Bidirectional electronic load circuit

Abstract

The invention, which relates to the technical field of the electronic measuring instrument, discloses a bidirectional electronic load circuit comprising a conditioning circuit and a power tube circuit. The conditioning circuit is used for generating a corresponding positive control signal or negative control signal according to the polarity of the input control voltage; the power tube circuit comprises a positive power switch tube, a negative power switch tube and a current sampling circuit which are connected in series; the power tube circuit responds to the positive control signal, controls the positive power switch tube to work in a constant current state so as to pull a positive load current, and simultaneously controls the negative power switch tube to be completely conducted; or in response to the negative control signal, the negative power switch tube is controlled to work in a constant current state so as to pull the negative load current, and meanwhile, the positive power switch tube is controlled to be completely conducted. The circuit provided by the invention can work under positive and negative voltages when in use, and can stabilize the load current under an extremely low voltage without manually switching the polarity.

Description

Technical Field

[0001] This invention relates to the field of electronic measuring instrument technology, and specifically to a bidirectional electronic load circuit. Background Technology

[0002] An electronic load is a general-purpose test and measurement device. It is a programmable load instrument designed to replace a fixed resistive load, achieving continuous and programmable load control. Its core components include a control CPU, a digital-to-analog converter (DAC), an error amplifier, and power MOSFETs.

[0003] Under normal circumstances, a DC load cell can achieve unidirectional load current control. When reverse current is applied, the load current will become uncontrollable. When testing the negative current, the wiring needs to be reversed.

[0004] An AC load cell adds a rectifier bridge to the DC load cell. This rectifies the AC current into DC, which is then passed through the DC load cell to achieve the function of an AC load. Therefore, an AC load cell contains a rectifier bridge, which has a voltage drop. When using a silicon rectifier bridge, the voltage drop is typically above 1.4V. Therefore, the load cell cannot draw current below 1.4V.

[0005] When testing the load-carrying capacity of some output low positive and negative voltages, the load tester mentioned above cannot meet the requirements. It is necessary to design a bidirectional electronic load circuit that can be compatible with operation below 1.4V. Summary of the Invention

[0006] The purpose of this invention is to provide a bidirectional electronic load circuit, including a voltage input interface, a positive voltage acquisition circuit, a negative voltage acquisition circuit, a positive error amplifier, a negative error amplifier, a positive power MOSFET, a negative power MOSFET, and a current sampling circuit. It can operate under both positive and negative voltages and can stably draw load current at extremely low voltages (such as ±0.1V) without the need for manual polarity switching, thus solving the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a bidirectional electronic load circuit, comprising a conditioning circuit and a power transistor circuit; The conditioning circuit is used to generate a corresponding positive or negative control signal based on the polarity of the input control voltage. The power transistor circuit includes a positive power switch, a negative power switch, and a current sampling circuit connected in series. The power transistor circuit responds to the positive control signal by controlling the positive power switch to operate in a constant current state to draw positive load current, while simultaneously controlling the negative power switch to be fully turned on; or responds to the negative control signal by controlling the negative power switch to operate in a constant current state to draw negative load current, while simultaneously controlling the positive power switch to be fully turned on. The current sampling circuit is connected in series in the current path of the positive power switch to generate a feedback signal to the conditioning circuit.

[0008] Preferably, the conditioning circuit includes: A positive voltage acquisition circuit is used to output a positive control voltage equal to the input control voltage when the input control voltage is positive, and to output zero voltage when the input control voltage is negative; A negative voltage acquisition circuit is used to output a negative control voltage equal to the input control voltage when the input control voltage is negative, and to output zero voltage when the input control voltage is positive. A positive error amplifier, whose first input terminal is connected to the output terminal of the positive voltage acquisition circuit, and whose second input terminal is connected to the feedback voltage of the current sampling circuit; A negative error amplifier, whose first input terminal is connected to the output terminal of the negative voltage acquisition circuit, and whose second input terminal is connected to the feedback voltage of the current sampling circuit; The output of the positive error amplifier drives the positive power switch, and the output of the negative error amplifier drives the negative power switch.

