Power supply circuit suitable for wide voltage range input and power supply

Abstract

The invention discloses a power supply circuit and a power supply suitable for wide voltage range input, the power supply circuit comprises a rectification filter circuit, a voltage detection and selection circuit, a relay input current-limiting protection circuit and an output converter circuit, the voltage detection and selection circuit comprises a low voltage circuit and a high voltage circuit, the voltage detection and selection circuit comprises a relay. When low voltage is input, the low-voltage circuit works, the high-voltage circuit does not work, the relay is powered on to be communicated with the low-end converter, the low-end converter works, and the low-voltage converter is suitable for low-voltage range input. When high voltage is input, the high-voltage circuit works and the low-voltage circuit does not work, so that the high-end converter works, and the circuit can be suitable for high-voltage range input. The power supply circuit can be suitable for input in an extremely wide voltage range, derating is not needed, the conversion efficiency is improved, and the conversion cost is reduced.

Description

Technical Field

[0001] The present application relates to the field of electrical engineering technology, and in particular to a power supply circuit and a power supply suitable for inputting a wide voltage range. Background Art

[0002] In the prior art, in order to allow the power supply to receive a wider input range voltage, two solutions are usually adopted. The first is to use a single converter solution, that is, to select a flyback topology solution with the maximum input range. However, under this solution, no matter how the converter parameters are adjusted, there will be a problem that the high and low input voltages cannot be taken into account. Generally, the rating will be greatly reduced when the low voltage input is low, and it cannot be fully loaded; the second is to use a two-stage converter, that is, a mode in which the converter is connected in series. However, under this solution, the first-stage converter will raise the low voltage very high, or lower the high voltage very low. The entire conversion process is costly and the conversion efficiency is very low, and the voltage resistance problem of the previous stage is also very difficult to solve. In summary, there is an urgent need for a power supply circuit that can be applied to inputs with an extremely wide voltage range, does not require derating, improves conversion efficiency, and reduces conversion costs. Summary of the invention

[0003] The present application provides a power supply circuit and power supply suitable for wide voltage range input. Compared with the prior art, it can be suitable for extremely wide voltage range input without derating, thereby improving conversion efficiency and reducing conversion cost.

[0004] In a first aspect, the present application provides a power supply circuit suitable for inputting a wide voltage range, characterized in that it includes:

[0005] A rectifier filter circuit, a voltage detection and selection circuit, a relay input current limiting protection circuit and an output converter circuit, wherein the voltage detection and selection circuit includes a low voltage circuit and a high voltage circuit; the relay input current limiting protection circuit includes a current limiting protection circuit and a relay; the low voltage circuit is connected to the relay; the current limiting protection circuit is connected to the relay; the output converter circuit includes a low-end converter and a high-end converter;

[0006] The rectifier and filter circuit is used to receive an input voltage, convert the input voltage into a direct current voltage, and input the direct current voltage into the low voltage circuit and the high voltage circuit;

[0007] The voltage detection and selection circuit is used to control the relay to be energized to input the DC voltage to the low-end converter when the low-voltage circuit is working and the high-voltage circuit is not working; or to input the DC voltage to the high-end converter when the low-voltage circuit is not working and the high-voltage circuit is working;

[0008] The relay input current limiting protection circuit is used to limit the current so that the relay operates within a preset current threshold range;

[0009] The low - end converter is used to receive the DC voltage, convert the DC voltage, and output the converted DC voltage;

[0010] The high - end converter is used to receive the DC voltage, convert the DC voltage, and output the converted DC voltage.

[0011] Optionally, the high - voltage circuit includes: a second resistor R2, a fourth resistor R4, and a first MOS transistor VT3;

[0012] The first end of the second resistor R2 is connected to the positive end of the first capacitor C1 in the rectifier filter circuit; the second end of the second resistor R2 is connected to the first end of the fourth resistor R4; the second end of the fourth resistor R4 is connected to the negative end of the first capacitor C1; the fourth resistor R4 is connected in parallel between the gate and the drain of the first MOS transistor VT3, and the drain of the first MOS transistor VT3 is connected to the negative end of the first capacitor C1;

[0013] The low - voltage circuit includes: a third resistor R3, a fifth resistor R5, a second capacitor C2, and a second MOS transistor VT4;

[0014] The first end of the third resistor R3 is connected to the positive end of the first capacitor C1, and the second end of the third resistor R3 is connected to the source of the first MOS transistor VT3; the fifth resistor R5 and the second capacitor C2 are connected in parallel, and the first end of the parallel connection of the fifth resistor R5 and the second capacitor C2 is connected to the gate of the second MOS transistor VT4 and the source of the first MOS transistor VT3 respectively, the second end of the parallel connection of the fifth resistor R5 and the second capacitor C2 is connected to the negative end of the first capacitor C1, the drain of the second MOS transistor VT4 is connected to the negative end of the first capacitor C1, and the source of the second MOS transistor VT4 is connected to one end of the control coil in the relay.

[0015] Optionally, the low - voltage circuit further includes a seventh resistor R7 and a first diode VD4;

[0016] Wherein, the first end of the seventh resistor R7 is connected to the gate of the second MOS transistor VT4, the second end of the seventh resistor R7 is connected to the anode of the first diode VD4, and the cathode of the first diode VD4 is connected to the auxiliary source of the low - end converter;

[0017] The auxiliary power source of the low-end converter is used to supply power to the second MOS transistor VT4 based on the hysteresis circuit formed by the seventh resistor R7 and the first diode VD4 when the low-end converter is operating, so that the second MOS transistor VT4 is in the on state.

[0018] Optionally, the high-voltage circuit further includes: a second diode VD5;

[0019] The second diode VD5 is connected in parallel with the second resistor R2. The anode end of the second diode VD5 is connected to the positive end of the first capacitor C1, and the cathode end of the second diode VD5 is connected to the gate of the first MOS transistor VT3;

[0020] The second diode VD5 is used to discharge the gate of the first MOS transistor VT3, so that the power supply circuit can achieve fast switching when switching between high voltage and low voltage.

[0021] Optionally, the high-voltage circuit further includes: a second diode VD5;

[0022] The second diode VD5 is connected in parallel with the second resistor R2. The anode end of the second diode VD5 is connected to the positive end of the first capacitor C1, and the cathode end of the second diode VD5 is connected to the gate of the first MOS transistor VT3;

[0023] The second diode VD5 is used to discharge the gate of the first MOS transistor VT3, so that the power supply circuit can achieve the switching between high voltage and low voltage.

