Switching conversion circuit
By simplifying the control method of the flyback switching circuit, using a sampling circuit, a comparison circuit, and a trigger circuit, and retaining only one loop, the system loop speed and dynamic response are improved. This solves the problems of complex control and poor dynamic response in the existing technology, and achieves a more stable output.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- SHENZHEN KIWI MICROELECTRONICS CO LTD
- Filing Date
- 2025-05-28
- Publication Date
- 2026-05-12
AI Technical Summary
Existing flyback switching circuits have slow system loop speeds, poor dynamic response, complex control, and the risk of unstable operation.
A switching conversion circuit is adopted, which simplifies the control loop by introducing sampling circuit, comparison circuit and trigger circuit in the primary circuit and secondary circuit, retaining only one loop to improve the system loop speed, and stabilizes the output through ramp signal generation circuit.
This achieves faster system loop speed, better dynamic response, simpler control circuit, improved output stability, and avoids unstable operation.
Smart Images
Figure CN224233561U_ABST
Abstract
Description
Technical Field
[0001] This utility model belongs to the field of power electronics, relates to switching technology, and particularly relates to a switching circuit. Background Technology
[0002] Switching power supplies are widely used due to their advantages such as high efficiency and energy saving, small size and light weight, stable output, multiple protection functions, and wide input voltage range. These advantages enable switching power supplies to perform well in various application scenarios and meet the power requirements of modern electronic devices.
[0003] In single-stage architecture constant voltage and constant current LED backlight applications, the flyback topology is a relatively common application topology. The secondary side of the flyback switching circuit can be designed with two windings, one winding for constant voltage output and the other winding for constant current output.
[0004] One existing implementation method is as follows Figure 1 As shown, the flyback switching circuit includes a primary-side circuit a and a secondary-side circuit. The secondary-side circuit includes a constant-current output circuit b and a constant-voltage output circuit c. Both the constant-current output circuit b and the constant-voltage output circuit c employ COMP compensation loop control. Specifically, the constant-voltage output circuit c uses CV constant-voltage loop control, sampling the output voltage of the constant-voltage output circuit c or a voltage divider thereof as feedback to control the magnitude of the primary-side output energy, thereby achieving a constant output voltage. The constant-current output circuit b uses CC constant-current loop control, sampling the output current IFB as feedback and comparing it with the internal constant-current reference signal VREF_CC to generate a secondary-side compensation signal COMP_CC to control the on-time of the secondary-side switch Q1, thereby maintaining a constant output current. The specific control logic can be further described in conjunction with... Figure 2 Within a single primary-side switching cycle, when the primary-side MOSFET is turned on, the secondary-side MOSFET Q1 is also turned on, and the RAMP ramp voltage gradually rises. When the primary-side MOSFET is turned off, the secondary circuit first freewheels through the transformer S1 winding, transferring energy to the constant current output circuit b. When the RAMP ramp voltage is higher than the secondary-side compensation signal COMP_CC, the secondary-side drive signal gate_cc goes low, and the secondary-side MOSFET Q1 is turned off. The secondary circuit then freewheels through the transformer S2 winding, transferring energy to the constant voltage output circuit c. The voltage feedback signal VFB, obtained by sampling the output voltage divider, is compared with the internal constant voltage reference signal VREF_CV to generate a compensation signal COMP, which is fed back to the primary-side circuit, thereby adjusting the energy output of the primary-side circuit. The existing control method suffers from a loop speed limitation due to the bandwidth difference between the outer and inner loops, resulting in poor dynamic response and complex control.
[0005] In view of this, a new structure is needed to solve at least some of the above problems. Utility Model Content
[0006] In view of one or more problems in the prior art, this utility model proposes a switching conversion circuit.
[0007] According to one aspect of this utility model, a switching circuit is disclosed, comprising a primary circuit and a secondary circuit. The primary circuit includes a primary winding, and the secondary circuit includes:
[0008] The first output circuit includes a secondary-side switching transistor, a first secondary-side winding coupled to the primary-side winding, a sampling circuit, a comparator circuit, and a trigger circuit. The sampling circuit is used to acquire a sampling signal characterizing the output voltage of the first output circuit. The first input terminal of the comparator circuit is coupled to the sampling circuit, the second input terminal of the comparator circuit is coupled to a constant voltage reference signal terminal, the trigger circuit is coupled to the comparator circuit, and the output terminal of the trigger circuit is coupled to the control terminal of the secondary-side switching transistor.