[0009] Preferably, the positive voltage acquisition circuit includes an operational amplifier U1A, a diode D1, and a resistor R2. The anode of the diode D1 is connected to the output terminal of the operational amplifier U1A, and the cathode is grounded through the resistor R2 and fed back to the negative input terminal of the operational amplifier U1A. When the positive input of operational amplifier U1A is a positive voltage, due to the action of diode D1, the output voltage of the operational amplifier is positive and diode D1 is turned on. At this time, the voltage across resistor R2 is positive, which is fed back to the negative input terminal of operational amplifier U1A, forming negative feedback. Operational amplifier U1A adjusts the output voltage to make the voltage across resistor R2 equal to the input control voltage. When the positive input of operational amplifier U1A is negative, due to the effect of diode D1, a negative output voltage cannot be output across resistor R2. At this time, the minimum voltage across resistor R2 is 0V. This voltage is fed back to the negative input terminal of operational amplifier U1A. Since the positive input terminal of operational amplifier U1A is negative, the output voltage of operational amplifier is negative. The reverse cutoff function of diode D1 keeps the voltage across resistor R2 at 0V, thus achieving the negative cutoff function.

[0010] Preferably, the negative voltage acquisition circuit includes an operational amplifier U2A, a diode D2, and a resistor R7. The cathode of the diode D2 is connected to the output terminal of the operational amplifier U2A, and the anode is grounded through the resistor R7 and fed back to the negative input terminal of the operational amplifier U2A. When the positive input of operational amplifier U2A is negative, due to the action of diode D7, the output of the operational amplifier is negative, and diode D2 conducts. At this time, the voltage across resistor R7 is negative, which is fed back to the negative input terminal of operational amplifier U2A, forming negative feedback. The operational amplifier adjusts the output voltage to make the voltage across resistor R7 equal to the input control voltage. When the positive input of operational amplifier U2A is positive, due to the effect of diode D2, a positive output voltage cannot be output across resistor R7. At this time, the highest voltage across resistor R7 is 0V. This voltage is fed back to the negative input terminal of operational amplifier U2A. Since the positive input terminal voltage of operational amplifier U2A is positive, the output voltage of operational amplifier is positive at this time. The reverse cutoff function of diode D2 keeps the voltage across resistor R7 at 0V, thus achieving the forward cutoff function.

[0011] Preferably, the forward error amplifier includes an operational amplifier U1B, a resistor R3, and a capacitor C1. The non-inverting input of the operational amplifier U1B is connected to the voltage across the resistor R2, and its output drives the gate of the forward power switch through the current-limiting resistor R1. The current sampling circuit is connected between the source of the forward power switch and the common ground GND. The voltage on the current sampling circuit is fed back to the inverting input of the operational amplifier U1B through the resistor R3.

[0012] Preferably, the negative error amplifier includes an operational amplifier U2B, a resistor R6, and a capacitor C2. The inverting input terminal of the operational amplifier U2B is connected to the voltage across the resistor R7, and its output drives the gate of the negative power switch through the current-limiting resistor R8. The voltage on the current sampling circuit is directly fed back to the non-inverting input terminal of the operational amplifier U2B.

[0013] Preferably, both the positive power switch and the negative power switch are power switches with heat sinks.

[0014] Preferably, the current sampling circuit includes multiple current sampling resistors connected in series.

[0015] Compared with the prior art, the beneficial effects of the present invention are: The present invention provides a bidirectional electronic load circuit, which is mainly used when there are positive and negative voltage outputs and a controllable electronic load is required. It can be used with positive voltage or negative voltage without manual polarity switching, and can be used in low voltage applications, even below 0.1V.

[0016] This invention discloses a bidirectional electronic load circuit, comprising an operational amplifier, diodes, resistors, capacitors, and a power MOSFET. In use, when a positive input voltage is applied, the power MOSFET draws a proportionally positive current; conversely, when a negative voltage is applied, the power MOSFET draws a proportionally negative current. Since there are no diodes in the main current loop, it can achieve lower voltage current loads, as low as 0.1V; therefore, it can be used in various scenarios, such as current load drawing for operational amplifiers, LDOs, and power modules. Attached Figure Description

[0017] Figure 1 The present invention provides an overall circuit module diagram of a bidirectional electronic load circuit.

[0018] Figure 2 The present invention provides an overall circuit diagram of a bidirectional electronic load circuit.

[0019] Figure 3 The diagram shows the forward current operation process of a bidirectional electronic load circuit provided by the present invention.

