JPH10146053A - Dc/dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the charging mode and improve the energy conversion efficiency by selecting the primary winding to be supplied with currents, so that the winding ratio may increase with the rise of detected charging voltage. SOLUTION: Energy efficiency is enhanced by switching primary windings to be supplied with currents in order such that (P1+P2) to P2 to P1 so as to raise the winding ratio, according to the rise of the charging voltage of a main capacitor C2 by a CPU 1. Hereby, a DC/DC converter high in conversion efficiency can be obtained, which switches the winding ratio of a transformer T1 into substantially three stages at least by at least two transformer primary windings P1 and P2 and switching circuits corresponding severally to the numbers of these primary windings.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a DC / DC converter, and more particularly, to a DC / DC converter applicable to a strobe charging device of a camera.

[0002]

2. Description of the Related Art As a step-up DC / DC converter circuit for charging a capacitor by boosting a low DC voltage by a switching circuit and a step-up transformer, see, for example,
Japanese Patent Publication No. 123713 discloses that a primary winding having a plurality of primary windings having different numbers of windings and a switching circuit connected to each of the primary windings are used to charge a primary winding which is energized according to a charging voltage of a capacitor. A DC / DC converter in which energy conversion efficiency is improved by switching in the middle is disclosed.

[0003]

However, in the DC / DC converter, the number of charging operation modes is limited to be equal to the number of transformer primary windings. And the number of oscillation circuits must be equal to the number of primary windings, and the circuit scale must be increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned technical problems, and has been made to improve the energy conversion efficiency by increasing the charging operation mode, and to realize a small-sized and low-cost DC / DC.
It is intended to provide a converter.

[0005]

Means for Solving the Problems In order to solve the above problems, the present invention employs the following means. That is, the DC / DC converter according to claim 1 is connected in full-bridge to each of a plurality of primary windings having different numbers of turns and a secondary winding, which are connected in series, and a step-up transformer having secondary windings. Switching means for selectively conducting bidirectional current to the primary winding, a capacitor charged by a current obtained by rectifying an induced voltage generated in the secondary winding, and means for detecting a charged voltage of the capacitor; And control means for controlling the switching means by selecting a primary winding to be energized so that the turns ratio is sequentially increased as the detected charging voltage rises.

A DC / DC converter according to a second aspect is the DC / DC converter according to the first aspect,
The number of types of charging operation modes is larger than the number of primary windings of the step-up transformer.

Further, the DC / DC converter according to claim 3 is the DC / DC converter according to claim 1, wherein the control signal of the switching means is given through a decoder means.

[0008]

Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a flash circuit of a camera according to a first embodiment of the present invention. In parallel with the power supply E, a PNP transistor Tr1 and an NPN transistor T
r4, a PNP transistor Tr2 and an NPN
A series circuit with the transistor Tr5 and a series circuit with the PNP transistor Tr3 and the NPN transistor Tr6 are connected respectively. And the transistor Tr1,
A primary winding P1 having a small number of turns of the transformer T1 is connected between the collector of the transistor Tr4 and the collectors of the transistors Tr2 and Tr5.
1 terminal 1 and a transistor T1 on the transistor Tr2 side.
No. 2 terminals are connected.

A primary winding P2 having a large number of turns of the transformer T1 is connected between the collectors of the transistors Tr2 and Tr5 and the collectors of the transistors Tr3 and Tr6. The second terminal of the transformer T1 is connected to the transistor Tr2 side. The third terminal of the transformer T1 is connected to the transistor Tr3 side. That is, the transistor Tr1
To Tr6 are connected to the two primary windings of the transformer T1, respectively, so that bidirectional current can be applied to any one of the primary windings. The bases of the transistors Tr1 to Tr6 are connected to output terminals S1 to S6 of the CPU 1 for controlling the operation of the strobe, respectively.

The primary windings P1, P2 of the transformer T1
The winding end of 1 and the winding start of P2 are connected inside the transformer, and the winding directions of the respective windings are also the same. The bridge rectifier circuit composed of the diodes D1 to D4 has its input side connected to the secondary winding S of the transformer T1, and its output side connected to GND and the anode of the diode D5. A series body of resistors R1 and R2 is connected to the output side of the diode bridge rectifier circuit, and a connection point between the resistors R1 and R2 is a CPU.
1 Vst terminal.

