KR100802918B1 - Power saving DC-DC Converter for OLED Driving circuit - Google Patents

Abstract

The present invention relates to a DC-DC converter having a power saving structure of an OLED driving circuit for minimizing power loss by improving the response of an inductor current according to a load current variation of a DC-DC converter applied to a passive matrix organic EL panel. in the DC-DC converter of the OLED drive circuit, a reference voltage generator for the CCM of using the voltage (V _i) inputted from the outside and the battery voltage (Vbat) generating a reference voltage for the CCM; A DCM reference voltage generator for generating a reference voltage for DCM by using the battery voltage Vbat and a voltage V _F input from the outside; The output voltage Vccm_en is generated by using the voltage V _F distributed by the load R1 and R2 and the voltage V _i sensed by the inductor current to generate the CCM reference voltage generator or DCM reference voltage generator. A load recognition unit for predicting a switching time point between the CCM and the DCM and outputting a switch switching signal; A comparator for comparing the CCM reference voltage or the DCM reference voltage output from the CCM reference voltage generator or the DCM reference voltage generator with a ramp waveform and outputting a reset signal; A switch for selectively connecting an output terminal of the CCM reference voltage generator or the DCM reference voltage generator and an input terminal of the comparator in response to a switch switching signal input from the load recognition unit; A delay circuit unit connected to a reset terminal (R), reset in response to a reset signal of the comparator, and outputting a transistor driving signal in response to a pulse clock input to a set (S) terminal; A power driving transistor driven by a transistor driving signal output from the delay circuit unit; And an inductor L for converting the battery voltage Vbat into a current and supplying the current to the organic EL panel when the power driving transistor Q is driven.

Passive, Matrix, Organic EL, DC-DC Converters, Power Saving

Description

DC-DC converter having a power saving structure of an OLED driving circuit {Power saving DC-DC Converter for OLED Driving circuit}

1 is a view showing a DC-DC converter of the OLED driving circuit according to the prior art,

2 shows a typical CCM waveform and a DCM waveform;

3 is a waveform diagram for explaining the response speed of the inductor current when switching the CCM-DCM in the conventional DC-DC converter,

4 is a waveform diagram showing an inductor current in a conventional DC-DC converter,

5 illustrates a DC-DC converter having a power saving structure of an OLED driving circuit according to the present invention;

6 is a diagram illustrating a configuration of a load recognition unit applied to FIG. 5;

7 is a waveform diagram illustrating a response speed of an inductor current when switching a CCM-DCM in a DC-DC converter according to the present invention;

8 is a waveform diagram illustrating an inductor current in the DC-DC converter according to the present invention.

*** Explanation of main parts of drawing ***

20: CCM reference voltage generator

22: DCM reference voltage generator

24: Load estimator

26: comparator

28: flip flop

The present invention relates to a power saving structure DC-DC converter of an OLED driving circuit.

More specifically, the present invention relates to a power-saving structure DC-DC converter of an OLED driving circuit for minimizing power loss by improving the response of an inductor current according to a load current variation of a DC-DC converter applied to a passive matrix organic EL panel.

The power source of the portable device is mainly a secondary battery such as lithium ion, nickel bath, etc. Each electronic component of the portable device uses a DC-DC converter, etc. to power up or down to a desired voltage from the battery. DC-DC converters applied to the above devices are mainly manufactured according to constant load current characteristics.

In case of the LCD provided in the existing portable device, since the backlight is always turned on during operation, the current consumption is always constant, so there is no problem even when using a conventional DC-DC converter.

However, in the case of the passive matrix organic EL, the current consumption varies rapidly depending on the type of image of the screen, and thus, when the existing DC-DC converter is used, power conversion efficiency is lowered.

1 is a view showing an example of a DC-DC converter of the PWM (pulse width modulation method) of the conventional DC-DC converter.

As shown in FIG. 1, a reference voltage generator 10 receiving a voltage divided by a battery voltage Vbat and resistors R1 and R2 to generate a reference voltage, and the reference voltage generator 10. A comparator 12 for comparing the reference voltage outputted from the ramp wave signal and outputting a reset signal, and an R / S flip-flop 14 for outputting a transistor Q driving signal in response to the reset signal of the comparator 12. And a transistor Q for driving the inductor current to be supplied to the organic EL panel in response to the driving signal of the R / S flip-flop 14.

