Auxiliary power supply control chip

Abstract

The utility model provides an auxiliary power supply control chip which comprises a power tube drain electrode pin, an enabling pin, a reference voltage source pin, a switching voltage source pin, a feedback voltage source pin, a power supply ground pin, a flyback power supply control circuit, a high-order linear voltage stabilizing circuit, a low-order linear voltage stabilizing circuit, an enabling selection circuit, a power tube and a diode. And when the MCU of the BMS enters a dormant state, the MCU is powered by the double-order linear voltage stabilizing circuit. When the control unit MCU exits the dormant state and starts to detect, a feedback voltage source VO1 generated by the switching power supply supplies power to the control unit MCU, the generated feedback voltage source VO1 supplies power to the driving circuit, and a generated isolation voltage source VO3 supplies power to the isolation communication chip. According to the utility model, non-isolated and isolated multi-path power supplies necessary for the BMS are realized through one control chip, the number of peripheral devices is very small, the reliability is improved, and the cost is reduced at the same time.

Description

Technical Field

[0001] The utility model relates to the technical field of auxiliary power supplies, and particularly relates to an auxiliary power supply control chip. Background Art

[0002] With the rapid development of new energy, batteries are more and more widely used. In order to ensure the reliable operation of the battery, a battery management system (Battery Management System, abbreviated as BMS) must be used to manage the battery. The BMS usually has the function of measuring the battery voltage, and preventing or avoiding abnormal conditions such as over-discharge, over-charge, and over-temperature of the battery. With the continuous development of battery technology and applications, there are more and more new function requirements for the battery. For example, shared tools such as shared electric vehicles often need to add GPS functions. These detection and execution components generally cannot directly draw power from the battery terminal, and an auxiliary power supply must be used to meet the power consumption requirements of various functional components.

[0003] As Figure 1 shown, it is a common BMS auxiliary power supply architecture, which consists of three power supplies. The first is a BUCK step-down switching power supply, the second is a linear voltage regulator, and the third is a micro-power isolated power supply. Since the charging state of the battery is different, a battery pack is composed of single batteries in series with different numbers of cells, so the input voltage VIN has a wide range. Therefore, a non-isolated BUCK step-down switching power supply is first used to convert the wide-range VIN voltage into a stable output voltage VO1, which can supply power to the drive circuit, generally about 12V. The working voltage of the microcontroller unit MCU (Micro controller Unit) is generally about 3.3V or 5.0V, and a high-quality voltage source with low noise is required. Therefore, a linear voltage regulator is used to step down VO1 to generate a stable VO2 to supply power to the MCU, or to supply power to the micro-power isolated power supply at the same time. The micro-power isolated power supply consists of an isolated transformer drive chip, an isolated transformer T1, rectifier diodes D1 and D2, and an output capacitor C3. Figure 1 The micro-power isolated power supply shown in Figure 2 uses VO2 as the input voltage because the micro-power isolated power supply with low-voltage input has lower cost. Of course, VO1 can also be used as the input voltage, as

[0004] shown. Since the current drawn does not pass through the linear voltage regulator, it has higher efficiency, but the cost will increase. The voltage VO3 generated by the micro-power isolated power supply supplies power to the isolation chip. In the BMS, isolated sampling data is often required, so the power supply for the sampling chip is also electrically isolated accordingly.

[0004] The disadvantages of the existing BMS auxiliary power supply scheme are:

[0005] 1. Complex structure and large number of components: Three chips and two magnetic components are required. The increase in the number of components means a rapid increase in the failure rate and also high costs.

[0006] 2. High standby power consumption: After the battery is produced until it is actually used, if the circuit of the battery management system continuously consumes the battery and causes the battery voltage to drop too low, the battery will fail. For packaged batteries, it is not convenient to frequently detect the power and charge. Especially for batteries transported over long distances, it is even more difficult to maintain. Therefore, standby power consumption is a key indicator of the BMS. In the existing technology solutions, the BUCK buck switching power supply and the linear voltage regulator have to keep working to ensure that the MCU always has power and cannot enter the deep sleep state to save power. If you want to turn off the BUCK switching power supply, you must additionally add a high-voltage linear voltage regulator to draw power from VIN to supply power to the MCU, further increasing costs and complexity. Summary of the Invention

