JPH10123596A - Capacitor boosting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a capacitor boosting circuit capable of preventing undesired loss generated when the capacitor is charged. SOLUTION: An FET as a switching element is shown by figure 21, the gate is connected to the output of an oscillation circuit 29, the source is connected to one end of a resistance 22, besides, the drain is connected to the base of a transistor 5. An FET as a switching element is shown by figure 24, the gate is connected to the output of a comparator 28, the source is connected to one end of a feed-back coil, besides, the drain is connected to the base of the transistor 5. A diode is shown by figure 25. The comparator is shown by figure 28, the output is connected to the gate of the FET 24. When a high-level signal is imparted to the input of the oscillation circuit 29, the oscillation is inhibited, and, the output is controlled to be at a low level, and when the low level signal is imparted to the circuit 29, the oscillation is started.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a booster circuit for a capacitor used in a flash device or the like.

[0002]

2. Description of the Related Art In a booster circuit which charges a capacitor via a secondary winding by turning on / off a transistor connected to a primary winding of a booster transformer by self-excited oscillation, generally, the capacitor voltage is increased. When it is high, that is, when the charging current to the capacitor becomes smaller than that of the secondary winding, the oscillation frequency increases.

In this state, the primary winding current immediately before the transistor is turned off is inevitably generated because the transistor is turned off, but does not contribute to the charging of the capacitor, resulting in wasted energy. I have. In a conventional booster circuit, this wasteful energy is repeatedly generated at the above-mentioned high frequency, resulting in a large energy loss.

The above-mentioned conventional booster circuit will be described in detail with reference to FIGS. 4, 5 and 6.

In FIG. 4, 1 is a power battery, 2 is a power switch, and one end is connected to a plus terminal of the power battery.
The other end is connected to an emitter of a transistor 5 described later. Reference numeral 3 denotes a resistor, and 4 denotes a capacitor, which are connected between the base and the emitter of the transistor 5, respectively.
Reference numeral 5 denotes a PNP transistor, the emitter of which is a positive terminal of the power supply battery 1, and the collector of which is a step-up transformer 7 described later.
And the base is connected to one end of the feedback winding of the step-up transformer 7, respectively.

Reference numeral 7 denotes a step-up transformer, one end of which is connected to the collector of the transistor 5, the other end of which is connected to the minus terminal of the power supply battery 1, and one end of which is connected to the base of the transistor 5 and a resistor 6. And a secondary winding having one end connected to the anode of a diode 8 described later and the other end connected to the base of the transistor 5 described above. Reference numeral 8 denotes a rectifying diode, whose cathode is connected to an anode of a main capacitor 9 described later. Reference numeral 9 denotes a main capacitor for providing luminous energy to a xenon discharge tube 17 described later. The anode is connected to the cathode of the diode 8 and the cathode is connected to the minus terminal of the power battery 1.

Reference numeral 10 denotes a resistor, one end of which is connected to a light emission signal transmission circuit 18 which will be described later, and the other end which is connected to the gate of an SCR 14 which will be described later. 11 is a resistor, 12 is a capacitor, which is connected in parallel.
It is connected between the gate and cathode of CR14. 13
Is a resistor, one end of which is connected to the anode of the main capacitor 9, and the other end of which is connected to the anode of the SCR 14.

A trigger capacitor 15 has one end connected to the anode of the SCR 14 and the other end connected to one end of a primary winding of a trigger transformer 16 described later. Reference numeral 14 denotes a gate at one end of the resistor 10, an anode at one end of the capacitor 15, and a cathode at the main capacitor 9.
SCRs connected to the respective negative electrodes. Reference numeral 16 denotes a trigger transformer having a primary winding and a secondary winding. One end of the primary winding is connected to one end of the capacitor 15 and the other end is connected to the SC.
One end of the secondary winding is connected to the trigger electrode of the xenon discharge tube 17, and the other end is connected to the cathode of the SCR.

Reference numeral 17 denotes a xenon discharge tube for emitting flash light. The anode is connected to the anode of the main capacitor 9, and the cathode is connected to the cathode of the main capacitor 9. Reference numeral 18 denotes a light emission signal transmission circuit which receives a signal from a camera (not shown) via light emission and generates a high level signal.

In FIG. 4, the resistors 10, 11, 13, the capacitors 12, 15, the SCR 14, the trigger transformer 16, the xenon discharge tube 17, and the light emission signal transmission circuit are well-known xenon tube light emission circuits, and respond to a light emission start signal. The xenon discharge tube 17 emits light, but the description of the operation here is omitted.

