Current-adjustable constant current output circuit

Abstract

The embodiment of the invention provides a current-adjustable constant current output circuit, and the circuit comprises a control signal generation module which is configured to generate a second number of control signals according to a first number of constant output currents needing to be generated; the fixed voltage generation module is configured to adjust the voltage of a voltage division node in the resistance voltage division circuit according to the state information of the control signal and output different fixed voltages; the operational amplifier is configured to use the fixed voltage as an input reference voltage and compare the input reference voltage with the current detection voltage to obtain an operational amplifier output voltage; the output current generation module is configured to generate an output current according to the operational amplifier output voltage and obtain a constant output current when the current detection voltage is equal to the input reference voltage; and the current detection voltage calculation module is configured to calculate the current detection voltage according to the output current and the current detection resistance. The problems that an existing circuit for achieving various constant current outputs is complex and high in cost are solved.

Description

Technical Field

[0001] Embodiments of the present disclosure relate to the field of power supply technology, and in particular, to a constant current output circuit with adjustable current. Background Art

[0002] As market demand changes, power modules are increasingly pursuing wide voltage input, which will cause the supply current to change with the input voltage. In order to ensure that a constant supply current can be obtained regardless of high or low voltage input, a constant current output circuit needs to be added to the input end to ensure performance consistency.

[0003] At present, the realization of constant current output circuit can directly select dedicated constant current output chip, or use the digital to analog converter (DAC) output plus op amp of microcontroller unit / microcontroller (MCU). For applications that require several constant current output currents, if a dedicated constant current output chip is used, although the accuracy is high, the cost is also high, and only one fixed current can be output. Multiple constant current outputs require multiple dedicated constant current output chips, which are more expensive and the circuit is more complicated; if the DAC output plus op amp of MCU is used, the output current size of this method can be adjusted, that is, multiple constant currents can be provided by adjustment, but the implementation of this method requires DAC, which makes the circuit implementation more complicated and the cost is also high.

[0004] In summary, the existing circuits for realizing multiple constant current outputs have the problems of complex circuits and high costs. Summary of the invention

[0005] The embodiments described herein provide a current-adjustable constant current output circuit in order to solve the problems of complex circuits and high costs in existing circuits for realizing multiple constant current outputs.

[0006] According to a first aspect of the present disclosure, a current-adjustable constant current output circuit is provided, the constant current output circuit comprising: a control signal generating module, a fixed voltage generating module, an operational amplifier, an output current generating module, and a current sensing voltage calculating module, wherein the control signal generating module is configured to generate a second number of control signals according to a first number of constant output currents required to be generated by the constant current output circuit, each control signal comprising two different state information, the first number being 2 N, the second number is N, N is a natural number; the fixed voltage generating module is configured to adjust the voltage of the voltage dividing node in the resistor voltage dividing circuit in the fixed voltage generating module according to the state information of the control signal of the second number, and output different fixed voltages from the voltage dividing node; the operational amplifier is configured to receive the fixed voltage output by the fixed voltage generating module and use the fixed voltage as the input reference voltage of the operational amplifier, and compare the input reference voltage with the received current sensing voltage output by the current sensing voltage calculation module to obtain the operational amplifier output voltage; the output current generating module is configured to generate an output current according to the operational amplifier output voltage, and adjust the magnitude of the output current, and finally generate a constant output current when the current sensing voltage is equal to the fixed voltage, and one fixed voltage corresponds to one constant output current; the current sensing voltage calculation module is configured to calculate the current sensing voltage according to the output current and the current sensing resistor.

[0007] Optionally, the fixed voltage generating module includes: the resistor voltage divider circuit and the voltage regulating circuit, wherein the resistor voltage divider circuit is configured to divide the preset reference voltage by sequentially connecting a first resistor and a second resistor in series between the preset reference voltage and the ground terminal, and the node between the first resistor and the second resistor is the voltage dividing node; the voltage regulating circuit is composed of the second number of regulating units, and is configured to couple each regulating unit to the voltage dividing node, and control the connection state of the parallel resistor in each regulating unit and the second resistor according to the state information of the control signal corresponding to each regulating unit, and one regulating unit corresponds to one control signal.

[0008] Optionally, the circuit structure of each adjustment unit is the same, and an adjustment unit includes: the parallel resistor, the first transistor, the third resistor, and the fourth resistor, wherein one end of the parallel resistor is coupled to the voltage dividing node, and the other end of the parallel resistor is coupled to the first electrode of the first transistor; the second electrode of the first transistor is coupled to the ground terminal, and the control electrode of the first transistor is respectively coupled to one end of the third resistor and one end of the fourth resistor; the other end of the third resistor is coupled to the ground terminal, and the other end of the fourth resistor is coupled to the control signal.

