Isolation power supply with wide voltage input and constant voltage output

Abstract

The utility model relates to the technical field of industrial control input power supplies, in particular to an isolation power supply with wide voltage input and constant voltage output, which comprises a switching power supply control chip and a transformer, and is characterized in that the switching power supply control chip comprises an enabling / undervoltage locking input pin, a grounding pin, a feedback pin, a switching output pin and a power supply input pin; two sides of the transformer are provided with a primary side circuit and a secondary side circuit; the primary side circuit comprises a primary winding leakage inductance peak surge absorption circuit connected with the switch output pin, and a primary winding of a transformer connected in series with the primary winding leakage inductance peak surge absorption circuit; the secondary side circuit comprises a secondary winding of the transformer and a power supply output circuit connected with the secondary winding; and a third resistor and a fourth resistor are connected between the feedback pin and the switch output pin. The isolation power supply is simple in structure, few in devices, low in cost, small in occupied space of a circuit board and convenient to control.

Description

Technical Field

[0001] This utility model relates to the field of industrial control input power supply technology, and in particular to an isolated power supply with wide voltage input and constant voltage output. Background Technology

[0002] A switching power supply is a type of power supply that uses modern electronic power technology to control the on-time ratio of a switching transistor to maintain a stable output voltage. As a type of switching power supply, the single-ended flyback switching power supply (SEPIC, Single-Ended Primary Inductor Converter) is a common DC-DC converter topology, widely used in various electronic devices, especially in applications requiring isolation and voltage conversion. Its working principle is as follows: 1. On-state stage: When the switching transistor (such as a MOSFET) is turned on, the primary winding of the transformer begins to store energy. Due to the coupling effect of the transformer, the secondary winding has no energy output at this time, the rectifier diode is in reverse cutoff, and the load is powered by the output capacitor. 2. Off-state stage: When the switching transistor is turned off, the energy stored in the primary winding of the transformer is released through the secondary winding, rectified by the rectifier diode (VD) and filtered by the capacitor C before being output to the load. At this time, the output diode is turned on, and the transformer's energy supplies power to the load through the diode, while simultaneously charging the capacitor to compensate for previous energy losses.

[0003] The term "single-ended" refers to the fact that the magnetic core of a high-frequency transformer operates only on one side of the hysteresis loop.

[0004] The so-called reaction, such as Figure 1 As shown, when the switching transistor Q1 is turned on, the induced voltage in the primary coil of the high-frequency transformer L3 is positive at the top and negative at the bottom, and the rectifier diode D1 is in the off state, storing energy in the primary coil. When the switching transistor Q1 is turned off, the peak leakage inductance energy of the primary coil of transformer L3 is absorbed by R1 and C1 through D2. At the same time, the energy stored in the primary coil of transformer L3 is output to the load R2 after being rectified by D1 and filtered by capacitor C4 through the secondary coil.

[0005] As described above, this MOSFET also requires a driver IC. As shown in Figure 2, the input voltage charges C7 via R3 and R5, providing the startup voltage for the driver IC, i.e., chip U2. After the IC starts up, the power supply voltage is provided by the secondary winding of transformer L3. The switching frequency of the IC driving the MOSFET can be set via resistors R16 and C15, and the frequency is fixed after setting. Pin 1 of U2 uses the feedback signal of the secondary voltage and the feedback signal of the primary current to regulate the switching duty cycle of the MOSFET, preventing output overvoltage and overcurrent.

[0006] The secondary voltage feedback is as follows: Figure 3As shown, the secondary voltage VCC feeds the voltage signal back to the voltage reference chip D4 through resistors R6, R10, and R11. Then, D4 controls the linear optocoupler U1 to feed the output voltage signal back to pin 1 of chip U2.

[0007] However, the aforementioned prior art has the following drawbacks:

[0008] 1. By absorbing the energy of the peak leakage inductance through R1 and C1, the MOSFET is protected from overvoltage damage. However, the MOSFET will also absorb energy from the primary coil during the turn-off period, resulting in reduced efficiency.

[0009] 2. The driver chip U2 is powered through the secondary coil, which increases the size of the transformer and the cost;

[0010] 3. The switching frequency of a MOSFET cannot be changed. Under light load, this increases the switching losses of the MOSFET, resulting in reduced efficiency.

[0011] 4. External MOSFETs and primary-side current feedback increase the board area;

[0012] 5. The secondary voltage is fed back through optocouplers and 431, which increases the board area and also increases the cost of the components.

