JP4744198B2 - Strobe device - Google Patents

Description

  The present invention relates to a strobe device used as an auxiliary light source during photography.

  In recent years, the miniaturization of cameras such as digital still cameras has progressed rapidly, and mobile phone devices equipped with small cameras are also rapidly spreading, so the demand for strobe devices as auxiliary light sources for taking pictures with them has also increased. There is a growing demand for very small ones.

  In the conventional example of the strobe device as described above (see, for example, Patent Document 1), in the separately excited DC / DC converter, the charging voltage of the main capacitor and the low-frequency triangular wave voltage from the triangular wave generator are used as the converter. The output frequency is converted into a PWM signal and driven, and when the charging voltage at startup is very low, the drive frequency is compared to the steady state so as not to cause overcurrent. By lowering, the pulse width of the ON period is relatively narrow with respect to the control cycle.

  In another conventional example (see, for example, Patent Document 2), in a separately excited DC / DC converter that performs PWM control with a microcomputer, no overcurrent occurs when the charging voltage of the main capacitor is very low. In this way, the control cycle is not changed, and the pulse width in the ON period is driven to be relatively narrow with respect to the steady state.

Furthermore, in another conventional example (for example, see Patent Document 3), in order to shorten the charging time of the main capacitor while controlling the inrush current when the main capacitor charging transformer is oscillated by the separately excited flyback method. When the detection value by the charging voltage detection circuit for detecting the charging voltage of the main capacitor takes a relatively high value, the pulse of the strobe pulse signal for driving the oscillation transformer output from the strobe pulse signal generation circuit under the control of the CPU The generation of the output pulse is controlled so that the width is relatively wide or the pulse period of the strobe pulse signal is relatively shortened.
JP-A-5-316729 Japanese Patent Laid-Open No. 11-84484 Japanese Patent Laid-Open No. 11-87083

  However, in the case of PWM driving with a microcomputer or the case of PWM driving with a comparison circuit with a triangular wave as in the prior art described above, when the driving frequency becomes high, the driving frequency is in the complete short-circuit state of the main capacitor. In the transformer inductor value variation and the power supply voltage change, there is no sufficient guarantee that the current does not increase and heat is not generated.

  In other words, when the frequency is high, due to fluctuations in parameters such as drive frequency, transformer inductor value and power supply voltage, inrush current due to overcurrent may occur due to magnetic saturation due to residual energy emission on the secondary side. In order to avoid this, if the pulse width period is set too short, there is a problem that the start of the charging operation is deteriorated.

  The present invention solves the above-described conventional problems, and the main capacitor can be reduced in size when the pulse width control is driven at an arbitrary control frequency not only at a low frequency but also at a high frequency. Even when the battery is in an overload condition such as a short circuit and its charging voltage is very low, overcurrent can be prevented to prevent heat generation and heat generation can be suppressed, and circuit elements can be protected from destruction due to heat generation. A strobe device that can be used is provided.

  In order to solve the above problems, a strobe device according to claim 1 of the present invention is a strobe device that charges a main capacitor via a separately excited DC / DC converter and emits strobe light with the energy of the main capacitor. A pulse width control circuit for controlling the energization pulse width on the primary side of the separately excited DC / DC converter is provided, and this pulse width control circuit is used to change the energization pulse width on the primary side of the separately excited DC / DC converter in a stepwise manner. When the PWM soft start driving is performed to widen to the maximum pulse width, and the charging voltage of the main capacitor does not reach a predetermined voltage even if the PWM soft start driving is continued, an overload to the separately excited DC / DC converter is detected. It is determined that the load is in a load state, and after the secondary current of the separately excited DC / DC converter is completely discharged, the primary side By repeating driving which moves to operation, characterized by being configured to perform said pulse width control.

  A strobe device according to claim 2 of the present invention is a strobe device that charges a main capacitor via a separately excited DC / DC converter and emits strobe light with the energy of the main capacitor. A pulse width control circuit for controlling the energization pulse width on the primary side is provided. When the main capacitor is less than a predetermined low voltage during charging, the pulse width control circuit is provided on the primary side of the separately excited DC / DC converter. PWM soft start drive is executed to gradually increase the energization pulse width to the maximum pulse width. When the main capacitor is equal to or higher than a predetermined low voltage, the PWM drive is executed with the maximum pulse width and the charging is performed. When the charging voltage of the main capacitor according to the above does not reach the predetermined voltage after a predetermined time has elapsed, the separately excited DC / DC converter The pulse width control is executed by repetitive driving in which it is determined that the state is an overload state, and the secondary-side DC / DC converter discharges the secondary-side current and shifts to the primary-side energization operation. It is characterized by that.

  The strobe device according to claim 3 of the present invention is a strobe device that charges a main capacitor via a separately excited DC / DC converter and emits strobe light with the energy of the main capacitor. A pulse width control circuit for controlling the energization pulse width on the primary side is provided. When the main capacitor is less than a predetermined low voltage during charging, the pulse width control circuit is provided on the primary side of the separately excited DC / DC converter. PWM soft start drive that gradually increases the energization pulse width to the maximum pulse width, and when the main capacitor is equal to or higher than a predetermined low voltage, executes PWM drive with the maximum pulse width, and When the main capacitor is less than a predetermined low voltage, the energization pulse width on the primary side of the separately excited DC / DC converter is gradually increased to the maximum pulse width. During WM soft start drive, it detects that the main capacitor has reached a predetermined voltage, terminates the PWM soft start drive, executes PWM drive with the maximum pulse width, and charges the main capacitor by the charging. If the predetermined voltage has not reached the predetermined voltage after a predetermined time has elapsed, it is determined that the over-excited DC / DC converter is overloaded, and the discharge of the secondary side current of the separately excited DC / DC converter is awaited. Thus, the pulse width control is performed by repetitive driving that shifts to the energization operation on the primary side.

