Device and method for symmetric load switching in an H bridge
View Patent ↗An H-bridge device and an associated method for controlling an H-bridge, driving a load such as a DC current electric motor, configured to prevent any reversal of polarity in the load in an unloading phase of said load, without having to limit use of the pulse generator supplying said H-bridge in terms of duty cycle. The H-bridge device includes independent comparators and independent slope control at each of the switches of the H-bridge. Furthermore, according to one aspect, the device includes ‘push-pull’ drivers imposing the potential VBAT/ 2 at the connection points OUT 0 , OUT 1 , on either side of the load, in order to limit electromagnetic interference.
1. An H-bridge device with symmetrical load switching, said H-bridge comprising:
a first, a second, a third and a fourth switches that are distributed over two branches of the H-bridge supplying power to a load, said four switches distributed over two branches being arranged, with respect to said load, such that the first and third switches are linked to the load via a first connection point, on one side of the load, and the second and fourth switches are linked to the load via a second connection point, on the other side of the load, such that the closure of one pair of switches, comprising the first and the fourth switches, allows a current to flow through the load in a forward direction, and that the closure of the other pair of switches, comprising the second and the third switches, allows a current to flow through the load in the reverse direction, an upper part of the H-bridge, called ‘high side’, comprising the first and second switches, being intended to be linked to a power supply, and a lower part of the H-bridge, called ‘low side’, comprising the third and fourth switches, being intended to be linked to ground, said H-bridge device being intended to be controlled by way of a pulse generator having a high state or a low state, and
independent comparators for comparing a magnitude of the current flowing through each of the switches with a reference magnitude,
wherein when the pulse generator is in a high state, the first and fourth switches are controlled to be closed, so that the current flows through the load in the forward direction, and
wherein when the pulse generator switches to a low state:
i. the first and fourth switches are opened,
ii. after the four switches are open in step i. for a predetermined amount of time, the second and third switches are closed, so that the current flows through the load in the reverse direction, the independent comparators comparing the magnitude of the current flowing through each of the switches with the reference magnitude,
iii. in response to the magnitude of the current flowing through one of the second and third switches during step ii. falling below the reference magnitude, the second and third switches are opened, and
iv. when the pulse generator switches to a subsequent high state:
if the second and third switches were opened in step iii., step i. is implemented again,
if the second and third switches were not opened in step iii., the second and third switches are opened and then, after a predetermined amount of time, step i. is implemented again.
2. The H-bridge device with symmetrical load switching as claimed claim 1 , wherein said switches and said comparators are configured so that, when the pulse generator is in a high state, the second and third switches being closed, so as to load the load in the reverse direction:
i. when the pulse generator switches to a low state, the second and third switches are opened,
ii. when the four switches are open, after a dead time, the first and fourth switches are closed, so as to unload the load, the independent comparators comparing the magnitude of the current flowing through each of the switches with the reference magnitude,
iii. if the magnitude of the current flowing through one of the switches falls below the reference magnitude, the first and fourth switches are opened,
iv. when the pulse generator switches to a new high state, if the first and fourth switches were opened in the previous step, step i. is implemented again; otherwise, the first and fourth switches are opened and then, after a dead time, step i. is implemented again.
3. The H-bridge device with symmetrical load switching as claimed in claim 2 , further comprising independent means for controlling the current and voltage slopes, controlling the evolution, as a function of time, of the magnitude of the current flowing through each of said switches and the evolution, as a function of time, of the voltage across the terminals of each of said switches, said independent means for controlling the current and voltage slopes being configured and driven so as to ensure that the negative evolution of the current and of the voltage on the side of the lower part of the H-bridge and the positive evolution of the current and of the voltage on the side of the upper part of the H-bridge, on each side of the load, occur at the same rate, such that the sum of the potentials at the connection points, on either side of the load, is constant.
