JPH09233809A - Dc power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To receive a wide range of a DC voltage as an input voltage and supply a DC voltage whose level can be selected among a plurality of levels as an output voltage without using a transformer and reduce the size and the cost of a power supply circuit. SOLUTION: An inductor L1 , a capacitor C1 and an inductor L2 are connected in series to each other and the series circuit is provided between an input voltage Vi and a ground potential and a first connection point A is intermittently connected to a ground terminal by a transistor TR1 . The capacitance of the capacitor C1 is so predetermined as to have the potential difference between the first connection point A and the ground when electrical energies stored in the inductors L1 and L2 are discharged larger than a predetermined output voltage V2 even if the input voltage Vi which is the lowest in the predetermined range of the input voltage is supplied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power supply circuit capable of generating a plurality of voltages from a wide range of DC voltages for an electric device such as a CCD camera which requires a plurality of voltage sources. It is a thing.

[0002]

2. Description of the Related Art Recent electric appliances are often equipped with electric circuits for performing actual operations and electronic circuits for controlling them, and thus a plurality of electronic circuits, electric circuits, etc. are combined. In most electric appliances, the voltage required by each circuit is different. However, it is wasteful to provide a power supply circuit for each individual device, and therefore a power supply circuit capable of generating a plurality of voltages is required to supply a voltage suitable for each circuit.

When the power supply circuit as described above is used in a stationary electric product, the size and weight of the product itself are not often strict, and the size and weight of the power supply circuit itself are not so strict. However, in the case of electrical products where portability is important, the size and weight of the products can be one of the main reasons for selection. Required. this is,
Power circuits are no exception.

For example, as one of the electric products for which portability is important, a video camera using a CCD (hereinafter referred to as C
CD camera). In a general CCD camera, three or more types of voltage sources are required inside. Specifically, 5 [V] (provisionally referred to as V ₁ ) is supplied to the timing generation circuit, the synchronization signal generation circuit, and the video signal processing circuit that drive the CCD, and CC
15 [V] (if V
₂ ), and -8 [V] (tentatively referred to as V ₃ ) must be supplied to the vertical transfer pulse of the CCD and the substrate of the CCD.

Therefore, conventionally, a power supply circuit as shown in FIG. 4 has been used for the purpose of supplying a plurality of voltages. In this power supply circuit, while the input voltage Vi is kept constant at 5 [V], the input voltage Vi is used as it is for V ₁ and the V ₂ is generated by a step-up method using PWM control. That is, by performing the ON / OFF of the transistor TR _10, when the transistor TR ₁₀ is ON, electric energy stored in the inductor L _10, the transistor TR ₁₀ is OFF
When becomes, the output side of the inductor L ₁₀ so that the sum of the voltage generated by the electric energy stored in the input voltage Vi and the inductor L ₁₀ is outputted. The voltage generated thereby is smoothed by the diode D ₁₀ and the capacitor C _10, and an output voltage V ₂ larger than the input voltage Vi is obtained.

The output voltage V ₂ is equal to the resistance R ₁₀ and the resistance R
After being divided by ₁₁ and ₁₁ , the voltage is input to the PWM control type switching regulator control circuit 10, and the output voltage V ₂
ON of the transistor TR ₁₀ so that the voltage becomes 15 [V].
The OFF duty ratio is controlled. In this case, it is possible to increase the output voltage when increasing the time that the transistor TR ₁₀ to ON, conversely, it is possible to lower the output voltage if the shorter the time that the transistor TR ₁₀ to ON. Further, an electric charge is charged by the load to the capacitor C ₁₂ through the collector voltage diode D ₁₁ caused by turning OFF the transistor TR _10, then when the transistor TR ₁₀ to ON, the charge stored in the capacitor C ₁₂ Is smoothed by the diode D ₁₂ and the capacitor C _13, and further, by the constant voltage circuit including the transistor TR ₁₁ , the resistor R _12, and the Zener diode Dz ₁₀ .
The above -8 [V] can be generated.

