JP5374942B2 - Flash charging circuit and flash charging control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flash charging circuit capable of achieving high efficiency in charging as well as longer life of a battery, with a necessary minimum configuration. <P>SOLUTION: The flash charging circuit includes a sep-up transformer 11 for stepping up a voltage of a power source, a capacitor 16 wherein the electric energy for flash emission is accumulated by the current supplied from a secondary coil 111 of the step-up transformer 11, a voltage detector 13 for detecting a voltage of a power source 10 before charging operation to the capacitor 16, a temperature detector 14 for detecting ambient temperature, a calculation part 13 for calculating the upper limit value of the current supplied to a primary coil 110 of the step-up transformer 11 based on the voltage detected with the voltage detector 13 as well as the temperature detected with the temperature detector 14, and a control part 13 for controlling current supply to the primary coil 110 based on the upper limit value calculated with the calculation part 13. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a flash charging circuit and a flash charging control method used in an imaging apparatus such as a camera.

  A flyback booster circuit is known as a flash charging circuit used in an imaging device such as a camera. In a flyback type booster circuit, boosting is performed by rectifying a flyback pulse generated in the secondary coil by turning off the primary current flowing in the primary coil of the boosting transformer and storing it in a capacitor. Since a large current is required for charging the capacitor, high charging efficiency is required.

  In the flyback type booster circuit, the charging efficiency may be lowered due to the temperature in the camera and the output voltage of the power source, and the battery life may be shortened. In addition, the charging efficiency decreases due to a change in the capacitance of the capacitor accompanying a change in temperature in the camera, a decrease in output voltage due to consumption of the battery serving as a power source, and the like.

Therefore, a charging device has been proposed in which battery information is detected before boosting and charging control is performed in accordance with the battery information to improve the charging efficiency (see, for example, Patent Document 1). Also, as a flash charging circuit that detects the temperature before boosting and performs charge control according to the temperature, the duty of the on / off time of the control signal supplied to the switching element (transistor) that turns on / off the primary side current Has been proposed in advance, and an apparatus has been proposed in which the charging efficiency is increased by controlling the on / off time of the control signal in accordance with the set duty (see, for example, Patent Document 2).
JP 2002-151290 A JP 2006-25597 A

  By the way, in recent years, the miniaturization of digital cameras has progressed, and the flash charging circuit is also required to be miniaturized and the number of components used is reduced due to restrictions on the mounting space of the circuit board. As a result, the use of, for example, a control IC (Integrated Circuit) for charging is increasing as a charging control means incorporating a switching element.

  However, the charging device described in Patent Document 1 requires a switching element, a current detection resistor, and a comparison circuit as components used in the flash charging circuit, and does not have a circuit configuration in consideration of a limited mounting space. Further, a specific control method for increasing the charging efficiency of the capacitor is not shown.

  Further, in the charging device described in Patent Document 2, it has been proposed to control the ON / OFF timing of the primary current, but in this case, the ON / OFF timing of the primary current is predetermined. The control IC for charging cannot be used.

  An object of the present invention is to provide a flash charging circuit and a flash charging control method capable of realizing high charging efficiency and long battery life with a minimum necessary configuration.

  A flash charging circuit according to the present invention includes a step-up transformer that boosts a voltage of a power supply, a capacitor that accumulates electric energy for flash light emission by a current supplied from a secondary coil of the step-up transformer, and before the capacitor is charged. A voltage detector for detecting a voltage of the power source, a temperature detector for detecting an ambient temperature, the voltage detected by the voltage detector and the voltage detected based on the temperature detected by the temperature detector. A calculation unit that calculates an upper limit value of the current supplied to the primary coil of the transformer, and a control unit that controls supply of current to the primary coil based on the upper limit value calculated by the calculation unit. And

Also, the flash charge control method of the present invention uses a voltage detector before charging the capacitor that stores electric energy for flash emission by the current supplied from the secondary coil of the step-up transformer that boosts the voltage of the power supply. Based on a voltage detection step for detecting the voltage of the power source, a temperature detection step for detecting an ambient temperature by a temperature detector , the voltage detected by the voltage detection step, and the temperature detected by the temperature detection step. A calculation step of calculating an upper limit value of the current supplied to the primary coil of the step-up transformer by the calculation unit , and supply of current to the primary coil by the control unit based on the upper limit value calculated by the calculation step And a control step for controlling.

