CN218499029U - Switching power supply, AC-DC circuit and input voltage detection circuit - Google Patents

Abstract

The utility model provides a switching power supply, exchange-DC circuit and input voltage detection circuitry, wherein, rectifier diode's positive pole is connected to rectifier diode's secondary coil's first end, filter capacitor's positive pole is connected to rectifier diode's negative pole, transformer's secondary coil's second end, filter capacitor's negative pole and sampling capacitor's positive pole are ground connection all, transformer's secondary coil's first end is connected to diode's negative pole, sampling capacitor's negative pole is connected to the positive pole, sampling capacitor's negative pole loops through third sampling resistor and second sampling resistor ground connection, voltage detection end is connected to third sampling resistor and second sampling resistor's common port, and connect the reference voltage input through first sampling resistor, reference voltage input reference voltage.

Description

Switching power supply, AC-DC circuit and input voltage detection circuit

Technical Field

The utility model relates to a power field, concretely relates to switching power supply, interchange-DC circuit and input voltage detection circuit.

Background

The ac-dc circuit is used in a switching power supply of various electronic devices, and in the ac-dc circuit, first, an ac voltage needs to be rectified into a dc voltage by a rectifying circuit and output to a bus, and then, a dc-dc unit converts the voltage on the bus into a desired target voltage.

In some cases, the ac-dc circuit needs to know the information of the magnitude of the input ac voltage, and some technical solutions exist in the existing ac-dc circuit for detecting the magnitude of the input ac voltage, but these solutions are either complicated or not accurate enough.

SUMMERY OF THE UTILITY MODEL

Based on the above current situation, the present invention is directed to a switching power supply, an ac-dc circuit, and an input voltage detection circuit.

In order to achieve the above object, the utility model adopts the following technical scheme:

an input voltage detection circuit of an alternating current-direct current circuit comprises a transformer, a filter capacitor and a rectifier diode, the input voltage detection circuit comprises a sampling capacitor, a first sampling resistor, a second sampling resistor, a third sampling resistor, a diode and a control chip, and the control chip is also provided with a reference voltage input end and a voltage detection end; the first end of a secondary coil of the transformer is connected with the anode of a rectifier diode, the cathode of the rectifier diode is connected with the anode of a filter capacitor, the second end of the secondary coil of the transformer, the cathode of the filter capacitor and the anode of a sampling capacitor are all grounded, and the end of the primary coil of the transformer, which is connected with a bus, and the second end of the secondary coil are dotted terminals; the cathode of the diode is connected with the first end of the secondary coil of the transformer, the anode of the diode is connected with the cathode of the sampling capacitor, the cathode of the sampling capacitor is sequentially grounded through a third sampling resistor and a second sampling resistor, the common end of the third sampling resistor and the second sampling resistor is connected with the voltage detection end and is connected with the reference voltage input end through the first sampling resistor, and the reference voltage is input into the reference voltage input end; the control chip is used for detecting the voltage of the voltage detection end and calculating the size of the input alternating voltage according to the relation between the alternating voltage and the voltage of the voltage detection end.

Preferably, the input voltage detection circuit further includes a dummy load resistor; the control chip is used for controlling the dummy load resistor to be connected or not connected with a discharging loop of the filter capacitor.

Preferably, the input voltage detection circuit further includes a resistor switch, the dummy load resistor and the resistor switch are connected in series between the positive electrode and the negative electrode of the filter capacitor, and the control chip further has a resistor control end connected to the control end of the resistor switch.

Preferably, the positive electrode of the filter capacitor is connected with the negative electrode of the filter capacitor through the dummy load resistor and the resistor switch in sequence.

Preferably, the ac-dc circuit further comprises a first bus capacitor, a second bus capacitor, a capacitive switch, and an optocoupler; one end of the first bus capacitor is connected with the bus, the other end of the first bus capacitor is connected with the ground, the second bus capacitor and the capacitive switch are connected between the bus and the ground in series, and the control chip is used for controlling the capacitive switch to be switched on or switched off through an optocoupler.