[0009] The second output circuit includes a second secondary winding coupled to the primary winding;
[0010] The primary circuit is coupled to the second output circuit to obtain a feedback signal characterizing the output current of the second output circuit.
[0011] In one embodiment, the first output circuit includes a constant voltage output circuit, which includes a secondary-side switching transistor; and the second output circuit includes a constant current output circuit.
[0012] In one embodiment, the sampling circuit includes a first sampling resistor and a second sampling resistor. The first end of the first sampling resistor is coupled to the first end of a first capacitor, the first end of the second sampling resistor is coupled to the second end of the first sampling resistor, and the second end of the second sampling resistor is coupled to the second end of the first capacitor. The first capacitor is the output capacitor of the first output circuit.
[0013] In one embodiment, the comparison circuit includes a first comparator, the non-inverting input of which is coupled to a first terminal of a second sampling resistor, and the inverting input of which is coupled to a constant voltage reference signal terminal to receive a constant voltage reference signal.
[0014] In one embodiment, the triggering circuit includes an RS flip-flop, the set terminal of which is coupled to the primary-side drive signal terminal to obtain the primary-side drive signal, the reset terminal of which is coupled to the output terminal of the comparator circuit, and the output terminal of which is coupled to the secondary-side switch.
[0015] In one embodiment, the second output circuit includes a transconductance amplifier circuit and a compensation capacitor. The first input terminal of the transconductance amplifier circuit is coupled to a constant current reference signal, the second input terminal of the transconductance amplifier circuit is used to couple to the load in the second output circuit, the output terminal of the transconductance amplifier circuit is coupled to the first terminal of the compensation capacitor, and the second terminal of the compensation capacitor is coupled to ground.
[0016] In one embodiment, the second output circuit further includes a third sampling resistor, the first end of which is used to couple to the load in the second output circuit, and the second end of which is coupled to ground.
[0017] In one embodiment, the primary-side circuit further includes a primary-side drive signal generation circuit, which generates a primary-side drive signal based on the compensation signal.
[0018] In one embodiment, the primary-side drive signal generation circuit includes a second comparator, a first input terminal of which is used to receive a primary-side current sampling signal, a second input terminal of which is used to receive a current reference signal, and an output terminal of which is used to couple to a primary-side switching transistor.
[0019] In one embodiment, the secondary circuit further includes a ramp signal generation circuit coupled to a comparator circuit, the ramp signal generation circuit being used to generate a constant voltage reference signal.
[0020] This invention proposes a switching converter circuit. The switching converter circuit includes a primary circuit and a secondary circuit. The primary circuit includes a primary winding, and the secondary circuit includes a first output circuit and a second output circuit. The first output circuit includes a secondary switching transistor, a first secondary winding coupled to the primary winding, a sampling circuit, a comparator circuit, and a trigger circuit. The sampling circuit is used to acquire a sampling signal characterizing the output voltage of the first output circuit. The first input terminal of the comparator circuit is coupled to the sampling circuit, and the second input terminal of the comparator circuit is coupled to a constant voltage reference signal terminal. The trigger circuit is coupled to the comparator circuit, and the output terminal of the trigger circuit is coupled to the control terminal of the secondary switching transistor. The second output circuit includes a second secondary winding coupled to the primary winding. The primary circuit is coupled to the second output circuit to acquire a feedback signal characterizing the output current of the second output circuit. The switching converter circuit proposed in this invention has a faster system loop speed, better dynamic response, and a simpler control circuit. Attached Figure Description
[0021] The accompanying drawings are provided to further illustrate the present invention and, together with the description, serve to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings:
[0022] Figure 1 A schematic diagram of the circuit structure of a prior art flyback switch circuit is shown.
[0023] Figure 2 This diagram illustrates the signal waveforms of relevant signals in a prior art flyback switching circuit.
[0024] Figure 3A schematic diagram of the circuit structure of a switching circuit according to an embodiment of the present invention is shown;
[0025] Figure 4 A schematic diagram of the signal waveforms of the switching circuit according to an embodiment of the present invention is shown.
[0026] Figure 5 A schematic diagram of the signal waveforms of the switching circuit according to another embodiment of the present invention is shown;
[0027] Figure 6 A schematic diagram of the signal waveforms of the switching circuit according to another embodiment of the present invention is shown. Detailed Implementation
[0028] To further understand this utility model, preferred embodiments of this utility model are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of this utility model, and not for limiting the scope of the claims of this utility model.