The comparator 12 performs a function of a filter, and the R / S flip-flop 14 performs a function of a delay circuit.

The diode is a component such that only a predetermined voltage is supplied to the organic EL panel.

The current supplied to the inductor L during voltage conversion by the DC-DC converter configured as described above has a triangular waveform as shown in FIG. 2.

At this time, the current flowing through the inductor (L) has a small amount of current consumption so that the inductor current flows discontinuously in the form of DCM (Discrete Conduction Mode) and the inductor (L) is a relatively large triangular waveform continuously, The case is divided into CCM (Continuous Conduction Mode).

As described above, the method of generating the value output from the reference voltage generator 10 of FIG.

Therefore, in a circuit having a consumption current structure that is converted from DCM to CCM, there is a problem that the supply current of the inductor L does not react quickly as the load current increases or decreases, as shown in FIG. 3.

In addition, when the load current changes rapidly as shown in FIG. 4 due to the slow reaction as described above, the inductor current maintains a substantially constant value, so that the inductor current flows excessively even in a section in which the load current is reduced. There is a problem that a factor of loss occurs.

The present invention has been made to solve the above problems of the prior art, an object of the present invention is to improve the power loss by improving the response of the inductor current according to the load current variation of the DC-DC converter applied to the passive matrix organic EL panel To provide a DC-DC converter having a power saving structure of the OLED driving circuit to minimize the.

The embodiment of the present invention proposed to solve the above technical problem, in the DC-DC converter of the OLED driving circuit, the reference voltage for CCM using the battery voltage (Vbat) and the voltage (V _i ) input from the outside CCM reference voltage generator for generating a; A DCM reference voltage generator for generating a reference voltage for DCM by using the battery voltage Vbat and a voltage V _F input from the outside; The output voltage Vccm_en is generated by using the voltage V _F distributed by the load R1 and R2 and the voltage V _i sensed by the inductor current to generate the CCM reference voltage generator or DCM reference voltage generator. A load recognition unit for predicting a switching time point between the CCM and the DCM and outputting a switch switching signal; A comparator for comparing the CCM reference voltage or the DCM reference voltage output from the CCM reference voltage generator or the DCM reference voltage generator with a ramp waveform and outputting a reset signal; A switch for selectively connecting an output terminal of the CCM reference voltage generator or the DCM reference voltage generator and an input terminal of the comparator in response to a switch switching signal input from the load recognition unit; A delay circuit unit connected to a reset terminal (R), reset in response to a reset signal of the comparator, and outputting a transistor driving signal in response to a pulse clock input to a set (S) terminal; A power driving transistor driven by a transistor driving signal output from the delay circuit unit; And an inductor L for converting the battery voltage Vbat into a current and supplying the current to the organic EL panel when the power driving transistor Q is driven.

Referring to the accompanying drawings, a DC-DC converter having a power saving structure of an OLED driving circuit configured as described above is as follows.

As shown in FIG. 5, a CCM reference voltage generator 20 generating a CCM reference voltage in response to a battery voltage Vbat and an output voltage V _{CCM_WAVE} of a load recognition unit 24 to be described later; The DCM reference voltage generator 22 generating the reference voltage for DCM in response to the battery voltage Vbat and the output voltage V _{DCM_WAVE} of the load recognition unit 24 described below, and the loads R1 and R2. The output voltage V _{CCM_WAVE} and the output voltage V _{DCM_WAVE} are generated by using the divided voltage V _F and the sensing voltage V _i sensed by the inductor current to generate the CCM reference voltage generator 20 and Outputs to the reference voltage generator 22 for DCM and predicts the transition time between the CCM and DCM. The predicted value is used to select one of the reference voltage generator 20 for the CCM and the reference voltage generator 22 for the DCM. A load recognition unit 24 for outputting a switch switching signal V _{CCM_EN} so that the CCM reference The voltage generator 20 is provided between the output terminal of the DCM reference voltage generator 22 and the input terminal of the comparator 26 so as to respond to the switch switching signal output from the load recognition unit 24. 20) or the switch 25 for selectively connecting the DCM reference voltage generator 22 to the comparator 26, and the CCM reference voltage generator 20 or the DCM reference voltage generator 22 A comparator 26 for comparing the output CCM reference voltage or DCM reference voltage with a ramp waveform and outputting a reset signal, and the comparator 26 is connected to a reset terminal to reset in response to the reset signal of the comparator 26. And an R / S flip-flop 28 for outputting a transistor driving signal in response to a pulse clock input to the set terminal, and a power driving transistor for driving the transistor driving signal output from the R / S flip-flop 28 ( Q) and above When the power driving transistor Q is driven, the battery voltage Vbat is configured to convert the battery voltage into a current and supply it to the organic EL panel.