  A strobe device according to a fourth aspect of the present invention is the strobe device according to the second or third aspect, wherein the pulse width control circuit includes a triangular wave voltage generating circuit that generates a triangular wave having a constant repetition frequency, and A soft start voltage generating circuit that generates a soft start voltage that rises with the passage of time after the start of charging, and the triangular wave and the soft start voltage are compared and gradually energized at a single frequency with the passage of time from the start of charging. Comparator that outputs a signal with a longer duty cycle, a soft start voltage cancel circuit that detects the terminal voltage of the main capacitor rising to the set voltage and cancels the soft start operation, and the main capacitor is fully charged Until the main capacitor is charged based on the output of the comparator until it is fully charged, charging is terminated. If the logic circuit acting as described above and the charging voltage of the main capacitor due to the charging do not reach a predetermined voltage after a predetermined time has passed, it is determined that the over-excited state is applied to the separately excited DC / DC converter, A means for outputting an overload signal indicating the overload state; and when receiving the overload signal, the secondary side current of the separately-excited DC / DC converter is detected and waiting for completion of the discharge, the primary side It is characterized by comprising a secondary coil current detection circuit that performs the pulse width control by repetitive driving that shifts to an energization operation.

  The strobe device according to claim 5 of the present invention is the strobe device according to claim 4, wherein the pulse width control circuit detects that an overcurrent has flowed to the primary side of the separately excited DC / DC converter. A primary coil overcurrent detection circuit for turning off the logic circuit is provided.

  A special purpose integrated circuit device according to claim 6 of the present invention is a special purpose integrated circuit device constituting the strobe device according to claim 4, wherein the triangular wave voltage generation circuit generates a single frequency triangular wave. And a soft start voltage generating circuit that generates a soft start voltage that rises with the passage of time after the start of charging, and the triangular wave and the soft start voltage are compared at a single frequency with the passage of time from the start of charging. A comparator that outputs a duty signal that gradually increases the energization period, a soft start voltage cancel circuit that detects when the terminal voltage of the main capacitor has risen to the set voltage, and cancels the soft start operation, and the main capacitor is fully charged Until it becomes, the main capacitor is charged based on the output of the comparator, and when it is fully charged, the charging is finished. When the logic circuit that acts as described above and the charging voltage of the main capacitor due to the charging does not reach a predetermined voltage after elapse of a predetermined time, it is determined that an overload state is applied to the separately excited DC / DC converter, Means for outputting an overload signal indicating an overload state, and when receiving the overload signal, the secondary side current of the separately excited DC / DC converter is detected and waiting for completion of the discharge, the primary side energization A secondary coil current detection circuit that performs the pulse width control by repetitive driving to shift to an operation is constructed.

  The application-specific integrated circuit device according to claim 7 of the present invention is the application-specific integrated circuit device according to claim 6, wherein the primary coil overcurrent that detects the occurrence of an overcurrent and turns off the logic circuit. A detection circuit is provided.

  An application specific integrated circuit device according to claim 8 of the present invention is the application specific integrated circuit device according to claim 6 or 7, wherein at least one of a triangular wave voltage generation circuit and a soft start voltage generation circuit. An external connection terminal for connecting a time constant determining element of one circuit is provided.

  A strobe device according to claim 9 of the present invention is the strobe device according to any one of claims 2 to 5 for determining that the main capacitor is overloaded. The predetermined time during the charging operation for the main capacitor includes the driving frequency of the pulse width control, the power supply voltage and current, the capacity of the main capacitor, the charging voltage of the main capacitor, and the charging efficiency of the main capacitor. According to the value, when the load state is normal, the voltage of the main capacitor is set to the minimum necessary time for reaching the voltage that can be determined to be normal compared to the predetermined voltage. It is characterized by that.

  A strobe device according to a tenth aspect of the present invention is the strobe device according to the ninth aspect, wherein the strobe device serves as a reference for comparison with a charging voltage of the main capacitor when determining an overload state for the main capacitor. The predetermined voltage is set to a voltage that is higher than a reactivation voltage generated in a state where the main capacitor is short-circuited and lower than a voltage of the main capacitor after strobe light emission in a normal load state.

  An application specific integrated circuit device according to claim 11 of the present invention is the application specific integrated circuit device according to any one of claims 6 to 8, wherein the main capacitor is overloaded. The predetermined time during the charging operation for the main capacitor for determining that there is a drive frequency, a power supply voltage and a current of the pulse width control, a capacity of the main capacitor, a charging voltage of the main capacitor, and the main capacitor When the load state is normal, the minimum voltage necessary for the voltage of the main capacitor to reach a voltage that can be determined to be normal compared to the predetermined voltage according to each value of the charging efficiency to A limited time is set.

  A special purpose integrated circuit device according to claim 12 of the present invention is the special purpose integrated circuit device according to claim 11, wherein when the overload state for the main capacitor is determined, the charging voltage of the main capacitor is determined. The predetermined voltage serving as a reference for comparison is set to a voltage that is higher than the reactivation voltage generated when the main capacitor is short-circuited and lower than the voltage of the main capacitor after strobe light emission in a normal load state. It is characterized by.

  As described above, in the case of an overload such as a short circuit to the main capacitor, the charging current is limited, and if the charging voltage of the main capacitor has not reached the predetermined voltage after a predetermined time from the start of the charging operation, the main capacitor Based on the overload signal indicating the overload state, it is determined that the overload state is present, and repeated driving for shifting to the primary side energizing operation after waiting for the completion of the secondary side current discharge is performed. When the charging voltage of the capacitor reaches the specified voltage, the pulse width is controlled by normal charging operation drive. When the charging is completed, the charging voltage of the main capacitor falls below the specified voltage and the charging operation is resumed. If the charging voltage of the main capacitor does not reach the predetermined voltage after a predetermined time has elapsed, it is determined that the main capacitor is in an overload state and the overload state is indicated. In accordance with the overload signal, repeat the drive to wait for the completion of the discharge of the secondary side current and shift to the primary side energization operation.If the charging voltage of the main capacitor reaches a predetermined voltage during this repeated drive, Pulse width control can be performed by charging operation driving.