[0024] Optionally, the current-limiting protection circuit includes a first resistor R1, a sixth resistor R6, a first triode VT1, and a second triode VT2;

[0025] The first end of the first resistor R1 is connected to the positive end of the first capacitor C1 in the rectifying and filtering circuit. The second end of the first resistor R1 is connected to the base of the first triode VT1 and the collector of the second triode VT2. The collector of the first triode VT1 is connected to the positive end of the first capacitor C1 in the rectifying and filtering circuit, and the emitter of the first triode VT1 is connected to the base of the second triode VT2;

[0026] The first end of the sixth resistor R6 is connected to the base of the second triode VT2, and the second end of the sixth resistor R6 is connected to the emitter of the second triode VT2;

[0027] The first end of the control coil of the relay is connected to the emitter of the second triode VT2, and the second end of the control coil of the relay is connected to the source of the second MOS transistor VT4; the first end of the switch terminal of the relay is connected to the positive end of the first capacitor C1, and the second end of the switch terminal of the relay is connected to the low-end converter;

[0028] The current-limiting protection current is used to limit the current value of the current flowing to the relay, so that the relay operates within the preset current threshold range.

[0029] Optionally, the current-limiting protection circuit includes a first resistor R1, a sixth resistor R6, a first triode VT1, and a second triode VT2;

[0030] The first end of the first resistor R1 is connected to the positive end of the first capacitor C1 in the rectifying and filtering circuit, and the second end of the first resistor R1 is connected to the base of the first triode VT1 and the collector of the second triode VT2; the collector of the first triode VT1 is connected to the positive end of the first capacitor C1 in the rectifying and filtering circuit, and the emitter of the first triode VT1 is connected to the base of the second triode VT2;

[0031] The first end of the sixth resistor R6 is connected to the base of the second triode VT2, and the second end of the sixth resistor R6 is connected to the emitter of the second triode VT2;

[0032] The first end of the control coil of the relay is connected to the emitter of the second triode VT2, and the second end of the control coil of the relay is connected to the source of the second MOS transistor VT4; the first end of the switch terminal of the relay is connected to the positive end of the first capacitor C1, and the second end of the switch terminal of the relay is connected to the low-end converter;

[0033] The current-limiting protection current is used to limit the current value of the current flowing to the relay, so that the relay operates within the preset current threshold range.

[0034] Optionally, the output converter circuit further includes a third diode VD2 and a fourth diode VD3; the high-end converter is a converter including an under-voltage protection Brown out setting circuit;

[0035] Wherein, the output end of the high-end converter is connected to the third diode VD2; the output end of the low-end converter is connected to the output end of the fourth diode VD3; the anodes of the third diode VD2 and the fourth diode VD4 are connected to each other;

[0036] The high-end converter is specifically configured to: receive the DC voltage, and when the voltage value of the DC voltage is within the first preset operating voltage range of the high-end converter, convert the DC voltage and output the converted DC voltage;

[0037] The low-end converter is specifically configured to: receive the DC voltage, and when the voltage value of the DC voltage is within the second preset operating voltage range of the low-end converter, convert the DC voltage and output the converted DC voltage.

[0038] Optionally, there is an overlapping operating voltage range between the first preset operating voltage range of the low-end converter and the second preset operating voltage range of the high-end converter.

[0039] Optionally, the rectifier filter circuit includes: a first rectifier bridge VD1 and a first capacitor C1;

[0040] The positive output terminal of the first rectifier bridge VD1 is connected to the positive terminal of the first capacitor C1; the grounded output terminal of the first rectifier bridge VD1 is connected to the negative terminal of the first capacitor C1;

[0041] The input terminal of the first rectifier bridge VD1 is used to receive the input voltage and convert the input voltage into an initial DC voltage; the input voltage includes a DC voltage and an AC voltage;

[0042] The first capacitor C1 is used to be connected in parallel with the first rectifier bridge VD1 to filter the initial DC voltage and output the DC voltage.

[0043] In a second aspect, the present application further provides a power supply, and the power supply includes the power supply circuit provided in the first aspect above.

[0044] Thus, the present application has the following beneficial effects:

[0045] The present application provides a power supply circuit and a power supply applicable to a wide voltage range input. The power supply circuit includes a rectifier and filter circuit, a voltage detection and selection circuit, a relay input current limiting protection circuit, and an output converter circuit. The voltage detection and selection circuit includes a low-voltage circuit and a high-voltage circuit; the relay input current limiting protection circuit includes a current limiting protection circuit and a relay; the low-voltage circuit is connected to the relay; the current limiting protection circuit is connected to the relay; the output converter circuit includes a low-end converter and a high-end converter; the rectifier and filter circuit is configured to receive an input voltage, convert the input voltage into a DC voltage, and input the DC voltage into the low-voltage circuit and the high-voltage circuit; the voltage detection and selection circuit is configured to, when the low-voltage circuit is working and the high-voltage circuit is not working, control the relay to be energized and input the DC voltage into the low-end converter; or, when the low-voltage circuit is not working and the high-voltage circuit is working, input the DC voltage into the high-end converter; the relay input current limiting protection circuit is configured to limit the current so that the relay works within a preset current threshold range; the low-end converter is configured to receive the DC voltage, convert the DC voltage, and output the converted DC voltage; the high-end converter is configured to receive the DC voltage, convert the DC voltage, and output the converted DC voltage.

[0046] In this way, the high-end converter responsible for high-voltage conversion is always connected in the power supply circuit, and the other low-end converter responsible for low-voltage conversion is separated by a relay. On the one hand, when the input voltage is low, the low-voltage circuit works and the high-voltage circuit does not work. The relay is energized and connected to the low-end converter, and the low-end converter works, thereby realizing the conversion of the DC voltage of the low voltage. That is, the power supply circuit can be applicable to the input of a low voltage range. On the other hand, the high-end converter responsible for high-voltage conversion is always connected in the power supply circuit. When the input voltage is low, the high-end converter will not start. When the input voltage is high, the high-voltage circuit works and the low-voltage circuit does not work. The high-end converter works and realizes the conversion of the DC voltage of the high voltage. That is, the power supply circuit can be applicable to the input of a high voltage range. Compared with the prior art, the power supply circuit of the present application can be applicable to a very wide voltage range input, does not require derating, improves the conversion efficiency, and reduces the conversion cost. Brief Description of the Drawings

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present application. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings.

