KR19990040838U - Constant Current Circuit with Temperature Compensation - Google Patents

Abstract

The constant current circuit of the present invention removes a direct current signal from a mixed signal of alternating current and direct current, and has a temperature compensation function. This allows the dummy circuit to be configured in the constant current circuit to compensate for the heat generated in the circuit. In addition, it is possible to compensate the heat generated in the circuit by configuring the capacitor and the resistor constituting the circuit with low-voltage surface-mount components that can be obtained more economically and easily.

Description

CONSTANT CURRENT CIRCUIT WITH THERMAL COMPENSATION FUNCTION

The present invention relates to a constant current circuit that removes a direct current signal from a mixture of alternating current and direct current components, and more particularly, to a constant current circuit having a temperature compensation function.

BACKGROUND ART A constant current circuit, which is widely used in an electronic device, is a circuit that outputs only an AC signal by removing a DC signal from a mixed signal of AC and DC components. In particular, it is arranged on the primary side of the transformer provided in the line interface circuit of the modem, and the alternating current and direct current components are mixed to remove the direct current component of the input signal. A modem (MOMulator / DEModulator) provided in a computer system is a device that connects a computer with a telephone line and is a device that enables a computer to communicate with another computer using a telephone system. The modem receives a digital signal from a computer and converts the signal into an analog signal so that the signal can be transmitted to the telephone line. The modem converts the analog signal from the telephone line into a digital signal and demodulates the signal.

1 is a circuit diagram showing some circuit configurations of a modem circuit having a constant current circuit.

Referring to FIG. 1, a line interface (or a data access arrangement (DAA) circuit) 200 configured between a modem circuit 100 and a jack 300 may include a transformer 210 and a DC signal. A constant current circuit 220, a hook switch 230, a surge arrester 240 to remove the surge voltage, and resistors R1, R2 and capacitors C1, C2. The constant current circuit 220 removes the DC component of the input signal and provides the same to the modem circuit 100 through the transformer 210.

FIG. 2 shows a detailed circuit diagram of the constant current circuit shown in FIG.

Referring to FIG. 2, the constant current circuit 220 connected between the A and B ends of the line interface 200 includes a bridge diode 222 composed of diodes D1, D2, D3, and D4, and a zener diode Z2. , Capacitor C3 and resistors R3, R4, R5 and transistors Q1, Q2. The two transistors are darlington circuits 224 having an emitter terminal of transistor Q1 connected to the base terminal of transistor Q2. The Darlington circuit has a very large current gain.

The constant current circuit 220 used in the conventional modem circuit is very sensitive to heat, and may cause malfunction due to heat. In addition, during the initial use, there is no problem at all, and at a certain temperature, the line connection speed drops periodically and the line connection is broken.

In order to solve this problem, a resistor having an appropriate resistance value and a suitable thermal compensation circuit should be used. However, the surface mount device (SMD) has a problem in that it is difficult to set a resistance value so that accurate power cannot be used.

Commonly used tantalum capacitors have a breakdown voltage of about 16V / 10V. However, since a high voltage may be applied to the line due to lightning, etc., the capacitor used for the line interface circuit 200 of the modem should usually be used as having a high breakdown voltage of about 25-50V. When using DIP-type electrolytic capacitors, there are no problems in supply and demand, but in the case of portable computer modems with limited space and size, surface-mount components (SMD) Should be used. At this time, the surface mounting capacitor having a breakdown voltage of 25V-50V has a disadvantage in terms of supply and demand, and is expensive.

Accordingly, an object of the present invention is to provide a constant current circuit having a temperature compensation function, which has been proposed to solve the above-mentioned problems.

1 is a circuit diagram showing a part of a circuit configuration of a modem circuit having a constant current circuit;

2 is a detailed circuit diagram of the constant current circuit shown in FIG. 1; And

3 is a circuit diagram showing in detail a constant current circuit according to a preferred embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

100: modem circuit 200: line interface (DAA)

210: transformer 220: constant current circuit

230: hook switch 300: jack

222: bridge diode 224: Darlington circuit

According to a feature of the present invention for achieving the object of the present invention as described above, the constant current circuit for removing the direct current component of the input signal mixed with alternating current and direct current component: a bridge diode for rectifying the input signal; ; A zener diode connected across the output terminal of the bridge diode; Voltage divider resistors connected across the Zener diode; A Darlington circuit, one end of which is connected to a cathode terminal of the zener diode and operated by a voltage applied to any node of the voltage divider; A dummyster connected between the cathode terminal of the zener diode and the node to perform a temperature compensation function; One or more capacitors connected in series between an anode terminal of the zener diode and the node; At least two resistors connected in parallel to the anode terminal of the zener diode and the other end of the Darlington circuit.

In this embodiment, the voltage divider resistors comprise: two or more resistors connected in series across the zener diode; At least one or more resistors connected in parallel across each of the resistors.

(Example)

Hereinafter, an embodiment according to the present invention will be described in detail with reference to FIG. 3.

