KR101075464B1 - constant current source circuit - Google Patents

Abstract

According to the present invention, a path having an increasing current with respect to an input voltage variation and a path having a decreasing current to compensate for an increasing current can be formed using only a transistor having a simple configuration, thereby making mutual compensation operation between the respective paths. By providing a constant current source circuit that can implement a precise constant current over a wide range.
To this end, the present invention is a constant current source circuit for implementing a constant current with respect to the input voltage supplied from the input voltage source to the load, the input voltage source and the load connected in parallel with the negative driver for the load, the voltage fluctuation from the input voltage source A definite call driver driven to increase the load current with respect to the input voltage source and the load and the definite call driver in parallel with each other to reduce the current to compensate for the increase in the load current by driving the definite call driver. And a reference voltage unit for providing a reference voltage for setting a driving current by the negative code driver and the negative code driver.

Description

Constant Current Source Circuit

The present invention relates to a constant current source circuit capable of supplying a constant current to a load in a wide range of voltages by mutual compensation operation between driver paths.

In general, all electronic devices must generate and supply a stable voltage or current from the main input power corresponding to the components and components of each part that implement the desired functions. In general, the state of the main input power is not always constant. Not only can it vary depending on external conditions or the power dissipation inside the device, but it also requires the use of a fairly wide input power range depending on the application.

Therefore, in recent years, there is a need for a technology capable of generating a stable voltage or current even when the main input voltage fluctuates and supplying it to each functional unit. As a configuration for supplying a stable voltage, a constant voltage circuit is applied and a stable current is supplied. A constant current circuit is applied as a configuration for the configuration, and a constant current / constant voltage circuit is applied as a configuration for stably supplying both voltage and current.

The constant current circuit is largely implemented using a unique characteristic of a device to implement a constant current, a field effect transistor (FET) or a combination of a transistor (TR) and an auxiliary device, and a method using an integrated circuit such as an OP AMP or a regulator. Etc.

A typical method using the inherent characteristics of the device is the diode's inherent voltage-current characteristics, which include a current regulative diode (CRD). The method using the CRD adjusts the pinch-off current to match the constant current. As a result, it is possible to implement a constant current in one device.

However, in the case of using the CRD method, it is not possible to adjust a desired amount of current for one selected item by using an external device, so that only an item suitable for a constant current value prepared by the manufacturer should be used selectively, as shown in FIG. As shown, varieties having excellent constant current characteristics over a wide input voltage range are limited to those having a low constant current value, which is disadvantageous in that they are suitable only for low power applications. Therefore, there is a problem that the number of light emitting diodes that can be driven with high performance is limited because of a flat voltage range, which is generally used for several tens of mA applications such as light emitting diodes (LEDs).

On the other hand, a method using a field effect transistor or a transistor and an accessory element is typically based on a constant current circuit using a two-seat transistor, a current mirror, and a constant voltage element such as a zener diode at the base of the transistor. The method of constructing the voltage is mainly applied.

Fig. 2 is a diagram showing the configuration of a constant current circuit using a conventional two-stone transistor.

As shown in FIG. 2, a conventional constant current circuit includes a load current path leading to a second transistor Q2 and a second resistor R2, and a path of a first resistor R1 and a first transistor Q1 for a reference voltage. It consists of a reference voltage path leading to and sets the load current as shown in the following equation.

I = Vbe1 / R2

Here, I denotes a current and Vbe1 denotes a voltage between the base terminal and the emitter terminal of the first transistor Q1.

The constant current circuit using the two-seat transistor can implement a constant current simply and a flexible current setting is possible than using the device characteristics, but the junction characteristic of the transistor is inclined according to the variation of the input voltage source V1 and the amount of load current. Since the load current also has a slope with respect to the fluctuation of the input voltage source V1, as shown in FIG. 3, the constant current source by the two-hole transistor changes the current with respect to the voltage when it is designed for a constant current of 20 mA, for example. Is large, which is not suitable for applications requiring precise current control.

In other words, when a field effect transistor or a transistor is used as a device that plays a leading role in the implementation of a constant current, it is possible to construct a low cost device so that a constant current source can be configured relatively simply and flexibly. The performance degradation problem can be a limitation depending on the application of the circuit, and it becomes very difficult to compensate for this characteristic.

