant frequency driving chip, and the other end of the seventh resistor is connected with the second end of the fifth resistor;
and two ends of the capacitor CT are respectively connected with an RT/CT pin and a GND pin of the constant frequency driving chip.
Optionally, the charging resistor unit includes a resistor RT, a second resistor, a third resistor, a fourth resistor and a third switching tube, and the charging capacitor unit includes a capacitor CT;
the two ends of the resistor RT are respectively connected with the Vref pin of the fixed frequency driving chip and the second end of the third switching tube, the first end of the third switching tube is connected with the RT/CT pin of the fixed frequency driving chip, the third end of the third switching tube is connected with the first end of the second resistor, the second end of the second resistor is respectively connected with the first end of the third resistor and the first end of the fourth resistor, the second end of the third resistor is connected with the Vref pin of the fixed frequency driving chip, and the second end of the fourth resistor is connected with the second end of the fifth resistor;
two ends of the capacitor CT are respectively connected with an RT/CT pin and a GND pin of the constant frequency driving chip;
the third switching tube Q3 is a triode, the first end of the third switching tube is an emitter, the second end of the third switching tube is a collector, and the third end of the third switching tube is a base.
Optionally, the constant frequency driving chip is a UCC28C44 chip.
The utility model has the beneficial effects that:
the utility model discloses a circuit structure capable of improving PWM pulse width, which comprises a fixed frequency driving chip, a first switching tube Q1, a flyback power supply transformer T10, a charging resistor unit, a charging capacitor unit, a first resistor R1, a first capacitor C1 and a fifth resistor R5. The OUT pin of the fixed frequency driving chip is connected with the third end of the first switching tube Q1, a charging resistor unit is connected between the Vref pin and the RT/CT pin of the fixed frequency driving chip, and a charging capacitor unit is connected between the RT/CT pin and the GND pin of the fixed frequency driving chip. The first end of the first switch tube Q1 is connected with one end of a primary side of the flyback power transformer T10, one end of the first resistor R1 is grounded, the other end of the first resistor R1 is respectively connected with the second end of the first switch tube Q1 and the first end of the fifth resistor R5, one end of the first capacitor C1 is grounded, and the other end of the first capacitor C1 is connected with the second end of the fifth resistor R5; the second end of the fifth resistor R5 is connected with the charging capacitor unit or the charging resistor unit. The first resistor R1 forms an overcurrent detection resistor, and the utility model provides a specific circuit structure of the charging resistor unit and the charging capacitor unit. The circuit can control and change the charging resistance unit and the charging capacitance unit through the output voltage of the overcurrent detection resistor (the first resistor), and can also independently control and change the charging resistance unit or the charging capacitance unit, so that the switching frequency can be reduced, the driving on time can be increased, namely the switching frequency of the constant-frequency PWM IC flyback auxiliary power supply can be actively reduced, the problem that the driving voltage is insufficient due to the fact that the pulse width of the PWM IC is too narrow under the high-voltage light load of the flyback power supply is solved, and the circuit is low in structural cost, simple in structure and easy to realize.
Drawings
The utility model is described in further detail below with reference to the drawings and the specific embodiments.
FIG. 1 is a general schematic diagram of the topology of the present utility model;
FIG. 2 is a schematic diagram of a topology according to an embodiment of the present utility model;
FIG. 3 is a schematic diagram of a second topology of an embodiment of the present utility model;
FIG. 4 is a three topology schematic of an embodiment of the present utility model;
fig. 5 is a schematic diagram of a fourth topology of an embodiment of the present utility model.
Detailed Description
The following description of the embodiments of the present utility model will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present utility model, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the utility model without making any inventive effort, are intended to be within the scope of the utility model.
Referring to fig. 1-5, the present utility model provides a technical solution:
fig. 1 is a general schematic diagram of a circuit structure capable of increasing PWM pulse width according to the present utility model. As shown in fig. 1, the circuit structure for increasing the PWM pulse width includes a constant frequency driving chip, a first switching tube Q1, a flyback power transformer T10, a charging resistor unit, a charging capacitor unit, a first resistor R1, a first capacitor C1, and a fifth resistor R5.
