RELATED APPLICATION

The present application claims priority to a Chinese Patent Application No. CN 202010180657.6, filed on March 16, 2020, the whole content of which is hereby incorporated by reference.

FIELD OF THE TECHNOLOGY

The present invention relates to the field of electronics, in particular to a circuit that can adjust the output current according to load changes.

BACKGROUND OF THE INVENTION

DALI dimming systems play an important role in the field of lighting control in the market, and a DALI power supply (hereinafter referred to as DALI PS) is an indispensable special device in DALI dimming systems, and it is the basis for guaranteed transmission of the DALI bus signal. According to the IEC82386 standard, the voltage output range of the DALI PS should be between 9.5V and 22.5 V, and the maximum output current should not exceed 250mA.

In the existing design of a DALI PS, the circuit is conventionally designed with the load end is connected to the power supply end through a single constant current source, such as shown in Fig. 1 . This kind of 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, which may cause the bus current I to reach 250mA, while the characteristics of single constant current source determine that in this situation, the MOS device Q1 in the constant current source will carry excessive voltage at both ends in this circuit, which may reach 15.3V in this circuit, and the maximum power may be as high as 3.8W, which may result in the destruction of the device due to excessive power and rapid heating, or increase the difficulty and cost of product design.

At the same time, the DALI signal will be carried on the load voltage by the carrier after a certain operation. However, the current single constant current source circuit design, will generate parasitic resistance, when the load line is very long, and this parasitic resistance will consume part of the voltage and then make the Dali device receive incomplete signals transmitted from the load end. In order to ensure the quality of the signal reception, the laying area of the DALI system has to be sacrificed, which greatly limits the application of DALI systems; moreover, the current circuit design is not ideal in the case when the external voltage is too high.

BRIEF SUMMARY OF THE INVENTION

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

In order to achieve the above purpose, according to the present invention there is provided a circuit capable of adjusting an output current according to load changes, comprising a power supply terminal and a load terminal, said circuit further comprising a controllable constant current source which is set between the power supply terminal and the load terminal and configured to adjust the bus output current according to the voltage change at the load terminal to control its own power and a voltage formed at the load terminal due to a parasitic resistance.

According to a further embodiment, the controllable constant current source comprises an adjusting component and an amplifying component connected to the adjusting component, wherein a current output by the adjusting component flows through the amplifying component; the adjusting component is respectively connected to the power supply terminal and the load terminal and configured to adjust its own output current according to a voltage at the load terminal; and the amplifying component is also connected to the load terminal and amplifies a current from the adjusting component to regulate the bus output current.

According to a further embodiment, the adjusting component comprises a regulator that is respectively electrically connected to the power supply terminal and the amplifying component, a first path respectively electrically connected to the power supply terminal and the regulator to provide a stable conduction current for the regulator, a second path that is respectively electrically connected to the first path and the load terminal and can be in conduction to adjust the operating (working) state of the regulator when the voltage at the load terminal becomes larger, and a third path that is electrically connected between the power supply terminal and the load terminal and can be in conduction to output current to the regulator when the voltage at the load terminal increases, wherein the second path is connected to the third path.

According to a further embodiment, the regulator is a PNP-type transistor, the base of the PNP-type transistor is connected to the first path, the emitter is connected to the power supply terminal, and the collector is connected to a input terminal of the amplifying component through a first resistor.

According to a further embodiment, the first path comprises a second resistor whose one end is electrically connected to the power supply terminal and the other end is grounded, and the base of the PNP transistor is connected to the one end of the second resistor, and the resistance value of the second resistor is at least 2MW.

According to a further embodiment, the second path comprises a third resistor and a Zener diode, and 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 terminal, and the resistance value of the third resistor is at least 5MW.

According to a further embodiment, the third path includes a first diode and a fourth resistor, and 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 Zener diode through the fourth resistor, and the cathode of the first diode is connected between the third resistor and the cathode of the Zener diode through wire.

According to a further embodiment, the amplifying component is an NPN type triode, the base of the NPN type triode is connected to the collector of the PNP type triode, the emitter is grounded, and the collector is connected to the anode of the Zener diode.

According to a further embodiment, the circuit also includes a high voltage protection module comprising a first diode, a second diode, a third diode and a third resistor; wherein the cathode of the second diode is connected to the anode of the Zener diode (D4) and the anode of the second diode is connected to the load terminal; and the anode of the third diode is connected to the one end of the second resistor (R4) and the cathode is connected to the power supply terminal.

