A circuit capable of adjusting output current according to load changes

Abstract

The present invention relates to a circuit capable of adjusting output current according to load changes, the circuit comprising a power supply end (1) and a load end (2), and characterized in that it also comprises a controllable constant current source (3) arranged between the power supply end (1) and the load end (2) and capable of adjusting bus output current (I) according to load end (2) voltage changes to control its own power and the voltage formed by parasitic resistance (R') at the load end (2). The circuit can effectively solve the problem of constant current source components being burned out and poor signal transmission quality.

Description

Technical Field

[0001] The present invention relates to the field of electronic technology, and in particular to a circuit capable of adjusting output current according to load changes. Background Art

[0002] DALI dimming system plays an important role in the field of lighting control in the market, and DALI Power Supply (hereinafter referred to as DALI PS) is an indispensable special device in the DALI dimming system and the guarantee basis for DALI bus signal transmission. The IEC82386 standard stipulates that the voltage output range of DALI PS should be between 9.5-22.5V, and the maximum output current should not exceed 250mA.

[0003] In the existing DALI PS design, the conventional circuit design is that the load end is connected to the power end through a single constant current source, such as Figure 1 As shown. This circuit design is simple, but it also has many problems. One of the problems is that the DALI system uses Manchester encoding to transmit data. When sending data, the DALI bus will be short-circuited, causing the bus current I to reach 250mA. The characteristics of a single constant current source determine that in this case, the MOS device Q1 in the constant current source will carry an excessive voltage across both ends, which may reach 15.3V in this circuit, and the maximum power can be as high as 3.8W, which may cause the device to heat up quickly due to excessive power and cause damage, or increase the difficulty and cost of product design.

[0004] At the same time, when the DALI signal is transmitted, the carrier will be carried on the load voltage after certain calculations. However, the current single constant current source circuit design will produce parasitic resistance in the wire when the load line is very long. The parasitic resistance will consume part of the voltage, making the signal transmitted from the load end received by the DALI device incomplete. In order to ensure the quality of signal reception, the laying area of ​​the DALI system has to be sacrificed, which greatly limits the application of the DALI system. Moreover, the current circuit design is not ideal in preventing high voltage when the external voltage is too high. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to provide a circuit that can effectively prevent circuit components from burning due to power overload, has good signal transmission quality, can be laid over a large area, has good high-voltage protection effect, and can adjust the output current according to load changes.

[0006] In order to achieve the above object, the technical solution of the present invention is: a circuit capable of adjusting output current according to load changes, the circuit comprising a power supply end and a load end, characterized in that:

[0007] It also includes a controllable constant current source which is arranged between the power supply end and the load end and can adjust the bus output current according to the load end voltage change to control its own power size and the voltage size formed by the parasitic resistance of the load end.

[0008] Furthermore, the controllable constant current source includes a regulating component and an amplifying component connected to the regulating component, and the current output by the regulating component flows through the amplifying component;

[0009] The regulating component is connected to the power supply end and the load end respectively and can regulate the current outputted by itself according to the voltage of the load end;

[0010] The amplifying component is also connected to the load terminal and amplifies the current from the regulating component to regulate the bus output current.

[0011] Furthermore, the regulating component includes a regulator electrically connected to the power supply terminal and the amplifying component respectively, a first path electrically connected to the power supply terminal and the regulator respectively to provide a stable conduction current to the regulator, a second path electrically connected to the first path and the load terminal respectively and capable of changing the working state of the regulator when the load terminal voltage increases and is turned on, and a third path electrically connected between the power supply terminal and the load terminal and capable of being turned on when the load terminal voltage increases to output current to the regulator, wherein the second path is connected to the third path.

[0012] Furthermore, the regulator is a PNP transistor, the base of which is connected to the first path, the emitter of which is connected to the power supply terminal, and the collector of which is connected to the input terminal of the amplifying component through a first resistor.

[0013] Furthermore, the first path includes a second resistor having one end electrically connected to the power supply end and the other end grounded, and the base of the PNP transistor is connected to the one end of the second resistor; the resistance of the second resistor is at least 2MΩ.

[0014] Furthermore, the second path includes a third resistor and a zener diode, the cathode of the zener diode is connected to the one end of the second resistor through the third resistor and the anode is electrically connected to the load end, and the resistance of the third resistor is at least 5 MΩ.

[0015] Furthermore, the third path includes a first diode and a fourth resistor, the anode of the first diode is connected to the one end of the second resistor and the cathode is connected to the anode of the voltage-stabilizing diode through the fourth resistor, and the cathode of the first diode is connected between the third resistor and the cathode of the voltage-stabilizing diode through a wire.

