JPH07101841B2 - Input drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is used in, for example, a solid state relay, and is for an input portion of a photocoupler that electrically insulates an input signal from an output signal and transmits the signal. Regarding a drive circuit.

[Prior Art] As a solid state relay using a photocoupler, the one shown in FIG. 2 is well known. In FIG. 2, the photodiode PD of the photocoupler PC is connected in series to the power supply terminal I ₀ and the input signal terminal I ₁ via the resistor R ₁ ,
Input signal terminal I ₁ to the high level of the input signal (hereinafter this H
When the input signal changes to a low level input signal (hereinafter referred to as L), a current flows and emits light. As a result, the phototriac PT is turned on, the voltage drop across the resistor R ₂ turns on the triac T, and the load L is driven by the AC power supply AC. R ₃ and C are resistors and capacitors connected in parallel to the triac T.

Such a solid state relay is also used for a three-phase load, in which case the input circuit of the photocoupler PC is
Shown in the figure. In FIG. 3, between the power supply terminal I ₀ and each input signal terminal I ₁ , I ₂ , I ₃ are connected to the photocouplers PC ₁ , PC ₂ , PC ₃ via resistors R ₁₀ , R ₂₀ , R ₃₀ , respectively. Diode PD ₁ , PD ₂ , PD ₃
(The photo triac is omitted in the figure). In the photocouplers PC _{1 to} PC ₃ shown in FIG. ₃ , when the input signal terminals I _{1 to} I _{3 change} from H to L, currents flow in the photodiodes PD _{1 to} PD ₃ , respectively, and the photocouplers
PC _{1 to} PC ₃ operate. At this time, the current consumption of the photocoupler shown in FIG. 3 is three times that of the photocoupler shown in FIG. Therefore, it is necessary to increase the capacity of the power supply according to the number of photo couplers.

FIG. 4 shows an input circuit of a photocoupler whose current consumption is constant regardless of the number of photocouplers. Photodiodes PD _{1 to} PD of photocouplers PC _{1 to} PC _{3 in} FIG.
₃ (phototriac omitted in the figure) are connected in series, and the anode of photodiode PD ₁ is resistor R ₄
To the power supply terminal I ₀ , and the cathode of the photodiode PD ₃ is connected to the negative electrode terminal I ₀₁ . Photodiode P
D ₁ is the -PD ₃ transistor T ₁ through T ₃ are connected in parallel, the resistance R _11, R ₂₁ together with the base of each transistor T ₁ through T ₃ are connected respectively to the input signal terminal I ₁ ~I _3, It is connected to the power supply terminal I ₀ via R ₃₁ . Current input signal of the input signal terminal I ₁ ~I ₃ is flowing in the photodiode PD ₁ -PD ₃ in the case of H photocoupler PC ₁ to PC ₃ because it is bypassed by the transistor T ₁ through T ₃ does not operate. When the input signals of the input signal terminals I _{1 to} I ₃ change from H to L, the transistors T _{1 to} T ₃ are turned off, so that current flows through the photodiodes PD _{1 to} PD ₃ and the photocouplers PC _{1 to} PC ₃ operate. . At this time, the current flowing through the photodiodes PD _{1 to} PD ₃ corresponds to the current flowing through one photodiode, and therefore the current consumption is constant regardless of the number of photodiodes.

[Problems to be Solved by the Invention]

In the conventional example shown in FIG. 4, the current flowing in the photodiode can be made constant, but in addition to the power supply terminal I ₀ and the input signal terminals I _{1 to} I ₃ , the negative electrode terminal I ₀₁ is separately prepared. The number of terminals must be increased. Also, while the photocouplers PC _{1 to} PC ₃ are off, transistors T _{1 to} T ₃
Is always on, wasteful power consumption due to the resistor R ₄ is required, and the photocouplers PC _{1 to} PC ₃ inadvertently malfunction due to failure of the transistors T _{1 to} T ₃ .

Therefore, an object of the present invention is to eliminate the drawbacks of the conventional device, reduce the number of terminals while keeping the power consumption during operation of a plurality of light emitting elements constant, and prevent inadvertent malfunction of the light emitting elements. To provide a circuit.

[Means for solving the problem]

In order to achieve this object, the present invention provides an input drive circuit in which n light emitting elements are connected in series and each light emitting element is individually controlled by n input signals. One end (anode side) of the upper light emitting element is connected to a power supply terminal through a resistor, and the other end (cathode side) of the final light emitting element is connected to one input signal terminal of n input signal terminals. A transistor is connected in parallel with each light emitting element except the light emitting element at the final stage of the connected and serially connected light emitting elements, and a diode in the reverse direction is connected between the base and emitter of each transistor. The base of the transistor is connected to each of the n-1 input terminals through a Zener diode provided corresponding to each transistor and having a cathode connected to each base. The connection point between the anode of each Zener diode and the n-1 input signal terminals is connected to the power supply terminal via a resistor, and the Zener voltage of each Zener diode is greater than the voltage applied to the power supply terminal. Is small, and the Zener voltage of the Zener diode located on the upper stage side is set to the Zener voltage of the Zener diode located on the next stage side so that the current is prevented from sneaking when an input signal is applied to a plurality of input signal terminals. It is characterized in that it is selected to be larger than the value obtained by adding the respective forward voltages of the light emitting element and the light emitting element.

