JP7103919B2 - OLED drive - Google Patents

Description

The present invention relates to an OLED driving device that drives an OLED used for inspection OLED lighting.

Applications of LED (Light Emitting Diode) lighting and OLED (Organic Light Emitting Diode) lighting include lighting of spaces such as living rooms. As a technique related to this application, for example, there is a dimming control device disclosed in Patent Document 1. This dimming control device corresponds to a switching element electrically connected between a light source circuit having a semiconductor light emitting element and a DC power supply, and a plurality of types of dimming signals for setting the dimming level of the light source circuit. A signal selection circuit for selecting a dimming signal to be used for dimming control from a plurality of signal input terminals provided in the above, and two or more dimming signals input to the plurality of signal input terminals, and the signal selection circuit. By switching the switching element at a duty ratio corresponding to the dimming level represented by the dimming signal selected by, the DC voltage output from the DC power supply is converted into a rectangular wave voltage and output to the light source circuit. The dimming signal includes a control circuit, and the dimming signal is a signal that sets the dimming level of the light source circuit to the maximum when the magnitude of the dimming signal is the minimum. It is configured to select a dimming signal having a smaller dimming level from the two or more dimming signals.

Other uses of LED lighting and OLED lighting include product inspection lighting. The products here are, for example, semiconductors, electronic / electrical parts, FPD-related, transport / robots, iron / metal parts, paper / film / glass, automobiles, rubber / resin / plastic products, foods, chemicals, containers, packaging, etc. It is a medical device. For example, when inspecting these using machine vision, LED lighting or OLED lighting may be used as the lighting.

The inspection LED lighting has been put into practical use as compared with the inspection OLED lighting. For example, an LED drive device having a strobe light emission (flash light emission) function has already been put into practical use. Strobe light emission is a method in which a light source (here, LED) is intermittently emitted with a current equal to or lower than the rated current (rated current value). The rated current is a current value guaranteed by the manufacturer of the lighting panel (here, the LED panel) so that the lighting panel can be used stably.

Japanese Unexamined Patent Publication No. 2017-45575

The present inventor has studied the practical application of an OLED drive device that causes an OLED to emit a strobe light. As a result of the examination, the following issues were found.

In order to light (emit) the OLED, it is necessary to set the voltage of the OLED to be equal to or higher than the forward voltage. Unlike LEDs, OLEDs have parasitic capacitance. The voltage of the OLED does not reach the forward voltage unless the charge accumulation in the parasitic capacitance of the OLED is completed. The larger the parasitic capacitance, the longer the time required for charge accumulation. Since OLED is surface emitting, it has a relatively large parasitic capacitance. Therefore, the start of lighting (start of light emission) of the OLED is delayed. In machine vision, a large number of inspection targets may be inspected at high speed, and in this case, the inspection target passes through the shooting range of the camera at high speed. Therefore, the shutter speed of the camera is set high. If the delay in starting lighting of the OLED that emits strobe light is large, the difference between the timing at which the OLED starts lighting and the timing of the shutter of the camera becomes large, and it becomes difficult to use this lighting for machine vision lighting.

An object of the present invention is to provide an OLED driving device capable of reducing a delay in starting light emission (lighting) of an OLED when the OLED for inspection lighting is made to emit a strobe light.

The OLED drive device according to the present invention is an OLED drive device that causes an OLED for inspection lighting to emit a strobe light, and is calculated in advance by performing a first control that causes the OLED to emit a strobe light using a first constant current. Under the accumulation period, a control unit that performs a second control of accumulating charges in the parasitic capacitance of the OLED by using a second constant current larger than the first constant current before the first control. And a period calculation unit that calculates the accumulation period in advance.

The forward voltage of the OLED changes over time and rises. If the storage period is fixed, it is not possible to respond to changes over time, and the effect of reducing the delay in starting lighting of the OLED is reduced in the strobe light emission of the OLED for inspection lighting. Since the OLED drive device according to the present invention includes a period calculation unit that calculates the storage period in advance, it is possible to deal with changes in the forward voltage of the OLED over time. Therefore, according to the OLED driving device according to the present invention, it is possible to reduce the delay in starting lighting of the OLED when the OLED for inspection lighting is made to emit a strobe light.

In the above configuration
A voltage source that can be connected to one electrode of the OLED and supplies a drive voltage to the OLED.
When the OLED is turned on, a third constant current which is smaller than the first constant current and the OLED can emit light is passed, and when the OLED is turned off, the third constant current is not passed. 3 constant current switching elements and
The third constant current switching element is further provided with a voltage measuring unit capable of measuring the voltage Vi3 applied to the other electrode of the OLED by switching from the off state to the on state.
In the mode for calculating the storage period, the voltage measuring unit switches the third constant current switching element from the off state to the on state, so that the charge is accumulated in the parasitic capacitance and the voltage is increased. The voltage Vi3 when the Vi3 becomes constant is measured, and the voltage Vi3 is measured.
The OLED drive device is
Further, using the following equation 1, a voltage calculation unit for calculating a deemed forward voltage which is regarded as the current forward voltage of the OLED is further provided.
The period calculation unit
The accumulation period is calculated using the following formula 2.

Vvf = Vin-Vi3_con ... Equation 1
Pacc = (Cd × Vvf) ÷ I2 ... Equation 2
Vvf is the deemed forward voltage, Vin is the drive voltage, Vi3_con is the voltage Vi3 when the voltage Vi3 becomes constant, Pacc is the storage period, Cd is the parasitic capacitance, and I2 is the parasitic capacitance. The second constant current is shown.