[0009] Optionally, the output current generating module includes: a second transistor, wherein the control electrode of the second transistor is coupled to the output end of the operational amplifier, the first electrode of the second transistor outputs the output current, and the second electrode of the second transistor is coupled to the current detection voltage calculation module.

[0010] Optionally, the current sensing voltage calculation module includes: the current sensing resistor, wherein one end of the current sensing resistor is coupled to the output current generating module and the negative input end of the operational amplifier respectively, and the other end of the current sensing resistor is coupled to the ground end, and the current sensing voltage is obtained at one end of the current sensing resistor.

[0011] Optionally, the current-adjustable constant current output circuit also includes: a filter capacitor and a fifth resistor, wherein the filter capacitor and the fifth resistor are coupled between the fixed voltage generating module and the operational amplifier, wherein one end of the filter capacitor is coupled to the voltage dividing node, and the other end of the filter capacitor is coupled to the ground terminal; one end of the fifth resistor is coupled to the voltage dividing node, and the other end of the fifth resistor is coupled to the positive input terminal of the operational amplifier.

[0012] Optionally, the status information of each control signal includes a high level and a low level, and the control signal generating module includes: a level generating circuit, a control signal generating circuit, and a status control circuit, wherein the level generating circuit is configured to generate a high level and a low level according to a microcontroller or a jumper cap coupled to a power supply; the control signal generating circuit is configured to generate a second number of control signals according to the high level and the low level generated by the level generating circuit; and the status control circuit is configured to control each control signal to output different status information.

[0013] Optionally, controlling the connection state of the parallel resistor in each adjustment unit and the second resistor according to the state information of the control signal corresponding to each adjustment unit includes: if the control signal is at a high level, the parallel resistor in the adjustment unit corresponding to the control signal is coupled in parallel with the second resistor; if the control signal is at a low level, the parallel resistor in the adjustment unit corresponding to the control signal is disconnected from the second resistor.

[0014] Optionally, the value of the constant output current is determined according to the following formula: Icc=Vin_ref / Rg, wherein Icc is the constant output current, Vin_ref is the input reference voltage of the operational amplifier, and Rg is the current sensing resistor; and the maximum output voltage of the current-adjustable constant current output circuit is determined according to the following formula: the maximum load corresponding to each constant output current is determined, RLmax=(Vmax-Vec-Vin_ref) / Icc, wherein RLmax is the maximum load, Vmax is the maximum output voltage, and Vec is the on-state voltage of the second transistor.

[0015] Optionally, the first transistor is an N-type MOS transistor, and the second transistor is a triode.

[0016] The current adjustable constant current output circuit of the embodiment of the present disclosure includes: a control signal generating module, a fixed voltage generating module, an operational amplifier, an output current generating module, and a current sensing voltage calculating module, wherein the control signal generating module is configured to generate a second number of control signals according to a first number of constant output currents required to be generated by the constant current output circuit, and each control signal includes two different state information, the first number is 2 N , the second number is N, N is a natural number; the fixed voltage generating module is configured to adjust the voltage of the voltage dividing node in the resistor voltage dividing circuit in the fixed voltage generating module according to the state information of the second number of control signals, and output different fixed voltages from the voltage dividing node; the operational amplifier is configured to receive the fixed voltage output by the fixed voltage generating module and use the fixed voltage as the input reference voltage of the operational amplifier, and compare the input reference voltage with the received current sensing voltage output by the current sensing voltage calculation module to obtain the operational amplifier output voltage; the output current generating module is configured to generate an output current according to the operational amplifier output voltage, and adjust the magnitude of the output current, and finally generate a constant output current when the current sensing voltage is equal to the input reference voltage, and a fixed voltage corresponds to a constant output current; the current sensing voltage calculation module is configured to calculate the current sensing voltage according to the output current and the current sensing resistor. It can be seen that the current adjustable constant current output circuit in the embodiment of the present disclosure can adjust the voltage of the voltage dividing node in the resistor voltage dividing circuit in the fixed voltage generating module through the control signal, so that it outputs different fixed voltages. Then the fixed voltage is used as the input reference voltage of the operational amplifier. Through negative feedback regulation, when the current-sense voltage obtained by the current-sense voltage calculation module is equal to the input reference voltage, the output current generation module can obtain a constant output current. A fixed voltage corresponds to a constant output current, so different fixed voltages can correspond to different constant currents (constant output currents), which is equivalent to obtaining multiple constant currents by adjusting the input reference voltage. Compared with the existing circuits for realizing multiple constant current outputs, it does not require DAC or a dedicated constant current output chip, and the circuit is simple to implement and low in cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings of the embodiments will be briefly described below. It should be noted that the drawings described below only relate to some embodiments of the present disclosure, but are not intended to limit the present disclosure, wherein:

