LDO circuit and wireless charging system

Abstract

The utility model discloses an LDO circuit and a wireless charging system, and belongs to the technical field of power management. The LDO circuit is composed of an error amplifier, a power tube and other modules, a temperature protection system is further arranged, the system comprises a positive temperature coefficient voltage generation module and a reference voltage selection module, and by comparing positive temperature coefficient voltage with reference voltage, the LDO stops working when the temperature is too high and recovers working after the temperature is lowered, and circuit devices are protected. The wireless charging system is based on the electromagnetic induction principle, is composed of a transmitting circuit, a transmitting coil, a receiving coil and a receiving circuit, and can achieve efficient charging, foreign matter detection and multi-device protocol recognition. The output end of the receiving circuit of the wireless charging system is connected with the input end of the LDO circuit, the receiving circuit and the LDO circuit work cooperatively, the problems that a traditional LDO and a traditional wireless charging system are slow in transient response, low in charging efficiency, large in potential safety hazard, poor in multi-device compatibility and the like are solved, and the efficient, stable, safe and multi-device compatible power management and charging functions are achieved.

Description

TECHNICAL FIELD

[0001] The utility model relates to power management technical field especially relates to a LDO circuit and wireless charging system. BACKGROUND

[0002] Under the trend of modern electronic equipment constantly miniaturization, multi-functional development, the power management system is put forward higher and higher requirement. As the key component of power management, the performance of low dropout regulator (LDO) is directly related to the stability, reliability and overall power consumption of electronic equipment. Traditional LDO has many problems:

[0003] Transient response speed is slow: when the load current changes rapidly, the output voltage of traditional LDO cannot be adjusted in time, and there will be a large amplitude overshoot or undershoot phenomenon. This not only affects the normal work of the rear-end circuit, but also may cause damage to some precision electronic components with very high voltage stability requirements, and reduces the service life of the equipment.

[0004] Output voltage fluctuation is large: due to the limitation of process and circuit design, the output voltage fluctuation of traditional LDO under different load conditions is obvious. This fluctuation will lead to unstable power supply quality of electronic equipment, and then affect the performance of the equipment, for example, it may produce noise in audio equipment, and may appear flicker in image display equipment.

[0005] Phase margin is insufficient: under light load condition, traditional LDO is prone to insufficient phase margin, which leads to oscillation of the circuit, so that the system cannot work stably. In order to solve this problem, a large capacitor is often connected externally, which not only increases the volume and cost of the system, but also is not conducive to the miniaturization design of electronic equipment.

[0006] High power consumption: the static current of traditional LDO is large, which will consume a lot of electric energy in the long-term working process. For battery-powered portable electronic equipment, it will seriously shorten the endurance time of the equipment and reduce the user experience.

[0007] At the same time, although wireless charging technology has been widely concerned and applied due to its convenience, there are still some problems to be solved in the existing wireless charging system:

[0008] Low charging efficiency: in the process of wireless charging, due to the limitation of electromagnetic induction principle, there will be a large loss of energy in the transmission process, which leads to generally low charging efficiency. This not only prolongs the charging time of the equipment, but also causes energy waste, which does not conform to the development trend of energy saving and environmental protection.

[0009] Safety hazards: When there are metal foreign objects in the charging area, the foreign objects will generate eddy currents under the action of alternating magnetic field, and then heat up. If the heat cannot be dissipated in time, it may cause fire and other safety accidents, threatening the life and property safety of users.

[0010] Poor multi-device compatibility: Different brands and models of electronic devices often use different charging protocols, and existing wireless charging systems are difficult to simultaneously support the charging needs of multiple devices. Users may need to equip multiple different charging devices, causing great inconvenience to users.

[0011] In addition, most of the current power management systems and wireless charging systems lack effective temperature protection mechanisms. During the operation of electronic devices, especially in high-load or high-temperature environments, the temperature inside the system will continue to rise. If the temperature cannot be monitored and controlled in time, the high temperature will cause the performance of electronic components to decline, the service life to be shortened, and even may cause device failure. Utility model content

[0012] The utility model aims at providing a kind of LDO circuit and wireless charging system, to solve the above-mentioned problems existing in traditional LDO and wireless charging system, realize efficient, stable, safe and compatible multi-device power management and charging function, with reliable temperature protection mechanism, improve the overall performance and safety of electronic device.

