Forward conversion auxiliary power supply circuit

Abstract

The utility model belongs to the technical field of circuits, and discloses an auxiliary power supply circuit for forward conversion, which comprises a port DC +, the port DC + is connected with the positive end of a diode D1, the negative end of the diode D1 is connected with one end of a resistor R1, one end of a resistor R2, one end of a resistor R3, one end of a capacitor C1 and a pin 1 of a transformer T1, and the other end of the transformer T1 is connected with a pin 2 of the transformer T1. The other end of the resistor R1 is connected with a pin 8 and a pin 5 of the power supply chip U1 and a port GND, the other end of the resistor R2 is connected with a pin 1 of the power supply chip U1 and a pin 3 of the transformer T1, and the other end of the resistor R3 is connected with the other end of the capacitor C1 and the negative end of the diode D2. The beneficial effects of the utility model are that the circuit does not need to input a filter capacitor, so that the circuit is more flexible, and the size of a PCB is reduced.

Description

Technical Field

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

[0002] Switching power supplies have a wide range of applications and are often referred to as converters. Forward switching power supplies are one of the most commonly used topologies for small and medium power step-down isolated DC / DC converters. The basic forward converter in the forward switching power supply is an ideal isolated version of the Buck converter. Common topologies include single-ended forward converters, symmetrically driven half-bridge converters, full-bridge converters, push-pull converters, and symmetrical push-pull forward converters. Forward switching power supplies have many advantages, such as simple peripheral circuits, low voltage and current stress, strong overload resistance, not easy to saturate, and easy integration. In existing circuits, filter capacitors are provided, which increases the circuit cost and is relatively complex.

[0003] Therefore, it is necessary to provide an auxiliary power supply circuit for forward conversion, simplify circuit design, reduce circuit cost, and provide a reliable auxiliary power supply circuit based on forward conversion without the need for input filter capacitors. Utility Model Content

[0004] The utility model discloses an auxiliary power supply circuit for forward conversion, relates to the technical field of forward power supply, and can effectively solve the technical problems involved in the background technology.

[0005] To achieve the above purpose, the technical solution of the utility model is:

[0006] An auxiliary power supply circuit for forward conversion, comprising a port DC+, wherein the port DC+ is connected to the positive end of a diode D1, the negative end of the diode D1 is connected to one end of a resistor R1, one end of a resistor R2, one end of a resistor R3, one end of a capacitor C1 and a pin 1 of a transformer T1, the other end of the resistor R1 is connected to pins 8 and 5 of a power chip U1, and a port GND, the other end of the resistor R2 is connected to pin 1 of the power chip U1 and pin 3 of the transformer T1, the other end of the resistor R3 is connected to the other end of the capacitor C1 and the negative end of the diode D2, the positive end of the diode D2 is connected to pin 2 of the transformer T1 and the drain of a MOS tube Q1, and the MOS tube Q The source of 1 is connected to pin 2 of the power chip U1, pin 4 of the transformer T1 and port GND, pin 3 of the power chip U1 is connected to one end of the resistor R4, the other end of the resistor R4 is connected to the gate of the MOS tube Q1, pin 4 of the power chip U1 is connected to one end of the resistor R5, the other end of the resistor R5 is connected to port GND, pin 6 of the power chip U1 is connected to the emitter of the optocoupler OT, the positive end of the voltage regulator and port GND, pin 7 of the power chip U1 is connected to the collector of the optocoupler OT, the negative end of the voltage regulator is connected to the negative end of the optocoupler OT, the positive end of the optocoupler OT is connected to one end of the resistor R6, and the other end of the resistor R6 is connected to port 13V;

[0007] Pin 5 of the transformer T1 is connected to the positive end of the diode D3, the negative end of the diode D3 is connected to one end of the capacitor C2 and one end of the inductor L1, the other end of the inductor L1 is connected to port 12V, pin 6 of the transformer T1 is connected to the other end of the capacitor C2 and port GNDA, and the port 12V is connected to the port 13V.