On the other hand, a method using an integrated circuit includes a feedback control constant current circuit using an op amp and a combination of transistors, a combination of various regulators and resistors, which are constant voltage elements, and a charge pump which is widely used for driving a light emitting diode. (Charge Pump).

However, the conventional constant current method using the conventional integrated circuit has the advantage of implementing high performance current control, but because it is relatively expensive and complicated in configuration, and the size of the circuit components is relatively large, space constraints may occur. The problem is that it is inefficient in all respects.

Accordingly, the present invention has been made to solve the above-described conventional problems, and an object thereof is to use a transistor having a simple configuration, and a path having an increasing current for input voltage variations, and a decreasing current to compensate for the increasing current. It is to provide a constant current source circuit that can implement a precise constant current in a wide range through the mutual compensation operation between each path by allowing a path having a.

According to the present invention to achieve the above object, in the constant current source circuit for implementing a constant current for the input voltage supplied from the input voltage source to the load, the input voltage source and the load is connected in parallel with a negative driver, An increase of the load current by driving the definite call driver is connected in parallel with the definite call driver which is driven to increase the load current against the voltage variation from the input voltage source, and the definite call driver with respect to the input voltage source and the load. It provides a constant current source circuit comprising a reference driver for reducing the current to compensate the current, and a reference voltage section for providing a reference voltage for setting the drive current by the definite driver and the negative driver. .

As described above, according to the present invention, by arranging two transistors in parallel, an increase and a decrease in current are generated with respect to an increase in the DC voltage input from the outside, and a constant by the combined current of the increase and decrease in current is generated. It allows the constant current source to be implemented and the proper bias configuration to adjust the input voltage range and current increase / decrease rate corresponding to the constant current section, and to use the saturation region of the transistor to implement the current increase and decrease. In addition, it is possible to realize constant current over a wide input voltage range, and to set a wide range of desired load current amounts, and to easily adjust the increase and decrease rates of the current according to the input voltage variation according to the circuit application to be applied. To increase the efficiency of the constant current circuit as a whole. And so, as the circuit for various current reference, there is an effect that can be broadly applied to all devices using a light emitting diode (LED) light-sensitive element for the current change.

1 is a view showing the voltage-current characteristics of a typical CRD device,
2 is a view showing the configuration of a constant current circuit using a conventional two-stone transistor;
3 is a view showing a constant current characteristic of the circuit shown in FIG.
4 is a diagram illustrating a configuration of a constant current source circuit using a plurality of transistors according to a first embodiment of the present invention;
FIG. 5 is a view showing states of a load current, a definite code, and a negative drive current when an input voltage is changed in a circuit according to the first embodiment of the present invention; FIG.
6, 7, and 8 are views showing waveform states of input voltage versus current according to a change in resistance value of the constant current source circuit shown in FIG. 4;
9 is a view showing an example in which a constant current is widely implemented through a constant current source circuit according to the present invention;
10 is a view showing the configuration of a constant current source circuit in which a bias is formed using a light emitting diode according to a second embodiment of the present invention;
FIG. 11 is a view showing current and voltage waveforms when a light emitting diode is connected to the constant current source circuit of FIG. 10; FIG.
12 is a diagram showing the configuration of a constant current source circuit in which a bias is formed using a light emitting diode according to a third embodiment of the present invention;
FIG. 13 is a diagram illustrating a state in which efficiency is increased through a constant current source circuit using the light emitting diode shown in FIG. 12;
14 is a view showing the configuration of a constant current source circuit using only a negative driver using a light emitting diode according to a fourth embodiment of the present invention;
FIG. 15 is a diagram showing a constant current operating state by the constant current source circuit using only the negative driver shown in FIG.

Hereinafter, the present invention configured as described above will be described in detail with reference to the accompanying drawings.

That is, FIG. 4 is a diagram showing a configuration of a constant current source circuit using a plurality of transistors according to the first embodiment of the present invention.

As shown in FIG. 4, in the constant current source circuit according to the first embodiment of the present invention, the negative terminal of the input voltage source V1 is connected to the ground side and the positive terminal thereof is connected to the load 10. ), One end of the load 10 is connected to the plus (+) terminal of the input voltage source (V1), and the other end thereof is connected to the first transistor (Q1).