[0013] To achieve the above-mentioned purpose, the utility model provides a kind of LDO circuit and wireless charging system, including LDO circuit, the LDO circuit is by error amplifier, power tube, feedback circuit, frequency compensation module, transient response enhancement circuit, band gap reference circuit and temperature protection system constitute;

[0014] The temperature protection system is composed of a comparator, a positive temperature coefficient voltage generating module and a reference voltage selection module.

[0015] The wireless charging system works based on the principle of electromagnetic induction, and is composed of a transmitting circuit, a transmitting coil, a receiving coil and a receiving circuit.

[0016] The receiving circuit output end of the wireless charging system is connected to the input end of the LDO circuit.

[0017] Preferably, the output end of the positive temperature coefficient voltage generating module is connected to the input end of the reference voltage selection module, and the output end of the reference voltage selection module is connected to the reference voltage input end of the error amplifier.

[0018] Preferably, the positive temperature coefficient voltage generating module comprises:

[0019] N-type field effect transistors N1, N2, N3, N4;

[0020] P-type field effect transistors P1, P2, P3;

[0021] Resistor R;

[0022] Wherein:

[0023] N1 and N2 constitute a current mirror, the drain of N1 is connected to a power supply Vdd, the source is grounded, and the gate is connected to the gate of N2;

[0024] The gates of N3 and N4 are connected to the same bias voltage, the sources are grounded, and the drains are respectively connected to the source of P2 and another circuit;

[0025] P1 and P3 constitute a current mirror, the source of P1 is connected to the drain of N2, and the gate is connected to the gate of P3;

[0026] The drain of P3 is connected to one end of resistor R, and the other end of resistor R is grounded;

[0027] The gate of P2 is connected to the gate of P1, the source is connected to the drain of N3, and the drain is connected to the input end of the reference voltage selection module.

[0028] Preferably, the output end of the error amplifier is connected to the input end of the driving circuit of the power tube;

[0029] One end of the feedback circuit is connected to the output end of the LDO circuit, and the other end is connected to the inverting input end of the error amplifier;

[0030] The frequency compensation module is arranged between the output end of the error amplifier and the gate of the power tube;

[0031] The overshoot / undershoot detection circuit input end of the transient response enhancement circuit is connected to the output end of the LDO circuit, and the output end of the fast current compensation circuit is connected to the gate of the power tube;

[0032] The bandgap reference circuit output end provides a reference voltage for the error amplifier.

[0033] Preferably, the power control module of the transmitting circuit is wirelessly connected to the communication module of the receiving circuit;

[0034] The output end of the oscillation circuit of the transmitting circuit is connected to the transmitting coil;

[0035] The receiving coil is magnetically coupled with the transmitting coil, and the output end of the receiving coil is connected to the input end of the rectification circuit of the receiving circuit;

[0036] The output end of the voltage stabilizing circuit of the receiving circuit is connected to the input end of the LDO circuit.

[0037] Therefore, the LDO circuit and the wireless charging system have the following beneficial effects:

[0038] (1) Compared with the traditional LDO, the overshoot and undershoot amplitude of the output voltage is significantly reduced, effectively ensuring the stable operation of the rear-end circuit. At the same time, the improved frequency compensation module and the reasonable circuit layout design accurately control the pole and zero point distribution of the circuit, effectively improve the phase margin of the system. Even in the light load condition, the LDO can operate stably, solving the problem of insufficient phase margin of the LDO without external capacitor. In addition, through the dynamic biasing circuit and reasonable selection of power tube and other measures, the power consumption of the LDO is reduced, and the energy utilization efficiency is improved.

[0039] (2) Compared with the traditional wireless charging system, it can quickly supplement the power of the device, effectively improve the safety and compatibility of wireless charging, avoid the safety hidden danger caused by foreign body heating, and adapt to the charging demand of different devices.

[0040] (3) The setting of the temperature protection system makes the LDO circuit stop working automatically when the temperature is too high, avoiding the damage of the device due to overheating. When the temperature decreases to the safe range, the LDO circuit can automatically resume work, ensuring the reliability and stability of the system in different temperature environments, prolonging the service life of the electronic device.