[0008] The forward switching power supply is one of the most commonly used topologies for small and medium power step-down isolated DC / DC converters. The utility model aims to provide a new type of forward power supply, which innovatively deletes the traditional forward circuit. The energy transmission circuit also serves as a magnetic reset circuit, which simplifies the processing difficulty of the forward transformer, simplifies the circuit design, reduces the circuit cost and PCB volume, and is widely used.

[0009] As a preferred improvement of the present invention: the model of the power chip U1 is OB2276.

[0010] As a preferred improvement of the present utility model: the voltage regulator tube model is AZ431.

[0011] As a preferred improvement of the present utility model: the positive end of the diode D3 is connected to one end of the resistor R7, the other end of the resistor R7 is connected to one end of the capacitor C6, the other end of the capacitor C6 is connected to the negative end of the diode D3, the other end of the inductor L1 is connected to one end of the capacitor C3, and the other end of the capacitor C3 is connected to the other end of the capacitor C2.

[0012] As a preferred improvement of the present utility model: pin 7 of the transformer T1 is connected to the positive end of the diode D4 and one end of the capacitor C5, the negative end of the diode D4 is connected to the other end of the capacitor C5, one end of the capacitor C4 and the port GNDA, and pin 8 of the transformer T1 is connected to the other end of the capacitor C4 and the port -VCC.

[0013] As a preferred improvement of the utility model: Pin 1 and Pin 2 of the transformer T1 share a coil, Pin 3 and Pin 4 of the transformer T1 share a coil, Pin 5 and Pin 6 of the transformer T1 share a coil, and Pin 7 and Pin 8 of the transformer T1 share a coil.

[0014] The beneficial effects of the utility model are as follows:

[0015] The feedback loop is composed of AZ431 voltage regulator and optocoupler. The secondary output voltage is compared with the reference voltage to generate a feedback signal. This feedback signal will be sent back to the PWM controller to adjust the switching frequency and duty cycle of the switch tube to stabilize the output voltage. This circuit does not require an input filter capacitor, making the circuit more flexible and reducing the size of the PCB. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present utility model, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative work, among which:

[0017] Figure 1 The utility model is a schematic diagram of an auxiliary power supply circuit of a forward conversion. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present invention will be described clearly and completely below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0020] In addition, in the present invention, the descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features.

[0021] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0022] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0023] See also Figure 1As shown, the utility model provides an auxiliary power supply circuit for forward conversion, including a port DC+ (input power supply), wherein the port DC+ is connected to the positive end of a diode D1, the negative end of the diode D1 is connected to one end of a resistor R1, one end of a resistor R2, one end of a resistor R3, one end of a capacitor C1 and a pin 1 of a transformer T1, the other end of the resistor R1 is connected to pins 8 and 5 of a power chip U1, and a port GND, the other end of the resistor R2 is connected to pin 1 of the power chip U1 and pin 3 of the transformer T1, the other end of the resistor R3 is connected to the other end of the capacitor C1 and the negative end of the diode D2, the positive end of the diode D2 is connected to pin 2 of the transformer T1 and the drain of a MOS tube Q1, the source of the MOS tube Q1 is connected to pin 2 of the power chip U1, pin 4 of the transformer T1 and the port GND, and pin 3 of the power chip U1 is connected to resistor R4 The pin 4 of the power chip U1 is connected to one end of the resistor R5, and the other end of the resistor R5 is connected to the port GND. The pin 6 of the power chip U1 is connected to the emitter of the optocoupler OT, the positive end of the voltage regulator tube and the port GND. The pin 7 of the power chip U1 is connected to the collector of the optocoupler OT, the negative end of the voltage regulator tube is connected to the negative end of the optocoupler OT, the positive end of the optocoupler OT is connected to one end of the resistor R6, and the other end of the resistor R6 is connected to the port 13V; the pin 5 of the transformer T1 is connected to the positive end of the diode D3, the negative end of the diode D3 is connected to one end of the capacitor C2 and one end of the inductor L1, and the other end of the inductor L1 is connected to the port 12V, the pin 6 of the transformer T1 is connected to the other end of the capacitor C2 and the port GNDA, and the port 12V is connected to the port 13V (for output voltage sampling). In this embodiment, the power chip U1 model is OB2276, and the voltage regulator tube model is AZ431.