[0007] The purpose of the present invention is to provide an auxiliary power control chip, which is applied to the BMS and can solve the problems of high costs caused by a large number of components and high standby power consumption in the existing technology.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] An auxiliary power control chip includes a power transistor drain pin DRN, an enable pin EN, a reference voltage source pin VREF, a transfer voltage source pin VDD, a feedback voltage source pin VFB, a power ground pin GND, a flyback power control circuit 101, a high-order linear voltage regulator circuit 102, a low-order linear voltage regulator circuit 103, an enable selection circuit 104, a power transistor NM0, and a diode D3; the input end of the high-order linear voltage regulator circuit 102 is connected to the power transistor drain pin DRN, and the output end is respectively connected to the input end of the low-order linear voltage regulator circuit 103 and the transfer voltage source pin VDD; the output end of the low-order linear voltage regulator circuit 103 is connected to the reference voltage source pin VREF; the input end of the enable selection circuit 104 is connected to the enable pin EN, and the output end outputs a first control signal ON / OFF to the flyback power control circuit 101; the power supply end of the flyback power control circuit 101 is connected to the feedback voltage source pin VFB, the first control end is connected to the gate of the power transistor NM0, and the second control end is connected to the high-order linear voltage regulator circuit 102; the drain of the power transistor NM0 is connected to the power transistor drain pin DRN, and the source is connected to the power ground pin GND; the anode of the diode D3 is connected to the feedback voltage source pin VFB, and the cathode is connected to the transfer voltage source pin VDD.

[0010] Further, the auxiliary power control chip further includes an input pin VIN, and the input end of the high-order linear voltage regulator circuit 102 is connected to the input pin VIN.

[0011] Further, the diode D3 is built inside the auxiliary power supply control chip or outside the auxiliary power supply control chip.

[0012] Further, the peripheral circuit of the auxiliary power supply control chip includes a first capacitor C1, a second capacitor C2, a fourth capacitor C4, a transformer T2, a control unit MCU of the BMS, and a drive circuit of the BMS; the first capacitor C1 is connected between the feedback voltage source pin VFB and the ground; the second capacitor C2 is connected between the reference voltage source pin VREF and the ground; the fourth capacitor is connected between the transfer voltage source pin VDD and the ground; the power supply terminal of the control unit MCU is connected to the reference voltage source pin VREF; the power supply terminal of the drive circuit is connected to the feedback voltage source pin VFB.

[0013] Further, the high-order linear voltage regulation circuit 102 steps down the input voltage V with a wide input range IN to generate a transfer voltage source VO4, which is output from the transfer voltage source pin VDD to provide a power supply terminal for transfer; the low-order linear voltage regulation circuit 103 further reduces the transfer voltage source VO4 of the VDD pin to generate a reference voltage source VO2, which is output from the reference voltage source pin VREF to supply power to the control unit MCU of the BMS;

[0014] When the flyback power supply control circuit 101 controls the power transistor NM0 to conduct, the transformer T2 stores energy through the primary winding excitation; when the power transistor NM0 is turned off, the transformer T2 demagnetizes and releases energy through the secondary winding and the auxiliary winding. Therefore, by controlling the on and off of the power transistor NM0, the input voltage V IN is transferred to the first capacitor C1 to generate a feedback voltage source VO1, and transferred to the third capacitor C3 to generate an isolated voltage source VO3; the feedback voltage source VO1 supplies power to the drive circuit of the BMS; the isolated voltage source VO3 supplies power to the isolated communication chip of the BMS.

[0015] Further, after the control unit MCU enters the sleep state, the control unit MCU outputs a low level to the enable pin EN, and the enable selection circuit 104 outputs a first control signal to turn off the flyback power supply control circuit 101. Furthermore, the flyback power supply control circuit 101 outputs a second control signal to turn on the high-order linear voltage regulation circuit 102, and supplies power to the control unit MCU through the dual-stage linear voltage regulation circuit. The feedback voltage source VO1 and the isolated voltage source VO3 drop to zero;

[0016] When the control unit MCU exits the sleep state and starts the detection work, the control unit MCU outputs a high level to the enable pin EN. The enable selection circuit 104 outputs a first control signal to turn on the flyback power control circuit 101. Further, the flyback power control circuit 101 outputs a second control signal to block the high-order linear voltage regulator circuit 102. The feedback voltage source VO1 generated by the switching power supply powers the control unit MCU. At the same time, the generated feedback voltage source VO1 powers the drive circuit, and the generated isolated voltage source VO3 powers the isolated communication chip.