The load estimator 24, the load estimator 24, may filter first and second low pass filters Low− to first filter the input sensing voltage Vi and the distribution voltage Vf as shown in FIG. 6. pass filter) (1) (2), a subtraction circuit (3) for subtracting the first filtered signal respectively through the first and second low pass filters (1) and (2), and the subtracted result value. A signal that is driven by the output values of the first and second comparators 4 and 5 having hysteresis characteristics received as an input and the output values of the first and second comparators 4 and 5 to recognize the CCM mode (V). _Gain is controlled by the RS F / F 6 outputting _{CCM_EN} ) and the signal V _{CCM_EN} of the RS F / F 6 to control the CCM reference voltage generator 20 and the DCM reference voltage. consists of a generator 22, the signal (V _{CCM_WAVE)} (V _{DCM_WAV)} gain amplifier (amp gain, 7) for outputting the input to the.

In this case, the first comparator 4 receives the result value as an input of the negative terminal, and the second comparator 5 receives the result value as an input to the positive terminal. The comparators 4 and 5 are connected to each other.

Here, the reference voltage REF_A of the first comparator 4 is the upper limit of the DCM mode, the reference voltage REF_B of the second comparator 5 is the lower limit of the CCM mode, and the reference voltages are shown in the drawing. Although not shown, a resistor divider is used and can be simply generated.

The R / S flip-flop 28 performs the function of a delay circuit as in the prior art.

When the DC-DC converter is configured as described above, as shown in FIG. 7, the response of the inductor current is increased when the CCM-DCM is switched.

Referring to the DC-DC converter having a power saving structure of the OLED driving circuit configured as described above are as follows.

As shown in FIG. 5, the load recognition unit 24 is connected between the power driving transistor Q and the resistor R3 to receive a voltage Vi sensing the inductor L current. The voltage VF divided by the loads R1 and R2 is input to predict a transition time between the DCM and the CCM.

The load recognizer 24 outputs the voltage Vccm_en generated by using the voltage Vi and VF to the CCM reference voltage generator 20 or the DCM reference voltage generator 22 according to the prediction result. On the other hand, the switch 25 outputs a switch switching signal to the switch 25 so that the switch 25 can select the CCM reference voltage generator 20 or the DCM reference voltage generator 22.

If it is determined that the load recognition unit 24 is the CCM switching time point, the voltage Vccm_en of the load recognition unit 24 is input to the CCM reference voltage generator 20, and the CCM reference voltage generator 20 is applied. Receives the voltage Vccm_en and the battery voltage Vbat, generates a CCM reference voltage, and outputs the reference voltage to the comparator 26. At this time, the switch 25 is switched so that the output terminal of the CCM reference voltage generator 20 and the input terminal of the comparator 26 are connected in response to the switch switching signal of the load recognition unit 24.

That is, the load estimator 24, the load estimator 24, may input the first and second low-pass filters 1 and 2 to the input voltage Vi and the voltage Vf as shown in FIG. 6. (2) are respectively filtered first, and the filtered signal is subtracted again by the subtraction circuit (3).

The subtracted result is used as an input for the first and second comparators 4 and 5 having hysteresis characteristics. In this case, the first comparator 4 receives the result value as an input of the negative terminal, and the second comparator 5 receives the result value as an input to the positive terminal. The first and second comparators 4 and 5 are connected to each other.

Here, the reference voltage REF_A of the first comparator 4 is the upper limit of the DCM mode, the reference voltage REF_B of the second comparator 5 is the lower limit of the CCM mode, and the reference voltages are shown in the drawing. Although not shown, a resistor divider is used and can be simply generated.

The output values of the first and second comparators 4 and 5 output a signal V _{CCM_EN} for driving the RS F / F 6 to recognize the CCM mode, and gain amplifier 7. By controlling the gain (Gain) of the output signal V _{CCM_WAVE} (V _{DCM_WAV} ) of the CCM reference voltage generator 20 and the DCM reference voltage generator 22.

