A constant current source and voltage-current conversion method

Abstract

A constant current source comprises a voltage-current conversion module; a soft start control module, one input end of which is connected to the output end of a voltage source, and the output end of which is connected to the voltage-current conversion module; and a power switch module, the output end of which is connected to the other input end of the soft start control module, for controlling the switch of the constant current source.

Description

Technical Field

[0001] The invention belongs to the technical field of electronic circuits, and in particular relates to a constant current source and a voltage-current conversion method. Background Art

[0002] A constant current source is a power supply whose output current remains constant. It is a widely used unit circuit. Its main feature is that the output current remains constant and does not change due to changes in the load.

[0003] In order to obtain a constant current source, the voltage source needs to be converted into a current source, which requires a voltage-to-current conversion circuit. There are many existing voltage-to-current conversion circuits, each with its own advantages and disadvantages. Generally, it is hoped that the output current has high accuracy, good stability, and the constant current source load can be connected to the ground. Summary of the invention

[0004] One embodiment of the present invention is a constant current source, comprising:

[0005] Voltage-current conversion module;

[0006] A soft start control module, one input end of which is connected to the output end of a voltage source, and the output end of which is connected to the voltage-current conversion module;

[0007] A power switch module, the output end of which is connected to another input end of the soft start control module, is used to control the switch of the constant current source.

[0008] The constant current source of the present invention is a constant current source circuit with soft start, which includes a voltage-current conversion circuit and a soft start / shutdown circuit, can effectively complete voltage-current conversion, realize constant current output, and can realize soft start and soft shutdown, avoiding over-current and over-voltage impact on power supply and load equipment, is stable and reliable, easy to realize, and low in cost, and can be widely used in various constant current source circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The above and other objects, features and advantages of the exemplary embodiments of the present invention will become readily understood by reading the detailed description below with reference to the accompanying drawings. In the accompanying drawings, several embodiments of the present invention are shown in an exemplary and non-limiting manner, in which:

[0010] Figure 1 A structural block diagram of a voltage-to-current conversion circuit capable of soft start according to one embodiment of the present invention.

[0011] Figure 2 A schematic diagram of a voltage-to-current conversion circuit capable of soft start according to one embodiment of the present invention. DETAILED DESCRIPTION

[0012] Constant current sources often carry inductive loads (for example, providing current to a solenoid that generates a magnetic field). If the constant current source is suddenly powered on to output a large current, or is suddenly turned off in the current output state, according to the circuit principle, the current of the inductor cannot change suddenly, and a large induced electromotive force will be generated at both ends of the inductive load:

[0013]

[0014] It can be seen that a sudden change in load current will cause a very large induced voltage, which often exceeds the withstand voltage of some electronic components in the constant current source, causing overvoltage damage. Therefore, for safety reasons, the current generated by the constant current source must be increased slowly, from small to large, gradually reaching the set value, so as to control the induced voltage of the inductive load within a safe range. This is the soft start of the constant current source. Similarly, when turning off the constant current source, the current also needs to decrease slowly, which is the soft shutdown of the constant current source.

[0015] According to one or more embodiments, a constant current source capable of soft start includes a voltage source input terminal, a start control signal input terminal, a power switch module, a soft start control module, and a voltage-current conversion module. The voltage-current conversion module further includes a voltage sampling module, a current amplification module, a load feedback module, and a current load module.

[0016] The voltage source input terminal of the soft start control module is connected to the output terminal of a voltage source, and the output terminal of the module is connected to the voltage-current conversion module;

[0017] The output end of the power switch module is connected to another input end of the soft start control module, and is used to control the switch of the constant current source, and the start control signal input end is connected to the power switch module;

[0018] The first input end of the voltage sampling module is connected to the output end of the soft start control module, the first output end of the voltage sampling module is connected to the input end of the current amplification module, the second output end of the voltage sampling module is connected to the input end of the load feedback module, and the output end of the load feedback module is connected to the first input end of the voltage sampling module.

[0019] The current load module of the constant current source is connected across the output end of the current amplification module and the input end of the load feedback module.

[0020] Therefore, the embodiment of the present invention can effectively complete the voltage-current conversion, realize constant current output, and realize soft start and soft shutdown, thereby avoiding over-current and over-voltage shocks to the power supply and load equipment.

[0021] According to one or more embodiments, Figure 2 As shown, a constant current source includes:

[0022] Power switch module, soft start control module, voltage sampling module, current amplification module, load feedback module, current load module.