4. The H-bridge device with symmetrical load switching as claimed in claim 1 , further comprising independent means for controlling the current and voltage slopes, controlling the evolution, as a function of time, of the magnitude of the current flowing through each of said switches and the evolution, as a function of time, of the voltage across the terminals of each of said switches, said independent means for controlling the current and voltage slopes being configured and driven so as to ensure that the negative evolution of the current and of the voltage on the side of the lower part of the H-bridge and the positive evolution of the current and of the voltage on the side of the upper part of the H-bridge, on each side of the load, occur at the same rate, such that the sum of the potentials at the connection points, on either side of the load, is constant.
5. A method for the symmetrical switching of an H-bridge device with symmetrical load switching as claimed in claim 4 , comprising the following steps, when the pulse generator is in a high state, the first and fourth switches being closed, so as to load the load in the forward direction, and the means for controlling the current and voltage slopes of said first and fourth switches ensuring that the sum of the potentials at the points of connection to the load, on either side of the load, is equal to a constant:
i. when the pulse generator switches to a low state, the first and fourth switches are opened, the means for controlling the current and voltage slopes of said first and fourth switches ensuring that the sum of the potentials at the points of connection to the load, on either side of the load, is equal to a constant,
ii. when the four switches are open, after a dead time, the second and third switches are closed, so as to unload the load, the independent comparators comparing the magnitude of the current flowing through each of the switches with the reference magnitude,
iii. if the magnitude of the current flowing through each of the switches falls below the reference magnitude, the second and third switches are opened, the means for controlling the current and voltage slopes of said second and third switches ensuring that the sum of the potentials at the points of connection to the load, on either side of the load, is equal to a constant,
iv. when the pulse generator switches to a new high state, if the second and third switches were opened in the previous step, step i. is implemented again; otherwise, the second and third switches are opened, the means for controlling the current and voltage slopes of said second and third switches ensuring that the sum of the potentials at the points of connection to the load, on either side of the load, is equal to a constant, and then, after a dead time, step i. is implemented again.
6. The method for the symmetrical switching of an H-bridge device as claimed in claim 5 , comprising the following steps, closing the second and third switches when the pulse generator is in a high so as to load the load in the reverse direction, and the means for controlling the current and voltage slopes of said second and third switches ensuring that the sum of the potentials at the points of connection to the load, on either side of the load, is equal to a constant:
i. when the pulse generator switches to a low state, the second and third switches are opened, the means for controlling the current and voltage slopes of said second and third switches ensuring that the sum of the potentials at the points of connection to the load, on either side of the load, is equal to a constant,
ii. when the four switches are open, after a dead time, the first and fourth switches are closed, so as to unload the load, the independent comparators comparing the magnitude of the current flowing through each of the switches with the reference magnitude,
iii. if the magnitude of the current flowing through each of the switches falls below the reference magnitude, the first and fourth switches are opened, the means for controlling the current and voltage slopes of said first and fourth switches ensuring that the sum of the potentials at the points of connection to the load, on either side of the load, is equal to a constant,
iv. when the pulse generator switches to a new high state, if the first and fourth switches were opened in the previous step, step i. is implemented again; otherwise, the first and fourth switches are opened, the means for controlling the current and voltage slopes of said first and fourth switches ensuring that the sum of the potentials at the points of connection to the load, on either side of the load, is equal to a constant, and then, after a dead time, step i. is implemented again.
7. The H-bridge device with symmetrical load switching as claimed in claim 1 , further comprising means for setting a reference potential equal to half the high state at the first and second connection points, on either side of the load, when each of said switches is open.
8. The H-bridge device with symmetrical load switching as claimed in claim 7 , wherein the means for setting the reference potential at the first and second connection points, on either side of the load, are formed by a resistive bridge and a ‘push-pull’ driver, on either side of the load, each of said ‘push-pull’ drivers being connected to one connection point, respectively.
