JP6183078B2 - Load drive circuit - Google Patents

Description

  The present invention relates to a load drive circuit that is connected to a low-voltage side of an inductive load to which a power supply voltage is applied and includes a transistor that switches the power supply voltage of the inductive load and is mounted on a circuit board.

  Some motors mounted on vehicles are connected to a low voltage side of a motor to which a power supply voltage is applied and are driven by a transistor that switches the power supply voltage of the motor. In such a motor drive circuit, the transistor, the load current circuit through which the motor current flows when the transistor is on, and the induced current generated by the motor when the transistor is off are smoothed and returned to the power source. The reflux circuit is often mounted on the same circuit board. A bus bar is used for a path through which a large current flows.

  Patent Document 1 discloses a PWM module structure including a single PWM module substrate in which all mounting components including a resistance element, a microcomputer, and a MOS transistor are arranged on a mounting-side surface of a substantially square flat plate-shaped printed circuit board. Is disclosed. The PWM module substrate is housed and fixed in a case having a heat sink with the mounting surface facing the heat sink and the non-mounting surface facing outward.

JP 2005-259757 A

In the motor drive circuit as described above, since the area of the plane formed by the loop of the reflux circuit is large, a large electromagnetic field emission occurs, and the motor current is turned on / off at a high speed, thereby generating a magnetic field. There is a problem.
The present invention has been made in view of the circumstances as described above, and has a small plane area formed by the loop of the reflux circuit, does not generate a large electromagnetic field emission, and the load current is turned on / off at high speed. An object of the present invention is to provide a load drive circuit that can suppress a magnetic field caused by the operation.

  A load driving circuit according to a first aspect of the present invention is connected to a low voltage side of an inductive load to which a power supply voltage is applied, a transistor for switching the power supply voltage of the inductive load, and a load current through which a load current flows when the transistor is on A circuit and a reflux circuit that smoothes the induced current generated by the inductive load and circulates it back to a power source when the transistor is off, and each of the load current circuit and the reflux circuit is provided on one side of the circuit board. In the load driving circuit having the first path mounted on the mounting surface, the load current circuit and the return circuit are each mounted on the other mounting surface of the circuit board in parallel with the first path. The first path and the second path are configured such that currents flow in opposite directions.

  In this load driving circuit, the transistor is connected to the low voltage side of the inductive load to which the power supply voltage is applied, switches the power supply voltage of the inductive load, and when the transistor is on, the load current flows through the load current circuit, and the transistor When is turned off, the return circuit smoothes the induced current generated by the inductive load and returns it to the power source. Each of the load current circuit and the return circuit is mounted on the mounting surface on one side of the circuit board. In the load current circuit and the return circuit, the second path mounted in parallel with the first path is mounted in parallel with the first path on the other mounting surface of the circuit board, and the first path and the second path are , Currents flow in opposite directions.

  A load driving circuit according to a second invention is connected to a low voltage side of an inductive load to which a power supply voltage is applied, and switches a power supply voltage of the inductive load, and a load current through which a load current flows when the transistor is on A circuit and a reflux circuit that smoothes the induced current generated by the inductive load when the transistor is off, and circulates it back to the power source, and the load current circuit includes a plurality of circuit boards stacked in parallel. And the return circuit has a second path mounted on the mounting surface, and the load current circuit includes the plurality of circuits. A third path mounted in parallel with the first path on the other mounting surface of the substrate; and the reflux circuit is mounted in parallel with the second path on a mounting surface other than the one mounting surface. Have a fourth route , Said first path and the third path, wherein the second path and the fourth path, characterized in that each current are constituted so as to flow in opposite directions.

  In this load driving circuit, the transistor is connected to the low voltage side of the inductive load to which the power supply voltage is applied, switches the power supply voltage of the inductive load, and when the transistor is on, the load current flows through the load current circuit, and the transistor When is turned off, the return circuit smoothes the induced current generated by the inductive load and returns it to the power source. The load current circuit has a first path mounted on one mounting surface of a plurality of circuit boards stacked in parallel, and the reflux circuit has a second path mounted on one mounting surface. In the load current circuit, the third path is mounted on the other mounting surface of the plurality of circuit boards in parallel with the first path, and in the reflux circuit, the fourth path is mounted on the mounting surface other than the one mounting surface. It is mounted parallel to the two paths. In the first path, the third path, and the second path, the fourth path, currents flow in opposite directions.