  As described above, according to the present invention, when the main capacitor and the separately-excited DC / DC converter are charged for a predetermined time and the charging voltage of the main capacitor does not reach the predetermined overload detection voltage, the converter output is It is determined that there is an overload condition, and in accordance with an overload signal indicating the overload condition, waiting for the completion of the discharge of the secondary current and performing a repetitive drive that shifts to the primary energization operation, Since the off time is very long compared to the on time, the power consumption during an overload condition becomes very small, reducing the wasteful power consumption during overload to the converter output as much as possible, and this repeated drive is It continues as long as the converter output overload condition continues, and once the overload condition is released, the transition to normal charging operation to the main capacitor can be performed quickly.

  In addition, the charging operation time for determining whether or not the converter output is in an overload state is set to a time as short as possible by setting the value of the overload detection voltage low. The power consumption can be reduced as much as possible, and the transition to the normal charging operation for the main capacitor can be quickly performed as soon as the overload state is released.

  As described above, the configuration can be made very small, and when the pulse width control is driven at an arbitrary control frequency not only at a low frequency but also at a high frequency, the main capacitor is in an overload state such as a short circuit and charged. Even when the voltage is very low, the charging operation can prevent the occurrence of overcurrent, suppress the heat generation, and protect the circuit elements from being damaged by the heat generation.

Hereinafter, a strobe device showing an embodiment of the present invention will be specifically described with reference to the drawings.
FIG. 1 is a circuit block diagram showing the configuration of the strobe device of the present embodiment. In this strobe device, as shown in FIG. 1, a field effect transistor Q1 is connected in series with a primary winding P of an oscillation transformer T1, and the switching of the transistor Q1 is performed by a control integrated circuit device 1. A main capacitor 2 is connected in parallel to the secondary winding S of the oscillation transformer T1 via a diode D1. A series circuit of a xenon tube 3 and an insulated gate bipolar transistor (Insulated Gate Bipolar Transistor) Q2 is connected in parallel with the main capacitor 2. R1 is a resistor for detecting a current flowing through the primary winding P of the oscillation transformer T1, R3 and R4 are resistors for detecting a voltage charged in the main capacitor 2, and 4 is a high voltage pulse for exciting the xenon tube 3. This is a high voltage trigger circuit.

  A control integrated circuit device 1 as a pulse width control circuit for controlling charging / light emission of a strobe includes a maximum duty setting voltage generation circuit 5, a triangular wave voltage generation circuit 6, a soft start voltage generation circuit 7, a comparator 8, To protect the circuit when the primary coil overcurrent detection circuit 9 that detects the overcurrent flowing through the primary winding P of the oscillation transformer T1 and the main capacitor 2 are overloaded due to, for example, a short circuit of a terminal. In addition, a current that flows through the secondary winding S of the oscillation transformer T1 is detected, and a control signal for performing pulse width control for repeating the operation of energizing the primary winding P after waiting for the completion of the discharge is output. The secondary coil current detection circuit 32, the full charge detection circuit 10 for detecting the completion of charging, and the division of resistors R3 and R4 that the terminal voltage of the main capacitor 2 has been charged to a predetermined voltage value. The soft start voltage canceling circuit 11 for detecting that the voltage has risen to the set voltage and suddenly increasing the soft start voltage to cancel the soft start operation, and the main capacitor 2 etc. are charged from the start of charging due to, for example, a short circuit of the terminal. Is determined to be overloaded with respect to the separately excited DC / DC converter when the predetermined voltage does not reach the predetermined voltage after a predetermined time elapses, and the secondary coil current detection circuit 32 is connected to the circuit in order to protect the circuit. On the other hand, the main capacitor low voltage detection circuit 30 that outputs an overload signal indicating an overload state, the AND gate 12, the drive circuit 13 that drives the field effect transistor Q1, and the like are constructed as an integrated circuit.

  The resistor R2 as a time constant determining element for setting the frequency of the triangular wave generated by the triangular wave voltage generating circuit 6 and the time constant determining element for setting the rising curve of the soft start voltage generated by the soft start voltage generating circuit 7 are used. The capacitor 14 is provided outside the control integrated circuit device 1 and is connected to the triangular wave voltage generation circuit 6 and the soft start voltage generation circuit 7 via the external connection terminals 19 and 20.

  2 and 3 show an initial charging state immediately after the power is turned on, specifically, a timing chart during charging from a state where the terminal voltage of the main capacitor 2 is 0 volts to a low voltage value. A timing chart of voltage values is shown in FIG. FIG. 4 shows a timing chart during charging up to a high voltage value. In FIG. 4D, the current in the secondary winding S of the oscillation transformer T1 is shown to continue to flow until the next rising timing of the gate signal 18 to the “H” level. Actually, the current does not flow earlier by the time corresponding to the terminal voltage of the main capacitor 2 than the next rising timing of the gate signal 18 to the “H” level.

  When the power is turned on, the soft start voltage generating circuit 7 that charges the capacitor 14 with a constant current outputs a soft start voltage 15 that increases linearly with the passage of time as shown in FIG.

  The comparator 8 compares the soft start voltage 15 with a triangular wave voltage 16 having a constant frequency (600 kHz in this case) generated by the triangular wave voltage generation circuit 6 and outputs a level determination signal 17 having logic levels “H” and “L”. To do. Specifically, since charging of the main capacitor 2 is not completed in the initial charging state, the output of the full charge detection circuit 10 is maintained at the logic level “H” state, and the primary winding of the oscillation transformer T1 If no overcurrent flows through P, the output of the primary coil overcurrent detection circuit 9 is maintained at the logic level “H”, and the AND gate 12 is opened / closed only in accordance with the level determination signal 17 of the comparator 8 to drive. A gate signal 18 having a logic level “H” is applied to the gate of the transistor Q1 through the circuit 13 during a period when the triangular wave voltage 16 is lower than the soft start voltage 15 as shown in FIG.