Preferably, the ac-dc circuit further includes a first voltage-dividing resistor and a second voltage-dividing resistor, the optical coupler includes an optical coupler emitting element and an optical coupler receiving element, the control chip further has an optical coupler control end, the control chip is configured to control the optical coupler emitting element to emit light or not to emit light through the optical coupler control end, the optical coupler receiving element and the second voltage-dividing resistor are connected in series between the driving voltage and the control end of the capacitive switch, and the control end of the capacitive switch is grounded through the first voltage-dividing resistor;

preferably, the bus bar is grounded through the second bus bar capacitor and the capacitor switch in sequence.

Preferably, the power supply end of the control chip is connected with the anode of the filter capacitor.

The utility model also provides an exchange-direct current circuit, including arbitrary input voltage detection circuit.

The utility model also provides a switching power supply, include alternating current-direct current circuit.

[ PROBLEMS ] the present invention

The utility model discloses a sampling electric capacity, first sampling resistor, second sampling resistor, third sampling resistor, diode and control chip have realized the detection to the alternating voltage of input, and the circuit is simple. In some embodiments, the dummy load resistor is controlled to be connected to a discharge loop of the filter capacitor to complete detection of the input voltage, and the voltage of the negative electrode of the sampling capacitor can be more stable rather than fluctuating greatly, so that the accuracy of the detected input voltage is higher.

Other advantages of the present invention will be described in the detailed description, and those skilled in the art can understand the technical advantages brought by the technical features and technical solutions through the descriptions of the technical features and the technical solutions.

Drawings

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. In the figure:

fig. 1 is a schematic diagram of an ac-dc circuit according to an embodiment of the present invention;

fig. 2 is a schematic diagram of an ac-dc circuit according to another embodiment of the present invention;

fig. 3 is a timing diagram of a plurality of voltages during power-up of an ac-dc circuit according to an embodiment of the present invention.

Detailed Description

The present invention will be described below based on examples, but the present invention is not limited to only these examples. In the following detailed description of the present invention, certain specific details are set forth, such that well-known methods, procedures, flows, and components have not been described in detail so as not to obscure the present invention.

Furthermore, those of ordinary skill in the art will appreciate that the drawings provided herein are for illustrative purposes and are not necessarily drawn to scale.

Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is, what is meant is "including, but not limited to".

In the description of the present invention, it is to be understood that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. In addition, in the description of the present invention, "a plurality" means two or more unless otherwise specified.

Fig. 1 is an ac-dc circuit (i.e., ac-dc conversion circuit) according to an embodiment of the present invention, which includes a rectifier circuit, a first bus capacitor EC1, a dc-dc unit (i.e., dc-dc conversion unit), and an input voltage detection circuit.

The input end of the rectifying circuit is used for inputting an alternating-current voltage Vac, and the rectifying circuit is used for rectifying the input alternating-current voltage Vac to obtain a direct-current voltage and supplying the direct-current voltage to the bus. The rectifying circuit may be a full-bridge rectifying circuit or a half-bridge rectifying circuit.

The input end of the dc-dc unit inputs a voltage on the bus, and the dc-dc unit is configured to convert the voltage on the bus into an output target voltage, specifically, the dc-dc unit is controlled to convert the voltage on the bus into the output target voltage, which may be set according to a suitable requirement, and for common consumer electronics, 5V, 12V, 24V, and the like are relatively common target voltages. As shown in fig. 2, the dc-dc unit includes a switch tube Q1, a transformer T, a rectifier diode D2 and a filter capacitor EC3, a first end of a primary coil of the transformer T is connected to a bus, a second end of the primary coil of the transformer T is grounded through the switch tube Q1, a first end of a secondary coil of the transformer T is connected to an anode of the rectifier diode D2, a cathode of the rectifier diode D2 is connected to an anode of the filter capacitor EC3, a cathode of the filter capacitor EC3 is grounded, a second end of a secondary coil of the transformer T is grounded, a cathode of the rectifier diode D2 is used as an output terminal Vout of the dc-dc unit, that is, an output terminal Vout of the ac-dc circuit, and the output terminal Vout outputs a target voltage, and the voltage of the output terminal Vout can be stabilized at a set target voltage by adjusting a duty ratio of a control signal PWM of the switch tube Q1.