A thyristor SCR, a capacitor C1, and a trigger coil T2 are connected from the cathode of the diode D5 via a resistor R3. Further, the arc tube Xe and I
A series body with the GBT is connected in parallel with the main capacitor C2, and the gate terminal of the thyristor SCR and the ST of the CPU 1 are connected.
ON terminal, IGBT gate terminal and CPU1 STOF
F terminals are connected to each other.

Before describing the operation of the circuit of FIG. 1, a basic strobe charging circuit will be described with reference to FIGS. FIG. 8 shows a basic circuit of a forward DC / DC converter. This circuit includes a power supply E, a step-up transformer T, an oscillation transistor Tr, a diode D, and a capacitor C. The power source E is V1 (v), the number of turns of the primary winding of the step-up transformer T is n1 (turn), the number of turns of the secondary winding is n2 (turn), the turn ratio is N (n2 / n1), and the capacitance of the capacitor C is electrostatic. The capacitance is set to CM (μF), and the transistor Tr is turned on / off to charge the capacitor C. According to the basic formula of the transformer, the voltage V2 of the capacitor C can be boosted to V2 = N × V1 (v)-(1), and the current I2 flowing through the transformer T is given by the following formula.

I 2 = I 1 / N (A) −−−−− (2) The charge Q (C) stored in the capacitor C is represented by Q = C × V = I × t, where charging time is t (s). (C)-From the equation (3), CM x V2 = I2 x t (C)-------------(4) From the formulas (2) and (4),
It is given by the following equation.

I1 × t = N × I2 × t (A × s) (5) Further, the unit voltage of the capacitor (for example, 10
(V)) The consumed charge per unit is given by N × CM × 10 = I1 × t (A × Sec) (6), which is represented by a graph as shown in FIG. It is not constant. In other words, the power consumption of the power supply of this circuit is equal to the capacitance CM of the capacitor C.
And the turns ratio N of the transformer.
Therefore, if the turns ratio N of the transformer T is reduced, the charge consumption can be reduced, but the capacitor voltage cannot be charged to V2.

Therefore, by preparing a plurality of primary windings having different numbers of windings and appropriately selecting the primary winding to be energized according to the capacitor charging voltage, current consumption can be reduced and the voltage can be boosted to a desired full charging voltage. A possible capacitor charging circuit is obtained.

This relationship will be described with reference to FIG. 7. Charging is performed using a transformer primary winding having a transformer turns ratio of half (N / 2) the normal winding voltage up to half the full charge voltage V2. Thereafter, charging is performed using the primary winding of the normal turns ratio (N). As a result, up to half of the full charge voltage is charged with half of the conventional charge, and thereafter up to the full charge voltage is charged with the same charge as before, so that 1/4 of the total charge can be reduced as a result. .

If an infinite number of primary windings having different numbers of windings are prepared and charged while continuously switching them sequentially, the electric charge consumption can be theoretically reduced to １ ／. When the power source is a battery as described above, it goes without saying that the life of the battery can be extended by reducing the electric charge consumed by the power source.

Next, the operation of the charging circuit of FIG. 1 will be described with reference to the time chart of FIG. First, FIG.
In the period (I) of (A), the output terminal S of the CPU 1
1, an ON signal is output to S6, and the transistor Tr is output.
By turning on 1 and Tr6 simultaneously, the power supply E
(+)-Transistor Tr1-Primary winding P1 of transformer T1-Primary winding P2-Transistor Tr6-Power supply E
A current flows through the closed circuit of (-). An electromotive force is generated in the secondary winding due to a temporal change in the current of the primary winding of the transformer, and a charging current for the capacitor flows. This current is generated by the secondary winding S of the transformer T1, the diode D3, the diode D5, the main capacitor C2, the diode D2, and the secondary winding S of the transformer T.
To charge the main capacitor C2. The current in the secondary winding of the transformer T1 stops when the generated electromotive force is released. After the charging current is stopped, it is useless to continue to flow the primary current any more.
And Tr6 are simultaneously turned off to stop the transformer primary winding current.

In the period (II) of FIG.
U1 outputs ON signals from the output terminals S3 and S4 to turn on the transistors Tr3 and Tr4 simultaneously,
By passing a current through the primary windings P1 and P2 of the transformer T1 in a direction opposite to the previous direction, the secondary current is changed from the secondary winding S of the transformer T1 to the diode D4 to the diode D5 to the main capacitor C2 to the diode D1 to the diode D2. The current flows to the next winding S, and the capacitor is charged in the same manner as described above by the secondary voltage associated therewith.