Next, the boosting operation of the main capacitor 9 in FIG. 4 will be described. When the power switch 2 is turned on, the base current of the transistor 5 as a switching element flows through the feedback winding of the step-up transformer 7 and the resistor 6, and the collector current of the transistor 5 flows through the primary winding of the transformer 7. An oscillation circuit composed of 6, a capacitor 4, a transistor 5, and a step-up transformer 7 starts self-excited oscillation.

The operation when the voltage of the main capacitor 9 is low will be described with reference to FIG. In FIG. 6, at t4, the base current of the transistor 5 flows and the increase in the feedback current is fed back to the primary winding, so that the primary winding current, that is, the collector current of the transistor 5 increases. Further, the current increase in the primary feedback winding is fed back to the feedback winding, and the current in the base winding increases, so that the transistor 5 is completely turned on.

When the transistor 5 is turned on, the transformer 2
A charging current flows through the main capacitor 9 via the diode 8 connected to the next side. At this time, the change in the collector current of the transistor 5 causes a very large current to flow between t4 and t5. However, since the voltage of the main capacitor 9 is low, the charging current of the capacitor 9 is reduced by the voltage of the capacitor 9. It is very large when high.

As time elapses from t4, the current irrelevant to the current supply to the secondary side gradually increases. With this current, the magnetic flux density of the magnetic material of the transformer 7 also gradually increases. When this current reaches IP shown in FIG. 6 and reaches the saturation region of the magnetic flux density of the magnetic material, the feedback operation is not performed, and the transistor 5 is turned off.

When turned on, the collector current is several times to several tens times as large as the current Ip. Further, the off transition point is t5. The time from t4 to t5 varies depending on the voltage of the main capacitor 9, and is longer as the voltage is lower. When the transistor 5 is turned off at t5, the output of the feedback winding oscillates due to the energy stored in the transformer 7, a reverse bias is applied to the base of the transistor 5 for a predetermined time, and then a forward bias is applied to the base of the transistor 5. The current flows and the operation from t4 is repeated again to continue the oscillation.

In the above description, the current irrelevant to the current supply to the secondary side is generally very small as compared with the collector current, so that the loss is very small.

Next, a case where the voltage of the main capacitor 9 is high will be described with reference to FIG. When the base current of the transistor 5 starts flowing at t1 due to the self-excited oscillation, the transistor 5 is turned on as described in the description of FIG. After this 2
The main capacitor 9 is charged through the next winding and the diode 8, but the charging current is small because the voltage of the main capacitor 9 is high, and therefore the collector current of the transistor 5 is also small.

However, as described above, the current irrelevant to the current supply to the secondary side gradually increases. This current also gradually increases the magnetic flux density of the magnetic material of the transformer 7,
At t2, the magnetic flux density starts to saturate, and the collector current of the transistor 5, that is, the primary winding current of the step-up transformer rapidly increases. When this current reaches Ip shown in the graph and reaches the saturation region of the magnetic flux density of the magnetic body, the feedback operation is not performed, and the transistor 5 is turned off. The above Ip
Is larger than the current from t1 to t2, and t
The time from 2 to t3 is a non-negligible value compared to the time from t1 to t2, and a large loss occurs from t2 to t3.

[0019]

In the conventional booster circuit, when the base current of the switching transistor on the primary winding side starts to flow at time t1 shown in FIG. 5 by self-excited oscillation, this transistor is turned on, and thereafter, The main capacitor is charged through the secondary winding, but the charging current is small because the voltage of the main capacitor is high, and the collector current of the transistor is also small.

However, as described above, the current irrelevant to the current supply to the secondary side gradually increases. This current also gradually increases the magnetic flux density of the magnetic material of the transformer, but the magnetic flux density starts to saturate at time t2, and the collector current of the transistor, that is, the primary winding current of the step-up transformer rapidly increases. When the current reaches Ip shown in FIG. 5 and reaches the saturation region of the magnetic flux density of the magnetic material, the feedback operation is not performed, and the transistor is turned off. The above Ip is large compared to the current from t1 to t2, and t2
The time from t2 to t3 is a value that cannot be ignored compared to the time from t1 to t2, and there is a disadvantage that a large loss occurs from t2 to t3.

The present invention relates to a capacitor boosting circuit made for the purpose of eliminating such a loss.