This configuration is an example of a specific configuration for calculating the accumulation period. The third constant current is, for example, a minute constant current such that the OLED emits a small amount of light, is larger than the leakage current of the OLED, and is the lower limit of the first constant current that can be set by the user for the OLED drive device. It is a constant current smaller than the value.

In the above configuration
A storage unit that stores the value of the third constant current in advance is further provided.
In the mode for calculating the accumulation period, the voltage measuring unit starts accumulating the electric charge in the parasitic capacitance by switching the third constant current switching element from the off state to the on state. In the state where the voltage Vi3 is changed, the voltage Vi3 is measured at the first timing and the second timing, respectively.
The OLED drive device is
A capacitance calculation unit for calculating the parasitic capacitance is further provided using the following equation 3.

Cd = (I3 × P_t1t2) ÷ ΔVi3 ... Equation 3
Cd is the parasitic capacitance, I3 is the third constant current, P_t1t2 is the period from the first timing to the second timing, ΔVi3 is the voltage Vi3 measured at the first timing. The difference between the voltage and the voltage Vi3 measured at the second timing is shown.

This configuration is an example of a specific configuration for calculating parasitic capacitance. The value of the parasitic capacitance may be stored in advance in the memory provided in the OLED panel. The OLED panel includes an OLED and a memory, and is a device separate from the OLED drive device.

In the above configuration
The second constant current current source for generating the second constant current and the OLED are provided in an OLED panel separate from the OLED drive device.
The OLED drive device is
A second constant current switching element that allows the second constant current to flow when turned on and does not allow the second constant current to flow when turned off is further provided.
The voltage measuring unit can measure the voltage Vi2 applied to the other electrode of the OLED by switching the second constant current switching element from the off state to the on state.
In the mode for calculating the accumulation period, the voltage measuring unit starts accumulating the electric charge in the parasitic capacitance by switching the second constant current switching element from the off state to the on state. In the state where the voltage Vi2 is changed, the voltage Vi2 is measured at the third timing and the fourth timing, respectively.
The OLED drive device is
Further, a current calculation unit for calculating the second constant current is provided by using the following equation 4.

I2 = (ΔVi2 × Cd) ÷ P_t3t4 ・ ・ ・ Equation 4
I2 is the second constant current, ΔVi2 is the difference between the voltage Vi2 measured at the third timing and the voltage Vi2 measured at the fourth timing, and Cd is the parasitic capacitance, P_t3t4. Indicates the period from the third timing to the fourth timing.

This configuration is an example of a specific configuration for calculating the second constant current. The value of the second constant current may be stored in advance in the memory provided in the OLED panel.

According to the present invention, when the OLED for inspection lighting is made to emit a strobe light, the delay in starting the emission (lighting) of the OLED can be reduced.

It is an equivalent circuit diagram of the OLED lighting system which concerns on embodiment. It is explanatory drawing explaining the light emission method and dimming method of OLED. It is a functional block diagram of the MCU provided in the OLED drive device which concerns on embodiment. It is a flowchart explaining the calculation of the accumulation period. It is a flowchart explaining the calculation of parasitic capacitance and deemed forward voltage. It is a timing chart explaining the calculation of parasitic capacitance and deemed forward voltage. It is a flowchart explaining the calculation of the 2nd constant current. It is a timing chart explaining the calculation of the 2nd constant current. It is a flowchart explaining operation of strobe light emission of OLED using the OLED drive device which concerns on embodiment. It is a timing chart explaining the operation of the strobe light emission of an OLED using the OLED drive device according to the embodiment and the comparative example. It is an equivalent circuit diagram of the OLED lighting system which concerns on a comparative example.

Before the OLED drive device controls the OLED to emit strobe light using the first constant current (for example, a constant current equal to or less than the rated current of the OLED), the OLED is generated from the first constant current under a predetermined storage period. A large second constant current (eg, overdrive current) is used to control the accumulation of charge in the parasitic capacitance of the OLED. In this way, it is possible to reduce the delay in starting the light emission of the OLED in the strobe light emission of the OLED.

If the storage period is short, the second constant current is switched from the second constant current to the first constant current before the charge accumulation in the parasitic capacitance of the OLED is completed by the second constant current. Therefore, the remaining charge must be accumulated in the parasitic capacitance of the OLED by the first constant current, and the effect of reducing the delay of the start of light emission of the OLED is reduced.

On the other hand, if the storage period is long, the second constant current completes the accumulation of charges in the parasitic capacitance of the OLED, the second constant current flows through the OLED, and the OLED emits light. Then, the OLED emits light by the second constant current until the second constant current is switched to the first constant current. Since the second constant current is larger than the first constant current, it causes the OLED to deteriorate faster.

Therefore, the present inventor has invented an OLED drive device capable of calculating an accumulation period of an appropriate length.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each figure, the configurations with the same reference numerals indicate that they are the same configuration, and the description of the configurations already described will be omitted.

FIG. 1 is an equivalent circuit diagram of the OLED lighting system 100 according to the embodiment. The OLED lighting system 100 is used for inspection lighting and includes an OLED panel 1, an OLED drive device 2, and a cable 3. The OLED panel 1 and the OLED drive device 2 are separate bodies, and these are connected by a cable 3.

