JPH0223716A - Integrated high breakdown voltage switch circuit - Google Patents

Abstract

PURPOSE:To prevent a pulse voltage from occurring in a switching terminal by executing switching between the emitter of a prescribed transistor and a ground in correspondence with a control signal. CONSTITUTION:When a control voltage equivalent to a reproduction mode is given to a control terminal (k), a recording reproduction mode switching circuit RED/PB supplies a constant voltage to the bases of transistors Q7 and Q8. Q7 supplies driving signals to the base of Q1 through a current mirror circuit consisting of diodes D1-D3, Q4 and Q3, and Q8 to the base of Q2 through a current mirror circuit consisting of Q6 and Q5, whereby the switching terminal (a) is equivalently grounded. When a potential equivalent to a recording mode is given to the terminal (k), the driving current for the bases of Q1 and Q2 is interrupted and the terminal (a) is opened.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an integrated switch circuit, and more particularly to an integrated switch high-voltage circuit suitable for use in switching heads of an audio recording/reproducing device such as a VTR.

2. Description of the Related Art First, how an integrated high-voltage switching circuit is used for head switching in an audio recording/reproducing device will be explained with reference to FIG.

FIG. 3 is a block diagram of an audio signal recording/reproducing circuit (hereinafter abbreviated as recording/reproducing circuit), and blocks shown within broken lines are formed on the same chip as a semiconductor integrated circuit. This recording/reproducing circuit has a recording/reproducing mode switching control circuit REC/PB in accordance with the voltage applied to the control terminal k, integrated switch circuits (hereinafter abbreviated as switches) SW1 to S,
Open and close to switch between recording mode and playback mode. The state of each switch shown in Figure 3 is the recording mode. First, to explain the flow of audio signals in this mode, the audio signal input from the line input terminal is level controlled by the auto level control circuit ^LC. is transmitted to the line amplifier A2 via the switch SW4, voltage amplified by the line amplifier A2, and supplied from the line output terminal 1 to other blocks such as the monitor circuit. The voltage is inputted to the recording amplifier A3 via the recording amplifier A3, receives voltage amplification by the recording amplifier A3, and is supplied to one end N1 of the recording/reproducing head H together with the AC bias from the bias oscillation circuit Ho5c via the RFC output terminal m and the resistor R9.

The remaining end N2 of the recording/reproducing head H is grounded by a switch SW2.

Through the above process, a recording current flows through the recording/reproducing head H, and an audio signal is recorded on the magnetic tape.

Next, the flow of signals in playback mode will be explained. In the reproduction mode, the recording/reproducing mode switching circuit REC/PB switches the switches SW1 to SW4 to the opposite state to that shown in FIG.

One end N of the recording/reproducing head H is grounded by a switch SW1, and an audio signal voltage is induced from the magnetic tape at the remaining terminal -t4N2, and is input to an equalizer amplifier A1. This audio signal is subjected to frequency response correction and voltage amplification by the equalizer amplifier Al, and then supplied to the line amplifier A2 via the capacitor C2, variable resistor VR, and switch SW4, and the voltage is further amplified to the required level by the line amplifier A2. The signal is then sent from the line output terminal i to an external circuit such as a power amplifier. At this time, bias oscillation circuit O
SC has stopped operating.

As explained above, the switches SWI and SW2 play the role of alternately grounding both ends of the recording/reproducing head I4 according to each mode, but the switch SW will now be explained in more detail. In the recording mode, the bias oscillator circuit O8C sends approximately 1
An AC voltage of 5θVp-p is applied. For this reason, the switch SW1 is required to have a withstand voltage of ±80 V or more, and a special circuit configuration is required, which is particularly referred to as a high-withstand voltage switch circuit.

FIG. 2 shows the circuit configuration of a conventional high voltage switch.

In FIG. 2, a indicates an open/close terminal as a switch, b indicates a power supply terminal, and d indicates a ground terminal. When a control potential corresponding to the reproduction mode is applied to the control terminal k, the recording/reproduction mode switching circuit REC /PB supplies a constant voltage to the base of the transistor Q6, the transistor Q6 and the resistor R6 act as a constant current source, and the transistors Q1... ' Supply drive current to the base of Q2. At this time, transistor Q+.