[0022]

According to the first aspect of the present invention, a boosting transformer for boosting a capacitor and first switching means connected in parallel with a primary winding of the boosting transformer are provided. In the configured capacitor booster circuit, a first charge voltage detection circuit for the capacitor is provided, and the self-excited oscillation operation is switched to a separately excited oscillation operation according to a detection result of the charge voltage detection circuit. According to a second aspect of the present invention, the step-up transformer has a primary winding, a feedback winding, and a secondary winding, the first switching means includes a transistor, and the transistor includes the primary winding. A second switching means connected between the base of the transistor and the feedback winding, and a second switching means provided between the base of the transistor and the power supply. A third switching means provided; and the capacitor charged from the secondary winding via a diode, wherein a capacitor voltage is set to a first predetermined voltage based on a detection result of the first charging voltage detection circuit. When the value is lower than the value, the first switching circuit is turned on to perform a self-excited oscillation operation, and when the capacitor voltage is equal to or more than the predetermined value, the second switching means is turned on for a first predetermined time, 2 for a predetermined period of time to perform a separately excited oscillation operation.

With this configuration, it is possible to switch from the self-excited oscillating operation to the separately excited oscillating operation in accordance with the detection result of the detection circuit, and to prevent a loss caused when the capacitor is charged to a relatively high voltage. it can.

The invention according to claim 3 of the present application further comprises a second charging voltage detection circuit for the capacitor,
And changing at least one of the ON time and the OFF time of the switch means during the separately excited oscillation to be shorter based on the detection result of the charging voltage detection circuit.

According to a fourth aspect of the present invention, the step-up transformer has a primary winding, a feedback winding, and a secondary winding, the first switching means includes a transistor, and the transistor includes the first winding. Connected between the next winding and the power supply,
Second switching means provided between the base of the transistor and the feedback winding, third switching means provided between the base of the transistor and a power supply, and the secondary winding. And a second charge voltage detection circuit for the capacitor, wherein the capacitor voltage is higher than a first predetermined value by detection of the second charge voltage detection circuit. When it is equal to or more than the second predetermined value, the second switching means is turned on for a third predetermined time, and the second or fourth switching means is turned on.
For a predetermined period of time to perform a separately excited oscillation operation.

By having these structures, unnecessary loss that occurs when the capacitor is further charged can be prevented as compared with the case of the structures of the first and second aspects.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIG. In FIG. 1, elements having the same functions as in FIG. 4 are given the same numbers as in FIG. 4, and the description of the configuration is omitted.

Reference numeral 20 denotes a resistor, one end of which is a FET 2 described later.
The other end is connected to the negative terminal of the power battery 1. Reference numeral 21 denotes an FET as a switching element. The gate is connected to the output of an oscillation circuit 29 described later, the source is connected to one end of the resistor 22, and the drain is connected to the base of the transistor 5. Reference numeral 22 denotes a resistor, one end of which is connected to the source of the FET 21 and the other end of which is connected to the minus terminal of the power supply battery 1. 23 is a resistor, one end of which is FE
The other end is connected to the gate of T24, and the other end is connected to the minus terminal of the power supply battery 1.

Reference numeral 24 denotes an FET as a switching element. The gate is connected to the output of a comparator 28 described later, the source is connected to one end of a feedback winding, and the drain is connected to the base of the transistor 5. Reference numeral 25 denotes a diode. The anode is connected to the negative terminal of the power supply battery 1 and the cathode is connected to the source of the FET 24.

Reference numerals 26 and 27 are resistors connected in series, and this series circuit is connected in parallel with the main capacitor 9. Reference numeral 28 denotes a comparator. The minus input is connected to the connection point between the resistors 26 and 27, the plus input is connected to a reference voltage source (not shown), and the output is connected to the gate of the FET 24.

An oscillation circuit 29 is turned on for a predetermined time and then turned off for a predetermined time, and is repeated at a predetermined cycle. The input of the oscillation circuit 29 is the comparator 2
8, and the output is connected to the gate of the FET 21. The oscillation circuit 29 is inhibited from oscillating when a high-level signal is applied to its input, and has a low-level output. Oscillation starts when a low-level signal is applied. Further, the comparator 28 and the oscillation circuit 29 are supplied with power from the power supply battery 1.

Next, the operation of FIG. 1 will be described. When the power switch 2 is turned on, the minus input of the comparator 28 is lower than the reference voltage because the main capacitor 9 is not charged, the output of the comparator 28 is at the high level, and the input of the oscillation circuit 29 is at the high level. Therefore, the oscillation operation is prohibited. Therefore, the FET 21 is off. Since the high level signal is given to the gate of the FET 24, the FET 24 is on. In this state, the main capacitor 9 shown in FIG.
When the voltage is low, the self-excited oscillation operation is performed in the same manner as the boost operation.