  According to the load driving circuit of the present invention, the area of the plane formed by the loop of the reflux circuit is small, no large electromagnetic field emission occurs, and the magnetic field due to the load current being turned on / off at high speed can be suppressed. A load driving circuit can be realized.

It is a circuit diagram which shows schematic structure of embodiment of the load drive circuit which concerns on this invention. It is a disassembled perspective view which shows the mounting form to the circuit board of embodiment of the load drive circuit which concerns on this invention. It is a perspective view which shows the structure of the circuit board shown in FIG. It is explanatory drawing which shows operation | movement of the load drive circuit which concerns on this invention. It is explanatory drawing which shows operation | movement of the load drive circuit which concerns on this invention.

Hereinafter, the present invention will be described with reference to the drawings illustrating embodiments thereof.
FIG. 1 is a circuit diagram showing a schematic configuration of an embodiment of a load driving circuit according to the present invention.
In this load driving circuit, the drain of an N-channel MOS FET (Field Effect Transistor) 3 is connected to the low voltage side of a load (inductive load) 4 to which the voltage of the power source 9 is applied, and the source of the FET 3 is grounded. The load 4 is a DC motor, for example. The gate of the FET 3 is connected to the gate drive circuit 2, and the gate drive circuit 2 is controlled by the control unit 1 to which an input signal from the outside is given.

The anode of the diode D is connected to the drain of the FET 3, and the cathode of the diode D is connected to the plus terminal of the smoothing capacitor C and one terminal of the smoothing coil L. The negative terminal of the smoothing capacitor C is grounded, and the other terminal of the smoothing coil L is connected to the power source 9 and the high voltage side of the load 4.
The FET 3 excluding the load 4, the gate drive circuit 2, the control unit 1, the diode D, the smoothing capacitor C, and the smoothing coil L are mounted on the circuit board 5.

  In such a load driving circuit, the gate driving circuit 2 performs PWM control on the FET 3 to drive the load 4. When the FET 3 is on, the load current flows through the power source 9, the load 4, the FET 3, and the ground path (first path). When the FET 3 is off, the diode D conducts, and the induced current generated in the load 4 flows back through the path of the smoothing capacitor C, the smoothing coil L, and the power source 9 (first path).

FIG. 2 is an exploded perspective view showing a mounting form of the load driving circuit according to the embodiment of the present invention on the circuit board 5. The circuit board 5 is actually one as shown in FIG. 3, but is disassembled into a front surface side 5a and a back surface side 5b in order to show the front surface and the back surface. The control unit 1, the gate drive circuit 2, the load 4 and the power source 9 are not shown.
In the exploded perspective view of FIG. 2, rectangular circuit patterns P1 to P4 are provided in parallel on the mounting surface on the front surface side 5a in the order of P4, P3, P2, and P1 from one side.

The circuit patterns P1 and P4 are for grounding, the circuit pattern P1 is provided by the through hole 7, and the circuit pattern P4 is provided by the through hole 8 so that the circuit pattern P5 (the first pattern) is provided on the entire back surface 5b. 2 paths).
The FET 3 is mounted with its source connected to the circuit pattern P4 and its drain connected to the circuit pattern P3.
The diode D is mounted with its anode connected to the circuit pattern P3 and its cathode connected to the circuit pattern P2.

The smoothing coil L is mounted with one terminal connected to the circuit pattern P2 and the other terminal connected to a power source 9 (not shown).
The smoothing capacitor C is mounted with a positive terminal connected to the circuit pattern P2 and a negative terminal connected to the circuit pattern P1.

In the load driving circuit thus mounted, when the FET 3 is on, the load current is changed from the circuit pattern P3 to the FET 3, the circuit pattern P4, the through hole 8, the circuit pattern P5, and the through hole as shown in FIG. 7. It flows through the path of the circuit pattern P1, the smoothing capacitor C, the circuit pattern P2, and the smoothing coil L. The current flowing through the circuit pattern P1, the smoothing capacitor C, the circuit pattern P2, and the smoothing coil L is a smooth current.

