JPH0342029B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a nurse call intercom,
In particular, when connecting the nurse call handset or hallway light, if you accidentally short-circuit the hallway light line,
To provide a nurse call intercom which prevents a call holding circuit in a handset from being destroyed in such a state and has extremely high reliability.

[Technical Background of the Invention] Generally, as this type of nurse call intercom, the one shown in FIG. 2 can be considered. In the figure, 11 is a nurse call base unit, 12 is a call detection circuit inside the nurse call base unit 11, 13 is a nurse call slave unit, and 14 is inside the nurse call slave unit 13 or outside the nurse call slave unit 13 by pulling out a wire. _{The call switch} installed in is a line connecting the hallway light 15 of the nurse call handset 13. Corridor light 15
is connected between the L line and the E line. Q ₁ and Q ₂ in the nurse call handset 13 are transistors forming a call holding circuit, and R ₁ , R ₂ and R ₃ are resistors.

In the conventional nurse call intercom circuit configured as described above, power (+) is applied to the line N from the nurse call base unit 11 via the call detection circuit 12, but when the call switch 14 is off. Since transistors Q ₁ and Q ₂ of the call holding circuit are both off, no current flows through the N and E lines, and therefore the call detection circuit 12 also remains off. When the call switch 14 is turned on, the transistor _Q1 of the call holding circuit is turned on.
N line → terminal N ₀ → emitter of transistor Q ₁ → collector of transistor Q ₁ → resistor R ₂ → terminal L ₀
A current flows through line L→corridor light 15→line E, and the corridor light 15 lights up.The call detection circuit 12 detects the current, and the nurse call base unit 11 recognizes the call. At the same time, transistor Q 2 is turned on by the path from the collector of transistor Q ₁ → resistor R ₂ → resistor R ₃ → base of transistor Q ₂ → → Even if the call switch 14 is turned off afterwards, both transistors Q ₁ and Q ₂ are turned on _. It continues to be on, the above-mentioned current continues to flow, and the lighting of the hallway light 15 and the call from the nurse call base unit 11 are maintained.

[Problems in the Background Art] However, when connecting the nurse call handset 13 and the hallway light 15, if the L line and the E line are accidentally shorted, the call switch 1
When you press 4, a larger current than usual flows through transistor _Q1 , causing it to be thermally overloaded.
destroy transistor _Q1 of the call hold circuit,
This will cause a significant loss of reliability. Furthermore, if the L line and E line are short-circuited with a certain resistance value due to line resistance, when the call switch 14 is pressed in this state, the transistor _Q2 of the call hold circuit turns on and holds. Even if the call switch 14 is released, the overload current continues to flow, and damage is more likely to occur.

[Object of the Invention] The present invention has been made in view of the above-mentioned conventional difficulties.
To provide a highly reliable nurse call intercom which prevents a call holding circuit in a handset from being destroyed when a corridor light line is accidentally short-circuited.

[Summary of the Invention] In order to achieve such an object, the nurse call intercom of the present invention includes: a nurse call base unit; a nurse call slave unit connected to the nurse call base unit via two lines; a hallway light connected to the nurse call handset by a separate line that shares a common ground line among the two lines;
The nurse call handset includes a calling switch installed inside the handset or outside the handset by pulling out a line, and a ringing current that flows when the calling switch is pressed to light up the hallway light and a part of the calling current. a ring holding circuit that keeps the ringing current flowing between the two lines and stops the self-holding when the hallway light is short-circuited; and a protection circuit that forcibly cuts off the ringing current after a predetermined period of time even if the ringing switch is kept pressed, and the nurse call base unit is equipped with a ringing detection circuit that detects the ringing current and recognizes the ringing. It is something.

[Embodiments of the Invention] Preferred embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the nurse call intercom of the present invention includes a nurse call base unit 1 and a nurse call base unit 1 connected to the nurse call base unit 1 by two lines N and E via terminals N ₀ and E ₀ . Out of the two lines N and E, the handset 3 and the nurse call handset 3 are connected to another line L, E that has the ground line E in common.
and a hallway light 5 connected via L ₀ .

The nurse call handset 3 has a call switch 4 installed inside the handset or outside the handset by pulling out a line, and when the call switch 4 is pressed, a calling current C flows to turn on the hallway light 5, and the calling current C is turned on. A ring holding circuit 6 which is self-holding by a part of the circuit, continues to flow the ringing current C between the two lines N and E, and stops the self-holding when the hallway light 5 is short-circuited.
and a protection circuit 8 which forcibly cuts off the calling current C after a certain period of time even if the calling switch 4 is kept pressed when the hallway light 5 is short-circuited.