[0016] Furthermore, the amplifying component is an NPN transistor, the base of the NPN transistor is connected to the collector of the PNP transistor, the emitter is grounded, and the collector is connected to the anode of the Zener diode.

[0017] Furthermore, the circuit also includes a high-voltage protection module composed of a first diode, a second diode, a third diode and a third resistor;

[0018] The cathode of the second diode is connected to the anode of the voltage stabilizing diode and the anode of the second diode is connected to the load end;

[0019] The anode of the third diode is connected to the one end of the second resistor and the cathode is connected to the power supply end.

[0020] Compared with the prior art, the advantages of the present invention are:

[0021] The previous single constant current source is replaced by a controllable constant current source, and the output current of the controllable constant current source can be adjusted by the load end voltage, which ensures that the constant current source device will not burn out due to excessive power when the circuit sends a signal and the load is short-circuited, and prevents the constant current source device from burning out when the output current reaches the upper limit and the load voltage is high when the load changes. At the same time, it effectively solves the problem of large voltage divided by parasitic resistance when sending signals, affecting the signal transmission quality, effectively improves the communication quality, and increases the wiring distance of the load end; and the setting of the anti-high voltage module can well solve the problem of circuit burning caused by excessive line voltage, thereby improving circuit safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The schematic diagram of the circuit of the prior art.

[0023] Figure 2 This is the overall structural diagram of this application.

[0024] Figure 3 This is a circuit diagram of a preferred embodiment of the present application.

[0025] Figure 4 For Figure 2 The I-Vrl curve graph produced. DETAILED DESCRIPTION

[0026] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0027] like Figure 2-3 The figure shows a preferred embodiment of a circuit of the present application which can adjust the output current according to load changes. Figure 2As shown, the circuit includes a power supply terminal 1, a load terminal 2, and a controllable constant current source 3 arranged between the power supply terminal 1 and the load terminal 2 and capable of adjusting the bus output current according to the voltage change of the load terminal 2 to control its own power size and the voltage size formed by the parasitic resistance R' of the load terminal 2.

[0028] like Figure 2 As shown, the controllable constant current source 3 includes a regulating component 31 and an amplifying component 32 connected to the regulating component 31. The current output by the regulating component 31 flows through the amplifying component 32. The regulating component 31 is respectively connected to the power supply terminal 1 and the load terminal 2 and can adjust its own output current according to the voltage of the load terminal 2. The amplifying component 32 is also connected to the load terminal 2 and can amplify the current from the regulating component 31 to adjust the bus output current. That is, the bus output current value of the circuit is equal to the current output after amplification by the amplifying component 32.

[0029] Specifically in this embodiment, the regulating component 31 includes a regulator 311 electrically connected to the power supply terminal 1 and the amplifying component 32, respectively, a first path 312 electrically connected to the power supply terminal 1 and the regulator 311 to provide a stable conduction current to the regulator 311, a second path 313 electrically connected to the first path 312 and the load terminal 2 and capable of changing the working state of the regulator 311 when the voltage at the load terminal 2 increases and is turned on, and a third path 314 electrically connected between the power supply terminal 1 and the load terminal 2 and capable of being turned on when the voltage at the load terminal 2 increases to output current to the regulator 311, and the third path 314 is connected to the second path 313.

[0030] For details, please see Figure 3 , the regulator 311 is a PNP transistor Q1, the base of the PNP transistor Q1 is connected to the first path 312, the emitter is connected to the power supply terminal 1, and the collector is connected to the input terminal of the amplifying component 32 through the first resistor R5; the first path 312 includes a second resistor R4 with one end electrically connected to the power supply terminal 1 and the other end grounded, the base of the PNP transistor Q1 is connected to the one end of the second resistor R4, the resistance of the second resistor R4 is at least 2MΩ, that is, in the circuit design, the resistance of R4 is very large, which can prevent the current flowing into the PNP transistor from being too large and burning the transistor, and at the same time, by designing R4 to be very large, it can ensure that the entire circuit effectively follows the load terminal voltage change and gradually realizes the regulation of the current, thereby achieving the desired effect. The specific analysis principle will be explained later.