The input voltage detection circuit comprises a sampling capacitor C1, a first sampling resistor R1, a second sampling resistor R2, a third sampling resistor R3, a diode D1 and a control chip IC, wherein the control chip IC is also provided with a reference voltage input end VREF and a voltage detection end Vsen, and a power supply end Vin of the control chip IC is connected with the anode of the filter capacitor, namely the power supply voltage of the control chip IC is the output voltage of the alternating current-direct current circuit; the first end of the secondary coil of the transformer T is connected with the anode of a rectifier diode D2, the cathode of the rectifier diode D2 is connected with the anode of a filter capacitor EC3, the second end of the secondary coil of the transformer T, the cathode of the filter capacitor EC3 and the anode of a sampling capacitor C1 are all grounded, and the end of the primary coil of the transformer T connected with a bus and the second end of the secondary coil are homonymy ends; the cathode of the diode D1 is connected with the first end of the secondary coil of the transformer T, the anode of the diode D1 is connected with the cathode of the sampling capacitor C1, the cathode of the sampling capacitor C1 is grounded through the third sampling resistor R3 and the second sampling resistor R2 in sequence, the common end of the third sampling resistor R3 and the second sampling resistor R2 is connected with the voltage detection end Vsen and is connected with the reference voltage input end VREF through the first sampling resistor R1, and the reference voltage input end VREF inputs reference voltage Vref; the control chip IC detects the voltage of the voltage detection terminal Vsen, and calculates the magnitude of the input ac voltage Vac according to the relationship between the ac voltage Vac and the voltage of the voltage detection terminal Vsen.

Because the positive pole of the sampling capacitor C1 is grounded, and the negative pole is connected with the first end of the secondary coil through the diode D1, the voltage VC1 of the negative pole of the sampling capacitor C1 meets the following conditions: VC1=0- (VDC × NS/NP-VD 1), where VDC is the voltage on the bus, VD1 is the voltage drop of diode D1, and NS and NP are the number of turns of the secondary and primary windings of transformer T, respectively. Since the voltage VC1 of the cathode of the sampling capacitor C1 is a negative value, the current flowing through the third sampling resistor R3 is equal to the sum of the current flowing through the first sampling resistor R1 and the current flowing through the second sampling resistor R2, that is: (Vsen-VC 1)/R3 = (Vref-Vsen)/R1 + Vsen/R2, where Vsen is a voltage detected by the voltage detection terminal, vref is a reference voltage, and R1, R2, and R3 are resistance values of the first sampling resistor R1, the second sampling resistor R2, and the third sampling resistor R3, respectively, the voltage VC1 can be calculated by solving the above equation, and the voltage VDC on the bus can be calculated by combining the above equation. If the ratio of the voltage output by the rectifier circuit (i.e., the voltage VDC on the bus) to the input ac voltage Vac is k (for example, in a certain type of rectifier circuit, k = √ 2 (i.e., the square root of 2)), the relationship between the ac voltage Vac and the voltage at the voltage detection terminal is:

Vac＝{-Vsen+[(Vref-Vsen)/R1+Vsen/R2]*R3+VD1}*NP/(NS*k)；

in this embodiment, the anode of the sampling capacitor C1 is grounded, the cathode of the sampling capacitor C1 is connected to the first end of the secondary coil through the diode D1, and the end of the primary coil of the transformer T connected to the bus and the second end of the secondary coil are dotted ends, so that the voltage VC1 of the cathode of the sampling capacitor C1 can change along with the voltage of the bus.

