Multi-output flyback converter with low cross regulation rate

Abstract

The invention belongs to the technical field of switching power supplies, and provides a multi-output flyback converter with a low cross regulation rate, which comprises a primary side loop comprising a switching tube and a primary side winding of a transformer, and the switching tube is used for controlling the energy transfer of the transformer; the secondary loop comprises a main output loop, a first secondary output loop and a second secondary output loop, the main output loop comprises a secondary winding of the transformer, and the secondary winding of the first secondary output loop is led out from the secondary winding of the main output loop through a tap; a secondary winding of the second secondary output loop is connected with an inductor; two ends of the inductor are connected with an energy absorption loop in parallel; and the feedback control loop is used for acquiring the sampling voltage of the main output loop, comparing the sampling voltage with the reference voltage, and controlling the output voltage of multi-path output by controlling the duty ratio of a switching tube. According to the flyback converter, the low cross adjustment rate of multi-path output of the flyback converter is realized, and mutual interference among the multi-path output is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of switching power supplies, and in particular to a multi-channel output flyback converter with low cross-regulation rate. Background Art

[0002] With the rapid development of power electronics technology, power electronics are becoming increasingly complex and intelligent. Today, individual electronic devices often require coordinated power supply at multiple voltage levels, such as 3.3V, 5V, and 12V. This has led to an explosive growth in demand for multi-output power supplies. Among various power supply topologies, the flyback converter stands out for its simple circuit architecture and reliable input-output electrical isolation. Multi-output power supplies based on this topology have found widespread application in numerous fields, including consumer electronics and industrial control.

[0003] Ideally, for a multi-output flyback switching power supply, the auxiliary output voltage and the main output voltage satisfy the transformer turns ratio. This means that as long as the main output voltage remains stable, the auxiliary output voltage will also remain stable. However, in reality, the auxiliary output voltage varies with output load due to factors such as the leakage inductance between transformer windings, winding resistance, and current loop parasitics. Typically, the auxiliary output voltage increases when the main output is fully loaded and the auxiliary output is lightly loaded; conversely, the auxiliary output voltage decreases when the main output is lightly loaded and the auxiliary output is fully loaded.

[0004] Cross regulation is defined as the maximum voltage change ΔV of a certain output voltage due to changes in its own load or other output loads at a certain input voltage. n The corresponding rated voltage V n The formula is S=ΔV n / V n .

[0005] In theory, a flyback converter has no output filter inductor, only output capacitors, and is equivalent to a voltage source. As long as one output is stable, the rest of the multi-channel outputs can basically output stably according to the turns ratio. However, in practice, the stability of one output is very good, but when there are multiple outputs, the voltage of the branch without feedback will change dramatically with the load changes of other branches. When the switch is turned off, the energy distribution at the secondary output is regular and is distributed according to the size of the leakage inductance. For example, the output V1, the number of turns N1, the leakage inductance L s1 , if the output is V2, the leakage inductance L of turns N2 turns s2 satisfy: L s2 =(N2 / N1) 2 ·L s1 The current change rate of the two outputs is the same, and there is no cross-regulation problem. However, if the leakage inductance does not match, cross-regulation problems will occur. Summary of the Invention

[0006] In response to the defects in the prior art, the present invention provides a multi-output flyback converter with low cross-regulation rate to solve the problem that the voltage of the auxiliary output branch without feedback in the current multi-output flyback converter will change dramatically with the load change of other branches.

[0007] The present invention provides a multi-output flyback converter with low cross-regulation rate, comprising: A primary circuit includes a switch tube and a primary winding of a transformer, wherein the switch tube is used to control energy transfer of the transformer; A secondary circuit includes a main output circuit, a first secondary output circuit, and a second secondary output circuit. The main output circuit includes a secondary winding of a transformer, and the first secondary output circuit is led out from the secondary winding of the main output circuit via a tap. The second secondary output circuits are independently provided and also include another secondary winding of the transformer. The secondary winding of the second secondary output circuit is connected to an inductor, and an energy absorption circuit is connected in parallel at both ends of the inductor. A feedback control loop obtains the sampled voltage of the main output loop and compares it with a reference voltage, and controls the output voltage of the multiple outputs by controlling the duty cycle of the switching tube.