[0048] Figure 1 It is a schematic diagram of the overall structure of a power supply circuit applicable to a wide voltage range input provided by the present application;

[0049] Figure 2 Schematic structural diagram of a rectifying and filtering circuit provided by the present application;

[0050] Figure 3 Schematic structural diagram of a rectifying and filtering circuit connected to a voltage detection and selection circuit provided by the present application;

[0051] Figure 4 Overall schematic structural diagram of a voltage detection and selection circuit provided by the present application;

[0052] Figure 5 Partial schematic structural diagram of a voltage detection and selection circuit provided by the present application;

[0053] Figure 6 Another partial schematic structural diagram of a voltage detection and selection circuit provided by the present application;

[0054] Figure 7 Schematic structural diagram of a relay input current limiting protection circuit connected to an output converter circuit provided by the present application;

[0055] Figure 8 Partial schematic structural diagram of a relay input current limiting protection circuit provided by the present application;

[0056] Figure 9 Overall schematic structural diagram of a relay input current limiting protection circuit provided by the present application. Detailed implementation manners

[0057] Multiple involved in the embodiments of the present application means greater than or equal to two. It should be noted that in the description of the embodiments of the present application, terms such as "first" and "second" are only used for the purpose of distinguishing descriptions, and cannot be understood as indicating or implying relative importance, nor can they be understood as indicating or implying an order.

[0058] To make the above objects, features, and advantages of the present application more obvious and understandable, the embodiments of the present application will be further described in detail below with reference to the drawings and specific implementation manners. It can be understood that the specific embodiments described herein are only for explaining the present application and are not intended to limit the present application. Additionally, it should be noted that for ease of description, only parts related to the present application are shown in the drawings, not all structures.

[0059] The applicant has found that in order to allow the power supply to receive a wider input range voltage, two solutions are usually adopted. The first is to use a single converter solution, that is, to select a flyback topology solution with the largest input range. However, under this solution, no matter how the converter parameters are adjusted, there will be a problem that the high-end and low-end converters cannot be taken into account at the same time. Generally, they will be greatly derated when the input voltage is low and cannot be fully loaded; the second is to use a two-stage converter, that is, a mode in which the converters are connected in series. However, under this solution, the first-stage converter will raise the low voltage very high, or drop the high voltage very low. The entire conversion process is costly and the conversion efficiency is very low, and the voltage resistance problem of the previous stage is also very difficult to solve.

[0060] In the prior art, the maximum value in the input voltage range is at most two to three times the minimum value, such as the low voltage range of 7V to 30V, or the high voltage range of 100V to 240V. However, there is currently no better solution to simultaneously apply to low voltage and high voltage inputs and to achieve an extremely wide input range (for example, 9V-420V DC voltage and 7V to 300V AC voltage).

[0061] Based on this, the present application provides a power supply circuit and power supply suitable for wide voltage range input, the power supply circuit including: a rectifier and filter circuit, a voltage detection and selection circuit, a relay input current limiting protection circuit and an output converter circuit, the voltage detection and selection circuit including a low voltage circuit and a high voltage circuit; the relay input current limiting protection circuit including a current limiting protection circuit and a relay; the low voltage circuit is connected to the relay; the current limiting protection circuit is connected to the relay; the output converter circuit includes a low-end converter and a high-end converter; the rectifier and filter circuit is used to receive the input voltage, convert the input voltage into a DC voltage, and input the DC voltage to the low voltage circuit and a high voltage circuit; a voltage detection and selection circuit, used to control the relay to energize and input the DC voltage to the low-end converter when the low voltage circuit is working and the high voltage circuit is not working; or, when the low voltage circuit is not working and the high voltage circuit is working, input the DC voltage to the high-end converter; a relay input current limiting protection circuit, used to limit the current so that the relay works within a preset current threshold range; a low-end converter, used to receive a DC voltage, convert the DC voltage, and output the converted DC voltage; a high-end converter, used to receive a DC voltage, convert the DC voltage, and output the converted DC voltage.

[0062] Thus, the high-end converter responsible for high-voltage conversion is always connected to the power supply circuit, and the low-end converter responsible for low-voltage conversion is separated by a relay. When the input voltage is low, the low-voltage circuit works and the high-voltage circuit does not work. The relay is energized to connect to the low-end converter, and the low-end converter works, thereby realizing the conversion of the DC voltage of the low voltage. That is, the power supply circuit can be applicable to the input in the low-voltage range. When the input voltage is low, the high-end converter will not start. When the input voltage is high, the high-voltage circuit works and the low-voltage circuit does not work. The high-end converter works to realize the conversion of the DC voltage of the high voltage. That is, the power supply circuit can be applicable to the input in the high-voltage range. Compared with the prior art, the power supply circuit of the present application can be applicable to the input in an extremely wide voltage range, does not require derating, improves the conversion efficiency, and reduces the conversion cost.

[0063] To facilitate the understanding of the specific implementation of the power supply circuit applicable to wide voltage range input provided by the embodiments of the present application, the following will be described in conjunction with the drawings.

[0064] Please refer to Figure 1 , which is Figure 1 the overall structural schematic diagram of a power supply circuit applicable to wide voltage range input provided by the embodiments of the present invention.

[0065] The power supply circuit applicable to wide voltage range input includes:

[0066] a rectifier filter circuit 100, a voltage detection and selection circuit 200, a relay input current limiting protection circuit 300, and an output converter circuit 400;

[0067] The voltage detection and selection circuit 200 includes a low-voltage circuit and a high-voltage circuit;

[0068] The relay input current limiting protection circuit 300 includes a current limiting protection circuit and a relay K1; the low-voltage circuit is connected to the relay K1; the current limiting protection circuit is connected to the relay K1; the output converter circuit 400 includes a low-end converter and a high-end converter;

[0069] The rectifier filter circuit 100 is used to receive the input voltage, convert the input voltage into a DC voltage, and input the DC voltage into the low-voltage circuit and the high-voltage circuit;

[0070] The voltage detection and selection circuit is used to control the relay to be energized and input the DC voltage into the low-end converter when the low-voltage circuit works and the high-voltage circuit does not work; or, input the DC voltage into the high-end converter when the low-voltage circuit does not work and the high-voltage circuit works;

[0071] The relay input current limiting protection circuit is used for current limiting so that the relay works within a preset current threshold range;

[0072] A low - end converter, which is used to receive a DC voltage, convert the DC voltage, and output the converted DC voltage;

[0073] A high - end converter, which is used to receive a DC voltage, convert the DC voltage, and output the converted DC voltage.

