JPS61114613A - Semiconductor device - Google Patents

Abstract

PURPOSE:To decrease the temperature change of a limit value of a current fed externally by connecting reversely in polarity the 1st and 2nd diodes in parallel between the base of a bipolar transistor (TR) and the cathode of a Zener diode so as to compensate the temperature change in the operating resistance of an FET. CONSTITUTION: One or plural temperature compensation dioded D1 are connected in a polarity in the direction passing through a base current IB. A communication diode D2 commutates a collector current Ic of a main TRQ1 to the Zener diode ZE when composite TRQ1, Q2 are turned off. A large temperature change in the limit value of the collector current Ic is suppressed easily based on the large temperature dependancy of the operating resistance of the FETQ2 without losing the high speed commutation function of the collector current when the composite TRs are turned off.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to a device mainly composed of a composite transistor of a bipolar transistor and a field effect transistor.

[Conventional technology and its problems]

In the following description of each figure, the same reference numerals indicate the same or corresponding parts.

First, the problems of the prior art will be explained based on FIGS. 2 and 3. Figure 2 shows what is called a cascode.
An example of a circuit consisting of this type of composite transistor called a connection, FIG. 3(4) shows another example of the same circuit, and FIG. 3(b) shows an example of the characteristics of the Zener diode shown in the same figure.

In FIG. 2, Ql is a main bipolar transistor (hereinafter also referred to as a main transistor), Q2 is a field effect transistor (hereinafter referred to as FET), and ZD is a Zener diode.

Collector C and emitter E of main transistor Q1 and FET
The drain D and source S of Q2 are connected in series at the emitter E and drain D to open and close a current (referred to as collector current for convenience) Ic supplied to a load not shown.

Note that the transistors Q1 and Q2 are collectively referred to as a composite transistor for convenience. Also, the bases B and F of the main transistor Q1
A Zener dynate ZD is connected between the sources S of F1TQ2 so that the base B side is the cathode side.

An opening/closing signal voltage eG is applied between the gate G and the source S of the FET Q2 to instruct the collector current Ic to turn on or off via a pulse circuit (not shown), and between the base B of the main transistor Q1 and the source S of the FET Q2. When FET Q 2 is turned on, a base current IB is supplied to the base B via a base power supply EB provided therebetween.

Focusing on the fact that the switching speed of FETs is generally faster than that of bipolar transistors, this circuit combines a high-speed, low-voltage F g 'r Q 2 and a low-speed, high-voltage bipolar transistor Q1 to create a high-speed, high-voltage composite switching element. In this circuit, we first turn on the composite transistors Ql and Q2. In this circuit, FF1TQ2 is connected to the emitter E of the main transistor Q1, and the base current IB can be switched on and off. Since the base voltage eB applied to the base B of the main transistor Q1 can be set to a relatively high voltage, when the switching signal voltage eG to turn on the transistor Q2 is applied to the FET Q2, its drain D and source S t&11 As the voltage VDS drops sharply, the base current IB rises sharply, and the main transistor Q1. Therefore, the composite transistors Ql and Q2 can be turned on at a lower level.

On the other hand, when turning off the composite transistors Ql and Q2, a switching signal voltage of 6G to turn off the transistor Q2 is applied to the FET Q2.
Q 20:) The I' force between 2 and 3 @EE V D 3 increases sharply, cutting off the collector current t flow Ic flowing through itself. At this moment, the collector current Ic flowing through the base and emitter of the main transistor Q1 is commutated to the Zener dihold ZD. In this way, the accumulated carriers at the base of the main transistor Q1 are rapidly discharged, so that the transistor Q1.

Therefore, the composite transistors Ql and Q2 can be quickly turned off and the collector current Ic can be cut off.

The reason for using the Zener diode ZD in the commutation path is that, as will be described later, during the commutation of the collector-return current Ic, the drain-source voltage V of FETQ2 is
ns is kept below the turn-off limit voltage (switching blocking voltage BVns), while the composite transistor Ql,
When Q2 is on, the base current I is supplied from the base power supply BB to the base B side of the main transistor Q1.
B.

This is necessary to prevent the current from being wastedly shunted to the Zener diode ZD and to effectively form the base current [IB].

By the way, the condition for 100% commutation of the collector current Ic from the base/emitter of the main transistor Q1 to the Zener diode ZD when the composite transistors Ql and Q2 are turned off is that a load current equal to the collector current Ic flows through the Zener diode ZD. When the voltage across it is the load Zener voltage VZL, the base-emitter collector current Ic of the main transistor Q1 is just before it disappears.
When the emitter-to-emitter forward voltage is V n ''to, the switching blocking voltage BVDS is expressed by the following equation (1).

