JP3246775B2 - Voltage compensation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage compensation circuit,
More specifically, the present invention relates to a voltage compensating circuit suitable for use in electrical components such as automobiles, outboard motors, and home appliances through which a large current flows.

[0002]

2. Description of the Related Art A circuit shown in FIG. 5 is known as a circuit for driving a load by supplying a specified current from a power supply to a load.

The circuit shown in FIG. 1 includes a current supply circuit 22 in which a coil (for example, an ignition coil of an automobile) L as a load and a power transistor 21 are connected in series to a power supply 20, and a drive voltage supplied from the power supply 20. The power transistor 21 is turned on / off at a predetermined timing based on a control signal from the input terminal 24, and the coil L
And a drive circuit 23 for controlling the energization of.

The driving circuit 23 has two transistors T1
, T2, the bases of both transistors T1, T2 are connected to an input terminal 24 via a resistor R1, and the collector of one of the transistors T1 is connected to a conducting circuit 22.
, The collector of the other transistor T2 is grounded, and the emitter of one transistor T1 is connected to the emitter of the other transistor T2. The connection point between the two emitters is connected to the gate of the power transistor 21 via a resistor R2.

In FIG. 5, R3 is a bias resistor, C1,
C2 is a smoothing capacitor.

Here, the power supply voltage of the circuit shown in FIG.
, The load voltage applied to the coil L is VC, the load current is I, and the gate voltage of the power transistor 21 is VG.

In the circuit shown in FIG. 5, when a control signal is inputted to the input terminal 24, since the power supply voltage VB is applied to one transistor T1 of the drive circuit 23, both transistors T1 and T2 are turned on. As a result, the gate voltage VG is applied to the gate of the power transistor 21, and the power transistor 21 is turned on, so that the load current I flows through the coil L.

In such an operation, when the load current I is as large as 50 A, for example, as shown in FIG. 4, the power supply voltage VB and the load voltage VC applied to the coil L are reduced. Accordingly, the gate voltage VG of the power transistor 21 also decreases, and the load current I flowing through the power transistor 21 cannot maintain the specified value as shown by the solid line in FIG.

Due to such a problem, conventionally, a power transistor 21 that allows a specified load current I to flow through the coil L even when the power supply voltage VB decreases is selected, or the power supply voltage VB decreases. C1, C2
The fact is that the capacity is increased.

[0010]

As described above, in the prior art, when a large current flows, the power supply voltage drops, and there is a problem that a specified load current cannot be flowed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a voltage compensating circuit which can compensate for a decrease in power supply voltage when a large current flows and can always supply a specified load current to a load.

[0012]

According to the present invention, there is provided a power transistor connected to a power supply circuit from a power supply to a load, a driving voltage obtained from the power supply, and turning on / off the power transistor at a predetermined timing based on a control signal; A voltage compensating circuit used in a circuit having a drive circuit for controlling the energization of a load, comprising: a current transformer for extracting a load current flowing from the power supply to the load to a secondary side; A backflow prevention element for preventing backflow of load current to the power supply, and a charging voltage that increases a drive voltage drop of a drive circuit when the load current flows from the power supply to the load while being charged by the load current extracted by the current transformer. A charge / discharge circuit for supplying a specified current to an energizing circuit including the power transistor.

[0013]

The operation of the voltage compensation circuit having the above configuration will be described below.

When a control signal is input to a drive circuit that obtains a drive voltage from a power supply, the drive circuit operates and turns on the power transistor at a predetermined timing. As a result, the load current from the power supply flows through the energizing circuit. At this time, the load current is taken out to the secondary side of the current transformer, and the charging / discharging circuit is charged. The backflow prevention element prevents backflow of the load current from the secondary side of the current transformer to the power supply side.

The charge / discharge circuit increases the drive voltage of the drive circuit when the load current flows from the power supply to the load by increasing the charge voltage.

Thus, even if the load current is large and the power supply voltage drops, the drive voltage of the power transistor is increased, so that a prescribed load current can be passed to the load.

[0017]

Embodiments of the present invention will be described below.

In the circuit of the electrical component shown in FIG. 1, components having the same functions as those shown in FIG. 5 are denoted by the same reference numerals.

The electric component circuit shown in FIG. 1 includes a power supply 20 and a coil L as a load and a power transistor 2.
1 are connected in series, and a drive circuit 23 for controlling the energization of the coil L is provided.