As described above, the transistors Tr1 and Tr6
2 and the pair of transistors Tr3 and Tr4 are alternately switched to charge the capacitor C2. From the time when one transistor pair is turned off until the time when the next transistor pair is turned on, FIG. As described above, by providing a quiescent period in which both transistor pairs are off, both the reduction of the reactive current and the reduction of the charging time due to the switching delay when the transistor is off are achieved.

The charging voltage of the capacitor C2 is equal to the resistance R1,
The voltage divided by the voltage dividing circuit composed of R2
A / D conversion by inputting to the Vst terminal of
t terminal voltage is a specified voltage (for example, 1 / full charge voltage)
3), the transistors Tr1, Tr
The switching operation of the pair of transistors Nos. 6 and Tr3 and Tr4 is stopped, and the first charging operation ends.

In the following step, the transistors Tr2,
The pair of transistors Tr6 and the pair of transistors Tr3 and Tr5 are alternately switched, and the primary winding P of the transformer T1 is switched.
2 is charged by bidirectional conduction, charging of the main capacitor C2 is continued, and a voltage Vb of 2/3 of the full charge voltage is applied.
Charge up to.

In the last step, the transistor Tr
2, the pair of Tr4 and the pair of transistors Tr1 and Tr5 are alternately switched to perform bidirectional current conduction only in the primary winding P1 of the transformer T1, and the main capacitor C2 reaches the full charge voltage value Vc. Then, a series of charging operations ends.

As described above, in the present embodiment, the primary windings to be energized are sequentially (P1 + P2) to P2 to P2 so as to increase the winding ratio in accordance with the increase in the charging voltage of the main capacitor C2.
By switching to P1, the energy conversion efficiency is increased.

Here, the power consumption of the power supply will be verified.
As conditions, the voltage of the power supply E is 3 (v), the number of turns of the primary winding P1 of the transformer T1 is 10 (turns), the number of turns of P2 is 20 (turns), and the number of turns of the secondary winding S is 1500.
(Turn). However, in the conventional DC / DC converter, there is no primary winding P2, the capacitance of the main capacitor C2 is 200 (μF), and the charge stop voltage of the main capacitor is 300 (v).

First, the charge consumed by the conventional charging circuit until the main capacitor C2 is fully charged is determined.
The total amount of charge flowing through the transformer secondary winding is given by the following equation.

I2 × t = 300 × 0.0002 = 0.06 (A × s) On the other hand, the total amount of charge flowing through the primary winding of the transformer is I1 × t = (I1 × t = N × I2 × t) 1500/10) × 0.06 = 9 (A × s)

Subsequently, in this embodiment, the electric charge required until the main capacitor C2 is fully charged is determined. However, in this embodiment, the voltage of the main capacitor C2 is 0.
From (v) to 100 (v), the primary winding is P1 + P2, and from 100 (v) to 200 (v), the primary winding is P1 + P2.
2, and charging is performed by setting the primary winding to P1 from 200 (v) to 300 (v).

First, the consumed electric charge from 0 (v) to 100 (v) is I1 × t1 = 1500 / (10 + 15) × 100 × 0.0002 = 60 × 0.02 = 1.2 (A × s) Subsequently, the consumed charge from 100 (v) to 200 (v) is I1 × t2 = (1500/15) × 100 × 0.0002 = 100 × 0.02 = 2 (A × s) The charge consumption from (v) to 300 (v) is: I1 × t3 = (1500/10) × 100 × 0.0002 = 150 × 0.02 = 3 (A × s) Therefore, the DC according to the present embodiment The total charge consumption of the / DC converter is 1.2 + 2 + 3 = 6.2 (A × s). In the present embodiment, the charge consumption is reduced by about 31% as compared with the conventional DC / DC converter.

Based on the above equation, a graph of current consumption for increasing the main capacitor voltage in units of 10 V is shown in FIG.
Shown in The broken line in the figure represents the current consumption of the conventional DC / DC converter, and the solid line drawn stepwise represents the current consumption of the DC / DC converter according to the present embodiment. According to this figure, the consumed charge is represented by the area, and the hatched portion in the figure corresponds to the charge reduced by the present invention.

In FIG. 1, when light emission is started after charging is completed, a light emission signal is output from the STON terminal of the CPU 1 to the thyristor SCR. The trigger capacitor C1 is a resistor R
3, and is charged to the same voltage as the main capacitor C2. Light emission signal ST is applied to the gate terminal of thyristor SCR.
When ON is input, the thyristor SCR is turned on, and the electric charge stored in the capacitor C1 is changed from SCR to the trigger coil T.
2, the high-voltage electromotive force is generated in the secondary winding of the trigger coil T2, and this high-voltage signal is applied to the glass tube portion of the xenon tube Xe. When the high voltage is applied to the xenon tube Xe, the xenon gas inside is excited and the internal resistance value of the tube rapidly decreases, so that the energy stored in the main capacitor C2 is discharged through the xenon tube and the flash light emission state starts. Become.

