CN111122946A - Current sampling circuit for inductive load driving circuit - Google Patents
Current sampling circuit for inductive load driving circuit Download PDFInfo
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- CN111122946A CN111122946A CN202010011311.3A CN202010011311A CN111122946A CN 111122946 A CN111122946 A CN 111122946A CN 202010011311 A CN202010011311 A CN 202010011311A CN 111122946 A CN111122946 A CN 111122946A
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- resistor
- circuit
- inductive load
- operational amplifier
- amplifier module
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current only
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R1/00—Details of instruments or arrangements of the types included in groups G01R5/00 - G01R13/00 and G01R31/00
- G01R1/30—Structural combination of electric measuring instruments with basic electronic circuits, e.g. with amplifier
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R1/00—Details of instruments or arrangements of the types included in groups G01R5/00 - G01R13/00 and G01R31/00
- G01R1/36—Overload-protection arrangements or circuits for electric measuring instruments
Abstract
A current sampling circuit for an inductive load driving circuit comprises a sampling resistor Rs, an operational amplifier module, a voltage source Vs, a first resistor network and a second resistor network. The first resistor network comprises a resistor R3 and a resistor R1 which are connected with each other in series, and the second resistor network comprises a resistor R4 and a resistor R2 which are connected with each other in series; one end of the resistor R3 and one end of the resistor R4 are commonly connected to a voltage source Vs, the common junction of the other end of the resistor R3 and one end of the resistor R1 is connected to the positive phase input end of the operational amplifier module, and the other end of the resistor R1 is respectively connected to the output end of the inductive load driving circuit, the second end of the freewheeling circuit and one end of the sampling resistor Rs; the other end of the resistor R4 and the common junction of one end of the resistor R2 are connected with the inverting input end of the operational amplifier module, and the other end of the resistor R2 is respectively connected with one end of the inductive load L and the other end of the sampling resistor Rs. The invention expands the application lower limit range of the common mode input voltage of the operational amplifier module with lower cost.
Description
Technical Field
The invention relates to a current sampling technology of an inductive load driving circuit.
Background
When an inductive load L (e.g., a solenoid valve, a motor, etc.) is driven, a current sampling circuit as shown in fig. 1 is generally required to collect an output current output to the inductive load, so as to perform constant current control or overcurrent protection on the output current. The output current of the inductive load driving circuit 1 flows through the precision resistor R12, a weak voltage drop is established at two ends of the precision resistor R12, the voltage drop is amplified by the operational amplifier module U1, and a voltage signal proportional to the current flowing through the precision resistor is output to the control circuit 2. The freewheeling diode D in fig. 1 may also be replaced with a MOSFET to freewheel (i.e., synchronous rectification).
Four places where the precision resistors can be placed are shown in fig. 1, and in addition to the resistor R12, the resistors R11, R13, and R14 can also be placed. The resistor R12 is located at a position as a precision resistor, which has the following advantages: 1. the same current as the output current can be detected; 2. the overcurrent caused by the short circuit of the ports P1 and P2 can be detected, and the other three positions do not have the advantages.
The voltage of the S + and S-across the precision resistor R12 is a periodic fluctuating signal when driving an inductive load, the highest voltage can reach the input voltage of the driver, and the lowest voltage can be lower than the conduction voltage drop of a diode D (or MOSFET) at the reference ground, so that the precision resistor R12 has special requirements on circuit devices for collecting current. It requires that the operational amplifier module U1 has a large common mode rejection ratio to amplify the weak differential mode voltage Vd (Vd ═ Vs + -Vs-) across the precision resistor in the original signal and filter out the common mode square wave voltage Vc (Vc ═ Vs + + Vs-)/2) in the original signal. Some common current detection operational amplifier modules in the market generally have the required characteristic of large common mode rejection ratio. However, the current detection operational amplifier module has a limited range for the input common-mode voltage, and a general current detection operational amplifier module allows the amplitude of the input common-mode voltage to be larger than the power supply voltage of the operational amplifier module, but does not allow too low common-mode voltage to be input, and the too low common-mode input voltage can cause the input ESD protection diode inside the operational amplifier module to be turned on, so that the normal operation of the device is influenced, and the serious too low common-mode input voltage can even cause the device to fail. In the specification of a general current detection operational amplifier module, the absolute minimum value of the common-mode input voltage is limited to minus 0.3V. In the example of fig. 1, the common-mode input voltage is-V when freewheeling diode D freewheelsdrop，VdropIs the conduction voltage drop of the freewheeling diode D; when replacing the diode with a MOSFETD when current continues, the common mode input voltage is-Vdrop，VdropIs the turn-on voltage drop of the MOSFET. According to the conditions of the model selection of the freewheeling diode D or the MOSFET, the current in actual operation, the temperature and the like, the voltage of S + and S-at the two ends of the precision resistor R12 is lower than minus 0.3V, so that a general current detection operational amplifier module cannot be directly used in the current sampling at the position R12.
