JP7303774B2 - DC power supply - Google Patents

Description

TECHNICAL FIELD The present invention relates to a DC power supply, and more particularly to a DC power supply with an output voltage selection function that is compatible with worldwide AC voltages and has a plurality of outputs that can be selected.

DC power supplies with multiple outputs are used not only in Japan but also overseas. be. A DC power supply that can meet this worldwide input specification and has multiple DC outputs that can be selected is usually difficult to realize with a single power supply due to the limitation of ON/OFF time of switching elements, and it is difficult to use multiple power supplies. The situation is unavoidable.
Therefore, a DC power supply with multiple outputs that can meet worldwide input specifications and is a single power supply can be used not only in Japan but also overseas where the voltage of the commercial power supply is different from that in Japan, making it easy to use. power supply.
In addition, for this type of DC power supply, there is an increasing demand for an extension of the holding time so that the output can be maintained even in the event of a momentary power failure.

Patent Document 1 discloses an invention of a power supply circuit and an image forming apparatus. In this Patent Document, as shown in FIG. It is a power supply switched by The switching voltages of the present invention are 24V and 6V, and the voltage 24V is used for normal loads, while the voltage 6V is used as a standby voltage and not for normal loads.
In addition, since the output voltage of 24 V and the output voltage of 6 V are controlled by one winding on the secondary side of the transformer used for the power supply, DUTY, that is, the ratio of the ON time TON to the period T of the switching element on the primary side of the transformer ( TON/T) had to be used in a wide control range (the control range of DUTY will be described later).

In addition, the input voltage range is wide, for example, the input voltage of the capacitor input rectification method without PFC (Power Factor Correction) circuit is AC85V to 264V, or the DC input voltage of the transformer fluctuates more than three times, and the output is different. When selecting and outputting one of the voltages (for example, output voltage 12V and output voltage 36V), it is difficult to configure with a single power supply, so a single DC/DC direct current with different output voltages Two power sources were required. In this case, there is a problem that the mounting area is large and the cost is also high.

FIG. 14 is a circuit diagram showing a configuration that requires two systems of the single DC/DC DC power supply. As shown in FIG. 14, this power supply includes control ICs (CONT11, CONT21), switching elements (Q11, Q21), transformers (T11, T21), overvoltage detection circuits (peripheral circuits including PC11, PC21), output voltage control A single DC/DC direct-current power source having circuits (peripheral circuits including SR11 and SR21) is configured in two systems, and the switch SW selects the output of any one system. However, with this method, the mounting area is large and the cost is high. Furthermore, only one of the DC/DC DC power supplies is supplied to the output, while the other system is idle, so it is useless from the viewpoint of operating conditions. However, there was a problem that it was not efficient due to the occurrence of

JP 2011-97792 A

In order to solve the above problems, the present invention provides a DC power supply that is a single power supply, is compatible with worldwide AC voltages, has a plurality of output voltages, and can select the output voltage. be.

The present invention is a DC power supply of worldwide input specifications, in which the secondary side of a transformer used in the DC power supply has a plurality of windings, and an output voltage superimposed by the plurality of windings can be selected.
That is, a DC power supply having a plurality of outputs includes a transformer, a switching element connected to the primary side of the transformer, and a DC circuit connected to the secondary side of the transformer. The side is composed of a plurality of windings having at least a first winding and a second winding, and the DC conversion circuit is a first DC conversion circuit that converts the induced voltage induced in the first winding into a DC voltage. and a second direct current converting means for converting the induced voltage induced in the second winding to a direct current, the output voltage of the first direct current converting means and the output voltage of the first direct current converting means An output voltage selection unit capable of selectively outputting an output voltage consisting of a sum voltage of the output voltage of the second direct-current conversion means as a plurality of outputs, and the output voltage output from the output voltage selection unit is held. and an output voltage control circuit for controlling the voltage so that the DC power supply is characterized in that it further comprises an output voltage control circuit.

By configuring in this way, a voltage generated by one winding and a voltage superimposed by a plurality of windings are generated, and by selecting and outputting these voltages, it is possible to correspond to worldwide AC voltages. A DC power supply with multiple outputs can be configured compactly and at low cost.

The output voltage selector of this DC power supply is characterized by being a connector or a switch.
With this configuration, the output voltage of the DC power supply can be selected with a simple operation using a connector or a switch.

Further, the output voltage control circuit has a shunt regulator and a plurality of output voltage detection resistors that determine the set voltage of the shunt regulator, and the output voltage selection unit determines the connection state of the output voltage detection resistors when the output voltage is selected. are switched at the same time, and the output voltage control circuit controls the output voltage by a set voltage corresponding to the selected output voltage.
By configuring in this way, voltage control suitable for the selected output voltage can be performed.