When the light emission stop signal is output from the STOFF terminal of the CPU 1, the IGBT is turned off, so that the light emission of the xenon tube Xe stops. In this embodiment, for the sake of explanation, the primary winding of the transformer T1 is divided into two systems of P1 and P2, but three or more primary windings and one set of switching units are connected to the connection between the primary windings. It goes without saying that if the means is connected, it belongs to the technical scope of the present invention.

According to this embodiment, at least two transformer primary windings and switching circuits respectively corresponding to the number of the primary windings can change the winding ratio of the transformer substantially in at least three stages, and have a high conversion efficiency. DC /
A DC converter can be provided.

By optimizing the control timing of each switching element, a DC / DC converter with reduced reactive current can be provided. Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 4 shows a strobe charging circuit according to a second embodiment of the present invention, which includes the PNP transistors Tr1 to Tr3 and the NPN transistor Tr4 according to the first embodiment.
To Tr6 are all changed to n-channel type MOSFETs, and a control circuit 101 shown in a dashed line is added.
To the control circuit 101 from the signal lines CLK and CHG, respectively.
1 and CHG2 are connected. Note that the xenon tube light emitting section and the control mode of light emission are the same as those in the above-described first embodiment, and a description thereof will be omitted.

The signal CLK output from the CPU 1 is a signal for determining the oscillation frequency of the DC / DC converter according to the present embodiment. The two signals CHG1 and CHG2 determine which winding is energized at the time of charging (four different designations are possible because of two bits). Next, the operation of the control circuit 101 driven by the above three signals will be described. The signals CHG1 and CHG2 are connected to an inverter (hereinafter, referred to as an inverter).
INV) 2, 3, AND gate (hereinafter, AN)
D) MOSFETs driven using AND1 to AND3 according to the charging voltage of the main capacitor (not shown)
Select a pair.

The table shown in FIG. 5 shows the DC / DC according to this embodiment.
This is the charging operation pattern of the converter.
When 1 is “H (high level)” and CHG2 is “L (low level)”, an instruction to perform low-voltage charging is given.
When CHG2 is "H", an instruction to perform medium-pressure charging, CHG1
Is "H" and CHG2 is "H", it is an instruction to perform high voltage charging. When CHG1 is "L" and CHG2 is "L", no charging signal is generated and the charging is off. AND4 to 9 and OR gate (hereinafter abbreviated as OR) OR1 to 6 are MO
The timing for turning on the SFETs (M1 to M6) is specified. When the voltage charged in the main capacitor is low and the clock signal is "H", the outputs of AND4, OR1, and OR6 become "H", and the MOSFET pair (M1, M6) turns on.

At this time, the current is changed from the power supply E (+) to the MOSFE.
T (M1) to primary winding P1 to primary winding P1 of transformer T1
2 to MOSFET (M6) to power supply E (-).
When the voltage for charging the main capacitor is low and the clock signal is "L", the outputs of AND5, OR3, and OR4 become "H" and the MOSFET pair (M3, M4) is turned on. At this time, the current flows from the power supply E (+) to the MOSFET (M
3) The primary winding P2 of the transformer T1 to the primary windings P1 to M
It flows from OSFET (M4) to power supply E (-). The voltage for charging the main capacitor is medium pressure and the clock signal is "H"
At this time, the outputs of AND6, OR2, and OR6 become "H", and the MOSFET pair (M2, M6) turns on. At this time, the current flows from the power supply E (+) to the MOSFET (M2) to the primary winding P2 of the transformer T1 to the MOSFET (M6) to the power supply E (-). When the voltage for charging the main capacitor is medium pressure and the clock signal is "L", AND7, OR
3. The output of OR5 becomes "H" and the MOSFET pair (M
3, M5) turns on. At this time, the current is from the power source E (+)
MOSFET (M3)-primary winding P2 of transformer T1
The current flows from the MOSFET (M5) to the power supply E (-).