The novel constant current circuit of the present invention removes a direct current signal from a mixed signal of alternating current and direct current, and has a temperature compensation function. A dummyster is formed in the constant current circuit to compensate for the heat generated in the circuit. In addition, it is possible to compensate the heat generated in the circuit by configuring the capacitor and the resistor constituting the circuit with low-voltage surface-mount components that can be obtained more economically and easily.

3 illustrates a constant current circuit according to a preferred embodiment of the present invention in detail.

Referring to FIG. 3, the constant current circuit 220 according to the present invention includes a bridge diode 222 composed of diodes D1, D2, D3, and D4, a zener diode Z2, and resistors R31, R32, R41, R42, R51, R52, R53, R54, capacitors C31, C32, dummyistors and transistors Q1, Q2. The two transistors are darlington circuits 224 having an emitter terminal of transistor Q1 connected to the base terminal of transistor Q2. The Darlington circuit 224 has a very large current amplification rate.

The resistors R31 and R32 and R41 and R42 are connected in parallel, respectively, and in parallel with the zener diode Z2. The capacitor C32 is connected in series with the capacitor C31. The resistors R51, R52, R53, R54 are connected in parallel to the emitter terminal of the transistor Q2.

The current flowing through the jack 300 of the modem circuit is at least 20 mA at a maximum of 120 mA. If the resistors R52, R53, R54 are not configured and only R51 is configured, the power at the resistor R51 is as follows.

Therefore, the power P is about 0.15 W when the resistor R51 is 10Ω, and the power P is about 0.3 W when the resistor R51 is 20Ω. The actual power range at the resistor is about 0.3 to 0.5 W when R51 is 10Ω and about 0.6 to 1 W when resistor R51 is 20Ω. Therefore, when using resistor R51 as a surface mount component (SMD), a power resistance of 0.5 W to 1 W should be considered.

When resistors R51 and R5 are configured, R51 = R52, R51 + R52 = 2 * R51 = 2 * R52, and when the current flowing through each resistor is I51 and I52, respectively, the sum of the currents flowing through the two resistors is I51. + I52 so

When the resistor R51 is 10 Ω and the current is 120 mA, the power P is

And the actual power P is 0.1 W.

When the resistor R51 is 10 Ω and the current is 20 mA, the power P is

And the actual power P is 0.02 W.

As described above, in the case where one resistor having the same value is configured in parallel, the power resistance can be reduced from 0.5 W to 0.1 W. Thus, the resistor can be used at high power as a conventional low power resistance surface mount component.

Typically temperature T T ∝ I ² There is a relationship. That is, as the amount of current increases, the heat generated by the component is proportional to the square of the amount of current. Therefore, it is necessary to reduce the amount of current flowing through each component to minimize the heat generated in each component. In addition, the circuit may be less sensitive to heat when configured in two parallel than one component. As described above, when the resistors R51 and R52 are configured in parallel, the amount of current flowing through each resistor is 1/4 of the amount of current when only the resistor R51 is formed. As a result, the heat generated by each resistor can be reduced to 1/16. In addition, when calculating the rate of change of resistance per temperature relative to external heat, each resistor is configured in parallel, making it less sensitive to changes caused by external heat.

The dummy TH1 is a device whose resistance value decreases with temperature. When the dummyster TH1 is connected between the collector of the transistor Q1 and the base terminal of the Darlington circuit 225, the base current of the Darlington circuit changes with respect to the temperature change. Thus, fundamental thermal compensation can be made for the heat generated in the circuit.

The resistors connected between the emitter terminal of the transistor Q2 and the anode terminal of the zener diode Z2 have been described so far, but the resistors R51, R52, and R53 are shown in this embodiment as shown in the drawing. And four resistors of R54. In addition, resistors R32 were configured in parallel at both ends of the resistor R31, and resistors R42 were configured in parallel at both ends of the resistor R41.

The capacitor C32 is configured in series with the capacitor C31, so that even if each capacitor has a low breakdown voltage, the total breakdown voltage may have a high breakdown voltage because it is equal to the sum of the breakdown voltages of the two capacitors. In other words, by using two low-voltage surface mount component capacitors, which are more economical and easier to obtain, the same effect as high breakdown voltage can be obtained.

According to the present invention as described above, the dummy current is configured in the constant current circuit to compensate for the heat generated in the circuit. In addition, it is possible to compensate the heat generated in the circuit by configuring the capacitor and the resistor constituting the circuit with low-voltage surface-mount components that can be obtained more economically and easily.

Claims (2)

A constant current circuit for removing the direct current component of an input signal in which alternating current and direct current components are mixed, A bridge diode for rectifying the input signal; A zener diode connected across the output terminal of the bridge diode; Voltage divider resistors connected across the Zener diode; A Darlington circuit, one end of which is connected to a cathode terminal of the zener diode and operated by a voltage applied to any node of the voltage divider; A dummyster connected between the cathode terminal of the zener diode and the node to perform a temperature compensation function; One or more capacitors connected in series between an anode terminal of the zener diode and the node; And at least two resistors connected in parallel to the anode terminal of the zener diode and the other end of the Darlington circuit. The method of claim 1, The divided resistances are, Two or more resistors connected in series across the zener diode; And at least one or more resistors connected in parallel across each of said resistors.