  As a result, the primary current DI1 flows through the primary winding P of the oscillation transformer T1 in accordance with the generation period of the gate signal 18. Accordingly, as shown in FIG. 2C, the voltage value of the terminal voltage DV1 of the resistor R1 gradually increases as the energization period becomes longer. Here, the period of energization of the gate signal 18 is short, and the terminal voltage DV1 of the resistor R1 is set according to the terminal voltage of the resistor R1 when the overcurrent value flows through the primary coil. Since it is lower than the voltage value, the output of the primary coil overcurrent detection circuit 9 is maintained at the logic level “H”.

  When the transistor Q1 is PWM pulse driven, a charging current flows through the charging circuit of the main capacitor 2 of the secondary winding S of the oscillation transformer T1, as shown in FIG. As a result, the main capacitor 2 is gradually charged, and the terminal voltage rises with a gentle curve as shown in FIG.

  Until the soft start voltage cancel circuit 11 detects that the terminal voltage of the main capacitor 2 has risen from the divided voltage DMCV of the resistors R3 and R4 to a preset medium voltage value (the terminal voltage of the main capacitor 2 is 100 volts). 2 and 3, the PWM soft start in which the energization period of the gate signal 18 is determined by the level determination signal 17 obtained by comparing the triangular wave voltage 16 and the soft start voltage 15 by the comparator 8 is executed. Thus, the occurrence of overcurrent is avoided even with 600 kHz high frequency driving.

  In order to prevent an overcurrent from flowing in the initial charging state immediately after the power is turned on, it is conceivable to operate the separately excited DC-DC converter by a low frequency drive of several tens of kilohertz. Ripple is generated in the power line. In particular, in the case of a strobe device for a camera-equipped mobile phone device in which a camera is incorporated in the mobile phone device, it has been confirmed that a low-frequency ripple occurs in the power supply line and the call is interrupted and it becomes difficult to hear the sound. In the case of frequency driving, it is necessary to take measures to reduce the line noise to the telephone side by inserting a large inductor in the power supply line in order to maintain the call quality, which is an obstacle to circuit miniaturization. Like this, by operating a separately-excited DC-DC converter by high-frequency driving, the generation of ripples in the power line is eliminated, and in the case of low-frequency driving, the communication quality is maintained without providing a large inductor that must be incorporated. can do. Moreover, overcurrent can be reliably prevented by executing PWM soft start even with high-frequency driving.

  At timing TT, the soft start voltage canceling circuit 11 indicates that the terminal voltage of the main capacitor 2 has risen from the divided voltage DMCV of the resistors R3 and R4 to a preset medium voltage value (terminal voltage of the main capacitor 2 is 100 volts). Upon detection, as shown in FIG. 3, the soft start voltage 15 of the soft start voltage generation circuit 7 is a maximum duty determined by the set voltage of the maximum duty setting voltage generation circuit 5 and the triangular wave voltage 16 (ON time 0.75, Since it is forcibly switched to the state driven by the gate signal 18 with an off time of 0.25), charging is performed more efficiently than when soft start is continued with a slope determined by the capacitor 14 until the charging of the main capacitor 2 is completed. it can.

  Note that the preset intermediate voltage value (the terminal voltage of the main capacitor 2 of 100 volts) is a voltage value at which no overcurrent is generated even when switching to driving of the gate signal 18 at the maximum duty, and is fully charged. When the terminal voltage of the main capacitor 2 was about 300 volts, it was around 100 volts. FIG. 6 shows the terminal voltage of the main capacitor 2 on the horizontal axis and the secondary-side discharge time coefficient on the vertical axis. Even when the energization period in the oscillation transformer T1 is lengthened, the slope of the increase in the terminal voltage of the main capacitor 2 is It suddenly becomes gentle around 100 volts.

  In FIG. 3, after the timing TT, the circuit is forcibly switched to a state driven by the gate signal 18 having the maximum duty determined by the setting voltage of the maximum duty setting voltage generation circuit 5 and the triangular wave voltage 16, but the terminal of the resistor R1 It can also be realized by performing a charging operation by expanding the voltage DV1 to a pulse width determined by a peak current reaching the set voltage 22 of the primary coil overcurrent detection circuit 9.

  Here, as shown in FIG. 3 and FIG. 4, after the forced switching to the state driven by the maximum duty gate signal 18 determined by the set voltage 21 of the maximum duty set voltage generation circuit 5 and the triangular wave voltage 16, the primary When the peak current is detected by the coil overcurrent detection circuit 9, the AND gate 12 is turned off to reliably prevent the occurrence of overcurrent.

When the charging voltage further rises and the full charging detection circuit 10 detects the completion of charging, the AND gate 12 is turned off to stop charging.
When the charge is full and the strobe is required for shooting, if a signal of “H” level is output from the terminal FSW, the transistor Q2 is turned on and a high voltage pulse of several kilovolts from the high voltage trigger circuit 4 is turned on. Is output and the xenon tube 3 is excited to emit light.

  The pulse width output from the terminal FSW varies depending on the photographing conditions. For example, when the subject distance is short or the subject reflectance is high, the pulse width is shortened and a light emission operation with a small amount of light is performed. On the other hand, when the subject distance is long or the subject reflectance is low, the pulse width is increased and a light emission operation with a large amount of light is performed. The value of the residual voltage of the main capacitor 2 varies depending on the amount of light during the light emission operation.

In addition, it is remarkable in the recharge after light emission that it is effective to switch to the maximum duty when the terminal voltage of the main capacitor 2 reaches the medium voltage value of 100 volts.
Specifically, as shown in FIG. 5, when the residual voltage of the main capacitor 2 is less than the medium voltage value (the terminal voltage of the main capacitor 2 is 100 volts) set in the soft start voltage cancel circuit 11. In the case of FIG. 2, the control integrated circuit device 1 generates a soft start voltage that outputs a voltage that increases linearly with time by charging the capacitor 14 with a constant current after rapidly discharging the capacitor 14. In the same manner as in FIG. 5, charging is performed efficiently while suppressing the inrush current due to magnetic saturation by narrowing the pulse width and gradually increasing, but the residual voltage of the main capacitor 2 is 60 volts as shown in FIG. In the case where there is a degree, as shown in FIG. 2, the terminal of the main capacitor 2 at an earlier time (timing TQ in FIG. 5) than when charging is performed immediately after power-on Since reaching the pressure 100 volts, when squeezing pulse width as to continue to charge gradually widening in accordance with soft-start voltage 15 based on the left capacitor 14 efficiency is reduced.

