Constant current circuit of high efficiency

The present inventive concept herein relates to circuits of electronic device, and more particularly, to a constant current circuit of high efficiency.

In general, when a current flows through a bipolar transistor, Joule's heat is produced and an electrical resistance of semiconductor device is reduced by the produced Joule's heat. Accordingly, larger currents flow through a bipolar transistor and more Joule's heat are produced. If this process is repeated, very large currents flow through a bipolar transistor and a power characteristic of bipolar transistor is degraded by the produced Joule's heat.

A bipolar transistor may be destroyed by more Joule's heat and this phenomenon is called a thermal runaway. A solution to prevent that thermal runaway is that a constant current flows through a bipolar transistor or a semiconductor transistor.

A well known constant current circuit essentially includes a comparator comparing a feedback current with a reference current in a load terminal. Since this constant current circuit should include a comparator, the constant current circuit has a complicated structure and is expensive. If large currents flow through the constant current circuit like that, a thermal runaway occurs in a semiconductor device itself. Thus, that constant current circuit is not suitable as a constant current circuit through which relatively large currents flow.

A constant current circuit in which a thermal runaway relatively does not occur and through which relatively large currents can flow is disclosed in K.R Patent No. 10-0964186-00-00, titled “heat control circuit of transistor using a metal-insulator transition (MIT) device and a heat control method” invented by multiple inventors besides Hyuntak kim.

As disclosed in claim 18 of the patent, a constant current circuit through which larger currents can flow may be developed using the MIT device and two electric power transistors.

However, when designing a constant current circuit using a bipolar transistor, a current may be inefficiently wasted. Thus, in a constant current circuit using a bipolar transistor, measures to increase an efficiency of transistor are required.

Embodiments of the inventive concept provide a constant current circuit. The constant current circuit may include a power supply voltage source; a load of which one end is connected to the power supply voltage source; a heat control portion connected between the other end of the load and a ground connection resistor to suppress a thermal runaway phenomenon of semiconductor; a first transistor connected to the other end of the load in parallel to the heat control portion to increase current efficiency of the heat control portion; and a second transistor switched depending on a node voltage of the ground connection resistor to maintain the flow of constant current to the ground connection resistor, the second transistor being connected between the ground connection resistor and the first transistor.

Embodiments of the inventive concept also provide a constant current circuit. The constant current circuit may include a power supply voltage source; a load of which one end is connected to the power supply voltage source; a bipolar power transistor connected between the other end of the load and a ground connection resistor; a first transistor connected to the other end of the load in parallel to the bipolar power transistor to increase current efficiency of the bipolar power transistor; and a second transistor switched depending on a node voltage of the ground connection resistor to maintain the flow of constant current to the ground connection resistor, the second transistor being connected between the ground connection resistor and the first transistor.

Embodiments of the inventive concept also provide a constant current circuit. The constant current circuit may include a power supply voltage source; a load of which one end is connected to the power supply voltage source; a PNP-type heat control transistor of HTR transistor type of which an emitter is connected to the other end of the load and a collector is connected to a ground connection resistor to suppress a thermal runaway phenomenon of semiconductor; a first transistor connected to the other end of the load in parallel to the heat control transistor to increase operation efficiency of the heat control transistor; and a second transistor switched depending on a node voltage of the ground connection resistor to maintain the flow of constant current to the ground connection resistor, the second transistor being connected between the ground connection resistor and the first transistor.

Embodiments of the inventive concept also provide a method of drive a constant current circuit. The method may include applying a power supply voltage source to one end of a load; applying a load voltage in common to a collector of a heat control transistor connected to the other end of the load and a collector of a first transistor connected to the other end of the load in parallel to the heat control transistor; applying a base voltage to a base of the first transistor so that an emitter voltage of the first transistor is applied to a base of the heat control transistor; and making a base current of the heat control transistor flow into a ground using a second transistor whenever a node voltage between an emitter of the heat control transistor and a ground connection resistor is greater than a predetermined voltage.

Since the constant current circuit of the inventive concept is strong against a thermal runaway phenomenon, relatively large constant currents can be flow through the constant current circuit. Also, since a base current of bipolar transistor is minimized or reduced, power consumption of the constant current circuit is minimized or reduced. Accordingly, a constant current circuit of high efficiency may be provided.