As another method of utilizing a transformer, there is a power supply circuit as shown in FIG. In this case, energy is stored in the primary side of the transformer 12 while the transistor TR ₁₅ is ON. At this time, a voltage is generated on the secondary side of the transformer 12, but a current does not flow to each of the diodes D ₁₅ , D ₁₆ , and D ₁₇ because of a reverse voltage,
When the transistor TR ₁₅ is turned off, the energy stored in the secondary side is converted into electric energy by the magnetic field on the primary side of the transformer 12, and the diode D ₁₅ and the capacitor C ₁₅ , the diode D ₁₆ and the capacitor C ₁₆ , and the diode D are converted.
Output voltage V ₁ = 5 [V] and output voltage V ₂ = 15 via a smoothing circuit composed of capacitor ₁₇ and capacitor C ₁₇ , respectively.
An output voltage of [V] and output voltage V ₃ = −8 [V] is obtained.

The output voltage V ₁ is divided by the resistors R ₁₅ and R ₁₆ , and the PWM is applied in the same manner as in the above case.
The transistor T is input to the switching regulator control circuit 11 of the control system so that the voltage becomes 5 [V].
The ON / OFF duty ratio of R ₁₅ is controlled. Further, the output voltages V ₁ , V ₂ and V _{3 have} a magnitude of the transformer 1
It can be selected by setting the turns ratio of the two primary side coils and the respective secondary side coils.

[0009]

However, in the above conventional configuration, in the case of the former configuration shown in FIG.
Since the input voltage Vi is supplied as it is to the output voltage V ₁ , it is not possible to accept an input voltage other than the initially set input voltage. Also, therefore, the fluctuation of the actual input voltage Vi affects the output voltage V ₁ .
On the other hand, in the case of the latter configuration shown in FIG. 5, a wide range of input voltage can be tolerated by the switching control on the primary side, but since a transformer is used, downsizing of the power supply circuit reduces the size of the transformer. Will be limited by
This hinders miniaturization and improvement of portability. The present invention has been made to solve the above problems, and an object thereof is to provide a small DC power supply circuit which can accept a wide range of input voltage and can supply a plurality of voltages. It is in.

[0010]

In order to solve the above-mentioned problems, a direct-current power supply circuit according to a first aspect of the present invention includes a first DC power supply circuit between an input terminal to which a DC voltage in a predetermined range is input and a ground potential.
An LC circuit in which an inductor, a capacitor, and a second inductor are interposed in this order, and a switching means for connecting and disconnecting the first connection point and the ground potential is provided at a first connection point between the first inductor and the capacitor. , The first voltage smoothing means are connected in parallel with each other, and the second voltage smoothing means is connected to the second connection point between the capacitor and the second inductor, and the second voltage smoothing means is connected. The output of the conversion means is fed back to turn ON / O between the first connection point and the ground potential.
The switching cycle and the duty ratio for FF are changed to perform the voltage control, and the pulse voltages generated before and after the capacitor due to the ON / OFF are rectified and smoothed by the respective voltage smoothing means. A DC power supply circuit capable of extracting the DC voltage of the first DC voltage, and the absolute value of the peak voltage at the first connection point is predetermined by the first smoothing means even when the minimum input voltage of the DC voltage is input. Is characterized in that the capacitance of the capacitor is set to be higher than the absolute value of the output voltage of.

In the above structure, the first inductor and the second inductor are switched by switching ON / OFF of the switching means.
When the electric energy stored in the inductor moves to the capacitor, by setting the capacitance of the capacitor,
The voltage across the capacitor is greatly increased by the electric energy, and at the first connection point, a pulse voltage having a peak value larger than the sum of the input voltage and the voltage obtained by the second smoothing means is obtained. By smoothing by the 1 smoothing means, the output voltage can be stably taken out without depending on the input voltage.