A second transistor Q2 and a third transistor Q3 are connected in parallel between the load 10 and the collector terminal of the first transistor Q1 through second and third resistors R2 and R3. The base end of the second transistor Q2 is connected between the second resistor R2 and the third resistor R3, and the emitter end of the second transistor Q2 is connected to the base end of the third transistor Q3. It is connected to each collector stage. In addition, the third transistor Q3 has a base end and a collector end connected in common with the emitter end of the second transistor Q2, and the emitter end is connected with the ground side.

Accordingly, the third transistor Q3 is configured as a reference voltage portion for the second transistor Q2, and the second transistor Q2 and the second and third resistors R2 and R3 are connected to the load 10. The first transistor Q1 and the first resistor R1 are configured as a negative current driver for the load 10.

The reference voltage unit functions to provide a reference voltage capable of appropriately setting the current driven by the definite current driver and the negative current driver. In the present invention, only a single third transistor Q3 is applied. The present invention is not limited thereto and may be configured by connecting at least one transistor or diode in series.

In the third transistor Q3 forming the reference voltage portion, the voltage Vc3 at the collector stage maintains approximately 0.7 V, which is a nominal diode forward voltage value, almost constant over the range of the wide input voltage source V1. When the total load current of the third transistor Q3 is "1" for the same set of bias resistors, a load current amount of (1 x number of transistors) is provided when a plurality of series reference voltage transistors are configured.

Next, FIG. 5 is a diagram showing the states of the load current, the definite code, and the negative drive current when the input voltage is changed in the circuit according to the first embodiment of the present invention.

In Fig. 5, the load current -I (V1), the negative code driver current IC Q2, and the negative driver current IC Q1 with respect to the 0 to 400 V variation of the input voltage source V1 are shown.

In the current flow of the constant current source circuit according to the first embodiment of the present invention, the load current I (VI) flows from the input voltage source V1 to the load 10 and the entire driving circuit, and the load current I (V1) Current of the definite driver path (i.e., the second transistor Q2 and the second and third resistors R2 and R3) and the unsignal driver path (i.e., the first transistor Q1 and the first resistor R1) Each is divided into

Therefore, the total load current I (V1) is the sum of the negative driver current IC (Q2) and the negative driver current IC (Q1), and the current IC (Q1) of the negative driver when viewed in the constant current section. Is reduced, while the current IC (Q2) of the definite-signal driver increases inversely so that the sum I (V1) is unique. In other words, the constant current source circuit according to the first embodiment of the present invention implements a mechanism in which the first transistor Q1 compensates for an increase in current caused by the second transistor Q2 when the input voltage source V1 changes. will be.

As described above, the description of the inclination of the opposite polarity with respect to the voltage fluctuation of the definite driver and the negative driver is as follows.

First, the base terminal voltage Vb2 of the second transistor Q2 is always higher than the collector terminal voltage Vc2 in the definite-signal driver path, and the base-to-collector stage junction is always forward biased, so only in the saturation region. It will work.

When the voltage difference Vbc2 between the base terminal and the collector terminal of the second transistor Q2 is smaller than the forward voltage of a general nominal diode, that is, when the input voltage source V1 is small, the base-collector stage junction is not completely conducted. The impedance becomes large. Therefore, the voltage difference Vce2 between the collector stage and the emitter stage is larger than the conduction state of the complete base-collector stage junction. As the input voltage source V1 becomes larger, the base-collector stage junction becomes closer to the conduction state. The collector stage and emitter stage voltage differences Vce2 are reduced.

Here, the emitter terminal voltage Ve2 of the second transistor Q2 is the same as the collector terminal voltage Vc3 of the third transistor Q3, and thus has a value of approximately 0.7 V as a reference voltage and has a full range of input voltages. I think it's almost constant for.

On the contrary, when the base terminal and collector terminal voltage difference Vbc2 of the second transistor Q2 becomes larger than the forward voltage of the nominal diode (that is, when the input voltage source V1 rises above the set voltage), the collector terminal and the emi The terminal voltage difference Vce2 reaches Vce2 (sat) of about 0.1 to 0.2V, which is a low collector-emitter voltage under saturation.

