JPH0415656B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a DC current supply circuit for telephones and the like in a telephone exchange, and more particularly to a DC supply cutoff circuit suitable for semiconductor integrated circuits.

For example, letter coils have been used as DC current supply circuits for telephones, but when trying to configure a time-sharing switch to provide a DC current supply circuit for each subscriber, there is a problem in that the mounting capacity becomes large. Ta. For this reason, various proposals have been made to reduce the size of the device by electronic or even semiconductor integrated circuits. Figure 1 shows its typical configuration. 1 is an electronic DC current supply circuit with characteristics equivalent to a letter coil; 2 is a circuit consisting of four PNPN switches S ₁ , S ₂ , S ₃ , and S ₄ . The DC current polarity reversing circuit is constructed, and 3 is a telephone.

In the DC current supply circuit having such a configuration, the electronic DC current supply circuit 1 is provided with a current switching function in order to open the PPN switches S ₁ , S ₄ or S ₂ , S ₃ forming the two sets of current paths. It is necessary to provide a gate turn-off function to the PNPN switches S ₁ to _{S 4} . Here, if it is necessary to cut off a large DC current of about 100 mA, it is difficult to perform gate turn-off operation with a PNPN switch made of a semiconductor integrated circuit.

The present invention was devised in view of the above situation, and an object of the present invention is to provide a DC supply cutoff circuit which is implemented as a semiconductor integrated circuit and can easily switch on and off the DC current.

In the present invention, a gate turn-off PNPN switch implemented as a semiconductor integrated circuit is used, and the DC current supply circuit is turned off to the extent that the gate of the PNPN switch can be turned off by short-circuiting its gate and cathode when shutoff is desired. The present invention is characterized in that the DC supply is cut off by performing a gate turn-off operation after reducing the current.

The present invention will be explained in detail below with reference to an embodiment circuit shown in the drawings. FIG. 2 shows the first embodiment of the present invention. In the figure, 11 is a DC current supply circuit with variable internal resistance, R ₀ is a reference resistance, Aa,
Ab, Ba, Bb, Ca, Cb are DC current supply circuit 11
Q ₁ and _{Q 2 are} transistors that cut off the negative feedback circuit. 12 is a DC current polarity inversion circuit, S ₁ to _{S 4} are PNPN switches,
_Q3 to _Q6 are gate turn-off transistors. 13 is a power supply having voltage V _BB (-48V).

The DC current supply circuit 11 is composed of a vertically symmetrical balanced circuit shown by suffixes a and b centered on the V _BB /2 point. To explain the operation of the upper circuit shown by suffix a, the current _IRO flowing through the resistor _R0 enters the input of the current transfer circuit Aa, and its output is multiplied by _αIRO and becomes the input current of the next current transfer circuit Ba. This is further multiplied by αβI _RO to become the input current of the next current transfer circuit Ca, and its output is further multiplied by αβγI _RO by γ. In other words, the input current Ia of the DC current supply circuit is the current flowing through R _O
If I _RO , then Ia=I _RO (1+α・β・γ) …(1) If the input voltage Va, then I _RO = Va/R _O …(2) Therefore, the internal resistance Rina is Rina=Va/Ia=R _O / 1+α・β・γ≒ R _O /α・β・γ …(3) The lower circuit shown by suffix b is found in the same way, and if the internal resistance is Rinb, then Rinb=Vb/Ib≒R _O /α・β・γ...(4) Therefore, the upper and lower internal resistances Rin _O are expressed as Rin _O = Rina + Rinb = 2R _O /1 + α・β・γ≒2R _O /α・β・γ (5). When the transistors Q ₁ and Q ₂ are turned on, the current transfer α in Aa and Ab becomes 0 and the negative feedback circuit is cut off, so that the internal resistance Rin0 becomes Rin0≈2R _O (6). In other words, the internal resistance is multiplied by α, β, and γ.

Usually Rin ₀ = 440Ω is chosen and power supply 4 is -48V
is used, so the current up to about 100mA
It will flow through PNPN switches _S1 to _S4 . It is not easy to cut off this current using a PNPN switch implemented in a semiconductor integrated circuit.

However, according to the present invention, the reference resistance R _O can be set to several tens of kilohms.
transistors Q ₁ and Q ₂ when the DC supply is cut off.
If the negative feedback path is cut off, the current flowing through the PNPN switches S ₁ to S ₄ can be reduced to about 1 mA since the internal resistance is increased as shown in equation (2) above. Therefore, if the current reaches this level, the PNPN switch S ₁ ~
_S4 can also be easily disconnected by short-circuiting the gate and cathode using transistors _Q3 to _Q0 , respectively.