  In this embodiment, it is detected that the terminal voltage of the main capacitor 2 has reached the medium voltage value of 100 volts, and the main capacitor 2 is charged after switching to the maximum duty. You can see that it can be fully charged.

  In this way, the main capacitor 2 can be efficiently charged while preventing overcurrent by high-frequency driving, and the triangular wave voltage 16 generated by the triangular wave voltage generation circuit 6 and the soft start voltage 15 generated by the soft start voltage generation circuit 7 are obtained. Since the PWM soft start is controlled by comparison, when the drive frequency or the inductor value of the oscillation transformer T1 needs to be changed, the resistor R2 and the capacitor 14 provided outside the control integrated circuit device 1 are connected. Appropriate responses can be made just by changing.

  When a similar PWM soft start is to be realized by a microcomputer without comparing the triangular wave voltage 16 generated by the triangular wave voltage generation circuit 6 with the soft start voltage 15 generated by the soft start voltage generation circuit 7. When there is a need to change the drive frequency or the inductor value of the oscillation transformer, it is necessary to provide an appropriate PWM drive pulse width correlation table corresponding to the main capacitor voltage in the microcomputer each time. Although annoying work is required, according to the specific configuration of the above-described embodiment, it is possible to quickly respond to changes in the drive frequency and the inductor value of the oscillation transformer.

  Further, since it is possible to cope with this by simply changing the resistor R2 and the capacitor 14 provided outside the control integrated circuit device 1, the control integrated circuit device can be controlled without creating a control integrated circuit device for each model having a different driving frequency and inductor value of the oscillation transformer. The integrated circuit device can be used for a plurality of models.

In the above description, the primary coil overcurrent detection circuit 9 is provided in the control integrated circuit device 1, but this can be omitted.
In each of the above embodiments, both the resistor R2 and the capacitor 14 are provided outside the control integrated circuit device 1, but one of the resistor R2 and the capacitor 14 is provided outside the control integrated circuit device 1. It can also be configured.

  The description so far has been made on the normal charging / light emission operation in the strobe device of the present embodiment. Hereinafter, in the output part of the DC / DC converter, which is a power source for causing the xenon tube 3 to emit light, for example, the main capacitor 2 etc. On the other hand, a charging operation in a case where the apparatus is temporarily overloaded for a certain period due to a short circuit caused by some cause will be described.

  As described above, in order to realize an operation corresponding to a case where the output part of the DC / DC converter is temporarily overloaded for a certain period, in FIG. 1, the main capacitor low voltage detection circuit 30 and the secondary coil current are A detection circuit 32 is provided.

  This main capacitor low-voltage detection circuit 30 is separately excited DC / DC when the main capacitor 2 or the like cannot be charged because the charging voltage does not reach the predetermined voltage after a predetermined time has elapsed since the start of charging due to, for example, a short circuit of the terminal. In order to determine that the converter is overloaded and to protect each circuit element, the secondary coil current detection circuit 32 is configured to output an overload signal indicating the overloaded state. In order to detect that the converter output is in an overload state based on the charging voltage of the main capacitor 2, the capacitor low voltage detection circuit 30 has a comparison reference voltage with respect to the charging voltage of the main capacitor 2, as shown in FIG. A predetermined overload detection voltage (B) 31 is set in advance. The strobe device may be configured so that the overload detection voltage (B) 31 is set outside the main capacitor low voltage detection circuit 30.

  Further, the secondary coil current detection circuit 32 is overloaded from the main capacitor low voltage detection circuit 30 in order to protect each circuit element when the main capacitor 2 or the like is overloaded due to, for example, a short circuit of a terminal. When a signal is received, the current DI2 flowing through the secondary winding S of the oscillation transformer T1 of the separately excited DC / DC converter is detected by converting it to the terminal voltage DV2 at the resistor R5, and the primary side is waited for the completion of the discharge. A control signal for performing pulse width control for repeating the operation of energizing the winding P is output to the AND gate 12.

First, the charging operation in the main capacitor low voltage detection circuit 30 when the power is turned on when the output unit of the DC / DC converter is already in an overload state will be described.
FIG. 7 is a timing chart in the overload state, and shows the operation when the power is turned on in the output overload state. When the power is turned on, the strobe device outputs a gate signal 18 as a converter drive signal from the drive circuit 13 as shown in FIG. 7 and starts a normal charging operation for the main capacitor 2.

  After that, in the main capacitor low voltage detection circuit 30, even if the normal charging operation is continued for a predetermined fixed time (A) as an overload determination period, the charging voltage of the main capacitor 2 remains at the predetermined overload detection voltage (B). If it does not reach 31, the converter output is determined to be in an overload state due to a short circuit or the like as a load state, and an overload signal indicating an overload state is output to the secondary coil current detection circuit 32.

  When the secondary coil current detection circuit 32 receives an overload signal from the main capacitor low voltage detection circuit 30, the secondary coil current detection circuit 32 performs a charge operation at the time of overload detection in the overload charging period as a separately excited DC / DC converter. Pulse width control is performed in which the current DI2 flowing through the secondary winding S of the oscillation transformer T1 is detected by converting it into the terminal voltage DV2 at the resistor R5, and the operation of energizing the primary winding P is waited for completion of the discharge. A control signal for output is output to the AND gate 12.

  During the charging operation when the secondary coil current detection circuit 32 detects an overload state, the main capacitor low voltage detection circuit 30 always charges the main capacitor 2 with the charging voltage and the overload detection voltage (B ) 31, and based on the comparison result, the load state is detected, and if it is an overload state, the secondary coil current detection circuit 32 is continuously charged when the overload state is detected. Output an overload signal.

  As described above, while the output of the overload signal from the main capacitor low voltage detection circuit 30 is continued, the secondary coil current detection circuit 32 performs the charging operation when the overload state is detected on the AND gate 12. Continue to output the control signal.