In order to solve the above problems, the following solutions are common at present:
1) a current detection operational amplifier module with lower common-mode input voltage is selected, and the operational amplifier module generally has special design on an internal analog input stage or an internal power supply circuit so as to realize a lower common-mode input voltage range, but the cost is increased;
2) a filter circuit composed of a resistor R5, a resistor R6 and a capacitor C is added to the input end of the operational amplifier module U1, as shown in fig. 2, fig. 2 also shows the internal structure of the operational amplifier module U1. In the freewheeling process of the freewheeling diode D or the MOSFET, the voltage of S + and S-at the two ends of the precision resistor Rs is-VdropWhen the operational amplifier module U1 is IN use, the ESD protection diodes D1 and D2 IN the operational amplifier module U1 are turned on, and their on-currents pass through the resistor R5 and the resistor R6, respectively, and voltage drops are established on the resistor R5 and the resistor R6, and the resistor R5 and the resistor R6 limit the current values passing through the ESD protection diodes D1 and D2, and raise the voltages of the input terminals IN + and IN-of the operational amplifier module U1, thereby protecting the device under the condition of too low common mode input voltage. However, this has the disadvantage that the ESD protection diodes D1 and D2 clamp the input signal at the input terminal of the operational amplifier module U1, which causes the voltage drop between the input differential mode signal and the precision resistor Rs to be inconsistent, so that the amplified signal cannot reflect the real current magnitude, resulting in a large sampling error.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a current sampling circuit for an inductive load driving circuit, which extends the application lower limit range of the common mode input voltage of a current detection operational amplifier module with low cost and has good sampling precision.
The embodiment of the invention provides a current sampling circuit for an inductive load driving circuit, which comprises a sampling resistor Rs and an operational amplifier module; the current sampling circuit is characterized by also comprising a voltage source Vs, a first resistor network and a second resistor network; the first resistor network comprises a resistor R3 and a resistor R1 which are connected with each other in series, and the second resistor network comprises a resistor R4 and a resistor R2 which are connected with each other in series; one end of the resistor R3 and one end of the resistor R4 are commonly connected to a voltage source Vs, the common junction of the other end of the resistor R3 and one end of the resistor R1 is connected to the positive phase input end of the operational amplifier module, and the other end of the resistor R1 is respectively connected to the output end of the inductive load driving circuit, the second end of the freewheeling circuit and one end of the sampling resistor Rs; the other end of the resistor R4 and the common junction of one end of the resistor R2 are connected with the inverting input end of the operational amplifier module, and the other end of the resistor R2 is respectively connected with one end of the inductive load L and the other end of the sampling resistor Rs.
The invention has at least the following technical effects:
1. the current sampling circuit provided by the embodiment of the invention has the advantages that the input voltages of the positive phase input end and the negative phase input end of the operational amplifier module U1 are raised by setting the voltage source Vs, the first resistance network and the second resistance network, so that the original signal lower than the lower limit of the common-mode input voltage of the operational amplifier module can be sampled by using the low-cost current detection operational amplifier module;
2. the output signal amplified by the operational amplifier module of the current sampling circuit in the embodiment of the invention is consistent with the real current, thereby ensuring the sampling precision of the current.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
Fig. 1 shows a schematic circuit diagram of a current sampling circuit for an inductive load driving circuit.
Fig. 2 shows a schematic circuit diagram of another prior art current sampling circuit for an inductive load driving circuit.
Fig. 3 shows a circuit schematic of a current sampling circuit for an inductive load driving circuit according to an embodiment of the present invention.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
Please refer to fig. 3. The current sampling circuit for the inductive load driving circuit according to an embodiment of the present invention includes a sampling resistor Rs, an operational amplifier module U1, a voltage source Vs, a first resistor network and a second resistor network.
The sampling resistor Rs is connected in series between one end of the inductive load L and the output end of the inductive load driving circuit 1, the other end of the inductive load L and the anode of the freewheeling diode D are connected to the ground together, and the cathode of the freewheeling diode D is connected to the common joint of the output end of the inductive load driving circuit 1 and the sampling resistor Rs.