[Action]

In the present invention configured as described above, the input signal terminal is also used as the input signal supply terminal and the current terminal, so that the input signal is applied to one of the n-1 input signal terminals. And the transistor corresponding to the input signal terminal thereof is turned off, and a current flows from the power supply terminal in the paths of the corresponding light emitting element-diode-zener diode-input signal terminal to cause the light emitting element to emit light. Also,
When an input signal is applied to a plurality of input signal terminals of the n-1 input signal terminals, only the Zener diode on the final stage side is turned on by each Zener diode selected so as to prevent the sneak of the current. Terminal-a light emitting element corresponding to an input signal terminal to which an input signal is applied-a diode and a Zener diode corresponding to the light emitting element on the final stage side of the light emitting element-a current in a path which is an input signal terminal connected to the Zener diode And the light emitting elements corresponding to the plurality of input signal terminals to which the input signal is applied emit light. When an input signal is applied to the n input signal terminals including the input signal terminal connected to the other end side (cathode side) of the light emitting element at the final stage, n-1
Since the sneak currents are blocked by the respective Zener diodes corresponding to the input signal terminals, all the light emitting elements corresponding to the n input signal terminals to which the input signals are applied emit light. Further, when the input signal is not applied to the n input signal terminals, the light emitting element at the final stage is turned off, so that the current path of each light emitting element is not formed, so that wasteful power consumption is eliminated. .

〔Example〕

FIG. 1 shows an input portion of a photocoupler showing an embodiment of the present invention. In FIG. 1, the same parts as those of the conventional device shown in FIG. 4 are designated by the same reference numerals.

In FIG. 1, the photodiodes PD _{1 to} PD ₃ of the photocouplers PC _{1 to} PC ₃ are connected in series and the photodiodes PD _{1 to} P ₃ are connected.
The point that the current consumption flowing in D ₃ is constant is the same as the conventional device, but the transistors T ₁ and T ₂ connected in parallel to the uppermost photodiode PD ₁ and the next photodiode PD ₂ have Reverse diodes D ₁ and D ₂ between base and emitter
, And zener diodes ZD ₁ and ZD ₂ are connected between the base input signal terminals I ₁ and I ₂ of the transistors T ₁ and T ₂ . Last-stage photocoupler PC ₃ connected in series
Of the cathode of the photodiode PD ₃ input signal terminal I ₃
Are directly connected. R ₄ is the photodiode PD _{1 to} PD ₃
R ₁₁ and R ₂₁ are resistors for supplying a base current to the transistors T ₁ and T ₂ .

Next, the operation of the circuit shown in FIG. 1 will be described.

(1) When the input signals of the input signal terminals I _{1 to} I ₃ are H.

Flow to the photodiode PD ₃ and the input signal of the transistor T _1, although T ₂ is in the on state the input signal terminal I ₃ is H when the input signal of the input signal terminals I _1, I ₂ is H Therefore, no current flows, so that no current path is formed in the input parts of the photocouplers PC _{1 to} PC ₃ , the photodiodes PD _{1 to} PD ₃ are off, and the current consumption is zero.

(2) When the input signals of the input signal terminals I ₂ and I ₃ are H and the input signal of the input signal terminal I ₁ changes from H to L.

When the input signal of the input signal terminal I ₁ changes from H to L, the resistance
The current flowing in the base of the transistor T ₁ via R ₁₁ flows into the input signal terminal I ₁ side and the transistor T ₁ is turned off. When the transistor T ₁ is turned off, the resistance R ₁₁
> Selected for resistor R ₄ and power supply Vcc> Zener diode ZD ₁
Power supply terminal I ₀ -Resistor R _4- Photodiode PD ₁ -Diode D ₁ -Zener diode Z
D ₁ − Current flows in the path of input signal terminal I ₁ , photodiode PD ₁ emits light, and photocoupler PC ₁ operates. At this time, no current flows in the photodiodes PD ₂ and PD _3, and the photocouplers PC ₂ and PC ₃ are inoperative.

(3) Input signal terminal I ₃ input signal is H and input signal terminal
When the input signals of I ₁ and I ₂ change from H to L.

