JP2008148434A - Semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device which lights LED according to the dispersion of forward voltage, without causing the output voltage of a DC-DC converter to increase. <P>SOLUTION: The device has a DC power source which generates DC voltage, an inductor with one end connected to the DC power source and other end connected to an output terminal to output drive voltage with respect to an LED, a capacitor inserted between the other end of the inductor and an earth point, and a switching element connected to the other end of the inductor, and supplies a pulse-shaped drive voltage by the resonance between the inductor and the capacitor to the LED. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor device that performs lighting / flashing control on a light emitting diode at a predetermined cycle using a DC input power supply.

Conventionally, in order to indicate a power supply state, a circuit that lights and blinks an LED (light emitting diode) at a constant cycle is used (for example, see Patent Document 1).
Here, in a conventional circuit for lighting a light emitting diode using a DC input power supply, a detection resistor is added to monitor the forward current flowing through the light emitting diode, and the voltage between the terminals of the resistor is switched. A method is used in which the luminance of light emission at the time of lighting is kept constant by feeding back a constant current to the LED by feedback by an output voltage control means such as a regulator.

As the circuit, for example, as shown in FIG. 3, a DC-DC converter circuit of a step-up type (or step-down type) composed of an inductor 203, a switching means 206 and a control circuit 207 from a DC voltage inputted from a power source 201 By using the pulse obtained as a result of rectification by the diode 204, a driving current is supplied to the LED in the H level period to perform lighting control.
That is, a voltage necessary for flowing a forward current to the LED is generated and output by a DC-DC converter, the output signal is given to the LED, and the LED is caused to emit light by passing the forward current to the LED.

At that time, as shown in FIG. 3, in order to keep the forward current of the LED constant, a constant current circuit that performs current control using a current detection resistor 208 connected in series to the LED is used. ing.
JP 05-64420 A

However, in the circuit shown in FIG. 1, extra power loss occurs due to the current flowing through the current detection resistor 208.
In addition, when the LED is lit at a high luminance, this power loss increases as the luminance increases because a larger forward current flows.
The forward voltage (VF) varies depending on the type of LED and individual differences. Therefore, in order to absorb this variation in forward voltage, it is necessary to set the output voltage of the DC-DC converter larger.
As a result, when the forward voltage varies to a smaller value, the forward current increases and the loss increases.

  The present invention has been made in view of such circumstances, and provides a semiconductor device that performs LED lighting driving to cope with variations in forward voltage without increasing the output voltage of the DC-DC converter. With the goal.

  The semiconductor device of the present invention is a semiconductor device that generates and supplies a pulse-shaped voltage signal that blinks an LED with a DC voltage, and is connected to a DC power source that generates a DC voltage, one end connected to the DC power source, and the other end. An inductor connected to an output terminal for outputting a drive voltage to the LED, a capacitor interposed between the other end of the inductor and a ground point, and a switching element connected to the other end of the inductor, And a pulse-shaped drive voltage is supplied to the LED by resonance between the inductor and the capacitor.

  In the semiconductor device of the present invention, when an LED is connected, a cathode is connected to the output terminal, an anode is connected to a ground point, and the LED is turned on when the pulsed drive voltage becomes the forward voltage of the LED. Features.

  The semiconductor device of the present invention includes a diode having an anode connected to the output terminal, a first resistor and a second resistor connected in series between the cathode of the diode and a ground point, and the first resistor. And a controller that performs on / off control of the switching element by a potential at a connection point of the first and second resistors.

  As described above, according to the present invention, on / off control of the current flowing from the coil to the ground point is performed by the switching element with respect to the DC voltage input from the DC power supply, and the electric energy accumulated in the coil By the resonance operation by the resonance circuit of the capacitor and the capacitor, the voltage supplied to the cathode of the LED is increased and decreased in a pulsed manner, and a forward current is supplied to the LED to control lighting so that a resistor connected in series with the LED can be obtained. When it becomes unnecessary and the luminance is increased, the loss of unnecessary power can be reduced as compared with the conventional example.

  Further, according to the present invention, the forward voltage of the LED varies due to individual differences or the like. However, as described above, since the resistor is not inserted in series with the LED, when the LED is used for an LED having a small forward voltage. In addition, even if a large amount of forward current flows, an effect of suppressing an increase in power loss can be obtained.

