JPH11103576A - Flyback-type dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flyback-type DC converter by which a constant voltage output can be obtained relatively easily, even if a power supply with current- limiting characteristics is connected. SOLUTION: A series circuit consisting of a main winding 5 of a transformer 4, a main switch 6 and a current detection resistor 7 is connected to a power supply 1 having a current-limiting functionality. A smoothing capacitor 12 is connected to an output winding 8 of the transformer 4 via a diode 11. One end of a drive winding 9 of the transformer 4 is connected to the gate of the main switch 6 via a drive capacitor 14. The other end of the drive winding 9 is connected to the source of the main switch 6. A charging circuit composed of resistors 15 and 51 is connected to the capacitor 14, and further, a discharge circuit composed of the resistor 51 and a transistor 53 is connected to the capacitor 14. The transistor 53 is turned on synchronously with the main switch 6. The capacitor 14 is made to be discharged to turn off the main switch 6. The maximum on-period width of the main switch 6 is so set as to make an input current of not larger than the current-limiting value of the power supply 1 flow.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flyback type DC converter, that is, a DC-DC converter capable of obtaining a constant voltage output even when a power supply has a current limiting characteristic.

[0002]

2. Description of the Related Art Conventional typical flyback type DC-D
The C converter is configured as shown in FIG. In this converter, a first power supply connected to a DC power supply 1
A series circuit of a primary winding of the transformer 4, that is, a main winding 5, an intermittent main switch 6, and a current detection resistor 7 is connected between the second power supply terminals 2, 3. The transformer 5 includes, in addition to the main winding 5, a secondary or output winding 8 and a tertiary or drive winding 9.
These are wound around the magnetic core 10 and are electromagnetically coupled to each other. The polarity of each of the windings 5, 8 and 9 is determined as indicated by a black circle, and the output winding 8 has a polarity opposite to that of the main winding 5. One end of the main winding 5 is connected to the first power supply terminal 2, and the other end is connected to a drain as a first main terminal of a main switch 6 composed of an insulated gate field effect transistor. A source as a second main terminal of the main switch 6 is connected to a second power supply terminal 3 as a ground terminal via a current detection resistor 7.

A rectifying / smoothing circuit including a rectifying diode 11 and a smoothing capacitor 12 is provided to constitute an output circuit. The smoothing capacitor 12 is connected in parallel with the output winding (secondary winding) 8 via the rectifier diode 11. The diode 11 has such a direction as to be kept off when the main switch 6 is on. The load 13 is connected to the smoothing capacitor 12 in parallel.

One end of a drive winding (tertiary winding) 9 is connected to a gate as a control terminal of the main switch 6 via a driving capacitor 14, and the other end of the main switch 6 is connected via a current detection resistor 7. It is connected to a source as a second main terminal. Further, a starting resistor 15 is connected between the first power supply terminal 2 and the gate of the main switch 6 in order to automatically start the main switch 6.

In order to form a constant voltage control circuit, an output voltage detection line 16, a reference voltage source 17, an error amplifier 18,
And a voltage control signal forming circuit 20 comprising a light emitting diode 19, a phototransistor 21, a transistor 22 as an off control switch, an off control resistor 23, a voltage control capacitor 24, first and second backflow prevention. Diodes 25 and 26 and a discharge resistor 27 are provided.

One input terminal of an error amplifier 18 as a difference signal forming means in the voltage control signal forming circuit 20 is connected to a voltage detecting line 16 as a voltage detecting means, and the other input terminal is connected to a reference voltage source 17. ing. Therefore, a voltage corresponding to the difference between the detection voltage and the reference voltage, that is, an error output is obtained from the error amplifier 18. Although the voltage detecting means is shown in principle by the detection line 16, a voltage detecting resistor for voltage division is connected between both ends of the smoothing capacitor 12, and the divided voltage obtained from the resistor can be used as the detection voltage. . Since the light emitting diode 19 is connected between one end of the smoothing capacitor 12 and the output terminal of the error amplifier 18, it emits light in response to the error output and outputs an optical signal as a voltage control signal.

Transistor 2 as off control switch
2 is connected to the drive winding 9 via the drive capacitor 14. That is, the collector of the transistor 22 is connected to the left end of the drive capacitor 14 and the gate of the main switch 6, and the emitter is connected to the lower end of the drive winding 9 and the lower end of the current detection resistor 7. A base current limiting and off control resistor 23 is connected between the upper end of the current detection resistor 7 and the base of the transistor 22.
3, a voltage control capacitor 24 is connected in parallel.

The collector of a phototransistor 21 as a control element optically coupled to the light-emitting diode 19 is connected to the upper end of the drive winding 9 via a backflow preventing diode 25. It is connected to the right end of the voltage control capacitor 24. One end of the discharging resistor 27 is connected to the voltage controlling capacitor 24.
And the other end is connected to the upper end of the drive winding 9 via a backflow preventing diode 26.

