H-bridge motor driving circuit

[0002] 1. Field of the Invention

[0003] The present invention relates to an H-bridge motor driving circuit for controlling a DC motor using pulse width modulation (PWM).

[0004] 2. Description of the Related Art

[0005] One general motor driving circuit for controlling a DC motor to rotate selectively in normal and reverse directions is an H-bridge motor driving circuit which has an H-shaped bridge circuit comprising four transistors and a DC motor. The four transistors are turned on and off to energize, de-energize, and rotate the DC motor selectively in the normal and reverse directions.

[0006] FIG. 1 of the accompanying drawings shows a typical conventional H-bridge motor driving circuit.

[0007] As shown in FIG. 1, the conventional H-bridge motor driving circuit comprises H-bridge output circuit 10, triangular wave oscillator 11, PWM comparator 12, inverter 13, and control circuit 14.

[0008] H-bridge output circuit 10 has MOS transistors Q₁, Q₂each having a drain connected to the positive terminal of a DC power supply E, a source connected to the circuit board, and a gate supplied with control signals S₁₁, S₁₂, respectively, for turning on and off MOS transistors Q₁, Q₂, and MOS transistors Q₃, Q₄, each having a drain connected to the sources of MOS transistors Q₁, Q₂, respectively, a source connected to the circuit boards and a ground potential point to which the negative terminal of the DC power supply E is connected, and a gate supplied with control signals S₁₃, S₁₄, respectively, for turning on and off MOS transistors Q₃, Q₄. Motor M is connected between the junction between MOS transistors Q₁, Q₃and the junction between MOS transistors Q₂, Q₄. Parasitic diodes D₁through D₄exist at the junctions between the sources of MOS transistors Q₁through Q₄, the circuit board, and the drains of MOS transistors Q₁through Q₄.

[0009] Triangular wave oscillator 11 generates triangular wave signal S₂₁.

[0010] PWM comparator 12 compares triangular wave signal S₂₁from triangular wave oscillator 11 with constant-level signal S₂₂, and outputs PWM pulse signal S₂₃.

[0011] Inverter 13 inverts pulse signal S₂₃from PWM comparator 12 into pulse signal S₂₄.

[0012] Control circuit 14 is supplied with pulse signals S₂₃, S₂₄, power-supply-level signals S₂₅, S₂₆, and rotation control signal S₀, and outputs signals S₂₅, S₂₄, S₂₆, S₂₃as control signals S₁₁through S₁₄for MOS transistors Q₁through Q₄.

[0013] Operation of the conventional H-bridge motor driving circuit shown in FIG. 1 will be described below with reference to a timing chart of FIG. 4 of the accompanying drawings.

[0014] Triangular wave signal S₂₁generated by triangular wave oscillator 11 and constant-level signal S₂₂are supplied to comparator 12, which generates PWM pulse signal S₂₃. PWM pulse signal S₂₃is inverted into signal S₂₄by inverter 13. Signals S₂₃, S₂₄, power-supply-level signal S₂₅. and ground-level signal S₂₆are supplied to control circuit 14, and then applied as respective control signals S₁₄, S₁₂, S₁₁, S₁₃to the gates of MOS transistors Q₄, Q₂, Q₁, Q₃, respectively. It is assumed that MOS transistors Q₁, Q₄are energized , and MOS transistor Q₄is PWM-controlled. During period T₁, signals S₂₃, S₂₅are high and MOS transistors Q₁, Q₄are turned on, causing a current to flow through motor M. During period T₂, signals S₂₄, S₂₅are high and MOS transistors Q₁, Q₂are turned on, entering a regenerative mode to produce a regenerative current flowing through a loop from motor M to MOS transistor Q₂to MOS transistor Q₁to motor M (in case of an inductive load). In case of a resistive load, the MOS transistors are not conducted.

[0015] The conventional H-bridge motor driving circuit described above is disadvantageous in that since MOS transistor Q₁is energized at all times and hence a current flows through MOS transistor Q₁at all times, a large amount of electric power needs to be supplied to the H-bridge motor driving circuit, which generates a large amount of heat and hence suffers poor reliability. The H-bridge motor driving circuit is necessarily of increased cost as it needs a high-performance device such as a low-on-resistance MOSFET or a low-saturation-voltage transistor for reducing the amount of generated heat.

[0016] It is an object of the present invention to provide an H-bridge motor driving circuit which includes a circuit arrangement for distributing an amount of applied electric power among a plurality of transistors to equalize the amounts of heat generated by the transistors.

[0017] To achieve the above object, an H-bridge motor driving circuit according to the present invention comprises, connected between a PWM comparator and a control circuit, first and second frequency dividers for frequency-dividing, by 2, an output signal from the PWM comparator with positive-going edges and negative-going edges, respectively, thereof, an AND gate for ANDing an output signal from the first frequency divider, an OR gate for ORing the output signal from the first frequency divider and the output signal from the second frequency divider, and first and second inverters for inverting an output signal from the AND gate and an output signal from the OR gate, respectively.

[0018] The control circuit applies an output signal from the first inverter, an output signal from the second inverter, the output signal from the AND gate, and the output signal from the OR gate to the gates of first, second, third, and fourth MOS transistors, respectively.

[0019] During a first period, the first and second transistors are turned on, and the second and third transistors are turned off, causing a current to flow through a motor. During a next second period, the third and fourth transistors are turned on, and the first and second transistors are turned off, causing a regenerative current to flow through the motor. During a next third period, the MOS transistors are turned on and off in the same manner as during the first period, causing a current to flow through the motor. During a final fourth period, the first and second transistors are turned on, and the third and fourth transistors are turned off, causing a regenerative current to flow through the motor.