  According to the flash charging circuit of the present invention, the upper limit value of the current supplied to the primary coil of the step-up transformer is calculated based on the voltage detected by the voltage detector and the temperature detected by the temperature detector. The supply of current to the primary coil is controlled based on the value. Therefore, it is possible to prevent a decrease in charging efficiency due to the ambient temperature and output voltage without using a complicated configuration, and it is possible to realize a high charging efficiency and a long battery life with the minimum necessary configuration. it can.

  According to the flash charge control method of the present invention, the upper limit value of the current supplied to the primary coil of the step-up transformer is calculated based on the voltage detected in the voltage detection step and the temperature detected in the temperature detection step. The supply of current to the primary coil is controlled based on the upper limit value. Therefore, it is possible to prevent a decrease in charging efficiency due to the ambient temperature and output voltage, so that it is possible to realize high charging efficiency and a long battery life.

  Hereinafter, a flash charging circuit according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a flash charging circuit according to this embodiment. The flash charging circuit according to this embodiment is applied to an imaging device such as a camera incorporating a flash, or a detachable flash device used in an imaging device such as a camera.

  The flash charging circuit shown in FIG. 1 is a flyback type booster circuit, which includes a power source 10, a step-up transformer 11, a control IC 12, an MPU (Micro Processing Unit) 13, a temperature sensor (temperature detection unit) 14, a rectifier diode 15, A main capacitor 16 and a light emitting circuit 17 are provided.

  The step-up transformer 11 that steps up the voltage from the power supply 10 includes at least two coils. In this embodiment, the step-up transformer 11 includes a primary coil 110 and a secondary coil 111. One end of the primary coil 110 of the step-up transformer 11 is connected to the plus terminal of the power supply 10, and the control IC 12 is connected to the other end of the primary coil 110. The negative terminal of the power supply 10 is connected to the ground 18.

  The control IC 12 incorporates a switching element (not shown) that periodically turns on / off the primary current supplied to the primary coil 110 of the step-up transformer 11 at high speed. The switching element according to this embodiment is a transistor of a MOS type FET (Metal Oxide Field Effect Transistor) capable of high-speed on / off switching. Note that a composite FET or a silicon transistor may be used as the switching element.

  The control IC 12 also includes a latch unit (not shown) that controls the start and end of charging of the main capacitor 16, and a monitor unit (not shown) that monitors the primary current and the rectified secondary current of the step-up transformer 11. )). The latch unit has two operation modes of H (High: on state) indicating the start of charging of the main capacitor 16 and L (Low: off state) indicating the end of charging of the main capacitor 16. Yes. The monitor unit monitors the primary side current flowing through the primary coil 110 and the secondary side current flowing through the secondary coil 111. In this embodiment, the monitor unit includes a primary current flowing in the primary coil 110 and a secondary current flowing in the secondary coil 111 from the current value or voltage value of the end of the primary coil 110 connected to the control IC 12. Although the side current is monitored, one end of the secondary coil 111 may be connected to the control IC 12 to monitor the current flowing through the primary coil 110 and the secondary coil 111. Further, one end of the primary coil 110 and the secondary coil 111 may be connected to the control IC 12 to monitor the current flowing through the primary coil 110 and the secondary coil 111.

  The rectifier diode 15 rectifies the flyback pulse generated from the secondary coil 111 of the step-up transformer 11 at the moment when the primary current flowing through the primary coil 110 is turned off. The main capacitor 16 performs boosting by storing the secondary current rectified by the rectifier diode 15 as electric energy. A light emission circuit 17 for flash emission is connected to the main capacitor 16, and the electric energy stored in the main capacitor 16 is used for flash emission.

  The light emitting circuit 17 is a circuit that converts electric energy charged in the main capacitor 16 into light energy. The light emitting circuit 17 is provided with, for example, a xenon tube, and flash emission is performed by discharging the xenon tube.