Furthermore, regardless of the output voltage selected by the output voltage selection unit, the turns ratio of the plurality of windings on the secondary side of the transformer is set so that the DUTY control range of the switching element is equal. .
With this configuration, even a single DC power supply can achieve performance equivalent to that of a plurality of DC power supplies.

In addition, the secondary side of the transformer is composed of a plurality of windings having a third winding in addition to the first winding and the second winding, and the direct-current circuit is induced in the third winding. The output voltage selection unit selects the output voltage of the first DC conversion means, the output voltage of the first DC conversion means, and the second DC conversion means. An output voltage consisting of the sum of the output voltage of the means and the sum of the output voltage of the first direct current converting means, the output voltage of the second direct current converting means and the output voltage of the third direct current converting means. It is characterized by being capable of selectively outputting the voltage as a plurality of outputs.
With this configuration, three different output voltages, that is, the output voltage of the first winding and the output voltage in which the induced voltages of the windings 1 and 2 or the three windings are superimposed, can be switched and output. can be done.

The number of turns of the primary side winding of the transformer and the turns ratio of the first winding of the secondary side are set so as to be within the range of DUTY that can be controlled by the control IC of the switching element. and
By configuring in this way, any one of the plurality of output voltages can be used within a predetermined control range of DUTY.

With the configuration of the present invention, it is possible to select the output voltage of a DC power supply with multiple outputs corresponding to worldwide AC voltages, and configure the DUTY to be within the same control range regardless of the output voltage. , miniaturization and cost reduction are possible.

1 is a circuit diagram of main parts of a DC power supply with an output voltage selection function according to an embodiment of the present invention; FIG. FIG. 3 is a diagram for explaining the relationship between the turns ratio, input voltage, and output voltage of a flyback type transformer; Fig. 3 shows an AC input voltage and its DC voltage; FIG. 4 is a diagram showing changes in input voltage and output voltage when the AC power supply is turned off; FIG. 4 is a diagram showing DUTY and voltage values when an output voltage of 12 V is selected and a voltage on the primary side of the transformer is DC 150 V; FIG. 10 is a diagram showing DUTY and voltage values when an output voltage of 12 V is selected and the transformer primary voltage is DC 50 V; FIG. 4 is a diagram showing DUTY and voltage values when an output voltage of 36 V is selected and a transformer primary voltage is DC 150 V; FIG. 4 is a diagram showing DUTY and voltage values when an output voltage of 36 V is selected and a transformer primary side voltage of DC 50 V; FIG. 5 is a diagram showing a control range of DUTY with respect to the primary side input voltage when the turns ratio between the primary side and the secondary side is changed; It is a figure which shows the relationship between DC input voltage and DUTY. This is a modification of the DC power supply in which the connector is changed to a switch. It is the figure which added the auxiliary winding for control IC power supplies to the transformer. It is a circuit diagram shown in patent document 1. FIG. FIG. 2 is a circuit diagram configured by two systems of power supplies provided with selection switches;

A DC power supply with an output voltage selection function according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram of main parts of a DC power supply 1 with an output voltage selection function according to an embodiment of the present invention.
The primary side of the transformer T1 is composed of a switching element Q1 connected in series with the primary winding Np and a control IC (CONT1) that controls the switching element Q1. A primary-side input voltage VIN of the transformer T1 is an output voltage of a rectifying/smoothing circuit composed of a diode bridge and a capacitor of an AC power supply. The rectifying/smoothing circuit is omitted in FIG.

The secondary side of the transformer includes two windings Ns1 and Ns2, a rectifying/smoothing circuit (corresponding to a "direct-current conversion circuit" in this application) 2, an overvoltage detection circuit 3, an output selection connector connection ("output voltage selection unit" in this application). ) 4 and an output voltage control circuit 5 .
As a result, a single DC power supply can be provided with a multi-output function, and a DC power supply whose output can be selected can be configured.

The secondary side of the transformer is composed of a first winding Ns1 and a second winding Ns2, and the output of the winding is connected to a rectifying/smoothing circuit 2 composed of diodes D1, D2 and capacitors C1, C2. and the respective output voltages are V1 and V2. These voltages are voltages (DC voltages) obtained by rectifying and smoothing the voltages generated by the respective windings by the rectifying/smoothing circuit 2, and when selected as the output voltages, they become the output voltages as they are. A first rectifying/smoothing circuit (corresponding to the "first direct-current conversion means" of the present application) composed of a diode D1 and a capacitor C1 converts the induced voltage induced in the first winding Ns1 into a direct current, and converts the voltage induced in the first winding Ns1 into a direct current. A second rectifying/smoothing circuit (corresponding to the "second direct current means" of the present application) composed of C2 converts the induced voltage induced in the second winding Ns2 into a direct current.