Then, the comparator 26 compares the input CCM reference voltage with a ramp wave and outputs a high or low level reset signal to the reset terminal of the R / S flip-flop 28.

The R / S flip-flop 28 receives a pulse clock through the set (S) terminal.

The gate of the power driving transistor Q is driven.

As described above, by separately providing the CCM reference voltage generator 20 and the DCM reference voltage generator 22 in the DC-DC converter, the inductor current reacts quickly when switching the CCM-DCM as shown in FIG. 7. You lose.

Accordingly, since the inductor current responds quickly even when the load current changes periodically rapidly as shown in FIG. 8, the inductor current exhibits a faster response than the inductor current response, and the current consumption is an integral value of the inductor current. The loss is reduced in the case of conventional DC-DC converters.

The invention is applicable to passive matrix driver ICs for OLEDs and DCDC converters for OLEDs.

The present invention is not limited to the above embodiments, and various modifications and changes can be made by those skilled in the art, which are included in the spirit and scope of the present invention included in the appended claims.

According to the present invention having the above-described configuration, operation and preferred embodiment, the organic EL panel is driven by predicting the CCM and DCM switching time and generating a CCM or DCM reference voltage at the corresponding time. There is an effect to improve the efficiency.

In addition, the present invention improves the power efficiency when driving the organic EL panel, thereby improving the characteristics of the portable device to which the organic EL panel is applied, and has an effect of extending the life.

In addition, the present invention can improve the power efficiency has the effect of expanding the portable product coverage of the passive matrix OLED panel.

Claims (4)

In the DC-DC converter of the OLED drive circuit, A reference voltage generator for the CCM of using the battery voltage (Vbat) and a voltage (V _i) sensing the inductor current to be input from an external generating a reference voltage for the CCM; A DCM reference voltage generator configured to generate a reference voltage for DCM using the voltage V _F divided by the battery voltage Vbat and the load R1 and R2 input from the outside; The output voltage Vccm_en is generated by using the voltage V _F distributed by the load R1 and R2 and the voltage V _i sensed by the inductor current to generate the CCM reference voltage generator or DCM reference voltage generator. A load recognition unit for predicting a switching time point between the CCM and the DCM and outputting a switch switching signal; A comparator for comparing the CCM reference voltage or the DCM reference voltage output from the CCM reference voltage generator or the DCM reference voltage generator with a ramp waveform and outputting a reset signal; A switch for selectively connecting an output terminal of the CCM reference voltage generator or the DCM reference voltage generator and an input terminal of the comparator in response to a switch switching signal input from the load recognition unit; A delay circuit unit connected to a reset terminal (R), reset in response to a reset signal of the comparator, and outputting a transistor driving signal in response to a pulse clock input to a set (S) terminal; A power driving transistor driven by a transistor driving signal output from the delay circuit unit; And When the power driving transistor Q is driven, the inductor L converting the battery voltage Vbat into a current and supplying the current to the organic EL panel. DC-DC converter having a power saving structure of the OLED drive circuit, characterized in that consisting of. The method of claim 1, wherein the load recognition unit First and second low-pass filters configured to first filter the voltage Vi sensed by the input inductor current and the voltage V _F distributed by the loads R1 and R2; A subtraction circuit for subtracting the first filtered signal through the first and second low pass filters, respectively; First and second comparators having hysteresis characteristics receiving the subtracted result as an input; RS F / F which is driven by the output values of the first and second comparators and outputs a signal (V _{CCM_EN} ) for recognizing CCM mode; The RS F / F of the signal (V _{CCM_EN)} gain (Gain) by this controlled the CCM reference voltage generator and the gain amplifier (Gain for the output DCM reference voltage generator signal (V _{CCM_WAVE)} (V _{DCM_WAV)} input to Amp), DC-DC converter having a power saving structure of the OLED drive circuit, characterized in that consisting of. The method of claim 2, wherein the resultant value of the subtraction circuit is A DC-DC converter having a power saving structure of an OLED driving circuit, which is input to the (-) terminal of the first comparator and to the (+) terminal of the second comparator. The method of claim 2, The reference voltage REF_A of the first comparator is an upper limit value of DCM mode, and the reference voltage REF_B of the second comparator is a lower limit value of CCM mode. DC converter.

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