[0029] The description in this section pertains to only a few typical embodiments, and this utility model is not limited to the scope of the embodiments described. Combinations of different embodiments, substitution of some technical features in different embodiments, and substitution of the same or similar prior art with some technical features in the embodiments are also within the scope of the description and protection of this utility model.
[0030] The terms "coupled" or "connected" in this specification include both direct and indirect connections. An indirect connection is a connection made through an intermediate medium, such as a connection through an electrically conductive medium like a conductor, which may contain parasitic inductance or capacitance. It can also be a connection through intermediate circuits or components described in the embodiments of this specification. Indirect connections may also include connections through other active or passive devices that achieve the same or similar functions, such as connections through switches, signal amplification circuits, follower circuits, or other circuits or components. "Multiple" or "more" indicates two or more. Furthermore, in this invention, terms such as "first" and "second" are primarily used to distinguish one technical feature from another, and do not necessarily require or imply any actual relationship or order between these technical features.
[0031] One embodiment of this utility model discloses a switching circuit. For example... Figure 3As shown, the switching converter circuit includes a primary circuit 10 and a secondary circuit. The primary circuit 10 includes a primary control circuit and a primary winding. The primary control circuit controls the operating state of the primary switching transistor. The secondary circuit includes a first output circuit 20 and a second output circuit 30. The first output circuit includes a constant voltage output circuit, and the second output circuit includes a constant current output circuit. The first output circuit 20 includes a secondary switching transistor Q1, a first secondary winding, a sampling circuit, a comparator circuit, and a trigger circuit. The first secondary winding is coupled to the primary winding. The first terminal of the secondary switching transistor is coupled to the first secondary winding, the first terminal of the first capacitor C1 is coupled to the second terminal of the secondary switching transistor, and the second terminal of the first capacitor C1 is coupled to ground. The sampling circuit includes a first sampling resistor R1 and a second sampling resistor R2. The sampling circuit is used to obtain a sampling signal characterizing the output voltage of the first output circuit, and the sampling signal is proportional to the output voltage. The first terminal of the first sampling resistor R1 is coupled to the first terminal of the first capacitor C1, the first terminal of the second sampling resistor R2 is coupled to the second terminal of the first sampling resistor R1, and the second terminal of the second sampling resistor R2 is coupled to the second terminal of the first capacitor C1. The first capacitor C1 is the output capacitor of the first output circuit. In another embodiment, the sampling signal is positively correlated with the output voltage.
[0032] In one embodiment, the first input terminal of the comparator circuit is coupled to the sampling circuit, and the second input terminal of the comparator circuit is coupled to the constant voltage reference signal terminal. For example... Figure 3 In one embodiment shown, the comparison circuit includes a first comparator, the non-inverting input of which is coupled to the first terminal of the second sampling resistor R2, and the inverting input of which is coupled to the constant voltage reference signal terminal to receive the constant voltage reference signal VREF_CV.
[0033] In one embodiment, a trigger circuit is coupled to a comparator circuit, and the output of the trigger circuit is coupled to the control terminal of the secondary-side switch. The trigger circuit includes an RS flip-flop, the set terminal of which is coupled to the primary-side drive signal terminal to obtain the primary-side drive signal, the reset terminal of which is coupled to the output of a first comparator, and the output of which is coupled to the control terminal of the secondary-side switch. The output signal of the RS flip-flop can be used to control the switching state of the secondary-side switch.
[0034] In one embodiment, such as Figure 3 As shown, the second output circuit 30 includes a second secondary winding, a second diode D2, a second capacitor C2, and a third sampling resistor R3. The second secondary winding is coupled to the primary winding. The anode of the second diode D2 is coupled to the second secondary winding, the first terminal of the second capacitor C2 is coupled to the cathode of the second diode D2, and the second terminal of the second capacitor C2 is coupled to ground. The first terminal of the load in the second output circuit is coupled to the first terminal of the second capacitor C2, the first terminal of the third sampling resistor R3 is coupled to the second terminal of the load in the second output circuit, and the second terminal of the third sampling resistor R3 is coupled to ground.