The positive side of the first winding Ns1 and the negative side of the second winding Ns2 are connected to the first winding Ns1 and the second winding Ns2 to obtain the output voltage V1 of the first rectifying/smoothing circuit, It is configured to generate two output voltages, the sum voltage (V1+V2) of the output voltage V1 of the first rectifying/smoothing circuit and the output voltage V2 of the second rectifying/smoothing circuit (hereinafter referred to as the superimposed voltage). .

The overvoltage detection circuit 3 is composed of Zener diodes ZN1 and ZN2, diodes D3 and D4, and a photocoupler PC1.
Zener diodes ZN1 and ZN2 are connected to the cathode side of diode D1 (the positive side of output voltage V1) and the cathode side of diode D2 (the positive side of output voltage (V1+V2)), respectively, and diodes D3 and D4 are connected in series. The cathodes of the two diodes are connected to each other and connected to one end of the photocoupler PC1 on the light emitting diode side via the resistor R3. The other end of the photocoupler PC1 on the light emitting diode side is connected to the minus side (GND side).

The Zener diode ZN1 and the diode D3 are set to detect an overvoltage of the output voltage V1, and the Zener diode ZN2 and the diode D4 are set to detect an overvoltage of the output voltage (V1+V2). An overvoltage signal OVP is sent to the primary side control IC (CONT1) by the current limiting resistor R3 and the photocoupler PC1 when any of the output voltages becomes overvoltage. The control IC (CONT1) executes processing such as turning on/off of the switching element Q1 by its function.
By arranging the overvoltage detection circuit 3 in front of the output selection connector connection portion 4 in this way, it is possible to detect protection caused by connector connection leakage or the like.

The output selection connector connection section 4 is composed of two connector terminal blocks and one connector CN1. The output voltage V1 is selected by connecting the connector CN1 to the connector terminal block A side (hereinafter simply referred to as "A side") shown in FIG. 1, and the connector terminal block B side (hereinafter simply referred to as "B side"). selects the output voltage (V1+V2).
Output voltage selection is performed at terminals i-ii and iii-iv of connector CN1 shown in FIG.
The connector CN1 short-circuits the terminals i and ii and between the terminals iii and iv, respectively, and the output voltage is selected by connecting to either the A side or the B side.

This connector CN1 is connected to the voltage input terminal of the shunt regulator SR1 that controls the output voltage V1 or the output voltage (V1+V2), and when the output voltage is switched, resistors R4 and R6 connected in parallel can be switched ON/OFF. It is also configured as
In the DC power supply configured in this manner, the output voltage V1 and the output voltage (V1+V2) are selected by connecting the connector CN1, and when one of the voltages is output, voltage control suitable for that output voltage is performed. be.

The output voltage control circuit 5 is composed of resistors R4 to R8, a shunt regulator SR1 and a photocoupler PC2.
By connecting the iii-iv terminals of the connector CN1 to the A side, the output voltage sense resistors (output voltage detection resistors) R4 and R6 of the output voltage control circuit 5 are connected in parallel (R4//R6).

By connecting the iii-iv terminals of the connector CN1 to the B side, the output voltage sense resistor becomes only R4, voltage control suitable for the output voltage (V1 + V2) is executed, and the two-system DC power supply shown in FIG. Equivalent properties can be obtained.
The shunt regulator SR1 is connected to a resistor R7 and a photocoupler PC2 connected in series, and the output of the photocoupler PC2 is transmitted as a feedback signal FB to the control IC (CONT1) on the primary side.
That is, the control IC (CONT1) on the primary side controls the ON/OFF time of the switching element Q1 according to the feedback signal FB.

Here, the voltage set to the input terminal of the shunt regulator SR1 will be described. When the connector CN1 shown in FIG. 1 is connected to the A side, the iii-iv terminals of the connector CN1 are connected in parallel with the output voltage sense resistor R4 and the resistor R6 (R4//R6) to provide a voltage suitable for the output voltage V1. When control is performed and connected to the B side, the output voltage sense resistor becomes only R4, and voltage control suitable for the output voltage (V1+V2) is performed. In this way, when the output voltage is selected in the output selection connector connection portion 4, the connection states of the output voltage sense resistors R4 and R6 are switched at the same time.

The voltage input terminal VREF (SR1) of the shunt regulator SR1 is kept constant even if the output voltage sense resistor is changed because the reference voltage in the shunt regulator SR1 that is compared with this voltage is kept constant. ) does not change, and the output voltage VOUT changes. This output voltage VOUT is set as follows.

When the connector CN1 is connected to the A side,
VOUT(V1)=(1+(RA/R5))×VREF(SR1) (1)
and when connected to the B side,
VOUT(V1+V2)=(1+(R4/R5))×VREF(SR1) (2)
becomes.
Here, RA=R4//R6, and VREF is the reference terminal voltage of the shunt regulator SR1, that is, the plus side voltage of the resistor R5 shown in FIG.