[0009]

[Basic operation] When a DC voltage is supplied between the first and second power supply terminals 2 and 3 of the converter of FIG. 1, a current for charging the drive capacitor 14 via the starting resistor 15 and the gate of the main switch 6 A current for charging a source-to-source capacitance (not shown) flows. When the voltage of the driving capacitor 14 reaches the threshold value of the main switch 6, the main switch 6 is turned on. When the main switch 6 is turned on, a power supply voltage is applied to the main winding 5, and the main winding 5, the main switch 6, and the current detection resistor 7 are turned on.
, A primary current I1 flows through the series circuit. Since the main winding 5 has an inductance, the current I1 increases with a slope, and the voltage V7 across the current detection resistor 7 has a slope from the on-start time t0 of the main switch 6 as shown in FIG. Have more. When the current I1 flows through the main winding 5, a positive feedback voltage is obtained in the driving winding 9, and the ON state of the main switch 6 is maintained by the sum of the positive feedback voltage and the voltage of the driving capacitor 14. Thereafter, when the current detection voltage V7 reaches the threshold voltage Vth of the off-control transistor 22, the transistor 22 is turned on, the gate of the main switch 6 is connected to the ground, and the main switch 6 is turned off. .
When the main switch 6 is turned off, a voltage is generated in each of the windings 5, 8, 9 in a direction opposite to that in the on-state based on the release of the magnetic energy stored in the magnetic core 10 of the transformer 4 during the on period. That is, a flyback voltage is generated. Since the voltage of the output winding 8 when the main switch 6 is off has the direction of turning on the diode 11, the smoothing capacitor 12 is charged with the voltage of the output winding 8 when the main switch 6 is off. Since the voltage of the drive winding 9 during the period of discharging the stored energy of the transformer 4 has a direction in which the gate and the source of the main switch 6 are reversely biased, the main switch 6 is kept off during this period. When the discharge of the energy stored in the transformer 4 is completed, the reverse bias voltage is not generated in the drive winding 9, so that the charging of the driving capacitor 14 and the charging of the gate-source capacitance are started again through the starting resistor 15. The same operation as described above is repeated.

[0010]

[Constant Voltage Control Operation] The voltage V24 of the voltage control capacitor 24 in FIG. 1 changes according to the change of the output voltage V0 of the smoothing capacitor 12. For example, when the output voltage V0 becomes higher than the reference voltage, the light output of the light emitting diode 19 increases,
The resistance value of the phototransistor 21 decreases. As a result, the voltage V24 of the voltage control capacitor 24 increases.
The voltage V24 of the capacitor 24 is a DC voltage as shown in FIG.
A voltage V7 + V24, which is the sum of the current detection voltage V7 shown in FIG. 2C and the voltage V24 of the capacitor 24, is applied between the emitters. When the output voltage V0 becomes higher than the reference voltage, the voltage V24 of the voltage control capacitor 24 also becomes higher. Therefore, the sum voltage V7 + V24 from the time when the main switch 6 starts to be turned on t0.
Until the voltage reaches the threshold voltage Vth of the off-control transistor 22 until time t1. Accordingly, the on-time width of the main switch 6 is shortened, the stored energy during the on-period of the transformer 4 is reduced, and the output voltage V0 is reduced to the reference value. When the output voltage V0 becomes lower than the reference value, a control operation reverse to that when the output voltage V0 becomes higher occurs.

[0011]

The converter shown in FIG. 1 has the advantage that DC-DC conversion and constant voltage control are possible with a relatively simple circuit configuration, but the power supply 1 is accompanied by current limitation. In such a case, the device may not be usable. FIG. 3 illustrates this type of problem.

When the input voltage Vin of the converter is gradually increased in a case where the power supply 1 of the converter shown in FIG. 1 is a voltage source having no current limitation, the input current (average value) I is increased as shown in FIG.
in changes. That is, when the input voltage Vin is equal to or lower than the predetermined value Vs, the ON time width of the main switch 6 becomes longer because the output voltage V0 is lower than the desired reference voltage, and the input current Iin is allowed to increase. When the duty ratio (on / off ratio) of the main switch 6 is substantially constant and the input voltage Vin increases, the load 13
Increases as the input voltage Vin increases, the input current Iin also increases as the input voltage Vin increases. When the input voltage Vin reaches the predetermined value Vs, the output voltage V0 reaches the reference value, so that the constant voltage control starts and the input voltage Vin
Is higher than the predetermined value Vs, the output voltage V0 becomes substantially constant. Now, assuming that the load 13 is constant, a constant power supply state is established in a region where the input voltage Vin is higher than the predetermined value Vs, and the input current I increases as the input voltage Vin increases.
The average value of in decreases.