[0041] The technical scheme of the utility model will be further described in detail below by means of the drawings and examples. DRAWINGS

[0042] Fig. 1 It is a structure schematic view of the utility model LDO circuit and wireless charging system.

[0043] Fig. 2 It is a structure schematic view of the utility model LDO circuit and wireless charging system in the positive temperature coefficient voltage generating module. CONCRETE IMPLEMENTATION

[0044] The technical scheme of the utility model will be further described in detail below by means of the drawings and examples.

[0045] Unless otherwise defined, the technical or scientific terms used in this utility model shall have the ordinary meaning understood by one of ordinary skill in the art to which this utility model pertains. The terms "first," "second," and similar words used in this utility model do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0046] Example

[0047] like Figs. 1-2 As shown, this utility model provides an LDO circuit and a wireless charging system, including an LDO circuit, which consists of an error amplifier, a power transistor, a feedback circuit, a frequency compensation module, a transient response enhancement circuit, a bandgap reference circuit, and a temperature protection system.

[0048] The temperature protection system consists of a comparator, a positive temperature coefficient voltage generation module, and a reference voltage selection module;

[0049] A wireless charging system works based on the principle of electromagnetic induction and consists of a transmitting circuit, a transmitting coil, a receiving coil, and a receiving circuit.

[0050] The output of the receiving circuit of the wireless charging system is connected to the input of the LDO circuit.

[0051] The output of the positive temperature coefficient voltage generation module is connected to the input of the reference voltage selection module, and the output of the reference voltage selection module is connected to the reference voltage input of the error amplifier.

[0052] The positive temperature coefficient voltage generation module includes:

[0053] N-type field-effect transistors N1, N2, N3, and N4;

[0054] P-type field-effect transistors P1, P2, and P3;

[0055] Resistance R;

[0056] in:

[0057] N1 and N2 form a current mirror. The drain of N1 is connected to the power supply Vdd, the source is grounded, and the gate is connected to the gate of N2.

[0058] The gates of N3 and N4 are connected to the same bias voltage, the source is grounded, and the drain is connected to the source of P2 and another circuit, respectively.

[0059] P1 and P3 form a current mirror, with the source of P1 connected to the drain of N2 and the gate of P3 connected to the gate of P3.

[0060] The drain of P3 is connected to one end of resistor R, and the other end of resistor R is grounded.

[0061] The gate of P2 is connected to the gate of P1, the source is connected to the drain of N3, and the drain is connected to the input of the reference voltage selection module.

[0062] The output of the error amplifier is connected to the input of the power transistor's drive circuit.

[0063] One end of the feedback circuit is connected to the output of the LDO circuit, and the other end is connected to the inverting input of the error amplifier.

[0064] The frequency compensation module is located between the output of the error amplifier and the gate of the power transistor;

[0065] The input terminal of the overshoot / undershoot detection circuit of the transient response enhancement circuit is connected to the output terminal of the LDO circuit, and the output terminal of the fast current compensation circuit is connected to the gate of the power transistor.

[0066] The output of the bandgap reference circuit provides a reference voltage for the error amplifier.

[0067] The power control module of the transmitting circuit is wirelessly connected to the communication module of the receiving circuit;

[0068] The output terminal of the oscillation circuit of the transmitting circuit is connected to the transmitting coil;

[0069] The receiving coil is magnetically coupled to the transmitting coil, and the output terminal of the receiving coil is connected to the input terminal of the rectifier circuit of the receiving circuit.

[0070] The output of the voltage regulator circuit of the receiving circuit is connected to the input of the LDO circuit.

[0071] Specifically, the error amplifier employs a unique, improved two-stage Class AB amplifier structure. The first stage features meticulously optimized input transistors, increasing transconductance through adjustments to their size and material parameters, and optimizing the current mirror ratio to enhance the circuit's equivalent transconductance. The second stage utilizes a common-source, common-gate structure, significantly increasing output resistance and thus boosting amplifier gain. Simultaneously, a dynamic bias circuit is introduced, connected to a load current detection circuit, to monitor load current changes in real time. Under light load conditions, the dynamic bias circuit automatically reduces the error amplifier's bias current, effectively reducing power consumption; under heavy load conditions, it increases the bias current, improving the amplifier's drive capability and slew rate, ensuring a rapid response to output voltage changes under varying load conditions.