Therefore, by connecting the connector CN1 (to the A side or the B side), one of the output voltages is selected. (Ratio of ON time TON to cycle T of switching element Q1 on the primary side of transformer (TON/T)) can be made almost the same to obtain characteristics equivalent to those of two systems of DC power supply, resulting in smaller size and lower cost. Cost can be reduced.
The resistors R4 to R6 function as resistors for determining the set voltage of the shunt regulator SR1, and the constants of the resistors R4 to R6 correspond to the output voltages of 12 V and 36 V in this embodiment, but are not fixed. The resistance value is set according to the output voltage.

Next, before calculating the DUTY range of the voltage input to the transformer T1 and the output voltage of the DC power supply 1 shown in FIG. A relationship between output voltages will be described.

FIG. 2 is a diagram for explaining the relationship between the turns ratio (Ns/Np=N) of a flyback type transformer, the input voltage VIN, and the output voltage VOUT.
Generally, the flyback voltage VOR of the flyback system is represented by the following basic equation.
VOR=VO×Np/Ns=TON/TOFF×VIN (3)
Here, VO=VOUT+VF, which is obtained by adding the diode voltage drop VF to the output voltage VOUT. TON and TOFF are the ON time and OFF time of the switching element Q1.

The DUTY of the switching element is
DUTY=TON/(TON+TOFF) (4)
Therefore, by modifying equation (3) and substituting TOFF=TON×N×VIN/VO,
DUTY=VO/(N×VIN+VO) (5)
becomes.

(Example)
In this embodiment, the transformer T1 has two windings on the secondary side, and the turns ratio of the transformer T1 is: number of windings on the primary side Np: number of first windings on the secondary side Ns1: second number of windings on the secondary side. Assuming that the number of windings is Ns2=8:1:2 and the primary side input voltage is VIN, the ON time TON of the switching element Q1 is given by equations (4) and (5) as T=TON+TOFF as follows:
TON=VO×T/(N×VIN+VO) (6)
can be used to obtain an approximate value.
Here, T is the period of the switching element Q1 (1/oscillation frequency kHz), VO=VOUT+VF, and N=Ns/Np.

The primary and secondary turn ratio of 8:1:2 is to make the DUTY approximately 50% at the lower limit of the AC input power supply (100V-15%) in normal use. It's for.
Note that T=10 μs in this embodiment. Also, taking into account the diode voltage drop VF, the voltage VO is calculated by adding VF to the output voltage VOUT.

Here, DUTY is calculated for DC100V, DC150V, DC390V, and DC50V within the range of the input voltage VIN. If the input voltage of the worldwide specification is changed from AC85V (100V-15%) to AC276V (240V+15%), the output of the rectifying/smoothing circuit 2 will be DC120V to 390V. The upper limit of the input voltage for normal domestic use is DC 150V.

As for the lower limit DC 100V, as shown in Fig. 3, when the AC input voltage reaches the lower limit (85V), the peak value is DC 120V. becomes. Therefore, the lower limit of normal input voltage fluctuation was set to DC 100V.
On the other hand, since it is necessary to hold the output voltage for a certain period of time when the AC power supply is turned off, in order to secure the holding time tc shown in FIG. , DC50V was used as a voltage for securing the retention time.
FIG. 4 is a diagram showing changes in the input voltage VIN and the output voltage VOUT when the AC power is turned off.

Therefore, the voltages for calculating the control range of DUTY are DC50V, DC100V, DC150V, and DC390V, and the output is 12V or 36V, and the DUTY is calculated for each of the two output voltages.

Hereinafter, the voltage VO is used instead of the output voltage VOUT with the diode voltage drop VF being 1.0V.
Also, in this embodiment, N=Ns1/Np=1/8=0.125.
First, VOUT=12V and the DUTY for each input voltage is calculated.
DUTY at this time is given by equations (4) and (5) assuming that VO = VOUT + 1.0 V.
DUTY(50V)=TON/10μs=13V/(0.125×50V+13V)
DUTY(100V)=13V/(0.125×100V+13V)
DUTY(150V)=13V/(0.125×150V+13V)
DUTY(390V)=13V/(0.125×390V+13V)
DUTY is 68%, 51%, 41%, and 21% in order from the top.

FIG. 5 is a diagram showing DUTY and voltage values when the output voltage of 12 V is selected and the transformer primary voltage is DC 150 V. In FIG.
FIG. 6 is a diagram showing DUTY and voltage values when the output voltage of 12 V is selected and the voltage on the primary side of the transformer is DC 50 V. In FIG.
5 and 6, the horizontal axis is time and the vertical axis is voltage. Two cycles of the switching element Q1 are shown. The voltage V1 is 12V and is the output voltage VOUT. Voltage V2 is 24V. The voltage VDS (Q1) is the voltage between the drain and source of the switching element Q1, and the LOW period is the time during which the switching element Q1 is on. Since the period of the switching element Q1 is 10 μs, the DUTY (%) can be easily calculated from the ON time of the switching element Q1.