BVns≧Vz L−V'n E, o, , , , , ,
, , , , , (1) On the other hand, if the no-load Zener voltage of the Zener diode ZD is vzo and the operating resistance is Rz,
Zener voltage Vz when loaded in a state where collector current Ic is flowing into the Zener diode ZD in the blocking direction
L is Vz L=V Zo+RZ −I c ,,
, , , , , , , , (2), so (
By substituting equation (2), equation (1) can be expressed as equation (3) below.

BVos≧VZ0+RZ-IC-VBE, o −・・−
(3) In general, the lower the switching blocking voltage BVns of an FET, the lower the drain-source voltage (also simply referred to as on-voltage) VDSON when turned on, and therefore the lower the loss when turned on, so in the circuit shown in Figure 2, This element with a low blocking voltage of 5 vDS is used. Therefore, from equation (3), it is desirable that the Zener diode ZD has a low no-load Zener voltage vz0 and a low operating resistance Rz. However, a normal Zener diode, which has a low Zener voltage vzo at no-load, has the disadvantage of a high operating resistance Rz. Therefore, as shown in Figure 3, a circuit equivalent to a Zener diode (hereinafter referred to as A Zener diode (referred to as a Zener diode ZDI for convenience) is used.

However, the characteristics of Zener current Iz and Zener voltage Vz of this Zener diode ZDI are as shown in Fig. 3 (B),
The zener voltage v3 shows a so-called soft constant voltage characteristic in which the zener voltage v3 gradually increases on the curve as the zener current z increases, and the no-load zener voltage Vzo is the same as when a zener current Iz equal to the collector current Ic flows. , has a considerably lower value than the Zener voltage Vz (Zener voltage VZL under load).

On the other hand, when the main transistor Q1 and FET Q2 are turned on, the base current IBI supplied from the base power supply En (not shown, described above) is supplied to the main transistor Q1 as the base current IB without bypassing to the Zener diode ZDI side, and Ql is In order to fully turn on, the forward voltage between the base and emitter of the main transistor Q1 in this state, that is, when the collector current Ic is flowing, must be Vn v (sa
t), the on-voltage of FBTQ2 is set to VpsON as described above.
Then, the Zener voltage Vz0 at no-load is Vzo≧
VBx(sat)-1-Vosos ・Song (4)
The following conditions must be met.

Therefore, if the Zener diode ZD1 is selected so as to satisfy the condition of equation (4), the Zener voltage under load V
zL also becomes a high value, so from equation (1), FETQ2
The switching blocking voltage BVDs of FETQ2 must also be selected with a high value, and therefore the on-voltage VDS of FETQ2
The ON score will be high, and as a result, the loss will not be sufficiently small, resulting in a loss of points.

In order to eliminate this drawback, there is a circuit shown in FIG. 1A, which has been filed by the present applicant as follows.

Special application Shora 59- "semiconductor device".

In the circuit of FIG. 1A, the Zener diode ZD2 and the auxiliary transistor Q3 create a circuit equivalent to an ideal Zener diode in which the no-load Zener voltage Vz and the loaded Zener voltage VzL in FIG. 3(B) are close to each other. (For convenience, it is also called an equivalent Zener diode circuit.) When you want to use a low-loss FBTQ2 with a low on-voltage VDSON, the no-load Zener voltage Vzo should be as low as possible within the range that satisfies the condition of equation (4). Select Zener diode ZD2 with With this configuration, when the composite transistors Ql and Q2 are on, the Zener current Iz does not flow through the Zener diode ZD2, and the collector current Ic of the auxiliary transistor Q3, which uses the current Iz as its base current, also does not flow. Therefore, the base current IB1 supplied from the base power supply EB (not shown) is effectively
B is supplied to the main transistor Q1, and Ql is fully turned on.

On the other hand, when the composite transistors Ql and Q2 are turned off, the collector current Ic commutates to the equivalent Zener diode circuit side, the voltage across the Zener diode ZD2 increases, and when it attempts to exceed the no-load Zener voltage Vz0,
The Zener current Iz flows, and the collector current Ic3 of the auxiliary transistor Q3 flows with this as the base current.As a result, most of the collector current Ic becomes the same current Ic, which is shunted to the auxiliary transistor Q3, and during this period The Zener current Iz is maintained at a value sufficiently smaller than the collector current Ic, and the Zener voltage in that state, and therefore the base voltage eB, is also equal to the no-load Zener voltage V of the Zener diode ZD2.
It is kept close to z. Therefore, by regarding the base voltage eB at this time as the load Zener voltage VZL of the ideal Zener diode, the condition of equation (1) is satisfied.

