JP2001292575A - Power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize reduction in size and total weight by eliminating a heat sink through reduction of heat generated in a transistor. SOLUTION: In a power supply for supplying a stabilized power source voltage to the secondary winding side of a transformer T1 by on-off controlling the voltage applied to the primary winding of the transformer T1, a GaN-FET 11 generating a small amount of heat is connected to the primary winding of the transformer T1 and the GaN-FET 11 is on/off controlled by a gate signal, to supply the power source voltage to the secondary winding of the transformer T1.

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 ") of the switching power supply.

[0002]

2. Related Art Conventionally, this kind of power supply circuit has been applied to, for example, automobiles, various consumer crises (videos, televisions, audios, etc.) and industrial equipments (personal computers, communication equipments, FA control equipments, etc.). . The power supply circuit includes a transformer, and a transistor including, for example, a power MOS element connected to a primary winding of the transformer is turned on and off in response to a gate signal.
An output voltage was generated on the secondary winding side.

[0003]

However, in the above power supply circuit, a power MOS type element used as a transistor, for example, a power MOS-FET (2SK231)
In 3), since heat generation is large, it is necessary to accurately design the heat radiation. That is, the power MOS-
Calculating the channel temperature Tch max of an independent FET, Here, Tamax: ambient temperature Ptotal: total loss Rth (ch-a): thermal resistance between the channel and the surroundings, and the temperature rises to the channel temperature or higher. Therefore,
It is necessary to provide a heat sink. In the heat sink design, assuming a derating of 50 ° C. for a channel temperature of 150 ° C., θf <θch-a− (θi + (θc + θs)) = 7.5 ° C./W−(0.833° C./W+0) 0.8 ° C / W) = 5.9 ° C / W where θf: thermal resistance of radiator θch-a: total thermal resistance between channel and surroundings θi: thermal resistance between junction and case (internal thermal resistance) θc + θs: It becomes the thermal resistance between the case and the radiator. From the above, it is necessary to select a radiator having a thermal resistance of 5.9 ° C./W or less. For this purpose, for example, 1 mm
A heat sink of 100 cm ² thick aluminum plate is required.

Therefore, in the conventional power supply circuit, 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 as its object to provide a power supply circuit capable of reducing heat generation of a transistor, eliminating the need for a heat sink, and reducing the size and weight of the circuit.

[0005]

In order to achieve the above-mentioned object, the present invention has a transformer, and controls on / off of a voltage applied to a primary winding of the transformer so that the voltage of the transformer is reduced. In a power supply circuit for supplying a stabilized power supply voltage to a next winding side, a power supply circuit provided with a GaN-FET connected to a primary winding of the transformer and controlled on / off by a gate signal is provided. .

That is, by using a GaN-FET, which generates a small amount of heat, as a switching element, a radiating plate having a large occupied area and a large weight is not required.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a circuit configuration of a power supply circuit according to the present invention will be described with reference to FIGS. In FIG. 1, the power supply circuit is, for example, a switching power supply circuit (single-forward type), and includes a transformer T1 to which an input voltage Ein is applied, a GaN-FET 11 connected to a primary winding of the transformer T1, and a transformer T1. , A diode D1 and a coil L1 connected to the secondary winding of the transformer T1, a diode D2 and a diode D2 connected in parallel to the secondary winding of the transformer T1. A voltage E2 is generated on the secondary winding side by the winding ratio.

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. GaN-
A gate signal (for example, 100 kHz) is applied to the gate of the FET 11.
When z) is input, the GaN-FET 11 performs an on / off operation according to the gate signal. At this time, the transformer T
At 1, the input voltage in is applied to the primary winding, and a voltage E2 is generated on the secondary winding side by the winding ratio.

Here, the ratio of the primary winding to the secondary winding is N
Assuming 1: N2, the voltage E2 becomes E2 = (N2 / N1) × Ein. At this time, a current Is flows when a positive voltage is applied to the diode D1, and this current Is charges the electrolytic capacitor C2 through the coil L1 and outputs Eo as an output voltage. At the same time, energy is stored inside the coil L1 by the current flowing through the coil L1.

As shown in FIG. 3, when the GaN-FET 11 is turned off after the ON period, the GaN-FET 11 becomes 1 through the transformer T1.
The transmission of power from the next winding side is stopped, and a voltage of the opposite polarity is generated in the coil L1. This is the back electromotive force due to the energy stored in the coil L1. Due to this back electromotive force, a current flows through the diode D2 to further charge the electrolytic capacitor C2. The electrolytic capacitor C1 is a smoothing capacitor, and operates so as to always input a flat voltage waveform to the transformer T1.