In order to reduce the influence on the actual load of the AC-DC circuit, the input voltage detection circuit completes the detection of the input voltage in a set period after the power-on of the AC-DC circuit is started (for example, in a period of time between 10ms and 1s after the power-on is started). However, in practical use, the ac-dc circuit may be in an idle state during this power-on process, and according to research, when the ac-dc circuit is in an idle state, the input voltage detected by the input voltage detection circuit has low accuracy, because the voltage VC1 at the negative pole of the sampling capacitor C1 is not stable. In order to reduce the influence on the actual load of the ac-dc circuit and also to consider the accuracy of the calculated ac voltage Vac, in some embodiments, the input voltage detection circuit further includes a dummy load resistor R6; when the alternating current-direct current circuit is powered on and started within a set time period (for example, a time period between 10ms and 1s after the power on is started), the control chip IC controls the dummy load resistor R6 to be connected to a discharge loop of the filter capacitor EC3, so that the direct current-direct current unit exits from a no-load mode (Burst mode), the dummy load resistor R6 exists as a load at the moment, and current is extracted from the filter capacitor EC3, therefore, the voltage VC1 of the negative electrode of the sampling capacitor C1 can be more stable rather than greatly fluctuated, and the accuracy of the detected input voltage is higher; in addition, because the detection of the input voltage is completed in the power-on process of the alternating current-direct current circuit, the influence on the actual load of the alternating current-direct current circuit is reduced. After the set period, the control chip IC controls the dummy resistance R6 not to be switched into the discharge loop of the filter capacitance EC3, and the control chip IC stops detecting the voltage of the voltage detection terminal Vsen.

In some embodiments, the input voltage detection circuit further includes a resistor switch Q2, the dummy load resistor R6 and the resistor switch Q2 are connected in series between the positive electrode and the negative electrode of the filter capacitor EC3, the control chip IC further includes a resistor control end IO1, and when the ac-dc circuit starts to be powered on, the control chip IC controls the resistor switch Q2 to be turned on through the resistor control end IO1 so that the dummy load resistor R6 is connected to the discharge loop of the filter capacitor EC 3; after a set time period, the control chip IC controls the resistor switch Q2 to be turned off through the resistor control terminal IO1, so that the dummy load resistor R6 is not connected to the discharge loop of the filter capacitor EC 3. Fig. 3 is a timing diagram of a plurality of voltages in the power-on process of the ac-dc circuit according to an embodiment of the present invention, as shown in fig. 3, when the ac-dc circuit starts to power on (i.e. at time 0), the reference voltage Vref is stable until a certain time (10 mS in fig. 3), and at this time, the control chip IC controls the resistor control terminal IO1 to output a high level, so that the dummy load resistor R6 is connected to the discharge loop of the filter capacitor EC 3; when a certain time (1S in fig. 3) is reached, the control chip IC controls the resistor control end IO1 to output a low level, so that the dummy load resistor R6 is not connected to the discharge loop of the filter capacitor EC 3.

Because the ac voltage Vac of the power grid in different areas is different in magnitude and has a large difference, for example, the ac voltage Vac in china is 220V, and the ac voltage Vac in the united states is 110V, which are different by one time, the voltages rectified and output by the rectifying circuit are also different, that is, the voltages on the bus voltages are different. When the output power requirement of the output terminal Vout is fixed, when the accessed ac voltage Vac is small, at this time, since the voltage on the bus is small, in order to meet the output power requirement of the output terminal Vout, the bus capacitor is required to provide a larger discharge current, and if only the first bus capacitor EC1 provides the discharge current, the first bus capacitor EC1 is caused to perform large-amplitude charging and discharging, which causes a large ripple on the bus, and further causes more harmonics in an ac circuit connected to a rectifier circuit, which may reduce the evaluation of the electromagnetic compatibility performance of the electronic device including the ac-dc circuit.