As described above, below the specific input voltage, the voltage difference Vce2 between the collector terminal and the emitter terminal of the second transistor Q2 is set to a voltage higher than Vce2 (sat), and the voltage difference Vce2 is the input voltage source ( In order to be gradually decreased with increasing V1), the ratio of the second resistor R2 and the third resistor R3 must be properly adjusted, and the second resistor R2 is smaller than the third resistor R3. The more you can expand the range.

This is because the smaller the second resistor R2 is, the smaller the distribution voltage Vr2 of the second resistor R2 of the input voltage source V1 is, and the increase rate of the distribution voltage Vr2 with respect to the increase of the input voltage source V1 is obtained. In addition, since the second resistor R2 is smaller, the second resistor R2 becomes smaller, so that it is possible to have a negative driver current capable of compensating for an increase in the negative driver current for a wider input voltage source V1.

The voltage difference Vce2 or collector terminal voltage Vc2 between the collector terminal and the emitter terminal of the second transistor Q2 in the definite arc current driver has a characteristic that the voltage becomes high when the input voltage source V1 has a low voltage. When the input voltage source V1 has a high voltage, it has a characteristic of converging to a low and constant Vce2 (sat), and thus the voltage characteristic directly affects the path current of the first transistor Q1 of the negative current driver. Can give

Meanwhile, since the collector terminal of the second transistor Q2 is directly connected to the base terminal of the first transistor Q1, the negative driver current IC Q1 is represented by Equation 1 below.

Where Vbe1 = Vc3 ≒ 0.7 V

Accordingly, the negative driver current IC Q1 has the characteristic that the voltage difference Vce2 between the collector terminal and the emitter terminal of the second transistor Q2 is reduced in the range of the specific low input voltage source V1, so It acts as a driver.

In addition, the current IC Q2 of the definite code driver path can be obtained as shown in Equation 2 below.

As described above, the voltage difference Vbc2 between the base terminal and the collector terminal of the second transistor Q2 has a low input voltage range (before the voltage difference Vce2 between the collector terminal and the emitter terminal reaches Vce2 (sat)). In the constant current region), the voltage tends to gradually increase from a low voltage according to the input voltage source V1, and if the voltage difference Vce2 becomes higher than the input voltage to reach a saturation voltage, despite the increase of the input voltage source V1, And maintain a constant voltage.

Accordingly, the second transistor Q2 has a negative voltage and a negative current change characteristic opposite to the voltage difference Vce2 or the negative driver current IC Q1 between the collector terminal and the emitter terminal in the constant current region. It can act as a driver.

In conclusion, the synthesized currents of the IC driver Q1 and the IC driver Q2 are constant in the constant current range due to their opposite current characteristics.

Next, FIGS. 6, 7, and 8 are diagrams showing waveform states of input voltage versus current according to resistance value variation of the constant current source circuit shown in FIG. The current waveforms of the current I (V1), the definite driver current (IC (Q2)) and the unsigned driver current (IC (Q1)) are shown.

6 shows an input voltage versus current waveform when the third resistor R3 is changed while the first and second resistors R1 and R2 are fixed. The waveform trends of)) and the negative driver current IC (Q1) are the same as described above, but the slope of each current may vary according to the change in the value of the third resistor R3.

In Fig. 6, the load current I (V1), the definite-signal driver current IC (Q2), and the unsignal driver current IC (Q1) all have a green line marked with the " It appears when R3) is changed to the smallest resistance value, and shows the narrowest constant current region and the sudden slope change, and the larger the resistance value of the third resistor R3, the wider constant current region and the gentle slope change. do.

This is in accordance with the voltage distribution ratios of the second and third resistors R2 and R3 that determine the magnitude and the slope of the collector stage voltage and the current of the second transistor Q2 that play a leading role in determining the overall current characteristics.

That is, as the resistance value of the third resistor R3 increases with respect to the second resistor R2 having a fixed resistance value, a smaller voltage is applied to the second resistor R2 so that the base end of the second transistor Q2 − Since the collector stage junction is completely conducting, the input voltage exiting the constant current region becomes high, so that the constant current region can be easily adjusted to a wider range than the conventional method.