As described above, in the power supply circuit, the current for charging the capacitor C2 continues to flow over the entire period.
By the way, the gate of the GaN-FET 11 may be controlled by monitoring the load current, changing the on / off control time of the GaN-FET 11 according to the load fluctuation, and using a stabilizing circuit for obtaining a stable output. .

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 embodiment shown in FIG. 1, an output current of 30 A at the maximum is obtained, so that the current Itmax flowing through the transformer T1 is: Itmax = (N2 / N1) × Is Determined by max. Here, the ratio of transformer T1 N1: N2 =
3: 1, assuming that the ripple current is 30% of the output current Io,
Since the current Ismax is Ismax = Io × 1.15, it is necessary to drive a current of Itmax = (１ ／) × 30 × 1.15 = 11.5 A on / off by the GaN-FET. .

Next, the total loss Ptotal can be obtained from the switching waveform shown in FIG. Ptotal = Ps (on) + Pc + Ps (off) Ps (on) = VDSmax × IL × tr × f / 6 Pc = RDS (on) × (IL + Ip) ² × Ton × f / 2 Ps (off) = Vp × Ip × tf × f / 6, where Ps (on): turn-on loss Pc: conduction loss Ps (off): turn-off loss VDSmax: drain-source voltage IL: minimum drain current tr: turn-on time f: frequency RDS ( on): ON resistance Ip: Maximum drain current Ton: ON time Vp: Surge voltage tf: Turn-off time For example, VDSmax = 50V, tr = tf = 50ns,
f = 100 kHz, RDS (on) = 0.013 / 100,
IL = 10 A, Ip = 11.5 A, Ton = 4.9 μs,
When Vp = 60 V (see FIG. 4), Ps (on) = 0.4 W Pc = 0.01 W Ps (off) = 0.57 W Therefore, Ptotal is: Ptotal = 0.4 + 0.01 + 0.57 = 0.98
W.

GaN-FET channel temperature Tch max
Is Therefore, even if a power supply circuit that outputs 30 A is configured, FE
T generates a small amount of heat and can operate at high temperatures (500 ° C.
(Stable operation described above) Because a GaN-FET is used,
Derating sufficient for the channel temperature can be achieved without a heat sink.

As described above, in the present embodiment, the on-resistance Ron max is smaller than that of a conventional power MOS device,
By using a GaN-FET that can operate at a high temperature, the transistor does not generate heat, can operate in the same manner as a conventional transistor, and does not require a heat sink, thereby reducing the manufacturing cost and the processing cost of the heat sink. In addition, the size of the ECU can be reduced.

Further, in the present embodiment, the heat radiation design of the power supply circuit can be simplified, and the circuit pattern design becomes easy, so that the ECU design time can be shortened. 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, the one-switch forward type has been described as an example of the switching power supply circuit. However, the present invention is not limited to this, and can be applied to, for example, chopper type, RCC type, and flyback type power supply circuits. .

[0020]

As described above, according to the present invention, a GaN-FET having low heat generation is used for a switching element of a power supply circuit.
Is used, the heat generation of the switching element is reduced, the heat radiation plate is not required, and the size and weight of the power supply circuit can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of a configuration of a power supply circuit 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 waveform diagram showing a relationship between a current of a coil L1 and an on / off operation of a GaN-FET 11.

FIG. 4 is a waveform diagram showing a current-voltage waveform on the primary side of the transformer shown in FIG. 1;

[Explanation of symbols]

 11 GaN-FET C1, C2 electrolytic capacitor T1 transformer D1, D2 diode L1 coil

Continued on the front page F term (reference) 5F102 FA02 GB01 GC01 GD01 GJ10 GK04 GL04 GM04 GM08 GR04 GR09 HC01 HC07 5G065 AA01 AA08 DA07 EA01 HA01 MA10 NA05 NA09 5H730 AA10 AA14 AA15 BB23 BB57 DD04 EE02 ZEE13Z01

Claims (1)

[Claims] 1. A power supply having a transformer and supplying a stabilized power supply voltage to a secondary winding side of the transformer by controlling on / off of a voltage applied to a primary winding of the transformer. A power supply circuit, comprising: a GaN-FET connected to a primary winding of the transformer and controlled on / off by a gate signal.