[0008] It can be seen from the above technical solution that the present invention provides a multi-output flyback converter with a low cross-regulation rate. First, the main output circuit is connected to the feedback control circuit to have a feedback regulation mechanism, and the output voltage is stable; secondly, the first auxiliary output circuit is led out from the secondary winding of the main output circuit through a tap, and the voltage is lower than the voltage of the main output circuit. Under the influence of the main output circuit, the output voltage of the first auxiliary output circuit is also relatively stable, and the cross-regulation rate is low; finally, by artificially increasing the leakage inductance in the second auxiliary output circuit to match the leakage inductance of the main output circuit, the cross-regulation rate is reduced, and an energy absorption circuit is connected in parallel at both ends of the inductor to absorb the energy of the artificially increased leakage inductance when the switch tube is turned on.

[0009] Optionally, the energy absorption circuit includes a first absorption resistor, an absorption capacitor, a first freewheeling diode and a second absorption resistor, the first absorption resistor, the absorption capacitor and the first freewheeling diode are sequentially connected in series and in parallel to the two ends of the leakage inductance, and the second absorption resistor is connected in parallel to the two ends of the first absorption resistor and the absorption capacitor; The cathode of the first freewheeling diode is connected to the absorption capacitor, and the anode of the first freewheeling diode is connected to the inductor.

[0010] Optionally, the primary circuit further includes an input capacitor and an RCD clamping circuit, wherein the input capacitor and the input voltage Vin are connected to both ends of the primary winding. The RCD clamping circuit primarily absorbs energy released by the transformer leakage inductance, thereby reducing the voltage spike of the switching tube and protecting the switching tube from high voltage damage.

[0011] Optionally, the RCD clamping circuit includes a protection resistor, a protection capacitor and a protection diode. The protection capacitor and the protection diode are connected in series and are connected to both ends of the primary winding, and the protection resistor is connected to both ends of the protection capacitor; the cathode of the protection diode is connected to the protection capacitor, and the anode of the protection diode is connected to the primary winding.

[0012] Optionally, the switch tube is a MOS tube. The gate of the switch tube is connected to the feedback control loop, the source of the switch tube is connected to the negative end of the input voltage Vin, and the drain of the switch tube is connected to the positive electrode of the protection diode.

[0013] Optionally, the main output circuit, the first secondary output circuit and the second secondary output circuit further include a second freewheeling diode, an output capacitor and a load resistor. The output capacitor and the load resistor are connected in parallel to both ends of the secondary winding, and the second freewheeling diode is connected between the output capacitor and the secondary winding; the positive electrode of the second freewheeling diode is connected to the secondary winding, and the negative electrode of the second freewheeling diode is connected to the output capacitor.

[0014] Optionally, the main output loop is further connected to a voltage-dividing sampling circuit, and the voltage-dividing sampling circuit includes a plurality of sampling resistors connected in series; the feedback control loop is connected to the sampling resistors.

[0015] By adopting the above technical solution, this application has the following beneficial effects: According to the present invention, firstly, the main output circuit is connected to the feedback control circuit to have a feedback regulation mechanism, and the output voltage is stable. Secondly, the first auxiliary output circuit is led out from the secondary winding of the main output circuit through a tap, and the voltage is lower than the voltage of the main output circuit. Under the influence of the main output circuit, the output voltage of the first auxiliary output circuit is also relatively stable, and the cross-regulation rate is low. Finally, by artificially increasing the leakage inductance in the second auxiliary output circuit to match the leakage inductance of the main output circuit, the cross-regulation rate is reduced, and an energy absorption circuit is connected in parallel at both ends of the inductor to absorb the energy of the artificially increased leakage inductance when the switch tube is turned on. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly describes the drawings required for the specific embodiments or the description of the prior art. Similar elements or parts are generally identified by similar reference numerals throughout the drawings. Elements or parts in the drawings are not necessarily drawn to scale.

[0017] Figure 1 A schematic diagram of a multi-output flyback converter with low cross-regulation rate provided by an embodiment of the present invention is shown; Figure 2 A schematic diagram of a feedback control loop provided by an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0018] The following embodiments of the technical solution of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and are therefore only examples and are not intended to limit the scope of protection of the present invention. It should be noted that, unless otherwise specified, the technical or scientific terms used in this application should have the common meanings understood by those skilled in the art to which the present invention belongs.