There is a low impedance between the collector and emitter of Q2, and the switching terminal a is isometrically grounded. When a control potential corresponding to the recording mode is applied to the control terminal k, the base of the transistor Q6 is approximately O.
A potential is applied to the transistor Q1. The drive current to the base of Q2 is cut off, high impedance exists between the collectors and emitters of transistors Ql and Q2, and the switching terminal a becomes open. The withstand voltage between switching terminal a and ground is ±
As mentioned above, 80V or more is required, but -a
Even in a bipolar integrated circuit having a structure of a P-type substrate and an N-type epitaxial layer, the transistor Ql is
, Q2 are commonly connected, and the emitter of the transistor Q1 is connected to the opening/closing terminal a to be used as a reverse transistor. As for the withstand voltage of the switching terminal a, the + side is the CE withstand voltage of the transistor Q2, and the - side is the Ct of the transistor Q1.
It is determined by the withstand voltage during t. Furthermore, L.V.C.
Since ER> LVcio, the transistor Ql
, Q2 between the base and emitter of resistors R, , R2, respectively.
is inserted, and the necessary withstand voltage is given to the opening/closing terminal a.

Problems to be Solved by the Invention In the conventional high-voltage switch described above, if the power to the device is accidentally turned off in the regeneration state, a pulse voltage is generated at the open/close ends of the high-voltage switch during the power down process. However, this has the disadvantage that current flows through the head and damages the content recorded on the magnetic tape. This phenomenon is explained in the second
This will be explained using FIG.

Figure 4 shows the operation time chart when the power is turned off in Figure 2, where 1 is the potential of the power supply terminal, 2 is the base potential of transistor Q6, 3 is the collector current of transistors Q3Q4, and 4
is the base inflow current of transistor Q2, and 5 is the opening/closing terminal a.
is the potential of At time t1, switch SWo is turned OFF.
When the power is turned off, the capacitor C8 starts discharging and the potential 1 of the power supply terminal S starts to drop.At time t2, the potential of the power supply terminal S changes to the recording/playback mode switching control circuit R.
When the operating limit value of EC/PB is below, the transistor Q
The base potential 2 of transistor Q3. Collector current 3 of Q4 begins to decrease. At time t3, the collector current of transistor Q4 is V
When BEQ 2 /R2(A) (Q 2 is the forward voltage between the base and emitter) or less, the base current 4 of the transistor Q 2 becomes 0, and the transistor Q 2 enters the cut-off state. And base of transistor Q1 → emitter of transistor Q1 → collector of transistor Q2 →
The path of the collector current 3 of the transistor Q3 that had been connected to GND is cut off, and the collector potential of the transistor Q3 rises to near the potential of the power supply terminal A, and this appears as the potential 5 of the switching terminal a via the resistor R1.

At time t4, the base potential 2 of transistor Q6 becomes 0.
Then transistor Q3. Q4 will be the cutoff,
The potential 5 of the opening/closing terminal a also returns to O.

A pulse voltage is generated at the opening/closing terminal a between times t3 and t4.

The present invention has been made in view of the above-mentioned conventional situation,
Accordingly, an object of the present invention is to provide a novel integrated high-voltage switch circuit that can solve the above-mentioned problems inherent in the conventional technology.

Means for Solving the Problems In order to achieve the above objects, the integrated high-voltage switch circuit according to the present invention is designed such that when the power is turned off, the base current of the transistor Q1 shown in the conventional example of FIG.
In other words, the lowest power supply voltage that can generate the collector current of transistor Q3 is higher than the lowest power supply voltage that can supply the base current to transistor Q2. .

That is, according to the present invention, a first transistor whose emitter is grounded, a second transistor whose collector is connected to the collector of the first transistor, a first current source, and the first current source. a second current source set higher than the minimum power supply voltage for starting operation;
, a control circuit that simultaneously controls ON and OFF of a second current source, wherein the first current source is connected between the base of the first transistor and the power supply, and the second current source is connected between the base of the first transistor and the power source.
An integrated high-voltage switching circuit is obtained, characterized in that the second transistor is connected between the bases of the transistors and the power source, and the emitter of the second transistor and the ground are opened and closed according to the control signal. .

Embodiment Next, a preferred embodiment of the present invention will be specifically explained with reference to the drawings.

FIG. 1 is a circuit configuration diagram showing an embodiment of a high voltage switch circuit according to the present invention.