[0074] The power supply circuit applicable to wide - voltage - range input in the embodiments of the present application includes a rectifier - filter circuit 100, a voltage detection and selection circuit 200, a relay input current - limiting protection circuit 300, and an output converter circuit 400.

[0075] It should be noted that the working principle of this power supply circuit is as follows: The rectifier - filter circuit 100 receives the input voltage and converts it into a DC voltage, and inputs the DC voltage into the voltage detection and selection circuit 200. The DC voltage is detected through the low - voltage circuit and the high - voltage circuit in the voltage detection and selection circuit 200. Specifically, the detection result shows that when the low - voltage circuit works and the high - voltage circuit does not work, that is, the DC voltage is detected as a low voltage. At this time, the relay K1 is energized and conducts with the low - end converter in the output converter circuit 400, and the DC voltage can be input into the low - end converter. The low - end converter receives the DC voltage and performs conversion to obtain the converted DC voltage; when the low - voltage circuit does not work and the high - voltage circuit works, that is, the DC voltage is detected as a high voltage. At this time, the DC voltage is input into the high - end converter, and the high - end converter receives the DC voltage and performs conversion to obtain the converted DC voltage.

[0076] It should be noted that since the power supply circuit in the embodiments of the present application is applicable to wide - voltage - range input, the relay K1 needs to be able to adapt to high - voltage and low - voltage working scenarios. However, in the high - voltage working scenario, there is a problem of device voltage withstand. For example, the relay K1 powered by 12V can only withstand a maximum voltage of about 25V, and in this case, the loss of the relay K1 is also very large. In a higher - input - voltage scenario, the relay K1 may even burn out. Therefore, in order to protect the safety of the relay K1 and enable the normal operation of this power supply circuit, the relay input current - limiting protection circuit 300 is introduced in the embodiments of the present application, which can limit the current flowing through the relay K1. That is to say, the relay input current - limiting protection circuit 300 is used for current limiting, so that the relay K1 works within a preset current threshold range, and better enables this power supply circuit to be applicable to wide - voltage - range input.

[0077] Thus, in the embodiment of the present application, the high-side converter responsible for high-voltage conversion in the output converter circuit 400 is always connected to the power supply circuit, and the other low-side converter responsible for low-voltage conversion is separated by a relay K1. On the one hand, when the input voltage is low, the low-voltage circuit works and the high-voltage circuit does not work. The relay K1 is energized and connected to the low-side converter, so as to realize the conversion of the low-voltage DC voltage. That is, the power supply circuit can be applied to the input in the low-voltage range. On the other hand, the high-side converter responsible for high-voltage conversion is always connected to the power supply circuit. Since the high-side converter only works when the voltage reaches the preset working threshold, when the input voltage is low, the high-side converter will not start. When the input voltage is high, the high-voltage circuit works and the low-voltage circuit does not work, and the high-side converter works to realize the conversion of the high-voltage DC voltage. That is, the power supply circuit can be applied to the input in the high-voltage range.

[0078] Embodiment 1

[0079] Please refer to Figure 2 , Figure 2 which is a schematic structural diagram of a rectifier and filter circuit provided by the embodiment of the present application.

[0080] In a possible implementation manner, the rectifier and filter circuit 100 of the embodiment of the present application includes: a first rectifier bridge VD1 and a first capacitor C1;

[0081] The positive output terminal of the first rectifier bridge VD1 is connected to the positive terminal of the first capacitor C1; the grounded output terminal of the first rectifier bridge VD1 is connected to the negative terminal of the first capacitor C1;

[0082] The input terminal of the first rectifier bridge VD1 is used to receive the input voltage and convert the input voltage into an initial DC voltage; the input voltage includes a DC voltage and an AC voltage;

[0083] The first capacitor C1 is used to be connected in parallel with the first rectifier bridge VD1 to filter the initial DC voltage to output a DC voltage.

[0084] In the embodiment of the present application, the input terminal of the first rectifier bridge VD1 is connected to the input voltage, the positive output terminal (HV+) of the first rectifier bridge VD1 is connected to the positive terminal of the first capacitor C1, GND is the common reference ground in the power supply circuit, the grounded output terminal of the first rectifier bridge VD1 is connected to the common reference ground, and the negative terminal of the first capacitor C1 is connected to the common reference ground, which can be regarded as the grounded output terminal of the first rectifier bridge VD1 being connected to the negative terminal of the first capacitor C1.

[0085] That is to say, when the input voltage is connected to the power supply circuit, it first passes through the first rectifier bridge VD1 to convert the input voltage into an initial DC voltage. The presence of the first rectifier bridge VD1 solves the problem of compatibility between DC and AC input voltages, and for DC input, there is no need to specifically specify the positive and negative terminals. It can be directly connected, and the power supply circuit can work properly without being damaged. The first capacitor C1 connected in parallel with the first rectifier bridge VD1 filters the initial DC voltage to output a DC voltage. After passing through the rectifier and filter circuit 100, the input voltage is divided into a positive terminal and a negative terminal. For specific details, please refer to Figure 3 , Figure 3 which is a schematic structural diagram of a rectifier and filter circuit connecting a voltage detection and selection circuit provided by an embodiment of the present application.

[0086] In the embodiment of the present application, the range of the input voltage includes 9VDC - 420VDC and 7Vac ~ 300Vac. Here, (Voltage Direct Current, VDC) represents DC voltage, and (Voltage Alternating Current, Vac) represents AC voltage. That is to say, the range of the input voltage includes DC voltages from 9V to 420V and AC voltages from 7Vac to 300Vac.

[0087] Embodiment Two

[0088] Please refer to Figure 3 and Figure 4 , Figure 3 which is a schematic structural diagram of a rectifier and filter circuit connecting a voltage detection and selection circuit provided by an embodiment of the present application, Figure 4 which is a schematic overall structural diagram of a voltage detection and selection circuit provided by an embodiment of the present application.