The OLED panel 1 includes an OLED 11, a first constant current diode D1, and a second constant current diode D2. The OLED 11 is one OLED element or a plurality of OLED elements connected in series, and emits surface light. Cd indicates the parasitic capacitance of OLED11. RI indicates the impedance caused by the leakage current of the OLED 11. R is a combination of the resistance of the wiring (cable 3, the wiring in the OLED panel 1, the wiring in the OLED drive device 2) connected to the OLED 11, the resistance of the anode electrode of the OLED 11, and the resistance of the cathode electrode of the OLED 11. Indicates resistance. Iin indicates the total current flowing through the OLED panel 1. Voled indicates the voltage applied to the OLED 11, that is, the voltage between the anode and the cathode of the OLED 11 (hereinafter, the voltage of the OLED 11). Iold indicates the current flowing through the OLED 11 (hereinafter, the current of the OLED).

When the voltage Voled of the OLED 11 reaches the forward voltage of the OLED 11, a current starts to flow in the OLED 11, and the OLED 11 starts lighting.

The anode of the first constant current diode D1 and the anode of the second constant current diode D2 are connected to the cathode of the OLED 11. The first constant current diode D1 is a current source that generates the first constant current I1. The first constant current I1 may be the rated current of the OLED 11 or may be a current smaller than the rated current. The second constant current diode D2 is a current source that generates the second constant current I2. The second constant current I2 is larger than the rated current of the OLED 11. In the embodiment, the second constant current I2 is used as the overdrive current. A constant current circuit may be used in place of the first constant current diode D1 and the second constant current diode D2.

The first constant current diode D1 and the second constant current diode D2 are arranged on the cathode side of the OLED panel 1, but may be arranged on the anode side of the OLED panel 1. The first constant current diode D1 and the second constant current diode D2 are arranged on the OLED panel 1, but may be arranged on the cable 3.

The OLED drive device 2 includes a voltage source 21, an MCU (Micro Controller Unit) 22, a third constant current diode D3, a first constant current switching element S1, and a second constant current switching element S2. A third constant current switching element S3 and a voltage detection circuit 26 are provided to drive the diode 11.

The MCU 22 has a function of controlling light emission of the OLED 11, a function of calculating parameters required for calculating the storage period Pacc (parasitic capacitance Cd of the OLED 11, a deemed forward voltage Vvf of the OLED 11, and a second constant current I2), and storage. It has a function to calculate the period Pacc. In addition, PLD (Programmable Logic Device) may be used instead of MCU22.

The deemed forward voltage Vvf of the OLED 11 is a voltage that is regarded as the current forward voltage of the OLED 11. The forward voltage of the OLED 11 changes with time. In order to correspond to this, the OLED drive device 2 calculates the deemed forward voltage Vvf as the current forward voltage of the OLED 11. The following relationship is established with the parasitic capacitance Cd of the OLED 11, the deemed forward voltage Vvf, the second constant current I2, and the accumulation period Pacc.

Cd x Vvf = I2 x Pacc
From this formula, the accumulation period Pacc is represented by the following formula 2. The MCU 22 calculates the accumulation period Pacc using Equation 2.

Pacc = (Cd × Vvf) ÷ I2 ... Equation 2
The voltage source 21 is, for example, an AC-DC converter or a DC-DC converter, and is connected to the anode (one electrode) of the OLED 11 via a cable 3. The voltage source 21 applies a positive voltage to the anode of the OLED 11. This voltage becomes the drive voltage Vin of the OLED 11.

The anode of the third constant current diode D3 is connected to the cathode of the second constant current diode D2 via the cable 3. The third constant current diode D3 is a current source that produces a third constant current I3. The third constant current I3 is smaller than the first constant current I1 and is a minute value (for example, 1 mA) that the OLED 11 emits slightly. The third constant current I3 is used to calculate the parasitic capacitance Cd and the deemed forward voltage Vvf. A constant current circuit may be used instead of the third constant current diode D3.

The first constant current switching element S1, the second constant current switching element S2, and the third constant current switching element S3 are, for example, N-channel power MOSFETs (Metal Oxide Semiconductor Field Effect Transistors).

The gate G of the first constant current switching element S1 is connected to the terminal 2221 of the MCU 22. The drain D of the first constant current switching element S1 is connected to the cathode of the first constant current diode D1 via a cable 3. The source S of the first constant current switching element S1 is grounded.

When the signal sg1 (pulse signal) generated by the MCU 22 and output from the terminal 2221 is input to the gate G of the first constant current switching element S1, the first constant current switching element S1 is turned on. During the period in which the signal sg1 is input to the gate G of the first constant current switching element S1, the first constant current switching element S1 is turned on and the first constant current I1 flows. During the period when the signal sg1 is not input to the gate G, the first constant current switching element S1 is turned off and the first constant current I1 does not flow.

The gate G of the second constant current switching element S2 is connected to the terminal 2222 of the MCU 22. The drain D of the second constant current switching element S2 is connected to the cathode of the second constant current diode D2 via the cable 3. The source S of the second constant current switching element S2 is grounded.

When the signal sg2 (pulse signal) generated by the MCU 22 and output from the terminal 2222 is input to the gate G of the second constant current switching element S2, the second constant current switching element S2 is turned on. During the period in which the signal sg2 is input to the gate G of the second constant current switching element S2, the second constant current switching element S2 is turned on and the second constant current I2 flows. During the period when the signal sg2 is not input to the gate G, the second constant current switching element S2 is turned off and the second constant current I2 does not flow.

The gate G of the third constant current switching element S3 is connected to the terminal 2223 of the MCU 22. The drain D of the third constant current switching element S3 is connected to the cathode of the third constant current diode D3. The source S of the third constant current switching element S3 is grounded.

