An LLC resonant half-bridge frequency regulation circuit

Abstract

The utility model discloses a LLC resonant half bridge frequency regulation circuit, it includes: transformer unit, the transformer unit includes: main winding N2 for energy transmission, auxiliary winding N1 is coupled with main winding, and is selectively accessed or disconnected through switch module, switch control module, the switch control module includes: relay JK1, this kind of LLC resonant half bridge frequency regulation circuit, has added a group N1 winding, through singlechip detection and control relay K1, whether N1 winding participates the work to change the turns ratio of transformer, realizes the regulation of LLC power switch frequency, makes the switch frequency of charger no matter when high voltage and low voltage of output voltage, all keep with the frequency similar when design, will not increase too much, has restrained the difficulty of EM I rectification that the frequency of rise leads to in low voltage charging, has improved the efficiency of charger in low output voltage section simultaneously.

Description

Technical Field

[0001] This utility model relates to the field of adjustment circuit technology, specifically an LLC resonant half-bridge frequency adjustment circuit. Background Technology

[0002] The lithium batteries or accumulators we use in daily life do not have a constant voltage. As the load discharges, the battery voltage gradually decreases until the stored energy is depleted or the battery enters an undervoltage protection state. This results in a significant voltage difference between a low-charge and fully charged battery. When designing LLC resonant transformers, we typically design parameters such as the turns ratio and inductance based on the highest output voltage and maximum load conditions (turns ratio defined as the ratio of the number of primary turns to the number of secondary turns). The switching frequency under the highest output voltage and maximum load conditions is our initial design frequency. As the charger's output voltage decreases, the LLC switching frequency tends to increase. The LLC switching frequency may differ by approximately 100% between the highest and lowest battery charging voltage. For example, a switching frequency designed at 80kHz at the highest voltage point might reach 160kHz at the lowest voltage point.

[0003] Thus, during low-voltage charging, the increased switching frequency will make EMI more severe, making EMI rectification a significant challenge. At the same time, the increased switching frequency will increase the switching losses of the LLC drive MOSFET, thereby affecting the charger's output efficiency.

[0004] In existing technologies, the fundamental reason for the increased frequency is that the change in output voltage during charging alters the equivalent turns ratio (equivalent turns ratio equals half the input bus voltage divided by the output voltage). However, the turns ratio is fixed in transformer design (designed based on the highest output voltage). When the output voltage decreases, a larger turns ratio is required to maintain a constant switching frequency. Because the transformer's turns ratio is fixed, it will be lower than the required equivalent turns ratio. This reduces the LLC's voltage gain and the load's equivalent impedance, forcing the LLC circuit to increase its switching frequency to stabilize the output voltage. Utility Model Content

[0005] The purpose of this section is to outline some aspects of the embodiments of this utility model and to briefly introduce some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be used to limit the scope of this utility model.

[0006] 1. Technical problems to be solved:

[0007] To address the issue that the root cause of the increased frequency is the change in equivalent turns ratio (equivalent turns ratio equal to half the input bus voltage divided by the output voltage) during charging, and the fact that the transformer's turns ratio is fixed (designed based on the highest output voltage), a larger turns ratio is needed to maintain a constant switching frequency when the output voltage decreases. Since the transformer's turns ratio is fixed, it will be lower than the required equivalent turns ratio. This reduces the LLC's voltage gain and the load's equivalent impedance, forcing the LLC circuit to increase its switching frequency to stabilize the output voltage. This invention addresses this problem.

[0008] Therefore, the purpose of this utility model is to provide an LLC resonant half-bridge frequency adjustment circuit, which adds an additional N1 winding. By using a microcontroller to detect and control relay K1, the N1 winding is controlled to determine whether it is engaged, thereby changing the turns ratio of the transformer and adjusting the switching frequency of the LLC power supply. This ensures that the switching frequency of the charger remains close to the designed frequency regardless of whether the output voltage is high or low, without increasing too much. This reduces the difficulty of EMI rectification caused by frequency increases during low-voltage charging and improves the efficiency of the charger in the low output voltage range.