[0017] The auxiliary power control chip of the present utility model applied to the BMS turns off the flyback switching power supply to reduce losses when the MCU enters the sleep state. The input power supply V IN Supplies power to the MCU through a dual-stage linear voltage regulator circuit. As is well known, the power consumption of the linear voltage regulator circuit can easily be made within 20 μA. If the semiconductor process can provide high-voltage depletion MOSFETs or JFETs, it can even be as low as 1 μA, greatly increasing the standby time of the battery. When the battery is in the charging or discharging state, it is necessary to comprehensively manage and detect the state of the battery. Each link, including the MCU, consumes a large amount of electricity. The switching power supply is started to generate multiple auxiliary power supplies to supply power to each power-consuming link, improving the energy conversion efficiency and avoiding excessive heating of the battery pack. One chip realizes the non-isolated and isolated multiple power supplies necessary for the BMS, with very few peripheral devices, improving reliability and reducing costs at the same time. Brief Description of the Drawings

[0018] Figure 1 Is one of the prior art BMS auxiliary power supply solutions;

[0019] Figure 2 Is the second of the prior art BMS auxiliary power supply solutions;

[0020] Figure 3 Is one of the embodiments of the BMS auxiliary power control chip of the present utility model and its peripheral circuit;

[0021] Figure 4 Is the second of the embodiments of the BMS auxiliary power control chip of the present utility model and its peripheral circuit. Detailed Embodiment

[0022] The following describes the embodiments of the present disclosure in detail with reference to the drawings.

[0023] The following describes the embodiments of the present disclosure through specific examples. Those skilled in the art can easily understand the other advantages and effects of the present disclosure from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all the embodiments. The present disclosure can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present disclosure. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present disclosure without creative efforts belong to the scope of protection of the present disclosure. In the description of this application document, the positive input terminal of the comparator is connected to the reference voltage, and the negative input terminal is connected to the voltage detection terminal. Of course, it can also be connected in the reverse way, as long as the output of the comparator is in reverse logic, which does not affect the normal function. In addition, the NMOS transistor can also be replaced by an NPN transistor. It should be understood that when an element described in the present invention "connects" to another element, it can be directly connected or coupled to the other element or there may be an intermediate element. Such simple logic reversal and device replacement, or simple changes in the circuit structure connection relationship without departing from the purpose of the present invention, cannot be used to avoid the present invention.

[0024] To solve the shortcomings of the BMS auxiliary power supply in the prior art, the present invention proposes an auxiliary power supply control chip, which is applied to the BMS, as Figure 3 shown by the thick solid line frame 10 in Figure 3Meanwhile, it is also shown that the dedicated chip 10 and the peripheral circuit form an overall application solution. The auxiliary power supply control chip 10 applied to the BMS includes an input pin VIN, a power transistor drain pin DRN, an enable pin EN, a reference voltage source pin VREF, a transfer voltage source pin VDD, a feedback voltage source pin VFB, and a power ground pin GND. Inside the chip, there are: a flyback power supply control circuit 101, a high-order linear voltage regulation circuit 102, a low-order linear voltage regulation circuit 103, an enable selection circuit 104, a power transistor NM0, and a diode D3. These circuits are implemented in a single-crystal form of a chip through semiconductor processes on the same wafer. It is also possible to implement the circuits except for the power transistor NM0 on the same wafer and then bond them with the single-body power transistor NMO in the same plastic package through a multi-lead packaging process to form a polycrystalline form of the chip. The input end of the high-order linear voltage regulation circuit 102 is connected to the input pin VIN, and the output end is respectively connected to the input end of the low-order linear voltage regulation circuit 103 and the transfer voltage source pin VDD. The output end of the low-order linear voltage regulation circuit 103 is connected to the reference voltage source pin VREF. The input end of the enable selection circuit 104 is connected to the enable pin EN, and the output end outputs a first control signal ON / OFF to the flyback power supply control circuit 101. The power supply end of the flyback power supply control circuit 101 is connected to the feedback voltage source pin VFB, the first control end is connected to the gate of the power transistor NM0, and the second control end is connected to the high-order linear voltage regulation circuit 102. The drain of the power transistor NM0 is connected to the power transistor drain pin DRN, and the source is connected to the power ground pin GND. The anode of the diode D3 is connected to the feedback voltage source pin VFB, and the cathode is connected to the transfer voltage source pin VDD.