Incidentally, the above-mentioned cascode-connected circuit generally has the following function of limiting the collector current Ic.

That is, in FIG. 2, the composite transistors Ql, Q
2 is on, the on-voltage VDSO of FETQ2
N is its no-load on voltage Vns0 operating resistance Ro
When s is represented by the following equation (5).

VD so rv=Rns @I C+VD go
-...--f5) By substituting this equation (5) into equation (4), the following equation (6) is obtained.

Vz0≧VB E (sat)-1-Rns-I
C+VD so-Bello) If this equation (6) is rewritten to obtain the collector current Ic, the following equation (6-1) is obtained.

Ic≦(VZo-VB x (s a t )-vn
s6 )/RD S・・・・・・・・・・・・・ (6-1
) That is, by selecting an ideal Zener diode ZD with an appropriate no-load Zener voltage Vz0 (therefore, by selecting the Zener diode 2D2 in FIG. 1A as well), the value of the collector current Ic can be determined as shown in equation (6-1). This means that it can be restricted. If the limit value of this collector current Ic is designated as Icmax for convenience, this limit value is expressed by the following equation (6-2) from equation (6-1°).

Icmax=(Vzo-VBE(Sat)
-VD30)/RD13 ---・----(6-2
) If an equivalent Zener diode circuit as shown in Fig. 1A is used instead of the Zener diode ZD in Fig. 2, (
As is easily understood from the above explanation, the voltage corresponding to the no-load Zener voltage vzo in equation 6-2) is the base voltage en (or the emitter-collector voltage of the auxiliary transistor Q3) at which the Zener current Iz begins to flow through the Zener diode ZD2. voltage), and this value (referred to as the equivalent no-load Zener voltage) Vz (,. is the no-load Zener voltage of the Zener diode ZD2, Vzo, and the base-emitter voltage at which the base current of the auxiliary transistor Q3 begins to flow). Vat
3, it is expressed by the following equation (6-3).

Vzo0=Vz(,,-)-VBg! ＋＋＋＋＋＋＋＋
+ (63) Therefore, instead of Vz in equation (6-2), (6
-3) Vzo of the formula. By using the value of (6-2)
The equation can be rewritten as equation (6-4).

Icmax=(VzH+VaE, -VBE(Sat)-
V o so) /RID s-・・-・-(6-4)
In this way, the limit value of collector tAIc is determined by equation (6-2) or equation (6-4).

However, as can be seen from equations (6-2) and (6-4), the operating resistance RIDS of FETQ2 changes predominantly with a large positive warm coefficient, so the limit value Icma
If x is greatly reduced by a large temperature change, for example, due to an increase in the temperature of the FET Q2 itself and its surroundings, there is a problem.

[Purpose of the invention]

The present invention provides a device in which a zener diode or an equal zener diode circuit is connected between the base and source of a composite transistor formed by cascode reading of a bipolar transistor and a FET, and a zener diode circuit with a polarity that blocks base current. An object of the present invention is to provide a semiconductor device in which the collector Tt current limit value of a composite transistor exhibits less temperature fluctuation.

[Key points of the invention]

The main point of the present invention is to connect the drain of the emitter field effect transistor of the bipolar transistor to the drain of the field effect transistor. A (first) Zener diode or a Zener diode (equivalent to the first, consisting of a second Zener diode, an auxiliary transistor, etc.) between the emitter of the good polar transistor and the source of the field effect transistor (composite transistor, etc.). A circuit (hereinafter referred to as an equivalent Zener diode circuit) is connected to a polarity that blocks the base current supplied from the outside to the bipolar transistor, and is connected between the gate and source of the field effect transistor (for switching operation, etc.). Applying a switching signal voltage, through a series circuit between the collector/emitter of the bipolar transistor and the drain/source of the field effect transistor,
In a device for switching on and off a current supplied to the outside, the base of the bipolar transistor and the terminal on the base side of the Zener diode or equivalent Zener diode circuit are connected in series with the polarity through which the base current is passed. By connecting one or more first diodes, parallel lζ with the plurality of male diodes, and connecting a second diode of opposite polarity to this diode, the temperature of the operating resistance of the field effect transistor can be reduced. The change is compensated for by the temperature change of the plurality of first diodes, and the temperature change of the limit value of the current supplied to the outside is reduced.

[Embodiments of the invention]

The present invention will be explained in detail below using FIG.

In FIG. 1, Dl is a temperature compensation diode, which is composed of one or more diodes connected in polarity to allow base current IB to pass.

Dl is a diode on the commutating side, and composite transistors Ql, Q
2, the collector current Ic flowing through the base and emitter of the main transistor Q1 is connected to the Zener diode Z.
This becomes a current path for commutating current to D.