Referring to Figure 1, a is an opening/closing terminal, b is a power supply terminal, and d
indicate the ground terminal, and when a control potential corresponding to the playback mode is applied to the control terminal k, the recording/playback mode switching circuit RFC/PB switches to the transistor Q7.
．． A constant voltage is supplied to the base of transistor Q8, and transistor Q7 connects diodes D, ~D3 and transistors Q4. Transistor Q8 connects to the base of transistor Q+ via a current mirror circuit consisting of transistors Q3 and Q6. Driving currents are supplied to the bases of the transistors Q2 through current mirror circuits formed by Q5, and the switching terminals a are grounded isometrically. Furthermore, when a potential corresponding to the recording mode is applied to the control terminal k, the drive currents to the bases of the transistors Ql and Q2 are cut off, and the open/close terminal a is opened.

Next, the operation process of each element when the power is turned off will be explained with reference to the operation time chart of FIG.

FIG. 5 is an operation chart 1 when the power is cut off in one embodiment of the present invention shown in FIG.

Referring to FIG. 5, 6 is the potential of the power supply terminal S, 10-7 is the transistor Q7. The base potential of Q8, 8, is 1 to Lancistor Q7. The collector current of Q3, 9 is the transistor Q8. 10 indicates the collector current of Q5, 10 indicates the base inflow current of transistor Q2, and 11 indicates the potential of the open/close terminal a.

Now, when the switch SWo is turned OFF at time t1, the capacitor C6 starts discharging and the potential 6 of the power supply terminal
starts to fall, and at time t2 it becomes below the operating limit value of the recording/playback mode switching control circuit RFC/Pit.
Transistor Q? , Q8's base potential 7 decreases, transistor Q7. QS collector current 8, transistor Q8
．． The collector current 9 of Q5 begins to decrease. Furthermore, the potential 6 of the power supply terminal S decreases, and at time t3, the base and emitter voltages VBB of the transistor Q4, the diode D,
The collector-emitter voltage of transistor Q7 is due to the forward voltage of ~D. When the voltage disappears, the collector current of the transistor Q7 and the collector current 8 of the transistor Q3 become "off".Furthermore, at time t4, the collector current of the transistor Q5 becomes V BEQ 5 /R.
When it becomes less than 2, the transistor 2 base inflow current IO
is the cutoff. Here, in the conventional example shown in FIG. 2, since the transistor Q2 was cut off before the transistor Q3, the collector potential of the 1 helang transistor Q appeared as a pulsed voltage at the opening/closing terminal a, but in this embodiment, By inserting the diodes D and D3, the transistor Q3 is cut off before the transistor Q2, so no pulse voltage is generated at the switching terminal a.

As described in detail, according to the present invention, the transistor Q3, which is the drive current source for the transistor Q+, is cut off before the transistor Q2 in the process of falling of the power supply terminal potential.

Since it is possible to prevent the generation of pulse voltage at the switching terminals,
If the integrated high-voltage switch of the present invention is used to switch the head of an audio recording/playback device such as a VTR or tape recorder, even if the device's power is accidentally turned off during playback, the recorded content on the magnetic tape will not be damaged. The effect is that there is no

[Brief explanation of the drawing]

Fig. 1 is a circuit configuration diagram showing an embodiment of the present invention, Fig. 2 is a circuit diagram according to the prior art, Fig. 3 is a block diagram of an audio signal recording/reproducing circuit, and Fig. 4 is a power supply in the circuit of Fig. 2. FIG. 5 is an operation time chart for the circuit shown in FIG. 1. Q1-Q8...1-ransistor, D1-D3...diode, R1-R9...resistor, Co-C9...capacitor, SWo...power switch, 8w1-SW4...
Integrated switch circuit, VCC...power supply, REC/Pi
t... Recording/playback mode switching control circuit, A1... Equalizer amplifier, A2... Line amplifier, A3... Recording amplifier.

Claims (1)

[Claims] a first transistor whose emitter is grounded; and a second transistor whose collector is connected to the collector of the first transistor.
a transistor, a first current source, a second current source whose minimum power supply voltage for starting operation is set higher than that of the first current source, and the first and second current sources according to a control signal. ON
, and a control circuit that simultaneously controls OFF of the first
a current source is connected between the base of the first transistor and the power supply, and a second current source is connected between the base of the second transistor and the power supply, and the current source is connected between the base of the first transistor and the power supply, and An integrated high-voltage switch circuit characterized in that it opens and closes between the emitter of a second transistor and ground.