[0023] The soft start control module is composed of a P-channel MOS tube Q3, a charging capacitor C1, a charging resistor R6 and a discharging resistor R5.

[0024] The gate of the P-channel MOS transistor Q3 is connected to the charging capacitor C1 and the charging resistor R6, the source of the P-channel MOS transistor Q3 is connected to the voltage source, and the drain of the P-channel MOS transistor is connected to the first input end of the voltage sampling module.

[0025] The power switch module is composed of an N-channel MOS tube Q2, a pull-down resistor R8, and a current limiting resistor R7. The gate of the N-channel MOS tube Q2 is connected to the current limiting resistor R7, the source of the N-channel MOS tube Q2 is grounded, and the drain of the N-channel MOS tube Q2 is connected to the charging resistor R6 of the startup control module.

[0026] The voltage sampling module is composed of an operational amplifier A1 and four voltage-dividing resistors divided into two groups. The positive input end of the operational amplifier A1 is connected to the voltage-dividing node of one group of voltage-dividing resistors, and the reverse input end of the operational amplifier is connected to the voltage-dividing node of another group of voltage-dividing resistors.

[0027] The output end of the operational amplifier A1 is connected to the input end of the current amplification module.

[0028] The current amplification module is composed of an NPN transistor B1 and a sampling resistor Rs. The base of the NPN transistor B1 is connected to the output end of the operational amplifier A1 in the voltage sampling module, the emitter of the NPN transistor B1 is connected to one end of the sampling resistor Rs, the collector of the NPN transistor B1 is connected to the power supply of the constant current source, and the other end of the sampling resistor Rs is connected to the load input end of the constant current source.

[0029] The load feedback module is composed of an operational amplifier A2, the positive input terminal of the operational amplifier A2 is connected to the load of the constant current source, and the negative input terminal of the operational amplifier A2 is connected to the output terminal of the operational amplifier A2 to form a voltage follower.

[0030] The load of the constant current source has one end connected to the sampling resistor Rs of the current amplification module and the other end connected to the ground.

[0031] like Figure 2 As shown, in the initial state, the start control signal Sc is at a low level, and the gate G2 of the MOS tube Q2 is also at a low level. At this time, the gate-source voltage V GS is 0V, so Q2 is in the cut-off state, and its drain D2 and source S2 are equivalent to the open circuit high resistance state. inWhen the input voltage source is connected, the source S3 of Q3 and the gate G3 of Q3 are both pulled up to U in , the gate-source voltage of Q3 is V GS is 0V, Q3 is cut off, and its drain D3 and source S3 are equivalent to the open circuit high resistance state, so the drain D3 (i.e. U S ) voltage is 0V, and the constant current source has no output. If Sc is not a certain low level, but in a floating high-resistance state, the resistor R8 will pull down the base of the gate G2 of the MOS tube Q2, fixing its level at a low level and preventing it from floating, to ensure that the constant current source has no current output.

[0032] When the start control signal Sc switches to a high level (taking 3.3V as an example), the gate G2 of the MOS tube Q2 jumps to a high level. At this time, the gate-source voltage V GS is 3.3V, Q2 is turned on, its drain D2 and source S2 are equivalent to a short circuit state, and the voltage of D2 becomes GND. in The charging capacitor C1 and the charging resistor R6 will form a charging circuit. As C1 continues to charge, the voltage at the connection point between C1 and R6 (i.e., the base G3 of the MOS tube Q3) will continue to decrease (it will become 0V when charging is completed), so the gate-source voltage V GS It will continue to rise until the capacitor C1 is fully charged and reaches the maximum V GS =U in During this charging process, the MOS tube Q3 will gradually change from cut-off to fully on, and accordingly, the Us voltage will slowly rise from 0 to U in , the output current of the constant current source also slowly rises to the set value. The speed of current rise can be controlled by adjusting the values ​​of the charging capacitor C1 and the charging resistor R6 according to specific needs.

[0033] When the start control signal Sc switches to a low level, the gate G2 of the MOS tube Q2 jumps to a low level. At this time, the gate-source voltage V GS 0V, Q2 is turned off, and its drain D2 and source S2 are equivalent to the open circuit state. Capacitor C1 and resistors R5 and R6 will form a discharge circuit. As C1 continues to discharge, the voltage at the connection point of C1 and R6 (i.e. the base G3 of MOS tube Q3) will continue to increase (it will become U after the discharge is completed). in ), so the gate-source voltage VGS of Q3 will continue to decrease, and will reach the minimum value V when the capacitor C1 is discharged. GS =0V. During this discharge process, the MOS tube Q3 will gradually change from fully on to fully off, and accordingly, the Us voltage will also change from U in It slowly drops to 0V, and the output current of the constant current source also slowly drops to 0.