[0024] As an implementation mode, the positive end of the diode D3 is connected to one end of the resistor R7, the other end of the resistor R7 is connected to one end of the capacitor C6, the other end of the capacitor C6 is connected to the negative end of the diode D3, the other end of the inductor L1 is connected to one end of the capacitor C3, and the other end of the capacitor C3 is connected to the other end of the capacitor C2. Pin 7 of the transformer T1 is connected to the positive end of the diode D4 and one end of the capacitor C5, the negative end of the diode D4 is connected to the other end of the capacitor C5, one end of the capacitor C4 and the port GNDA, and pin 8 of the transformer T1 is connected to the other end of the capacitor C4 and the port -VCC. Pin 1 and pin 2 of the transformer T1 share a coil, pin 3 and pin 4 of the transformer T1 share a coil, pin 5 and pin 6 of the transformer T1 share a coil, and pin 7 and pin 8 of the transformer T1 share a coil.

[0025] The circuit includes a clamping absorption circuit, a forward switching power supply chip, an optocoupler feedback circuit, an AZ431 voltage regulator chip and a secondary circuit.

[0026] The forward switching power supply chip uses OB2276, a highly integrated current mode PWM control IC suitable for offline flyback converter applications requiring high performance, low standby power consumption and cost-effectiveness. It uses a SOP8 package with a total of 8 functional pins. 1-VCC: power supply. 2-GND: ground. 3-GATE: totem pole gate output drives Mosfet. 4-CS: current sampling input. 5-BO: line voltage detection pin, depending on whether the voltage of this pin will trigger undervoltage protection. 6-RT: dual-function pin, connected to ground through an NTC resistor to achieve over-temperature shutdown / latch control, or connected to VDD through a Zener diode to achieve adjustable overvoltage protection. 7-FB: feedback input pin, PWM duty cycle is determined by the voltage value entering this pin and the current detection signal of pin 4. 8-Demag: output detection pin through the transformer winding for output overvoltage protection.

[0027] The clamping absorption circuit is composed of resistor R3, capacitor C1 and diode D2. The main function of the RCD absorption circuit is to protect other components in the circuit from damage by voltage spikes and ensure the stable operation of the circuit. When a voltage spike appears in the circuit, the capacitor will instantly charge or discharge, playing a buffering role, so that other components in the circuit are not impacted by the voltage spike. The diode will conduct the excessive voltage spike and shunt it to the ground to prevent it from affecting the normal operation of the circuit.

[0028] The circuit uses a pulse width modulation (PWM) driver chip to control the switching frequency and duty cycle of the switch tube (Q1). The PWM controller generates an appropriate PWM signal based on the feedback signal of the output voltage (port 12V) and the reference voltage to control the on and off of the switch tube, thereby adjusting the output voltage. At the same time, the AZ431 voltage regulator tube and the optocoupler form a feedback loop, and the secondary output voltage is compared with the reference voltage to generate a feedback signal. This feedback signal will be sent back to the PWM controller to adjust the switching frequency and duty cycle of the switch tube to stabilize the output voltage.

[0029] The forward transformer module is divided into four windings. The auxiliary winding on the primary side supplies power to the forward open-tube power supply chip. The secondary side is divided into two circuits, which output different voltage values ​​(adjusted according to the coil turns ratio). In this embodiment, the port 12V is connected to the power supply port of the fan, and the port -VCC is connected to the power supply port of other circuits (such as the output sampling amplifier circuit).

[0030] The working process of the forward switching power supply circuit is as follows:

[0031] 1. When Q1 is turned on:

[0032] The like-name ends of the transformer primary side Np and the amplitude sides Ns1 and Ns2 are positive relative to the opposite-name ends, the rectifier diode D3 is forward biased, and the current is input from the like-name ends through D3 and L1 into the C2 filter capacitor and the load.

[0033] The voltage across the primary winding Nr of the transformer is positive (the same-name end is relative to the opposite-name end), and the voltage on the winding is Vdc (Np=Nr), and no current flows through the winding Nr.