When the signal sg3 (pulse signal) generated by the MCU 22 and output from the terminal 2223 is input to the gate G of the third constant current switching element S3, the third constant current switching element S3 is turned on. During the period in which the signal sg3 is input to the gate G of the third constant current switching element S3, the third constant current switching element S3 is turned on and the third constant current I3 flows. During the period when the signal sg3 is not input to the gate G, the third constant current switching element S3 is turned off and the third constant current I3 does not flow.

The voltage detection circuit 26 is a resistance dividing circuit in which a resistor R1 and a resistor R2 are connected in series. The terminal on the high voltage side of the voltage detection circuit 26 is connected to the cathode (the other electrode) of the OLED 11 via the cable 3. The terminal on the low voltage side of the voltage detection circuit 26 is grounded. The connection point between the resistance R1 and the resistance R2 and the terminal 2224 of the MCU 22 are connected.

The voltage detection circuit 26 detects the voltage Vi2 applied to the cathode (the other electrode) of the OLED 11 by switching the second constant current switching element S2 from the off state to the on state. Here, the voltage Vi2 is the voltage between the cathode and ground of the OLED 11. The voltage Vi2 is used to calculate the second constant current I2.

The voltage detection circuit 26 detects the voltage Vi3 applied to the cathode (the other electrode) of the OLED 11 by switching the third constant current switching element S3 from the off state to the on state. Here, the voltage Vi3 is the voltage between the cathode and ground of the OLED 11. The voltage Vi3 is used to calculate the parasitic capacitance Cd and the deemed forward voltage Vvf.

The voltage detection circuit 26 is not limited to the resistance dividing circuit, and may be any circuit that can detect the voltage Vi2 and the voltage Vi3.

FIG. 2 is an explanatory diagram illustrating a light emitting method and a dimming method of the OLED 11. The light emitting method of the OLED 11 includes a continuous light emitting method and an intermittent light emitting method. The continuous light emitting method causes the OLED 11 to emit light constantly. In the intermittent light emission method, the OLED 11 is made to emit light in pulses. Strobe flash and overdrive flash are intermittent flash methods, and pulse flash is controlled by an external trigger.

The strobe light emission is a method in which a current equal to or lower than the rated current is passed through the OLED 11. Overdrive light emission is a method in which a current larger than the rated current is passed through the OLED 11. As a result, the lighting can be made brighter. The overdrive period is shortly limited (for example, 1 μs to 1000 μs) in order to prevent the failure and deterioration of the OLED 11 from accelerating.

The dimming method of the OLED 11 includes a continuous dimming method and an intermittent dimming method. In the continuous dimming method, the OLED 11 is DC (Direct Current) dimmed. In the intermittent dimming method, the OLED 11 is PWM (Pulse Width Modulation) dimmed.

FIG. 3 is a functional block diagram of the MCU 22 provided in the OLED drive device 2 according to the embodiment. The MCU 22 includes a control processing unit 221, an I / O unit 222, a control unit 223, a period calculation unit 224, a voltage calculation unit 225, a storage unit 226, a voltage calculation unit 227, and a capacity calculation unit 228. It includes a current calculation unit 229.

The control processing unit 221 includes each functional block (I / O unit 222, control unit 223, period calculation unit 224, voltage calculation unit 225, storage unit 226, voltage calculation unit 227, capacity calculation unit 228, current calculation unit 229). , Control and process according to the function of each functional block.

The I / O unit 222 outputs a signal to the outside of the MCU 22, and the signal is input from the outside of the MCU 22. More specifically, with reference to FIGS. 1 and 3, the I / O section 222 includes terminals 2221 to 2224. The I / O unit 222 outputs the signal sg1 from the terminal 2221 to the gate of the first constant current switching element S1, outputs the signal sg2 from the terminal 2222 to the gate of the second constant current switching element S2, and outputs the terminal. The signal sg3 is output from 2223 to the gate of the third constant current switching element S3. A signal Vout indicating the voltage at the connection point between the resistance R1 and the resistance R2 is input to the I / O unit 222 via the terminal 2224.

The control unit 223 performs the first control and the second control. The first control is a control in which the OLED 11 is made to emit a strobe light by using the first constant current I1. The second control is a control for accumulating charges in the parasitic capacitance Cd of the OLED 11 by using the second constant current I2 before the first control under the pre-calculated storage period Pacc. The second control and the first control are continuous, and there is no time interval between these controls. The control unit 223 can reduce the delay in starting lighting of the OLED 11 by performing the second control before the first control.

The control unit 223 generates the signal sg1, the signal sg2, and the signal sg3, respectively, and sends them to the I / O unit 222. The control unit 223 uses the signal sg1 to turn on the first constant current switching element S1, performs the first control, and uses the signal sg2 to turn on the second constant current switching element S2. And perform the second control. The control unit 223 controls the second constant current switching element S2 to be turned on by using the signal sg2 in the mode of calculating the accumulation period Pacc, and uses the signal sg3 to control the third constant current. Control is performed to turn on the switching element S3.

The period calculation unit 224 calculates the accumulation period Pacc at a predetermined timing. The predetermined timing is, for example, the timing when the power of the OLED driving device 2 is turned on, in other words, the timing when the OLED driving device 2 is started up.

The voltage calculation unit 225 calculates the voltage Vi2 and the voltage Vi3 based on the signal Vout output from the voltage detection circuit 26. The voltage calculation unit 225 and the voltage detection circuit 26 constitute a voltage measurement unit 4 for measuring the voltage Vi2 and the voltage Vi3.

The storage unit 226 stores various programs, data, and information necessary for the operation of the OLED drive device 2. The information includes the value of the third constant current I3 and the value of the drive voltage Vin. The storage unit 226 stores in advance the value of the third constant current I3 and the value of the drive voltage Vin.