When the input signals at the input signal terminals I ₁ and I ₂ change from H to L, the transistors T ₁ and T ₂ are both turned off. Here, the voltage V ₁ seen from the input signal terminal I ₂ is the Zener voltage of the Zener diode ZD ₂ is VZD ₂ , the armature voltage of the diode D ₂ is VD ₂ , and the forward voltage of the photodiode PD ₂ of the photocoupler PC ₂ is When VPC ₂ is set, V ₁ = VZD ₂ + VD ₂ + VPC ₂ and at this time, the Zener voltage VZD ₁ of the Zener diode ZD ₁ is changed to VZD.
Selected so that ₁ > V ₁ . As a result, a current path of the current terminal I ₀ -resistor R _4- photodiode PD _1- photodiode PD ₂ -diode D ₂ -zener diode ZD ₂ -input signal terminal I ₂ is formed and photocouplers PC ₁ and PC _{2 are connected.}
Works on.

Incidentally, VZD ₂ zener voltage VZD ₂ of the Zener diode ZD ₂ is an input signal terminal I ₃ seen from the voltage V ₂ (= VPC _3)>
Selected for V ₂ .

(3) When the input signals of the input signal terminals I ₁ and I ₂ are H and the input signal of the input signal terminal I ₃ changes from H to L.

When the input signals of the input signal terminals I ₁ and I ₂ are H, the transistors T ₁ and T ₂ are in the ON state, and when the input signal of the input signal terminal I ₃ changes from H to L in this state, the power supply Terminal I ₀
- resistance R ₄ transistors T ₁ - transistor T ₂ - photodiode PD ₃ - current path of the input signal terminal I ₃ are formed, thereby the photo-coupler PC ₃ is turned on.

(4) When the input signals of the input signal terminals I _{1 to} I ₃ change from H to L.

When the input signals of the input signal terminals I _{1 to} I ₃ change from H to L, the zener diode ZD ₁ is selected as VZD ₁ > V ₁ and the zener diode ZD ₂ is selected as VZD ₂ > V ₂ , so the power supply terminal I ₀ −
Photodiode PD _1- Photodiode PD _2- Photodiode PD _3- Current path of input signal terminal I ₃ is formed,
This turns on the photocouplers PC _{1 to} PC ₃ . As is clear from the above, the Zener diode ZD ₁ ,
Zener voltage VZD _1, VZD ₂ of ZD _2, when the simultaneous input signal to the input signal terminal I _1, I ₂ is applied, only the Zener diode ZD ₂ is rendered conductive, the input signal terminal by the Zener diode ZD ₁ I VZD so that current does not flow around the _{1 1>} VZ
Due to the relationship of D ₂ , the Zener voltage VZD ₁ of the Zener diode ZD ₁ on the upper stage side is selected to be larger than the Zener voltage VZD ₂ of the Zener diode ZD ₂ on the next stage side.

In the above-mentioned embodiment, the case where the number of photocouplers is three has been described, but the number of photocouplers is not limited to this. When n photocouplers are used, a diode and a Zener diode are added to the (n-1) photocoupler. It may be added, and it can be applied not only to a photocoupler but also to a drive circuit for a light emitting element such as an LED.

〔The invention's effect〕

According to the present invention described above, even when a plurality of light emitting elements are operated in series by connecting a plurality of light emitting elements in series, the current consumption is only the current required to drive one light emitting element. While reducing the current consumption, the current path is not formed in the input off state of multiple light emitting elements to eliminate unnecessary power consumption and the transistors connected in parallel to multiple light emitting elements emit multiple light. It is said that the light emitting element does not malfunction accidentally even if the element fails in the input off state, and the number of terminals can be reduced by using the input signal terminal as the input signal supply terminal and the power supply terminal. Have advantages.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an input drive circuit showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a solid state relay, and FIGS. 3 and 4 are circuit diagrams showing conventional devices. . PC _{1 to} PC ₃ : Photo coupler, PD _{1 to} PD ₃ : Photo diode,
T ₁ through T _3: the transistor, D _1, D _2: diodes, ZD _1, ZD _2: Zener diode, I _0: power supply terminals, I ₁ ~I _3: input signal terminal.

Claims (1)

[Claims] 1. An input drive circuit in which n light emitting elements are connected in series and each light emitting element is individually controlled by n input signals, wherein one of the uppermost light emitting elements connected in series is The side end (anode side) is connected to a power supply terminal via a resistor, and the other end (cathode side) of the last-stage light emitting element is connected to one input signal terminal of n input signal terminals, and connected in series. A transistor is connected in parallel with each light-emitting element except the light-emitting element at the final stage of the light-emitting element, and a diode in the reverse direction is connected between the base and emitter of each transistor, and the base of each transistor is Each Zener diode is connected to each of n-1 input terminals through a Zener diode provided corresponding to the transistor and having a cathode connected to each base. The connection point between the anode and the n-1 input signal terminals, will be connected to the power supply terminal via resistors, Zener voltage of each Zener diode,
It is smaller than the voltage applied to the power supply terminal, and the Zener voltage of the Zener diode located on the upper stage side is located on the next stage side so as to prevent current sneak when the input signals are applied to multiple input signal terminals. An input drive circuit is selected to be larger than a value obtained by adding the forward voltage of each of the diode and the light emitting element to the Zener voltage of the Zener diode.