The first resistor network includes a resistor R3 and a resistor R1 connected in series with each other, and the second resistor network includes a resistor R4 and a resistor R2 connected in series with each other.
One end of the resistor R3 and one end of the resistor R4 are commonly connected to the voltage source Vs, a common junction of the other end of the resistor R3 and one end of the resistor R1 is connected to the positive input terminal IN + of the operational amplifier module U1, and the other end of the resistor R1 is respectively connected to the output terminal of the inductive load driving circuit 1, the negative electrode of the freewheeling diode D, and one end S + of the sampling resistor Rs.
The other end of the resistor R4 and the common junction of one end of the resistor R2 are connected with the inverting input end IN-of the operational amplifier module U1, and the other end of the resistor R2 is connected with one end of the inductive load L and the other end S-of the sampling resistor Rs respectively.
Furthermore, the current sampling circuit further comprises a capacitor C, one end of the capacitor C is respectively connected to the non-inverting input terminal of the operational amplifier module U1 and the common junction point of the other end of the resistor R3 and one end of the resistor R1, and the other end of the capacitor C is respectively connected to the inverting input terminal of the operational amplifier module and the common junction point of the other end of the resistor R4 and one end of the resistor R2. The capacitor C has a filtering effect.
Optionally, the first resistive network and the second resistive network are both linear resistive networks.
As another alternative embodiment, a MOSFET may be used instead of the freewheeling diode D in fig. 3.
According to the superposition principle, the open-circuit voltage V of the non-inverting input end IN + of the operational amplifier module U1IN+(i.e., when the first resistor network is not connected to the input resistive load of the operational amplifier module U1) is the original signal voltage Vs+(i.e., the voltage at point S +) and the voltage source Vs are each a superposition of the open-circuit voltage at point IN +, i.e.
VsIs the output voltage of the voltage source Vs. From this equation, it can be seen that the voltage V at the point S + at which the freewheeling diode D freewheels (or the MOSFET freewheels in place of the freewheeling diode D)s+When negative, the resistor R3 and the voltage source Vs can control the voltage V at the point IN +IN+And is lifted upwards. V can be adjusted by adjusting the resistance values of the resistor R1 and the resistor R3IN+Greater than or equal to 0V when the freewheeling diode D (or MOSFET) freewheels. Similarly, the open circuit voltage of point IN-
Can be raised up to greater than or equal to 0V by resistor R4 and voltage source Vs as freewheeling diode D (or MOSFET) freewheels.
When the first and second resistor networks are connected to the input end load of the operational amplifier module U1, since the operational amplifier module U1 has a large input impedance, the resistor network can be adjusted to make its output impedance much smaller than the input impedance of the operational amplifier module U1, and the connection of the operational amplifier module to the voltage V can be neglected in engineeringIN+And VIN-The influence of (c).
Optionally, the resistance of the resistor R1 is equal to the resistance of the resistor R2, the resistance of the resistor R3 is equal to the resistance of the resistor R4, and the resistance of the resistor R1 is equal to the resistance of the resistor R2, and the resistance of the resistor R3 is equal to the resistance of the resistor R4, so that the output of the operational amplifier module U1 is proportional to the input-output amplification factor of the operational amplifier module U1.
Further, the resistance values of the resistor R3 and the resistor R4 are both less than or equal to Vs*R1/Vdrop，VdropThe voltage of the voltage source Vs is V for the voltage drop of the freewheeling diode D (or MOSFET) during freewheelingsTherefore, the common-mode input voltage of the operational amplifier module U1 can be ensured to be more than or equal to 0V when the freewheeling diode D conducts freewheeling, and the excessively low common-mode input voltage is avoided.
Alternatively, R1 ═ R2 ═ 100ohm, R3 ═ R4 ═ Vs*R1/Vdrop. The resistances of the resistors R1, R2, R3 and R4 are too large, which may cause an excessive output resistance of the original signal to the operational amplifier module, resulting in an additional error, while the resistances of the resistors R1 and R2 are too small, which may cause an excessive loss of the resistor network, and the resistances of the resistors R1 and R2 are selected to be 100 ohms, which may achieve a balance in practical applications.