Therefore, in order to reduce the above influence, in some embodiments, the ac-dc circuit further includes a second bus capacitor EC2, a capacitor switch Q3, and an optocoupler, where the second bus capacitor EC2 and the capacitor switch Q3 are connected in series between the bus and the ground, and when the ac voltage Vac is less than the voltage threshold, the control chip IC controls the capacitor switch Q3 to be turned on, so that the second bus capacitor EC2 is connected to the charge-discharge loop of the bus; when the alternating voltage Vac is greater than or equal to the voltage threshold, the control chip IC controls the capacitor switch Q3 to be turned off, so that the second bus capacitor EC2 is not connected to the charge-discharge loop of the bus. In some embodiments, the capacitive switch Q3 may be a MOS transistor, such as an N-channel MOS transistor. When the alternating-current voltage Vac is smaller than the voltage threshold, the second bus capacitor EC2 is connected to the charge-discharge loop of the bus by controlling the conduction of the capacitor switch Q3, the second bus capacitor EC2 can also provide a part of discharge current, the first bus capacitor EC1 and the second bus capacitor EC2 only need to be charged and discharged with a small amplitude as a whole, ripple waves on the bus are relatively small, and harmonic waves in an alternating-current circuit connected with the rectifying circuit are less. When the ac voltage Vac is greater than or equal to the voltage threshold, at this time, since the voltage on the bus is relatively large, in order to meet the output power requirement of the output terminal Vout and the requirement of maintaining the output power at the target voltage, only the bus capacitor is required to provide a relatively small discharging current, and the discharging current provided by the first bus capacitor EC1 does not cause a relatively large ripple on the bus, so that the second bus capacitor EC2 is not connected to the charging and discharging loop of the bus by controlling the capacitor switch Q3 to be turned off, thereby preventing more devices such as the second bus capacitor EC2 and the capacitor switch Q3 from being connected to the bus to cause more power consumption, and simultaneously, the ripple caused in the ac circuit due to the relatively small bus ripple is relatively small.

In addition, in some embodiments, the bus is grounded through the second bus capacitor EC2 and the capacitor switch Q3 in sequence, at this time, because the capacitor switch Q3 is connected to the bus through the second bus capacitor EC2, that is, is not directly connected to the bus, the high voltage on the bus is prevented from being directly applied to the capacitor switch Q3, and therefore, the capacitor switch Q3 is not broken down by the high voltage of the bus, and in other respects, the capacitor switch Q3 may use a device with a smaller withstand voltage, so that the cost may be saved. In addition, the capacitor switch Q3 is controlled through the optocoupler, so that the isolation between the input side and the output side of the direct current-direct current unit can be realized, and the output side is prevented from being damaged by the high voltage of the input side.

The alternating current-direct current circuit further comprises a first divider resistor R4 and a second divider resistor R5, the optocoupler comprises an optocoupler emitting element U1A and an optocoupler receiving element U1B, and the control chip IC further comprises an optocoupler control end IO2; the control chip IC controls the optocoupler emitting element U1A to emit light or not to emit light through the optocoupler control end IO2; the optocoupler receiving element U1B and the second voltage-dividing resistor R5 are connected in series between the driving voltage VCC and the control end of the capacitor switch Q3, and the control end of the capacitor switch Q3 is grounded through the first voltage-dividing resistor R4; and satisfies the following conditions: (VCC-V0) × R4/(R5 + R4) > Vth2; wherein Vth2 is a starting voltage of the capacitor switch Q3, VCC is a driving voltage, V0 is a conduction voltage drop of the optocoupler receiving element U1B, and R4 and R5 are a resistance value of the first voltage dividing resistor and a resistance value of the second voltage dividing resistor, respectively. Fig. 2 shows that the second voltage-dividing resistor R5 is located between the driving voltage VCC and the optical coupler receiving element U1B, but the positions of the second voltage-dividing resistor R5 and the optical coupler receiving element U1B may be interchanged. Fig. 2 shows one form of the optocoupler emitting element U1A and the optocoupler receiving element U1B, which may also be implemented by other existing optocoupler devices. When the bus capacitor is in work, when the alternating-current voltage Vac is smaller than a voltage threshold, the control chip IC controls the optocoupler emitting element U1A to emit light, the optocoupler receiving element U1B is conducted after receiving the light, and the voltage of the control end of the capacitor switch Q3 is maintained at a voltage (namely (VCC-V0) × R4/(R5 + R4)) larger than Vth2, so that the capacitor switch Q3 is controlled to be conducted, and the second bus capacitor EC2 is connected to a charge-discharge loop of a bus; when the alternating voltage Vac is greater than or equal to the voltage threshold, the control chip IC controls the optocoupler emitting element U1A not to emit light, the optocoupler receiving element U1B does not receive light and is not turned on, and the voltage at the control end of the capacitor switch Q3 is pulled down to zero by the first voltage dividing resistor R4, so that the capacitor switch Q3 is controlled to be turned off, and the second bus capacitor EC2 is not connected to the charge-discharge loop of the bus.