[0018] Figure 1 A schematic block diagram of a current-adjustable constant current output circuit according to an embodiment of the present disclosure is shown;

[0019] Figure 2 An exemplary circuit diagram of a current-adjustable constant current output circuit according to an embodiment of the present disclosure is shown;

[0020] Figure 3 An exemplary circuit diagram showing another current-adjustable constant current output circuit according to an embodiment of the present disclosure;

[0021] Figure 4 A schematic block diagram of another current-adjustable constant current output circuit according to an embodiment of the present disclosure is shown;

[0022] The elements in the drawings are schematic and not drawn to scale. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the embodiments of the present disclosure clearer, the technical solution of the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without creative work also fall within the scope of protection of the present disclosure.

[0024] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by a person skilled in the art to which the subject matter of the present disclosure belongs. It will be further understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the specification and the relevant art, and will not be interpreted in an idealized or overly formal form unless otherwise explicitly defined herein. As used herein, a statement that two or more parts are "connected" or "coupled" together shall mean that the parts are joined together directly or through one or more intermediate components.

[0025] In all embodiments of the present disclosure, since the source and drain of the metal oxide semiconductor (MOS) transistor are symmetrical, and the conduction current directions between the source and drain of the N-type transistor and the P-type transistor are opposite, in the embodiments of the present disclosure, the controlled middle end (gate or gate end) of the MOS transistor is referred to as the control electrode, and the remaining two ends of the MOS transistor are referred to as the first electrode and the second electrode, respectively. In addition, for the sake of uniformity, the base of the transistor is also referred to as the control electrode, and the remaining two ends of the transistor (emitter and collector) are referred to as the first electrode and the second electrode, respectively. In addition, terms such as "first" and "second" are only used to distinguish one component (or a part of a component) from another component (or another part of a component).

[0026] In order to solve the problems of complex circuits and high costs in existing circuits for realizing multiple constant current outputs, a new current-adjustable constant current output circuit is proposed. The current-adjustable constant current output circuit of the disclosed embodiment changes the input reference voltage of the operational amplifier according to the adjustment of the state information of the control signal, thereby changing the current detection voltage, and finally changing the output current. Different input reference voltages can correspond to different constant current outputs, and it is realized that by adjusting the constant current output value of the control signal state, multiple constant current outputs can be obtained more conveniently. The current-adjustable constant current output circuit 100 disclosed in the present invention is described in detail below.

[0027] Figure 1 FIG. 1 is a schematic block diagram of a current-adjustable constant current output circuit 100 according to an embodiment of the present disclosure. Figure 1 As shown, the current adjustable constant current output circuit 100 includes: a control signal generating module 110, a fixed voltage generating module 120, an operational amplifier 130, an output current generating module 140, and a current sensing voltage calculating module 150.

[0028] The control signal generating module 110 is coupled to the fixed voltage generating module 120, and the control signal generating module 110 is configured to generate a second number of control signals CCVR according to a first number of constant output currents Icc required to be generated by the constant current output circuit 100, and each control signal CCVR includes two different state information. N , then the second number is N, where N is a natural number. Specifically, the control signal CCVR includes two state information, high level and low level. The control signal CCVR is generated to change the voltage of the voltage dividing node in the fixed voltage generating module 120.

[0029] The fixed voltage generating module 120 is coupled to the control signal generating module 110 and the operational amplifier 130 respectively. The fixed voltage generating module 120 is configured to adjust the voltage of the voltage dividing node in the resistor voltage dividing circuit in the fixed voltage generating module 120 according to the state information of the second number of control signals CCVR, and output different fixed voltages Vf from the voltage dividing node. Since each control signal CCVR includes two state information, N control signals CCVR can obtain 2 N There are control combinations, each of which can determine a voltage value of the voltage division node. N The control combination can determine the voltage divider node 2 N It can be seen that adjusting the voltage of the voltage dividing node in the resistor voltage dividing circuit 122 in the fixed voltage generating module 120 according to the state information of the second number of control signals CCVR is to change the voltage of the voltage dividing node by changing the above control combination. In addition, the resistor voltage dividing circuit in the fixed voltage generating module 120 is a voltage dividing circuit composed of series resistors.