FIG. 3 is an equivalent circuit showing a second embodiment of the present invention, in which the reference resistor R _O of the DC current supply circuit 11 shown in FIG. 2 is connected to the midpoint potential V _BB /2 side. This is an example. In FIG. 3, I _O is a constant current source, A, B, and C are current transfer circuits similar to those in FIG. 2, and negative feedback reduces the internal resistance of the DC current supply circuit 21 to 1/n of the reference resistance R _O. Configure the circuit.

The operation of the DC current supply circuit 21 in this circuit configuration will be explained using the circuit above V _BB /2 as in FIG. 2. The current flowing through the resistor R _O is multiplied by α in the current transfer circuit Aa, and this is further The current is multiplied by β in circuit Ba, and the difference between this current and constant current I _O enters the input of current transfer circuit Ca, where it is multiplied by γ. In other words, the input current Ia of the DC current supply circuit is
If the current flowing through R _O is I _RO , then Ia = −I _RO + (I _O − I _RO α・β) γ …(7) When transistor Q7 is turned on, the current transfer α at Aa and Ab becomes 0. Ia=−I _RO + I _O …(8). At this time, since I _O is a constant current, the internal resistance Rina≒
R _O and the internal resistance Rin1 of the upper and lower parts of the DC current supply circuit 21 appears to be Rin1=Rina+Rinb≒2R _O (9). That is, similar to the configuration shown in FIG. 2, the internal resistance of the DC current supply circuit is made high, and the gate turn-off operation of the PNPN switches _S1 to _S4 is performed, thereby easily interrupting the DC current.

Although the above-mentioned embodiments all show configuration examples of balanced circuits, the present invention can also be applied to unbalanced circuits. In addition, current transfer circuit A in the embodiment,
B and C can be constructed from well-known current mirror circuits. Furthermore, PNPN switch S ₁ ~
Of course, the gate turn-off operation of _S4 may be performed not only by a short circuit between the gate and cathode, but also by a circuit configuration in which the gate current flows backward from the gate toward a lower potential.

As explained above in detail, the present invention lowers the resistance (1/n) of the reference resistance R _O in the DC current supply circuits 11 and 21 in normal times to supply a large current to the PNPN switch, thereby supplying DC current. When shutting off,
By increasing the resistance value in the supply circuits 11 and 21, the current flowing to the PNPN switches S ₁ to S ₄ is reduced, and at this time the gate of the PPNN switch is turned off. It is extremely easy to open and close the circuit, making it extremely convenient for converting this type of circuit into a semiconductor integrated circuit.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional DC current supply circuit, and FIGS. 2 and 3 are circuit diagrams showing two embodiments of the DC current supply circuit, including one embodiment of the DC supply cutoff circuit according to the present invention. . 11, 21...DC current supply circuit, 12...DC current polarity inversion circuit, R _O ...Reference resistance, A, B,
C...Current transfer circuit, _Q1 , _Q2 , _Q7 ...Transistor, _S1 to _S4 ...PNPN switch, _Q3 to _Q0 ...
Gate turn-off transistor, I _O ...constant current source.

Claims (1)

[Scope of Claims] 1. A switch circuit coupled to a terminal and having a gate turn-off function, a power supply, and a switch circuit provided between the power supply and the switch circuit, and supplying a first large current to the switch circuit. A DC supply cutoff circuit that is capable of turning off the gate of the circuit, and is composed of a DC current supply circuit that switches and supplies a second small current whose current value is higher than the holding current and which is smaller than the first large current. The DC current supply circuit includes a reference resistor having a predetermined resistance value coupled between the switch circuit and the power supply, and amplifies the current flowing through the reference resistor and supplies the amplified current to the terminal through the switch circuit. the current transfer circuit means; and means coupled to the current transfer circuit means for controlling the current transfer circuit means when the DC supply to the switch circuit is cut off and increasing the internal equivalent resistance of the DC current supply circuit; When the DC supply to the switch circuit is cut off,
The current transfer circuit means is controlled to increase the internal equivalent resistance value of the DC current supply circuit, and the current supplied from the DC current supply circuit to the switch circuit is changed from the first large current to the second large current. A DC supply cutoff circuit characterized in that after switching to a small current, the switch circuit is operated to turn off the gate, thereby cutting off the current.