Forward active clamping power supply auxiliary power supply circuit

Abstract

The utility model discloses an auxiliary power supply circuit of a forward active clamping power supply, which comprises a forward active clamping topological structure, and the forward active clamping topological structure comprises a PWM (Pulse Width Modulation) chip and a transformer. An auxiliary power supply circuit is connected between the PWM chip and the transformer. The auxiliary power supply circuit comprises a first rectifier tube, a second rectifier tube, a first capacitor, a second capacitor, a first resistor, a first winding and a second winding; the forward active clamping topological structure has the advantages that the auxiliary power supply circuit is added in the existing forward active clamping topological structure, a rectifier tube, a capacitor, a resistor and a corresponding auxiliary winding which are constructed in the auxiliary power supply circuit are utilized, stable output can be provided under the conditions of input voltage fluctuation and load fluctuation, the number of components is small, the circuit is relatively simple, and cost is low. The reliability is high, and a secondary voltage stabilizing circuit is not needed.

Description

Technical Field

[0001] The utility model relates to the technical field of power supply circuits, in particular to a forward active clamping power supply auxiliary power supply circuit. Background Art

[0002] With the development of chip integration technology, electronic equipment systems require power products to meet the needs of high power density, low voltage and high current, high dynamic performance and diversified output voltage. The forward active clamp topology has been widely used in the power range of 50W-500W DC-DC conversion due to its simple circuit structure, high efficiency, low ripple noise, and good dynamic performance. In the field of low power, high power density, and wide range input on-board module power supply, the advantages of the forward active clamp topology are more obvious.

[0003] In the power supply circuit, the startup circuit of the PWM chip only provides a microampere startup current. After the chip is started, an auxiliary power supply circuit is required to keep the chip working. Because the optimal operating range of the PWM chip and MOS tube drive voltage is 10V to 15V, the auxiliary power supply is required to be relatively stable under various input voltages and load conditions. The auxiliary power supply scheme currently used in the forward active clamp topology is as follows:

[0004] First, the transformer auxiliary winding (single winding) is powered, such as Figure 1 As shown. This circuit is realized through the transformer auxiliary winding forward circuit, D1 is a freewheeling tube, D2 is a rectifier tube, and L2 is an energy storage inductor. Because the load of the auxiliary winding is very small, in order to ensure the interactive regulation rate with the main output winding, the inductor L2 needs to have an inductance of at least 1mH. In the on-board power supply with a very high density of components, the selection of L2 is more difficult; at the same time, in the case of input voltage fluctuations and duty cycle changes, the auxiliary winding forward circuit alone cannot achieve a good voltage stabilization effect. It is necessary to add another level of linear voltage stabilization to ensure that the chip works within a safe voltage range. The circuit is relatively complex.

[0005] Second, the energy storage inductor is powered by the auxiliary winding. This circuit uses the auxiliary winding of the energy storage inductor to achieve flyback power supply. In the design of isolated power supply, the circuit requires that the auxiliary winding and its flyback circuit have sufficient creepage distance with the main winding of the energy storage inductor and the secondary circuit of the main circuit, that is, both the main transformer and the energy storage inductor need to be isolated, which brings difficulties to the layout of the product. At the same time, the inductor auxiliary winding and the main winding also have the problem of interactive regulation, especially in no-load or light-load state. If the coupling between the auxiliary winding and the main winding is not good, the auxiliary power supply energy is insufficient, and the output voltage will be unstable. Utility Model Content

[0006] In view of the defects in the prior art, the purpose of the utility model is to provide a simple, practical, forward active clamping power supply auxiliary power supply circuit that can provide stable output.

[0007] The technical solution adopted by the utility model is: a forward active clamp power auxiliary power supply circuit, including a forward active clamp topology structure, the forward active clamp topology structure includes a PWM chip and a transformer; an auxiliary power supply circuit is also connected between the PWM chip and the transformer; the auxiliary power supply circuit includes a first rectifier, a second rectifier, a first capacitor, a second capacitor, a first resistor, a first winding and a second winding, a power supply VCC is respectively connected to the VCC pin of the PWM chip, one end of the first capacitor and one end of the first resistor, the other end of the first resistor is connected to the cathode of the first rectifier, the anode of the first rectifier is respectively connected to one end of the second capacitor and the cathode of the second rectifier, the anode of the second rectifier is respectively connected to one end of the first winding and one end of the second winding, the other end of the first winding is connected to the other end of the second capacitor, the other end of the second winding is connected to the other end of the first capacitor, and the other end of the first capacitor is also connected to the ground.

[0008] Preferably, the same-name end of the first winding is connected to the anode of the second rectifier tube; the same-name end of the second winding is connected to the other end of the first capacitor.

[0009] Preferably, the first winding and the second winding have the same number of turns.

[0010] Preferably, the first resistor is a current limiting resistor.