  Here, during the overload charging period, the main capacitor low voltage detection circuit 30 detects the load state based on the comparison result between the charging voltage of the main capacitor 2 and the overload detection voltage (B) 31, If the overload state has already been canceled and the charging voltage of the main capacitor 2 is equal to or higher than the overload detection voltage (B) 31 and is in a normal load state, the secondary coil current detection circuit 32 is Then, the output of the overload signal is stopped so as to switch to the normal charging operation and continue the charging operation.

  Thus, when the output of the overload signal from the main capacitor low voltage detection circuit 30 is stopped, the secondary coil current detection circuit 32 causes the AND gate 12 to continue the same charging operation as in the normal time. Output a control signal.

As described above, since the off time becomes very long compared to the on time during repeated driving, the power consumption in the overload state becomes very small.
Next, the charging operation in the main capacitor low voltage detection circuit 30 when the output part of the DC / DC converter is in an overload state when the main capacitor 2 is in the charging completion state will be described.

  FIG. 8 is a timing chart in the overload state, and shows the operation in the output overload state in the charging completed state. As shown in FIG. 8, in the strobe device, in the main capacitor low voltage detection circuit 30, the charging voltage of the main capacitor 2 suddenly becomes lower than the overload detection voltage (B) 31 for some reason, and the normal charging operation is performed. Even if it continues, when the state continues for a predetermined fixed time (C) as the overload determination period, it is determined that the converter output is in an overload state due to a short circuit or the like, and the secondary coil current detection circuit 32 is Output an overload signal indicating an overload condition.

  When the secondary coil current detection circuit 32 receives an overload signal from the main capacitor low voltage detection circuit 30, the secondary coil current detection circuit 32 performs a charge operation at the time of overload detection in the overload charging period as a separately excited DC / DC converter. Pulse width control is performed in which the current DI2 flowing through the secondary winding S of the oscillation transformer T1 is detected by converting it into the terminal voltage DV2 at the resistor R5, and the operation of energizing the primary winding P is waited for completion of the discharge. A control signal for output is output to the AND gate 12.

  During the charging operation when the secondary coil current detection circuit 32 detects an overload state, the main capacitor low voltage detection circuit 30 always charges the main capacitor 2 with the charging voltage and the overload detection voltage (B ) 31, and based on the comparison result, the load state is detected, and if it is an overload state, the secondary coil current detection circuit 32 is continuously charged when the overload state is detected. Output an overload signal.

  As described above, while the output of the overload signal from the main capacitor low voltage detection circuit 30 is continued, the secondary coil current detection circuit 32 performs the charging operation when the overload state is detected on the AND gate 12. Continue to output the control signal.

  Here, during the overload charging period, the main capacitor low voltage detection circuit 30 detects the load state based on the comparison result between the charging voltage of the main capacitor 2 and the overload detection voltage (B) 31, If the overload state has already been canceled and the charging voltage of the main capacitor 2 is equal to or higher than the overload detection voltage (B) 31 and is in a normal load state, the secondary coil current detection circuit 32 is Then, the output of the overload signal is stopped so as to switch to the normal charging operation and continue the charging operation.

  Thus, when the output of the overload signal from the main capacitor low voltage detection circuit 30 is stopped, the secondary coil current detection circuit 32 causes the AND gate 12 to continue the same charging operation as in the normal time. Output a control signal.

As described above, since the off time becomes very long compared to the on time during repeated driving, the power consumption in the overload state becomes very small.
In the main capacitor low voltage detection circuit 30, the charging operation time (A or C: overload determination period) for determining whether the output unit of the DC / DC converter is in an overload state is an overload detection voltage (B). By setting the value of 31 low, the time is set as short as possible.

  The predetermined time (A) changes in inverse proportion to the oscillation frequency of the triangular wave voltage generation circuit 6, that is, changes in accordance with the value of the resistor R 2. Based on the simulation result of the charging voltage of the main capacitor 2 and the limit value of the charging efficiency to the main capacitor 2, when the load state is normal, the voltage of the main capacitor 2 is a predetermined overload detection voltage (B). The minimum time required for reaching the voltage that can be determined to be normal as compared with 31 is set. Here, the oscillation frequency of the triangular wave voltage generation circuit 6 is set to 600 kilohertz (KHz) as a circuit condition, but the main capacitor 2 uses a small capacity (about 50 microfarad (μF) or less) for this frequency. If the main capacitor 2 is used with a larger capacity, it is used for a longer time as the predetermined time (A) by lowering the frequency. .

  The predetermined voltage (B) is set in consideration of the following conditions. That is, the main capacitor voltage after strobe light emission usually decreases to about 40 to 50 volts (V) (end voltage of xenon tube light emission (minimum voltage at which discharge can continue)). Further, the aluminum electrolytic capacitor used for the main capacitor 2 may generate a regenerative voltage of about 10 volts (V) due to the polarization action even after the terminals are short-circuited and completely discharged. Therefore, the voltage of the main capacitor 2 in the overload state is set to a voltage that is higher than the reactivation voltage generated when the main capacitor 2 is short-circuited and lower than the voltage after light emission in the normal load state. That is, the value is set between 10 and 40 volts (V).

  In addition, as the predetermined time (C), when the voltage of the main capacitor 2 sharply decreases from the steady state after the completion of charging, for example, the load state is overloaded or the load is in a normal state. In order to detect the load condition (overload condition), there is a clear cause that the load condition has changed at least for some reason against the steep voltage drop of the main capacitor 2 such as strobe light emission. As the overload determination period, there is no problem even if the time is sufficiently shorter than the predetermined time (A), but the detection result of the load state is obtained more accurately, and the predetermined time (A) For the same reason as in the case, the same time as the predetermined time (A) may be set. However, considering that no erroneous determination is made due to noise or the like, a time of at least 1 millisecond (ms) is required.