Call holding circuit 6 in nurse call handset 3
is a set of transistors Q ₁ , Q ₂ , resistors R ₁ , R ₂ ,
Consists of R ₃ and R ₄ . Two lines N and E are connected to the emitter of transistor _Q1 and the emitter of transistor _Q2 , respectively. Resistor R ₁ is connected between the base of transistor Q ₁ and the collector of transistor Q ₂ . A series circuit of resistors R ₂ and R ₃ is connected between the collector of transistor Q ₁ and the base of transistor Q ₂ . R ₄ is the base of transistor Q ₂
Connected between the emitters. Call switch 4 is a resistor
Connected via _R5 between the base of transistor _Q1 and the emitter of transistor _Q2 .

The protection circuit 8 in the nurse call handset 3 includes a pair of transistors Q ₃ , Q ₄ , resistors R ₆ , R ₇ , and a resistor.
R ₈ , resistor R ₉ , time constant circuit (resistor R ₆ × capacitor
C ₁ ) and diode D ₁ . A series circuit consisting of the emitter and base of transistor _Q4 , resistor _R9 , collector and emitter of transistor _Q3 is connected between lines N and E. The collector of transistor Q ₄ is connected to the base of transistor Q ₁ . Further, the connection point between the call switch 4 and the resistor _R5 is connected to the line E via a time constant circuit (resistance _R6 x capacitor _C1 ). The connection point of the resistor R ₆ and the capacitor C ₁ of the time constant circuit is connected to the collector of the transistor Q ₂ through the diode D ₁ , to the line E through the resistor R ₇ , to the line E through the resistor R _{7, to the resistor R 7 and} to the resistor R ₈ The connection points of are respectively connected to the base of transistor _Q3 .

The nurse call base unit 1 includes a call detection circuit 2 that detects a call current C and recognizes a call, and a power source 9.

Next, the operation of the nurse call intercom configured as described above will be explained.

Power (+) is applied to the line N from the nurse call base unit 1 via the call detection circuit 2.
When the switch 4 is off, the transistors in the call holding circuit 6 and protection circuit 8 of the handset 3
Q ₁ , Q ₂ , Q ₃ , and Q ₄ are all off, and N, E
No current flows through the line, and the call detection circuit 2
remains off.

First, normal calling operation will be explained. When call switch 4 is turned on, N line → terminal N ₀ → emitter of transistor Q ₁ of call hold circuit 6 → base of transistor Q ₁ → switch 4 → resistor R ₅ → terminal E ₀ → E line and bias current Flow, transistor Q ₁ turns on, and the calling current follows the path of N line → terminal N ₀ → emitter of transistor Q ₁ → collector of transistor Q ₁ → resistor R ₂ → terminal L ₀ → line L → corridor light 5 → line E. C flows to separate lines L and E, the hallway light 5 lights up, and the call detection circuit 2 detects the current, and the base unit 1 recognizes the call.

At the same time, part of the calling current C is transferred to the transistor Q ₁
collector → resistor R ₂ → resistor R ₃ → transistor Q ₂
The base bias current of transistor Q ₁ also flows through the path of base of transistor Q ₁ → resistor R ₁ → collector of transistor Q ₂ → emitter of transistor _{Q 2 ,} so that After that, even if the switch 4 is turned off, the transistors Q ₁ and Q ₂ of the call holding circuit 6 continue to be turned on, and the call holding circuit 6 maintains its self-holding state, and the ring current C flows between the two lines N and E. Continue to turn on hallway light 5 and main unit 1
calls are retained.

From the moment switch 4 is turned on, switch 4
A part of the current flowing through resistor R ₆ begins to flow to charge up capacitor C ₁ with a time constant (resistance R ₆ × C ₁ ), but almost instantaneously, transistor Q ₂ is turned on via the above. , the charge current to capacitor C ₁ flows from the collector of transistor _{Q 2 to} the emitter of transistor Q ₂ via diode D 1, so the voltage at point b in Figure 1 is equal to the on-state voltage of diode D ₁ and the transistor
The voltage does not rise above the sum of the collector-emitter voltage when Q ₂ is on, and at this voltage the protection circuit 8
resistor R ₇ to prevent transistor Q ₃ from turning on,
Since resistor R ₈ is set, transistor Q ₃ remains off, and therefore transistor Q ₄ remains off, so that the call hold function of transistors Q ₁ and Q ₂ is improved as compared to the conventional circuit. It is done in the same way.