Compared with the prior art, the advantages of the present invention are in particular the following:

The conventional single constant current source is replaced with a controllable constant current source, and the output current of the controllable constant current source can be adjusted by the voltage at the load terminal, which ensures that the constant current source device will not be burn out due to excessively high power when the signal that is short circuited to the load, which prevents the constant current source device from being burn out when the output current reaches the upper limit and the load voltage is higher when the load changes. At the same time, it effectively solves the problem that the parasitic resistor divides a large voltage when sending signals, which affects the transmission quality of signal, effectively improves the quality of communication and increases the wiring distance at the load terminal. The setting of the high voltage protection module can solve the problem of excessively high voltage in line, which causes the circuit to be burned, and improves the safety of the circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG.1 is a schematic circuit diagram according to the prior art.

FIG.2 is a block diagram of the overall structure according to the present invention.

FIG.3 is a schematic circuit diagram of a preferred embodiment according to the present invention.

FIG.4 is an l-Vrl curve diagram for the embodiment of Fig. 2.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings, in which the same or similar reference numerals indicate the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the drawings are exemplary, and are only used to explain the present invention, and shall not be understood as a limitation to the present invention. Figs. 2 and 3 show a preferred embodiment of a circuit capable of adjusting the output current according to load changes. As shown in the Fig. 2, the circuit includes a power supply terminal 1 , a load terminal 2, and a controllable constant current source 3 which is arranged between the power supply terminal 1 and the load terminal 2 and can adjust the bus output current according to the voltage change of the load terminal 2 to control its own power and the voltage formed at the load terminal 2 due to the parasitic resistance R

As shown in Fig. 2, the controllable constant current source 3 includes an adjusting component 31 (regulating component) and an amplifying component 32 connected to the adjusting component 31. The current output by the adjusting component 31 flows through the amplifying component 32. The adjusting component 31 is connected to the power supply terminal 1 and the load terminal 2 respectively and can adjust its own output current according to the voltage at the load terminal 2. The amplifying component 32 is also connected to the load terminal 2 and can amplify the current from the adjusting component 31 to adjust the bus output current. That is, the bus output current value of this circuit is equal to the output current amplified by the amplifying component 32.

Specifically in this embodiment, the adjusting component 31 includes a regulator 311 that is respectively electrically connected to the power supply terminal 1 and the amplifying component 32, and a first path 312 that is respectively electrically connected to the power supply terminal 1 and the regulator 311 to provide the regulator 311 with a stable conduction current, and a second path 313 that is respectively electrically connected to the first path 312 and the load terminal 2 and can change the operation state of the regulator 311 when the voltage at the load terminal 2 becomes larger and in the on-state (becomes in conduction), and a third path 314 that is electrically connected between the power terminal 1 and the load terminal 2 and become in conduction to output current to the regulator 311 when the voltage of the load terminal 2 increases, and the third path 314 is connected to the second path 313.

For details, please refer to Fig. 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 end of the amplifying component 32 through the first resistor R5. The first path 312 includes a second resistor R4 electrically connected to the power supply terminal 1 at one end and grounded at the other end. The base of the PNP transistor Q1 is connected to the one end of the second resistor R4, and the resistance of the second resistor R4 is at least 2MW, that is to say, the resistance of the second resistor R4 in the circuit design is very large, which can prevent the current flowing into the PNP transistor from being too large and burn the transistor. At the same time, by designing the resistance of the second resistor R4 to be large, it can be ensured that the entire circuit effectively follows the voltage changes at the load terminal and gradually realize the adjustment (regulation) of the current, so as to achieve the desired effect,. The specific analysis of the principle will be explained later.

As shown in Fig. 3, the second path 313 includes a third resistor R2 and a Zener diode D4. The cathode of the Zener 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. The third resistor R2 has a value of at least 5MW. 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 Zener diode D4 through the fourth resistor R1. The cathode of the first diode D2 is connected between the third resistor R2 and the cathode of the Zener 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 Zener diode D4.