[0013] Therefore, a new technical solution is urgently needed to solve the above-mentioned technical problems. Utility Model Content

[0014] The purpose of this invention is to overcome the problems of the prior art and provide an isolated power supply with wide input voltage and constant output voltage. This solves the technical problems of existing single-ended flyback switching power supplies, such as complex structure, large board area, high cost, low power conversion efficiency, and high energy loss.

[0015] The above objectives are achieved through the following technical solutions:

[0016] An isolated power supply with wide input voltage and constant output voltage includes a switching power supply control chip and a transformer. The switching power supply control chip includes an enable / undervoltage lockout input pin, a ground pin, a feedback pin, a switching output pin, and a power input pin. The transformer has a primary side circuit and a secondary side circuit on its two sides. The primary side circuit includes a primary winding leakage inductance spike surge absorption circuit connected to the switching output pin, and the primary winding of the transformer connected in series with the primary winding leakage inductance spike surge absorption circuit. The secondary side circuit includes the secondary winding of the transformer and a power output circuit connected to the secondary winding. A first resistor and a second resistor are connected to the enable / undervoltage lockout input pin, and the first resistor is connected to the input voltage. The power input pin is connected to the input voltage. A third resistor and a fourth resistor are connected between the feedback pin and the switching output pin.

[0017] Furthermore, the primary winding leakage inductance spike surge absorption circuit includes a fourth diode and a second diode connected to each other.

[0018] Furthermore, the second diode is a transient voltage suppression diode, used to prevent voltage spikes.

[0019] Furthermore, the model number of the switching power supply control chip is JW3510SOTA#TRPBF.

[0020] Furthermore, the power output circuit includes a first power output circuit and a second power output circuit connected to the secondary winding, for realizing dual output terminals.

[0021] Furthermore, the first power output circuit includes a first diode connected to the secondary winding and a first power output terminal, and a fourth capacitor is connected in parallel to the first diode.

[0022] Furthermore, a fifth resistor is connected in parallel with the first diode.

[0023] Furthermore, the second power output circuit includes a third diode connected to the secondary winding and a second power output terminal, and a fifth capacitor is connected in parallel to the third diode.

[0024] Furthermore, a sixth resistor is connected in parallel with the third diode.

[0025] Furthermore, the power input pin is also connected to a first capacitor, a second capacitor, and a third capacitor.

[0026] This invention provides a wide-input, constant-output isolated power supply. By using a bidirectional TVS to absorb peak leakage inductance energy, losses are significantly reduced. Furthermore, measured results show that the bidirectional TVS provides better suppression of peak voltages than a unidirectional TVS. The switching power supply control chip uses primary-side voltage feedback, saving one set of transformer windings and a series of peripheral components such as feedback optocouplers, thus facilitating power module miniaturization. The chip also incorporates a MOSFET with an adjustable switching frequency, saving space and reducing switching losses. This isolated power supply is not only simple in structure, with fewer components, low cost, and minimal circuit board space requirements, but also convenient to control. Attached Figure Description

[0027] Figure 1 This is a circuit diagram showing the connection between the switching transistor and the transformer in a traditional isolated power supply.

[0028] Figure 2 This is a circuit diagram showing the connection between the switching power supply chip and the transformer in a traditional isolated power supply.

[0029] Figure 3This is a circuit diagram showing the connection between the secondary voltage and the switching power supply chip in a traditional isolated power supply.

[0030] Figure 4 This is a circuit diagram of an isolated power supply with wide input voltage and constant output voltage as described in this utility model. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. The described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0032] like Figure 4 As shown, this solution provides an isolated power supply with wide input voltage and constant output voltage, including a switching power supply control chip U1 and a transformer T1. The switching power supply control chip U1 includes an enable / undervoltage lockout input pin ENA / UVLO, a ground pin GND, a feedback pin RFB, a switch output pin SW, and a power input pin VIN. The transformer T1 has a primary side circuit and a secondary side circuit on its two sides, respectively.

[0033] The primary side circuit includes a primary winding leakage inductance spike surge absorption circuit connected to the switch output pin SW, and the primary winding Np of the transformer T1 connected in series with the primary winding leakage inductance spike surge absorption circuit.

[0034] The secondary side circuit includes the secondary winding Ns of the transformer T1, and a power output circuit connected to the secondary winding Ns.

[0035] The enable / undervoltage lockout input pin ENA / UVLO is connected to a first resistor R1 and a second resistor R2. The first resistor R1 is connected to the input voltage, and the voltage across the second resistor R2 is used as the soft-start voltage of the switching power supply control chip U1.

