JPS6352804B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an isolated variable resistance device in which an input side and an output side are insulated and the resistance value of the output side can be controlled from the input side.

Conventionally, this type of device includes LED and phototransistor, LED and photodiode, LED and Cds.
Many photocouplers were used. However, these devices control the amount of light emitted from the LED and use phototransistors, photodiodes, or CdS.
Since it changes the equivalent resistance value of the circuit, it has the drawback of large variations in input/output characteristics. That is,
Variations in the luminous efficiency of LEDs, the degree of coupling between LEDs and phototransistors, etc., and the photocurrent characteristics of phototransistors, etc., directly lead to variations in input/output characteristics. Another drawback was that it was highly temperature dependent. Furthermore, since phototransistors and photodiodes are essentially current control elements, they have the disadvantage that the equivalent resistance value is affected by changes in the circuit.

The present invention has been made in view of the above circumstances, and provides an insulated variable resistance device that eliminates the above-mentioned drawbacks.

Hereinafter, the present invention will be explained in detail based on embodiments shown in the drawings.

Reference numeral 1 shown in FIG. 1 is an embodiment of the insulated variable resistance device of the present invention, which includes a photocoupler 2 consisting of an LED 2a and a phototransistor 2b, a pulse drive circuit 3 for pulse-driving the LED 2a of the photocoupler 2, and a pulse drive circuit 3 for pulse-driving the LED 2a of the photocoupler 2. It basically comprises a resistor r connected in series with the phototransistor 2b, and a capacitor c connected in parallel to the series circuit formed by the resistor r and the phototransistor 2b.

Photocoupler 2 includes an LED and a photodiode,
It may be a combination of an LED and a CdS, or it may be a combination of an LED and a phototransistor, etc., separated by a long distance, and coupled with an optical fiber or the like.

As shown in Fig. 2, the pulse drive circuit 3 operates only for T ₁ hour every T ₀ time (for example, 10 μsec.).
A drive current _i0 is supplied to the LED 2a, and the _T1 time can be set arbitrarily between 0 and _T0 . Further, the magnitude of the drive current i ₀ is set to a magnitude that completely conducts the phototransistor 2b. Therefore, phototransistor 2
b is turned ON for only T ₁ hour every T ₀ hour, and the ratio of T ₁ hour to T ₀ hour, that is, the energization rate α can be arbitrarily changed between 0 and 1. 3' shown in FIG. 3 is a specific example of the pulse drive circuit 3, which is composed of amplifiers _A1 and _A2 , a triangular wave generation circuit, and a comparator _A3 .
Comparator A ₃ by potentiometer etc.
By changing the comparison voltage V _i , the energization rate α can be changed in the range of 0 to 1. T ₀ is determined by the period of the triangular wave.

Referring again to FIG. 1, the values of resistor r and capacitor C are selected such that their time constant is sufficiently larger (for example, 100 times or more) than T ₀ .

Therefore, although the current flowing through resistor r is actually pulse-like, if we consider a steady state that takes into account the function of capacitor C, the potential difference V between points P and Q is approximately constant, and is substantially constant. Current I is at point P-Q
It is thought that it flows between

Now, considering the amount of electricity q flowing between points P and Q per T ₀ time in a steady state, since the current value is 1, q=I·T ₀ ...(1). However, since the amount of electricity that actually flows is only that flowing through the phototransistor 2b, q=V/r·T ₁ (2) where r is the resistance value of resistor r. If we eliminate q from these equations (1) and (2) and rearrange them, we get l=V/r・T ₁ /T ₀ ...(3).

The equivalent resistance value R between points P and Q is calculated as follows, considering equation (3): R=V/1=r・T ₀ /T ₁ = r/α ……(4) However, T ₁ /T ₀ = α.

From equation (4), it can be seen that the equivalent resistance value R between points P and Q is determined in proportion to the resistance value r of resistor r and inversely proportional to the energization rate α; however, in this device 1, α is 0
Since it is variable between ~1, the equivalent resistance value R
is variable between r and ∞.

Reference numeral 10 shown in FIG. 4 is an example of a thermostat circuit using the device 1 described above. This circuit 10
The comparator 11 energizes the relay coil 12 when the thermistor R _T is at a low temperature, and stops the relay coil 12 from energizing when the thermistor (R _T ) reaches a high temperature. The operating point of this switching is the point where the following equation is satisfied.

R ₁ +R/R _T =R ₂ /R ₃ (5) From equation (5), it can be seen that the operating point can be changed by changing the equivalent resistance value R. In other words, R
If R is made large, the operating point will move to the low temperature side, and if R is made small, the operating point will be moved to the high temperature side.

As can be understood from the above description, the insulated variable resistance device of the present invention has an insulated switch means whose input side and output side are insulated and whose output is turned ON/OFF according to an input signal. An energization rate control means for variable control of the ON/OFF time ratio is connected to the input side, a resistor is connected in series to one output side, and a capacitor is connected in parallel to the series circuit. The equivalent resistance value can be changed by changing the energization rate. Since the equivalent resistance value is determined by the current conductivity and the resistance value of the resistor as shown in equation (4) above, the variation is significantly smaller than in the past. Furthermore, temperature dependence is also reduced. Furthermore, the equivalent resistance value is no longer affected by the circuit voltage. Furthermore, since it is a method that controls the energization rate, it is resistant to analog nozzles, and since the input side and output side are insulated, the insulated switch means and the energization rate control means can be separated far apart, making it suitable for remote control systems. There are also features that can be used.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the configuration of one embodiment of the insulated variable resistance device of the present invention, FIG. 2 is a diagram of the LED drive current waveform in the device shown in FIG. 1, and FIG. 3 is a diagram of the LED drive current waveform in the device shown in FIG. FIG. 4 is a circuit configuration diagram of a specific example of a pulse drive circuit, and FIG. 4 is an explanatory diagram of the configuration of a thermostat circuit using the device shown in FIG. 1. 1...Insulated variable resistance device, 2...Photocoupler, 3...Pulse drive circuit, r...Resistor,
C...Capacitor.

Claims (1)

[Claims] 1. An insulated switch means whose input side and output side are insulated and whose output is turned ON/OFF according to an input signal, wherein the input side is provided with a variable ON/OFF time ratio. A series-parallel circuit formed by connecting a resistor in series to one output side, and further connecting a capacitor in parallel to the series circuit, is connected to a DC power source via the resistor. an insulated variable resistance device, wherein a discharge time constant of a resistor and a capacitor of the series-parallel circuit is set so that a voltage across the series-parallel circuit is substantially constant. 2. The insulated variable resistance device according to claim 1, wherein the insulated switch means is a photocoupler.