[0030] The operational amplifier 130 is respectively coupled to the fixed voltage generation module 120, the output current generation module 140 and the current detection voltage calculation module 150. The operational amplifier 130 is configured to receive the fixed voltage Vf output by the fixed voltage generation module 120 and use the fixed voltage Vf as the input reference voltage Vin_ref of the operational amplifier 130, and compare the input reference voltage Vin_ref with the received current detection voltage Vc output by the current detection voltage calculation module 150 to obtain the operational amplifier output voltage. Specifically, as Figure 1 As shown, the fixed voltage Vf output by the fixed voltage generating module 120 is coupled to the positive input terminal of the operational amplifier 130, and the current sensing voltage Vc output by the current sensing voltage calculating module 150 is coupled to the negative input terminal of the operational amplifier 130. The operational amplifier 130 compares the voltage at the positive input terminal with the voltage at the negative input terminal, and the positive input terminal is used as a reference terminal. The greater the difference between the voltage at the negative input terminal and the voltage at the positive input terminal, the greater the output voltage of the operational amplifier. When the voltage at the negative input terminal is equal to the voltage at the positive input terminal, a stable state is reached.

[0031] The output current generating module 140 is configured to generate an output current Icc according to the output voltage of the operational amplifier, and adjust the magnitude of the output current Icc, and finally generate a constant output current Icc when the current sensing voltage Vc is equal to the fixed voltage Vf (i.e., the input reference voltage Vin_ref). A fixed voltage Vf corresponds to a constant output current Icc.

[0032] The current sensing voltage calculation module 150 is configured to calculate the current sensing voltage Vc according to the output current Icc and the current sensing resistor Rg (not shown in the figure). The current sensing voltage calculation module 150, the output current generating module 140, and the operational amplifier 130 constitute feedback regulation. When the voltage at the negative input terminal of the operational amplifier 130 is different from the voltage at the positive input terminal, that is, when there is a difference between the current sensing voltage Vc and the input reference voltage Vin_ref, the operational amplifier output voltage will continuously change the magnitude of the output current Icc, and the current sensing voltage Vc calculated according to the output current Icc will also change with the change of the output current Icc. The change of the current sensing voltage Vc is then fed back to the negative input terminal, and finally when the current sensing voltage Vc is equal to the input reference voltage Vin_ref, a balance is reached, and at this time, the output current Icc is also constant, that is, a constant output current Icc is generated. Each input reference voltage Vin_ref of different values ​​can determine a balance state, and each balance state can obtain a constant output current Icc. Therefore, multiple fixed voltages Vf are used as the input reference voltage Vin_ref, and multiple constant output currents Icc can be obtained.

[0033] From the above description, it can be seen that the current-adjustable constant current output circuit in the embodiment of the present disclosure can adjust the voltage of the voltage dividing node in the resistor voltage dividing circuit in the fixed voltage generating module 120 through the control signal CCVR, so that it outputs different fixed voltages Vf. Then the fixed voltage Vf is used as the input reference voltage Vin_ref of the operational amplifier 130. Through negative feedback regulation, when the current sensing voltage Vc obtained by the current sensing voltage calculation module 150 is equal to the input reference voltage Vin_ref, the output current generating module 140 can obtain a constant output current Icc. A fixed voltage Vf corresponds to a constant output current Icc, so different fixed voltages Vf correspond to different constant currents (constant output currents Icc), which is equivalent to obtaining multiple constant currents by adjusting the input reference voltage Vin_ref. Compared with the existing circuits for realizing multiple constant current outputs, no DAC or dedicated constant current output chip is required, and the circuit is simple to implement and low in cost.

[0034] Further, such as Figure 2 As shown, the fixed voltage generating module 120 includes: a voltage regulating circuit 121, the resistor voltage dividing circuit 122,

[0035] The resistor voltage divider circuit 122 is configured to divide the preset reference voltage Vref by a first resistor R1 and a second resistor R2 which are sequentially connected in series between the preset reference voltage Vref and the ground terminal, and a node A between the first resistor R1 and the second resistor R2 is a voltage dividing node. Figure 2 As shown, one end of the first resistor R1 is coupled to a preset reference voltage Vref, the other end of the first resistor R1 is coupled to the other end of the second resistor R2, and the other end of the second resistor R2 is coupled to the ground. The resistor voltage divider circuit 122 outputs a fixed voltage Vf from the node A.