Next, the main capacitor 9 is charged by the self-excited oscillation operation, and the voltage of the main capacitor 9 becomes a predetermined value determined by the resistance values of the resistors 26 and 27 and the voltage of the reference voltage source connected to the plus input of the comparator 28. Upon reaching, the output of the comparator 28 shifts to the low level. The final charging voltage of the main capacitor 9 is set to 330 V, and the main capacitor voltage that shifts to the low level is 10 V.
It is set between 0 and 200 volts. When the output of the comparator 28 becomes low level, FET2
4 is turned off, and the oscillation circuit 29 starts the oscillating operation, and the boosting operation by the separately excited oscillation is started.

The operation of the oscillation circuit 29 and the boosting operation will be described with reference to FIG. The oscillation operation of the oscillation circuit 29 is shown in FIG.
As shown in (1), a high-level voltage is output from t1 to t2, and a low-level voltage is output from t2 to t3, and this is repeated. The high level voltage causes the FET 21
Is turned on from t1, the base current of the transistor 5 flows through the FET 21 and the resistor 22, and the transistor 5
Turns on. The turning on of the transistor 5 is continued until t2, and charges the main capacitor 9 via the secondary winding of the step-up transformer, the diode 8, and the diode 25.

At this time, the collector current of the transistor 5
That is, the primary winding current of the step-up transformer 7 is shown in FIG.
The FET 21 is turned off at t2, and is kept off until t3. Thereafter, this is repeated, and the main capacitor 9 is charged. Here, t1 to t2, that is, Ton3, is set shorter than t1 to t2 in FIG. 5, that is, Ton1. Therefore, it is possible to prevent the loss occurring from t2 to t3 in FIG.

Next, the off time from t2 to t3 in FIG. 2 will be described. As shown in the waveform of the anode voltage of the diode 8 in FIG. 2, when the transistor 5 is turned off at t2, the voltage temporarily shifts to a negative voltage due to the energy stored in the transformer 7, becomes a positive voltage again, and charges the main capacitor once. The oscillation circuit is set so that the transistor 5 is turned on. If the off time is too short, the energy loss when the transistor 5 is turned on increases.

FIG. 3 shows another embodiment of the present invention. FIG. 3 shows another embodiment of the circuit within the dotted line in FIG.
In FIG. 1, the main capacitor 9 is charged during the period from t1 to t2. When the charging proceeds and the battery is fully charged, the charging is completed before reaching t2, and then unnecessary power is supplied until t2. FIG. 3 aims to prevent this unnecessary power loss.

In FIG. 3, reference numeral 28 denotes a comparator having the same function as 28 in FIG. 1. The minus input, the plus input and the output are connected in the same manner as in FIG. 29 also has the same function as the oscillation circuit of FIG. A comparator 31 has a negative input connected to a connection point between the resistors 26 and 27, and an output connected to an input of an oscillation circuit 32 described later. The plus input is connected to a second reference voltage source.

Reference numeral 32 denotes an oscillation circuit which is oscillated by a high-level signal input, outputs a low-level signal, and starts oscillating by a low-level signal input. The oscillation circuit 3
The output during the oscillation of No. 2 is set such that the high-level signal output period is shorter than the period from t1 to t2 in FIG. 2, and the low-level signal output period is equal to or longer than the period from t2 to t3 in FIG. An AND circuit 33 has one end connected to the output of the oscillation circuit 29 and the other end connected to the output of the comparator 31. An OR circuit 34 has one end connected to the output of the AND circuit, the other end connected to the output of the oscillation circuit 32, and the output connected to the gate of the FET 21.

Next, the operation of FIG. 3 will be described with reference to FIG. When the power switch 2 is turned on, the comparator 28,
31, the oscillation circuits 29 and 32, the AND circuit 33, and the OR circuit 34 are supplied with power. When the voltage of the main capacitor 9 is low, the outputs of the comparators 28 and 31 are at a high level, the oscillation circuits 29 and 32 are inactive, and the FET 24
Is on. This state is the same operation as when the main capacitor 9 of the circuit within the dotted line in FIG. 1 is low.

Next, when the main capacitor 9 is charged and the output of the comparator 28 shifts to the low level, the FET
24 is turned off, and the oscillation circuit 29 starts operating. The output voltage of the oscillation circuit 29 is turned on / off by the FET 21 via the AND circuit 33 and the OR circuit 34 in accordance with the output of the oscillation circuit 29. This state is the same as the operation of the circuit within the dotted line in FIG. 1 when the voltage of the main capacitor 9 is high.