A semiconductor device according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of the semiconductor device according to the embodiment.
In this figure, the DC power source 101 has a positive electrode (+ side) connected to one end of an inductance (coil) 110 and a negative electrode (− side) connected to a ground point (GND: ground).
The other end of the inductor 110 is connected to one end of the capacitor 113 at the connection point A.
The other end of the capacitor 113 is connected to the ground point, that is, the capacitor 113 is connected in series with the inductor 110 between the positive electrode of the DC power supply 101 and the ground point.

  The switching element 111 is turned on by a control signal (control pulse) from the control circuit unit 120, for example, an H level pulse, and causes a current to flow from the DC power supply 101 to the ground via the inductor 110, thereby Accumulate energy (charge). The switching element 111 is turned off when a control signal is input at the L level from the control circuit unit 120, and no current flows from the inductor 110 to the ground point.

Under the control of the control circuit unit 120 described above, the resonance operation by the inductor 110 and the capacitor 113 occurs due to the electrical energy accumulated in the inductor 110.
The LED 112 has a cathode connected to a point A (output terminal) and the other end connected to a ground point.
The diode 102 has an anode connected to the point A. The capacitor 105 is inserted between the cathode of the diode 102 and the ground point.
In this configuration, the switching element 111, the capacitor 113, the inductor 110, the diode 102, and the control circuit unit 120 form a DC-DC converter.

The resistor 103 has one end connected to the cathode of the diode 102 and the other end connected to one end of the resistor 104 at point B.
The other end of the resistor 104 is connected to the ground point, that is, connected in series with the resistor 103 between the cathode of the diode 102 and the ground point.
The control circuit unit 120 changes the duty of a control pulse having a constant period to be output to the switching element 111 by the voltage VB at the connection point B as control for causing the above-described resonance operation by the inductor 110 and the capacitor 113. 111 on / off control is performed. Here, when the control circuit unit 120 detects that the voltage VB has decreased with respect to the preset setting voltage VSET, the control circuit unit 120 extends the H level period and outputs the control pulse at the L level period in the preset period. , And when it is detected that the voltage VB has increased with respect to the preset set voltage VSET, the H level period is shortened and the L level period is extended.

Next, the operation of the semiconductor device of this embodiment will be described with reference to FIGS. FIG. 2 is a waveform diagram showing an operation example of the semiconductor device of this embodiment.
At time t <b> 1, the control circuit unit 120 outputs an H level control pulse to the switching element 111.
As a result, the switching element 111 is turned on, and the inductor 110 accumulates electric energy (charge) corresponding to the period during which this current flows when a current flows from the positive electrode of the DC power supply 101 to the ground point.

At time t2, the control circuit unit 120 changes the control pulse to the L level, and turns off the switching element 111. At this time, the current IL flowing through the inductor 110 becomes the maximum current ILpeak flowing through the inductor 110.
The resonance operation is performed in the inductor 110 and the capacitor 113 between the time t2 and the time t4 by the electric energy accumulated in the inductor 110.
As shown in FIG. 2, from time t2 to time t3, a current flows through the inductor 110 due to the accumulated electric energy.

Then, as the electric energy is transferred to the capacitor 113, the current flowing through the inductor 110 gradually decreases. When the electric energy becomes zero at time t3, the current IL is also zero, and the voltage value at the point A becomes the maximum value VH. .
Next, due to the resonance operation, a negative current gradually flows through the inductor 110 due to the electrical energy accumulated in the capacitor 113, and this current value increases as an absolute value.
At this time, the voltage decreases until the current value (absolute value) is the same as the negative current value (−ILpeak) of the maximum current ILpeak when the switching element 111 is turned off.

As described above, at time t3, the current IL flowing through the inductor 110 becomes “0”, the voltage value at the point A becomes the maximum value VH, and at time t4, the current IL becomes −ILpeak. Here, the maximum value VH is obtained by the following equation.
VH = 2π × f × L × ILpeak + Vin
In this equation, f is a resonance frequency in the inductor 110 and the capacitor 113, L is an inductance of the inductor 110, and Vin is an output voltage value of the DC power supply 101.

At this time t4, the maximum current ILpeak is reached, and when the voltage difference between the point A, that is, the voltage generated at the cathode of the LED 112 and the ground point exceeds the forward voltage of the LED 112, the forward current flows through the LED 112 and the LED 112 is lit. .
At this time, the voltage difference between the voltage at the point A and the ground point is a voltage that is substantially close to the forward voltage (VF) of the LED 112.
At time t <b> 5, the control circuit unit 120 sets the control pulse to the H level for the switching element 111.