[0034] According to the "virtual short" and "virtual break" principles of operational amplifiers

[0035] U1=U2 (2)

[0036] U3=U4 (3)

[0037]

[0038]

[0039]

[0040]

[0041]

[0042] Select the appropriate resistance value,

[0043]

[0044] Then we can get

[0045]

[0046] It can be seen that the load current output by the circuit will not change with the change of load, and is proportional to the input voltage, realizing the voltage-current conversion required by the constant current source. In actual use, Rs is generally selected as a small resistor in the milliohm level to reduce power consumption. By adjusting the value of the resistor to make k very small, the voltage-current ratio can be reduced, which facilitates the output current adjustment of the constant current source. The specific value is determined according to actual needs.

[0047] In summary, the constant current source circuit of the embodiment of the present invention can effectively complete the voltage-current conversion, realize the constant current output, and realize soft start and soft shutdown, so as to avoid the sudden current during power-on and shutdown from causing over-current and over-voltage shock to the power supply and load equipment. After reading the patent of the present invention, those skilled in the art can make subtle changes and adjustments, such as changing the selection of MOS tubes according to the circuit principle, changing the selection of operational amplifiers, or changing the capacitance and resistance of capacitors, etc., which will still be the essence of the present invention and will not deviate from the spirit and scope of the patent of the present invention.

[0048] According to one or more embodiments, Figure 2As shown, the OPA2187 dual op amp chip is selected, which contains two low-power zero-drift operational amplifiers, which can meet the requirements of operational amplifiers A1 and A2 in the circuit. The current amplifier transistor Q1 is selected from KSD1691, the power switch MOS tube Q2 is selected from BSS138, and the soft start control MOS tube Q3 is selected from CSD25404Q3; R2 and R3 are selected from 0.1% high-precision 1K precision resistors, R1 and R4 are selected from 0.1% high-precision 100K precision resistors, and the sampling resistor Rs is selected from RS02BR low-temperature drift 100mΩ precision wirewound resistors. C1 is 10uF, and R5, R6, R7, and R8 are all 22K; U in The adjustment range is 0 to 10 V. Then the output current range of this constant current source is 100 mA to 1 A.

[0049] In the initial state, the start control signal Sc is at a low level, and the gate G2 of the MOS tube Q2 is also at a low level. At this time, the gate-source voltage V GS is 0V, so Q2 is in the cut-off state, and its drain D2 and source S2 are equivalent to the open circuit high resistance state. in When the input voltage source is connected, the source S3 of Q3 and the gate G3 of Q3 are both pulled up to U in , the gate-source voltage of Q3 is V GS is 0V, Q3 is cut off, and its drain D3 and source S3 are equivalent to the open circuit high resistance state, so the drain D3 (i.e. U S ) voltage is 0V, and the constant current source has no output. If Sc is not a certain low level, but in a floating high-resistance state, the resistor R8 will pull down the base of the gate G2 of the MOS tube Q2, fixing its level at a low level and preventing it from floating, to ensure that the constant current source has no current output.

[0050] When the start control signal Sc switches to a high level (taking 3.3V as an example), the gate G2 of the MOS tube Q2 jumps to a high level. At this time, the gate-source voltage V GS is 3.3V, Q2 is turned on, its drain D2 and source S2 are equivalent to a short circuit state, and the voltage of D2 becomes GND. in The charging capacitor C1 and the charging resistor R6 will form a charging circuit. As C1 continues to charge, the voltage at the connection point between C1 and R6 (i.e., the base G3 of the MOS tube Q3) will continue to decrease (it will become 0V when charging is completed), so the gate-source voltage V GS It will continue to rise until the capacitor C1 is fully charged and reaches the maximum V GS =U in During this charging process, the MOS tube Q3 will gradually change from cut-off to fully on, and accordingly, the Us voltage will slowly rise from 0 to U in, the output current of the constant current source also slowly rises to the set value. According to the specific needs, the value of the charging capacitor C1 and the charging resistor R6 can be adjusted to control the speed of the current rise. According to the above capacitor and resistor values, C1 is 10uF, R6 = 22K, then the charging constant τ

[0051] τ=R*C=0.22 sec (11)

[0052] It can be seen that the time it takes for the constant current source to fully output the set current is approximately 3 times the time constant, that is, 0.66 seconds.