When the power supply 1 of FIG. 1 is a mere voltage source and does not have a current limiting function, the converter of FIG. 1 can be used as it is. However, if the power supply 1 is configured not to allow a current larger than the predetermined current Im in FIG. 3 to flow, the input current Iin becomes the predetermined value Im when the input voltage Vin becomes Vb. Since the input current Iin cannot be increased, the input voltage Vin is stabilized at Vb and the input current Iin is stabilized at the point B, and the input voltage Vin cannot be further increased. Therefore, the voltage Va at point A (for example, 25 V) or the voltage Vc of C (for example, 60 V) where the input voltage Vin is higher than the predetermined value Vs.
This operation becomes impossible even if it is attempted to operate at V).

FIG. 4 shows a telephone power supply having a current limit that may cause the above-described problems. The power supply shown in FIG. 4 is composed of a combination of an exchange or office-side power supply circuit 1a and a converter-side power supply circuit 1b, both of which are connected to each other by first and second terminals 31 and 32. The output terminals 33 and 34 of the converter-side power supply circuit 1b are connected to portions corresponding to the first and second power supply terminals 2 and 3 of the converter of FIG. The office-side or exchange-side power supply circuit 1a includes a voltage / current source circuit 35, two changeover switches 36 and 37, and a control circuit 38. The voltage / current source circuit 35 has current-voltage characteristics shown in FIG.
(39mA) Maximum voltage Vm (60V) in current range below
It is configured to output the following voltages. Further, it is configured to supply voltages in opposite directions between the first and second terminals 31 and 32 when the telephone is on standby and when the telephone is busy. For this purpose, switches 36 and 37 and a control circuit 38 are provided as switching means.
The control circuit 38 detects the hook-on / off signal of the telephone, and switches the switches 31 and 32 during the hook-on state, that is, during standby.
The contacts a of the switches 31 and 32 are turned on when the telephone is busy. Switch 3
6 and the contact b of the switch 37 are connected to the first terminal 31.
The contact b of the switch 36 and the contact a of the switch 37 are connected to the second terminal 32. The common terminals of the switches 36 and 37 are connected to the voltage / current source circuit 35.

The converter-side power supply circuit 1b comprises a bridge type full-wave rectifier circuit 39 composed of diodes D, D2, D3 and D4, and a voltage stabilizing capacitor 40. The pair of DC input terminals of the rectifier circuit 39 are the first and second terminals 31,
32, a pair of rectified output terminals is connected to a pair of power output terminals 33 and 34, and a capacitor 40 is connected between the output terminals 33 and 34.

In FIG. 4, when the telephone is on standby, the voltage / current source circuit 35 starts operating in the constant voltage supply mode and supplies, for example, 60V. In addition, when the telephone is busy, the voltage / current source circuit 35 starts the operation in the constant current supply mode.
Supply 9 mA.

The voltage / current source circuit 35 shown in FIG. 4 has the maximum current Im (39 m) shown in FIG. 5 even in the constant voltage supply mode.
It cannot supply a larger current than A). Therefore, the terminals 33 and 34 of the power supply of FIG.
3 are connected to the power terminals 2 and 3 of FIG.
The point voltage and current cannot be supplied. That is, the first and second power terminals 2,
3, when the voltage Vin starts rising and reaches the point B, the maximum current I
m flows, and a current larger than this cannot flow to the point A or the point C because the current is limited.

To solve this problem, a separately-excited converter may be used instead of the self-excited flyback converter shown in FIG. However, in a converter that obtains power from a telephone line, the power consumption is limited, and the power consumption of the separately-excited control circuit may not be obtained. In addition, the separately excited control circuit necessarily has a complicated circuit configuration.

An object of the present invention is to provide a flyback type DC converter which can relatively easily obtain a constant voltage output even when a power supply having current limiting characteristics is connected. is there.