[0031] Continue to see Figure 3The second path 313 includes a third resistor R2 and a voltage-stabilizing diode D4, the cathode of the voltage-stabilizing diode D4 is electrically connected to the one end of the second resistor R4 through the third resistor R2, and the anode is electrically connected to the load terminal 2, and the third resistor R2 is at least 5MΩ; the third path 314 includes a first diode D2 and a fourth resistor R1, the anode of the first diode D2 is connected to the one end of the second resistor R4, and the cathode is connected to the anode of the voltage-stabilizing diode D4 through the fourth resistor R1, and the cathode of the first diode D2 is connected between the third resistor R2 and the cathode of the voltage-stabilizing diode D4 through a wire. In this embodiment, the amplifying component 32 is an NPN transistor Q2, the base of the NPN transistor Q2 is connected to the collector of the PNP transistor Q1, the emitter is grounded, and the collector is connected to the anode of the voltage-stabilizing diode D4.

[0032] In this circuit, the PNP transistor Q1 and the NPN transistor Q2 form a composite tube to increase the current amplification factor. That is, if the amplification factor of the PNP transistor Q1 is β1 and the amplification factor of the NPN transistor Q2 is β2, the current amplification factor of the entire circuit is β = β1 × β2. The reason why two transistors are used to form a composite tube for current amplification output is to cleverly use the current amplification function of the transistor to achieve the purpose of adjusting the output current by the load terminal voltage.

[0033] Although the standard stipulates that the operating voltage of the system must be between 9.5-22.5V, the global mains power lines are between 85V and 265V, and the voltage loaded at the peak of the AC power is higher. This is easy to cause misconnection during the system installation process, resulting in the circuit being burned. In order to overcome this problem, the circuit also includes an anti-high voltage module 315 composed of a first diode D2, a second diode D3, a third diode D1 and a third resistor R2. The cathode of the second diode D3 is connected to the anode of the voltage regulator diode D4 and the anode of the second diode D3 is connected to the load terminal 2. The anode of the third diode D1 is connected to the one end of the second resistor R4 and the cathode is connected to the power supply terminal 1.

[0034] The working principle of the circuit is described below. First, let the bus output current be I, the maximum bus output current be Imax, the voltage value of the voltage regulator diode D4 be Vd4, the current flowing through the voltage regulator diode D4 be Id4, the voltage across the NPN transistor Q2 be Vce, the current flowing through the first diode D2 be Id2, the current flowing through the fourth resistor R1 be Ir1, the base current of the PNP transistor Q1 be Iqb1, the base current of the NPN transistor Q2 be Iqb2, and at the same time, let the resistance value of the load end be rl.

[0035] Now, we will discuss the magnitude of the bus output current I one by one as the load terminal voltage gradually increases from 0. First, it should be clear that when the circuit is in a normal wiring state, both transistors Q1 and Q2 are in the conducting state, and the conduction voltages of Q1 and Q2 are both 0.7V. When Vrl < 0.7V, it corresponds to a short circuit of the load, and rl = 0. Since Vrl is close to 0V, it can be considered that the voltage at point A = the voltage at point B. And the voltage at point A is always 16V, so the voltage at point B is also 16V. This makes D3 conduct, and the voltage at point D is 15.3V. Also, the voltage at point E is (16 - Vq1)V = (16 - 0.7)V = 15.3V. Therefore, the first transistor D2 is cut off because the voltage across it Vd2 < 0.7V, corresponding to Id2 = 0. The base current Iqb1 of the PNP transistor Q1 exists as Iqb1 = Ve / R4 = (16 - Vq1) / R4 = (16 - 0.7) / R4. Since the resistance value of the second resistor R4 is very large, Iqb1 is very small. At this time, both transistors Q1 and Q2 are operating in the amplification region. In this case of a short circuit, the bus output current I = β1 * β2 * Iqb1 = 15.3 * β1 * β2 / R4;

[0036] As Vrl gradually increases, that is, as rl increases and the load decreases, according to Vce = 16 - Vrl - Vd3, it can be known that Vce gradually decreases, that is, the voltage at point C = 15.3 - Vrl. And the voltage at point C is the voltage at point D. Therefore, it can be obtained that D2 conducts and Id2 gradually increases. Then Iqb1 = 15.3 / R4 + Id2, and I = β1 * β2 * Iqb1 continuously increases. Due to the existence of the zener diode D4, here, Vrl also needs to be compared with Vd4.