Further, in order to solve the above-mentioned problems, a DC power supply circuit according to a second aspect of the present invention, in addition to the configuration of the first aspect, has a polarity opposite to the smoothed voltage of the second voltage smoothing means. The third voltage smoothing means for smoothing the voltage component of is connected to the second connection point. In the above configuration, on the second connection point side, the sum of the voltage generated by the capacitor and having the peak value of the opposite polarity to the voltage appearing at the first connection point and the voltage obtained by the second inductor is obtained, In this case, the absolute value of the voltage generated by the capacitor is larger than the absolute value of the voltage generated by the inductor, so that the output voltage having the opposite polarity to the input voltage can be obtained by passing through the third smoothing circuit.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. In the power supply circuit 1 of the present invention, three output voltages generally used in a CCD camera, V ₁ = 5 [V], V ₂
= 15 [V], has a structure for supplying the V ₃ = -8 [V], The input voltage Vi is + 4 + 15
The variation in the range of [V] is allowed. The values of the output voltages V ₁ , V ₂ , and V ₃ described above are set as an example of the voltage values necessary for the CCD camera, and are applied when the power supply circuit according to the present embodiment is applied to another device. It does not prevent that the value of the output voltage is set to a value different from the above.

First, the output voltage V ₁ (= 5) which serves as the main power source.
The configuration and operation for obtaining [V] will be described. As shown in FIG. 1, in the power supply circuit 1, the inductor L ₁ , the capacitor C _1, and the inductor L ₂ are connected in series in this order between the input voltage Vi and the GND. For the sake of simplicity, the inductor L ₁ and the capacitor C ₁ are referred to as a first connection point A, the capacitor C ₁ and the inductor L ₂ are referred to as a second connection point B, and for convenience, The respective potentials are Va and Vb. Then, while the collector terminal of the transistor TR ₁ of npn type, which is an emitter grounded is connected to the first connecting point A, the base terminal of the transistor TR ₁ is connected to the switching regulator control circuit 2, the transistor TR ₁ It controls ON / OFF between the emitter and collector terminals. Further, the second connection point B is provided with a smoothing circuit 3 including a diode D ₁ and a capacitor C ₂ whose cathode side is connected to the second connection point, and further the voltage from the smoothing circuit 3 is provided. Is divided by resistors R ₁ and R ₂ and input to the switching regulator control circuit 2. In the above, the inductances of the inductors L ₁ and L ₂ are both 56 μH, and the capacitances of the capacitors C ₁ and C ₂ are 0.015 μF and 150 μF, respectively. The resistance values of the resistors R ₁ and R ₂ are 18 kΩ and 2.2 k, respectively.
Ω.

In the following description, in order to facilitate understanding, the capacitance of the capacitor C ₁ is, for example, 100 μF.
It is described that the increase in the voltage across the terminals of the capacitor C ₁ is almost negligible even if the electric energy stored in the inductors L ₁ and L ₂ moves to the capacitor C ₁ side.

In the above structure, the potential Va and the potential Vb
The change in the electric potential at the time point will be described. Since this case corresponds to the case where the transient phenomenon in the direct current is repeatedly performed, the following cases will be considered. Steady state with transistor TR ₁ in OFF state (initial state) Transistor TR ₁ changing from OFF state to ON state Transistor TR ₁ changing from ON state to OFF state And after the first power-ON , And are repeated.

First, in the steady state, the potential differences V _L1 and V _L2 across the inductor L ₁ and the inductor L ₂ are both 0 V, and the input voltage Vi is applied to the capacitor C ₁ , so the capacitor C ₁ is applied. Potential difference V at both ends of _1
C1 (= Vab) = Vi. Therefore, the transistor TR
_{When 1 is set} to the ON state (), the potential Va at the first connection point becomes equal to the GND potential, that is, 0 [V] (the actual potential is 0 [0] by the internal resistance between the collector and the emitter of the transistor TR ₁ . V], but the internal resistance is ignored in the following description). Therefore, the current I _L1 such that the potential difference across the inductor L ₁ becomes Vi begins to flow while gradually increasing, and electrical energy is stored in the inductor L ₁ .