[0009] 2. Technical Solution:

[0010] To solve the above-mentioned technical problems, according to one aspect of the present invention, the present invention provides the following technical solution:

[0011] An LLC resonant half-bridge frequency adjustment circuit includes:

[0012] Transformer unit, the transformer unit comprising:

[0013] The main winding N2 is used for energy transfer;

[0014] The auxiliary winding N1 is coupled to the main winding and can be selectively connected or disconnected via a switching module.

[0015] The switch control module includes:

[0016] Relay JK1, whose contacts are connected in series in the power supply circuit of the auxiliary winding N1, is normally in a closed state;

[0017] The driving circuit, including optocoupler U3 and switching transistor Q9, is used to receive control signals and drive the relay JK1 to operate;

[0018] The voltage detection module is used to acquire the charger's output voltage in real time and output a voltage feedback signal;

[0019] The control unit is electrically connected to the voltage detection module and the switch control module. It generates control commands based on the feedback signal and dynamically adjusts the connection state of the auxiliary winding N1 to change the equivalent turns ratio of the transformer.

[0020] In a preferred embodiment of the LLC resonant half-bridge frequency adjustment circuit of this utility model, the control unit is a single-chip microcomputer (MCU) with a built-in preset voltage threshold. When the output voltage is detected to be lower than the threshold, a high-level signal is output to drive the optocoupler U3 to conduct, causing the relay JK1 to engage and disconnecting the auxiliary winding N1. When the output voltage is higher than the threshold, a low-level signal is output, the relay JK1 is released, and the auxiliary winding N1 is connected to the circuit.

[0021] As a preferred embodiment of the LLC resonant half-bridge frequency adjustment circuit of this utility model, the driving circuit further includes a voltage divider resistor network R87 and R88, which are connected between the IO port of the microcontroller and the input terminal of the optocoupler U3, and are used to adjust the driving current.

[0022] The driving circuit further includes a freewheeling diode D1, which is connected in parallel across the coil of the relay JK1 to suppress the reverse electromotive force generated when the coil is disconnected.

[0023] In a preferred embodiment of the LLC resonant half-bridge frequency adjustment circuit of this utility model, the number of turns of the auxiliary winding N1 accounts for 5%-30% of the number of turns of the main winding N2;

[0024] The switching module also includes a filter capacitor C1, which is connected between the output terminal of the voltage detection module and ground, and is used to filter out high-frequency noise.

[0025] As a preferred embodiment of the LLC resonant half-bridge frequency adjustment circuit of this utility model, the number of turns of the auxiliary winding N1 accounts for 10% of the number of turns of the main winding N2.

[0026] As a preferred embodiment of the LLC resonant half-bridge frequency adjustment circuit of this utility model, the switching transistor Q9 is an NPN transistor, the base is connected to the output terminal of the optocoupler U3 through the current limiting resistor R78, the collector is connected to the positive terminal of the coil of the relay JK1, and the emitter is grounded.

[0027] The negative terminal of the coil of relay JK1 is connected to a 12V auxiliary power supply 12V2, and a reverse diode D1 is connected in parallel across the two ends of the contacts to prevent the back electromotive force of the coil from damaging the switching transistor.

[0028] 3. Beneficial effects:

[0029] Compared with the prior art, the beneficial effects of this utility model are:

[0030] This LLC resonant half-bridge frequency adjustment circuit adds an extra set of N1 windings. The microcontroller detects and controls relay K1 to determine whether the N1 windings are engaged, thereby changing the transformer turns ratio and adjusting the LLC power supply switching frequency. This ensures that the charger's switching frequency remains close to the design frequency regardless of whether the output voltage is high or low, without increasing too much. This reduces the difficulty of EMI rectification caused by frequency increases during low-voltage charging and improves the charger's efficiency in the low output voltage range. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of this utility model, the present utility model will be described in detail below with reference to the accompanying drawings and detailed embodiments. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Among them:

[0032] Figure 1 This is a schematic diagram of an LLC resonant half-bridge frequency adjustment circuit according to the present invention. Detailed Implementation

[0033] To make the above-mentioned objectives, features and advantages of this utility model more apparent and understandable, the specific embodiments of this utility model will be described in detail below with reference to the accompanying drawings.