[0019] In one embodiment, Figure 1 As shown, a multi-output flyback converter with low cross-regulation rate is provided, comprising: The primary circuit includes the switch Q1 and the primary windings 1 and 2 of the transformer. The switch Q1 is used to control the energy transfer of the transformer. The secondary circuit includes a main output circuit Vo1, a first secondary output circuit Vo2, and a second secondary output circuit. The main output circuit Vo1 includes secondary windings 3 and 5 of the transformer. The secondary windings 4 and 5 of the first secondary output circuit Vo2 are led out from the secondary windings 3 and 5 of the main output circuit Vo1 through taps. The second secondary output circuits are independently arranged and also include another secondary winding of the transformer. The secondary winding of the second secondary output circuit is connected to an inductor, and an energy absorption circuit is connected in parallel at both ends of the inductor. The feedback control loop obtains the sampled voltage of the main output loop Vo1 and compares it with the reference voltage, and controls the output voltage of the multiple outputs by controlling the duty cycle of the switch tube.

[0020] First, the main output loop Vo1 is connected to the feedback control loop with a feedback regulation mechanism, and the output voltage is stable. Secondly, the first secondary output loop Vo2 is led out from the secondary windings 3 and 5 of the main output loop Vo1 through a tap, and its voltage is lower than the voltage of the main output loop. Under the influence of the main output loop Vo1, the output voltage of the first secondary output loop Vo2 is also relatively stable, and the cross-regulation rate is low. Finally, by artificially increasing the leakage inductance in the second secondary output loop to match it with the leakage inductance of the main output loop, the cross-regulation rate is reduced, and an energy absorption circuit is connected in parallel at both ends of the inductor to absorb the energy of the artificially increased leakage inductance when the switch tube is turned on.

[0021] The output voltage of the first secondary output circuit Vo2 can be adjusted accordingly by adjusting the tap position according to actual needs.

[0022] like Figure 1 As shown, the second output circuit is set to two, namely Vo3 and Vo4; in specific applications, the second output circuit can be set to one or more.

[0023] Taking the second output circuit Vo3 as an example, the energy absorption circuit includes a first absorption resistor R6, an absorption capacitor C7, a first freewheeling diode D6 and a second absorption resistor R11. The first absorption resistor R6, the absorption capacitor C7 and the first freewheeling diode D6 are connected in series in sequence and in parallel to the two ends of the leakage inductance L1. The second absorption resistor R11 is connected in parallel to the first absorption resistor R6 and the absorption capacitor C7; the cathode of the first freewheeling diode D6 is connected to the absorption capacitor C7, and the anode of the first freewheeling diode D6 is connected to the inductor L1.

[0024] Optionally, the primary circuit further includes an input capacitor C1 and an RCD clamping circuit. The input capacitor C1 and the input voltage Vin are connected across primary windings 1 and 2. The RCD clamping circuit absorbs energy released by the transformer's leakage inductance, thereby reducing the voltage spike across the switch Q1 and protecting it from high voltage damage.

[0025] Specifically, the RCD clamp circuit includes a protection resistor R1, a protection capacitor C2 and a protection diode D1. The protection capacitor C2 and the protection diode D1 are connected in series and are connected to both ends of the primary windings 1 and 2. The protection resistor R1 is connected to both ends of the protection capacitor C2. The cathode of the protection diode D1 is connected to the protection capacitor C2, and the anode of the protection diode D1 is connected to the primary windings 1 and 2.

[0026] Optionally, the switch tube Q1 is a MOS tube, the gate of the switch tube Q1 is connected to the feedback control loop, the source of the switch tube Q1 is connected to the negative end of the input voltage Vin, and the drain of the switch tube Q1 is connected to the positive electrode of the protection diode D1.

[0027] Optionally, the main output circuit Vo1, the first auxiliary output circuit Vo2 and the second auxiliary output circuit each further include a second freewheeling diode, an output capacitor and a load resistor. The output capacitor and the load resistor are connected in parallel to both ends of the secondary winding, and the second freewheeling diode is connected between the output capacitor and the secondary winding; the positive electrode of the second freewheeling diode is connected to the secondary winding, and the negative electrode of the second freewheeling diode is connected to the output capacitor.