[0036] The power input pin VIN is connected to the input voltage;

[0037] A third resistor R3 and a fourth resistor R4 are connected between the feedback pin RFB and the switch output pin SW. The reflected voltage on the secondary side is collected through the third resistor R3 and the fourth resistor R4 to control the switching of the MOS inside the switching power supply control chip U1, thereby stabilizing the output voltage without the need for a third winding or optocoupler for feedback regulation.

[0038] The isolated power supply designed in this proposal is a single-ended flyback switching power supply with an input voltage of 12V to 30V, two stable voltage outputs, an output voltage of 9V, and an output current of 167mA, meaning that the power module supports a stable power output of 3W.

[0039] In this embodiment, the primary winding leakage inductance spike surge absorption circuit includes a fourth diode D4 and a second diode D2 connected to each other. Specifically, the leakage inductance spike energy passes through the fourth diode D4 and is absorbed by the second diode D2. After the leakage inductance energy is absorbed, the voltage reflected from the secondary side output voltage to the primary side is insufficient to break down the second diode D2, thus avoiding the energy loss stored in the primary winding Np when the internal MOSFET of the switching power supply control chip U1 is turned off.

[0040] The second diode D2 is a transient voltage suppressor diode (TVS) used to prevent voltage spikes.

[0041] The switching power supply control chip U1 described in this embodiment is model JW3510SOTA#TRPBF. It has high integration, a built-in 65V N-channel DMOS power switch, a peak current of 1.4A, and integrates soft-start, compensation circuitry, and multiple protection functions, such as short-circuit protection and over-temperature protection. This chip has a built-in switching MOS, with the switch output pin SW serving as the source of the MOS. The primary-side circuit consists of a transformer primary winding Np connected at one end to VCC and at the other end to the switch output pin SW. A diode + TVS structure is connected in parallel across the primary winding Np to absorb the surge caused by the leakage inductance of the primary winding Np when the MOS is turned off.

[0042] The chip's switching frequency is controllable, with three modes to handle different loads: critical mode for heavy loads with a fast switching frequency, intermittent mode for medium loads with a constant switching frequency but a different duty cycle, and burst mode for light loads with a reduced switching frequency.

[0043] like Figure 4 As shown, the power output circuit in this embodiment includes a first power output circuit and a second power output circuit connected to the secondary winding Ns, for realizing dual output terminals.

[0044] The first power output circuit includes a first diode D1 connected to the secondary winding Ns and a first power output terminal 9V-1. A fourth capacitor C4 is connected in parallel with the first diode D1 for filtering. A fifth resistor R5 is also connected in parallel with the first diode D1 for voltage regulation.

[0045] The second power output circuit includes a third diode D3 connected to the secondary winding Ns and a second power output terminal 9V-2. A fifth capacitor C5 is connected in parallel with the third diode D3 for filtering. A sixth resistor R6 is also connected in parallel with the third diode D3 for voltage regulation.

[0046] Specifically, in this embodiment, the first diode D1 and the third diode D3 are both secondary-side rectifier diodes, such as fast recovery diode FR107 or Schottky diode SS1060, located between the transformer secondary winding Ns and the power output terminals (9V-1 and 9V-2). They are used to convert the high-frequency AC pulses of the transformer secondary winding (generated by the primary-side switch action) into unidirectional pulsating DC, preventing the reverse voltage generated by the transformer leakage inductance, such as negative voltage spikes, from damaging subsequent circuits when the primary winding leakage inductance spike surge absorption circuit is turned off.

[0047] The fourth capacitor C4 and the fifth capacitor C5 are output filter capacitors connected in parallel between the power output terminals 9V-1 and 9V-2 and ground. They are used to absorb the pulsating current after rectification, convert the pulsating DC into a stable DC voltage, and filter out the high-frequency ripple generated by the reverse recovery of the diode and the switching action.

[0048] The fifth resistor R5 and the sixth resistor R6 are both dummy load resistors / bleeder resistors, connected across the power output terminals (9V-1 and 9V-2) and ground. They provide a minimum current path when the load is disconnected, preventing the output voltage from rising uncontrollably due to no-load conditions. When the power is off, they accelerate the discharge of the fourth capacitor C4 and the fifth capacitor C5, preventing residual voltage from posing a risk to equipment or personnel.