Therefore, when the output voltage is 12V, the DUTY of the switching element Q1 is in the range of 21% to 68% with respect to the input voltage of DC50V to DC390V.

Next, similar calculations are made for the case of VOUT=36V. In this case, the diode drop VF=1.0 V and the voltages of the two windings are superimposed, so N=(Ns1+Ns2)/Np=3/8=0.375. The DUTY of each input voltage is
DUTY(50V)=TON/10μs=37V/(0.375×50V+37V)
DUTY(100V)=37V/(0.375×100V+37V)
DUTY(150V)=37V/(0.375×150V+37V)
DUTY(390V)=37V/(0.375×390V+37V)
, which are 66%, 50%, 40%, and 20% in order from the top.

FIG. 7 is a diagram showing the DUTY and the voltage value when the output voltage of 36V is selected and the transformer primary voltage is DC 150V. FIG. 8 is a diagram showing DUTY and voltage values when the output voltage of 36V is selected and the transformer primary voltage is DC 50V.
7 and 8 are diagrams showing the output voltage and the ON time of the switching element Q1 with the same configuration as in FIGS. 5 and 6, but the output voltage VOUT shown in FIGS. is 36 V of the superimposed voltage of .

Therefore, when the output voltage is 36V, the DUTY of the switching element Q1 is in the range of 20% to 66% with respect to the input voltage of DC50V to DC390V.

The DUTY of the output voltage of 12V and that of the output voltage of 36V are almost the same. This is configured so that the number of windings on the secondary side is equal to the DC voltage (rectified and smoothed voltage) ratio, and even if the output voltage is tripled, the winding ratio (N) to the output voltage is is tripled, the ON time of the switching Q1, DUTY, is also tripled in the numerator and the denominator from equation (5), and the DUTY does not change. Therefore, even if the output voltages are different, the DUTY can be set in the same range by selecting the turns ratio of the secondary side as the DC voltage ratio of the windings.
Since the output voltage VOUT is calculated as the voltage VO in consideration of the diode drop VF, the calculation results of this embodiment do not completely match.

(Comparative example 1)
The above embodiment has two secondary windings with a turns ratio of 8:1:2. Comparative Example 1 calculates the DUTY corresponding to the two outputs of 12V and 36V with the secondary side having one winding instead of two windings. The number of turns of one winding was set so that the output would be 24V, which is the center value between 12V and 36V. In Comparative Example 1, N=Ns/Np=2/8=0.25.

From equation (5), similarly assuming that the diode voltage drop is 1.0 V, VOUT = 12 V, and the input voltage is DC 50 V,
DUTY(50V)=TON/10μs=13V/(0.25×50V+13V)
, the DUTY is 51%.
Also, at input voltages of DC100V, DC150V and 390V, the DUTY is 34%, 26% and 12%, respectively. The range of DUTY is 12% to 51%.

Similarly, with an output voltage of 36 V, the DUTY for an input voltage of 50 V is
DUTY(50V)=TON/10μs=37V/(0.25×50V+37V)
, 75%.
Also, at input voltages of DC100V, DC150V and DC390V, the DUTY is 60%, 50% and 28%, respectively.
Therefore, the DUTY with respect to the input voltage of 36V is in the range of 28% to 75%. The DUTY range for selecting and using output voltages of 12V and 36V is 12% to 75%.

(Comparative example 2)
Next, the secondary side is set to one winding, and the output voltage is selected to be 12V or 36V. The turns ratio is N=Ns/Np=3/8=0.375. Also in Comparative Example 2, the diode drop VF is set to 1.0V.
When VOUT=12V and input voltage is DC50V,
From DUTY (50V)=TON/10 μs=13V/(0.375×50V+13V), DUTY is 41%.
At input voltages of DC100V, DC150V, and DC390V, the DUTY is 26%, 19%, and 8.2%, respectively, and the range of DUTY is 8.2% to 41%.

Then, when VOUT=36V and input voltage is DC50V,
DUTY(50V)=TON/10μs=37V/(0.375×50V+37V)
, the DUTY is 66%.
Also, the DUTY is 50%, 40%, and 20% at input voltages of DC100V, DC150V, and DC390V, respectively.
Therefore, the combined DUTY range of the output voltages of 12V and 36V is 8.2% to 66%.

Table 1 shows the results of DUTY with respect to the input voltage in the above example and comparative examples 1 and 2.

この表２によれば、ＤＵＴＹの最大は標準値（Typ．）では８３％であるが、最大の最小値（Min.）は７３％となっている。よって、ＤＵＴＹの制御範囲は７３％以下に抑える必要がある。 Here, when judging whether the result of DUTY in Table 1 is appropriate, the effective control range of DUTY will be examined. Table 2 shows the maximum and minimum values of pulse width modulation DUTY of the control IC (CONT1) shown in FIG. It is a data sheet of a control IC (CONT1).