In this circuit, the PNP type transistor Q1 and the NPN type transistor Q2 form a composite tube, which is used to increase or improve the current amplification factor, that is, the amplification factor of the PNP type transistor Q1 is b1, and the amplification factor of the NPN type transistor Q2 is b2, then the amplification factor of the current in the entire circuit is b=b1 ^c b2. 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 (triode) to achieve the purpose of adjusting or regulating the output current via the voltage at the load terminal.

Although the standard regulations stipulate that the operating voltage of the system should be between in the range between 9.5V and 22.5V, since the global mains lines are at levels between 85V and 265V, and the voltage applied at the peak of the AC power is higher, it is easy to misconnect during the system installation process and cause the circuit burning. In order to overcome this problem, the circuit also includes a high voltage prevention module 315 comprising 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 Zener diode D4 and the anode of the second diode D3 is connected to the load terminal 2, and 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.

The operating principle of this circuit is explained below. First, suppose that the bus output current is I, the maximum bus output current is Imax, the voltage stabilization value of Zener diode D4 is Vd4, the current flowing through Zener diode D4 is Id4, and the voltage across both ends of the NPN transistor Q2 is Vce. The current flowing through the first diode D2 is Id2, the current flowing through the fourth resistor R1 is Ir1 , the base current of the PNP transistor Q1 is Iqb1, and the base current of the NPN transistor Q2 is Iqb2. At the same time, let us assume that the resistance value at the load end is rl.

Now let the voltage at the load terminal gradually increase from 0 to discuss the value of the bus output current I one by one. First of all, it should be clear that when the circuit is in the normal wiring state, the transistors Q1 and Q2 are in the conducting state (on-state), and the conduction voltage of the transistors Q1 and Q2 both are 0.7V. When Vrl <0.7v, the corresponding load is short-circuited, rl=0, because Vrl is close to Ov. It can be considered that the voltage at point A is equal to the voltage at point B, and the voltage at point A is always 16V, so the voltage at point B is also 16V, which makes D3 conductive, the voltage at point D is 15.3V, and the voltage at point E is (16-Vq1)V = (16-0.7)V = 15.3V, so the first transistor D2 is stopped due to the voltage Vd2 at both ends being lower than 0.7V, correspondingly, Id2 = 0. The base current Iqb1 on the PNP transistor Q1 exists that lqb1=Ve/R4=(16-Vq1)/R4=(16-0.7)/R4, because the resistance value of second resistor R4 is very large, making Iqb1 very small. At this time, the transistors Q1 and Q2 are working in the amplifying area, so when there is a short circuit, the bus output current is I=b1 ^* p2 ^* lqb1 =15.3 ^* b1 ^* 2/R4.

As Vrl gradually increases, that is, rl increases, when the load decreases, Vce is gradually reduced according to Vce=16-Vrl-Vd3, that is, the voltage at point C is 15.3-Vrl, and the voltage at point C is the voltage at point D, so the first diode D2 conducts, Id2 gradually increases, then Iqb1=15.3/R4+Id2, I=b1 *p2*lqb1 which keeps increasing. Due to the existence of the Zener diode D4, is is also necessary here to compare Vrl and Vd4.

When the Zener diode D4 is not conducting, there is Vgd<Vd4, that is Ve-Vd2-Vd<Vd4, and Vd=Vb-0.7, Ve=15.3, Vb=16-Vrl, the conversion gets Vrl-Vd2<Vd4, because Vd2=0.7V is relatively small and negligible. Then there is Vrl <Vd4, in other words, as Vrl gradually increases, but the Zener diode D4 is still non-conductive, correspondingly, Vrl<Vd4. At this time, the transistors Q1 and Q2 are working in the amplifying area, and because the third resistor R2 is very large, the current on the branch E-G-F-D is neglected, then ld2=lr1=Vfc/R1 =(16-Vq1-Vd2-Vd3-Vrl)/R1 =(16-0.7-0.7-0.7-Vrl)/R1 ,

I=b1 ^* b2 ^* (15.3/R4+(13.9-Vrl)/R1 );

When the Zener diode D4 conducts (is on), it corresponds that Vrl>At Vd4, the conduction of the Zener diode D4 will cause the current on the branch E-F-G-C to increase sharply, which will cause the transistor Q1 to immediately enter the saturation region while Q2 is still in the amplification region, then lqb2=(16-0.7)/R5, I =b2*^2=b2*15.3^5;

When the voltage Vrl at the load terminal continues to increase, the transistor Q2 will also enter the saturation zone. At this time, the transistor Q2 is equivalent to a wire, with Vrl=(16-0.7), 5.3/RL.