The utility model also provides an exchange-DC circuit, including arbitrary input voltage detection circuitry.

The utility model also provides a switching power supply, include input voltage detection circuit.

It will be appreciated by those skilled in the art that the above-described preferred embodiments may be freely combined, superimposed, without conflict.

It should be understood that the above-described embodiments are illustrative only and not restrictive, and that various obvious or equivalent modifications and substitutions may be made by those skilled in the art without departing from the basic principles of the invention, and are intended to be included within the scope of the appended claims.

Claims (10)

1. An input voltage detection circuit of an alternating current-direct current circuit, wherein the alternating current-direct current circuit comprises a transformer, a filter capacitor and a rectifier diode, and is characterized in that the input voltage detection circuit comprises a sampling capacitor, a first sampling resistor, a second sampling resistor, a third sampling resistor, a diode and a control chip, and the control chip is also provided with a reference voltage input end and a voltage detection end; the first end of the secondary coil of the transformer is connected with the anode of the rectifier diode, the cathode of the rectifier diode is connected with the anode of the filter capacitor, the second end of the secondary coil of the transformer, the cathode of the filter capacitor and the anode of the sampling capacitor are all grounded, and the end of the primary coil of the transformer, which is connected with the bus, and the second end of the secondary coil are homonymous ends; the cathode of the diode is connected with the first end of the secondary coil of the transformer, the anode of the diode is connected with the cathode of the sampling capacitor, the cathode of the sampling capacitor is sequentially grounded through a third sampling resistor and a second sampling resistor, the common end of the third sampling resistor and the second sampling resistor is connected with the voltage detection end and is connected with the reference voltage input end through the first sampling resistor, and the reference voltage is input into the reference voltage input end; the control chip is used for detecting the voltage of the voltage detection end and calculating the size of the input alternating voltage according to the relation between the alternating voltage and the voltage of the voltage detection end.

2. The input voltage detection circuit of claim 1, further comprising a dummy load resistor; the control chip is used for controlling the dummy load resistor to be connected or not connected with a discharging loop of the filter capacitor.

3. The input voltage detection circuit of claim 2, further comprising a resistor switch, wherein the dummy resistor and the resistor switch are connected in series between the positive electrode and the negative electrode of the filter capacitor, and wherein the control chip further has a resistor control terminal connected to the control terminal of the resistor switch.

4. The input voltage detection circuit of claim 3, wherein the anode of the filter capacitor is connected to the cathode of the filter capacitor sequentially through the dummy resistance and the resistance switch.

5. The input voltage detection circuit of claim 4, wherein the AC-DC circuit further comprises a first bus capacitor, a second bus capacitor, a capacitive switch, and an optocoupler; one end of the first bus capacitor is connected with the bus, the other end of the first bus capacitor is connected with the ground, the second bus capacitor and the capacitive switch are connected between the bus and the ground in series, and the control chip is used for controlling the capacitive switch to be switched on or switched off through an optocoupler.

6. The input voltage detection circuit according to claim 5, wherein the ac-dc circuit further comprises a first voltage-dividing resistor and a second voltage-dividing resistor, the optical coupler comprises an optical coupler emitting element and an optical coupler receiving element, the control chip further comprises an optical coupler control end, the control chip is configured to control the optical coupler emitting element to emit light or not to emit light through the optical coupler control end, the optical coupler receiving element and the second voltage-dividing resistor are connected in series between the driving voltage and the control end of the capacitive switch, and the control end of the capacitive switch is grounded through the first voltage-dividing resistor.

7. The input voltage detection circuit of claim 5, wherein the bus is grounded via the second bus capacitor and the capacitive switch in sequence.

8. The input voltage detection circuit of claim 1, wherein a power supply terminal of the control chip is connected to a positive electrode of the filter capacitor.

9. An ac-dc circuit comprising the input voltage detection circuit according to any one of claims 1-8.

10. A switching power supply comprising the ac-dc circuit according to claim 9.

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