According to Table 2, the maximum DUTY is 83% at the standard value (Typ.), but the maximum minimum value (Min.) is 73%. Therefore, it is necessary to suppress the control range of DUTY to 73% or less.

The minimum value is 0%, but if the DUTY is less than 10%, the capacitor input rectification method requires a PFC circuit to suppress noise, causing unstable operation due to delays in the rise and fall of the switching element. Sometimes. Therefore, the minimum value of the DUTY control range is set to 10%.

Assuming that the DUTY is operated within a control range of 10% to 73% (predetermined control range), the embodiment of the present invention is within that range, but in Comparative Example 1 of a 1-winding 24V output circuit, 36V output 75% at DC50V, exceeding the predetermined control range.
In Comparative Example 2 of the 1-winding 36V output circuit, the 12V output of DC 390V is 8.2% below the predetermined control range.
Therefore, the direct-current power supplies configured with one winding in Comparative Examples 1 and 2 cannot meet worldwide specifications. For example, if the input voltage of DC50V exceeds the predetermined control range, and the output voltage must be maintained for a predetermined time after the input power supply is turned off, measures such as increasing the capacitance of the primary side capacitor can be taken. necessary.

In addition, in the two-system example shown in Table 1, two DC power supplies are used, so the DUTY control range is the same as in the embodiment, but the two-system power supply requires a large mounting area and is cost-effective. There is a problem of increasing
Furthermore, since the DC/DC DC power supply of one of the systems is out of service, it is wasteful and inefficient from the viewpoint of operating conditions.

In the example shown in Table 1, the output voltage is 36V, which is obtained by superimposing the DC voltages of 12V and 24V of the two windings on the secondary side.
Therefore, instead of superimposed voltages, a two-winding configuration, for example, two windings with an output voltage of 12 V and an output voltage of 36 V, respectively. can do.
However, in this case, even with two windings, the turns ratio is 8:1:3, and the number of turns on the secondary side increases.

Next, a case where the turns ratio between the primary side and the secondary side is changed will be examined.
FIG. 9 is a diagram showing the control range of DUTY with respect to the primary side input voltage when the turns ratio between the primary side and the secondary side is changed.
The horizontal axis represents the range of DUTY from 0% to 100%, and the vertical axis represents a horizontal bar graph showing the DUTY control range from (A) to (G). Note that the control range of DUTY shown in the upper part of the figure is a predetermined control range (10% to 73%).
Also, in any bar graph shown in FIG. 9, the diode voltage drop VF of 1.0 V is added to the output voltage VOUT.
Furthermore, the maximum value of the DUTY control range from (A) to (G) shown in FIG. 9 is the DUTY of the input voltage DC 50V, and the minimum value is the DUTY of the input voltage DC 390V.

FIG. 9A is a bar graph of DUTY of a DC power supply that selects and outputs output voltages controlled to be 12V and 36V from the 36V output of one secondary winding with a turns ratio of 8:3. The control range of DUTY from the input voltage of DC50V to DC390V on the primary side is shown to be 8.2% to 66%.
FIG. 9(A) is a bar graph of the control range of Comparative Example 2 shown in Table 1 as it is. As can be seen from the results in Table 1, the 1-winding DC power supply with this winding ratio is a DC power supply below the predetermined control range of DUTY.

Next, FIG. 9(C) is a bar graph showing the control range of DUTY when only the turn ratio is changed from FIG. 9(A) to 6:3. The control range of DUTY at this time is 6.3% to 60%.
Further, FIG. 9(E) is a bar graph showing the control range of DUTY when only the turn ratio is changed from FIG. 9(A) to 4:3. The control range of DUTY at this time is 4.3% to 50%.

When the turns ratio between the primary side and the secondary side of the DC power supply of this comparative example 2 is increased from 3/8 to 3/6 and 3/4 (approaching 1), even with the same input voltage, the DUTY becomes The control range is shifted leftward in FIG. 9, and the DUTY is reduced. As can be seen from equation (5), even if the input voltage is the same, the larger the turns ratio, the larger the value of the denominator and the smaller the DUTY.
In this comparative example 2, when the turns ratio is changed, the DUTY becomes smaller, but even the turns ratio of FIG. But even below the lower limit.

FIG. 9(B) is a bar graph of DUTY of a DC power supply for selecting output voltages of 12V and 36V from two secondary windings with a turns ratio of 8:1:2 according to the present invention. The input voltage on the primary side is DC50V to DC390V. The control range of DUTY at this time is 20% to 68%. This is the range shown in the examples (present invention) in Table 1.
Similarly to the change in the winding ratio in Comparative Example 2, the winding ratio in the present embodiment is changed from 8:1:2 to 6:1:2, 4:1:2, and 3:1:2. Calculate the control range of DUTY by changing.