The OUT pin of the fixed frequency driving chip is connected with the third end of the first switching tube Q1, a charging resistor unit is connected between the Vref pin and the RT/CT pin of the fixed frequency driving chip, and a charging capacitor unit is connected between the RT/CT pin and the GND pin of the fixed frequency driving chip. The first end of the first switch tube Q1 is connected with one end of a primary side of the flyback power transformer T10, one end of the first resistor R1 is grounded, the other end of the first resistor R1 is respectively connected with the second end of the first switch tube Q1 and the first end of the fifth resistor R5, one end of the first capacitor C1 is grounded, and the other end of the first capacitor C1 is connected with the second end of the fifth resistor R5; the second end of the fifth resistor R5 is connected with the charging capacitor unit or the charging resistor unit. The first switching tube Q1 may be a MOS tube, a first end of the first switching tube Q1 is a drain, a second end of the first switching tube Q1 is a source, and a third end of the first switching tube Q1 is a gate.
As an alternative embodiment, as shown in fig. 2, the charging resistor unit includes a resistor RT, and the charging capacitor unit includes a capacitor CT and a second capacitor C2. And two ends of the resistor RT are respectively connected with an RT/CT pin and a Vref pin of the constant frequency driving chip. Two ends of the capacitor CT are respectively connected with the RT/CT pin and the GND pin of the constant frequency driving chip, and two ends of the second capacitor C2 are respectively connected with the RT/CT pin of the constant frequency driving chip and the second end of the fifth resistor R5.
In this embodiment, the constant frequency driving chip may be a UCC28C44 or other chips with similar functions, the first resistor R1 forms an overcurrent detecting resistor, and D10 is a flyback power supply secondary diode. When the flyback power transformer T10 is connected to the flyback power transformer, the current ids flowing through the current detection resistor R1 becomes small, the output voltage vo=ids of the filter of the fifth resistor R5 and the first capacitor C1 is lower, the current ic=c2×d (Vct-Vo)/dt flowing through the second capacitor C2 becomes large, the current ict =ct×dcvt/dt flowing through the capacitor CT becomes small, the charging resistor RT is unchanged, the charging current irt = (Vref-Vct)/RT is unchanged, the charging time of CT becomes long, the switching frequency is reduced, and the pulse width is increased.
As an alternative embodiment, as shown in fig. 3, the charging resistor unit includes a resistor RT, a sixth resistor R6, and a second switching tube Q2, and the charging capacitor unit includes a capacitor CT. The two ends of the resistor RT are respectively connected with an RT/CT pin and a Vref pin of the constant frequency driving chip, a first end of the second switching tube Q2 is connected to the RT/CT pin, a second end of the second switching tube Q2 is grounded, one end of the sixth resistor R6 is connected with a third end of the second switching tube Q2, and the other end of the sixth resistor R6 is connected with a second end of the fifth resistor R5. And two ends of the capacitor CT are respectively connected with an RT/CT pin and a GND pin of the constant frequency driving chip. The second switching tube Q2 may be a triode, the first end of the second switching tube Q2 is an emitter, the second end of the second switching tube is a collector, and the third end of the second switching tube is a base.
In this embodiment, the constant frequency driving chip may be UCC28C44, or may be a chip with other similar functions, so that the second switching tube Q2 works in an amplified state, the first resistor R1 forms an overcurrent detecting resistor, and D10 is a flyback power supply secondary diode. When the flyback power supply connected with the flyback power supply transformer T10 is in high-voltage light-load operation, the current ids flowing through the current detection resistor R1 becomes small, the output voltage vo=ids filtered by the fifth resistor R5 and the first capacitor C1 is lower, the current iq= (1+β) (Vct-0.3-Vo)/R6 flowing through the second switching tube Q2 is larger (0.3 is a germanium tube voltage drop, if the flyback power supply is a silicon tube, 0.3 is changed into 0.7), the charging resistor RT is unchanged, the charging current irt = (Vref-Vct)/RT is unchanged, the time for charging CT to 3.34V becomes long, the switching frequency is reduced, and the pulse width is increased.
As an alternative embodiment, as shown in fig. 4, the charging resistor unit includes a resistor RT and a seventh resistor R7, and the charging capacitor unit includes a capacitor CT. Two ends of the resistor RT are respectively connected with an RT/CT pin and a Vref pin of the constant frequency driving chip, one end of the seventh resistor R7 is connected with the RT/CT pin of the constant frequency driving chip, and the other end of the seventh resistor R7 is connected with the second end of the fifth resistor R5. And two ends of the capacitor CT are respectively connected with an RT/CT pin and a GND pin of the constant frequency driving chip.
In this embodiment, the constant frequency driving chip may be UCC28C44, or may be another chip with similar functions, where the first resistor R1 forms an overcurrent detecting resistor, and D10 is a flyback power supply secondary diode. When the flyback power transformer T10 is connected to the flyback power transformer, the current ids flowing through the current detection resistor R1 becomes small, the output voltage vo=ids R1 filtered by the fifth resistor R5 and the first capacitor C1 is lower, the current ir= (Vct-Vo)/R7 flowing through the seventh resistor R7 is larger, the current ict =ct=dcvt/dt flowing through the capacitor CT is smaller, the charging resistor RT is unchanged, the charging current irt = (Vref-Vct)/RT is unchanged, the charging time of the capacitor CT is prolonged, the switching frequency is reduced, and the pulse width is increased.