When the resistor R3, the resistor R4, and the voltage source Vs are added, and when the freewheeling diode D is in the freewheeling state or the power switch M of the inductive load driving circuit 1 is in the on state, the output voltage of the operational amplifier module 1 (i.e., the output voltage of the current sampling circuit) is equal to the output voltage of the operational amplifier module 1 when the R1 is R2 and the R3 is R4
The current sampling circuit has consistent amplification factors under different states, wherein A is the input and output amplification factor of the operational amplifier module U1, and V isdIs the differential mode voltage in the original signal.
The current sampling circuit of the embodiment of the invention enables a general operational amplifier module to be used in the application that the original signal voltage is lower than the lower limit of the common-mode input voltage of the operational amplifier module, reduces the cost, has consistent amplification factors under the conditions that the inductive load driving circuit outputs the driving signal and the follow current state, and ensures good sampling precision.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (9)
1. A current sampling circuit for an inductive load driving circuit comprises a sampling resistor Rs and an operational amplifier module; the current sampling circuit is characterized by further comprising a voltage source Vs, a first resistor network and a second resistor network;
the first resistor network comprises a resistor R3 and a resistor R1 connected in series with each other, and the second resistor network comprises a resistor R4 and a resistor R2 connected in series with each other;
one end of the resistor R3 and one end of the resistor R4 are commonly connected to a voltage source Vs, a common junction of the other end of the resistor R3 and one end of the resistor R1 is connected to a positive phase input end of the operational amplifier module, and the other end of the resistor R1 is respectively connected to an output end of the inductive load driving circuit, a second end of the freewheeling circuit and one end of the sampling resistor Rs;
the other end of the resistor R4 and the common junction of one end of the resistor R2 are connected with the inverting input end of the operational amplifier module, and the other end of the resistor R2 is respectively connected with one end of the inductive load L and the other end of the sampling resistor Rs.
2. The current sampling circuit of claim 1, wherein the resistor R1 has a resistance equal to that of the resistor R2, and the resistor R3 has a resistance equal to that of the resistor R4.
3. The current sampling circuit for an inductive load driving circuit as claimed in claim 2The resistance of the resistor R3 and the resistance of the resistor R4 are both less than or equal to Vs*R1/VdropIn which V isdropIs the conduction voltage drop of the follow current circuit.
4. The current sampling circuit of claim 2, wherein the resistance of each of the resistor R1 and the resistor R2 is 100 ohms, and the resistance of each of the resistor R3 and the resistor R4 is equal to Vs*R1/VdropIn which V isdropIs the conduction voltage drop of the follow current circuit.
5. The current sampling circuit of claim 1, further comprising a capacitor C, wherein one end of the capacitor C is connected to the non-inverting input terminal of the operational amplifier module and a common node of the other end of the resistor R3 and one end of the resistor R1, respectively, and the other end of the capacitor C is connected to the inverting input terminal of the operational amplifier module and a common node of the other end of the resistor R4 and one end of the resistor R2, respectively.
6. The current sampling circuit for an inductive load driving circuit according to claim 1, wherein said first resistive network and said second resistive network are both linear resistive networks.
7. The current sampling circuit for an inductive load driving circuit according to claim 1, wherein said freewheeling circuit is a freewheeling diode, the anode of said freewheeling diode being the first end of said freewheeling circuit and the cathode of said freewheeling diode being the second end of said freewheeling circuit.
8. The current sampling circuit for an inductive load driving circuit according to claim 1, wherein said freewheeling circuit is a MOSFET.
9. The current sampling circuit for an inductive load driving circuit as claimed in claim 1, wherein said inductive load driving circuit is a solenoid driving circuit or a motor driving circuit.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202010011311.3A CN111122946A (en) | 2020-01-06 | 2020-01-06 | Current sampling circuit for inductive load driving circuit |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202010011311.3A CN111122946A (en) | 2020-01-06 | 2020-01-06 | Current sampling circuit for inductive load driving circuit |
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| CN111122946A true CN111122946A (en) | 2020-05-08 |
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| CN202010011311.3A Pending CN111122946A (en) | 2020-01-06 | 2020-01-06 | Current sampling circuit for inductive load driving circuit |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114251503A (en) * | 2021-12-22 | 2022-03-29 | 奇瑞汽车股份有限公司 | Driving circuit of inductive load, and method and device for detecting driving current |
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2020
- 2020-01-06 CN CN202010011311.3A patent/CN111122946A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114251503A (en) * | 2021-12-22 | 2022-03-29 | 奇瑞汽车股份有限公司 | Driving circuit of inductive load, and method and device for detecting driving current |
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