JP2001277937A - Large current load control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a small size and a light weight of circuit by requiring no heat release plate by making a heat generation of a switching element for ON/OFF control less. SOLUTION: In a large current load control device, a micro-computer 14 ON/OFF controls a current from a battery corresponding to an instruction of switch for ON/OFF switching and the current is fed to a head lamp 10. GaN-FET11 is connected to a power source wire 1 connecting the battery and the head lamp 10. The GaN-FET11 is ON/OFF operated by a control of the micro-computer 14 to feed the current to the head lamp 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gallium nitride-field effect transistor (hereinafter referred to as "GaN-FE").
T ").

[0002]

2. Related Background Art Conventionally, this kind of large current load control apparatus is applied to, for example, lighting control of a headlamp for an automobile. In the large current load control device, for example, a power MOS-F including a switching element for on / off control provided on a power supply line connecting a battery and a lamp.
By turning on and off the ET under the control of a microcomputer (hereinafter, referred to as a “microcomputer”), lighting control of a headlamp has been performed.

[0003]

However, in the above control device, the power MOS-FET used as a switching element for on / off control generates a large amount of heat.
It is necessary to design the heat radiation accurately. That is, the power M
When the channel temperature Tch max of the OS-FET is calculated, Tch max = (Ta max) + (Ron max) × (lo max) × (lo max) × Rth (ch-a) (1) = 85 ° C. + 0. 013Ω × 10A × 10A × 50 ° C./W=150° C. Here, Ta max: ambient temperature Ron max: on-resistance lo max: current value Rth (ch-a): thermal resistance between the channel and the surroundings, up to the channel temperature The temperature rises. Therefore, it is necessary to provide a heat sink. Heatsink design: channel temperature 1
Assuming that the derating is 50 ° C. with respect to 50 ° C., θf <θj-a− (θi + (θc + θs)) = 11.5 ° C./W−
(0.833 ° C./W+0.8° C./W)=9.9° C./W where θ f: radiator thermal resistance θ j-a: total thermal resistance between junction and outside air θ i: junction-to-case heat Resistance (internal thermal resistance) θc + θs: The thermal resistance between the case and the radiator. From the above, it is necessary to select a radiator having a thermal resistance of 9.9 ° C./W or less. For this purpose, for example, 1 mm
A heat sink having a thickness of 6 cm ² and a weight of about 10 g is required.

Therefore, in the conventional large current load control device,
There is a problem that the circuit configuration is large and heavy due to the heat sink. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a large current load control device capable of reducing heat generation of a switching element for on / off control, eliminating the need for a heat sink, and reducing the size and weight of a circuit. The purpose is to provide.

[0005]

In order to achieve the above object, according to the present invention, there is provided a large current load control device for supplying a current from a power supply to an electric load by controlling on and off in accordance with a predetermined instruction. A GaN-connected to a power supply line connecting a power supply and a load, and turned on and off by the control.
A large current load control device including an FET is provided.

That is, the switching element for on / off control is operated at a high temperature (500 ° C. or higher) with small heat generation.
By using a GaN-FET capable of the above, the occupied area is large and a heavy heat sink is not required.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a circuit configuration of a large current load control device according to the present invention will be described with reference to FIGS. FIG. 1 is a circuit diagram showing a circuit block of a large current load control device used for controlling a headlamp in an automobile. In the present invention, the element for controlling the on / off of the headlamp 10 is G instead of the power MOS-FET.
A circuit was formed using the aN-FET11.

As shown in FIG. 2, for example, a GaN-FET 11 is provided on a semi-insulating sapphire substrate 11a.
An N buffer layer 11b is laminated, and a semi-insulating Ga
N layer 11c and n-type AlGaN layer 11d are sequentially laminated,
Further, the I-type AlGaN layer 11d has an I
A diffusion layer 11e doped with n and C or Mg is formed, and an electrode of a gate G is loaded on the diffusion layer 11e.

An n-type GaN layer 11f is laminated on the other portion of the surface layer of the n-type AlGaN layer 11d.
Among other portions of the surface portion of the n-type AlGaN layer 11d, an electrode of the source S is loaded on one n-type GaN layer 11f, and an electrode of the drain D is loaded on the other n-type GaN layer 11f. Have been. Portions other than the gate G, source S, and drain D electrodes are covered with a SiO insulating film 11g.

[0010] Each semiconductor layer of the GaN-FET 11 shown in FIG.
The film is formed using an epitaxial crystal growth method such as a CVD method or an MBE method. GaN-based compound semiconductor
aN, AlGaN, InGaN, InAlGaN, In
It is a general term for GaNAs, InGaNP and the like. In the figure, in this embodiment, a GaN-FE is connected to a power supply line 1 between a battery as an internal power supply and a headlamp 10 as an electric load.
This shows a high-side drive circuit to which T11 is connected. The drain of the GaN-FET 11 is connected to a battery, and the source is connected to two headlamps 10. A resistor R1 and a capacitor C1 are connected to the gate of the GaN-FET 11, and the FET 12 and the FE
A microcomputer 14 as a control circuit is connected via T13, and the GaN-FET 1 is controlled by the microcomputer 14.
1 performs an on / off operation. A diode D1, a Zener diode D2 and a resistor R are provided between the gate and the source.
2 are connected in series.

A charge pump circuit 15 is connected to the source of the FET 12, and a resistor R 3 is connected between the source and the gate of the FET 12 to increase the voltage applied to the FET 12. Further, the resistor R4 is connected to the gate of the FET 12, the resistors R5 and R6 and the capacitor C2 are connected to the gate of the FET 13, and the microcomputer 14 is connected thereto.