[0035] In one embodiment, the primary-side circuit is coupled to a second output circuit via an optocoupler to obtain a feedback signal characterizing the output current of the second output circuit. The second output circuit includes a transconductance amplifier circuit and a compensation capacitor C3. The first input terminal of the transconductance amplifier circuit is coupled to a constant current reference signal VREF_CC, and the second input terminal is coupled to a load in the second output circuit. The output terminal of the transconductance amplifier circuit is coupled to a first terminal of the compensation capacitor, and the second terminal of the compensation capacitor is grounded. In another embodiment, the primary-side circuit further includes a primary-side drive signal generation circuit, which generates a primary-side drive signal based on the compensation signal. The primary-side drive signal generation circuit includes a second comparator. The first input terminal of the second comparator receives a primary-side current sampling signal, which can be a signal characterizing the current flowing through the primary-side switch. The second input terminal of the second comparator receives a current reference signal, which can be a signal converted from the secondary-side compensation signal fed back to the primary-side circuit via the optocoupler. The output terminal of the second comparator is coupled to the primary-side switch.
[0036] like Figure 3 As shown, the first output circuit includes a constant voltage output circuit, and the second output circuit includes a constant current output circuit. The constant current output circuit uses CC constant current loop control, and controls the output energy of the primary circuit by sampling the output current of the constant current output circuit as feedback, thereby achieving a constant output current. The constant voltage output circuit uses hysteresis control to control the turning on and off of the secondary switch Q1, thereby keeping the output voltage constant.
[0037] Combination Figure 4 It can be seen that during one switching cycle of the primary-side switch, when the primary-side switch MOSFET is turned on, the secondary-side drive signal gate_cv becomes the first level (e.g., high level), and the secondary-side switch Q1 is turned on. When the primary-side switch MOSFET is turned off, the secondary circuit first freewheels through the transformer S1 winding, and energy is transferred to the constant voltage output circuit, such as... Figure 3As shown, the CV voltage at the CV terminal gradually increases, and the sampling signal VFB, as a voltage divider of the CV voltage, also increases synchronously. When the sampling signal VFB is greater than the constant voltage reference signal VREF_CV, the secondary-side drive signal gate_cv changes to the second level (e.g., low level), the secondary-side switch Q1 is turned off, and the secondary-side circuit freewheels through the transformer S2 winding, transferring energy to the constant current output circuit. The sampling constant current output circuit feeds back the sampling current signal IFB, which is compared with the internal constant current reference signal VREF_CC to generate a compensation signal Vcomp, which is fed back to the primary-side circuit through an optocoupler, thereby adjusting the energy output of the primary-side circuit. In existing technologies, the overall system control is achieved through an inner current loop (the loop controlling the secondary-side switch Q1) and an outer current loop (the loop controlling the primary-side output energy). When the system has two control loops, the bandwidth of the two loops needs to have a certain difference to ensure system stability when designing the loop speed. This limits the design of the outer loop speed to be relatively slow, resulting in a slower overall system loop speed. The system's dynamic response depends on the system loop speed; the faster the speed, the better the dynamic response. Therefore, the dual-loop control method has a relatively poor dynamic response, and designing a stable dual-loop control is more complex. In contrast, this invention uses a trigger circuit to control the secondary-side switch Q1 and the constant current output loop. The system has only one loop, resulting in a very fast system loop speed, better dynamic response, and a simpler control circuit.
[0038] In another embodiment, the secondary-side circuit further includes a ramp signal generation circuit coupled to the comparator circuit, which is used to generate a constant voltage reference signal VREF_CV. Figure 6 As shown, when the primary-side drive signal changes to the second level (e.g., low level), the primary-side switch is off, and the primary-side current IL_p becomes zero. When the primary-side drive signal changes to the second level (e.g., low level), the constant voltage reference signal VREF_CV begins slope compensation, gradually decreasing until the current cycle's slope compensation ends when the primary-side drive signal changes to the first level (e.g., high level). When the constant voltage output circuit has a heavy load and the constant current output circuit has a light load, instability can easily occur. Therefore, adding a certain slope compensation to the constant voltage reference signal VREF_CV can solve the instability problem. Figure 5 This is an embodiment without a ramp signal generation circuit. Figure 6 This is an embodiment of a ramp signal generation circuit. (Comparison) Figure 5 and Figure 6It is known that in circuits without a ramp signal generation circuit, the turn-on period of the primary-side switching transistor varies, and there are even instances where it does not turn off during some switching cycles, resulting in large output voltage ripple and potentially causing instability in the outer loop. In circuits with a ramp signal generation circuit, the transistor switches once per switching cycle, ensuring loop stability. In a preferred embodiment, the descent rate of the ramp compensation is greater than the descent ramp rate of the sampled signal VFB.