  The MPU 13 incorporates an A / D converter 20 that functions as a voltage detector. The MPU 13 detects the voltage value of the power supply 10 by converting the voltage S4 of the power supply 10 input to the A / D converter 20 into a digital value. In addition, a temperature sensor (temperature detector) 14 is connected to the MPU 13, and the MPU 13 receives a signal S 6 output from the temperature sensor 14. The MPU (arithmetic unit) 13 detects the voltage value of the power supply 10 before the charging operation to the main capacitor 16 and receives the signal S6 output from the temperature sensor 14 to thereby detect the temperature inside the camera (ambient temperature). ) And the upper limit value of the primary current supplied to the primary coil 110 of the step-up transformer 11 is calculated based on the detected voltage value and temperature.

  Further, the MPU 13 transmits a signal S1 indicating the start of charging of the main capacitor 16 or a signal S2 indicating the stop of charging to the control IC 12. In addition, the MPU (control unit) 13 transmits a signal S3 indicating an upper limit value of a primary current described later to the control IC 12, and controls the supply of current to the primary coil 110. These signals S1, S2 and S3 are output from an I / O output port (not shown) of the MPU 13. The signal S3 indicating the upper limit value of the primary side current may be an output signal from the D / A output port or a serial signal from the serial output port in accordance with the control IC 12.

  When the main capacitor 16 is boosted and the voltage of the main capacitor 16 reaches the fully charged voltage, the control IC 12 outputs a signal S5 to the MPU 13. The MPU 13 determines that the main capacitor 16 has reached full charge by receiving the signal S5.

Next, a method for calculating the upper limit value of the primary current by the MPU 13 will be described. First, the energy J required for charging the main capacitor 16 can be expressed by equation (1), where C is the capacitance of the main capacitor 16 and Vout is the charging end voltage of the main capacitor 16.
J = 1/2 (C × Vout ² ) [joule] (1)

Next, the charging efficiency k can be expressed by equation (2), where Vin is the voltage value of the power supply 10, Iin is the primary current during charging, and T is the charging time.
k = (J / (Vin × Iin × T)) × 100 [%] (2)

Substituting equation (1) into equation (2) and rearranging results in equation (3).
k = (C × Vout ² ) / (Vin × Iin × T) × 50 [%] (3)

  The value of the primary side current Iin that maximizes the charging efficiency k in the equation (3) is calculated, and the calculated value becomes the upper limit value of the primary side current Iin.

Therefore, first, the electrostatic capacitance C of the main capacitor 16 in the equation (3) is obtained. The capacitance C of the main capacitor 16 varies with temperature. FIG. 2 is a graph showing the relationship between the temperature (horizontal axis) and the capacitance of the main capacitor 16 (vertical axis). As shown in FIG. 2, when the capacitance of the main capacitor 16 at a certain temperature is Ctmp, the rate of change of the capacitance of the main capacitor 16 with temperature is α, and the capacitance of the main capacitor 16 is C. The capacitance Ctmp of the main capacitor 16 at temperature can be expressed by equation (4).
Ctmp = α × C (4)

  The MPU 13 receives the output signal S6 from the temperature sensor 14 and detects the temperature inside the camera. Then, the capacitance Ctmp of the main capacitor 16 is calculated from the detected temperature and the change rate α of the capacitance of the main capacitor 16 according to the temperature shown in FIG. 2, and Ctmp is substituted into C in the equation (3).

  Next, the charging end voltage Vout of the main capacitor 16 in the equation (3) is obtained. Vout is the voltage of the main capacitor 16 when the control IC 12 detects the charging end voltage. Since the rated voltage of the main capacitor 16 in this embodiment is 350V, Vout is adjusted to a winding ratio of the primary coil 110 and the secondary coil 111 of the step-up transformer 11 so that it is generally 300V to 320V. Determined.

  Next, the voltage value Vin of the power supply 10 in the equation (3) is obtained. The MPU 13 detects the voltage value Vin of the power supply 10 by inputting the signal S4 to the A / D converter 20 and converting it into a digital value.

  Next, the primary-side current Iin and the charging time (time required until the main capacitor 16 finishes charging) T during charging in the expression (3) will be described. When the primary side current Iin is increased, the charging time T decreases in inverse proportion. Since the upper limit value of the primary current Iin is a value determined by the specifications of the control IC 12 and the step-up transformer 11, it is desirable to measure the charging characteristics according to the configuration of the flash charging circuit. FIG. 3 is a diagram showing an example of the charging characteristics by the configuration of the flash charging circuit, and shows the relationship between the voltage Vin (horizontal axis) of the power supply 10 and the charging efficiency k (vertical axis) using the primary side current Iin as a parameter. It is a graph.