[0049] As an optimization of this solution, the power input pin VIN is also connected to a first capacitor C1, a second capacitor C2, and a third capacitor C3, wherein:

[0050] The first capacitor C1 is a high-capacity electrolytic capacitor, such as 47μF / 50V; it is used to absorb low-frequency fluctuations at the power input, such as surge currents during power-on or voltage drops caused by sudden load changes; and to smooth long-cycle fluctuations from external power sources, such as 24V DC input. Through its high capacitance, the electrolytic capacitor stores energy when the switching transistor is on and releases energy when the input voltage drops instantaneously, thus maintaining a stable input voltage.

[0051] The second capacitor C2 is a medium-capacity surface-mount capacitor, such as a 10μF / 25V MLCC or a tantalum capacitor; it is used to suppress mid-frequency noise (10kHz~1MHz) caused by internal switching operations of the chip (such as PWM frequency and its harmonics), and to quickly respond to instantaneous changes in load current (such as a sudden increase in current demand during chip startup). It utilizes its low equivalent series resistance (ESR) characteristic for rapid charging and discharging, compensating for the insufficient performance of the first capacitor C1 in the high-frequency range.

[0052] The third capacitor C3 is a small-capacity ceramic capacitor, such as 0.1μF / 50V; it is used to filter out high-frequency spike noise generated by the operation of the switching transistor (such as ringing noise during MOSFET switching, frequency band >1MHz), and to provide the shortest high-frequency current loop for the switching power supply control chip U1, preventing noise from radiating through the power line. The extremely low equivalent series inductance (ESL) characteristic of the ceramic capacitor makes it present extremely low impedance to high-frequency interference, forming a "high-frequency ground" path.

[0053] The above description is only for illustrating the embodiments of this utility model and is not intended to limit this utility model. For those skilled in the art, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A wide-voltage input, constant-voltage output isolated power supply, characterized in that, The power supply includes a switching power supply control chip (U1) and a transformer (T1). The switching power supply control chip (U1) includes an enable / undervoltage lockout input pin (ENA / UVLO), a ground pin (GND), a feedback pin (RFB), a switch output pin (SW), and a power input pin (VIN). The transformer (T1) has a primary side circuit and a secondary side circuit on its two sides, respectively. The primary side circuit includes a primary winding leakage inductance spike surge absorption circuit connected to the switch output pin (SW), and the primary winding (Np) of the transformer (T1) connected in series with the primary winding leakage inductance spike surge absorption circuit. The secondary side circuit includes the secondary winding (Ns) of the transformer (T1) and a power output circuit connected to the secondary winding (Ns). The enable / undervoltage lockout input pin (ENA / UVLO) is connected to a first resistor (R1) and a second resistor (R2), and is connected to the input voltage through the first resistor (R1). The power input pin (VIN) is connected to the input voltage; A third resistor (R3) and a fourth resistor (R4) are connected between the feedback pin (RFB) and the switch output pin (SW).

2. The isolated power supply with wide input voltage and constant output voltage according to claim 1, characterized in that, The primary winding leakage inductance spike surge absorption circuit includes a fourth diode (D4) and a second diode (D2) connected to each other.

3. The isolated power supply with wide input voltage and constant output voltage according to claim 2, characterized in that, The second diode (D2) is a transient voltage suppressor diode (TVS) used to prevent voltage spikes.

4. The isolated power supply with wide input voltage and constant output voltage according to claim 1, characterized in that, The switching power supply control chip (U1) is model JW3510SOTA#TRPBF.

5. The isolated power supply with wide input voltage and constant output voltage according to claim 1, characterized in that, The power output circuit includes a first power output circuit and a second power output circuit connected to the secondary winding (Ns) to achieve dual output terminals.

6. The isolated power supply with wide input voltage and constant output voltage according to claim 5, characterized in that, The first power output circuit includes a first diode (D1) connected to the secondary winding (Ns) and a first power output terminal (9V-1). A fourth capacitor (C4) is also connected in parallel to the first diode (D1).

7. The isolated power supply with wide input voltage and constant output voltage according to claim 6, characterized in that, A fifth resistor (R5) is also connected in parallel with the first diode (D1).

8. The isolated power supply with wide input voltage and constant output voltage according to claim 5, characterized in that, The second power output circuit includes a third diode (D3) connected to the secondary winding (Ns) and a second power output terminal (9V-2). A fifth capacitor (C5) is also connected in parallel to the third diode (D3).

9. The isolated power supply with wide input voltage and constant output voltage according to claim 8, characterized in that, A sixth resistor (R6) is also connected in parallel with the third diode (D3).

10. The isolated power supply with wide input voltage and constant output voltage according to claim 1, characterized in that, The power input pin (VIN) is also connected to a first capacitor (C1), a second capacitor (C2), and a third capacitor (C3).

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