[0072] The power tube selects a PMOS tube as the power tube, and the width-length ratio thereof is accurately calculated based on the maximum load current and process parameters. A plurality of small-size PMOS tubes are connected in parallel to increase the effective area, reduce the on-resistance and improve the current carrying capacity. A specially designed driving circuit is connected to the gate of the power tube, which is connected to the output end of the error amplifier to receive the control signal of the error amplifier, so as to improve the charging and discharging speed of the gate and accelerate the response time of the power tube, thereby improving the transient performance of the LDO.

[0073] The feedback circuit adopts a resistance voltage division type feedback network composed of two high resistance and low power consumption resistors. One resistor is connected between the output end and the inverting input end of the error amplifier, and the other resistor is connected between the inverting input end of the error amplifier and the ground. By reasonably selecting the resistance values of the two resistors, the feedback voltage is accurately adjusted to ensure that the output voltage is stabilized at the set value. At the same time, the resistors are optimally laid out to reduce the influence of parasitic capacitance and improve the feedback accuracy and stability of the system.

[0074] The frequency compensation module adopts an improved Currentbuffer Miller compensation technology. A compensation capacitor is connected between the output end of the error amplifier and the gate of the power tube, and the equivalent capacitance of the compensation capacitor is reduced by using the characteristics of the Currentbuffer, thereby reducing the required on-chip capacitor area. By adjusting the size and position of the compensation capacitor, the pole and zero point distribution of the circuit is accurately controlled, the phase margin of the system is effectively improved, and the LDO is ensured to work stably in the full load range. In addition, combined with the feedforward compensation technology, when the load current suddenly changes, the feedforward compensation circuit quickly responds to obtain additional current from the power supply end or other stable voltage source and quickly provide it to the power tube, thereby further improving the transient response of the system.

[0075] The transient response enhancement circuit is composed of an overshoot / undershoot detection circuit and a fast current compensation circuit. The input end of the overshoot / undershoot detection circuit is directly connected to the output voltage to monitor the change of the output voltage in real time. When an overshoot or undershoot of the output voltage is detected, the fast current compensation circuit is triggered quickly. The fast current compensation circuit includes a switch tube and a capacitor, the control end of the switch tube receives the trigger signal of the overshoot / undershoot detection circuit, one end of the switch tube is connected to the gate of the power tube, and the other end is connected to the power supply or the ground according to the charging or discharging requirement. In the transient process, additional charging or discharging current is provided for the power tube, so that the output voltage can quickly recover to the stable value, effectively reducing the overshoot and undershoot amplitude of the output voltage and improving the transient response speed of the LDO.

[0076] The bandgap reference circuit adopts a bandgap reference circuit structure based on curvature compensation, which is composed of a bipolar transistor, a plurality of resistors and an amplifier. By accurately controlling the parameters of the bipolar transistor and the resistors, the negative correlation between the base-emitter voltage of the transistor and the temperature and the positive correlation between the resistance voltage and the temperature are utilized to realize the first-order and second-order temperature compensation of the reference voltage. At the same time, the layout and process of the circuit are optimized, and methods such as symmetrical layout and matching design are used to reduce the mismatch and noise influence of the device, improve the stability and precision of the reference voltage, and provide a stable and reliable reference voltage for the LDO circuit.

[0077] The wireless charging system works based on the principle of electromagnetic induction, mainly composed of a transmitting circuit, a transmitting coil, a receiving coil and a receiving circuit.

[0078] The transmitting circuit is connected with the power supply to obtain electric energy. The internal integrated power control module, oscillation circuit and foreign matter detection module. The power control module is connected with the receiving circuit through the wireless communication module, receives the charging demand and battery state information sent by the receiving circuit, and adjusts the output power according to these information. The oscillation circuit generates alternating current and is connected to the transmitting coil to convert electric energy into alternating magnetic field. The foreign matter detection module detects the changes of current, voltage and phase of the transmitting coil to determine whether there is metal foreign matter in the charging area. If foreign matter is detected, the foreign matter detection module sends a signal to the power control module, and the power control module automatically reduces the transmitting power or stops charging to prevent foreign matter from heating and causing safety problems.