[0089] In a possible implementation, the high - voltage circuit includes: a second resistor R2, a fourth resistor R4, and a first MOS transistor VT3;

[0090] The first end of the second resistor R2 is connected to the positive end of the first capacitor C1 in the rectifier and filter circuit 100; the second end of the second resistor R2 is connected to the first end of the fourth resistor R4; the second end of the fourth resistor R4 is connected to the negative end of the first capacitor C1; the fourth resistor R4 is connected in parallel between the gate and the drain of the first MOS transistor VT3, and the drain of the first MOS transistor VT3 is connected to the negative end of the first capacitor C1;

[0091] The low - voltage circuit includes: a third resistor R3, a fifth resistor R5, a second capacitor C2, and a second MOS transistor VT4;

[0092] The first end of the third resistor R3 is connected to the positive end of the first capacitor C1, and the second end of the third resistor R3 is connected to the source of the first MOS transistor VT3; the fifth resistor R5 and the second capacitor C2 are connected in parallel. The first end after the parallel connection of the fifth resistor R5 and the second capacitor C2 is respectively connected to the gate of the second MOS transistor VT4 and the source of the first MOS transistor VT3. The second end after the parallel connection of the fifth resistor R5 and the second capacitor C2 is connected to the negative end of the first capacitor C1. The drain of the second MOS transistor VT4 is connected to the negative end of the first capacitor C1, and the source of the second MOS transistor VT4 is connected to one end of the control coil in the relay K1.

[0093] In the embodiment of the present application, the high-voltage circuit in the voltage detection and selection circuit 200 includes the second resistor R2, the fourth resistor R4, and the first MOS transistor VT3; the low-voltage circuit in the voltage detection and selection circuit 200 includes: the third resistor R3, the fifth resistor R5, the second capacitor C2, and the second MOS transistor VT4.

[0094] It should be noted that the working principle of the voltage detection and selection circuit 200 is as follows: the second resistor R2 and the fourth resistor R4 form a voltage division network, and the third resistor R3 and the fifth resistor R5 form a voltage division network. Among them, the turn-on voltages of the first MOS transistor VT3 and the second MOS transistor VT4 are approximately the same, and it is set that the voltage division on the fourth resistor R4 is lower than the voltage division on the fifth resistor R5. In the specific implementation process, the switching point can be flexibly changed by adjusting the resistance value of the fourth resistor R4 according to the actual working requirements.

[0095] It should be noted that in the low-voltage circuit in the embodiment of the present application, due to the presence of the second capacitor C2 and the parallel connection of the fifth resistor R5 and the second capacitor C2, the voltage of the fifth resistor R5 gradually rises. Therefore, the voltage rise rate of the fifth resistor R5 is always slower than the voltage rise rate of the fourth resistor R4. The gate voltage of the first MOS transistor VT3 is obtained by pure resistor voltage division and is very sensitive. When the input DC voltage is a high voltage, the first MOS transistor VT3 will definitely turn on prior to the second MOS transistor VT4. Therefore, in the case of a high input DC voltage, the relay K1 will not be accidentally turned on. When the input DC voltage is a low voltage, because the voltage value of the input voltage is too low, the voltage divided by the first MOS transistor VT3 is less than the turn-on voltage of the first MOS transistor VT3, and the first MOS transistor VT3 will not turn on. The voltage divided by the second MOS transistor VT4 is greater than the turn-on voltage of the second MOS transistor VT4, and the second MOS transistor VT4 turns on. That is to say, when the input DC voltage is a low voltage, the high-voltage circuit does not work while the low-voltage circuit works. In this way, the control winding of the relay K1 is energized, the relay K1 is attracted, and the DC voltage is introduced into the low-end converter in the output converter circuit 400, so that the low-end converter works.

[0096] To facilitate the understanding of the solution of the embodiments of the present application, the following is described with reference to examples. The turn-on voltage can be set to about 2.4V, for example.

[0097] When a low voltage is input, the voltage obtained by the fourth resistor R4 is too low, the voltage of Vgs1 is less than 2.4V, the first MOS transistor VT3 cannot reach 2.4V, and the first MOS transistor VT3 will not turn on. However, the voltage of Vgs2 is greater than 2.4V, and the second MOS transistor VT4 turns on. In this way, the control winding of the relay K1 is energized, the relay K1 is attracted, and the DC voltage is introduced into the low-end converter in the output converter circuit 400, so that the low-end converter works.

[0098] Among them, Vgs is the voltage difference between the gate (G) and the source (S) of a Metal Oxide Semiconductor Field Effect Transistor (MOSFET). MOSFET is abbreviated as MOS transistor.

[0099] When a high voltage is input, the voltage division on the fourth resistor R4 quickly exceeds the threshold voltage of 2.4V, and the first MOS transistor VT3 turns on quickly. After turning on, it will pull the gate of the second MOS transistor VT4 to the ground, and the voltage division on the fifth resistor R5 cannot rise, so the second MOS transistor VT4 will remain in the off state. The control coil of the relay K1 is not energized and will not be attracted, and the low-voltage circuit will be completely isolated from the high-voltage circuit, so the low-end converter will not be powered.

[0100] In a possible implementation manner, in order to make the embodiments of the present application have better implementation effects, in terms of device selection, some low-voltage devices can be selected for the low-end converter without being damaged. There is no great requirement for the breakdown voltage of the first MOS transistor VT3. For example, it can be set to be greater than 30V or about 30V. The second MOS transistor VT4 requires a high breakdown voltage, for example, it can be 650V.

[0101] In this way, the power supply circuit provided by the embodiments of the present application can distinguish the high and low input voltages and perform switching by using the charging time difference generated by the second capacitor C2. That is to say, it is possible to select whether to turn on the MOS transistor and which MOS transistor to turn on according to the high and low input voltages, so as to realize the selection of the converter corresponding to the input voltage to work. When a low voltage is input, the low-end converter works. When a high voltage is input, the high-end converter works, so as to be applicable to a wide voltage range input.

[0102] Embodiment III

[0103] It should be noted that in the specific implementation process, if in a high-voltage state, the voltage of the first MOS transistor VT3 is very high. Then when the input DC voltage switches from high voltage to low voltage, there is a situation where the voltage of the first MOS transistor VT3 cannot drop rapidly, and the first MOS transistor VT3 cannot be turned off quickly, which in turn causes the second MOS transistor VT4 not to be turned on quickly.