[0036] The voltage regulating circuit 121 is composed of a second number (N) of regulating units 1211. The voltage regulating circuit 121 is configured to couple each regulating unit 1211 to a voltage dividing node A, and control the connection state of the parallel resistor Rp and the second resistor R2 in each regulating unit 1211 according to the state information of the control signal CCVR corresponding to each regulating unit 1211. One regulating unit 1211 corresponds to one control signal CCVR (the number of control signals CCVR in the above is N, so the number of regulating units 1211 is also N. In addition, in order to distinguish the N control signals CCVR, the i-th control signal CCVR is recorded as CCVRi, where i=1, 2, ..., N.). The circuit structure of each regulating unit 1211 is the same, such as Figure 2As shown, each adjustment unit 1211 includes: a parallel resistor Rp, a first transistor Q1, a third resistor R3, and a fourth resistor R4, wherein one end of the parallel resistor Rp is coupled to the voltage dividing node A, and the other end of the parallel resistor Rp is coupled to the first electrode of the first transistor Q1; the second electrode of the first transistor Q1 is coupled to the ground terminal, and the control electrode of the first transistor Q1 is respectively coupled to one end of the third resistor R3 and one end of the fourth resistor R4; the other end of the third resistor R3 is coupled to the ground terminal, and the other end of the fourth resistor R4 is coupled to the control signal CCVRi. Among them, the first transistor Q1 is an N-type MOS tube, therefore, the connection state of the parallel resistor Rp and the second resistor R2 in each adjusting unit 1211 is controlled according to the state information of the control signal CCVR corresponding to each adjusting unit 1211, including: if the control signal CCVR is at a high level, the parallel resistor Rp in the adjusting unit 1211 corresponding to the control signal CCVR is coupled in parallel with the second resistor R2; if the control signal CCVR is at a low level, the parallel resistor Rp in the adjusting unit 1211 corresponding to the control signal CCVR is disconnected from the second resistor R2. It can be seen from the circuit structure of the adjusting unit 1211 that when the parallel resistor Rp is coupled in parallel with the second resistor R2, the voltage of the voltage dividing node A will be changed. Therefore, multiple adjusting units 1211 are set, and the voltage dividing node A can output a fixed voltage Vf of more values ​​through the adjustment of the control signal CCVR.

[0037] Further, such as Figure 2 As shown, the output current generating module 140 includes: a second transistor Q2, wherein the control electrode of the second transistor Q2 is coupled to the output terminal of the operational amplifier 130, the second electrode of the second transistor Q2 is coupled to the current detection voltage calculation module 150, and the first electrode of the second transistor Q2 outputs the output current Icc. Specifically, the second transistor Q2 is a triode, the control electrode of the second transistor Q2 is the base, the first electrode is the collector, and the second electrode is the emitter. When the voltages of the positive input terminal and the negative input terminal of the operational amplifier 130 are different, the operational amplifier output voltage output by the operational amplifier 130 will change the state of the second transistor Q2, thereby changing the output current Icc.

[0038] Further, such as Figure 2 As shown, the current-sense voltage calculation module 150 includes: a current-sense resistor Rg, wherein one end of the current-sense resistor Rg is respectively coupled to the output current generation module 140 (specifically, coupled to the emitter of the second transistor Q2 in the current generation module) and the negative input terminal of the operational amplifier 130, and the other end of the current-sense resistor Rg is coupled to the ground terminal, and a current-sense voltage Vc is obtained at one end of the current-sense resistor Rg. The current-sense resistor Rg is used to detect the output current Icc, and the current flowing through the current-sense resistor Rg is equal to the output current Icc. The current-sense voltage Vc can be obtained by multiplying the current-sense resistor Rg and the output current Icc.

[0039] Furthermore, in order to explain the principle of the current-adjustable constant current output circuit of the embodiment of the present disclosure, N=2 is taken as an example for explanation. Figure 3 FIG. 1 is an exemplary circuit diagram of a current-adjustable constant current output circuit 100 corresponding to N=2, which includes two control signals CCVR1 and CCVR2. In addition, the resistance values ​​of Rp in different adjustment units 1211 may be different. Therefore, in order to distinguish, the Rp corresponding to CCVR1 is recorded as Rp1, and the Rp corresponding to CCVR2 is recorded as Rp2. Figure 3 The principle of the current adjustable constant current output circuit 100 of the embodiment of the present disclosure is described in detail:

[0040] 1) When CCVR1 and CCVR2 are both low, the control electrodes of the two Q1s are both low, the two Q1s are blocked, and the two parallel resistors Rp1 and Rp2 are both suspended; at this time, the voltage at the voltage divider node A is Vf = Vref*(R2) / (R1+R2), assuming Vref = 3.0V, R1 = 20KΩ, R2 = 10KΩ, then Vf = 1.0V, and Vin_ref = 1.0V. At this time, if Vc is less than 1.0V, the output voltage of the op amp is high, and the collector of Q2 is The electrode current increases, and the current passing through Rg is the same as the current of Q2, so the voltage across Rg (i.e., Vc) will also increase, and Vc will be fed back to the negative input terminal of the operational amplifier 130, so that the difference between the positive input terminal and the negative input terminal of the operational amplifier 130 becomes smaller, and the final difference is zero, reaching a balanced state. At this time, Vc=Vin_ref=1.0V, assuming Rg=100Ω, the current passing through Rg is 1.0V / Rg=10mA, and the constant output current Icc is also 10mA.

[0041] 2) When CCVR1 is at a low level and CCVR2 is at a high level, since the control of Q1 corresponding to CCVR1 is extremely low, it is not turned on; the control of Q1 corresponding to CCVR2 is extremely high, so it is turned on; at this time, Rp1 is suspended and Rp2 is grounded; at this time, the voltage at the voltage divider node A is Vf=Vref*(R2 / / Rp2) / (R1+(R2 / / Rp2)), assuming Rp2=6.65KΩ, then Vf=0.499V, and Vin_ref=0.499V is obtained. Similarly to the above 1), finally when Vc=Vin_ref=0.499V, a constant output current Icc=0.499V / Rg=4.99mA is obtained.

[0042] 3) When CCVR1 is at a high level and CCVR2 is at a low level, since the control of Q1 corresponding to CCVR1 is extremely high, it is turned on; the control of Q1 corresponding to CCVR2 is extremely low, so it is not turned on; at this time, Rp2 is suspended and Rp1 is grounded; at this time, the voltage at the voltage divider node A is Vf=Vref*(R2 / / Rp1) / (R1+(R2 / / Rp1)), assuming that Rp1=1.27KΩ, then Vf=0.16V, and Vin_ref=0.16V is obtained. The same as in the above 1), finally when Vc=Vin_ref=0.16V, a constant output current Icc=0.16V / Rg=1.6mA is obtained.

[0043] 4) When CCVR1 and CCVR2 are both at high levels, the control electrodes of the two Q1s are both high, so they are both turned on; at this time, Rp1 and Rp2 are both grounded; at this time, the voltage at the voltage divider node A is Vf=Vref*(R2 / / Rp1 / / Rp2) / (R1+(R2 / / Rp1 / / Rp2)), then Vf=0.137V, and Vin_ref=0.137V is obtained. Similarly to the above 1), finally when Vc=Vin_ref=0.137V, a constant output current Icc=0.137V / Rg=1.37mA is obtained.

[0044] From the above circuit principle analysis, it can be obtained that the value of the constant output current Icc can be determined according to the formula Icc = Vin_ref / Rg. When Vin_ref is adjusted by the control signal CCVR to obtain different voltage values, different values ​​of Icc can be obtained. In practical applications, the resistance values ​​of each resistor (R1, R2, Rp, Rg) in the circuit can be adjusted according to the actual constant current value required and the various calculation formulas in the above principle.

[0045] In addition, after obtaining a constant Icc, the maximum output voltage of the current-adjustable constant current output circuit 100 can be determined according to the following formula to determine the maximum load RLmax corresponding to each constant output current Icc:

[0046] RLmax=(Vmax-Vec-Vin_ref) / Icc,

[0047] Wherein, RLmax is the maximum load, Vmax is the maximum output voltage, and Vec is the voltage when the second transistor Q2 is fully turned on, which is usually 0.7V.

[0048] The maximum load RLmax means that when the load resistance is less than RLmax, a constant Icc can be output. At this time, the voltage Vec between the collector and emitter of Q2 is not the voltage when it is fully turned on, but is in the amplification area, and Vec is greater than 0.7 V. If the load resistance is greater than RLmax, the output current Icc is less than the constant value of Icc.

[0049] For the above Figure 3 In the embodiment of the two control signals CCVR, assuming that the maximum output voltage Vmax = 12V, taking 1) as an example, based on the above formula, we can get RLmax = (12-0.7-1.0)V / 10mA = 1030Ω, which means that when the load resistance is less than 1030Ω, a constant current of 10mA can be output, and when the load resistance is greater than 1030Ω, the output current Icc will be less than 10mA. Calculating RLmax can provide a reference for the design of actual circuits.