The voltage calculation unit 227 calculates the deemed forward voltage Vvf, which is regarded as the current forward voltage of the OLED 11. The capacitance calculation unit 228 calculates the parasitic capacitance Cd of the OLED 11. The current calculation unit 229 calculates the second constant current I2.

In order to calculate the storage period Pacc, the parasitic capacitance Cd, the deemed forward voltage Vvf, and the second constant current I2 are required. FIG. 4 is a flowchart illustrating the calculation of the accumulation period Pacc. With reference to FIGS. 3 and 4, each time the power of the OLED drive device 2 is turned on, the storage period Pacc is calculated, and the second control is performed under the calculated storage period Pacc. When the power of the OLED drive device 2 is turned on, the control mode of the control unit 223 becomes the calculation mode of the storage period Pacc (step S1). The capacitance calculation unit 228 and the voltage calculation unit 227 calculate the parasitic capacitance Cd and the deemed forward voltage Vvf, respectively (step S2). The current calculation unit 229 calculates the second constant current I2 (step S3). The period calculation unit 224 calculates the accumulation period Pacc using the above formula 2 (step S4).

The value of the parasitic capacitance Cd of the OLED 11 and the value of the second constant current I2 may be stored in advance in a memory (not shown) mounted on the OLED panel 1. In this case, it is not necessary to calculate the parasitic capacitance Cd and the second constant current I2. Instead, the period calculation unit 224 reads the value of the parasitic capacitance Cd and the value of the second constant current I2 from the memory mounted on the OLED panel 1, and these and the deemed forward voltage calculated in step S2. The storage period Parasitic is calculated using Vvf and Equation 2.

The calculation of the parasitic capacitance Cd and the deemed forward voltage Vvf will be described in detail. FIG. 5 is a flowchart illustrating the calculation of the parasitic capacitance Cd and the deemed forward voltage Vvf. FIG. 6 is a timing chart for explaining these calculations. The horizontal axis of FIG. 6 indicates the time t, and the vertical axis indicates the on / off state voltage Vi3 of the third constant current I3 and the third constant current switching element S3.

With reference to FIGS. 1 and 3, the third constant current I3 is set to be larger than the leak current caused by the impedance RI. This is so that the third constant current I3 and the leak current can be distinguished. The impedance RI is about several hundred kΩ, and the forward voltage of the OLED 11 is about several V to 20 V. Therefore, the value of the third constant current I3 may be about 1 mA. The third constant current I3 is such a minute current. Therefore, the deemed forward voltage Vvf calculated based on this can be set to a value close to the forward voltage.

With reference to FIGS. 1, 3 and 6, the control unit 223 sets the first constant current switching element S1, the second constant current switching element S2, and the third constant current switching element S3. Turn it off (step S21 in FIG. 5). In this state, no electric charge is accumulated in the parasitic capacitance Cd, and the voltage Vi3 is substantially equal to the drive voltage Vin (voltage Vi3 ≈ drive voltage Vin). explain in detail. A drive voltage Vin is applied to the OLED 11, but the first constant current switching element S1, the second constant current switching element S2, and the third constant current switching element S3 are in the off state. .. Therefore, the voltage Voled of the OLED 11 becomes almost zero. Therefore, the following relationship is established between the drive voltage Vin and the voltage Vi3.

Vi3 = {(R1 + R2) ÷ (R1 + R2 + RI)} × Vin
RI << R1 + R2. Therefore, the voltage Vi3 is substantially equal to the drive voltage Vin in the state where the electric charge is not accumulated in the parasitic capacitance Cd.

The control unit 223 generates a signal sg3 (pulse signal), and the signal sg3 is output from the I / O unit 222 and applied to the gate G of the third constant current switching element S3. As a result, the third constant current switching element S3 is switched from the off state to the on state (step S22 in FIG. 5). Let this timing be the time t_on. The circuit composed of the OLED 11, the second constant current diode D2, the third constant current diode D3, and the third constant current switching element S3 is a closed circuit. As a result, the third constant current I3 generated by the third constant current diode D3 flows through the third constant current switching element S3, and the charge accumulation in the parasitic capacitance Cd is started. Since the charge accumulation in the parasitic capacitance Cd is not completed, no current is flowing through the OLED 11 at this point (the OLED 11 does not emit light).

The voltage measuring unit 4 monitors the value of the voltage Vi3 by measuring the voltage Vi3 at predetermined timings (step S23 in FIG. 5). Since the electric charge is accumulated in the parasitic capacitance Cd by the third constant current I3, the voltage Vi3 drops. The formula showing this decrease can be regarded as a linear function.

The voltage measuring unit 4 determines whether or not the voltage Vi3 is constant (step S24 in FIG. 5). When the voltage measuring unit 4 determines that the voltage Vi3 is not constant (No in step S24), the voltage measuring unit 4 returns to the process of step S23.

When the voltage measuring unit 4 determines that the voltage Vi3 is constant (Yes in step S24), the voltage measuring unit 4 has two timings (first timing t1 and second timing t2) from the period during which the voltage Vi3 is decreasing (changing). ) Is selected. An example of this selection will be described. The first timing t1 is the timing at which the voltage Vi3 starts to decrease, and the second timing t2 is the timing when a predetermined period elapses from the first timing t1. In the case of this example, the first timing t1 and the time t_on match. The designer, manufacturer, and the like of the OLED drive device 2 have previously obtained a period during which the voltage Vi3 is low, and a predetermined period is set shorter than this period. The voltage measuring unit 4 sends the voltage Vi3 at the first timing t1 and the voltage Vi3 at the second timing t2 to the capacity calculation unit 228.