[0020] In a regenerative mode, the first and second MOS transistors, and the third and fourth MOS transistors are alternately turned on. Therefore, the amount of applied electric power is distributed among the MOS transistors, thus equalizing the amounts of heat generated by the MOS transistors.

[0021] The above and other objects, features, and advantages of the present invention will become apparent from the following description with reference t the accompanying drawing s which illustrate an example of the present invention.

[0022] FIG. 1 is a circuit diagram of a conventional H-bridge motor driving circuit;

[0023] FIG. 2 is a diagram showing waveforms in various portions of the conventional H-bridge motor driving circuit shown in FIG. 1;

[0024] FIG. 3 is a circuit diagram of an H-bridge motor driving circuit according to the present invention; and

[0025] FIG. 4 is a diagram showing waveforms in various portions of the H-bridge motor driving circuit shown in FIG. 3.

[0026] As shown in FIG. 3, an H-bridge motor driving circuit according to an embodiment of the present invention comprises triangular wave oscillator 1, PWM comparator 2 for comparing triangular wave signal S₁and an input signal S₂with each other, frequency dividers 3, 4 for frequency-dividing, by 2, output signal S₃from PWM comparator 2 with positive-going edges and negative-going edges, respectively, thereof, AND gate 5 and OR gate 6 for ANDing and ORing, respectively, output signals S₄, S₅from frequency dividers 3, 4, inverters 7, 8 for inverting output signals S₆, S₈, respectively, from AND gate 5 and OR gate 6 into respective signals S₇, S₉, H-bridge output circuit 10, and control circuit 9 for outputting control signals S₁₁, S₁₂, S₁₃, S₁₄from signals S₆, S₇, S₈, S₉and rotation control signal S₀indicative of whether motor M spins in a normal or reverse direction, to turn on and off MOS transistors Q₁, Q₂, Q₃, Q₄. H-bridge output circuit 10 is of an arrangement identical to the arrangement of H-bridge output circuit 10 of the conventional H-bridge motor driving circuit shown in FIG. 1.

[0027] Operation of the H-bridge motor driving circuit according to the present embodiment will be described below with reference to FIG. 4. FIG. 4 shows waveforms in various portions of the H-bridge motor driving circuit at the time motor M rotates in the normal direction. When motor M rotates in the reverse direction, signals S₁₃, S₁₁and signals S₁₄, S₁₂are switched around.

[0028] Triangular wave signal S₁generated by triangular wave oscillator 1 and input signal S₂are supplied to PWM comparator 2, which generates PWM pulse signal S₃. Frequency dividers 3, 4 frequency-divide, by 2, PWM pulse signal S₃from PWM comparator 2 with positive-going edges and negative-going edges, respectively, thereof. Specifically, frequency divider 3 frequency-divides PWM pulse signal S₃with positive-going edges thereof, producing pulse signal S₄, and frequency divider 4 frequency-divides PWM pulse signal S₃with negative-going edges thereof, producing pulse signal S₅. These pulse signals S₄, S₅have the same frequency as the frequency of triangular wave signal S₁output from triangular wave oscillator 1, and are shifted out of phase with triangular wave signal S₁by the period of the high level of PWM pulse signal S₃. Pulse signals S₄, S₅output from frequency dividers 3, 4 are applied to AND gate 5 and OR gate 6, respectively, which generate pulse signals S₆, S₈, respectively. Pulse signals S₆, S₈are then inverted by respective inverters 7, 8 into inverted pulse signals S₇, S₉. Pulse signals S₆, S₇, S₈, S₉are supplied to control circuit 9, which apply them as control signals S₁₃, S₁₁, S₁₄, S₁₂to the gates of MOS transistors Q₃, Q₁, Q₄, Q₂, respectively.

[0029] It is assumed that MOS transistors Q₁, Q₄are energized. With the conventional H-bridge motor driving circuit, only MOS transistor Q₁or only the MOS transistor Q₄is switched to drive motor M according to PWM. According to the present invention, MOS transistors Q₁, Q₄are alternatively switched to drive motor M according to PWM. Pulse signal S₇is applied as the gate signal S₁₁for MOS transistor Q₁, pulse signal S₉is applied as the gate signal S₁₂for MOS transistor Q₂, pulse signal S₆is applied as the gate signal S₁₃for MOS transistor Q₃, and pulse signal S₈is applied as the gate signal S₁₄for MOS transistor Q₄. One sequence of operating patterns of MOS transistors Q₃, Q₁, Q₄, Q₂is indicated in periods T₁through T₄. States of signals and MOS transistors in each of periods T₁through T₄will be described below.

[0030] During period T₁, pulse signals S₇, S₈are high. As a result, MOS transistors Q₁, Q₄are turned on, and MOS transistors Q₂, Q₃are turned off, causing a current to flow through motor M.

[0031] During period T₂, pulse signals S₆, S₈are high. As a result, MOS transistors Q₃, Q₄are turned on, and MOS transistors Q₁, Q₂are turned off. At this time, H-bridge output circuit 10 enters a regenerative mode to produce a regenerative current flowing through a loop from motor M to MOS transistor Q₄to MOS transistor Q₃to motor M (in case of an inductive load). In case of a resistive load, the MOS transistors are not conducted.

[0032] During period T₃, pulse signals S₇, S₈are high. As a result, MOS transistors Q₁, Q₂are turned on, and MOS transistors Q₃, Q₄are turned off. At this time, H-bridge output circuit 10 enters the regenerative mode to produce a regenerative current flowing through a loop from motor M to MOS transistor Q₂to MOS transistor Q₁to motor M (in case of an inductive load). In case of a resistive load, the MOS transistors are not conducted.

[0033] While a preferred embodiment of the present invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.