JPS5975718A - Transistor switching circuit - Google Patents

Abstract

PURPOSE:To reduce loss during saturation and to prevent an element from breaking down owing to abnormal heating by connecting a resistance with a desired value to the collector of a TR bipolar TR connected to an MOSTR field effect TR on Darlington basis. CONSTITUTION:The resistance Rc (with a resistance value Rc) is added between the collector electrode Co of the transistor (TR) Q2 and the drain electrode D of the MOSTRQ1. Thus, the resistance Rc having the value close to Ron/hfe where Ron is the ON resistance of the MOSTRQ1 and hfe is the current amplification factor of the TRQ2 is inserted as shown in a figure to supply a base current IB proportional to a collector current IC, and the TRQ2 is saturated sufficiently to obtain a small saturation voltage VCE(sat). The loss during saturation is VCE(sat).Ic, so it is preferable that the saturation voltage VCE(sat) is extremely small.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a MOS field effect transistor (hereinafter referred to as MO8).
This invention relates to a transistor switching circuit that prevents abnormal heat generation when used in switching mode in a Darlington connection of a transistor (hereinafter referred to as a transistor) and a bipolar transistor (hereinafter referred to as a transistor).

The conventional circuit of this type is MO8I- as shown in Figure 1.
In the Darlington connection of transistor Q and transistor Q, MOS) transistor Q.

A bias is applied between the gate G of the transistor Q2 and the emitter of the transistor Q2, and a driving voltage is applied between the collector side terminal C and the emitter side terminal E of the transistor Q, thereby performing a switching operation.

Although such a conventional circuit has good switching characteristics and drive power, the collector-emitter saturation voltage VCB (sat) of the transistor Q2 increases as the collector current Ic increases, resulting in loss at saturation. Missing P□H-Vc
E(sat') x i c had the disadvantage of becoming a dog and causing abnormal fever.

That is, the reason will be explained with reference to FIG. 2 showing the equivalent circuit of FIG. 1. Here, the junction stiffness between each channel of the MOS transistor (11) is ignored.

In FIG. 2, let the collector-emitter saturation voltage of transistor Q2 be VcE (sat) and 1 to Ron.
・・・・・・・・・MOS）Resistance Ic when transistor drain-source load (ON)・・・・・・Collector current V of transistor
IIE・・・・・・Transistor pace-emitter voltage hfe・・・・・・Transistor current amplification factor I
Iu......If it is the base current of the transistor, then VCE(sat)=1(,on4B-)-VBE-...
・------・tl) 1 B = IC/h f e
・= −−−12) is established, +11
, From formula +21, VCE (sat)= ) is also on
・ :(2!-+VBE ---+3)hfe holds true.

Equation (3) is the saturation voltage VCE (Sat
) indicates that if the collector current Ic increases, it similarly increases. Therefore, the loss P□n at saturation is VcE
(sat)·Ic, the switching circuit generates heat in proportion to this.

Increasing the current amplification factor hfe may be considered as a way to reduce the loss Pon at saturation, which is the cause of this heat generation, as much as possible, but this is not a fundamental solution.

This invention was made by focusing on the problems mentioned above.
In the Darlington connection between a transistor and a transistor (MOS), by connecting a resistor of the desired value to the collector of the transistor, the loss at saturation of the switching circuit is minimized, heat generation is suppressed as much as possible, and good switching characteristics of this type of switching circuit are achieved. The object of the present invention is to provide a transistor switching circuit which completely prevents destruction of switching circuit elements due to abnormal heat generation without impairing properties such as low driving power.

Embodiments of the present invention will be described below with reference to FIG. 3 and subsequent figures.

From each of the above equations (11, (21, (31), the saturation voltage VC
In order to lower E(sat), a pace current LB-j' proportional to the collector current, that is, a state where Ib=IC/hfe must be maintained at all times. In other words, (3
) The circuit may be configured so that the influence of the drain-source ON resistance ROn of the MOS transistor in the equation is eliminated.

In FIG. 3, descriptions of parts that have the same functions and are the same as those in FIG. 1 will be omitted.

The basic difference between the circuit in Figure 3 and the circuit in Figure 1 is that a resistor Rc (resistance value is also indicated by the same symbol) is added between the collector electrode co of the transistor Q2 and the drain electrode of the MOS transistor Q. This is what I did.

The isostatic circuit of the circuit shown in FIG. 3 is shown in FIG. 4, and its operation will be explained with reference to mathematical formulas. In FIG. 4, formulas (4) to (111) hold true.

Ic 1B=Yoshi ・・・・・・・・・・・・・・・
・・・・・・・・・(4)113=Vc−Vnn
, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,
, , , , , (5) 1 is also on Vc= l is also C・I C-)VeB(sat)
−−−−+6) Substituting equation (6) into equation (5), IB=
) equation (7) and organize it, we get ■8ic (R
C-Ic+VcB(sat))-VT3E-shoulder τ-.