[0020] Figure 4 The diagram shows the negative current operation process of a bidirectional electronic load circuit provided by the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] Figure 1 The present invention provides an overall circuit module diagram of a bidirectional electronic load circuit. Figure 2 The present invention provides an overall circuit diagram of a bidirectional electronic load circuit, wherein the input control voltage is connected through interface P1.

[0023] The positive voltage acquisition circuit consists of an operational amplifier U1A, a diode D1, and a resistor R2.

[0024] When the positive input of operational amplifier U1A is positive, due to the action of diode D1, the op-amp outputs a positive voltage, and diode D1 conducts. At this time, the voltage across resistor R2 is positive, which is fed back to the negative input of operational amplifier U1A, forming negative feedback. The operational amplifier adjusts the output voltage to make the voltage across resistor R2 equal to the input control voltage.

[0025] When the positive input of operational amplifier U1A is negative, due to the effect of diode D1, a negative output voltage cannot be output across resistor R2. At this time, the minimum voltage across resistor R2 is 0V. This voltage is fed back to the negative input terminal of operational amplifier U1A. Since the positive input terminal of operational amplifier U1A is negative, the output voltage of operational amplifier is negative. The reverse cutoff function of diode D1 keeps the voltage across resistor R2 at 0V, thus achieving the negative cutoff function.

[0026] The negative voltage acquisition circuit consists of operational amplifier U2A, diode D2, and resistor R7.

[0027] When the positive input of operational amplifier U2A is negative, due to the action of diode D7, the op-amp outputs a negative voltage, and diode D2 conducts. At this time, the voltage across resistor R7 is negative, which is fed back to the negative input terminal of operational amplifier U2A, forming negative feedback. The operational amplifier adjusts the output voltage to make the voltage across resistor R7 equal to the input control voltage.

[0028] When the positive input of operational amplifier U2A is positive, due to the effect of diode D2, a positive output voltage cannot be output across resistor R7. At this time, the highest voltage across resistor R7 is 0V. This voltage is fed back to the negative input terminal of operational amplifier U2A. Since the positive input terminal voltage of operational amplifier U2A is positive, the output voltage of operational amplifier is positive at this time. The reverse cutoff function of diode D2 keeps the voltage across resistor R7 at 0V, thus achieving the forward cutoff function.

[0029] The forward error amplifier circuit consists of operational amplifier U1B, resistor R3, and capacitor C1.

[0030] When the output voltage of operational amplifier U1B increases, the gate voltage of MOSFET Q1 increases after passing through drive resistor R1. This increases the on-state current of MOSFET Q1, and simultaneously increases the current flowing through current sampling resistor R4. Consequently, the voltage across resistor R4 increases, and this voltage is fed back to the negative input terminal of operational amplifier U1B through resistor R3, causing the output voltage of the operational amplifier to drop, thus forming a negative feedback loop. Due to the virtual short and virtual open circuit properties of the operational amplifier, the voltage across resistor R4 eventually stabilizes at the positive input pin voltage of operational amplifier U1B.

[0031] The resistor R1 is placed to isolate the output of the operational amplifier U1B from the gate parasitic capacitance of the MOSFET Q1. Since the gate capacitance of a high-power MOSFET is generally above 1nF, directly connecting it to the output of the operational amplifier will reduce the phase margin of the operational amplifier, resulting in oscillation.

[0032] The combination of resistor R3 and capacitor C1 is used to reduce the loop bandwidth, increase the phase margin, stabilize the control loop, and prevent oscillations.

[0033] As the output voltage of operational amplifier U2B increases, the gate voltage of MOSFET Q2 rises after passing through drive resistor R8. This increases the on-state current of MOSFET Q2, and simultaneously increases the current flowing through current sampling resistors R5 and R4. Since the reference ground is between resistors R4 and R5, the voltage across R4 is negative. To mitigate this negative feedback, the voltage drops directly to the positive input of operational amplifier U2B, causing a decrease in the output voltage and forming a negative feedback loop. Due to the virtual short and virtual open circuit properties of the operational amplifier, the voltage across resistor R4 eventually stabilizes at the negative input pin voltage of operational amplifier U2B.

[0034] The resistor R8 is placed to isolate the output of the operational amplifier U1B from the gate parasitic capacitance of the MOSFET Q1, in order to stabilize the loop.