[0025] The peripheral circuit of the auxiliary power supply control chip includes: a first capacitor C1, a second capacitor C2, a fourth capacitor C4, a transformer T2, a control unit MCU of the BMS, and a drive circuit of the BMS. The first capacitor C1 is connected between the feedback voltage source pin VFB and the ground. The second capacitor C2 is connected between the reference voltage source pin VREF and the ground. The fourth capacitor is connected between the transfer voltage source pin VDD and the ground. The power supply end of the control unit MCU is connected to the reference voltage source pin VREF. The power supply end of the drive circuit is connected to the feedback voltage source pin VFB.

[0026] Combined with Figure 3 The working principle of the auxiliary power supply control chip of the present invention and its peripheral circuit will be described:

[0027] The high-order linear voltage regulation circuit 102 regulates the voltage V with a wide input range INThe step-down converter generates a transfer voltage source VO4, which is output from the transfer voltage source pin VDD. The low-order linear voltage regulator circuit 103 further reduces the transfer voltage source VO4 of the VDD pin to generate a reference voltage source VO2, which is output from the reference voltage source pin VREF. In this way, the double-stage linear voltage regulator circuit formed by the series connection of the high-order linear voltage regulator circuit 102 and the low-order linear voltage regulator circuit 103 reduces the input voltage V IN Step down to generate a stable reference voltage source VO2, which supplies power to the MCU in the BMS. Generally, it is about 3.3V or 5.0V, and the specific value depends on the model of the MCU. The series intermediate link forms a transfer voltage source VO4 for some special uses of users.

[0028] The flyback power control circuit 101 and the power transistor NM0 form the control unit of the flyback switching power supply. When the flyback power control circuit 101 controls the power transistor NM0 to conduct, the transformer T2 stores energy through the primary winding NP. When the power transistor NM0 is turned off, the transformer T2 demagnetizes and releases energy through the secondary winding NS and the auxiliary winding NA. Therefore, by controlling the turn-on and turn-off of the power transistor NM0, energy can be transferred from the input terminal V IN To the capacitors C1 and C3 to generate a feedback voltage source VO1 and an isolated voltage source VO3. By controlling the ratio of the on-time of the power transistor to the switching period, that is, the duty cycle, the voltages of the feedback voltage source VO1 and the isolated voltage source VO3 can also be stabilized at the set values. When the voltage at the VFB pin is lower than the set value, the flyback power control circuit 101 outputs a pulse width with a larger duty cycle, increasing the ratio of the conduction time of the power transistor NM0 to the switching period. Then, the energy transferred by the flyback transformer T2 increases, causing the feedback voltage source VO1 at the VFB pin to rise. Conversely, when the voltage at the VFB pin is higher than the set value, the flyback power control circuit 101 outputs a pulse width with a smaller duty cycle, making the ratio of the conduction time of the power transistor NM0 to the switching period smaller. Then, the energy transferred by the flyback transformer T2 is smaller, causing the feedback voltage source VO1 at the VFB pin to decrease. In this way, the duty cycle is continuously adjusted repeatedly, so that the feedback voltage source VO1 is finally stabilized at the set value. The feedback voltage source VO1 supplies power to the drive circuit in the BMS, generally about 12V.

[0029] Since the polarities of the transformer windings NS and NA are the same, according to the principle of the flyback power supply, the voltage values of the feedback voltage source VO1 and the isolated voltage source VO3 are proportional to the number of turns of the windings. Then, as long as the feedback voltage source VO1 is stabilized at the set value, the isolated voltage source VO3 will also be stabilized at the set value, and the isolated voltage source VO3 is electrically isolated from other voltage sources and supplies power to the isolated communication chip in the BMS.