[0037] When the zener diode D4 is not conducting, that is, Vgd < Vd4, that is, Ve - Vd2 - Vd < Vd4, and Vd = Vb - 0.7, Ve = 15.3, Vb = 16 - Vrl. After conversion, Vrl - Vd2 < Vd4. Since Vd2 = 0.7V is relatively small and can be ignored, then Vrl < Vd4. In other words, as Vrl gradually increases, but when the zener diode D4 is still not conducting, corresponding to Vrl < Vd4. At this time, both transistors Q1 and Q2 are operating in the amplification region. Also, since the third resistor R2 is very large, the current in the branch E - G - F - D can be ignored. Then Id2 = Ir1 = Vfc / R1 = (16 - Vq1 - Vd2 - Vd3 - Vrl) / R1 = (16 - 0.7 - 0.7 - 0.7 - Vrl) / R1, and I = β1 * β2 * (15.3 / R4 + (13.9 - Vrl) / R1);

[0038] When the voltage zener diode D4 is turned on, that is, when Vrl>Vd4, the conduction of the voltage zener diode D4 will cause the current on the branch EFGC to surge, which will cause the transistor Q1 to immediately enter the saturation region while Q2 is still in the amplification region, then Iqb2=(16-0.7) / R5, I=β2*Iqb2=β2*15.3 / R5;

[0039] When the load-end voltage Vrl continues to increase, the transistor Q2 will also enter the saturation region. At this time, the transistor Q2 is equivalent to a wire, and Vrl=(16-0.7), I=15.3 / RL.

[0040] When the load voltage Vrl>15.3V, because Vb<0.7v, the diode D3 is cut off, and the circuit is in protection state; on the contrary, if Vrl<0V, because R2 is much larger than R1 and R3, the resistance of R1 and R3 can be ignored, and R1 and R3 can be equivalent to a wire, so Vg=Vf=Vc, Vrl<0v means Vb>16v, Vc>16-0.7=15.3v, so Vf>Ve, corresponding to D2 cut off, when the current flowing through R2 When the current on R1 is less than the current flowing through R4, (Ve-Vg) / R2<15.3 / R4, that is, (15.3-(16-Vrl-0.7)) / R2<15.3 / R4, corresponding to I=β1*β2*(15.3 / R4-(15.3-(16-Vrl-0.7)) / R2), and when (15.3-(16-Vrl-0.7)) / R2>15.3 / R4, Q1 is cut off, thereby causing Q2 to be cut off, and the circuit enters the protection state. Therefore, through the joint action of D1, D2, D3 and R2, the situation that the circuit is burned due to excessive voltage can be effectively prevented. Moreover, since the mains voltage is generally 220V, there is no situation where the voltage is greater than 16V, such as 19V and 30V as described in this paragraph. Therefore, the situation that the current flowing through R2 is less than the current flowing through R4 does not exist in actual applications. In other words, in actual application, once the wiring voltage is too high, the circuit immediately enters the protection state, thereby playing a good role in preventing high voltage.

[0041] Through the above analysis of the bus output current I when Vrl gradually increases from 0, it can be concluded that Figure 4The shown I-Vrl curve graph clearly shows that as the voltage at the load end increases, the bus output current first continuously increases, then remains stable, and finally shows a cliff-like decrease as Vrl continues to increase. When the output current I increases, it does not correspond to a continuous increase in Vce, that is, the voltage across Q2, but only reaches a maximum value at a certain moment and then continuously decreases. In other words, in this application, the output power of the controllable constant current source is made to follow the change of the voltage at the load end, thereby adjusting and improving the voltage across Q2, and further improving the power borne by Q2 in actual operation so that it will not be too large, thus well protecting the Q2 device. Specifically, when Vd4 < Vrl < 15.3, the corresponding I is the largest. When Vrl continues to increase, D3 is not conducting, that is, the circuit enters a protection state without current. From this curve, it can be obtained that the situation where the current and voltage across Q2 are both at the maximum is the moment when D4 just starts to conduct. At this time, the maximum power Pmax on Q2 = Vce * Imax = (Ve - Vd2 - Vd4) * Imax = (15.3 - 0.7 - Vd4) * Imax = (14.6 - Vd4) * Imax. Since the maximum current allowed to flow through DALI PS is 250 mA, if Imax is set to the upper limit value of 0.25 A at this time, there is still Pmax = (14.6 - Vd4) * 0.25. Obviously, at this time, the value of Pmax on Q2 can be adjusted by adjusting the value of Vd4, thereby preventing the MOS device from being burned out due to excessive power in the existing solution.