[0035] The combination of resistor R6 and capacitor C2 is used to reduce the loop gain, stabilize the control loop, and prevent oscillations.

[0036] When the input signal is a positive voltage V1, the voltage across resistor R2 is the positive input voltage V1, and the voltage across resistor R7 is 0V. Error amplifier U1B operates, causing the voltage across resistor R4 to be V1. At this time, current flows from pin 1 of output port P2 sequentially to resistors R4 and R5, then through the body diode of MOSFET Q2, and finally to pin 2 of output port P2. At this time, the positive input of op-amp U2B is V1, and the negative input is 0V. Therefore, op-amp U2B outputs a positive full-swing output, which drives MOSFET Q2 to fully conduct. The on-state voltage drop of MOSFET Q2 is close to 0V, as shown in the attached diagram. Figure 3 As shown.

[0037] When the input signal is a negative voltage -V2, the voltage across resistor R2 is 0V, and the voltage across resistor R7 is -V2. Error amplifier U2B operates, causing the voltage across resistor R4 to be -V2. At this time, current flows from pin 2 of output port P2 sequentially to resistor R5, resistor R4, and through the body diode of MOSFET Q1 to pin 1 of output port P2. At this time, the positive input of op-amp U1B is 0V, and the negative input is -V2, so the output of op-amp U2B is a positive full-swing output, which will drive MOSFET Q1 to fully conduct. The on-state voltage drop of MOSFET Q1 is close to 0V, as shown in the attached diagram. Figure 4 As shown.

[0038] In summary, with positive and negative voltage inputs, the MOSFETs Q1 and Q2 can be switched on alternately through the operational amplifier conditioning circuit, enabling bidirectional electronic load functionality and compatibility with loads operating at lower voltages.

[0039] In practical applications, signals are input to the P1 interface via the DAC, allowing for software control. Furthermore, GND and the power supply under test need to be isolated in the circuit.

[0040] Table 1 shows the measured data of a bidirectional electronic load circuit provided by the present invention when testing the output characteristics of an operational amplifier.

[0041]

[0042]

[0043] As shown in the table above, the error between the measured IH_A and IH_B of the output Iource positive current load ISet is less than 1%. The error between the measured IL_A and IL_B of the output Isink negative current load ISet is also less than 1%. This error is caused by the components. Actual data shows that the circuit is working perfectly.

[0044] Compared to other electronic load circuits, this circuit enables bidirectional electronic loads while also being compatible with lower voltage loads, down to ±0.1V.

[0045] The present invention provides a bidirectional electronic load circuit, which is mainly used when there are positive and negative voltage outputs and a controllable electronic load is required. It can be used with positive voltage or negative voltage without manual polarity switching, and can be used in low voltage applications, even below 0.1V.

[0046] This invention discloses a bidirectional electronic load circuit, comprising an operational amplifier, diodes, resistors, capacitors, and a power MOSFET. In use, when a positive input voltage is applied, the power MOSFET draws a proportionally positive current; conversely, when a negative voltage is applied, the power MOSFET draws a proportionally negative current. Since there are no diodes in the main current loop, it can achieve lower voltage current loads, as low as 0.1V; therefore, it can be used in various scenarios, such as current load drawing for operational amplifiers, LDOs, and power modules.

[0047] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0048] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A bidirectional electronic load circuit, characterized in that, This includes conditioning circuitry and power transistor circuitry; The conditioning circuit is used to generate a corresponding positive or negative control signal based on the polarity of the input control voltage. The power transistor circuit includes a positive power switch, a negative power switch, and a current sampling circuit connected in series. The power transistor circuit responds to the positive control signal by controlling the positive power switch to operate in a constant current state to draw positive load current, while simultaneously controlling the negative power switch to be fully turned on; or responds to the negative control signal by controlling the negative power switch to operate in a constant current state to draw negative load current, while simultaneously controlling the positive power switch to be fully turned on. The current sampling circuit is connected in series in the current path of the positive power switch to generate a feedback signal to the conditioning circuit.