[0030] After the feedback voltage source VO1 rises after the flyback switching power supply has been operating for a period of time, the flyback power control circuit 101 outputs a control signal Ctrl to block the high-order linear voltage regulator circuit 102, and the current no longer flows from V IN through the high-order linear voltage regulator circuit 102 to the VDD pin. At this time, the current sequentially passes through the VFB pin, the diode D3 to the VDD pin, and at the same time passes through the diode D3 and the low-order linear voltage regulator circuit 103 to the VREF pin to supply power to the MCU. Since the input and output voltage difference of the high-order linear voltage regulator circuit 102 is large, a large amount of heat will be generated when the current flows through, and the flyback switching power supply converts the input voltage V IN step-down to the feedback voltage source VO1 with high efficiency. After the flyback switching power supply works, the MCU obtains power from the input V IN and changes to obtaining power from VO1, greatly improving the efficiency.

[0031] Once the BMS is installed in the battery pack, the MCU, as the brain of the BMS, must be able to continuously obtain power supply in order to detect the state of the battery in real time and manage the interaction between the battery and the outside world. Of course, when the battery is not charging or discharging with the outside world, the MCU can enter the sleep state to save standby power consumption. Correspondingly, the auxiliary power control chip provided by the present invention provides a deep sleep mode for the BMS. After the MCU enters the sleep state, the MCU outputs a low level to the enable pin EN, which is sensed by the enable selection circuit 104, and its output ON / OFF signal becomes the corresponding OFF logic level, turning off the flyback power control circuit 101. Furthermore, the flyback power control circuit 101 outputs a control signal Ctrl to turn on the high-order linear voltage regulator circuit 102, and supplies power to the MCU through the dual-stage linear voltage regulator circuit. The feedback voltage source VO1 and the isolated voltage source VO3 both drop to zero, and ultra-low standby power consumption can be achieved.

[0032] When the MCU exits the sleep state and starts the detection work with high power consumption, the MCU outputs a high level to the enable pin EN, which is sensed by the enable selection circuit 104, and the output ON / OFF signal becomes the corresponding ON logic level, turning on the flyback power control circuit 101. Furthermore, the flyback power control circuit 101 outputs a control signal Ctrl to block the high-order linear voltage regulator circuit 102, and supplies power to the MCU through the feedback voltage source VO1 generated by the switching power supply, improving the overall efficiency of the machine. At the same time, the generated feedback voltage source VO1 supplies power to the drive circuit, and the generated isolated voltage source VO3 supplies power to the isolated communication chip.

[0033] In the above function description, when the enable pin EN is at a low level, the switching power supply is turned off, and when it is at a high level, the switching power supply is turned on. This logical relationship is only for intuitively understanding the working principle of this embodiment. In practice, the logical relationship can be designed conversely, and it will not have a great impact on the final effect. The diode D3 connected between the VDD pin and the VFB pin is cut off when the switching power supply is not working. When the feedback voltage source VO1 is established after the switching power supply starts working, the diode D3 is conducting, and only the natural properties of the diode's cut-off and conduction are used. Similarly, a triode in the form of a diode connection or a MOS transistor in the form of a diode connection also has the same function and can be used to replace the diode D3, which also falls within the protection scope of the present invention. In addition, D3 can also be placed outside the chip. The anode of D3 is connected to the VFB pin, and the cathode is connected to the VDD pin. Simple changes in such logical relationships, simple replacements of devices, or position changes cannot be used to circumvent the present invention.

[0034] In addition, the high-order linear voltage regulation circuit 102 and the low-order linear voltage regulation circuit 103 of the present invention can be implemented by using a linear voltage regulation circuit in the prior art, as long as the purpose of linear voltage regulation can be achieved. The two are connected in series to form the dual-stage linear voltage regulation circuit of the present invention. The enable selection circuit 104 and the flyback power supply control circuit 101 can also be implemented by using the prior art. The purpose of the present invention is not to improve the above four circuits themselves, but to integrate them together, and use simple components to form a control logic to supply power to the MCU of the BMS, so as to achieve the purpose of reducing the number of peripheral devices, reducing costs, and reducing standby power consumption. The present invention is not a simple stacking of existing circuits, but produces unexpected beneficial effects, achieving the effect that one plus one is greater than two.