In Fig. 7, the load current I (V1), the negative driver current IC (Q2) and the negative driver current IC (Q1) represent the first resistor R1 and the third resistor R3. Appears when the second resistor R2 is fixed and the second resistor R2 is changed. The waveform changes when the resistance value of the second resistor R2 is changed to the smallest value from the green line on which the "

The change in the current waveform in FIG. 7 is the same as in the variation of the third resistor R3 in FIG. 6, but there is no constant current region when the resistance value of the second resistor R2 is excessively set. The difference is that it can be turned off.

This is related to entering the saturation region of the second transistor Q2. When the resistance value of the second resistor R2 is changed too large, a large voltage is distributed and the collector stage and the emitter are easily subjected to the small change of the input voltage source V1. The voltage difference Vce2 between terminals enters Vce2 (sat) and its slope may change too rapidly. Therefore, it is preferable that the second resistor R2 is sufficiently small compared to the third resistor R3 to allow entry into Vce2 (sat) at a relatively high input voltage.

In Fig. 8, the load current I (V1), the negative driver current IC (Q2) and the negative driver current IC (Q1) fix the second and third resistors R2 and R3. Appears when the first resistor R1 is varied, and corresponds to a waveform change that occurs when the green line marked with the ㅁ marker is the lowest variation in the first resistor R1. As IC (Q1) = Vce2 / R1, as the resistance value of the first resistor R1 decreases, the IC Q1 increases, and the negative compensation slope with respect to the first transistor Q1 on the negative driver side also increases. .

Therefore, the resistance value of the first resistor R1 should also be set to a suitable value to secure a flat area in conjunction with the second resistor R2 and the third resistor R3, and accordingly, the slope of the load current and Not only the constant current range but also its size can be adjusted to the desired level.

Next, FIG. 9 is a view showing an example in which a constant current is widely implemented through a constant current source circuit according to the present invention, in which the first to third resistors R1 to R3 are each adjusted to adjust wide resistances. The result of implementing constant current in the voltage range is shown.

In the present invention, various current amounts can be set, but as shown in FIG. 9, when a desired current is assumed as 20 mA, a constant current within 10% of 20 mA can be generated in the range of 50 V to 400 V input voltage. In particular, it can be seen that a high-performance constant current characteristic with almost no slope exists over a wide range of input voltages from 200V to 400V. That is, in the present invention, it is possible to flexibly adjust the constant current operating voltage range and the rate of change of current thereof by merely adjusting the resistance values of the first to third resistors R1 to R3 in combination. That widens.

On the other hand, the conventional power supply driving circuit needs to improve power efficiency by minimizing reactive power by minimizing reactive power and delivering as much power as possible to the load side as well as supplying stable power. This affects the consumption time of the battery in the case of the application of secondary battery, and also affects the power usage cost in case of using commercial power and increases the efficiency of the device due to the heat generation. It can't be.

Accordingly, the present invention proposes a bias method that can improve the efficiency by using a light emitting diode used in a lighting device based on the basic configuration of the constant current source circuit according to the first embodiment shown in FIG.

That is, FIG. 10 is a diagram showing the configuration of a constant current source circuit in which a bias is formed using a light emitting diode according to a second embodiment of the present invention.

As shown in FIG. 10, the constant current source circuit according to the second embodiment of the present invention includes four first through fourth light emitting devices between the input voltage source V1 and the connection point of the negative driver path and the negative driver path. Diodes D1 to D4 are connected in series.

The current and voltage waveforms of the respective portions of the constant current source circuits for driving the light emitting diodes D1 to D4 represent load currents desired for the series connection of the four light emitting diodes D1 to D4, as shown in FIG. The nominal Vf @ 20mA of each light emitting diode D1 to D4 is about 3.0V, and the evaluation of the increase in efficiency is the voltage of the first transistor Q1 collector at 18mA, corresponding to -10% of 20mA. Vdrop)

In FIG. 11, as a result, the input voltage for stably driving the four light emitting diodes D1 to D4 within 10% of the desired driving current is 15.5V, and the remaining voltage is approximately 3.5 except 12V corresponding to Vf of the light emitting diode. V is applied to the collector terminal of the first transistor Q1, which is a driving circuit, so that a loss of 3.5 V x 18 mA = 63 mW is generated by the first transistor Q1.