2. The bidirectional electronic load circuit according to claim 1, characterized in that, The conditioning circuit includes: A positive voltage acquisition circuit is used to output a positive control voltage equal to the input control voltage when the input control voltage is positive, and to output zero voltage when the input control voltage is negative; A negative voltage acquisition circuit is used to output a negative control voltage equal to the input control voltage when the input control voltage is negative, and to output zero voltage when the input control voltage is positive. A positive error amplifier, whose first input terminal is connected to the output terminal of the positive voltage acquisition circuit, and whose second input terminal is connected to the feedback voltage of the current sampling circuit; A negative error amplifier, whose first input terminal is connected to the output terminal of the negative voltage acquisition circuit, and whose second input terminal is connected to the feedback voltage of the current sampling circuit; The output of the positive error amplifier drives the positive power switch, and the output of the negative error amplifier drives the negative power switch.

3. The bidirectional electronic load circuit according to claim 2, characterized in that, The positive voltage acquisition circuit includes an operational amplifier U1A, a diode D1, and a resistor R2. The anode of the diode D1 is connected to the output terminal of the operational amplifier U1A, and the cathode is grounded through the resistor R2 and fed back to the negative input terminal of the operational amplifier U1A. When the positive input of operational amplifier U1A is a positive voltage, due to the action of diode D1, the output voltage of the operational amplifier is positive and diode D1 is turned on. At this time, the voltage across resistor R2 is positive, which is fed back to the negative input terminal of operational amplifier U1A, forming negative feedback. Operational amplifier U1A adjusts the output voltage to make the voltage across resistor R2 equal to the input control voltage. When the positive input of operational amplifier U1A is negative, due to the effect of diode D1, a negative output voltage cannot be output across resistor R2. At this time, the minimum voltage across resistor R2 is 0V. This voltage is fed back to the negative input terminal of operational amplifier U1A. Since the positive input terminal of operational amplifier U1A is negative, the output voltage of operational amplifier is negative. The reverse cutoff function of diode D1 keeps the voltage across resistor R2 at 0V, thus achieving the negative cutoff function.

4. The bidirectional electronic load circuit according to claim 3, characterized in that, The negative voltage acquisition circuit includes an operational amplifier U2A, a diode D2, and a resistor R7. The cathode of the diode D2 is connected to the output terminal of the operational amplifier U2A, and the anode is grounded through the resistor R7 and fed back to the negative input terminal of the operational amplifier U2A. When the positive input of operational amplifier U2A is negative, due to the action of diode D7, the output of the operational amplifier is negative, and diode D2 conducts. At this time, the voltage across resistor R7 is negative, which is fed back to the negative input terminal of operational amplifier U2A, forming negative feedback. The operational amplifier adjusts the output voltage to make the voltage across resistor R7 equal to the input control voltage. When the positive input of operational amplifier U2A is positive, due to the effect of diode D2, a positive output voltage cannot be output across resistor R7. At this time, the highest voltage across resistor R7 is 0V. This voltage is fed back to the negative input terminal of operational amplifier U2A. Since the positive input terminal voltage of operational amplifier U2A is positive, the output voltage of operational amplifier is positive at this time. The reverse cutoff function of diode D2 keeps the voltage across resistor R7 at 0V, thus achieving the forward cutoff function.

5. A bidirectional electronic load circuit according to claim 4, characterized in that, The forward error amplifier includes an operational amplifier U1B, a resistor R3, and a capacitor C1. The non-inverting input of the operational amplifier U1B is connected to the voltage across the resistor R2, and its output drives the gate of the forward power switch through the current-limiting resistor R1. The current sampling circuit is connected between the source of the forward power switch and the common ground GND. The voltage on the current sampling circuit is fed back to the inverting input of the operational amplifier U1B through the resistor R3.

6. A bidirectional electronic load circuit according to claim 5, characterized in that, The negative error amplifier includes an operational amplifier U2B, a resistor R6, and a capacitor C2. The inverting input of the operational amplifier U2B is connected to the voltage across the resistor R7, and its output drives the gate of the negative power switch through the current-limiting resistor R8. The voltage on the current sampling circuit is directly fed back to the non-inverting input of the operational amplifier U2B.

7. A bidirectional electronic load circuit according to any one of claims 1-6, characterized in that, Both the positive power switch and the negative power switch are power switches with heat sinks.

8. A bidirectional electronic load circuit according to claim 7, characterized in that, The current sampling circuit includes multiple current sampling resistors connected in series.

Images