Preferred embodiments of the inventive concept will be described below in more detail with reference to the accompanying drawings. The embodiments of the inventive concept may, however, be embodied in different forms and should not be constructed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout.

FIG. 1 is a graph showing a characteristic of a power relative to a temperature of a transistor.

FIG. 2 is a circuit of Hyuntak Transistor (HTR) having MIT (metal-insulator transition).

FIG. 3 is a symbol indicating the HTR of FIG. 2 .

FIG. 4 is a graph showing dependence on an external environment among characteristics of the HTR of FIG. 2 .

FIG. 5 is a circuit illustrating a case of when the load is taken to the HTR of FIG. 2 .

FIG. 6 is a circuit such that a first transistor for amplification is additionally connected to the circuit of FIG. 5 .

FIG. 7 is a circuit such that a second transistor for constant current drive is additionally connected to the circuit of FIG. 5 .

FIG. 8 is a constant current circuit in accordance with some embodiments of the inventive concept.

FIG. 9 is a circuit such that a collector resistance is additionally connected to the circuit of FIG. 8 .

FIG. 10 is an application circuit such that a power LED is connected to the circuit of FIG. 8 as an example of load.

FIG. 11 is a table illustrating power consumption and a drive efficiency measured by the circuit of FIG. 10 .

Embodiments of inventive concepts will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. Like numbers refer to like elements throughout.

It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present.

FIG. 1 is a graph showing a characteristic of a power relative to a temperature of a transistor. In the graph, a horizontal axis represents a temperature and a vertical axis represents a power.

A graph G 2 represents a characteristic of power relative to a temperature of conventional transistor. The graph G 2 shows that if a temperature of transistor becomes high, a characteristic of power is rapidly deteriorated. Thus, as a temperature is high, large currents flow and thereby probability that a thermal runaway occurs is increased. A desirable characteristic of power relative to a temperature of transistor is that a power is constant regardless of a temperature as a graph G 1 represented by a dash line. A constant current circuit having a characteristic like the graph G 1 is required in a lightning control field or a motor control field.

As a prior art that larger currents can flow by reducing a thermal runaway phenomenon, there is a K.R Patent No. 10-0964186-00-00, titled “heat control circuit of transistor using a metal-insulator transition (MIT) device and a heat control method”. In that patent, a circuit of FIG. 2 is disclosed as a part of the description.

Referring to FIG. 2 , a circuit including two bipolar transistors BT 1 and BT 2 and a metal-insulator transition (MIT) device M 1 is illustrated. The MIT device M 1 is connected between a base of the master bipolar transistor BT 1 and a base of the slave bipolar transistor BT 2 . The MIT device M 1 has a characteristic such that it transits to a metal when temperatures of the bipolar transistors BT 1 and BT 2 increase to a critical temperature. Accordingly, since a current flow is reduced or cut off, heat is stopped or reduced and thereby the bipolar transistors BT 1 and BT 2 are cooled. If the bipolar transistors BT 1 and BT 2 are cooled below a specific temperature, the MIT device M 1 transits to an insulator again and thereby a normal power is obtained by the bipolar transistors BT 1 and BT 2 .

In some embodiments of the inventive concept, the circuit of FIG. 2 is named a Hyuntak Transistor (HTR) after the inventor's name. The Hyuntak Transistor (HTR) is represented by a symbol illustrated in FIG. 3 .

FIG. 3 is a symbol indicating the HTR of FIG. 2 . The symbol is a thing briefly indicating the circuit of FIG. 2 .

FIG. 4 is a graph showing dependence on an external environment among characteristics of the HTR of FIG. 2 . A horizontal axis and a vertical axis represent an ambient temperature and a temperature of the HTR transistor respectively. A longitudinal axis represents a collect current. The graph of FIG. 4 shows that if a collector current increases, a heat temperature of the HTR becomes high and a heat characteristic also dependents on an ambient temperature.

FIG. 5 is a circuit illustrating a case of when the load is taken to the HTR of FIG. 2 . Herein, the load is connected between one end of power supply voltage source Vpower and a collector of the HTR transistor. In a simple circuit like FIG. 5 , a base current is great and thereby an efficiency of circuit is low.