  As shown in FIG. 3, as the voltage Vin of the power supply 10 increases, the charging efficiency k increases regardless of the magnitude of the primary current Iin. However, the slope at which the charging efficiency k increases varies depending on the magnitude of the primary current Iin. For example, when the value of the primary side current Iin is A, B, C (A> B> C), the solid line shown in FIG. 3 indicates the voltage Vin (horizontal axis) and the charge when the value of the primary side current Iin is A. It is a graph showing the relationship with efficiency k (vertical axis), the broken line is a graph showing the relationship between voltage Vin (horizontal axis) and charging efficiency k (vertical axis) when the value of primary side current Iin is B, The one-dot chain line is a graph showing the relationship between the voltage Vin (horizontal axis) and the charging efficiency k (vertical axis) when the value of the primary side current Iin is C. When primary side current Iin is large (in the case of A indicated by a solid line), the slope of increase in charging efficiency k increases as a whole, and when primary side current Iin is small (in the case of C indicated by a one-dot chain line), charging efficiency k is Increasing slope decreases as a whole.

  On the other hand, as shown in FIG. 3, when the voltage Vin of the power supply 10 is low, the charging efficiency k increases as the primary current Iin decreases. Therefore, the charging efficiency k can be maximized by setting the primary current Iin suitable for the voltage Vin of the power supply 10. Further, as shown in FIG. 2, since the capacitance C of the main capacitor 16 changes depending on the temperature inside the camera, in addition to the charging characteristics according to the configuration of the flash charging circuit, the charging characteristics when the temperature is changed should be measured. Thus, it is possible to calculate the upper limit value of the primary side current Iin set so that the charging efficiency k is maximized in consideration of the voltage Vin of the power source 10 and the temperature inside the camera.

  Next, charge control is performed in which the type of the power supply 10 is determined from the voltage value of the power supply 10 detected by the MPU (voltage detector) 13 and charging is performed by switching the upper limit value of the primary current Iin according to the type of the power supply 10. Will be described.

  When a lithium ion battery is used as the power source 10, the nominal voltage of the lithium ion battery is 3.7V. On the other hand, since the AC adapter and the external power supply also charge the lithium ion battery, the voltage is designed to be higher than 3.7V and is about 4.2V or more. When the voltage detected based on the signal S4 input to the A / D converter 20 is larger than the voltage of the lithium ion battery, the MPU (determination unit) 13 determines that an AC adapter or an external power source is connected.

  Here, in the AC adapter or the external power source, the output voltage does not decrease as the battery is consumed, and the output voltage is constant. Therefore, charge control is performed in which priority is given to shortening the charging time T over the charging efficiency k. That is, the primary side current Iin shown in FIG. 3 is increased (solid line A in FIG. 3), charging is performed, and the charging time T is shortened.

  In addition, when an alkaline battery is used as the battery, the voltage of the alkaline battery gradually decreases as the voltage of the lithium ion battery is consumed, but rapidly decreases during the consumption. Therefore, the MPU (determination unit) 13 determines which of the lithium ion battery and the alkaline battery is connected by monitoring the voltage decrease rate detected based on the signal S4 input to the A / D converter 20. can do. As a method for monitoring the voltage decrease rate, for example, the voltage when the power is turned on last time is stored, and the voltage decrease rate is monitored by comparing the stored voltage with the voltage when the power is turned on this time. After the determination, the MPU 13 performs charge control by switching the upper limit value of the primary current Iin according to the type of battery. As a method for determining the type of the power supply 10, a user (user) of the camera may selectively input the type of the power supply 10 to be used in advance. For example, the user may determine the type of the power supply 10 by inputting information indicating a lithium ion battery, an alkaline battery, an AC adapter, or the like.

  Next, a flash charge control method using the flash charge circuit according to this embodiment will be described with reference to the flowchart shown in FIG. FIG. 5 is a timing chart for explaining a flash charging control method using the flash charging circuit according to this embodiment.