The capacity calculation unit 228 calculates the difference ΔVi3 between the voltage Vi3 at the first timing t1 and the voltage Vi3 at the second timing t2 (step S25 in FIG. 5). Then, the capacity calculation unit 228 calculates the period P_t1t2 from the first timing t1 to the second timing t2 (step S26 in FIG. 5).

The capacitance calculation unit 228 reads the value of the third constant current I3 from the storage unit 226, the third constant current I3, the difference ΔVi3 calculated in step S25, the period P_t1t2 calculated in step S26, and the equation 3. Is used to calculate the parasitic capacitance Cd (step S27 in FIG. 5). The capacitance calculation unit 228 stores the calculated value of the parasitic capacitance Cd in the storage unit 226.

Cd = (I3 × P_t1t2) ÷ ΔVi3 ... Equation 3
The voltage measuring unit 4 sends the value of the voltage Vi3 (voltage Vi3_con) when the voltage Vi3 becomes constant to the voltage calculating unit 227. The voltage calculation unit 227 reads the value of the drive voltage Vin from the storage unit 226, and calculates the deemed forward voltage Vvf using the drive voltage Vin, the voltage Vi3_con, and Equation 1 (step S28 in FIG. 5). The voltage calculation unit 227 stores the calculated value of the deemed forward voltage Vvf in the storage unit 226.

Vvf = Vin-Vi3_con ... Equation 1
When the period in which the signal sg3 (pulse signal) is applied to the gate G of the third constant current switching element S3 ends, the third constant current switching element S3 is switched from the on state to the off state (FIG. Step S29 of step 5). This timing is set to time t_off.

Next, the calculation of the second constant current I2 will be described. FIG. 7 is a flowchart illustrating the calculation of the second constant current I2. FIG. 8 is a timing chart for explaining this calculation. The horizontal axis of FIG. 8 indicates the time t, and the vertical axis indicates the on / off state voltage Vi2 of the second constant current I2 and the second constant current switching element S2.

With reference to FIGS. 1, 3 and 8, after step S29 of FIG. 5, the control unit 223 does not generate the signal sg1, the signal sg2, and the signal sg3. Therefore, the first constant current switching element S1, the second constant current switching element S2, and the third constant current switching element S3 are turned off (step S31 in FIG. 7). As a result, the electric charge accumulated in the parasitic capacitance Cd disappears. Therefore, the voltage Vi2 is substantially equal to the drive voltage Vin (voltage Vi2 ≈ drive voltage Vin). The reason is the same as the reason why the voltage Vi3 becomes almost equal to the drive voltage Vin.

The control unit 223 generates the signal sg2 (pulse signal). By applying the signal sg2 to the gate G of the second constant current switching element S2, the second constant current switching element S2 is switched from the off state to the on state (step S32 in FIG. 7). Let this timing be the time t_on. The circuit composed of the OLED 11, the second constant current diode D2, and the second constant current switching element S2 is a closed circuit. As a result, the second constant current I2 generated by the second constant current diode D2 flows through the second constant current switching element S2, and the charge is started to be accumulated in the parasitic capacitance Cd. Since the charge accumulation in the parasitic capacitance Cd is not completed, no current is flowing through the OLED 11 at this point (the OLED 11 does not emit light).

The voltage measuring unit 4 monitors the value of the voltage Vi2 by measuring the voltage Vi2 at predetermined timings (step S33 in FIG. 7). Since the electric charge is accumulated in the parasitic capacitance Cd by the second constant current I2, the voltage Vi2 drops. The formula showing this decrease can be regarded as a linear function.

The voltage measuring unit 4 determines whether or not the voltage Vi2 is constant (step S34 in FIG. 7). When the voltage measuring unit 4 determines that the voltage Vi2 is not constant (No in step S34), the voltage measuring unit 4 returns to the process of step S33.

When the voltage measuring unit 4 determines that the voltage Vi2 is constant (Yes in step S34), the voltage measuring unit 4 has two timings (third timing t3, fourth timing t4) from the period during which the voltage Vi2 is decreasing (changing). ) Is selected. An example of this selection will be described. The third timing t3 is the timing at which the voltage Vi2 starts to decrease, and the fourth timing t4 is the timing when a predetermined period elapses from the third timing t3. In the case of this example, the third timing t3 and the time t_on match. The designer, manufacturer, and the like of the OLED drive device 2 have previously obtained a period during which the voltage Vi2 is low, and a predetermined period is set shorter than this period. The voltage measuring unit 4 sends the voltage Vi2 at the third timing t3 and the voltage Vi2 at the fourth timing t4 to the current calculating unit 229.

The current calculation unit 229 calculates the difference ΔVi2 between the voltage Vi2 at the third timing t3 and the voltage Vi2 at the fourth timing t4 (step S35 in FIG. 7). Then, the current calculation unit 229 calculates the period P_t3t4 from the third timing t3 to the fourth timing t4 (step S36 in FIG. 7).

The current calculation unit 229 reads the value of the parasitic capacitance Cd from the storage unit 226, and uses the parasitic capacitance Cd, the difference ΔVi2 calculated in step S35, the period P_t3t4 calculated in step S36, and the second equation. The constant current I2 is calculated (step S37 in FIG. 7). The current calculation unit 229 stores the calculated value of the second constant current I2 in the storage unit 226.

I2 = (ΔVi2 × Cd) ÷ P_t3t4 ・ ・ ・ Equation 4
When the period in which the signal sg2 (pulse signal) is applied to the gate G of the second constant current switching element S2 ends, the second constant current switching element S2 is switched from the on state to the off state (FIG. Step S38 of 7. This timing is set to time t_off.