When the voltage at load terminal Vrl> 15.3V, because Vb<0.7v, making the diode D3 cut off, the circuit is in the protection state; on the contrary, if Vrl<0V, because R2 is much larger than R1 and R3, the resistance value of R1 and R3 can be ignored. At this time, R1 and R3 can be equivalent to a wire, so that Vg=Vf=Vc, Vrl<0v, it means that Vb>16v, while Vc>16-0.7=15.3v, then there is Vf>Ve, correspondingly, D2 cut-off, when the current flowing through R2 is lower than the current flowing through R4, there is (Ve-Vg)/R2<15.3/R4, that is, (15.3-(16-Vrl-0.7))/R2<15.3/R4, correspondingly, I=b1 *b2*(15.3/R4-(15.3-(16-Vrl-0.7))/R2), and when (15.3-(16-Vrl-0.7))/R2>15.3/R4, it corresponds to that Q1 cut off, which causes Q2 to cut off, at this time the circuit enters the protection state. Therefore, through the joint action of D1 , D2, D3 and R2, it is possible to prevent the circuit from being burnt due to the excessively high voltage connected to the circuit, and since the mains voltage is generally 220V, there is no such thing as 16V, as in the case of 19V and 30V. Therefore, in practical applications the situation does not exist that the current flowing through R2 is lower than the current flowing through R4. In other words, in practical applications, once the wiring voltage is too high, the circuit will immediately enter the protection state, which plays a good role in preventing high voltage.

Through the above analysis about the bus output current I in the case that Vrl is gradually increased from 0, the l-Vrl curve diagram shown in Fig. 4 can be derived. According to the curve diagram, it can be clearly seen that with the increase of the load terminal voltage, the bus output current first continuously increases, then remains stable, and finally appears a cliff-like decrease while Vrl continues to increase. And the increase of the output current (I) does not correspond to the continuous increase of Vce, that is, the voltage across Q2, but only the 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 follows the change of the load terminal voltage to adjust and improve the voltage at both ends of Q2, thereby improving the power carried by Q2 in actual use so as not to be too large and well protecting the Q2 device. Specifically, the corresponding current I is the largest when Vd4<Vrl<15.3 , and when Vrl continues to increase, D3 does not conduct, that is, the circuit enters the protection state without current, and it can be concluded from the curve that the situation where the current across Q2 is at the maximum and the voltage is also at the biggest is the moment when D4 just conducts. There is a maximum power on Q2 Pmax=Vce ^* lmax=(Ve-Vd2-Vd4) ^* lmax=(15.3-0.7-Vd4) ^* lmax=(14.6-Vd4 ) ^* lmax, since the maximum current allowed to flow through the DALI PS is 250mA, if Imax is set to the upper limit of 0.25A at this time, there is also Pmax=(14.6-Vd4) ^* 0.25. Obviously, it can adjust the value of Vd4 to adjust the maximum power point that exists on Q2, so as to prevent the MOS device from being burned due to excessive power in the existing solution.

Similarly, the output current of the designed controllable constant current source changes with the change of the load terminal voltage, which 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, which is corresponding to the load short-circuit, at this time rl=0, l= 15.3 ^* b1 ^* p2/R4. In other words, the voltage divided by the parasitic resistance R' changes from V'=R' ^* 0.25A in the prior art to V'=R ' ^* 15.3 ^* b1 ^* p2/R4, according to the graph, and it can be determined that the circuit design of this application makes the short-circuit current 15.3*pi*p2/R4 far less than 0.25A. Hence, the value of V can be reduced by adjusting the resistance value of R4, thereby effectively improving the communication quality and increasing the wiring distance of the DALI system.

In summary, the circuit design of the present application makes it possible to avoid the problems of burned-out constant current source devices and poor signal transmission quality by selecting appropriate device parameters as needed when using this circuit, regardless of whether it is for Pmax or V. And the circuit structure can quickly enter the protection state once the high voltage is connected (accessed), which has a good high voltage protection effect.

The above disclosure has been described by way of example and in terms of exemplary embodiment, and it is to be understood that the disclosure is not limited thereto. Rather, any modifications, equivalent alternatives or improvement etc. within the spirit of the invention are encompassed within the scope of the invention as set forth in the appended claims.