[0011] Preferably, the VCC pin of the PWM chip is also grounded via a filter capacitor.

[0012] Preferably, the first capacitor and the second capacitor are both energy storage capacitors to achieve output uniformity.

[0013] The beneficial effects of the utility model are embodied in that an auxiliary power supply circuit is added to the existing forward active clamping topology structure, and the rectifier tube, capacitor, resistor and corresponding auxiliary winding constructed in the auxiliary power supply circuit are utilized to provide a stable output in the case of input voltage fluctuation and load fluctuation, and the number of components is small, the circuit is relatively simple, the reliability is high, and no secondary voltage stabilization circuit is required. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the specific implementation of the utility model or the technical solution in the prior art, the following is a brief introduction to the drawings required for the specific implementation or the prior art description. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, each element or part is not necessarily drawn according to the actual scale.

[0015] Figure 1 A circuit schematic diagram of a transformer auxiliary winding provided by the prior art;

[0016] Figure 2 A circuit schematic diagram of a forward active clamp power auxiliary power supply circuit provided by an embodiment of the utility model;

[0017] Figure 3A A schematic diagram of a Vds potential provided by an embodiment of the utility model;

[0018] Figure 3B A potential schematic diagram of V1 provided in an embodiment of the utility model;

[0019] Figure 3C A potential schematic diagram of V2 provided in an embodiment of the utility model;

[0020] Figure 4 A current flow diagram inside a winding in an auxiliary power supply circuit provided by an embodiment of the utility model;

[0021] Figure 5 Another winding internal current flow diagram in an auxiliary power supply circuit provided by an embodiment of the utility model;

[0022] Figure 6 This is a diagram showing the relationship between the power supply voltage VCC and the input voltage detected when the embodiment of the present utility model is used. DETAILED DESCRIPTION

[0023] The following embodiments of the technical solution of the utility model are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the utility model, and are therefore only used as examples, and cannot be used to limit the protection scope of the utility model.

[0024] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in this application should have the common meanings understood by technicians in the field to which the utility model belongs.

[0025] like Figure 2As shown, an embodiment of the present invention provides a forward active clamp power auxiliary power supply circuit, including a forward active clamp topology structure, the forward active clamp topology structure includes a PWM chip and a transformer; an auxiliary power supply circuit is also connected between the PWM chip and the transformer; the auxiliary power supply circuit includes a first rectifier, a second rectifier, a first capacitor, a second capacitor, a first resistor, a first winding and a second winding, the power supply VCC is respectively connected to the VCC pin of the PWM chip, one end of the first capacitor and one end of the first resistor, the other end of the first resistor is connected to the cathode of the first rectifier, the anode of the first rectifier is respectively connected to one end of the second capacitor and the cathode of the second rectifier, the anode of the second rectifier is respectively connected to one end of the first winding and one end of the second winding, the other end of the first winding is connected to the other end of the second capacitor, the other end of the second winding is connected to the other end of the first capacitor, and the other end of the first capacitor is also connected to ground.

[0026] It should be noted that, refer to Figure 1 The existing forward active clamping topology structure also includes MOS tubes V1 and V2 between the PWM chip and the primary winding of the transformer, and inductors, capacitors and diodes connected to the secondary winding of the transformer; they will not be described in detail here.

[0027] The first rectifier is represented by D1, the second rectifier is represented by D2, the first capacitor is represented by C1, the second capacitor is represented by C2, the first resistor is represented by R1, the first winding is represented by Na, and the second winding is represented by Nb; an auxiliary double winding is formed by the first winding and the second winding.

[0028] like Figure 2 As shown, in this embodiment, the same-name end of the first winding is connected to the anode of the second rectifier tube; the same-name end of the second winding is connected to the other end of the first capacitor.

[0029] Further, the first winding and the second winding have the same number of turns;

[0030] The first resistor is a current limiting resistor;

[0031] The VCC pin of the PWM chip is also grounded via a filter capacitor;

[0032] The first capacitor and the second capacitor are both energy storage capacitors to achieve output uniformity.

[0033] For ease of understanding of this embodiment, refer to Figures 2 to 6 , its working process is as follows:

[0034] Input voltage Vin, output voltage Vo, auxiliary power supply voltage VCC, the turns ratio of the primary, secondary and power supply windings of the transformer is Np:Ns:Na:Nb, the power supply working cycle is T, the duty cycle is D, and this duty cycle is defined as the ratio of the time when the MOS tube V1 is turned on in a single cycle to the cycle T. Assume that the diodes in the figure are all ideal diodes and ignore the conduction voltage drop. Take the main circuit power ground or the signal ground of the auxiliary power supply VCC as zero potential, assume that the drain-source potential of the main MOS tube is Vds, the anode voltage of the diode D2 is V1, the cathode voltage is V3, and the potential of the winding Na output side is V2; the potentials of Vds, V1, and V2 are as follows Figure 3A , Figure 3B and Figure 3C shown.