The operation of strobe light emission of the OLED 11 using the OLED driving device 2 according to the embodiment will be described. FIG. 9 is a flowchart illustrating this operation. FIG. 10 is a timing chart illustrating this operation. The horizontal axis of FIG. 10 indicates the time t, and the vertical axis represents the on / off state of the first constant current switching element S1 and the on / off state of the second constant current switching element S2. The constant current I2, the voltage Voled of the OLED11, and the current Iold of the OLED11 are shown. Note that FIG. 10 includes a timing chart for explaining the operation of strobe light emission of the OLED 11 using the OLED driving device 2 according to the comparative example, which will be described later.

With reference to FIGS. 1, 3 and 10, the user sets the operation mode of the OLED drive device 2 to the strobe light emission mode (step S51 in FIG. 9). The control unit 223 turns off the first constant current switching element S1, the second constant current switching element S2, and the third constant current switching element S3 (step S52 in FIG. 9).

In machine vision, the OLED drive device 2 causes the OLED 11 to emit light from a strobe when a trigger signal (pulse signal) is input from the outside. The trigger signal is a timing signal when the camera (not shown) releases the shutter. The camera generates and outputs a trigger signal, and the trigger signal output by the camera is input to the OLED drive device 2.

The control unit 223 determines whether or not a trigger signal has been input to the OLED drive device 2 (step S53 in FIG. 9). When the control unit 223 determines that the trigger signal has not been input to the OLED drive device 2 (No in step S53), the control unit 223 returns to the process of step S52.

When the control unit 223 determines that the trigger signal has been input to the OLED drive device 2 (Yes in step S53), the control unit 223 performs the second control under the pre-calculated storage period Pacc (step S54). explain in detail. The control unit 223 generates a signal sg2 (pulse signal), and the signal sg2 is output from the I / O unit 222 and applied to the gate G of the second constant current switching element S2. As a result, the second constant current switching element S2 is switched from the off state to the on state. The period during which the signal sg2 is applied to the gate G of the second constant current switching element S2 is the accumulation period Pacc.

When the second constant current switching element S2 is turned on, the circuit composed of the OLED 11, the second constant current diode D2, and the second constant current switching element S2 becomes a closed circuit. As a result, the second constant current I2 generated by the second constant current diode D2 flows through the second constant current switching element S2, and the charge is started to be accumulated in the parasitic capacitance Cd. Since the charge has not been accumulated in the parasitic capacitance Cd, no current is flowing through the OLED 11 during the accumulation period Pacc (the OLED 11 does not emit light).

The control unit 223 determines whether or not the accumulation period Pacc has elapsed (step S55 in FIG. 9). When the control unit 223 determines that the accumulation period Pacc has not elapsed (No in step S55), the control unit 223 repeats the process of step S55.

When the control unit 223 determines that the accumulation period Pacc has elapsed (Yes in step S55), the control unit 223 executes the first control (strobe light emission) (step S56 in FIG. 9). explain in detail. When the storage period Pacc elapses, the voltage Voled of the OLED 11 reaches the deemed forward voltage Vvf. Since a minute current (for example, 1 mA) flows through the OLED 11, the OLED 11 emits a small amount of light. The period of slight light emission is a moment. This is because, as described below, when the storage period Pacc elapses, the second constant current switching element S2 is turned off and the first constant current switching element S1 is turned on, whereby the OLED 11 This is because the first constant current I1 is supplied to.

When the storage period Pacc elapses, the signal sg2 is no longer applied to the gate G of the second constant current switching element S2. As a result, the second constant current switching element S2 is switched from the on state to the off state.

When the control unit 223 determines that the accumulation period Pacc has elapsed, the control unit 223 generates a signal sg1 (pulse signal), the signal sg1 is output from the I / O unit 222, and the gate of the first constant current switching element S1. It is applied to G. As a result, the first constant current switching element S1 is switched from the off state to the on state. The period during which the first constant current switching element S1 is on (that is, the period during which the signal sg1 is applied to the gate G of the first constant current switching element S1) is the strobe light emission period Pstr.

The circuit composed of the OLED 11, the first constant current diode D1 and the first constant current switching element S1 is a closed circuit. As a result, the first constant current I1 generated by the first constant current diode D1 flows through the first constant current switching element S1. Then, the voltage Voled of the OLED 11 and the current Iold of the OLED 11 increase, and the OLED 11 reaches the voltage V1 and the current (first constant current I1) required for strobe light emission. The above is the first control.

After step S56, the control unit 223 returns to the process of step S53 of FIG. As a result, each time an external trigger signal is input to the OLED drive device 2, the OLED drive device 2 causes the OLED 11 to emit a strobe light.

A comparative example will be described. In the comparative example, the OLED 11 is strobe-emitting only with the first constant current I1. FIG. 11 is an equivalent circuit diagram of the OLED lighting system 100a according to the comparative example. The difference between the OLED lighting system 100a and the OLED lighting system 100 shown in FIG. 1 will be described. The OLED panel 1 of the OLED lighting system 100a does not include a second constant current diode D2. The OLED driving device 2 of the OLED lighting system 100a does not include a third constant current diode D3, a second constant current switching element S2, a third constant current switching element S3, and a voltage detection circuit 26.