As an alternative embodiment, as shown in fig. 5, the charging resistor unit includes a resistor RT, a second resistor R2, a third resistor R3, a fourth resistor R4, and a third switching tube Q3, and the charging capacitor unit includes a capacitor CT. The two ends of the resistor RT are respectively connected with the Vref pin of the fixed frequency driving chip and the second end of the third switching tube Q3, the first end of the third switching tube Q3 is connected with the RT/CT pin of the fixed frequency driving chip, and the third end of the third switching tube Q3 is connected with the first end of the second resistor R2. The second end of the second resistor R2 is respectively connected with the first end of the third resistor R3 and the first end of the fourth resistor R4, the second end of the third resistor R4 is connected with the Vref pin of the constant frequency driving chip, and the second end of the fourth resistor R4 is connected with the second end of the fifth resistor R5. And two ends of the capacitor CT are respectively connected with an RT/CT pin and a GND pin of the constant frequency driving chip. The third switching tube Q3 may be a triode, a first end of the third switching tube Q3 is an emitter, a second end of the third switching tube Q3 is a collector, and a third end of the third switching tube Q3 is a base.
In this embodiment, the constant frequency driving chip may be UCC28C44, or may be another chip with similar functions, where the first resistor R1 forms an overcurrent detecting resistor, and D10 is a flyback power supply secondary diode. When the flyback power transformer T10 is connected to the flyback power transformer, the current ids flowing through the current detecting resistor R1 becomes small, the output voltage vo=ids×r1 is filtered by the fifth resistor R5 and the first capacitor C1 to be lower, the voltage Vr 2= (Vref-Vo) ×r4/(r3+r4) of the second resistor R2, the third resistor R3 and the fourth resistor R4 connected to the potential Vr 2= (Vref-Vo) is reduced, the charging current iq=0.5×1+β (Vr 2-0.3-Vct)// R2 (0.3 is a germanium tube voltage drop, if the voltage is a silicon tube, 0.3 is changed to 0.7), and the charging time of CT is prolonged, the switching frequency is reduced, and the pulse width is increased.
In summary, the circuit structure capable of increasing PWM pulse width provided by the present utility model includes a constant frequency driving chip, a first switching tube Q1, a flyback power transformer T10, a charging resistor unit, a charging capacitor unit, a first resistor R1, a first capacitor C1, and a fifth resistor R5. The OUT pin of the fixed frequency driving chip is connected with the third end of the first switching tube Q1, a charging resistor unit is connected between the Vref pin and the RT/CT pin of the fixed frequency driving chip, and a charging capacitor unit is connected between the RT/CT pin and the GND pin of the fixed frequency driving chip. The first end of the first switch tube Q1 is connected with one end of a primary side of the flyback power transformer T10, one end of the first resistor R1 is grounded, the other end of the first resistor R1 is respectively connected with the second end of the first switch tube Q1 and the first end of the fifth resistor R5, one end of the first capacitor C1 is grounded, and the other end of the first capacitor C1 is connected with the second end of the fifth resistor R5; the second end of the fifth resistor R5 is connected with the charging capacitor unit or the charging resistor unit. The first resistor R1 forms an overcurrent detection resistor, and the utility model provides a specific circuit structure of the charging resistor unit and the charging capacitor unit. The circuit can control and change the charging resistance unit and the charging capacitance unit through the output voltage of the overcurrent detection resistor (the first resistor), and can also independently control and change the charging resistance unit or the charging capacitance unit, thereby realizing the reduction of the switching frequency and the increase of the driving conduction time, namely actively reducing the switching frequency of the fixed-frequency PWM IC flyback auxiliary power supply, solving the problem of insufficient driving voltage caused by the too narrow pulse width of the PWM IC under the high-voltage light load of the flyback power supply.
The foregoing describes one embodiment of the present utility model in detail, but the description is only a preferred embodiment of the present utility model and should not be construed as limiting the scope of the utility model. All equivalent changes and modifications within the scope of the present utility model are intended to be covered by the present utility model.