[0050] Furthermore, in order to improve the accuracy of the circuit, Figure 4 As shown, the current adjustable constant current output circuit 100 also includes: a filter capacitor C, a fifth resistor R5, the filter capacitor C and the fifth resistor R5 are coupled between the fixed voltage generating module 120 and the operational amplifier 130, wherein one end of the filter capacitor C is coupled to the voltage dividing node A, and the other end of the filter capacitor C is coupled to the ground terminal; one end of the fifth resistor R5 is coupled to the voltage dividing node A, and the other end of the fifth resistor R5 is coupled to the positive input terminal of the operational amplifier 130. The filter capacitor C can eliminate interference signals, and the fifth resistor R5 is input resistance matching, and can also be used as an input current limiting resistor of the operational amplifier 130.

[0051] Furthermore, the control signal CCVR can be generated by providing two high and low voltages through a microcontroller MCU or a jumper cap. Figure 4 As shown, the control signal CCVR generating module 110 in the embodiment of the present disclosure includes: a level generating circuit 111, a control signal generating circuit 112, and a state control circuit 113.

[0052] The level generating circuit 11 is configured to generate a high level and a low level according to the microcontroller MCU or the jumper cap coupled to the power supply. The voltage values ​​corresponding to the high level and the high level can be determined according to the performance of the first transistor Q1, for example, the low level can be a voltage value less than 0.5V, and the high level value is a voltage value greater than 2.0V. The jumper cap coupled to the power supply can generate a high level and a low level by connecting the voltage source in series with the jumper cap.

[0053] The control signal generating circuit 112 is configured to generate a second number of control signals CCVR according to the high level and the low level generated by the level generating circuit 111. Because each control signal CCVR includes two states, a high level and a low level, a second number (N) of control signals CCVR need to be obtained through conversion.

[0054] The state control circuit 113 is configured to control each control signal CCVR to output different state information. Figure 3 In the example, it can be seen that when different constant output currents Icc are obtained, the states of the corresponding two control signals CCVR1 and CCVR2 are also changing. Here, the state control circuit adjusts the state of the control signal CCVR according to the value of the output current Icc required. For example, for Figure 3 In the example, when a constant Icc of 10mA is required, CCVR1 needs to be controlled to be 0 and CCVR2 needs to be 0; when a constant Icc of 4.99mA is required, CCVR1 needs to be controlled to be 0 and CCVR2 needs to be controlled to be 1.

[0055] In summary, the current-adjustable constant current output circuit 100 in the embodiment of the present disclosure does not require a DAC or a dedicated constant current chip, and the circuit is simple to implement and has low cost.

[0056] Unless the context clearly indicates otherwise, the singular form of the words used herein and in the appended claims includes the plural and vice versa. Thus, when referring to the singular, the plural form of the corresponding term is generally included. Similarly, the words "comprise" and "include" are to be interpreted as inclusive rather than exclusive. Likewise, the terms "include" and "or" should be interpreted as inclusive, unless such interpretation is expressly prohibited herein. Where the term "example" is used herein, particularly when it is placed after a group of terms, "example" is merely exemplary and illustrative and should not be considered exclusive or comprehensive.

[0057] Further aspects and scopes of adaptability become apparent from the description provided herein. It should be understood that various aspects of the present disclosure can be implemented individually or in combination with one or more other aspects. It should also be understood that the description and specific embodiments herein are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

[0058] Several embodiments of the present disclosure are described in detail above, but it is obvious that those skilled in the art can make various modifications and variations to the embodiments of the present disclosure without departing from the spirit and scope of the present disclosure. The protection scope of the present disclosure is defined by the attached claims.

Claims

1. A current-adjustable constant current output circuit, characterized in that: The constant current output circuit includes: a control signal generating module, a fixed voltage generating module, an operational amplifier, an output current generating module, and a current detection voltage calculating module. The control signal generating module is configured to generate a second number of control signals according to a first number of constant output currents that the constant current output circuit needs to generate, each control signal including two different state information, the first number being 2 N , the second number is N, and N is a natural number; The fixed voltage generating module is configured to adjust the voltage of a voltage dividing node in a resistor voltage dividing circuit in the fixed voltage generating module according to the state information of the second number of control signals, and output different fixed voltages from the voltage dividing node; The operational amplifier is configured to receive the fixed voltage output by the fixed voltage generating module and use the fixed voltage as an input reference voltage of the operational amplifier, and compare the input reference voltage with the received current sensing voltage output by the current sensing voltage calculating module to obtain an operational amplifier output voltage; The output current generating module is configured to generate an output current according to the output voltage of the operational amplifier, and adjust the magnitude of the output current, and finally generate a constant output current when the current sensing voltage is equal to the input reference voltage, and a fixed voltage corresponds to a constant output current; The current-sense voltage calculation module is configured to calculate the current-sense voltage according to the output current and the current-sense resistor.