[0079] The transmitting coil is connected with the output end of the oscillation circuit of the transmitting circuit, generates alternating magnetic field through alternating current, and adopts high permeability magnetic material and optimized coil turns and wire diameter to improve the quality factor of the coil and reduce energy loss in the transmission process.

[0080] The receiving coil is coupled with the transmitting coil through magnetic field, receives alternating magnetic field energy and converts it into electric energy, and is connected to the input end of the receiving circuit to transmit the sensed electric energy to the receiving circuit.

[0081] The receiving circuit receives the electric energy transmitted by the receiving coil, including a rectifier circuit, a voltage stabilizing circuit and a communication module. The rectifier circuit converts alternating current into direct current, and the voltage stabilizing circuit stabilizes the output voltage to charge the device. The communication module performs wireless communication with the power control module of the transmitting circuit, sends the charging demand and battery state information to the transmitting circuit, and receives the control signal sent by the transmitting circuit to realize dynamic adjustment of the transmitting power. In addition, the receiving circuit also has the function of identifying multiple device protocols, automatically adjusts the output voltage and current by detecting the charging protocol of the connected device, and realizes fast and safe charging for different devices.

[0082] Connection of LDO circuit and wireless charging system: the output end of the receiving circuit of the wireless charging system is connected to the input end of the LDO circuit. The receiving circuit inputs the electric energy wirelessly transmitted and processed to the LDO circuit, and the LDO circuit provides stable power supply for the rear-end device after voltage stabilization processing.

[0083] The N-type field effect transistor N1 and the N-type field effect transistor N2 constitute a current mirror in the positive temperature coefficient voltage generation module, the drain of the N-type field effect transistor N1 is connected to a power supply Vdd, the source is grounded, and the gate is connected to the gate of the N-type field effect transistor N2, which is used to generate a reference current. The gates of the N-type field effect transistor N3 and the N-type field effect transistor N4 are connected to the same bias voltage, the sources are grounded, and the drains are respectively connected to the source of P2 and another circuit, and N3 and N4 work in the sub-threshold region.

[0084] The P-type field effect transistor P1 and the P-type field effect transistor P3 constitute a current mirror, the source of the P-type field effect transistor P1 is connected to the drain of N2, the gate of the P-type field effect transistor P1 is connected to the gate of the P-type field effect transistor P3, which is used to mirror copy the current of N2. The drain of the P-type field effect transistor P3 is connected to one end of a resistor R, and the other end of the resistor R is grounded, which converts the current into a positive temperature coefficient voltage V_PTC. The gate of the P-type field effect transistor P2 is connected to the gate of the P-type field effect transistor P1, the source is connected to the drain of the N-type field effect transistor N3, and the drain is connected to the input end of the reference voltage selection module, and the P-type field effect transistor P2 works in the sub-threshold region.

[0085] The working steps are as follows:

[0086] N1 and N2 current mirror generates a reference current, which is mirrored to the resistor R through P1 and P3 current mirror to generate a voltage V_PTC.

[0087] N2 works in the linear region, and its drain-source voltage Vds satisfies the formula:

[0088]

[0089] wherein, k n3 and k n4 are the transconductance parameters of N3 and N4, k p2 and k p1 are the transconductance parameters of P2 and P1, n is the slope factor of the N-type transistor, and V T is the thermal voltage.

[0090] The drain current of N2 is:

[0091]

[0092] By adjusting the width-length ratio of N3, N4, P2 and P1 The voltage V_PTC on the resistor R has a positive temperature coefficient characteristic.

[0093] The reference voltage selection module includes a comparator and a double reference voltage source (denoted by Vref1 and Vref2), which switches the output reference voltage according to the comparison result of the positive temperature coefficient voltage V_PTC and the reference voltage, and controls the enable state of the LDO. The positive input terminal of the comparator receives V_PTC, and the negative input terminal is connected to the output terminal through a feedback resistor to realize hysteresis comparison. The output terminal of the comparator controls the enable terminals of the switch circuit and the LDO respectively. The switch circuit switches the reference voltage source (Vref1 or Vref2) according to the output of the comparator, and inputs the selected reference voltage Vref_sel to the error amplifier.