[0104] In a possible implementation manner, in order to accelerate the turn-off of the first MOS transistor VT3 and ensure the switching rate from high voltage to low voltage, based on the above-mentioned second embodiment, the high-voltage circuit provided by the embodiment of the present application further sets a second diode VD5. Specifically, reference can be made to Figure 5 the partial structural schematic diagram of a voltage detection and selection circuit shown in

[0105] The high-voltage circuit provided by the embodiment of the present application may further include: a second diode VD5;

[0106] The second diode VD5 and the second resistor R2 are connected in parallel. The anode end of the second diode VD5 is connected to the positive end of the first capacitor C1, and the cathode end of the second diode VD5 is connected to the gate of the first MOS transistor VT3;

[0107] The second diode VD5 is used to discharge the gate of the first MOS transistor VT3, so that the power supply circuit can achieve the switching between high voltage and low voltage.

[0108] In the embodiment of the present application, a second diode VD5 is further set in the high-voltage circuit. The cathode end of the second diode VD5 is connected to the gate of the first MOS transistor VT3 (the gate can also be represented by the G pole). When the input voltage switches from high voltage to low voltage, the second diode VD5 can quickly discharge the gate of the first MOS transistor VT3. The quick discharge ensures the reliability during the large-range switching of the input DC high voltage and low voltage, realizes the quick switching of the power supply circuit between high voltage and low voltage, ensures the stability of the real-time voltage of the power supply circuit, and especially improves the reliability of the power supply circuit in extreme working conditions such as quick on / off.

[0109] Embodiment Four

[0110] It should be noted that there is also a problem in the low-voltage working scenario. That is, in order to be compatible with high-voltage input and reduce losses, the resistance value of the third resistor R3 is usually selected in the megohm level. However, in the case of low-voltage input, the driving ability of the second MOS transistor VT4 is weak. Based on the above-mentioned second embodiment, the embodiment of the present application introduces a first diode VD4 and a seventh resistor R7 to form a hysteresis circuit. Specifically, please refer to Figure 6 the partial structural schematic diagram of another voltage detection and selection circuit shown in

[0111] Then, in a possible implementation, the low-voltage circuit further includes a seventh resistor R7 and a first diode VD4;

[0112] Wherein, the first end of the seventh resistor R7 is connected to the gate of the second MOS transistor VT4, the second end of the seventh resistor R7 is connected to the anode of the first diode VD4, and the cathode of the first diode VD4 is connected to the auxiliary source of the low-end converter; the low-end transformer is the transformer in the output converter circuit;

[0113] The auxiliary source of the low-end converter is used to supply power to the second MOS transistor VT4 based on the hysteresis circuit formed by the seventh resistor R7 and the first diode VD4 when the low-end converter is working, so that the second MOS transistor VT4 is in the on state.

[0114] In the embodiment of the present application, the low-voltage circuit further includes a seventh resistor R7 and a first diode VD4. After the low-end converter works, the auxiliary source of the low-end converter supplies driving energy to the second MOS transistor VT4 through the hysteresis circuit formed by the seventh resistor R7 and the first diode VD4, so as to ensure that the second MOS transistor VT4 is in the on state, that is, the second MOS transistor VT4 can be in a stable working state, the voltage of the control winding of the relay K1 is stable, and further the reliability of the entire power supply circuit is ensured.

[0115] Embodiment Five

[0116] It should be noted that, according to the above, there is a problem in the high-voltage working scenario, that is, the device withstand voltage problem. The voltage of the control winding of the relay K1 powered by 12V can only withstand about 25V at most, and the loss of the relay K1 is also very large in this case. To solve this problem, the relay input current limiting protection circuit 300 is introduced in the embodiment of the present application. For details, please refer to Figure 7 and Figure 8 , Figure 7 is a schematic structural diagram of a relay input current limiting protection circuit connected to an output converter circuit provided by the present application, Figure 8 is a partial structural schematic diagram of a relay input current limiting protection circuit provided by the present application.

[0117] In a possible implementation, the current limiting protection circuit includes a first resistor R1, a sixth resistor R6, a first triode VT1 and a second triode VT2;

[0118] The first end of the first resistor R1 is connected to the positive end of the first capacitor C1 in the rectifying and filtering circuit 100, and the second end of the first resistor R1 is connected to the base of the first triode VT1 and the collector of the second triode VT2; the collector of the first triode VT1 is connected to the positive end of the first capacitor C1 in the rectifying and filtering circuit, and the emitter of the first triode VT1 is connected to the base of the second triode VT2;

[0119] The first end of the sixth resistor R6 is connected to the base of the second triode VT2, and the second end of the sixth resistor R6 is connected to the emitter of the second triode VT2;

[0120] The first end of the control coil of the relay K1 is connected to the emitter of the second triode VT2, and the second end of the control coil of the relay K1 is connected to the source of the second MOS transistor VT4; the first end of the switch terminal of the relay is connected to the positive end of the first capacitor C1, and the second end of the switch terminal of the relay is connected to the low-end converter;

[0121] The current limiting protection current is used to limit the current value of the current flowing to the relay, so that the relay operates within a preset current threshold range.

[0122] In the embodiment of the present application, the current limiting protection circuit includes a first resistor R1, a sixth resistor R6, a first triode VT1, and a second triode VT2. The working principle of the relay input current limiting protection circuit 300 is that as the current increases, the current flowing through the sixth resistor R6 will increase, and a voltage drop will be generated. When the voltage of the sixth resistor R6 is higher than the turn-on voltage of the second triode VT2 (where the turn-on voltage of the second triode VT2 can be set according to requirements. For the convenience of understanding the embodiment of the present application, 0.7V is taken as an example here), the second triode VT2 conducts, and the first triode VT1 turns off. At this time, the current divided by the sixth resistor R6 decreases. After the decrease, the voltage of the sixth resistor R6 is lower than the turn-on voltage of the second triode VT2, the second triode VT2 turns off, and the first triode VT1 turns on. This cycle repeats, so that the current I flowing through the sixth resistor R6 R6 is not greater than And the sixth resistor R6 and the relay K1 are in a series relationship, that is, the current value of the current flowing to the relay K1 is limited, so that the relay K1 operates within a preset current threshold range, where I R6 represents the current value flowing through the sixth resistor R6, and R R6 represents the resistance value of the sixth resistor R6.