FIG. 9D is a bar graph obtained by calculating the DUTY control range by changing the turns ratio to 6:1:2. The range is 16% to 61%. As the turns ratio increases (approaches 1), the DUTY becomes smaller, but even with this turns ratio, the DUTY control range is within the predetermined control range, and can be used as a DC power supply.
FIG. 9(F) is a bar graph obtained by calculating the DUTY control range by changing the turns ratio to 4:1:2. The control range is from 11% to 51%. Even with this turn ratio, the control range of DUTY is within a predetermined control range, and can be used as a DC power supply.

Further, FIG. 9G is a bar graph obtained by calculating the control range of DUTY by changing the turns ratio to 3:1:2. This control range is 8.7% to 44%. At this turn ratio, the DUTY falls below the predetermined control range, and a DC power supply with this turn ratio is not suitable.
Therefore, the lower limit of the turns ratio between the primary side and the secondary side is 4:1:2 in the case of a DC power supply with one winding on the secondary side under the conditions shown in the embodiment.

On the other hand, when the turns ratio is decreased from the turns ratio of 8:1:2 in FIG. 9B, the DUTY increases and approaches the upper limit of 73%.
In this case, the upper limit turns ratio of 73% is 10:1:2. The DUTY at this time is 72% with an input voltage of 12V and an input voltage of DC 50V.
Therefore, in the embodiment of the present invention, the input voltage is from DC50V to DC390V, and the turns ratio of the DC power supply composed of two windings on the secondary side is suitable in the range of 4:1:2 to 10:1:2. .

Here, when there is a margin up to the upper limit of 73% of the control range of the DUTY of the switching element, the input voltage on the primary side of the transformer is calculated at DC 50V in the above calculation. The output voltage can be maintained up to the upper limit of the predetermined control range.
Since this increases the holding time tc, if it is not necessary to lengthen the holding time beyond the specified time, it is possible to reduce the cost by reducing the capacitance of the primary side capacitor.

FIG. 10 is a diagram showing the relationship between the DC input voltage and DUTY. Two curves are displayed in FIG. The solid curve shows the input voltage and DUTY when the turns ratio is 4:1:2 and the output voltage is 12V. That is, it is a graph showing the relationship between the input voltage and the DUTY value of the bar graph shown in FIG. 9(F).
The dotted line curve is an example of VOUT36V with one winding 24V output in Comparative Example 1 shown in Table 1. In this case, as shown in Table 1, at DC50V, the DUTY is 75%, and the upper limit of the predetermined control range of DUTY exceeds At this time, if the upper limit of the control range is 73%, the input voltage is DC 55V.

Here, the maximum control range for the turns ratio of 4:1:2 shown in FIG. 9(F) is 51%. This maximum 51% input voltage was 50V DC, but if the upper limit of the predetermined control range of DUTY is 73%, this input voltage becomes 19V DC.
If the output voltage is maintained up to the input voltage of DC 19 V and the retention time tc is lengthened, the capacitor with a predetermined capacity can be reduced. The predetermined capacitance is a capacitance required for design and is 470 μF.

For example, the description will be made based on the diagram in FIG. 4 when the input power supply is turned off.
The capacity Cp of the capacitor on the primary side can be calculated by Equation (7).
Cp=2×Pin×tc/(VIN ² −VINmin ² ) (7)
where Pin=Po/η, where Po is the output power (W) and η is the efficiency. tc is the holding time, VIN is the input voltage when the power is turned off, and VINmin is the minimum operating voltage of the input voltage.

Specifically, in order to maintain tc=10 ms, if the output power is 100 W and the efficiency is 80%, Pin is 125 W, and if VIN=100 V and VINmin is 19 V and 55 V, the values are 259 μF and 358 μF, respectively.
This means that the holding time tc can continue even if VINmin drops to 19V. Since the output can be maintained even if the voltage drops to this level, it is possible to reduce the capacitance of the capacitor.

Although the DC power supply 1 for selecting the output voltage shown in FIG. 1 has been described above, the power supply shown in FIG. 1 switches between two outputs by means of the connector CN1. A switch shown in FIG. 11 may be provided instead of the connector CN1 for selection.
FIG. 11 shows a modification of the DC power supply with an output voltage selection function in which the connector is changed to a switch. The connector CN1 in the circuit diagram shown in FIG. 1 is changed to a switch SW1, and other circuits are the same.
For the switch SW1, for example, a two-circuit, two-contact switch is used, and two output voltages are connected to each contact in one circuit and selected by the switch SW1. One end of a resistor R6 connected in parallel with the resistor R4 is connected to the other circuit, and the connection of the resistor R6 is turned on and off by a switch SW1.
Thus, switch SW1 may be used instead of connector CN1.