  First, the MPU 13 receives an instruction for flash charging from the camera side, and detects the temperature inside the camera by receiving the signal S6 from the temperature sensor 14 before starting the charging operation (step S101, temperature detection step). Next, the MPU 13 calculates the capacitance of the main capacitor 16 based on the temperature detected by the temperature sensor 14 (step S102). Note that the MPU 13 may include a storage unit that stores, for example, a capacitance change rate table shown in FIG. 2. In this case, the MPU 13 changes the capacitance stored in the storage unit. The capacitance of the main capacitor 16 is calculated with reference to the rate table.

  Next, the MPU 13 detects the voltage of the power supply 10 based on the signal S4 input to the A / D converter 20 (step S103, voltage detection step). Then, the MPU 13 determines the type of the power supply 10 from the voltage of the power supply 10 detected in step S103. That is, it is determined whether or not the voltage of the power source 10 is higher than the nominal voltage of the battery (step S104, determination step).

  When the voltage of the power source 10 is equal to or lower than the nominal voltage of the battery (No in step S104), the MPU 13 determines that the power source 10 is a battery, and the capacitance calculated in step S102 and the voltage detected in step S103 (battery From the voltage), the primary side current Iin that maximizes the charging efficiency k in the equation (3) is calculated using the above equation (3) (step S105, calculation step).

  On the other hand, when the voltage of the power supply 10 is higher than the nominal voltage of the battery (step S104, Yes), the MPU 13 determines that the power supply 10 is an AC adapter or an external power supply, and the primary current Iin within the allowable range of the power supply 10. Is set (step S107, calculation step). That is, since the upper limit of the current that can be passed in the AC adapter or the external power source is determined, the primary side that has the charging efficiency k that is the current within the upper limit that can be passed from the voltage Vin detected in step S103. The current Iin is obtained. Note that the MPU 13 may include a storage unit that stores a table indicating the charging efficiency as illustrated in FIG. 3, for example. In this case, the MPU 13 displays a table indicating the charging efficiency stored in the storage unit. Referring to the voltage Vin (horizontal axis) detected in step S103, a primary current Iin that is the current within the upper limit that can be passed and has the best charging efficiency k (vertical axis) is obtained.

  Next, the MPU 13 performs supply control of the primary side current Iin to the primary coil 110 based on the upper limit value of the primary side current Iin obtained in step S105 or step S107 (control step). That is, the signal S3 indicating the upper limit value of the primary current Iin is output to the control IC 12, and the upper limit value of the primary current Iin is set in the control IC 12 (step S106).

Next, the MPU 13 outputs a signal S1 indicating the start of charging to the control IC 12. Control IC12, as shown in FIG. 5 (a), and shifts the latched portion by receiving the signal S1 at time _{T 1} from L (off state) to the H (on state). Then, charging of the main capacitor 16 is started (step S108).

  Next, the control IC 12 turns on the switching element (step S109). As shown in FIG. 5B, when the switching element is turned on (Ton), the primary current starts to flow through the primary coil 110. The monitor unit in the control IC 12 monitors whether or not the primary side current has reached the upper limit value (step S110). The monitoring unit continues monitoring until the primary side current reaches the upper limit value (step S110, No). Then, when the primary current Iin reaches the upper limit as shown in FIG. 5B (step S110, Yes), the control ICl2 turns off the switching element (step S111).

  When the switching element is turned off (Toff), the primary current flowing in the primary coil 110 is stopped as shown in FIG. 5B, and at the same time, the secondary coil 111 is turned on as shown in FIG. 5C. Secondary current starts to flow. That is, as shown in FIGS. 5B and 5C, while the switching element is turned on (Ton), the primary side current flows and the secondary side current does not flow. While the switching element is turned off (Toff), the primary current does not flow, and the secondary current flows.

  When the secondary side current starts to flow through the secondary coil 111, the secondary side current is rectified by the rectifier diode 15, and the rectified secondary side current is supplied to the main capacitor 16 as electric energy as shown in FIG. Charged.

  Next, the monitor unit of the control IC 12 monitors the secondary side current (step S112). The monitor unit continues monitoring until it detects the end of charging of the secondary current to the main capacitor 16 (No in step S112). When the secondary current ends as shown in FIG. 5C and charging of the main capacitor 16 is completed (step S112, Yes), the MPU 13 determines whether or not the main capacitor 16 is fully charged. Is determined (step S113). That is, the MPU 13 determines whether or not the signal S5 indicating that the main capacitor 16 has reached full charge has been received from the control IC 12.