In this case, the current flowing through the circuit pattern P3, FET3, and circuit pattern P4 and the current flowing through the circuit pattern P1, the smoothing capacitor C, and the circuit pattern P2 flow from the other side of the mounting surface of the front surface side 5a to the one side. The current flowing through P5 flows from one side of the mounting surface on the back surface side 5b to the other side.
Therefore, the current flowing through the mounting surface on the front surface side 5a and the current flowing through the mounting surface on the back surface side 5b flow in parallel by being separated by the thickness of the circuit board 5, and are opposite to each other. The electromagnetic fields generated by the two cancel out each other. In addition, the area of the plane formed by the loops of both currents is small, and radiated electromagnetic field emissions are also suppressed.

When FET3 is off, the induced current is, as shown in FIG. 5, the circuit pattern P3, the diode D, the circuit pattern P2, the path of the smoothing coil L, and the circuit pattern P3, the diode D, the circuit pattern P2, smooth It flows through the path of the capacitor C, the circuit pattern P1, the through hole 7, the circuit pattern P5, the through hole 8, and the circuit pattern P4.

In this case, the current that flows from the circuit pattern P3 to the diode D, the circuit pattern P2, the smoothing capacitor C, and the circuit pattern P1 flows from one side of the mounting surface of the surface side 5a to the other side, and the current that flows to the circuit pattern P5 is It flows from the other side of the mounting surface of the back side 5b to one side.
Therefore, the current flowing through the mounting surface on the front surface side 5a and the current flowing through the mounting surface on the back surface side 5b flow in parallel by being separated by the thickness of the circuit board 5, and are opposite to each other. The electromagnetic fields generated by the two cancel out each other. In addition, the area of the plane formed by the loops of both currents is small, and radiated electromagnetic field emissions are also suppressed.

  In the present embodiment, the front and back surfaces of the circuit board 5 are used as mounting surfaces. For example, when a plurality of circuit boards are stacked in parallel, the two surfaces of the two circuit boards are replaced with the front surface of the circuit board 5. The same effect can be obtained by mounting in the same manner as the two mounting surfaces on the back surface. Even if one mounting surface and the other mounting surface of the two circuit boards are mounted in the same manner as the two mounting surfaces of the front surface and the back surface of the circuit substrate 5, the same effect can be obtained.

DESCRIPTION OF SYMBOLS 1 Control part 2 Gate drive circuit 3 FET
4 load (inductive load)
5 Circuit board 7 Through hole 9 Power supply C Smoothing capacitor D Diode L Smoothing coil P1, P2, P3, P4, P5 Circuit pattern

Claims (2)

A transistor that is connected to the low voltage side of an inductive load to which a power supply voltage is applied and that switches the power supply voltage of the inductive load, a load current circuit through which a load current flows when the transistor is on, and when the transistor is off And a return circuit for smoothing the induced current generated by the inductive load and returning it to the power source, wherein the load current circuit and the return circuit are each mounted on a mounting surface on one side of the circuit board. In a load drive circuit having
Each of the load current circuit and the return circuit has a second path mounted in parallel to the first path on the other mounting surface of the circuit board, and the first path and the second path have currents mutually connected to each other. A load driving circuit configured to flow in the reverse direction. A transistor that is connected to the low voltage side of an inductive load to which a power supply voltage is applied and that switches the power supply voltage of the inductive load, a load current circuit through which a load current flows when the transistor is on, and when the transistor is off And a reflux circuit for smoothing the induced current generated by the inductive load and returning it to the power source, and the load current circuit is mounted on one mounting surface of a plurality of circuit boards stacked in parallel. In the load driving circuit having the second path mounted on the mounting surface, the return circuit includes:
The load current circuit has a third path mounted in parallel with the first path on another mounting surface of the plurality of circuit boards, and the reflux circuit is mounted on a mounting surface other than the one mounting surface. A fourth path mounted in parallel with the second path, and the first path and the third path, and the second path and the fourth path are configured such that currents flow in opposite directions, respectively. And a load driving circuit.

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