As described above, FIG. 10 includes a timing chart for explaining the operation of strobe light emission of the OLED 11 using the OLED driving device 2 according to the comparative example. In the comparative example, the vertical axis shows the on / off state of the first constant current switching element S1, the first constant current I1, the voltage Voled of the OLED 11, and the current Iold of the OLED 11. In the comparative example, since the electric charge is accumulated in the parasitic capacitance Cd only by the first constant current I1, the period for completing the accumulation of the electric charge in the parasitic capacitance Cd is longer than that in the embodiment. As a result, the period until the current Iold of the OLED 11 reaches the first constant current I1 becomes longer (that is, the start of lighting of the OLED 11 is delayed).

On the other hand, according to the embodiment, before the first control (the first constant current I1 is used to make the OLED 11 strobe light), the second control (the second larger than the first constant current I1). The constant current I2 is used to accumulate an electric charge in the parasitic capacitance Cd). Therefore, in the embodiment, the delay in starting lighting of the OLED 11 can be reduced as compared with the comparative example. This will be described in detail. The following equations are established for the storage period Pacc, the second constant current I2, the storage period Pacc_1 using the first constant current I1, and the first constant current I1.

Pacc x I2 = Pacc_1 x I1
For example, the second constant current I2 is set to be five times the first constant current I1. The accumulation period Pacc_1 is 5 times the accumulation period Pacc.

Further, since the OLED drive device 2 according to the embodiment includes a period calculation unit 224 that calculates the accumulation period Pacc in advance, it is possible to reduce the delay in starting lighting of the OLED 11 even if the forward voltage of the OLED 11 increases due to a change with time. ..

1 OLED panel 2 OLED drive device 4 Voltage measuring unit 11 OLED
26 Voltage detection circuit 100 OLED lighting system Cd OLED parasitic capacity D1 First constant current diode D2 Second constant current diode D3 Third constant current diode I1 First constant current I2 Second constant current I3 Third Constant current Pacc storage period S1 First constant current switching element S2 Second constant current switching element S3 Third constant current switching element

Claims (4)

It is an OLED drive device that flashes an OLED for inspection lighting.
The first control for causing the OLED to emit light from the strobe is performed using the first constant current, and the second is larger than the first constant current before the first control under a pre-calculated storage period. A control unit that performs a second control of accumulating charges in the parasitic capacitance of the OLED using the constant current of
An OLED drive device including a period calculation unit that calculates the accumulation period in advance. A voltage source that can be connected to one electrode of the OLED and supplies a drive voltage to the OLED.
When the OLED is turned on, a third constant current which is smaller than the first constant current and the OLED can emit light is passed, and when the OLED is turned off, the third constant current is not passed. 3 constant current switching elements and
The third constant current switching element is further provided with a voltage measuring unit capable of measuring the voltage Vi3 applied to the other electrode of the OLED by switching from the off state to the on state.
In the mode for calculating the storage period, the voltage measuring unit switches the third constant current switching element from the off state to the on state, so that the charge is accumulated in the parasitic capacitance and the voltage is increased. The voltage Vi3 when the Vi3 becomes constant is measured, and the voltage Vi3 is measured.
The OLED drive device is
Further, using the following equation 1, a voltage calculation unit for calculating a deemed forward voltage which is regarded as the current forward voltage of the OLED is further provided.
The period calculation unit
The OLED drive device according to claim 1, wherein the storage period is calculated using the following formula 2.
Vvf = Vin-Vi3_con ... Equation 1
Pacc = (Cd × Vvf) ÷ I2 ... Equation 2
Vvf is the deemed forward voltage, Vin is the drive voltage, Vi3_con is the voltage Vi3 when the voltage Vi3 becomes constant, Pacc is the storage period, Cd is the parasitic capacitance, and I2 is the parasitic capacitance. The second constant current is shown. A storage unit that stores the value of the third constant current in advance is further provided.
In the mode for calculating the accumulation period, the voltage measuring unit starts accumulating the electric charge in the parasitic capacitance by switching the third constant current switching element from the off state to the on state. In the state where the voltage Vi3 is changed, the voltage Vi3 is measured at the first timing and the second timing, respectively.
The OLED drive device is
The OLED drive device according to claim 2, further comprising a capacitance calculation unit for calculating the parasitic capacitance using the following equation 3.
Cd = (I3 × P_t1t2) ÷ ΔVi3 ... Equation 3
Cd is the parasitic capacitance, I3 is the third constant current, P_t1t2 is the period from the first timing to the second timing, ΔVi3 is the voltage Vi3 measured at the first timing. The difference between the voltage and the voltage Vi3 measured at the second timing is shown. The second constant current current source for generating the second constant current and the OLED are provided in an OLED panel separate from the OLED drive device.
The OLED drive device is
A second constant current switching element that allows the second constant current to flow when turned on and does not allow the second constant current to flow when turned off is further provided.
The voltage measuring unit can measure the voltage Vi2 applied to the other electrode of the OLED by switching the second constant current switching element from the off state to the on state.
In the mode for calculating the accumulation period, the voltage measuring unit starts accumulating the electric charge in the parasitic capacitance by switching the second constant current switching element from the off state to the on state. In the state where the voltage Vi2 is changed, the voltage Vi2 is measured at the third timing and the fourth timing, respectively.
The OLED drive device is
The OLED drive device according to claim 2 or 3, further comprising a current calculation unit for calculating the second constant current using the following formula 4.
I2 = (ΔVi2 × Cd) ÷ P_t3t4 ・ ・ ・ Equation 4
I2 is the second constant current, ΔVi2 is the difference between the voltage Vi2 measured at the third timing and the voltage Vi2 measured at the fourth timing, and Cd is the parasitic capacitance, P_t3t4. Indicates the period from the third timing to the fourth timing.

Images