[0123] It should be noted that in the embodiment of the present application, two triodes are introduced to limit the current. The sixth resistor R6 is a current limiting resistor, and the resistance value of the sixth resistor R6 can be set according to the current required by the relay K1. That is, the current limiting protection circuit in the relay input current limiting protection circuit 300 is used to limit the current, so that the relay K1 operates within the normal current threshold range, ensuring the normal operation of the power supply circuit.

[0124] Please refer to Figure 9 , which is a schematic diagram of the overall structure of another relay input current limiting protection circuit provided by the embodiment of the present application.

[0125] In a possible implementation, the relay input current limiting protection circuit 300 further includes: a first voltage stabilizing diode ZD1;

[0126] The first voltage stabilizing diode ZD1 is connected in parallel across both ends of the control coil of the relay K1. The anode of the first voltage stabilizing diode ZD1 is connected to the emitter end of the second triode VT2, and the cathode of the first voltage stabilizing diode ZD1 is connected to the source of the second MOS transistor;

[0127] The first voltage stabilizing diode ZD1 is used to keep the voltage of the control coil of the relay K1 within a preset voltage threshold range.

[0128] In the embodiment of the present application, by connecting the first voltage stabilizing diode ZD1 in parallel across both ends of the control coil of the relay K1, the voltage of the control coil of the relay K1 can be kept within a preset voltage threshold range, improving the reliability of the entire power supply circuit. In the specific implementation process, the first voltage stabilizing diode ZD1 can be added to the control coil of the relay K1.

[0129] Embodiment Six

[0130] In a possible implementation, the output converter circuit 400 in the embodiment of the present application further includes: a third diode VD2 and a fourth diode VD3; the high-end converter is a converter including an under-voltage protection Brown out setting circuit;

[0131] Wherein, the output end of the high-end converter is connected to the third diode VD2; the output end of the low-end converter is connected to the output end of the fourth diode VD3; the anodes of the third diode VD2 and the fourth diode VD4 are connected to each other;

[0132] The high-end converter is specifically configured to: receive a DC voltage, and when the voltage value of the DC voltage is within the first preset operating voltage range of the high-end converter, convert the DC voltage and output the converted DC voltage;

[0133] The low-end converter is specifically configured to: receive a DC voltage, and when the voltage value of the DC voltage is within the second preset operating voltage range of the low-end converter, convert the DC voltage and output the converted DC voltage.

[0134] In the embodiment of the present application, the high-end converter is equipped with a BO setting circuit. When the input voltage is low, the high-end converter will not start, and it will only work when the operating high voltage threshold set by the BO setting circuit is reached. In the specific implementation process, those skilled in the art can set the operating voltage threshold of the high-end converter according to actual needs.

[0135] For example, the first preset operating voltage range of the low-end converter is 7V to 90V, and the second preset operating voltage range of the high-end converter is above 85V.

[0136] The high - end converter receives a DC voltage. Only when the voltage value of the DC voltage is greater than 85V does the high - end converter work and convert the DC voltage to output a converted DC voltage. Because when the DC voltage is a high voltage, the low - end converter cannot be connected to the power supply circuit. Only when the voltage value of the DC voltage is in the range of 7V to 90V does the low - end converter work. That is, at this time, the low - end converter receives the DC voltage, converts the DC voltage, and outputs a converted DC voltage.

[0137] In a possible implementation, a difference can be set between the voltage value of the DC voltage output by the low - end converter and the voltage value of the DC voltage output by the high - end converter. The high - end converter output takes precedence to ensure smooth output when the input voltage switches.

[0138] It should be noted that since the voltage switching point is determined by the turn - on voltage of the first MOS transistor VT3, and the turn - on voltage has a certain range, it is impossible to achieve a smooth transition between high voltage and low voltage, and there is a situation of output power - off. Therefore, the solution provided in the embodiments of this application is to create an overlap between the operating voltage range of the high - end converter and the operating voltage range of the low - end converter.

[0139] In a possible implementation, there is an overlapping operating voltage range between the first preset operating voltage range of the low - end converter and the second preset operating voltage range of the high - end converter.

[0140] In the embodiments of this application, considering the smooth transition of the input voltage at the switching point, an overlapping operating voltage range is set between the first preset operating voltage range of the low - end converter and the second preset operating voltage range of the high - end converter.

[0141] For example, the first preset operating voltage range of the low - end converter is 7V to 90V, and the second preset operating voltage range of the high - end converter is above 85V. Thus, there is an overlapping operating voltage range of 85V to 90V. Within this overlapping operating voltage range, both the high - end converter and the low - end converter work and serve as backups for each other, so that the voltage switching point can be smoothly passed, and the output will not lose power.

[0142] In addition, the embodiments of this application also provide a power supply including any one of the above - mentioned power supply circuits.

[0143] For the introduction of the power supply provided in this application, please refer to the embodiments of the above - mentioned power supply circuit, and this application will not elaborate here.

[0144] Each embodiment in this specification is described in a progressive manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for the apparatus embodiments, since they are basically similar to the method embodiments, the description is relatively simple. For the relevant parts, reference can be made to the description of the method embodiments. The apparatus embodiments described above are merely illustrative. The modules described as separate components may or may not be physically separated. The components shown as modules may or may not be physical modules, that is, they may be located in one place or distributed to multiple network elements. Some or all of the modules can be selected according to actual needs to achieve the objectives of the solution of this embodiment. A person of ordinary skill in the art can understand and implement it without creative work.

[0145] The above is only the preferred embodiment of the present application and is not intended to limit the protection scope of the present application. It should be noted that for those of ordinary skill in the art in the technical field of the present application, without departing from the premise of the present application, several improvements and modifications can still be made, and these improvements and modifications should also be regarded as the protection scope of the present application.

Claims

1. A power supply circuit suitable for wide voltage range input, characterized in that: include: A rectifier filter circuit, a voltage detection and selection circuit, a relay input current limiting protection circuit and an output converter circuit; the voltage detection and selection circuit includes a low voltage circuit and a high voltage circuit; the relay input current limiting protection circuit includes a current limiting protection circuit and a relay; the low voltage circuit is connected to the relay; the current limiting protection circuit is connected to the relay; the output converter circuit includes a low-end converter and a high-end converter; The rectifier and filter circuit is used to receive an input voltage, convert the input voltage into a direct current voltage, and input the direct current voltage into the low voltage circuit and the high voltage circuit; The voltage detection and selection circuit is used to control the relay to be energized to input the DC voltage to the low-end converter when the low-voltage circuit is working and the high-voltage circuit is not working; or to input the DC voltage to the high-end converter when the low-voltage circuit is not working and the high-voltage circuit is working; The relay input current limiting protection circuit is used for current limiting so that the relay operates within a preset current threshold range; The low-end converter is used to receive the DC voltage, convert the DC voltage, and output the converted DC voltage; The high-end converter is used to receive the DC voltage, convert the DC voltage, and output the converted DC voltage.