2. The current-adjustable constant current output circuit according to claim 1, characterized in that: The fixed voltage generating module comprises: the resistor voltage dividing circuit and the voltage regulating circuit. The resistor voltage divider circuit is configured to divide the preset reference voltage by a first resistor and a second resistor which are sequentially connected in series between the preset reference voltage and a ground terminal, and a node between the first resistor and the second resistor is the voltage dividing node; The voltage regulation circuit is composed of the second number of regulation units, and is configured to couple each regulation unit to the voltage dividing node, and control the connection state of the parallel resistor in each regulation unit and the second resistor according to the state information of the control signal corresponding to each regulation unit, and one regulation unit corresponds to one control signal.

3. The current-adjustable constant current output circuit according to claim 2, characterized in that: The circuit structure of each adjustment unit is the same, and one adjustment unit includes: the parallel resistor, the first transistor, the third resistor, and the fourth resistor. Wherein, one end of the parallel resistor is coupled to the voltage division node, and the other end of the parallel resistor is coupled to the first electrode of the first transistor; The second electrode of the first transistor is coupled to the ground terminal, and the control electrode of the first transistor is respectively coupled to one end of the third resistor and one end of the fourth resistor; The other end of the third resistor is coupled to the ground terminal, and the other end of the fourth resistor is coupled to the control signal.

4. The current-adjustable constant current output circuit according to claim 3, characterized in that: The output current generating module comprises: a second transistor, The control electrode of the second transistor is coupled to the output terminal of the operational amplifier, the first electrode of the second transistor outputs the output current, and the second electrode of the second transistor is coupled to the current detection voltage calculation module.

5. The current-adjustable constant current output circuit according to claim 1, characterized in that: The current sensing voltage calculation module includes: the current sensing resistor, One end of the current sensing resistor is coupled to the output current generating module and the negative input end of the operational amplifier respectively, and the other end of the current sensing resistor is coupled to the ground end, and the current sensing voltage is obtained at one end of the current sensing resistor.

6. The current-adjustable constant current output circuit according to claim 1, characterized in that: The current-adjustable constant current output circuit further includes: a filter capacitor and a fifth resistor, wherein the filter capacitor and the fifth resistor are coupled between the fixed voltage generating module and the operational amplifier. Wherein, one end of the filter capacitor is coupled to the voltage division node, and the other end of the filter capacitor is coupled to the ground terminal; One end of the fifth resistor is coupled to the voltage division node, and the other end of the fifth resistor is coupled to the positive input terminal of the operational amplifier.

7. The current-adjustable constant current output circuit according to claim 2, characterized in that: The state information of each control signal includes a high level and a low level, and the control signal generating module includes: a level generating circuit, a control signal generating circuit, and a state control circuit. Wherein, the level generating circuit is configured to generate a high level and a low level according to a microcontroller or a jumper cap coupled to a power supply; a control signal generating circuit configured to generate a second number of control signals according to the high level and the low level generated by the level generating circuit; The state control circuit is configured to control each control signal to output different state information.

8. The current-adjustable constant current output circuit according to claim 7, characterized in that: The controlling the connection state of the parallel resistor in each adjustment unit and the second resistor according to the state information of the control signal corresponding to each adjustment unit comprises: If the control signal is at a high level, the parallel resistor in the adjustment unit corresponding to the control signal is coupled in parallel with the second resistor; If the control signal is at a low level, the parallel resistor in the adjustment unit corresponding to the control signal is disconnected from the second resistor.

9. The current-adjustable constant current output circuit according to claim 4, characterized in that: The value of the constant output current is determined according to the following formula: Icc=Vin_ref / Rg, Wherein, Icc is the constant output current, Vin_ref is the input reference voltage of the operational amplifier, and Rg is the current sensing resistor; The maximum output voltage of the current-adjustable constant current output circuit is determined according to the following formula to determine the maximum load corresponding to each constant output current. RLmax=(Vmax-Vec-Vin_ref) / Icc, Wherein, RLmax is the maximum load, Vmax is the maximum output voltage, and Vec is the on-voltage of the second transistor.

10. The current-adjustable constant current output circuit according to claim 4, characterized in that: The first transistor is an N-type MOS transistor, and the second transistor is a triode.

Images