When the voltage of the main capacitor 9 further rises and the output of the comparator 31 shifts to the low level, the oscillation circuit 32 starts operating. At this time, since the low level is transmitted to the input of the AND circuit 33, the output of the oscillation circuit 29 is not transmitted to the OR circuit. From the above, the output of the oscillation circuit 32 is connected to the FET via the OR circuit 34.
21 is transmitted to the gate. As described above, the oscillation circuit 32
, The transistor 5 is turned on for a time shorter than the time from t1 to t2 in FIG. 1, so that the above-described loss can be prevented. The voltage of the main capacitor 9 when the output of the comparator 31 shifts to the low level is about 300
V is set. In FIG. 3, two comparators are provided, but three or more comparators can be further provided to perform more detailed control.

(Correspondence between the Invention and the Embodiment) The first charging voltage detection circuit according to the invention of the present application comprises the circuit comprising the comparator 28 and the oscillation circuit 24 in the embodiment, The charging voltage detection circuit is also a circuit including a comparator 31 and an oscillation circuit 32. Further, the first switching means represents the transistor 5 in the embodiment, the second switching means also represents the FET 24, and the third switching means represents the FET 21.

[0044]

According to the first or second aspect of the present invention, it is possible to prevent a loss caused when the capacitor is charged to a relatively high voltage in the boosting operation of the capacitor.

According to the third or fourth aspect of the present invention, it is possible to prevent a loss that occurs when the capacitor is charged to a relatively high voltage in the boosting operation of the capacitor. Further, unnecessary loss that occurs when the capacitor is charged further than the voltage can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a time chart showing the operation of FIG.

FIG. 3 is a block diagram showing another embodiment of the present invention.

FIG. 4 is a block diagram showing a conventional example.

FIG. 5 is a time chart showing the operation of FIG. 4;

FIG. 6 is a time chart illustrating the operation of FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power supply battery 2 Power switch 5 Transistor 7 Step-up transformer 8 Rectifier diode 9 Main capacitor 17 Flash discharge tube 21, 24 FET 28, 31 Comparator 29, 32 Oscillation circuit 33 AND circuit 34 OR circuit

Claims (4)

[Claims] 1. A capacitor boosting circuit comprising a boosting transformer for boosting a capacitor and a first switching means connected in parallel with a primary winding of the boosting transformer. A boosting circuit for a capacitor, comprising: a charging voltage detection circuit; and switching from a self-excited oscillation operation to a separately excited oscillation operation according to a detection result of the charging voltage detection circuit. 2. The step-up transformer has a primary winding, a feedback winding and a secondary winding, and the first switching means comprises a transistor;
The transistor is connected between the primary winding and a power supply, a second switching means provided between the base of the transistor and the feedback winding, and between a base of the transistor and a power supply. A third switching means provided in each case, and the capacitor charged from the secondary winding via a diode, wherein the capacitor voltage is set to a first voltage based on a detection result of the first charging voltage detection circuit. When the voltage is lower than a predetermined value, the first switching circuit is turned on to perform a self-excited oscillation operation. When the capacitor voltage is equal to or higher than the predetermined value, the second switching means is turned on for a first predetermined time, 2. The capacitor booster circuit according to claim 1, wherein the capacitor is stepped off for a second predetermined time to perform a separately excited oscillation operation. 3. A second charging voltage detection circuit for the capacitor is provided, and at least one of an on time and an off time of the switch means at the time of the separately excited oscillation based on a detection result of the second charging voltage detection circuit. 2. The capacitor boosting circuit according to claim 1, wherein the time is changed so as to shorten the time. 4. The step-up transformer has a primary winding, a feedback winding, and a secondary winding, and the first switching means comprises a transistor;
The transistor is connected between the primary winding and a power supply, a second switching means provided between the base of the transistor and the feedback winding, and between a base of the transistor and a power supply. A third switching means provided therein, and the capacitor charged from the secondary winding via a diode, further comprising a second charging voltage detection circuit for the capacitor, When the capacitor voltage is equal to or higher than a second predetermined value higher than the first predetermined value by the detection of the charging voltage detection circuit, the second switching means is turned on for a third predetermined time, and the second or fourth switching means is turned on. 3. The capacitor booster circuit according to claim 2, wherein the capacitor is stepped off for a predetermined time to perform a separately excited oscillation operation.