Note that Zener diode ZD may alternatively be the equivalent Zener diode circuit described above consisting of Zener diode ZD2 and auxiliary transistor Q3 in FIG. 1A.

In the circuit of FIG. 1, the composite transistor Ql.

When Q2 is on, the collector current Ic reaches the limit value I
cmax, that is, a part of the base current In1 begins to flow into the Zener diode ZD as the Zener current Iz, and the base current In flowing into the main transistor Q1 begins to decrease, at the base B of the compound fist transistors Ql and Q2. The voltage between the source S becomes Vzo-Vr, where VF is the forward voltage drop of the temperature compensation diode D1. Therefore, in the equation (6-2), the limit tIcmaX of the collector current Ic in FIG.
It is expressed by the following equation (6-5) in which Vzo-VF is substituted for 0.

Icmax=(Vz(,-Vv-Vnz(sat)-V
DSO)/R, Dll =-...-(6-5) Similarly, instead of the Zener diode ZD in Fig. 1,
Human figure Zener diode ZD2. Auxiliary transistor Q3
When using an equivalent Zener diode circuit consisting of
Vz instead of the no-load Zener voltage Vz of the Zener diode ZD2 in equation (6-4). , -VF and the next (
It is expressed by the formula 6-6).

Icmax=(Vzo, -Vr-1-Vng, -VBE
(5at) Vos, )/Rns −・−,, (6−
6) As is well known, the forward voltage drop of one diode decreases as the temperature rises with a temperature change of approximately -2mv/"0. Therefore, if the number of temperature compensation diodes D1 connected in series is N, then Forward voltage drop (-VF) therefore (
The molecule of formula 6-5) or (6-6) increases with temperature with a temperature change of +2Nmv/'O.

Therefore, the effect on the limit value ICmax of the temperature change of this numerator and the temperature change of the operating resistance RD3 in the denominator of equation (6-s) or (6-6), which also changes with a positive temperature gradient, can be expressed as follows. By selecting the number N, it is possible to cancel each other out. In this way, temperature changes in the limit value ICmax of the collector current C# can be reduced.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a Zener diode or an equivalent Zener diode is connected between the base and source of a composite transistor formed by cascode-connecting a bipolar transistor and an FgT to block the base current of the bipolar transistor. In a device in which a diode circuit is connected, the base of the bipolar transistor,
One or more diodes connected in series with the polarity through which the base current passes between the Zener diode or the terminal on the base side of the equivalent Zener diode circuit, and a diode of opposite polarity connected in parallel with the plurality of diodes. , without impairing the high-speed commutation function of the collector current at turn-off of the composite transistor.
It is possible to easily suppress a large temperature change in the limit value of the collector current, which is based on the large temperature dependence of the operating resistance of the IT.

In the above explanation, the main transistor Q1 is of NPN type.

FETQ2 is N-channel type, auxiliary transistor Q3 is N-channel type.
Although the PN type or N-channel type has been described, the PNP type, P-channel type, PNP type, or P-channel type may be used instead. In the latter case, the polarities of the Zener diodes ZD, ZD2 and the diodes Di, D2 must be reversed.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, Fig. 1A, Fig. 2, and Fig. 3 (5) are diagrams showing different examples of conventional circuit configurations, and Fig. 3 (to). FIG. 5 is a diagram showing an example of the characteristics of the Zener diode shown in FIG. Ql...Bipolar transistor (main transistor)
, Q2... field effect transistor (F'F!T),
ZD, ZD2... Zener diode, Q3... Auxiliary transistor, Dl... Temperature compensation diode, D2
...Commuting side diode. ,! ) Figure 1 OIA diagram, t2 Figure 3

Claims (1)

[Claims] 1) The emitter of a bipolar transistor and the drain of a field effect transistor are connected, and a Zener diode or a circuit equivalent to the Zener diode (hereinafter referred to as an equivalent Zener diode) is connected between the base of the bipolar transistor and the source of the field effect transistor. A diode circuit (called a diode circuit) is connected to a polarity that blocks the base current supplied from the outside to the bipolar transistor, and also applies a switching signal voltage between the gate and source of the field effect transistor, and connects the collector and emitter of the bipolar transistor. A device for switching an externally supplied current through a series circuit of a drain and a source of the field effect transistor, the base of the bipolar transistor and the base side of the Zener diode or equivalent Zener diode circuit. One or more first diodes in series are connected between the terminal and the polarity through which the base current flows, and a second diode of opposite polarity is connected in parallel to the plurality of first diodes.
A semiconductor device characterized in that it is formed by connecting diodes.