[0035] In the active clamp topology, the drain potential of MOS tube V1 is:

[0036] The positive and negative amplitude voltage difference V of the transformer winding Np in the working stage Np for:

[0037] The positive and negative amplitude voltage difference V of the transformer winding Nb in the working stage Nb for:

[0038] The positive and negative amplitude voltage difference V(Na+Nb) of the transformer winding Na+Nb in the working stage is:

[0039]

[0040] According to the volt-second balance principle, the positive and negative amplitudes of windings Nb and Na+Nb are:

[0041] Nb positive amplitude: D×V Nb ; Nb negative amplitude: -(1-D)×V Nb

[0042] Na+Nb positive amplitude: D×V (Na+Nb) ; Na+Nb negative amplitude: -(1-D)×V (Na+Nb)

[0043] During the time DT when the main circuit MOS tube V1 is turned on, the current in the auxiliary power supply winding flows as follows: Figure 4 As shown, diode D2 is turned on, V3 = V1, at this time V1 and V2 are both negative potentials, and V1 = V3> V2, so diode D1 is turned off, and V3 potential is -(1-D)V Nb , V2 potential is -(1-D)(V Na +V Nb ), the potential difference between the two ends of C2 is:

[0044] During the time (1-D)T when the main circuit MOS tube V1 is turned off, the current in the auxiliary power supply winding flows as follows: Figure 5 As shown, at this time, V1 and V2 flip to positive potential DV Na+Nb , and V2>V1, because the voltage on both sides of capacitor C2 cannot change suddenly, so at this time V3>V2>V1, V3 potential is D(V Na +V Nb )+△C2, diode D2 is cut off, diode D1 is turned on, and capacitor C1 is charged through current limiting resistor R1. The resistance of resistor R1 is very small, and the voltage drop is ignored. At this time, VCC=V3, so the VCC potential is calculated as follows:

[0045]

[0046] Taking our company's actual product design as an example, 1 / 4 to 200W product, input voltage Vin = 36-72V, output voltage Vo = 5V, Np:Ns:Na:Nb = 8:2:1:1, according to the attached Figure 6 It can be seen that within the input range of 36-72V, the VCC voltage fluctuation range is 10.2V-12.5V, which is completely within the safe operating voltage range of the chip and MOS tube gate drive, and there is no need to add a secondary voltage stabilization circuit in the subsequent stage.

[0047] The utility model adds an auxiliary power supply circuit to the existing forward active clamping topology structure, and utilizes the rectifier tube, capacitor, resistor and corresponding auxiliary winding constructed in the auxiliary power supply circuit to provide a stable output in the case of input voltage fluctuation and load fluctuation, and has fewer components, a relatively simple circuit, high reliability, and no need for a secondary voltage stabilization circuit.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the utility model, rather than to limit it. Although the utility model has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the utility model, and they should all be included in the scope of the claims and specification of the utility model.

Claims

1. A forward active clamp power auxiliary power supply circuit, comprising a forward active clamp topology structure, wherein the forward active clamp topology structure comprises a PWM chip and a transformer; characterized in that An auxiliary power supply circuit is also connected between the PWM chip and the transformer; the auxiliary power supply circuit includes a first rectifier, a second rectifier, a first capacitor, a second capacitor, a first resistor, a first winding and a second winding, the power supply VCC is respectively connected to the VCC pin of the PWM chip, one end of the first capacitor and one end of the first resistor, the other end of the first resistor is connected to the cathode of the first rectifier, the anode of the first rectifier is respectively connected to one end of the second capacitor and the cathode of the second rectifier, the anode of the second rectifier is respectively connected to one end of the first winding and one end of the second winding, the other end of the first winding is connected to the other end of the second capacitor, the other end of the second winding is connected to the other end of the first capacitor, and the other end of the first capacitor is also connected to the ground.

2. A forward active clamp power supply auxiliary power supply circuit according to claim 1, characterized in that , the same-name end of the first winding is connected to the anode of the second rectifier tube; the same-name end of the second winding is connected to the other end of the first capacitor.

3. A forward active clamp power supply auxiliary power supply circuit according to claim 2, characterized in that , the number of turns of the first winding and the second winding is the same.

4. A forward active clamp power supply auxiliary power supply circuit according to claim 3, characterized in that , the first resistor is a current limiting resistor.

5. The forward active clamp power auxiliary power supply circuit according to claim 1, characterized in that ,The VCC pin of the PWM chip is also grounded through a filter capacitor.

6. A forward active clamp power supply auxiliary power supply circuit according to any one of claims 1 to 5, characterized in that ,The first capacitor and the second capacitor are both energy storage capacitors to achieve output uniformity.

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