FIG. 12 is a diagram in which an auxiliary winding for a control IC power supply is added to the transformer T1 shown in FIG. FIG. 12 is the same as the circuit diagram of the main part of the DC power supply with output voltage selection function shown in FIG. Since the auxiliary winding 21 is added to the transformer T1, description of the circuit is omitted.
For example, if the turns ratio between the number of turns on the primary side and this auxiliary winding is 8:2, an output voltage of 24 V can be obtained from the auxiliary winding. In this case, the DUTY of the switching element Q1 is irrelevant and the output voltage is almost constant because the load is small.

Further, embodiments of the present invention have been described as DC power supplies with selectable output voltages of 12V and 36V. In this case, the turns ratio between the primary side and the two secondary sides was set to 8:1:2, but the setting of the output voltage is not limited to this, and the turns ratio of the secondary side also depends on the output voltage. can be set
For example, if the secondary side is configured with three windings and the turns ratio is 8:1:1:1, the superimposed output voltages are three outputs of DC12V, DC24V, and DC36V. can also be

In addition, although the embodiment of the present invention has been described using a flyback type DC power supply, the present invention is not limited to a flyback type DC power supply, and a forward type or current resonance type DC power supply can also be used.
Furthermore, in parallel with the number of turns (Ns1, Ns2, . . . Nsn) on the secondary side of the transformer T1, the terminals (A side, B side, . The number of different output voltage selections can also be increased by increasing the connected resistors (R6, . . . Rn).

For example, a third winding Ns3 is provided on the secondary side of the transformer T1 in addition to the first winding Ns1 and the second winding Ns2, and the induced voltage induced in the third winding Ns3 A third rectifying/smoothing circuit (third conversion means) for converting to direct current is further provided, and the output selection connector connection unit 4 is configured to connect the output voltage of the first rectifying/smoothing circuit and the output voltage of the first rectifying/smoothing circuit. and the output voltage of the second rectifying/smoothing circuit, the output voltage of the first rectifying/smoothing circuit, the output voltage of the second rectifying/smoothing circuit, and the output voltage of the third rectifying/smoothing circuit It is also possible to selectively output the output voltage composed of the sum voltage of the above as a plurality of outputs. At this time, the connection state of the output voltage sensing resistor is switched to three states corresponding to three different output voltages.

1, 10, 20, 30... DC power supply, 2... Rectification/smoothing circuit (DC circuit), 3... Overvoltage detection circuit, 4... Connector connection part for output selection (output voltage selection part) , 5... output voltage control circuit, 14... output selection switch section, 21... auxiliary winding for power supply.

Claims (6)

A DC power supply with multiple outputs,
a transformer;
a switching element connected to the primary side of the transformer;
A DC circuit connected to the secondary side of the transformer,
a secondary side of the transformer comprising a plurality of windings having at least a first winding and a second winding;
The direct current circuit includes first direct current converting means for converting the induced voltage induced in the first winding to direct current, and second direct current converting means for converting the induced voltage induced in the second winding to direct current. and a means for converting
Selectively outputting the output voltage of the first direct current means and the sum voltage of the output voltage of the first direct current means and the output voltage of the second direct current means as a plurality of outputs an output voltage selection unit capable of outputting;
The DC power supply further comprising an output voltage control circuit that controls voltage so that the output voltage output from the output voltage selection unit is held. The DC power supply according to claim 1,
The DC power supply, wherein the output voltage selector is a connector or a switch. The DC power supply according to claim 1 or 2,
The output voltage control circuit has a shunt regulator and a plurality of output voltage detection resistors that determine a set voltage of the shunt regulator,
The output voltage selection unit is configured to simultaneously switch the connection state of the output voltage detection resistor when the output voltage is selected,
The DC power supply, wherein the output voltage control circuit controls the output voltage with the set voltage corresponding to the selected output voltage. The DC power supply according to any one of claims 1 to 3,
The turns ratio of the plurality of windings on the secondary side of the transformer is set so that the DUTY control range of the switching element is equal regardless of the output voltage selected by the output voltage selection unit. DC power supply. The DC power supply according to any one of claims 1 to 4,
the secondary side of the transformer is composed of a plurality of windings having a third winding in addition to the first winding and the second winding;
The direct current circuit further includes third direct current means for converting the induced voltage induced in the third winding to direct current,
The output voltage selection unit includes an output voltage composed of the output voltage of the first DC conversion means and the sum voltage of the output voltage of the first DC conversion means and the output voltage of the second DC conversion means; Selectively outputting an output voltage composed of a sum voltage of the output voltage of the first direct current means, the output voltage of the second direct current means and the output voltage of the third direct current means as a plurality of outputs. A DC power supply, characterized in that: The DC power supply according to any one of claims 1 to 5,
The number of turns of the primary side winding of the transformer and the turns ratio of the first winding of the secondary side are set so as to be within the range of DUTY that can be controlled by the control IC of the switching element. DC power supply characterized by:

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