[0034] This utility model is described in detail with reference to the schematic diagrams. When describing the embodiments of this utility model, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not adhering to the usual scale. Furthermore, the schematic diagrams are merely examples and should not be construed as limiting the scope of protection of this utility model. In actual manufacturing, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0035] The orientation or positional relationship indicated in the terminology is based on the orientation or positional relationship shown in the accompanying drawings and is only for the convenience of describing the present invention and simplifying the description. It is not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0036] The term "connection method" should be interpreted broadly. For example, "connection" 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 a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0037] The embodiments of this utility model will now be described in further detail with reference to the accompanying drawings.

[0038] This utility model provides an overall structural schematic diagram of an embodiment of an LLC resonant half-bridge frequency adjustment circuit, including:

[0039] Please see Figure 1 This embodiment of an LLC resonant half-bridge frequency adjustment circuit includes:

[0040] Transformer unit, the transformer unit comprising:

[0041] The main winding N2 is used for energy transfer;

[0042] The auxiliary winding N1 is coupled to the main winding and can be selectively connected or disconnected via a switching module.

[0043] The switch control module includes:

[0044] Relay JK1, whose contacts are connected in series in the power supply circuit of the auxiliary winding N1, is normally in a closed state;

[0045] The driving circuit, including optocoupler U3 and switching transistor Q9, is used to receive control signals and drive the relay JK1 to operate;

[0046] The voltage detection module is used to acquire the charger's output voltage in real time and output a voltage feedback signal;

[0047] The control unit is electrically connected to the voltage detection module and the switch control module. It generates control commands based on the feedback signal and dynamically adjusts the connection state of the auxiliary winding N1 to change the equivalent turns ratio of the transformer.

[0048] It is worth noting that the control unit is a single-chip microcomputer (MCU) with a built-in preset voltage threshold. When the output voltage is detected to be lower than the threshold, a high-level signal is output to drive the optocoupler U3 to conduct, causing the relay JK1 to engage and disconnecting the auxiliary winding N1. When the output voltage is higher than the threshold, a low-level signal is output, the relay JK1 is released, and the auxiliary winding N1 is connected to the circuit.

[0049] Next, the driving circuit also includes a voltage divider resistor network R87 and R88, which are connected between the I / O port of the microcontroller and the input terminal of the optocoupler U3, and are used to adjust the driving current.

[0050] The driving circuit further includes a freewheeling diode D1, which is connected in parallel across the coil of the relay JK1 to suppress the reverse electromotive force generated when the coil is disconnected.

[0051] Meanwhile, the number of turns of the auxiliary winding N1 accounts for 5%-30% of the number of turns of the main winding N2; more specifically, the number of turns of the auxiliary winding N1 accounts for 10% of the number of turns of the main winding N2.

[0052] The switching module also includes a filter capacitor C1, which is connected between the output terminal of the voltage detection module and ground, and is used to filter out high-frequency noise.

[0053] Furthermore, the switching transistor Q9 is an NPN transistor, with its base connected to the output terminal of the optocoupler U3 through a current-limiting resistor R78, its collector connected to the positive terminal of the coil of the relay JK1, and its emitter grounded.

[0054] The negative terminal of the coil of relay JK1 is connected to a 12V auxiliary power supply 12V2, and a reverse diode D1 is connected in parallel across the two ends of the contacts to prevent the back electromotive force of the coil from damaging the switching transistor.

[0055] In addition, the circuits, electronic components and modules involved in this utility model are all existing technologies, which can be fully implemented by those skilled in the art, and need not be elaborated upon. The content protected by this utility model does not involve any improvement to the internal structure and method.

[0056] Combination Figure 1 The specific usage process of an LLC resonant half-bridge frequency adjustment circuit in this embodiment is as follows:

[0057] 1. The switching frequency adjustment circuit mainly consists of: a primary LLC resonant half-bridge management chip U1 and a frequency adjustment control circuit; the frequency adjustment control circuit includes: a microcontroller detection circuit, an optocoupler isolation drive circuit, a relay (normally closed contacts), and a transformer;

[0058] 2. When the charger is powered on, the microcontroller will detect the output voltage. The design defines the voltage point at which frequency adjustment begins. When the microcontroller detects that the output charging voltage is lower than the set voltage, the microcontroller's IO control port will output a high level. After voltage division by resistors R87 and R88, it drives the LED in optocoupler U3, causing the phototransistor in U3 to conduct. The 12V2 voltage is then supplied to the transistor Q9 through R78 to provide a positive drive current. Transistor Q9 conducts and relay JK1 operates. At this time, the contacts of pins 3 and 4 of the relay are disconnected, and the N1 winding of transformer T1 participates in the operation. At this time, the number of primary turns of the transformer increases, which increases the turns ratio of the transformer and reduces the switching frequency of the charger, making it close to the designed frequency.