[0042] Similarly, designing the output current of the controllable constant current source to follow the change of the voltage at the load end can effectively reduce the short-circuit current value when the load is short-circuited, thereby reducing the voltage divided by the parasitic resistance. Specifically, when the line sends a signal and the corresponding load is short-circuited, at this time rl = 0, and I = 15.3 * β1 * β2 / R4. In other words, the voltage divided by the parasitic resistance R' changes from V' = R' * 0.25 A in the prior art to V' = R' * 15.3 * β1 * β2 / R4. According to this curve graph, it can be determined that the circuit design of this application makes the short-circuit current 15.3 * β1 * β2 / R4 much smaller than 0.25 A. Therefore, by adjusting the resistance value of R4, the value of V' can be reduced, thereby effectively improving the communication quality and increasing the wiring distance of the DALI system.

[0043] In summary, it can be seen that the circuit design of this application enables both Pmax and V' to well avoid the problems of the constant current source device being burned out and poor signal transmission quality as long as appropriate device parameters are selected according to needs when using this circuit; and this circuit structure can quickly enter a protection state once a high voltage is connected, achieving a good high-voltage protection effect.

[0044] Although embodiments of the present invention have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A circuit capable of adjusting output current according to load changes, the circuit comprising a power supply end (1) and a load end (2), characterized in that: It also includes a controllable constant current source (3) which is arranged between the power supply end (1) and the load end (2) and can adjust the bus output current (I) according to the voltage change of the load end (2) to control its own power and the voltage formed by the parasitic resistance (R') of the load end (2); The controllable constant current source (3) comprises a regulating component (31) and an amplifying component (32) connected to the regulating component (31), and the current output by the regulating component (31) flows through the amplifying component (32); the regulating component (31) is respectively connected to the power supply end (1) and the load end (2) and can adjust the current outputted by itself according to the voltage of the load end (2); the amplifying component (32) is also connected to the load end (2) and amplifies the current from the regulating component (31) to adjust the bus output current (I); The regulating component (31) comprises a regulator (311) electrically connected to the power supply end (1) and the amplifying component (32), a first path (312) electrically connected to the power supply end (1) and the regulator (311) to provide the regulator (311) with a stable conduction current, a second path (313) electrically connected to the first path (312) and the load end (2) and capable of changing the working state of the regulator (311) when the voltage at the load end (2) increases and the regulator is turned on, and a third path (314) electrically connected between the power supply end (1) and the load end (2) and capable of being turned on when the voltage at the load end (2) increases to output current to the regulator (311), wherein the second path (313) is connected to the third path (314); The regulator (311) is a PNP type transistor, the base of which is connected to the first path (312), the emitter of which is connected to the power supply terminal (1), and the collector of which is connected to the input terminal of the amplifier component (32) via a first resistor (R5).

2. The circuit capable of adjusting output current according to load changes according to claim 1, characterized in that: The first path (312) comprises a second resistor (R4) having one end electrically connected to the power supply end (1) and the other end grounded, and the base of the PNP transistor is connected to the one end of the second resistor (R4); The resistance of the second resistor (R4) is at least 2 MΩ.

3. The circuit capable of adjusting output current according to load changes according to claim 2, characterized in that: The second path (313) comprises a third resistor (R2) and a voltage-stabilizing diode (D4), wherein the cathode of the voltage-stabilizing diode (D4) is connected to the one end of the second resistor (R4) through the third resistor (R2) and the anode is electrically connected to the load end (2), and the resistance value of the third resistor (R2) is at least 5 MΩ.

4. The circuit capable of adjusting output current according to load changes according to claim 2, characterized in that: The third path (314) comprises a first diode (D2) and a fourth resistor (R1), the positive electrode of the first diode (D2) being connected to the one end of the second resistor (R4) and the negative electrode being connected to the positive electrode of the voltage-stabilizing diode (D4) through the fourth resistor (R1), and the negative electrode of the first diode (D2) being connected between the third resistor (R2) and the negative electrode of the voltage-stabilizing diode (D4) through a wire.

5. The circuit capable of adjusting output current according to load variation according to claim 3, characterized in that: The amplifying component (32) is an NPN transistor, the base of the NPN transistor is connected to the collector of the PNP transistor, the emitter is grounded, and the collector is connected to the positive electrode of a voltage-stabilizing diode (D4).

6. The circuit capable of adjusting output current according to load variation according to claim 3, characterized in that: The circuit also includes a high-voltage protection module (315) composed of a first diode (D2), a second diode (D3), a third diode (D1) and a third resistor (R2); The cathode of the second diode (D3) is connected to the anode of the voltage-stabilizing diode (D4), and the anode of the second diode (D3) is connected to the load end (2); The anode of the third diode (D1) is connected to the one end of the second resistor (R4) and the cathode is connected to the power supply terminal (1).

Images