9. A method for the symmetrical switching of an H-bridge device with symmetrical load switching as claimed in claim 8 , comprising, closing the first and fourth switches when the pulse generator is in a high state so as to load the load in the forward direction, and the means for controlling the current and voltage slopes of said first and fourth switches ensuring that the sum of the potentials at the points of connection to the load, on either side of the load, is equal to a constant:
i. when the pulse generator switches to a low state, the first and fourth switches are opened, the means for controlling the current and voltage slopes of said first and fourth switches ensuring that the sum of the potentials at the points of connection to the load, on either side of the load, is equal to a constant,
ii. when the four switches are open, after a dead time, the second and third switches are closed, so as to unload the load, the independent comparators comparing the magnitude of the current flowing through each of the switches with the reference magnitude,
iii. if the magnitude of the current flowing through each of the switches falls below the reference magnitude, the second and third switches are opened, the means for controlling the current and voltage slopes of said second and third switches ensuring that the sum of the potentials at the points of connection to the load, on either side of the load, is equal to a constant,
iv. when the pulse generator switches to a new high state, if the second and third switches were opened in the previous step, step i. is implemented again; otherwise, the second and third switches are opened, the means for controlling the current and voltage slopes of said second and third switches ensuring that the sum of the potentials at the points of connection to the load, on either side of the load, is equal to a constant, and then, after a dead time, step i. is implemented again.
10. A method for the symmetrical switching of an H-bridge device with symmetrical load switching as claimed in claim 7 , comprising, closing the first and fourth switches when the pulse generator is in a high state so as to load the load in the forward direction, and the means for controlling the current and voltage slopes of said first and fourth switches ensuring that the sum of the potentials at the points of connection to the load, on either side of the load, is equal to a constant:
i. when the pulse generator switches to a low state, the first and fourth switches are opened, the means for controlling the current and voltage slopes of said first and fourth switches ensuring that the sum of the potentials at the points of connection to the load, on either side of the load, is equal to a constant,
ii. when the four switches are open, after a dead time, the second and third switches are closed, so as to unload the load, the independent comparators comparing the magnitude of the current flowing through each of the switches with the reference magnitude,
iii. if the magnitude of the current flowing through each of the switches falls below the reference magnitude, the second and third switches are opened, the means for controlling the current and voltage slopes of said second and third switches ensuring that the sum of the potentials at the points of connection to the load, on either side of the load, is equal to a constant,
iv. when the pulse generator switches to a new high state, if the second and third switches were opened in the previous step, step i. is implemented again; otherwise, the second and third switches are opened, the means for controlling the current and voltage slopes of said second and third switches ensuring that the sum of the potentials at the points of connection to the load, on either side of the load, is equal to a constant, and then, after a dead time, step i. is implemented again.
11. The H-bridge device with symmetrical load switching as claimed in claim 1 , wherein the reference magnitude is equal to 100 μA.
12. A method for the symmetrical switching of an H-bridge device with symmetrical load switching as claimed in claim 11 , comprising, closing the first and fourth switches when the pulse generator is in a high state so as to load the load in the forward direction, and the means for controlling the current and voltage slopes of said first and fourth switches ensuring that the sum of the potentials at the points of connection to the load, on either side of the load, is equal to a constant:
i. when the pulse generator switches to a low state, the first and fourth switches are opened, the means for controlling the current and voltage slopes of said first and fourth switches ensuring that the sum of the potentials at the points of connection to the load, on either side of the load, is equal to a constant,
ii. when the four switches are open, after a dead time, the second and third switches are closed, so as to unload the load, the independent comparators comparing the magnitude of the current flowing through each of the switches with the reference magnitude,
iii. if the magnitude of the current flowing through each of the switches falls below the reference magnitude, the second and third switches are opened, the means for controlling the current and voltage slopes of said second and third switches ensuring that the sum of the potentials at the points of connection to the load, on either side of the load, is equal to a constant,
iv. when the pulse generator switches to a new high state, if the second and third switches were opened in the previous step, step i. is implemented again; otherwise, the second and third switches are opened, the means for controlling the current and voltage slopes of said second and third switches ensuring that the sum of the potentials at the points of connection to the load, on either side of the load, is equal to a constant, and then, after a dead time, step i. is implemented again.