As a result, a current to the ground point is forced to flow through the inductor 110, the resonance operation of the inductor 110 and the capacitor 113 is stopped, the voltage at the point A becomes “0”, which is lower than the forward voltage of the LED 112, and the LED 112 Turns off.
Thereafter, the processing from time t1 to time t5 is repeated, and a drive voltage having a pulse shape (a pulse having a time width from time t4 to time t5) is applied to the LED 112. The lighting time of the LED 112 is proportional to the amount of electrical energy (charge) accumulated in the capacitor 113.

In the processing described above, the control circuit unit 120 compares the voltage value at the point B with the set voltage VSET, thereby controlling the width of the control pulse for the switching element 111 (H level time, that is, output of the control pulse). (Duty in a certain period) is changed.
The voltage at the point B is a voltage obtained by dividing the voltage value VK obtained by subtracting the forward voltage of the diode 102 from the maximum voltage value VH of the voltage waveform at the point A input via the diode 102 by the resistor 103 and the resistor 104. Value.
Therefore, since the resistance values of the resistors 103 and 104 constituting the voltage dividing circuit that outputs VB as a feedback voltage to the control circuit unit 120 are not connected in series with the diode 102, The resistance can be higher than the resistance 207 in the example. That is, the power consumption of the voltage dividing circuit that detects the voltage supplied to the LED 112 can be suppressed as compared with the configuration of the conventional example.

Here, also at point A, a negative voltage VHM similar to the maximum value VH at time t3 is generated after a predetermined time from time t4 if no current flows through the LED 112 due to the resonance operation by the inductor 110 and the capacitor 113.
That is, the voltage at the cathode of the diode 102 becomes a voltage value VK obtained by subtracting the forward voltage of the diode 102 from the maximum value VH, and the value of the negative voltage VHM can be estimated by detecting this voltage VK.

Therefore, in the control circuit unit 120, the set voltage VSET is set so that the forward voltage VF of the LED 112 is exceeded and the voltage VK corresponding to the set brightness is equal to or higher than the voltage divided by the resistors 103 and 104. Keep it.
Thereby, the control circuit unit 120 performs control to give a control pulse having a necessary H-level pulse width to the switching element 111 so that the voltage at the point A turns on the LED 112 at time t4. Therefore, the adjustment of the luminance emitted by the LED 112 can be easily adjusted by adjusting the set voltage VSET.

  With the configuration described above, the semiconductor device according to the present embodiment is configured such that the voltage value detected by the control circuit unit 120 is not connected in series to the LED 112 as in the prior art, so that extra power consumption is reduced and set. By adjusting the brightness by adjusting the value VSET, it is possible to easily absorb variations in the forward voltage VF of the LED 112.

It is a conceptual diagram which shows the structural example of the circuit of the semiconductor device which performs lighting control of LED by one Embodiment of this invention. FIG. 2 is a waveform diagram for explaining the operation of the semiconductor device of FIG. 1. It is a conceptual diagram which shows the structural example of the circuit of the semiconductor device which performs lighting control of the conventional LED.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... DC power supply 102 ... Diode 103, 104 ... Resistance 105, 113 ... Capacitor 110 ... Inductor 111 ... Switching element 112 ... LED
120 ... Control circuit section

Claims (3)

A semiconductor device that generates and supplies a pulse-shaped voltage signal that blinks an LED with a DC voltage,
A DC power source for generating a DC voltage;
An inductor having one end connected to a DC power source and the other end connected to an output terminal that outputs a drive voltage to the LED;
A capacitor interposed between the other end of the inductor and a ground point;
A switching element connected to the other end of the inductor,
A semiconductor device characterized in that a pulse-shaped drive voltage is supplied to an LED by resonance between the inductor and the capacitor. When connecting the LED, connect the cathode to the output terminal, the anode to the ground point,
2. The semiconductor device according to claim 1, wherein the semiconductor device is turned on when the pulsed drive voltage becomes a forward voltage of the LED. A diode having an anode connected to the output terminal;
A first resistor and a second resistor interposed between the cathode and ground of the diode and connected in series;
The semiconductor device according to claim 1, further comprising: a control unit that performs on / off control of a switching element by a potential at a connection point of the first and second resistors.

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