Claims (9)
1. The circuit structure capable of improving PWM pulse width is characterized by comprising a fixed frequency driving chip, a first switching tube, a flyback power supply transformer, a charging resistor unit, a charging capacitor unit, a first resistor, a first capacitor and a fifth resistor;
the OUT pin of the fixed frequency driving chip is connected with the third end of the first switching tube, a charging resistor unit is connected between the Vref pin and the RT/CT pin of the fixed frequency driving chip, and a charging capacitor unit is connected between the RT/CT pin and the GND pin of the fixed frequency driving chip;
the first end of the first switch tube is connected with one end of a primary side of the flyback power transformer, one end of the first resistor is grounded, the other end of the first resistor is respectively connected with the second end of the first switch tube and the first end of the fifth resistor, and one end of the first capacitor is grounded, and the other end of the first capacitor is connected with the second end of the fifth resistor; and the second end of the fifth resistor is connected with the charging capacitor unit or the charging resistor unit.
2. The circuit structure of claim 1, wherein the first switching tube is a MOS tube, a first end of the first switching tube is a drain, a second end of the first switching tube is a source, and a third end of the first switching tube is a gate.
3. The circuit structure for improving PWM pulse width according to claim 1, wherein said charging resistor unit comprises a resistor RT, and said charging capacitor unit comprises a capacitor CT and a second capacitor;
two ends of the resistor RT are respectively connected with an RT/CT pin and a Vref pin of the constant frequency driving chip;
and two ends of the capacitor CT are respectively connected with the RT/CT pin and the GND pin of the constant frequency driving chip, and two ends of the second capacitor are respectively connected with the RT/CT pin of the constant frequency driving chip and the second end of the fifth resistor.
4. The circuit structure capable of improving pulse width of PWM according to claim 1, wherein the charging resistor unit comprises a resistor RT, a sixth resistor and a second switch tube, and the charging capacitor unit comprises a capacitor CT;
the two ends of the resistor RT are respectively connected with an RT/CT pin and a Vref pin of the constant frequency driving chip, the first end of the second switching tube is connected to the RT/CT pin, the second end of the second switching tube is grounded, one end of the sixth resistor is connected with the third end of the second switching tube, and the other end of the sixth resistor is connected with the second end of the fifth resistor;
and two ends of the capacitor CT are respectively connected with an RT/CT pin and a GND pin of the constant frequency driving chip.
5. The circuit structure of claim 4, wherein the second switching tube is a triode, the first end of the second switching tube is an emitter, the second end of the second switching tube is a collector, and the third end of the second switching tube is a base.
6. The circuit structure for improving PWM pulse width according to claim 1, wherein the charging resistor unit comprises a resistor RT and a seventh resistor, and the charging capacitor unit comprises a capacitor CT;
two ends of the resistor RT are respectively connected with an RT/CT pin and a Vref pin of the constant frequency driving chip, one end of the seventh resistor is connected with the RT/CT pin of the constant frequency driving chip, and the other end of the seventh resistor is connected with the second end of the fifth resistor;
and two ends of the capacitor CT are respectively connected with an RT/CT pin and a GND pin of the constant frequency driving chip.
7. The circuit structure capable of improving pulse width of PWM according to claim 1, wherein the charging resistor unit comprises a resistor RT, a second resistor, a third resistor, a fourth resistor and a third switching tube, and the charging capacitor unit comprises a capacitor CT;
the two ends of the resistor RT are respectively connected with the Vref pin of the fixed frequency driving chip and the second end of the third switching tube, the first end of the third switching tube is connected with the RT/CT pin of the fixed frequency driving chip, the third end of the third switching tube is connected with the first end of the second resistor, the second end of the second resistor is respectively connected with the first end of the third resistor and the first end of the fourth resistor, the second end of the third resistor is connected with the Vref pin of the fixed frequency driving chip, and the second end of the fourth resistor is connected with the second end of the fifth resistor;
and two ends of the capacitor CT are respectively connected with an RT/CT pin and a GND pin of the constant frequency driving chip.
8. The circuit structure of claim 7, wherein the third switching tube is a triode, the first end of the third switching tube is an emitter, the second end of the third switching tube is a collector, and the third end of the third switching tube is a base.
9. The circuit structure of claim 1, wherein the constant frequency driving chip is a UCC28C44 chip.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202320834048.7U CN219812075U (en) | 2023-04-14 | 2023-04-14 | Circuit structure capable of improving PWM pulse width |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202320834048.7U CN219812075U (en) | 2023-04-14 | 2023-04-14 | Circuit structure capable of improving PWM pulse width |
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| Publication Number | Publication Date |
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| CN219812075U true CN219812075U (en) | 2023-10-10 |
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| CN202320834048.7U Active CN219812075U (en) | 2023-04-14 | 2023-04-14 | Circuit structure capable of improving PWM pulse width |
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