Next, from the ON state of the transistor TR ₁ to O
In the FF state (), a voltage V ₁ ′ is generated when the electric energy stored in the inductor L ₁ as a magnetic field is discharged as a current, so that the potential Va at the point A becomes the input voltages Vi and V ₁ ′. Is the sum of In addition, this voltage V ₁ ′
The value of is not constant because it changes depending on the input voltage Vi and the ON period of the transistor TR ₁ in the switching cycle, so that the execution voltage after passing through the smoothing circuit 3 becomes the desired output voltage V _1. Is controlled by the switching regulator control circuit 2 as described later.

Then, the transistor TR ₁ is turned off again.
When the state is changed to the ON state (), the potential Va at the first connection point A also becomes 0 [V], and the above changes are repeated. Therefore, the change in the pattern shown in FIG. 2A is obtained as the potential Va at the first connection point A.

On the other hand, the potential Vb of the second connection point B is 0 [V] in the above steady state, and V _C1 = Vi as described above.
The potential Vb at the second connection point B is lower than the potential Va at the first connection point A by Vi. Therefore, when the transistor TR ₁ is turned on (), the potential of the first connection point A becomes 0 [V], but the potential Vb of the second connection point B is only the voltage Vi of the potential Va of the first connection point A. Because it is low, -Vi
Becomes Therefore, at the potential Vb at the second connection point B, the current I _L2 begins to flow while gradually increasing so that the potential difference across the inductor L ₂ becomes −Vi, and electrical energy is stored in the inductor L _2. .

Next, when the transistor TR ₁ is changed from the ON state to the OFF state (), the potential Va at the first connection point A becomes Vi + V ₁ ′, but the potential difference Vi is still across the capacitor C _1. Exists, the potential Vb at the second connection point B becomes lower than Va by Vi. That is, Va
-Vi = Vi + V ₁ becomes a '-Vi = V _1'. Then, in the inductor L ₁ , electric energy is being emitted so as to maintain Vi + V ₁ ′.
_{Also in 2} , the electric energy stored to maintain V ₁ 'is released. Again, the transistor TR
_{When you} turn from the OFF state of ₁ to the ON state (), after all,
The potential Vb of the second connection point B becomes -Vi, and the second connection point B
A change in the pattern shown in FIG. 2 (b) is obtained as the potential Vb. Therefore, by the smoothing circuit 3 connected to the second connection point B side, the negative side electric energy can be removed and the output voltage V ₁ can be taken out smoothed.

In the above, the transistor TR ₁
The longer the ON period of, the larger the electric energy stored in the inductor L ₁ and the inductor L ₂ ,
Since V ₁ ′ can be boosted, the switching regulator control circuit 2 monitors the voltage proportional to the output voltage V ₁ divided by the resistors R ₁ and R ₂ , and the obtained output voltage V ₁ is If it is judged to be low, the transistor TR
If it is judged to be high while lengthening the ON period of ₁ , it is ON
The value of the output voltage V ₁ is controlled by performing duty control of the ratio of ON / OFF periods so as to shorten the period. Further, in the above description, the capacitor C ₁ has a capacitance such that the voltage increment is sufficiently smaller than the voltage between the terminals of the capacitor C ₁ even when the current in the inductor L ₁ and the inductor L ₂ increases. However, the value of the output voltage V ₁ is equal to that of the inductors L ₁ and L ₂
Of the capacitor C ₁ because it is maintained constant by duty-controlling the ON / OFF period of the transistor TR ₁ as described above.
It does not change even if the value of changes.

Next, the structure and operation for obtaining the output voltage V ₂ (= 15 [V]) will be described. As shown in FIG. 1, a smoothing circuit 4 including a diode D ₂ having a cathode side connected thereto and a capacitor C ₃ (2.2 μF) is connected to the first connection point A, and further, a transistor TR ₂ and a resistor R ₂ are connected. _A so-called shunt regulator 6 composed of ₄ (5.6 kΩ) and the Zener diode Dz ₁ is connected, and its output becomes the output voltage V ₂ . Therefore, the voltage input to the shunt regulator 6 needs to be equal to or higher than the required output voltage V ₂ .