Further, the electric component circuit shown in FIG. 1 includes a current transformer 2 for extracting a load current I flowing from the power supply 20 to the coil L to the secondary side, and a current transformer 2 for the current transformer 2.
The current transformer 2 is connected between the
And a diode D as a backflow prevention element for preventing a back current of the load current I from the secondary side to the power supply 20 side, and a load current from the power supply 20 to the coil L while being charged by the load current I extracted by the current transformer 2. A voltage compensating circuit 1 comprising a charge / discharge circuit 3 for increasing a drive voltage drop of the drive circuit 23 when I flows by a charging voltage and flowing a prescribed load current I to an energizing circuit 22 including the power transistor 21; ing.

The charging / discharging circuit 3 includes a current transformer 2
It is constructed by grounding a capacitor C0 connected between the next side and one transistor T1.

Next, the operation of the circuit of the electrical component shown in FIG.
The operation of the voltage compensation circuit 1 will be mainly described.

When a control signal is input from an input terminal 24 to a drive circuit 23 which obtains a drive voltage from a power supply 20, a transistor T1 of the drive circuit 23 is turned on, thereby
A gate voltage VG is applied to the gate of the power transistor 21. The power transistor 21 is turned on, and the load current I flows through the coil L. At this time, the load current I is taken out to the secondary side of the current transformer 2 and charges the capacitor C0 of the charge / discharge circuit 3.

In such an operation, when the load current I is as large as 50 A, for example, the power supply voltage VB drops as shown in FIG. 3, but at this time, the capacitor C0 of the charge / discharge circuit 3 The drive voltage of the drive circuit 23 when the load current I flows from the coil L to the coil L is increased by the charging voltage.

Thus, even if the load current I is large and the power supply voltage VB decreases, the power transistor 21
The gate voltage VGO is increased as shown in FIG. 3, and the load voltage VC applied to the coil L is also increased, contrary to the conventional example, so that a specified load current I can flow through the coil L.

By the operation of the voltage compensation circuit 1 as described above,
Even when the load current I is as large as 50 A, for example,
It is possible to compensate for a decrease in the load voltage VC applied to the coil L and to allow a prescribed load current I to flow through the coil L.
The performance of electrical components can be fully exhibited. Also,
By such an operation of the voltage compensation circuit 1, a power transistor having a smaller rating than that of the conventional example can be used as the power transistor 21, and the range of selecting the power transistor 21 can be wider than that of the conventional example. .

FIG. 2 shows another embodiment of the present invention, and shows an example in which power is supplied to four coils L1 to L4 by a power supply 20 to which the above-described voltage compensation circuit 1 is added.

That is, the circuit shown in FIG.
The discharge voltage VK of the capacitor C0 of the four driving circuits 23
Drive voltage. In this case, by appropriately setting the timings of the first to fourth control signals to the respective input terminals 24 of the four drive circuits 23 so as to cause a time difference, one power supply 20 and one voltage compensation circuit 1 The four coils L1 to L4 can be energized with a time difference, and the voltage compensating circuit 1 allows a prescribed load current I to flow to each of the coils L1 to L4 as described above.

The circuit shown in FIG. 2 is suitable for use as an ignition circuit for a four-cylinder engine.

The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the invention.

[0031]

According to the present invention described in detail above, since the above-described configuration is employed, a voltage compensation that can compensate a decrease in the power supply voltage when a large current flows and can always supply a specified load current to the load. A circuit can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the present invention.

FIG. 3 is a timing chart showing an operation in the embodiment of the present invention.

FIG. 4 is a timing chart showing an operation of a conventional example.

FIG. 5 is a circuit diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Voltage compensation circuit 2 Current transformer 3 Charge / discharge circuit 21 Power transistor 22 Current supply circuit L coil

Continuation of the front page (56) References JP-A-2-55538 (JP, A) JP-A-63-174563 (JP, A) JP-A-3-116770 (JP, U) JP-A-60-10883 (JP (58) Fields surveyed (Int. Cl. ⁷ , DB name) F02P 15/00 F02P 3/045 303

Claims (1)

(57) [Claims] A power transistor connected to a power supply circuit from a power supply to a load, a drive circuit for obtaining a drive voltage from the power supply and turning on and off the power transistor at a predetermined timing based on a control signal to control the load power supply. A voltage compensation circuit used for a circuit having
A current transformer for taking out a load current flowing from the power supply to the load to a secondary side, a backflow prevention element for preventing a backflow of the load current from the secondary side of the current transformer to the power supply side, and a load current taken out by the current transformer And a charge / discharge circuit for increasing a drive voltage drop of the drive circuit when the load current flows from the power supply to the load by the charging voltage and flowing a specified current to the energizing circuit including the power transistor. Voltage compensation circuit.