[0035] Further, as an embodiment of the present invention, an auxiliary power supply control chip for a BMS is as Figure 4 shown by the thick solid line frame 11. Compared with Figure 3 the dedicated chip 10 shown, the dedicated chip 11 does not have an input pin VIN, and the high-order linear voltage regulation circuit 102 takes power from the drain pin DRN of the power transistor. When the MCU is in the sleep state, the current passes through the NP winding of the transformer T2 and flows into the control chip 11 from the DRN pin. After passing through the high-order linear voltage regulation circuit 102, a transfer voltage source VO4 is generated, and then a reference voltage source VO2 is generated through the low-order linear voltage regulation circuit 103 to supply power to the MCU. Since the power transistor NM0 is not switched and the transformer T2 passes direct current, the feedback voltage source VO1 and the isolation voltage source VO3 do not generate voltage. In the normal dynamic working state of the MCU, the high-order linear voltage regulation circuit 102 is blocked, and energy is transferred from the input voltage V INConvert to the feedback voltage source VO1, the reference voltage source VO2, the isolated voltage source VO3, and the transfer voltage source VO4 to supply power to each power-consuming link. The chip 11 uses DRN as the input terminal of the high-order linear voltage regulator circuit, eliminating the VIN pin and the corresponding ESD protection device (in integrated circuit design, each pin requires an ESD device to protect the internal circuit from damage). However, the withstand voltage of the input terminal of the high-order linear voltage regulator circuit 102 also needs to be increased correspondingly to the same level as the DRN pin. According to the principle of the flyback power supply, the voltage of the DRN pin is higher than the input voltage V IN is higher.

[0036] The above is only to illustrate the implementation mode of the present invention and is not used to limit the present invention. For those skilled in the art, any modification, equivalent replacement, improvement, etc. made without creative labor within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An auxiliary power supply control chip, characterized in that, It includes a power transistor drain pin (DRN), an enable pin (EN), a reference voltage source pin (VREF), a transfer voltage source pin (VDD), a feedback voltage source pin (VFB), a power ground pin (GND), a flyback power control circuit (101), a high-order linear voltage regulator circuit (102), a low-order linear voltage regulator circuit (103), an enable selection circuit (104), a power transistor (NM0), and a diode (D3); the input end of the high-order linear voltage regulator circuit (102) is connected to the power transistor drain pin (DRN), and the output end is respectively connected to the input end of the low-order linear voltage regulator circuit (103) and the transfer voltage source pin (VDD); the output end of the low-order linear voltage regulator circuit (103) is connected to the reference voltage source pin (VREF); the input end of the enable selection circuit (104) is connected to the enable pin (EN), and the output end outputs a first control signal to the flyback power control circuit (101); the power supply end of the flyback power control circuit (101) is connected to the feedback voltage source pin (VFB), the first control end is connected to the gate of the power transistor (NM0), and the second control end is connected to the high-order linear voltage regulator circuit (102); the drain of the power transistor (NM0) is connected to the power transistor drain pin (DRN), and the source is connected to the power ground pin (GND); the anode of the diode (D3) is connected to the feedback voltage source pin (VFB), and the cathode is connected to the transfer voltage source pin (VDD).

2. The auxiliary power supply control chip according to claim 1, wherein It further includes an input pin (VIN), and the input end of the high-order linear voltage regulator circuit (102) is connected to the input pin (VIN).

3. The auxiliary power supply control chip according to claim 1 or 2, characterized in that, The diode (D3) is built inside the auxiliary power control chip or outside the auxiliary power control chip.

4. The auxiliary power supply control chip according to claim 1 or 2, characterized in that The peripheral circuit of the auxiliary power control chip includes a first capacitor (C1), a second capacitor (C2), a fourth capacitor (C4), a transformer (T2), a control unit MCU of the BMS, and a drive circuit of the BMS; the first capacitor (C1) is connected between the feedback voltage source pin (VFB) and the ground; the second capacitor (C2) is connected between the reference voltage source pin (VREF) and the ground; the fourth capacitor (C4) is connected between the transfer voltage source pin (VDD) and the ground; the power supply end of the control unit MCU is connected to the reference voltage source pin (VREF); the power supply end of the drive circuit is connected to the feedback voltage source pin (VFB).

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