. -+8) Rc-Ic+VcE(sat) = ・4"υ1'+
yBE1fe 0n-IC ILC-IC==+(VBE-VCE(sat)) Here, (VBE-VcFi(sat)%) If deviated from 0, ac, ・I C, L'on φI C hfe Ron Therefore, RCL, 11fe...
......(9) Substituting the result of equation (9) into equation (7).

■, :■ is also on/hfe -1c+vcE(sat
-VBE,,,o.

Ron VCI;', (5at)-VnE=o, then 00
The formula is ■, t<, on-Kenichi”Ron-hfe Therefore, B-Ic-・・・・・・・・・・・・・・・
・(lI+fe Resistance Rci with a value shown by equation (9)) A transistor Q.

collector Co and drain D of MOS transistor Q.
By inserting the pace electrode between them, a pace electrode aIE having a value proportional to the collector current IC is supplied, and the transistor Q2 is sufficiently saturated.

A small saturation voltage Vc+v (sat) will be obtained.

Therefore, the loss POn at saturation in Fig. 4 is Pon=
VCB (sat) - IC necessarily has a saturation voltage VCE (s
Although it is desirable that a be as small as possible, it can be made small in the circuit shown in FIG. 3 (equivalent circuit shown in FIG. 4). For example, the ON resistance F of the MOS transistor Q (if ON is 1Ω and the current amplification factor hfe of the transistor Q2 is 20, the resistance to be inserted) < the resistance value Rc of C is Rc=l is also on/hfe=IQ/
2O-=0.0.5Ω, and the heat generated by the resistor Rc, which has a small resistance value, can be suppressed to a small level. However, as the resistance Rc increases, this heat generation increases.

Therefore, in order to prevent this heat generation in this case, in order to increase the current amplification factor hfe of the transistor, the transistor Q2 in FIG.
Transistors (co3, transistors Q4 and 'i1, which are Darlington connected to
The resistance RC in this case is B C:= 1('o n hfe, X hfe2 °−°−= °aδ
hfe is the current amplification factor of transistor Q3>
h fe·fd″2″″pQ, (7) “l amplification factor.

By formula 02, the resistance ReO value becomes extremely small, and the power loss due to the resistance He can be reduced.

An actual example of the circuit shown in Figure 3 is shown below: Ic=15
A, VcB(5at)=1.5V, hfe=
20 (MIN), and as a MOS transistor QI, I is also on=lj3Ω(MAX), and resistance Re=0.
Under 20 conditions, the following effects were obtained depending on the presence or absence of resistance Hc.

However, when IC=12A, as mentioned above, it was confirmed that connecting the 0.2Ω resistor E to the collector of the transistor Q2 has almost no effect on the switching characteristics.

In other words, the conventional Darlington-connected switching circuit of an MO8 transistor and a bipolar transistor has no transistor storage effect (storage time) and requires very little driving power, so it is effective when driving high-power transistors. Although this method has the disadvantage of being prone to abnormal heat generation, it is possible to eliminate this disadvantage without degrading the switching characteristics.

As described above, according to the present invention, by inserting an appropriate resistor on the collector side of the bipolar transistor connected to the MOS field effect transistor and Darlington, the loss at saturation of the switching circuit can be minimized. Since the structure is designed so as not to impair the switching characteristics, a switching circuit with good switching characteristics and prevention of abnormal heat generation can be obtained, making it reliable as a switching circuit for electrical discharge machine power supplies, motor controls, and switching regulators. A suitable one can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional transistor switching circuit, FIG. 2 is an equivalent circuit diagram of the circuit in FIG. 1, and FIG. 3 is a circuit diagram showing an embodiment of a transistor switching circuit according to the present invention. FIG. 4 is an equivalent circuit diagram of the circuit of FIG. 3, and FIG. 5 is a circuit diagram showing another embodiment according to the present invention. Q, MOS field effect transistor Q2
...Bipolar transistor Rc...
・・・・・・Resistance Ron・・・・・・Resistance at load of MOS field effect transistor (+ & hfe・・・・・・Current amplification factor of bipolar transistor

Claims (1)

[Claims] In a Darlington connection circuit of a MOS field effect transistor and a bipolar transistor, a resistance value under load between the drain and source of the MOS field effect transistor is connected between the drain of the MOS field effect transistor and the collector of the bipolar transistor. A transistor switching circuit, characterized in that the transistor switching circuit is connected to a resistor having a resistance value obtained by dividing the current amplification factor of the bipolar transistor by the current amplification factor of the bipolar transistor and an approximate value thereof.