If currents flowing an emitter, a base and a collector of the HTR transistor are called I E , I B and I C respectively, I E =I B +I C .

In case of I C =h I B , h represents a gain. Thus, it becomes that I E =(1+h)I B ≈hI B . For example, in case of h=100, I C =1 A, it becomes that I B =1 A/100=0.01 A.

A circuit having a better efficiency may be provided by reducing a base current.

To reduce a base current, a circuit like FIG. 6 is suggested. FIG. 6 is a circuit such that a first transistor 12 for amplification is additionally connected to the circuit of FIG. 5 .

In the circuit like FIG. 6 having a Darlington transistor structure, a base current may be reduced to 1/100th. If assume that a gain h of the first transistor 12 and the HTR transistor 10 is 100 and a collector current of the HTR transistor 10 is 1 A, a base current (I HTR B ) of the HTR transistor 10 becomes 1 A/h=0.01 A. Since I TR1 E =I HTR B , it becomes that I TR1 B =I TR1 E /h=I HTR B /100=0.0001 A. Thus, an efficiency of base current is improved by adopting the first transistor 12 and the circuit may be precisely controlled.

FIG. 7 is a circuit such that a second transistor 14 for constant current drive is additionally connected to the circuit of FIG. 5 . In FIG. 7 , a resistor RE 16 added together with the second transistor 14 is an emitter resistor 16 connected to an emitter of the HTR transistor 10 .

In FIG. 7 , if an emitter voltage V E of the HTR transistor 10 is higher than 0.7V, the second transistor 14 is driven. Accordingly, since a base current of the HTR transistor 10 flows to a ground through the second transistor 14 , a base current of the HTR transistor is reduced. If a base current of the HTR transistor is reduced, an emitter voltage of the HTR transistor becomes lower than 0.7V and thereby the second transistor 14 is not driven. If the second transistor 14 is not driven, an emitter voltage V E of the HTR transistor 10 becomes higher than 0.7V again. As a turn-on/turn-off operations or a current control operation of the second transistor 14 is repeated, a constant current flows through the emitter of the HTR transistor while an emitter voltage V E of the HTR transistor 10 is maintained at 0.7V.

FIG. 8 is a constant current circuit in accordance with some embodiments of the inventive concept.

Referring to FIG. 8 , the constant current circuit includes a power supply voltage source Vpower, a load 2 , a heat control portion 10 and first and second transistors 12 and 14 .

One end of the load 2 is connected to the power supply voltage source Vpower.

The heat control portion 10 is connected between the other end of the load 2 and a ground connection resistor 16 to suppress a thermal runaway phenomenon of semiconductor. The resistor 16 is an emitter resistor RE.

The first transistor 12 is connected to the other end of the load 2 in parallel to the heat control portion 10 to increase a current efficiency of the heat control portion 10 .

The second transistor 14 is connected between the ground connection resistor 16 and the first transistor 12 . The second transistor 14 is switched depending on a node voltage V E of the ground connection resistor 16 to maintain a constant current flow.

The heat control portion 10 may be the HTR transistor including a t least two bipolar transistors and a metal-insulator transition device.

The HTR transistor 10 , as illustrated in FIG. 2 , may include a master bipolar transistor BT 1 of which a collector is connected to the other end of the load 2 and an emitter is connected to the ground connection resistor, a slave bipolar transistor BT 2 of which a collector is connected to a collector of the master bipolar transistor and an emitter is connected to the ground connection resistor and a metal-insulator transition device M 1 of which resistance is changed depending on a temperature, the metal-insulator transition device M 1 being connected between a base of the master bipolar transistor and a base of the slave bipolar transistor.

The first transistor 12 may be an NPN type bipolar transistor of which a collector is connected to the other end of the load 2 and an emitter is connected to a base of the master bipolar transistor BT 1 . The first transistor 12 receives a base voltage being applied through its base.

The second transistor 14 may be an NPN-type bipolar transistor of which a collector is connected to the emitter of the first transistor 12 and an emitter is connected to the ground. The second transistor 14 receives a node voltage V E of the ground connection resistor 16 through its base.

The load 2 may be a load requiring a constant current and may be one of LED, a power LED for lightning and a motor.