2. The power supply circuit according to claim 1, characterized in that: The high voltage circuit comprises: a second resistor R2, a fourth resistor R4 and a first MOS transistor VT3; The first end of the second resistor R2 is connected to the positive end of the first capacitor C1 in the rectifier and filter circuit; the second end of the second resistor R2 is connected to the first end of the fourth resistor R4; the second end of the fourth resistor R4 is connected to the negative end of the first capacitor C1; the fourth resistor R4 is connected in parallel to the gate and drain of the first MOS transistor VT3, and the drain of the first MOS transistor VT3 is connected to the negative end of the first capacitor C1; The low voltage circuit includes: a third resistor R3, a fifth resistor R5, a second capacitor C2 and a second MOS transistor VT4; The first end of the third resistor R3 is connected to the positive end of the first capacitor C1, and the second end of the third resistor R3 is connected to the source of the first MOS tube VT3; the fifth resistor R5 is connected in parallel with the second capacitor C2, and the first end of the fifth resistor R5 and the second capacitor C2 after being connected in parallel is respectively connected to the gate of the second MOS tube VT4 and the source of the first MOS tube VT3, the second end of the fifth resistor R5 and the second capacitor C2 after being connected in parallel is connected to the negative end of the first capacitor C1, the drain of the second MOS tube VT4 is connected to the negative end of the first capacitor C1, and the source of the second MOS tube VT4 is connected to one end of the control coil in the relay.

3. The power supply circuit according to claim 2, characterized in that: The low voltage circuit also includes a seventh resistor R7 and a first diode VD4; Wherein, a first end of the seventh resistor R7 is connected to the gate of the second MOS transistor VT4, a second end of the seventh resistor R7 is connected to the anode of the first diode VD4, and a cathode of the first diode VD4 is connected to the auxiliary source of the low-end converter; The auxiliary source of the low-end converter is used to provide power to the second MOS transistor VT4 based on the hysteresis circuit formed by the seventh resistor R7 and the first diode VD4 when the low-end converter is working, so that the second MOS transistor VT4 is in an on state.

4. The power supply circuit according to claim 2, characterized in that: The high voltage circuit further includes: a second diode VD5; The second diode VD5 is connected in parallel with the second resistor R2, the anode end of the second diode VD5 is connected to the positive end of the first capacitor C1, and the cathode end of the second diode VD5 is connected to the gate of the first MOS transistor VT3; The second diode VD5 is used to discharge the gate of the first MOS transistor VT3, so that the power supply circuit can switch between high voltage and low voltage.

5. The power supply circuit according to claim 1, characterized in that: The current limiting protection circuit includes a first resistor R1, a sixth resistor R6, a first transistor VT1 and a second transistor VT2; The first end of the first resistor R1 is connected to the positive end of the first capacitor C1 in the rectifying and filtering circuit, and the second end of the first resistor R1 is connected to the base of the first transistor VT1 and the collector of the second transistor VT2; the collector of the first transistor VT1 is connected to the positive end of the first capacitor C1 in the rectifying and filtering circuit, and the emitter of the first transistor VT1 is connected to the base of the second transistor VT2; A first end of the sixth resistor R6 is connected to the base of the second transistor VT2, and a second end of the sixth resistor R6 is connected to the emitter of the second transistor VT2; The first end of the control coil of the relay is connected to the emitter of the second triode VT2, and the second end of the control coil of the relay is connected to the source of the second MOS tube VT4; the first end of the switch end of the relay is connected to the positive end of the first capacitor C1, and the second end of the switch end of the relay is connected to the low-end converter; The current limiting protection current is used to limit the current value of the current flowing to the relay so that the relay operates within the preset current threshold range.

6. The power supply circuit according to claim 5, characterized in that: The relay input current limiting protection circuit also includes: a first voltage regulator tube ZD1; The first voltage regulator tube ZD1 is connected in parallel to the two ends of the control coil of the relay, the anode of the first voltage regulator tube ZD1 is connected to the emitter end of the second transistor VT2, and the cathode of the first voltage regulator tube ZD1 is connected to the source of the second MOS tube; The first voltage regulator ZD1 is used to keep the voltage of the control coil of the relay within a preset voltage threshold range.

7. The power supply circuit according to claim 1, characterized in that: The output converter circuit further includes a third diode VD2 and a fourth diode VD3; the high-end converter is a converter including an undervoltage protection Brown out setting circuit; The output end of the high-end converter is connected to the third diode VD2; the output end of the low-end converter is connected to the output end of the fourth diode VD3; the anode of the third diode VD2 and the anode of the fourth diode VD4 are connected to each other; The high-end converter is specifically used to: receive the DC voltage, and when the voltage value of the DC voltage is within the first preset working voltage range of the high-end converter, convert the DC voltage and output the converted DC voltage; The low-end converter is specifically used to: receive the DC voltage, and when the voltage value of the DC voltage is within the second preset operating voltage range of the low-end converter, convert the DC voltage and output the converted DC voltage.

8. The circuit according to claim 7, characterized in that The first preset operating voltage range of the low-end converter and the second preset operating voltage range of the high-end converter have overlapping operating voltage ranges.

9. The power supply circuit according to claim 1, characterized in that: The rectification and filtering circuit comprises: a first rectifier bridge VD1 and a first capacitor C1; The output positive terminal of the first rectifier bridge VD1 is connected to the positive terminal of the first capacitor C1; the output ground terminal of the first rectifier bridge VD1 is connected to the negative terminal of the first capacitor C1; The input end of the first rectifier bridge VD1 is used to receive the input voltage and convert the input voltage into an initial DC voltage; the input voltage includes a DC voltage and an AC voltage; The first capacitor C1 is connected in parallel with the first rectifier bridge VD1 to filter the initial DC voltage to output the DC voltage.

10. A power supply, characterized in that: The invention comprises a power supply circuit as claimed in any one of claims 1 to 9.

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