  From the above, in the present embodiment, for example, as the above circuit conditions, a ceramic product is used for the evaluation board, the drive frequency is 600 kilohertz (KHz), the power supply voltage is 4.2 volts (V), and the oscillation transformer T1 The primary winding P has an inductance of 2.2 microhenry (μH), the boost ratio to the secondary winding S is 17.5, and the primary detection resistor R1 is 0.1 ohm (Ω). 7, the predetermined time (A) during the charging operation in FIG. 7 is about 250 milliseconds (ms), the predetermined voltage (B) of the overload detection voltage 31 in FIGS. 7 and 8 is about 20 volts (V), Each predetermined value is set so that the predetermined time (C) during the charging operation in FIG. 8 is about 10 milliseconds (ms).

As described above, the charging current for the main capacitor 2 can be limited by the primary coil overcurrent detection circuit 9 when the main capacitor 2 is overloaded such as a short circuit.
The main capacitor low voltage detection circuit 30 determines that the main capacitor 2 is in an overload state when the charging voltage of the main capacitor 2 has not reached the predetermined voltage after a predetermined time has elapsed since the start of the charging operation. Then, an overload signal indicating the overload state is output, and the secondary coil current detection circuit 32 that has received the overload signal causes the drive circuit 13 to wait for the completion of the discharge of the secondary side current and perform the energization operation on the primary side. The main capacitor low voltage detection circuit 30 determines that the main capacitor 2 is in a normal load state when the charging voltage of the main capacitor 2 reaches a predetermined voltage during the repeated driving. Then, the output of the overload signal is stopped, and the secondary coil current detection circuit 32 controls the AND gate 12 so that the drive circuit 13 performs normal charge operation drive. By outputting, it is possible to perform pulse width control.

  In addition, the main capacitor low voltage detection circuit 30 causes the charging voltage of the main capacitor 2 to become a predetermined voltage or lower when charging is completed, the charging operation is restarted, and the charging voltage of the main capacitor 2 reaches the predetermined voltage after a predetermined time has elapsed. If the voltage has not been reached, it is determined that the main capacitor 2 is in an overload state, an overload signal indicating the overload state is output, and the secondary coil current detection circuit 32 receiving this overload signal Then, the driving circuit 13 waits for the completion of the discharge of the secondary current and performs the repetitive driving to shift to the primary energizing operation. During this repetitive driving, the main capacitor low voltage detection circuit 30 determines the charging voltage of the main capacitor 2. When the predetermined voltage is reached, it is determined that the main capacitor 2 is in a normal load state, the output of the overload signal is stopped, and the secondary coil current detection circuit 32 causes the drive circuit 1 to So it performs normal charging operation driven by outputting a control signal to the AND gate 12, it is possible to perform pulse width control.

  As a result, the configuration can be reduced in size and the main capacitor 2 is in an overload state such as a short circuit when the pulse width control is driven at an arbitrary control frequency not only at a low frequency but also at a high frequency. Even when the charging voltage is very low, overcurrent can be prevented to suppress heat generation, and circuit elements can be protected from destruction due to heat generation.

  The strobe device of the present invention can be miniaturized in size, and when the pulse width control is driven at an arbitrary control frequency not only at a low frequency but also at a high frequency, the main capacitor is in an overload state such as a short circuit. Even when the charging voltage is very low, it is possible to prevent overcurrent, suppress heat generation, and protect circuit elements from destruction due to heat generation. The present invention can be applied to an application specific integrated circuit device having the function.

Configuration diagram of an embodiment of a strobe device of the present invention Main part waveform diagram immediately after power-on of the same embodiment Main part waveform diagram of medium voltage value state of the same embodiment Main part waveform diagram of high voltage value state of the same embodiment Waveform diagram of the main part of the recharge state after shooting in the same embodiment Relationship diagram between terminal voltage of main capacitor 2 and secondary side discharge time coefficient of the same embodiment Main part waveform diagram and timing chart in overload state of same embodiment (1) Main part waveform diagram and timing chart in the overload state of the embodiment (2)

Explanation of symbols

T1 Oscillation transformer Q1 Field effect transistor D1 Diode Q2 Insulated gate bipolar transistor 1 Control integrated circuit device (specific application integrated circuit device)
2 main capacitor 3 xenon tube 4 high voltage trigger circuit 5 maximum duty setting voltage generation circuit 6 triangular wave voltage generation circuit 7 soft start voltage generation circuit 8 comparator 9 primary coil overcurrent detection circuit 10 full charge detection circuit 11 soft start voltage cancellation circuit 12 Andgate 13 drive circuit R2 resistance (time constant determining element)
14 Capacitor (time constant determining element)
19, 20 External connection terminal 30 Main capacitor low voltage detection circuit 32 Secondary coil current detection circuit

Claims (12)

