Current sensor device
View Patent ↗A current sensor senses the current at a sense transistor and generates an output current that is an accurate proportional representation of the current at the sense transistor. Furthermore, the sensed current is relatively independent of the resistive load of the feedback path at feedback control module to which it is applied. In one embodiment, the feedback control module uses the sensed current in a DC-DC voltage converter to regulate a voltage. The current sensor employs a pair of operational amplifiers to match a voltage at a current electrode of a transistor that generates the output current to a voltage at a current electrode of the sense transistor, such that an effective resistance of the transistor generating the output current is significantly higher than the resistive load of the feedback control module, thereby ensuring that the output current is relatively independent of the resistive load of the feedback control module.
1. A device comprising:
a first transistor comprising a first current electrode, a second current electrode, and a control electrode to receive a first control signal;
a first operational amplifier comprising a first input terminal coupled to the second current electrode of the first transistor, a second input terminal, and an output terminal; and
a second operational amplifier comprising a first input terminal coupled to the second input terminal of the first operational amplifier a second input terminal, and an output terminal;
a second transistor comprising a first current electrode, a second current electrode coupled to the second input terminal of the second operational amplifier, and a control electrode coupled to the output of the second operational amplifier; and
a feedback control module coupled to the first current electrode of the second transistor, the feedback control module configured to provide a second control signal based on a current through the second transistor, the first control signal based on the second control signal.
2. The device of claim 1 , further comprising a third transistor comprising a first current electrode coupled to the second current electrode of the second transistor, a second current electrode coupled to the first voltage reference, and a control electrode coupled to the output terminal of the first operational amplifier.
3. The device of claim 2 , further comprising a fourth transistor comprising a first current electrode coupled to the first input terminal of the first operational amplifier, a second current electrode coupled to a first voltage reference, and a control electrode coupled the output terminal of the first operational amplifier.
4. The device of claim 1 , further comprising a fourth transistor comprising a first current electrode coupled to the first current electrode of the first transistor, a second current electrode coupled to the second current electrode of the first transistor, and a control electrode to receive the first control signal.
5. The device of claim 4 , further comprising an inductor comprising a first terminal coupled to the second current electrode of the fifth transistor and a second terminal coupled to a load.
6. A voltage converter, comprising:
a power switch;
a control circuit including an output to provide a control signal to control the conductivity of the power switch; and
a current sensor having an input to receive the control signal and an output to provide a signal to the control circuit, the current sensor comprising:
a first transistor ( 230 ) comprising a first current electrode, a second current electrode, and a control electrode to receive the control signal;
a first operational amplifier ( 228 ) comprising a first input terminal coupled to the second current electrode of the first transistor, a second input terminal, and an output terminal;
a second operational amplifier ( 222 ) comprising a first input terminal coupled to the second input terminal of the first operational amplifier, a second input terminal, and an output terminal;
a second transistor ( 232 ) comprising a first current electrode coupled to the first input terminal of the first operational amplifier, a second current electrode coupled to a first voltage reference, and a control electrode coupled to the output terminal of the first operational amplifier; and
a third transistor ( 226 ) comprising a first current electrode coupled to the second input terminal of the second operational amplifier, a second current electrode coupled to the first voltage reference, and a control electrode coupled to the output terminal of the first operational amplifier.
7. The voltage converter of claim 6 , wherein the current sensor further comprises:
a fourth transistor ( 224 ) comprising a first current electrode to provide the signal to the control circuit, a second current electrode coupled to the second input terminal of the second operational amplifier, and a control electrode coupled to the output terminal of the second operational amplifier.
8. The voltage converter of claim 6 further comprising:
a diode comprising a first electrode coupled to the second input terminal of the first operational amplifier, and a second electrode coupled to the first voltage reference.
9. The voltage converter of claim 6 further comprising:
an inductor comprising a first electrode coupled to the second input terminal of the first operational amplifier, and a second electrode.
10. The voltage converter of claim 9 further comprising:
a first capacitor comprising a first electrode coupled to the second electrode of the inductor, and a second electrode coupled to the first voltage reference.
11. The voltage converter of claim 9 further comprising:
a load comprising a first terminal coupled to the second electrode of the inductor, and a second terminal coupled to the first voltage reference.
12. The voltage converter of claim 11 , further comprising:
a first resistor comprising a first electrode coupled to the second electrode of the inductor and a second electrode;
a second resistor comprising a first electrode coupled to the second electrode of the first resistor and a second electrode coupled to the first voltage reference.
13. The voltage converter of claim 6 , wherein the control circuit further comprises:
a driver module comprising a first terminal coupled to provide the control signal, a second terminal, and a third terminal.
14. The device of claim 13 further comprising:
a fourth transistor ( 102 ) comprising a first current electrode coupled to the first current electrode of the first transistor, a second current electrode coupled to the second terminal of the driver, and a control electrode.
15. The device of claim 13 further comprising:
a capacitor comprising a first electrode coupled to the second terminal of the driver, and a second electrode coupled to the third terminal of the driver.
16. A method, comprising:
receiving a first current at a first node connected to a first input of an operational amplifier, wherein at least a portion of the first current is to drive a load;
matching a voltage at a second node to a voltage at the first node to generate a second current proportional to the first current, wherein the second node is connected to a second input of the first operational amplifier;
matching a voltage at a third node to the voltage at the second node, wherein the second node is connected to a first input of a second operational amplifier and the third node is connected to a second input of the second operational amplifier; and
generating a third current at a transistor based on the voltage at the third node and a voltage at an output of the second operational amplifier.
17. The method of claim 16 further comprising applying a voltage to the load based on the first current.
18. The method of claim 17 further comprising regulating the voltage based on the third current.
19. The method of claim 18 , further comprising regulating the voltage based on a portion of the voltage.
20. The method of claim 19 , further comprising regulating the voltage by controlling the conductivity of a switch.