As described above, at the first connection point A, it is known that the voltage whose maximum value is the input voltage Vi + V ₁ ′ can be obtained.
_If a smoothing circuit with the same configuration as when taking out ₁ is used, Vi
A voltage of + V ₁ will be obtained. However, since V ₁ is constant, for the required output voltage V ₂ , Vi
The relationship of + V ₁ > V ₂ must be established. In other words, if it is left as it is, it becomes impossible to take out a voltage higher than the sum of the input voltage Vi and the output voltage V ₁ as V ₂ .

By the way, when the capacitance of the capacitor C ₁ is sufficiently large in the above description, even if the electric energy stored in the inductors L ₁ and L ₂ is absorbed, the capacitor C ₁
Although it has been described that the increment of the voltage between them becomes small enough to be ignored, in the present embodiment, the capacitance of the capacitor C ₁ is
Since the values of the voltage V ₁ ′ and the output voltage V ₁ are hardly influenced, the increase in the voltage between the terminals of the capacitor C ₁ is caused by the electric energy stored in the inductor L ₁ and the inductor L ₂ by turning on / off the transistor TR _1. The capacitance of the capacitor C ₁ is set to be small so that Specifically, as described above, the capacitor C
The capacitance of ₁ is 0.015 μF.

Considering this case, as shown in FIG. 3A, in the steady state of, the potential Va at the first connection point A is V
i, and when the transistor TR ₁ is changed from the OFF state to the ON state (), Va = 0 [V], but when the transistor TR ₁ is changed from the ON state to the OFF state (), first, Va is As in the above, it rises to Vi + V ₁ '. At this time, the electric energy stored as a current in the inductor L ₁ does not stop suddenly, and the capacitor C
Although flows into the _1, the capacitance of the capacitor C ₁ is small, Vi by the accumulation of electrical energy +
Further increase from the potential of V ₁ ′ to the potential V of the first connection point A
a becomes a peak voltage V ₂ ′ that exceeds Vi + V ₁ ′. Of course, the capacitance of the capacitor C ₁ is set so that the value of the peak voltage V ₂ ′ is V ₂ ′> V ₂ . However, as the value of this capacitance, at least at the minimum inputtable voltage Vimin (here, 4 [V]), 15 [V] is maintained even by smoothing the obtained peak voltage V ₂ ′. It is necessary to select a value that can be used.

If the above setting is made, the input voltage V
When i becomes high, it is possible to easily reduce the output voltage by controlling the duty ratio in the ON / OFF period to be small.

Further, the configuration and operation for obtaining the output voltage V ₃ (= -8 [V]) will be described. As shown in FIG. 1, a smoothing circuit 5 including a diode D ₃ and a capacitor C ₄ whose anodes are connected to the second connection point B is connected to smooth the negative voltage at the second connection point B. A shunt regulator 7 including a Zener diode Dz ₂ , a transistor TR ₃ and a resistor R ₃ is connected together.

From the above, it can be seen that the negative-side peak voltage V ₃ ′ appearing at the second connection point B has a relationship of V ₃ ′ = V ₁ ′ −V ₂ ′, and in reality, the second The potential Vb at the connection point B changes as shown in FIG. Therefore, the output voltage V ₃ obtained by smoothing the negative voltage which becomes the peak voltage V ₃ ′ by passing through the above circuit is obtained.

As described above, the power supply circuit 1 of the present embodiment
Then, the power supply circuit is configured using the inductor and the capacitor, and the input voltage V in a wide range of 4 to 15 [V]
From i, three types of output voltages V ₁ = 5 [V], V ₂ = 15
[V], while V ₃ = -8 can be obtained [V], it is not necessary to use a transformer, can be expected cost with can be miniaturized.

In the above configuration, by appropriately setting the capacitance of each capacitor or inductor, a plurality of outputs in which output voltages of the same polarity or different polarities are mixed are used by using an arbitrary value of the DC voltage in a wide range. It is possible to obtain the voltage.