[0053] When the start control signal Sc switches to a low level, the gate G2 of the MOS tube Q2 jumps to a low level. At this time, the gate-source voltage V GS 0V, Q2 is turned off, and its drain D2 and source S2 are equivalent to the open circuit state. Capacitor C1 and resistors R5 and R6 will form a discharge circuit. As C1 continues to discharge, the voltage at the connection point of C1 and R6 (i.e. the base G3 of MOS tube Q3) will continue to increase (it will become U after the discharge is completed). in ), so the gate-source voltage VGS of Q3 will continue to decrease, and will reach the minimum value V when the capacitor C1 is discharged. GS =0V. During this discharge process, the MOS tube Q3 will gradually change from fully on to fully off, and accordingly, the Us voltage will also change from U in It slowly drops to 0V, and the output current of the constant current source also slowly drops to 0.

[0054] It is worth noting that, although the foregoing content has described the spirit and principle of the invention with reference to several specific embodiments, it should be understood that the invention is not limited to the disclosed specific embodiments, and the division of various aspects does not mean that the features in these aspects cannot be combined, and such division is only for the convenience of expression. The invention is intended to cover various modifications and equivalent arrangements included in the spirit and scope of the appended claims.

Claims

1. A constant current source, characterized in that: include, Voltage-current conversion module; A soft start control module, one input end of which is connected to the output end of a voltage source, and the output end of which is connected to the voltage-current conversion module; A power switch module, the output end of which is connected to another input end of the soft start control module, for controlling the switch of the constant current source, The voltage-current conversion module includes: Voltage sampling module, current amplification module, load feedback module, The first input end of the voltage sampling module is connected to the output end of the soft start control module, the first output end of the voltage sampling module is connected to the input end of the current amplification module, the second output end of the voltage sampling module is connected to the input end of the load feedback module, the output end of the load feedback module is connected to the first input end of the voltage sampling module, and the load of the constant current source is connected across the output end of the current amplification module and the input end of the load feedback module. The start control signal is input into the power switch module, and the switch of the constant current source is controlled by the power switch module. The soft start control module is composed of a P-channel MOS tube Q3, a charging capacitor C1, a charging resistor R6 and a discharging resistor R5. The gate of the P-channel MOS transistor Q3 is connected to the charging capacitor C1 and the charging resistor R6, the source of the P-channel MOS transistor Q3 is connected to the voltage source, and the drain of the P-channel MOS transistor is connected to the first input terminal of the voltage sampling module. The power switch module is composed of an N-channel MOS tube Q2, a pull-down resistor R8, and a current limiting resistor R7. The gate of the N-channel MOS tube Q2 is connected to the current limiting resistor R7, the source of the N-channel MOS tube Q2 is grounded, and the drain of the N-channel MOS tube Q2 is connected to the charging resistor R6 of the soft start control module. The voltage sampling module is composed of an operational amplifier A1 and four voltage-dividing resistors divided into two groups. The positive input end of the operational amplifier A1 is connected to the voltage-dividing node of one group of voltage-dividing resistors, and the reverse input end of the operational amplifier is connected to the voltage-dividing node of another group of voltage-dividing resistors. The output end of the operational amplifier A1 is connected to the input end of the current amplification module. The current amplification module is composed of an NPN transistor B1 and a sampling resistor Rs. The base of the NPN transistor B1 is connected to the output end of the operational amplifier A1 in the voltage sampling module, the emitter of the NPN transistor B1 is connected to one end of the sampling resistor Rs, the collector of the NPN transistor B1 is connected to the power supply of the constant current source, and the other end of the sampling resistor Rs is connected to the load input end of the constant current source. The load feedback module is composed of an operational amplifier A2, the positive input terminal of the operational amplifier A2 is connected to the load of the constant current source, and the negative input terminal of the operational amplifier A2 is connected to the output terminal of the operational amplifier A2 to form a voltage follower. The load of the constant current source has one end connected to the sampling resistor Rs of the current amplification module and the other end connected to the ground.

2. A voltage-to-current conversion method, based on the constant current source as claimed in claim 1, characterized in that: The following steps are included: When soft start is required, a start control signal is input to the power switch module, and the soft start control module is controlled by the power switch module. The voltage-current conversion module is controlled by the soft start control module to perform voltage-to-current conversion.

Images