The microcomputer 14 is connected to a battery via a power supply circuit 16. The power supply circuit 16 converts a power supply voltage from the battery and supplies the converted voltage to the microcomputer 14.
The microcomputer 14 is connected to a switch 17 for switching the headlamp 10 on and off. In this embodiment, the on / off switch 17 is used. However, the on / off control may be performed using, for example, a CAN (controller area network) which is an in-vehicle LAN (local area network).

In the large current load control device, when the switch 17 is turned on, the microcomputer 14 detects the on state from the input port to which the switch 17 is connected, and outputs a high level signal to the output port for controlling the headlamp 10. (5V) signal is output. With this output, FET1
2 and 13 are turned on, the GaN-FET 11 is turned on, and the headlamp 10 is turned on. In the present embodiment, since the GaN-FET 11 is driven on the high side on the upstream side (battery side) of the headlamp 10, the F
The charge pump circuit 15 is provided on the source side of the ET 12. This charge pump circuit 15 is a GaN-FE
To turn on T11, the battery voltage + GaN-F
The voltage higher than the gate-source voltage of ET11 is GaN-
The input is set to the gate of the FET 11.
The charge pump circuit 15 of the present embodiment is set so that, for example, the battery voltage is converted to 21 V and supplied to the gate of the GaN-FET 11.

When the switch 17 is turned off,
The microcomputer 14 detects the off state and outputs a low level (0 V) to an output port for controlling the headlamp 10. With this output, the FETs 12 and 13 are turned off, the GaN-FET 11 is turned off, and the headlamp 10 is turned off. In the present embodiment, the GaN-FE
A shunt resistor R7 is connected between T11 and the battery, and an overcurrent detection circuit 18 is connected to both ends of the shunt resistor R7 to detect an overcurrent flowing through the GaN-FET 11. As shown in FIG. 3, the overcurrent detection circuit 18 has two operational amplifiers 19 and 20 and amplifies and detects the value of the current flowing through the shunt resistor R7.
4, and based on the above detection result, the microcomputer 14 has a possibility that the wire harness may be heated and deteriorated or smoke if the excessive current continues to flow.
The N-FET 11 is turned off.

Next, a circuit design using the GaN-FET 11 will be described. Conventionally, when designing such a circuit, it is necessary to accurately design the heat dissipation of the FET,
For this reason, the design time becomes longer, and it is necessary to consider the layout on the printed circuit board, and the degree of freedom of the layout is limited. Along with this, in recent years, F
It has been desired to simplify and shorten the heat dissipation design of the ET.

On the other hand, in the present embodiment shown in FIG. 1, since two headlamps 10 are turned on, 60
Since an electric power of W × 2 = 120 W is required and a maximum current of about 10 A flows in a steady state, an ambient temperature of 85 ° C.
Calculating the channel temperature of the GaN-FET 11 at
From the equation (1), Tch max = 85 ° C. + (0.013Ω / 100) × 10A
× 10A × 50 ° C./W=85.65° C. Since no heat is generated even when a current of 10 A is always supplied, a heat sink required when a power MOS-FET is used becomes unnecessary.

When a large-current load control device is used in a severe temperature environment such as an engine room, the operating temperature range of the device is required to be 125 ° C. or higher.
-By using a GaN-FET that can operate at a different high temperature than the FET (stable operation even at 500 ° C),
Derating sufficient for channel temperature (50 ° C
Above), and it is easy to design a highly reliable and compact ECU.

As described above, in the present embodiment, G having a smaller on-resistance Ron max than that of a conventional power MOS device is used.
By using the aN-FET, the element for on / off control does not generate heat, the same operation as the conventional element for on / off control can be performed, and a heat sink is not required. The processing cost of the heat sink is reduced and the ECU is downsized.

Further, in the present embodiment, the heat radiation design of the circuit can be simplified and the circuit pattern design can be facilitated.
ECU design time can be reduced. The present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the present invention. In the present embodiment, a preferred example of a high-side type headlamp control circuit for an automobile has been described. However, the present invention is not limited to this, and for example, a G between the headlamp 10 and GND as shown in FIG.
It is also possible to adopt a low-side drive circuit configuration in which the aN-FET 11 is connected. In the figure, a control unit 20 has a unit configuration of each element such as a microcomputer and an FET for controlling on / off of the GaN-FET 11.

The GaN-FET according to the present invention has
-GaN-FET of both channel type and P-channel type
May be used. Further, the large current load control device of the present invention may be used for controlling other than a headlamp, for example, a tail lamp, a fog lamp, or may have a function of controlling these lamps, and may further control a motor,
For example, blower motors and wiper motors (H
I, LOW, INT, MIST) can be used for load on / off control.

[0021]

As described above, according to the present invention, a GaN-FET which generates a small amount of heat and can be operated at a high temperature (500 ° C. or higher) is used as a switching element for on / off control of a large current load control device. Therefore, the heat generation of the switching element is reduced to eliminate the need for a heat radiating plate, and the size and weight of the circuit can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a circuit configuration of a large current load control device according to the present invention.

FIG. 2 is a configuration diagram showing one embodiment of the GaN-FET shown in FIG.

FIG. 3 is a circuit diagram showing a circuit configuration of the overcurrent detection circuit shown in FIG.

FIG. 4 is a circuit diagram showing another circuit configuration of the large current load control device according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power supply line 10 Headlamp 11 GaN-FET 12, 13 FET 14 Microcomputer 15 Charge pump circuit 16 Power supply circuit 17 ON / OFF switch C1, C2 Capacitor R1-R7 Resistance D1, D2 Diode

Claims (1)

[Claims] 1. A large-current load control device for controlling a current from a power supply to turn on and off according to a predetermined instruction and supplying the current to an electric load, wherein the control device is connected to a power supply line connecting the power supply and a load. A large current load control device comprising a GaN-FET that operates on and off.