[0032]

The DC power supply circuit according to the invention of claim 1 is
As described above, the first inductor, the capacitor, and the second inductor are provided between the input terminal to which the DC voltage in the predetermined range is input and the ground potential.
A first connecting point between the first inductor and the capacitor, and a switching means for connecting and disconnecting the first connecting point and the ground potential;
The voltage smoothing means is connected in parallel with each other, and the second voltage smoothing means is connected to the second connection point between the capacitor and the second inductor. The output is fed back to control the voltage by changing the switching cycle and the duty ratio when turning on / off between the first connection point and the ground potential.
A DC power supply circuit capable of extracting a plurality of DC voltages by rectifying and smoothing a pulse voltage generated before and after a capacitor in accordance with ON / OFF by each voltage smoothing unit, and having a minimum input of the DC voltage. Even when the voltage is input, the absolute value of the peak voltage at the first connection point is
In this configuration, the capacitance of the capacitor is set to be higher than a predetermined absolute value of the output voltage of the first smoothing means.

Therefore, by utilizing the high voltage appearing at the first connection point by setting the capacitance of the capacitor, an output voltage higher than the sum of the output voltage obtained from the second voltage smoothing means and the input voltage is taken out. It becomes possible to obtain a plurality of predetermined output voltages in a wide range of input voltages, particularly when the input voltage is small, without using a large-sized component such as a transformer. Therefore, it is possible to reduce the size of the device including the DC power supply circuit.

As described above, in the DC power supply circuit according to the invention of claim 2, in addition to the configuration of claim 1, the voltage component having the opposite polarity to the voltage to be smoothed by the second voltage smoothing means is smoothed. The third voltage smoothing means is connected to the second connection point. Therefore, in addition to the effect of the configuration according to the first aspect, there is an effect that the output voltage having the opposite polarity to the input power source can be taken out.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration example of a power supply circuit according to the present invention.

FIG. 2 is a graph showing the time change of the voltage on the circuit when the capacitance of the capacitor is sufficient in FIG. 1, and FIG. 2 (a) is a graph showing the voltage value at the first connection point A. FIG. 3B is a graph showing the voltage value at the second connection point B.

FIG. 3 is a graph showing the time variation of the voltage on the circuit when the capacitance of the capacitor is small in FIG. 1, and FIG. 3 (a) is a graph showing the voltage value at the first connection point A. FIG. 6B is a graph showing the voltage value at the second connection point B.

FIG. 4 is a circuit diagram showing an example of a power supply circuit configured without using a conventional transformer.

FIG. 5 is a circuit diagram showing an example of a power supply circuit configured using a conventional transformer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 power supply circuit (DC power supply circuit) 2 switching regulator control circuit (switching means) 3 smoothing circuit (second voltage smoothing means) 4 smoothing circuit (first voltage smoothing means) 5 smoothing circuit (third voltage smoothing means) 6 shunt regulator (first voltage smoothing means) 7 shunt regulator (third voltage smoothing means) C ₁ capacitor (capacitor) L ₁ inductor (first inductor) L ₂ inductor (second inductor) TR ₁ transistor (Switching means)

Claims (2)

[Claims] 1. An LC circuit in which a first inductor, a capacitor, and a second inductor are provided in this order between an input terminal to which a DC voltage in a predetermined range is input and a ground potential, and the first inductor and the capacitor are provided. A switching means for connecting and disconnecting the first connection point and the ground potential and a first voltage smoothing means are connected in parallel to each other at a first connection point between the capacitor and the second inductor. The second voltage smoothing means is connected to the second connection point between the two, and when the output of the second voltage smoothing means is fed back to turn ON / OFF between the first connection point and the ground potential. The voltage control is performed by changing the switching cycle and duty ratio of
A DC power supply circuit capable of extracting a plurality of DC voltages by rectifying and smoothing a pulse voltage generated before and after a capacitor with ON / OFF by each voltage smoothing unit, and having a minimum input of the DC voltage. The capacitance of the capacitor is set such that the absolute value of the peak voltage at the first connection point is higher than the absolute value of the output voltage of the first smoothing unit, which is determined in advance, even when the voltage is input. DC power supply circuit characterized in that. 2. A third voltage smoothing means for smoothing a voltage component having a polarity opposite to that of the voltage smoothed by the second voltage smoothing means is connected to the second connection point. 1. The DC power supply circuit according to 1.