When the voltage for charging the main capacitor is high and the clock signal is "H", AND8, OR1, OR5
Becomes "H" and the MOSFET pair (M1, M5)
Turns on. At this time, the current is from power supply E (+) to MOSFE
T (M1) to primary windings P1 to MOSFE of transformer T1
It flows from T (M5) to power supply E (-). When the voltage for charging the main capacitor is high and the clock signal is "L",
The outputs of AND9, OR2, and OR4 become “H”, and MO
The SFET pair (M2, M4) turns on. At this time, the current flows from the power supply E (+) to the MOSFET (M2) to the primary winding P1 of the transformer T1 to the MOSFET (M4) to the power supply E (-).

By using the control circuit 101 as a decoder, only three control output signals from the CPU 1 are required, and a DC / DC converter with easy CPU control can be provided.

In this embodiment, the frequency of the CLK signal is fixed. However, by increasing the frequency of the CLK signal, the charging time can be shortened and the power consumption of the power supply can be reduced.

According to the above-described embodiment of the present invention, the following configuration is derived. (1) a step-up transformer having a plurality of primary windings and secondary windings having different numbers of windings, and a plurality of switching elements connected in a bridge type to the plurality of primary windings of the step-up transformer;
Control means for controlling the plurality of switching elements;
A DC / DC converter comprising: a main capacitor charged by a charging current obtained by rectifying an induced voltage of a secondary winding of the step-up transformer; and means for detecting a charging voltage of the main capacitor. (2) The DC / DC converter according to (1), wherein the control means selectively obtains a plurality of turns ratios by selectively turning on the plurality of switching elements. (3) The control means according to (1), wherein the control means controls the switching element so as to select a desired turns ratio from among the plurality of turns ratios according to a charging voltage of the main capacitor. DC / DC converter. (4) The DC / DC converter according to (1), wherein the control means changes an operating frequency of a switching element to be turned on in accordance with a charging voltage of a main capacitor. (5) The switching element which is turned on so that the turns ratio of the primary winding of the transformer is reduced when the charging voltage of the main capacitor is low, and the turns ratio of the primary winding of the transformer is increased when the charging voltage of the main capacitor is high. The DC / DC converter according to (1), wherein is selected. (6) A transformer having a plurality of primary windings and secondary windings connected in series, switching means for energizing one or more of the primary windings in two directions, and controlling the switching means A DC / DC converter, comprising:

[0042]

As described above, according to the present invention, one or more primary windings are selectively bidirectionally energized by switching means connected in full bridge, and charged by the output of the secondary winding. By appropriately switching the primary windings to be bidirectionally energized according to the charging voltage of the transformer, it is possible to provide a DC / DC converter having a charging operation mode larger than the number of transformer primary windings and having high energy conversion efficiency. it can.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a strobe device to which a DC / DC converter according to a first embodiment of the present invention is applied.

2A is a time chart showing the operation of the DC / DC converter of FIG. 1 and a charging waveform of a capacitor, and FIG. 2B is an enlarged view of the time chart.

FIG. 3 is a diagram illustrating a relationship between a capacitor voltage and a charge consumption in the first embodiment.

FIG. 4 is a circuit diagram showing a DC / DC converter according to a second embodiment of the present invention.

FIG. 5 is a table showing states of control signals of a CPU according to the second embodiment.

FIG. 6 is a graph showing a relationship between a capacitor voltage and a charge consumption when the primary winding is fixed.

FIG. 7 is a graph showing a relationship between a capacitor voltage and a charge consumption when the primary winding is switched.

FIG. 8 is a circuit diagram showing a DC / DC converter according to the related art.

[Explanation of symbols]

E DC power supply, Tr1-Tr6 transistor, D1-D4 bridge rectifier diode, T1 step-up transformer (P1, P2 is primary winding, S is secondary winding), T2 trigger transformer, C1 trigger capacitor, C2 main capacitor, R1-R1 R3 resistor, SCR thyristor, IGBT insulated gate bipolar transistor, Xe xenon discharge tube, CPU central processing unit.

Claims (3)

[Claims] 1. A step-up transformer having a plurality of primary windings having different numbers of windings and a secondary winding connected in series, and a full-bridge connection with each of the plurality of primary windings,
Switching means for selectively conducting bidirectional current to the primary winding; a capacitor charged by a current obtained by rectifying an induced voltage generated in the secondary winding; means for detecting a charged voltage of the capacitor; A DC / DC converter, comprising: a control unit for selecting a primary winding to be energized so as to sequentially increase the turns ratio as the detected charging voltage increases, and controlling the switching unit. 2. The DC / DC converter according to claim 1, wherein the number of types of charging operation modes is larger than the number of primary windings of the step-up transformer. 3. The DC / DC converter according to claim 1, wherein the control signal of said switching means is given through a decoder means.