[0028] Taking the main output circuit Vo1 as an example, the output capacitor C3 and the load resistor R2 are connected in parallel at both ends of the secondary windings 3 and 5, and the second freewheeling diode D2 is connected between the output capacitor C3 and the secondary winding 3; the positive electrode of the second freewheeling diode D2 is connected to the secondary winding 3, and the negative electrode of the second freewheeling diode D2 is connected to the output capacitor C3.

[0029] Optionally, the main output circuit is further connected to a voltage-dividing sampling circuit, which includes a plurality of sampling resistors connected in series; the feedback control circuit is connected to the sampling resistors. Figure 1 As shown, the sampling resistors R8, R9, and R10 are connected to the feedback control loop, thereby realizing feedback regulation of the output voltage.

[0030] In one embodiment, Figure 2 As shown in the figure, after the feedback control chip of the feedback control loop collects the voltage of the main output loop based on the voltage divider sampling circuit, it drives the switch tube Q1 on and off through PWM to adjust the output voltage of multiple outputs; the feedback control loop only implements feedback adjustment for the main output loop, and the auxiliary output loop has no feedback adjustment mechanism.

[0031] The above embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A multi-output flyback converter with low cross-regulation, characterized in that: include: A primary circuit includes a switch tube and a primary winding of a transformer, wherein the switch tube is used to control energy transfer of the transformer; A secondary circuit includes a main output circuit, a first secondary output circuit, and a second secondary output circuit. The main output circuit includes a secondary winding of a transformer, and the first secondary output circuit is led out from the secondary winding of the main output circuit via a tap. The second secondary output circuits are independently provided and also include another secondary winding of the transformer. The secondary winding of the second secondary output circuit is connected to an inductor, and an energy absorption circuit is connected in parallel at both ends of the inductor. The feedback control loop obtains the sampled voltage of the main output loop and compares it with the reference voltage, and controls the output voltage of the multiple outputs by controlling the duty cycle of the switching tube.

2. The multi-output flyback converter with low cross-regulation according to claim 1, wherein: The energy absorption circuit includes a first absorption resistor, an absorption capacitor, a first freewheeling diode and a second absorption resistor, wherein the first absorption resistor, the absorption capacitor and the first freewheeling diode are sequentially connected in series and in parallel to the two ends of the leakage inductance, and the second absorption resistor is connected in parallel to the two ends of the first absorption resistor and the absorption capacitor; The cathode of the first freewheeling diode is connected to the absorption capacitor, and the anode of the first freewheeling diode is connected to the inductor.

3. The multi-output flyback converter with low cross-regulation according to claim 2, wherein: The primary loop further includes an input capacitor and an RCD clamping circuit. The input capacitor and the input voltage Vin, and the RCD clamping circuit are connected to both ends of the primary winding.

4. The multi-output flyback converter with low cross-regulation according to claim 3, wherein: The RCD clamping circuit includes a protection resistor, a protection capacitor and a protection diode. The protection capacitor and the protection diode are connected in series and are connected to both ends of the primary winding, and the protection resistor is connected to both ends of the protection capacitor; the cathode of the protection diode is connected to the protection capacitor, and the anode of the protection diode is connected to the primary winding.

5. The multi-output flyback converter with low cross-regulation according to claim 4, characterized in that: The switch tube is a MOS tube, The gate of the switch tube is connected to the feedback control loop, the source of the switch tube is connected to the negative end of the input voltage Vin, and the drain of the switch tube is connected to the positive electrode of the protection diode.

6. The multi-output flyback converter with low cross-regulation according to claim 2, wherein: The main output circuit, the first auxiliary output circuit and the second auxiliary output circuit also include a second freewheeling diode, an output capacitor and a load resistor. The output capacitor and the load resistor are connected in parallel to both ends of the secondary winding, and the second freewheeling diode is connected between the output capacitor and the secondary winding; the positive electrode of the second freewheeling diode is connected to the secondary winding, and the negative electrode of the second freewheeling diode is connected to the output capacitor.

7. The multi-output flyback converter with low cross-regulation according to claim 1, wherein: The main output loop is further connected to a voltage-dividing sampling circuit, which includes a plurality of sampling resistors connected in series; the feedback control loop is connected to the sampling resistors.

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