In a strobe device that charges a main capacitor via a separately excited DC / DC converter and emits strobe light with the energy of the main capacitor,
A pulse width control circuit for controlling the energization pulse width on the primary side of the separately excited DC / DC converter;
This pulse width control circuit
While performing PWM soft start drive that gradually increases the energization pulse width on the primary side of the separately excited DC / DC converter to the maximum pulse width,
If the charging voltage of the main capacitor does not reach a predetermined voltage even after the PWM soft start drive is continued, it is determined that the separately excited DC / DC converter is overloaded, and the separately excited DC / DC converter is determined. A strobe device configured to execute the pulse width control by repetitive driving that waits for the completion of discharge of the secondary side current and shifts to the energization operation on the primary side. In a strobe device that charges a main capacitor via a separately excited DC / DC converter and emits strobe light with the energy of the main capacitor,
A pulse width control circuit for controlling the energization pulse width on the primary side of the separately excited DC / DC converter;
This pulse width control circuit
When the main capacitor is less than a predetermined low voltage at the time of charging, PWM soft start driving is executed to gradually increase the energization pulse width on the primary side of the separately excited DC / DC converter to the maximum pulse width. When the capacitor is equal to or higher than a predetermined low voltage, while performing the PWM drive with the maximum pulse width,
When the charging voltage of the main capacitor due to the charging does not reach a predetermined voltage after a predetermined time has elapsed, it is determined that the over-excited DC / DC converter is overloaded, and the separately-excited DC / DC converter A strobe device configured to execute the pulse width control by repetitive driving in which a transition to the primary-side energization operation is performed after completion of discharge of a secondary-side current. In a strobe device that charges a main capacitor via a separately excited DC / DC converter and emits strobe light with the energy of the main capacitor,
A pulse width control circuit for controlling the energization pulse width on the primary side of the separately excited DC / DC converter;
This pulse width control circuit
When the main capacitor is less than a predetermined low voltage at the time of charging, PWM soft start driving is executed to gradually increase the energization pulse width on the primary side of the separately excited DC / DC converter to the maximum pulse width. When the capacitor is equal to or higher than a predetermined low voltage, PWM driving is performed with the maximum pulse width, and when the main capacitor is lower than the predetermined low voltage, the energization pulse on the primary side of the separately excited DC / DC converter During PWM soft start drive that gradually increases the width to the maximum pulse width, it detects that the main capacitor has reached a predetermined voltage, ends the PWM soft start drive, and executes PWM drive with the maximum pulse width. ,
When the charging voltage of the main capacitor due to the charging does not reach a predetermined voltage after a predetermined time has elapsed, it is determined that the over-excited DC / DC converter is overloaded, and the separately-excited DC / DC converter A strobe device configured to execute the pulse width control by repetitive driving in which a transition to the primary-side energization operation is performed after completion of discharge of a secondary-side current. Pulse width control circuit
A triangular wave voltage generating circuit for generating a triangular wave with a constant repetition frequency;
A soft start voltage generating circuit that generates a soft start voltage that rises with the passage of time after the start of charging;
A comparator that compares the triangular wave with the soft-start voltage and outputs a duty signal that gradually increases the energization period at a single frequency as time elapses from the start of charging;
A soft start voltage cancel circuit for detecting that the terminal voltage of the main capacitor has risen to the set voltage and canceling the soft start operation;
Until the main capacitor is fully charged, the logic circuit that charges the main capacitor based on the output of the comparator, detects that the capacitor is fully charged, and terminates the charging;
When the charging voltage of the main capacitor due to the charging does not reach a predetermined voltage after a predetermined time has elapsed, it is determined that the over-excited DC / DC converter is in an overload state, and the overload indicating the overload state Means for outputting a signal;
When the overload signal is received, the pulse width control is performed by repetitive driving that detects the secondary current of the separately excited DC / DC converter, waits for the completion of discharge, and shifts to the primary-side energization operation. 4. A strobe device according to claim 2, wherein the strobe device comprises a secondary coil current detection circuit. Pulse width control circuit
5. The strobe device according to claim 4, further comprising a primary coil overcurrent detection circuit that detects that an overcurrent has flowed to a primary side of a separately excited DC / DC converter and turns off the logic circuit. An application specific integrated circuit device constituting the strobe device according to claim 4,
A triangular wave voltage generating circuit for generating a single frequency triangular wave;
A soft start voltage generating circuit that generates a soft start voltage that rises with the passage of time after the start of charging;
A comparator that compares the triangular wave with the soft-start voltage and outputs a duty signal that gradually increases the energization period at a single frequency as time elapses from the start of charging;
A soft start voltage cancel circuit for detecting that the terminal voltage of the main capacitor has risen to the set voltage and canceling the soft start operation;
Until the main capacitor is fully charged, the logic circuit that charges the main capacitor based on the output of the comparator, detects that the capacitor is fully charged, and terminates the charging;
When the charging voltage of the main capacitor due to the charging does not reach a predetermined voltage after a predetermined time has elapsed, it is determined that the over-excited DC / DC converter is in an overload state, and the overload indicating the overload state Means for outputting a signal;
When the overload signal is received, the pulse width control is performed by repetitive driving that detects the secondary current of the separately excited DC / DC converter, waits for the completion of discharge, and shifts to the primary-side energization operation. A special-purpose integrated circuit device characterized in that a secondary coil current detection circuit is constructed. 7. The application specific integrated circuit device according to claim 6, further comprising a primary coil overcurrent detection circuit that detects the occurrence of an overcurrent and turns off the logic circuit. 8. The application specific integrated circuit device according to claim 6, further comprising an external connection terminal for connecting a time constant determining element of at least one of the triangular wave voltage generation circuit and the soft start voltage generation circuit. . The strobe device according to any one of claims 2 to 5,
The predetermined time during the charging operation for the main capacitor for determining that the main capacitor is in an overload state is:
When the load state is normal according to each value of the driving frequency of the pulse width control, the power supply voltage and current, the capacity of the main capacitor, the charging voltage of the main capacitor, and the charging efficiency of the main capacitor, A strobe device characterized in that a minimum time required for the voltage of the main capacitor to reach a voltage that can be determined to be normal compared to the predetermined voltage is set. The strobe device according to claim 9,
When determining the overload state for the main capacitor, the predetermined voltage serving as a comparison reference for the charging voltage of the main capacitor is:
A strobe device characterized in that the strobe device is set to a voltage higher than a reactivation voltage generated when the main capacitor is short-circuited and lower than a voltage of the main capacitor after strobe light emission in a normal load state. The application specific integrated circuit device according to any one of claims 6 to 8,
The predetermined time during the charging operation for the main capacitor for determining that the main capacitor is in an overload state is:
When the load state is normal according to each value of the driving frequency of the pulse width control, the power supply voltage and current, the capacity of the main capacitor, the charging voltage of the main capacitor, and the charging efficiency of the main capacitor, An application specific integrated circuit device characterized in that a minimum time required for the voltage of the main capacitor to reach a voltage that can be determined to be normal as compared with the predetermined voltage is set. An application specific integrated circuit device according to claim 11,
When determining the overload state for the main capacitor, the predetermined voltage serving as a comparison reference for the charging voltage of the main capacitor is:
An application specific integrated circuit device characterized in that it is set to a voltage that is higher than a reactivation voltage generated when the main capacitor is short-circuited and lower than a voltage of the main capacitor after strobe light emission in a normal load state.

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