[0039] Those skilled in the art should know that the logic controls such as "high level" and "low level", "set" and "reset", "AND gate" and "OR gate", "non-inverting input" and "inverting input" in the logic control involved in the specification or drawings can be interchanged or changed, and the same function or purpose as the above embodiment can be achieved by adjusting the subsequent logic control.
[0040] The description and application of this utility model herein are illustrative and not intended to limit the scope of the utility model to the above embodiments. The effects or advantages described in the specification may not be apparent in actual experimental examples due to uncertainties in specific conditions or parameters or other factors, and such descriptions are not intended to limit the scope of the utility model. Variations and modifications to the embodiments disclosed herein are possible, and various substitutions and equivalent components of the embodiments are well known to those skilled in the art. It should be clear to those skilled in the art that this utility model can be implemented in other forms, structures, arrangements, proportions, and with other components, materials, and parts without departing from the spirit or essential characteristics of the utility model. Other variations and modifications can be made to the embodiments disclosed herein without departing from the scope and spirit of the utility model.
Claims
1. A switching converter circuit, comprising a primary circuit and a secondary circuit, wherein the primary circuit includes a primary winding, characterized in that, The secondary circuit includes: The first output circuit includes a secondary-side switching transistor, a first secondary-side winding coupled to the primary-side winding, a sampling circuit, a comparator circuit, and a trigger circuit. The sampling circuit is used to acquire a sampling signal characterizing the output voltage of the first output circuit. The first input terminal of the comparator circuit is coupled to the sampling circuit, the second input terminal of the comparator circuit is coupled to a constant voltage reference signal terminal, the trigger circuit is coupled to the comparator circuit, and the output terminal of the trigger circuit is coupled to the control terminal of the secondary-side switching transistor. The second output circuit includes a second secondary winding coupled to the primary winding; The primary circuit is coupled to the second output circuit to obtain a feedback signal characterizing the output current of the second output circuit.
2. The switching circuit as described in claim 1, characterized in that, The first output circuit includes a constant voltage output circuit, which includes a secondary-side switching transistor; and the second output circuit includes a constant current output circuit.
3. The switching conversion circuit as described in claim 1, characterized in that, The sampling circuit includes a first sampling resistor and a second sampling resistor. The first end of the first sampling resistor is coupled to the first end of the first capacitor. The first end of the second sampling resistor is coupled to the second end of the first sampling resistor. The second end of the second sampling resistor is coupled to the second end of the first capacitor. The first capacitor is the output capacitor of the first output circuit.
4. The switching circuit as described in claim 3, characterized in that, The comparison circuit includes a first comparator, the non-inverting input of which is coupled to the first terminal of the second sampling resistor, and the inverting input of which is coupled to the constant voltage reference signal terminal to receive the constant voltage reference signal.
5. The switching conversion circuit as described in claim 1, characterized in that, The triggering circuit includes an RS flip-flop, the set terminal of which is coupled to the primary-side drive signal terminal to obtain the primary-side drive signal, the reset terminal of which is coupled to the output terminal of the comparator circuit, and the output terminal of which is coupled to the secondary-side switch.
6. The switching conversion circuit as described in claim 1, characterized in that, The second output circuit includes a transconductance amplifier circuit and a compensation capacitor. The first input terminal of the transconductance amplifier circuit is coupled to a constant current reference signal, the second input terminal of the transconductance amplifier circuit is used to couple to the load in the second output circuit, the output terminal of the transconductance amplifier circuit is coupled to the first terminal of the compensation capacitor, and the second terminal of the compensation capacitor is coupled to ground.
7. The switching circuit as described in claim 6, characterized in that, The second output circuit also includes a third sampling resistor. The first end of the third sampling resistor is used to couple to the load in the second output circuit, and the second end of the third sampling resistor is coupled to ground.
8. The switching circuit as described in claim 6, characterized in that, The primary-side circuit also includes a primary-side drive signal generation circuit, which is used to generate a primary-side drive signal based on the compensation signal.
9. The switching conversion circuit as described in claim 8, characterized in that, The primary-side drive signal generation circuit includes a second comparator. The first input terminal of the second comparator is used to receive the primary-side current sampling signal, the second input terminal of the second comparator is used to receive the current reference signal, and the output terminal of the second comparator is used to couple to the primary-side switching transistor.
10. The switching circuit as described in claim 1, characterized in that, The secondary circuit also includes a ramp signal generation circuit, which is coupled to a comparator circuit and is used to generate a constant voltage reference signal.