In this case, as the input voltage increases, the total Vf of the four series-connected light emitting diodes D1-4 also increases, but the collector voltage Vc of the first transistor Q1 also increases from a small input voltage to reach a desired load current. In this case, the collector voltage Vc also reaches a large value.

The constant current source circuit according to the third embodiment of the present invention shown in FIG. 12 is to solve the problem caused when the collector voltage Vc of the first transistor Q1 reaches a large value. As in the circuit of the second embodiment of the present invention, four light emitting diodes are driven, and the three light emitting diodes D1 to D3 connected in series are connected between the connection point of the negative driver path and the negative driver path and the input voltage source V1. The fourth light emitting diode D4 may be disposed between the definite driver path and the subsignal driver path.

In this case, as shown in FIG. 13, 12.8 V is applied as an input voltage for stably driving the four light emitting diodes D1 to D4 within 10% of a desired driving current, and corresponds to Vf of the light emitting diode. Only about 0.8V other than 12V is applied to the collector terminal of the first transistor Q1, which is a driving circuit, so that a small loss of 0.8V × 18mA = 14.4mW is generated by the first transistor Q1.

The reason why the loss caused by the first transistor Q1 is reduced as described above is that the fourth light emitting diode D4 acts as a bias of the coupler driver stage, so that the current is almost reduced at low Vf due to the characteristics of the diode. This is because the first transistor Q1 does not operate until the Vf of the fourth light emitting diode D4 reaches 3.0 V, which is the nominal forward voltage, so that the collector voltage Vc1 does not increase. Therefore, at the time of securing a stable load current of 18 mA, almost all voltage drops of the unloading driver stage appear at both ends of the fourth light emitting diode D4, which is used for light emission of the fourth light emitting diode D4, not a loss. The power loss of the lower driver stage becomes very small.

On the other hand, as shown in Figs. 12 and 13 by using a method in which the load is placed in front of the input voltage source V1 and the stationary driver / load driver as in the constant current source circuit according to the first embodiment of Fig. By arranging the light emitting diodes as described above, a configuration in which the composite currents from the stationary driver and the coupler driver is a constant current can be made. However, according to the present invention, as shown in FIG. D1) should be placed only between the definite driver path and the definite driver path.

In the fourth embodiment of the present invention, the first light emitting diode D1 is disposed between the decoded driver path and the decoded driver path so that the constant current source can be configured using only the decoded driver current.

The constant current of the negative driver path can be adjusted by adjusting the bias resistor as in the configuration according to the first embodiment of the present invention, and FIG. 15 as a result shows that the constant current is in a wide range in which the current of the first transistor Q1 is wide. It is showing that it is working.

While specific embodiments of the present invention have been described and illustrated above, it will be apparent that the present invention may be embodied in various modifications by those skilled in the art. Such modified embodiments should not be understood individually from the technical spirit or the prospect of the present invention, but should fall within the claims appended to the present invention.

10: Load, Q1 to Q3: Transistor,
R1 to R3: resistance, V1: input voltage,
D1 to D4: Light emitting diodes.

Claims (2)

A constant current source circuit for causing a constant current to be implemented for an input voltage supplied from an input voltage source to a load,
A definite code driver connected in parallel with a negative driver for the input voltage source and the load, and driven to increase the load current against a voltage change from the input voltage source;
A minus driver coupled in parallel with the minus code driver for the input voltage source and the load to reduce the current to compensate for an increase in load current by driving the minus code driver; And
It comprises a reference voltage portion for providing a reference voltage for setting the drive current by the definite code driver and the negative code driver,
The definite driver includes a transistor having a base end coupled between a plurality of distribution resistors, and a plurality of distribution resistors having one end connected in parallel with the load and a base end of the transistor connected between each resistor,
The negative current driver includes a transistor having a base end connected to the definite code driver and a collector end connected in parallel with the load, and a resistor connected between the emitter end and the ground end of the transistor. The method of claim 1,
The load is a constant current source circuit, characterized in that at least one light emitting diode (LED).

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