  If the main capacitor 16 is not fully charged (No at Step S113), the process returns to Step S109, and the operations of Step S109 to Step S113 are repeated until the main capacitor 16 is fully charged. That is, the control IC 12 repeats ON / OFF of the switching element, and continues charging the main capacitor 16 by alternately flowing the primary side current and the secondary side current.

When the main capacitor 16 is fully charged (step S113, Yes), the MPU 13 outputs a signal S2 indicating the end of charging to the control IC 12. Control IC12 receives the signal S2 at time _{T 2,} to shift the latch portion as shown in FIG. 5 (a) from H (on state) to L (off state). Then, the charging of the main capacitor 16 is terminated (step S114). After charging the main capacitor 16, a flash signal is emitted from the light emitting circuit 17 by transmitting a trigger signal from the camera side.

  According to the flash charging circuit of this embodiment, the upper limit value of the primary current Iin supplied to the primary coil 110 of the step-up transformer 11 is calculated based on the voltage detected by the MPU 13 and the temperature detected by the temperature sensor 14. Then, the supply of the primary current to the primary coil 110 is controlled based on the calculated upper limit value. Therefore, it is possible to prevent a decrease in charging efficiency due to the ambient temperature and output voltage without using a complicated configuration, and it is possible to realize a high charging efficiency and a long battery life with the minimum necessary configuration. it can.

  Further, according to the flash charge control method according to this embodiment, the supply of the primary side current can be controlled, so that a decrease in charge efficiency due to the ambient temperature and output voltage is prevented, and the charge efficiency is increased. The battery life can be extended.

It is a block diagram which shows the structure of the flash charging circuit which concerns on embodiment of this invention. It is a graph which shows the relationship between temperature and the electrostatic capacitance of a main capacitor. It is a graph which shows the relationship between the power supply voltage which used the primary side current as a parameter, and charging efficiency. It is a flowchart for demonstrating the flash charge control method using the flash charge circuit which concerns on embodiment of this invention. It is a time chart for demonstrating the flash charge control method using the flash charge circuit which concerns on embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Boost transformer, 12 ... Control IC, 13 ... MPU, 14 ... Temperature sensor, 15 ... Rectifier diode, 16 ... Main capacitor, 17 ... Light emitting circuit, 20 ... A / D converter, 110 ... Primary coil, 111 ... Secondary coil.

Claims (6)

A step-up transformer that boosts the voltage of the power supply;
A capacitor for accumulating electric energy for flash emission by a current supplied from a secondary coil of the step-up transformer;
A voltage detector for detecting a voltage of the power supply before charging the capacitor;
A temperature detector that detects the ambient temperature;
A calculation unit that calculates an upper limit value of a current supplied to the primary coil of the step-up transformer based on the voltage detected by the voltage detector and the temperature detected by the temperature detector;
A control unit for controlling supply of current to the primary coil based on the upper limit value calculated by the calculation unit;
A flash charging circuit comprising:   2. The flash charging circuit according to claim 1, wherein the controller turns off the supply of the current to the primary coil when the current supplied to the primary coil reaches the upper limit value. 3. A discriminator for discriminating the type of the power source from the voltage detected by the voltage detector;
3. The flash charging circuit according to claim 1, wherein the calculation unit calculates the upper limit value according to the type of the power source determined by the determination unit. A voltage detection step of detecting the voltage of the power supply by a voltage detector before the charging operation of the capacitor for storing the electric energy for flash light emission by the current supplied from the secondary coil of the step-up transformer for boosting the voltage of the power supply; ,
A temperature detecting step of detecting the ambient temperature by the temperature detector,
A calculation step of calculating an upper limit value of the current supplied to the primary coil of the step-up transformer by the calculation unit based on the voltage detected by the voltage detection step and the temperature detected by the temperature detection step;
A control step of controlling the supply of current to the primary coil by the control unit based on the upper limit value calculated in the calculation step;
A flash charge control method comprising: 5. The flash charge control according to claim 4, wherein, in the control step , the control unit turns off the supply of the current to the primary coil when the current supplied to the primary coil reaches the upper limit value. Method. A determination step of determining the type of the power source by the determination unit from the voltage detected by the voltage detection step;
6. The flash charge control method according to claim 4, wherein, in the calculation step , the calculation unit calculates the upper limit value according to the type of the power source determined in the determination step.

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