[0059] 3. When the microcontroller detects that the output charging voltage is higher than the set voltage, the microcontroller's IO control port will output a low level, the optocoupler will not work, the relay will not work, and the contacts of the relay will be normally closed when it is not working. In this way, the N1 winding is short-circuited (does not participate in the work), the number of turns of the primary winding will be reduced, and the turns ratio will be reduced accordingly. At this time, the charging voltage is close to the design maximum voltage, and the operating frequency is close to the design switching frequency.

[0060] 4. By controlling the opening and closing of relay contacts through a microcontroller, the N1 winding of the transformer is controlled to determine when it engages in operation, thereby controlling the turns ratio of the transformer. This ensures that the frequency of the LLC circuit charger remains similar throughout the entire charging voltage phase, preventing excessive frequency changes during low-voltage charging that could increase the difficulty of EMI rectification. It also improves the overall efficiency of the charger throughout the entire charging process.

[0061] Although the present invention has been described above with reference to embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of the present invention. In particular, as long as there is no structural conflict, the features in the embodiments disclosed in this invention can be combined with each other in any way. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. An LLC resonant half-bridge frequency adjustment circuit, comprising: Transformer unit, the transformer unit comprising: The main winding (N2) is used for energy transfer; An auxiliary winding (N1) is coupled to the main winding and can be selectively connected or disconnected via a switching module. The switch control module includes: The relay (JK1) has its contacts connected in series in the power supply circuit of the auxiliary winding (N1), and is normally in a closed state; The driving circuit, including an optocoupler (U3) and a switching transistor (Q9), is used to receive control signals and drive the relay (JK1) to operate. The voltage detection module is used to acquire the charger's output voltage in real time and output a voltage feedback signal; The control unit is electrically connected to the voltage detection module and the switch control module. It generates control commands based on the feedback signal and dynamically adjusts the connection state of the auxiliary winding (N1) to change the equivalent turns ratio of the transformer.

2. The LLC resonant half-bridge frequency adjustment circuit according to claim 1, characterized in that, The control unit is a microcontroller with a built-in preset voltage threshold. When the output voltage is detected to be lower than the threshold, a high-level signal is output to drive the optocoupler (U3) to conduct, causing the relay (JK1) to engage and disconnecting the auxiliary winding (N1). When the output voltage is higher than the threshold, a low-level signal is output, the relay (JK1) is released, and the auxiliary winding (N1) is connected to the circuit.

3. The LLC resonant half-bridge frequency adjustment circuit according to claim 2, characterized in that, The driving circuit also includes a voltage divider resistor network (R87, R88), connected between the I / O port of the microcontroller and the input terminal of the optocoupler (U3), for adjusting the driving current. The driving circuit further includes a freewheeling diode (D1) connected in parallel across the coil of the relay (JK1) to suppress the reverse electromotive force generated when the coil is disconnected.

4. The LLC resonant half-bridge frequency adjustment circuit according to claim 3, characterized in that, The number of turns in the auxiliary winding (N1) accounts for 5%-30% of the number of turns in the main winding (N2); The switching module also includes a filter capacitor (C1), which is connected between the output terminal of the voltage detection module and ground to filter out high-frequency noise.

5. The LLC resonant half-bridge frequency adjustment circuit according to claim 4, characterized in that, Furthermore, the number of turns of the auxiliary winding (N1) accounts for 10% of the number of turns of the main winding (N2).

6. The LLC resonant half-bridge frequency adjustment circuit according to claim 4, characterized in that, The switching transistor (Q9) is an NPN transistor. Its base is connected to the output terminal of the optocoupler (U3) through a current-limiting resistor (R78), its collector is connected to the positive terminal of the relay coil (JK1), and its emitter is grounded. The negative terminal of the relay (JK1) coil is connected to a 12V auxiliary power supply (12V2), and a reverse diode (D1) is connected in parallel across the two ends of the contacts to prevent the back electromotive force of the coil from damaging the switching transistor.

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