Next, a description will be given of a protective operation when the call switch 4 is pressed while the hallway light 5 is short-circuited due to incorrect connection of the L line and the E line.

When the call switch 4 is pressed, the base current of the transistor _Q1 of the call hold circuit 6 flows as described above.
Transistor Q ₁ turns on, and an overload current begins to flow through transistor Q ₂ from the emitter of transistor Q ₁ → collector → resistor R ₂ → terminal L ₀ → terminal E ₀ . By the way, in this state, the voltage at point a in FIG. 1 is almost 0 volts when the short circuit is completely shorted, and the self-holding of the call holding circuit 6 is stopped, but in general, the voltage at point a in FIG. When short-circuited through a resistor, the above overload current
A voltage equal to the line resistance is generated. However, the voltage division of the resistor R ₃ and the resistor R ₄ of the call holding circuit 6 prevents the transistor Q ₂ from being turned on at this voltage, so even in this case, the self holding of the call holding circuit 6 is stopped.

Furthermore, even if switch 4 is held down, switch 4
Part of the current flowing through the capacitor C 1 passes through the resistor R ₆ with a time constant (resistance R ₆ × capacitor C ₁ ) _.
However, for the above-mentioned reason, _Q2 is not turned on, so the voltage at point b in _FIG . Transistor Q ₄ is then turned on via resistor R ₉ , and as a result, the base of transistor Q ₁ is turned on.
Since the emitter and collector are short-circuited by the emitter and collector of transistor _Q4 , transistor _Q1 is turned off, and the calling current C, which is an overload current,
is forcibly cut off after a certain period of time defined by the time constant. Thereafter, even if the switch 4 is kept pressed, transistor Q ₃ and transistor Q ₄ continue to be turned on, and transistor Q ₁ and transistor Q ₂ remain turned off. When switch 4 is turned off, the charge in capacitor _C1 is discharged through resistor _R6 , resistor _R5 , resistor _R7 , and resistor _R8 , returning to the initial state.

[Effects of the Invention] As is clear from the above embodiments, the nurse call intercom of the present invention has a nurse call handset that is connected to the nurse call main unit through two lines, and a nurse call handset that is connected to the nurse call handset by two lines. The nurse call handset consists of a hallway light that is connected to a separate line that shares a common ground line among the main lines, and a call switch that is installed inside the handset or outside the handset by pulling out a line, and a call switch that is pressed. The corridor light is turned on by the ringing current flowing through the ring, and the ringing current is self-maintained by a part of the ringing current, so that the ringing current continues to flow between the two lines, and when the corridor light is short-circuited, the self-holding is carried out. It has a call holding circuit that stops, and a protection circuit that forcibly cuts off the ringing current after a certain period of time even if you keep pressing the ringing switch when the hallway light is short-circuited, and the nurse call base unit detects the ringing current. Equipped with a call detection circuit that recognizes calls, so if you accidentally short-circuit the hallway light line when connecting a nurse call handset or hallway light,
Even if the call switch is pressed in this state, the call holding circuit in the handset is prevented from being destroyed, and an inexpensive transistor with a relatively small allowable power is used.
A nurse call intercom with extremely high reliability is obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a nurse call intercom according to the present invention, and FIG. 2 is a circuit diagram of a conventional nurse call intercom. 1... Nurse call base unit, 2... Call detection circuit, 3... Nurse call slave unit, 4... Call switch, 5... Corridor light, 6... Call holding circuit, 8...
Protection circuit, N, E...2 lines, L, E...
Separate line, C... Ringing current.

Claims (1)

[Claims] 1 A nurse call base unit, a nurse call slave unit that is connected to the nurse call base unit by two lines, and a nurse call slave unit that is connected to the nurse call slave unit by a separate line that shares a ground line among the two lines. The nurse call handset consists of a calling switch installed inside the handset or outside the handset by pulling out a line, and a ringing current that flows when the calling switch is pressed to light up the hallway light. a ring holding circuit that holds the ring current by a portion of the ring current, continues to flow the ring current between the two lines, and stops the self holding when the hallway light is short-circuited; and a protection circuit that forcibly cuts off the calling current after a certain period of time even if the calling switch is kept pressed when the hallway light is short-circuited, and the nurse call base unit detects the calling current and stops calling. A nurse call intercom characterized by being equipped with a call detection circuit that recognizes calls.