[0034] 2. When Q1 is turned off:

[0035] The energy stored in transformer T1 reverses the voltage of Np (the voltage at the opposite end of Np rises rapidly and is much larger than Vdc). At this time, the same-name ends of the primary / secondary sides of all windings are negative relative to the opposite-name ends.

[0036] This circuit does not require an input filter capacitor, making the circuit more flexible, reducing the size of the PCB, simplifying the circuit design and reducing the circuit cost.

[0037] Although the implementation scheme of the utility model has been disclosed as above, it is not limited to the applications listed in the specification and the implementation scheme. It can be fully applied to various fields suitable for the utility model. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the utility model is not limited to the specific details and the illustrations shown and described herein.

Claims

1. An auxiliary power supply circuit for forward conversion, characterized in that: The invention comprises a port DC+, wherein the port DC+ is connected to the positive end of a diode D1, the negative end of the diode D1 is connected to one end of a resistor R1, one end of a resistor R2, one end of a resistor R3, one end of a capacitor C1 and a pin 1 of a transformer T1, the other end of the resistor R1 is connected to pins 8 and 5 of a power chip U1, and a port GND, the other end of the resistor R2 is connected to pin 1 of the power chip U1 and pin 3 of the transformer T1, the other end of the resistor R3 is connected to the other end of the capacitor C1 and the negative end of the diode D2, the positive end of the diode D2 is connected to pin 2 of the transformer T1 and the drain of a MOS tube Q1, and the source of the MOS tube Q1 is connected to the Pin 2 of the power chip U1, pin 4 of the transformer T1 and port GND, pin 3 of the power chip U1 is connected to one end of the resistor R4, the other end of the resistor R4 is connected to the gate of the MOS tube Q1, pin 4 of the power chip U1 is connected to one end of the resistor R5, the other end of the resistor R5 is connected to port GND, pin 6 of the power chip U1 is connected to the emitter of the optocoupler OT, the positive end of the voltage regulator and port GND, pin 7 of the power chip U1 is connected to the collector of the optocoupler OT, the negative end of the voltage regulator is connected to the negative end of the optocoupler OT, the positive end of the optocoupler OT is connected to one end of the resistor R6, and the other end of the resistor R6 is connected to port 13V; Pin 5 of the transformer T1 is connected to the positive end of the diode D3, the negative end of the diode D3 is connected to one end of the capacitor C2 and one end of the inductor L1, the other end of the inductor L1 is connected to port 12V, pin 6 of the transformer T1 is connected to the other end of the capacitor C2 and port GNDA, and the port 12V is connected to the port 13V.

2. The auxiliary power supply circuit of forward conversion according to claim 1, characterized in that: The power chip U1 model is OB2276.

3. The auxiliary power supply circuit of forward conversion according to claim 1, characterized in that: The voltage regulator tube model is AZ431.

4. The auxiliary power supply circuit for forward conversion according to claim 1, characterized in that: The positive end of the diode D3 is connected to one end of the resistor R7, the other end of the resistor R7 is connected to one end of the capacitor C6, the other end of the capacitor C6 is connected to the negative end of the diode D3, the other end of the inductor L1 is connected to one end of the capacitor C3, and the other end of the capacitor C3 is connected to the other end of the capacitor C2.

5. The auxiliary power supply circuit of forward conversion according to claim 1, characterized in that: Pin 7 of the transformer T1 is connected to the positive end of the diode D4 and one end of the capacitor C5, the negative end of the diode D4 is connected to the other end of the capacitor C5, one end of the capacitor C4 and the port GNDA, and pin 8 of the transformer T1 is connected to the other end of the capacitor C4 and the port -VCC.

6. The auxiliary power supply circuit for forward conversion according to claim 5, characterized in that: Pin 1 and pin 2 of the transformer T1 share a coil, pin 3 and pin 4 of the transformer T1 share a coil, pin 5 and pin 6 of the transformer T1 share a coil, and pin 7 and pin 8 of the transformer T1 share a coil.

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