[0094] The comparator detects V_PTC and the reference voltage, outputs a control signal to switch Vref1 / Vref2, and controls the LDO enablement.

[0095] Taking 120℃ as the high temperature and 80℃ as the low temperature as examples, when the temperature is greater than or equal to 120℃, V_PTC>Vref1, and the LDO is disabled; when the temperature is less than or equal to 80℃, V_PTC<Vref2, and the LDO is restored.

[0096] Therefore, the LDO circuit and the wireless charging system can realize efficient charging, foreign matter detection and multi-device protocol identification. The output end of the receiving circuit of the wireless charging system is connected to the input end of the LDO circuit, and the two work cooperatively, solving the problems of slow transient response, low charging efficiency, great safety hazards and poor multi-device compatibility of the traditional LDO and the wireless charging system, and realizing efficient, stable, safe and compatible multi-device power management and charging functions.

[0097] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the utility model and not to limit them, although the utility model has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that: it can still modify or equivalently replace the technical solutions of the utility model, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the utility model.

Claims

1. An LDO circuit and wireless charging system, characterized by, The application relates to a low dropout regulator (LDO) circuit. The LDO circuit is composed of an error amplifier, a power tube, a feedback circuit, a frequency compensation module, a transient response enhancement circuit, a bandgap reference circuit and a temperature protection system. The temperature protection system is composed of a positive temperature coefficient voltage generation module and a reference voltage selection module. The wireless charging system is based on the electromagnetic induction principle and is composed of a transmitting circuit, a transmitting coil, a receiving coil and a receiving circuit. The output end of the receiving circuit of the wireless charging system is connected with the input end of the LDO circuit. 2.The LDO circuit and wireless charging system of claim 1, wherein: The output end of the positive temperature coefficient voltage generation module is connected with the input end of the reference voltage selection module, and the output end of the reference voltage selection module is connected with the reference voltage input end of the error amplifier. 3.The LDO circuit and wireless charging system of claim 1, wherein: The positive temperature coefficient voltage generation module comprises: N-type field effect transistors N1, N2, N3 and N4; P-type field effect transistors P1, P2 and P3; a resistor R; N1 and N2 constitute a current mirror, the drain of N1 is connected with a power supply Vdd, the source is grounded, and the gate is connected with the gate of N2; the gates of N3 and N4 are connected with the same bias voltage, the sources are grounded, and the drains are respectively connected with the source of P2 and another circuit; P1 and P3 constitute a current mirror, the source of P1 is connected with the drain of N2, and the gate is connected with the gate of P3; the drain of P3 is connected with one end of the resistor R, and the other end of the resistor R is grounded; the gate of P2 is connected with the gate of P1, the source is connected with the drain of N3, and the drain is connected with the input end of the reference voltage selection module. The reference voltage selection module is composed of a comparator and two reference voltage sources.

4. The LDO circuit and wireless charging system of claim 1, wherein: The output end of the error amplifier is connected with the input end of the driving circuit of the power tube; 5. The LDO circuit and wireless charging system of claim 1, wherein: one end of the feedback circuit is connected with the output end of the LDO circuit, and the other end is connected with the inverting input end of the error amplifier; the frequency compensation module is arranged between the output end of the error amplifier and the gate of the power tube; the overshoot / undershoot detection circuit input end of the transient response enhancement circuit is connected with the output end of the LDO circuit, and the fast current compensation circuit output end is connected with the gate of the power tube; the bandgap reference circuit output end provides a reference voltage for the error amplifier. The power control module of the transmitting circuit is wirelessly connected with the communication module of the receiving circuit; 6. The LDO circuit and wireless charging system of claim 1, wherein: the output end of the oscillation circuit of the transmitting circuit is connected with the transmitting coil; the receiving coil is magnetically coupled with the transmitting coil, and the output end of the receiving coil is connected with the input end of the rectification circuit of the receiving circuit; the output end of the voltage stabilizing circuit of the receiving circuit is connected with the input end of the LDO circuit. ​

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