The constant current circuit of FIG. 8 may be packaged in one chip package. The constant current circuit except the metal-insulator transition device may be packaged in one chip package and the one chip package may include terminals to connect the metal-insulator transition device at outside of the package.

Because the constant current circuit like FIG. 8 has the advantages described in FIGS. 6 and 7 , it is strong on a thermal runaway phenomenon.

Thus, a relatively great current can flow through the constant current circuit and a base current of bipolar transistor is minimized or reduced and thereby power consumption of the constant current circuit is minimized or reduced. Accordingly, a constant current of higher efficiency is provided.

FIG. 9 is a circuit such that a collector resistance is additionally connected to the circuit of FIG. 8 .

Referring to FIG. 9 , a resistor Rc for current limit 18 is additionally connected between a base of the HTR transistor 10 and a collector of the second transistor 14 . The circuit like FIG. 9 may also have the advantages which the circuit like FIG. 8 has.

In the constant current circuit of FIG. 8 or FIG. 9 , a high efficiency constant current circuit may be provided even in the case of adopting a bipolar power transistor instead of the HTR transistor.

FIG. 10 is an application circuit such that a power LED is connected to the circuit of FIG. 8 as an example of load.

FIG. 11 is a table illustrating power consumption and a drive efficiency measured by the circuit of FIG. 10 .

First, referring to FIG. 10 , a constant current circuit may include a power supply voltage source Vin, a LED array in which a common node is connected to the power supply voltage source Vin and LED is arranged in a matrix shape of a row and column, a heat control portion 10 connected between a common cathode of the LED array and a ground connection resistor R E to suppress a thermal runaway phenomenon of semiconductor, a first transistor TR 1 connected to the common cathode in parallel to the heat control portion to increase a current efficiency of the heat control portion 10 , and a second transistor TR 2 switched depending on a node voltage of the ground connection resistor to maintain the flow of constant current to the ground connection resistor, the second transistor TR 2 being connected between the ground connection resistor and the first transistor.

The number of row and column of the LED array is 11 and 16. That is, the LED array is a load structure in which eleven LEDs are connected in parallel and six LEDs are connected in series.

The transistor used as the heat control portion 10 is the HTR transistor, the first bipolar transistor TR 1 is SN222 and the second bipolar transistor TR 2 is 2N3 904 .

Also, a power of 82 Kw is consumed in R b , a power of 1.3 W is consumed in R e and a rated I F =I CE =550 Ma. When a LED for lightning is produced, a LED applying voltage has a deviation of maximum 0.4V (e.g., 2.8V˜3.2V). Thus, when six LEDs are connected in series, a LED applying voltage has a deviation of maximum 2.4V (i.e., 16.2V˜19.2V). An input voltage of HTR is 20.5V including a HTR emitter resistor voltage. In this case, a voltage difference of maximum 3V is generated and thereby a great heat may occur in the HTR.

However, if using the constant current circuit like FIG. 8 , a deviation of a collector-emitter current I F of the HTR transistor may be reduced to 9 mA and a heat of the device may be greatly reduced as illustrated in FIG. 11 .

In general, in a constant current circuit, a deviation of 9 mA with respect to 550 mA is considered to be a good efficiency. This is because an allowable deviation in a well known constant current circuit is 40 mA or so. Referring to the table of FIG. 11 , in the constant current circuit of FIG. 10 , heat efficiency is about 82.0%˜90.7%, power consumption of constant current is 1.07 W˜2.11 W. The constant current circuit of FIG. 10 has a superior characteristic compared with a general constant current circuit.

Using the HTR transistor and auxiliary transistors, the high efficient constant current circuit like FIG. 10 may be simply designed without adopting a comparator.

According to some embodiments of the inventive concept, since the HTR transistor is used as a heat control portion, even if large currents flow, it is difficult for a thermal runaway to occur. Also, a base current is minimized by adopting the first bipolar transistor and thereby a power waste is greatly reduced. Thus, high efficiency of the HTR transistor is accomplished. An operation of the constant current circuit is smoothly performed by adopting the second bipolar transistor.

The above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true spirit and scope of the inventive concept. Thus, to the maximum extent allowed by law, the scope of the inventive concept is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.