[0020]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems and to achieve the above-mentioned object, the present invention provides a DC power supply having means for restricting a supply current from increasing beyond a predetermined limit value. The first and second DC power terminals connected to the DC power source configured as described above, a main winding having one end connected to the first DC power terminal, the first and second main terminals, A main switch having a control terminal, the first main terminal being connected to the other end of the main winding, and the second main terminal being connected to the second DC power supply terminal; A rectifier diode for accumulating energy in the main winding during the on period of the main switch and discharging the stored energy of the main winding during the off period of the main switch, and a smoothing capacitor for smoothing the rectified output of the diode. Output circuit for supplying DC power to the load The polarity is determined so as to be electromagnetically coupled to the main winding, one end thereof is connected to the control terminal of the main switch, and the other end is connected to the second main terminal, and the main switch is driven in a positive feedback manner. Drive current, a constant voltage control circuit for controlling the output voltage of the smoothing capacitor to a constant value, and a current flowing through the first and second DC power supply terminals. The present invention relates to a flyback type DC converter including on-time width limiting means for limiting the on-time width of the main switch so that the value can be limited to a value lower than the predetermined limit value. The on-time width limiting means is constituted by a driving capacitor connected to the control terminal of the main switch, a charging means for the capacitor, and a discharging means for the capacitor. The ON time width of the main switch can be set based on the time constant and the discharge time constant. Also, as shown in claim 3,
An on-time width limiting switch is provided, which is turned on in synchronization with the main switch to start discharging the driving capacitor, and thereafter the main switch can be turned off. It is desirable that the constant voltage control circuit be configured as specified in the embodiment. According to a fifth aspect of the present invention, the constant voltage control circuit is a circuit having a dummy resistor, and a current flowing through the dummy resistor is controlled by a difference signal (error signal) to control power consumption and achieve a constant voltage. Can be. According to a sixth aspect of the present invention, the DC power supply is capable of selectively obtaining a constant voltage supply mode with current limitation and a constant current supply mode, and the polarity of the current voltage source is switched. Means and a rectifier circuit. Further, the constant voltage control system of the DC converter can be switched in accordance with the switching between the constant voltage supply mode and the constant current supply mode of the power supply. It is preferable that an output winding (secondary winding) is provided, and a smoothing capacitor is connected to the output winding via a diode. Further, a part or the whole of the drive winding can be used also as an output winding. Further, a boosting converter can be configured by connecting a smoothing capacitor to a main switch in parallel via a diode, as described in claim 10.

[0021]

According to the present invention, the input current of the DC converter is limited so as not to reach the current limit value in the power supply. Therefore, since the current of the power supply does not reach the current limit value, an increase in the voltage of the power supply is not suppressed. This allows
In a state where the input current does not reach the limit value, the increase of the input voltage increases and the output voltage enters the constant voltage control range. This allows
The power supply at the point A or the point C in FIG. 3 becomes possible. For this reason, the voltage of the power supply having current limitation can be stably controlled by the flyback type DC converter having a relatively simple configuration. Further, when the on-time width limiting means is provided as described in claims 2 and 3, the on-time limit of the main switch can be achieved with a relatively simple circuit configuration.
When the constant voltage control circuit is configured as described in claims 4 and 5, constant voltage control can be achieved with a relatively simple circuit. Further, when the constant voltage control mode is switched according to the power supply mode change, optimal voltage control can always be performed.

[0022]

Embodiments and Examples Next, embodiments and examples of the present invention will be described with reference to the drawings.

[0023]

First Embodiment First, a self-excited flyback converter according to a first embodiment of the present invention will be described with reference to FIGS. However, in FIG. 6 and FIGS. 9 to 12 showing the second to sixth embodiments to be described later, substantially the same parts as those in FIG. The converter of the first embodiment shown in FIG. 6 is different from the converter of FIG. 1 in that a resistor 51, a diode 52, a transistor 53, a resistor 54, and a capacitor 55 are added to the converter of FIG. It has the same configuration and operates the same as the converter of FIG. 1 except for the added parts.

The ON time width limiting means for limiting the ON time width of the main switch 6 includes a starting resistor 15 and a driving capacitor 14 in addition to the above-mentioned added parts. The first resistor 51 of the ON time width limiting means is connected to the driving capacitor 14.
And one end of which is connected to the main switch 6 of the driving capacitor 14.
Connected to the side terminal. Second of the on-time width limiting means
The starting resistor 15 as the resistor of the first power supply terminal 2
And is connected to the other end of the resistor 51 and is involved in determining the charging time constant of the driving capacitor 14. A transistor 53 as an on-time width limiting switch is connected between the first resistor 51 and the lower end of the drive winding 9 via a backflow preventing diode 52. That is, the collector of the NPN transistor 53 is connected to the first resistor 5 through the diode 52.
1 and the emitter is connected to the lower end of the drive winding 9. The base (control terminal) of the on-time width limiting transistor 53 is a resistor
4 is connected to the upper end of the drive winding 9. Also,
A capacitor 55 is connected in parallel with the resistor 54.

Next, the operation of the on-time width limiting means of FIG. 6 will be described with reference to FIG. When the main switch 6 is turned off at the time t0 in FIG. 7 and the voltage V9 of the drive winding 9 is turned to reverse bias the main switch 6 as shown in FIG. The charging of the driving capacitor 14 is started via the line V.
As shown in (A), it increases with a slope. This slope is determined by the charging time constant of the resistors 15 and 51 and the capacitor 14. At time t1 in FIG. 7, the sum of the voltage V14 of the driving capacitor 14 and the voltage V9 of the driving winding 9 is determined by the main switch 6.
, The main switch 6 is turned on. When the main switch 6 is turned on, positive feedback generates a voltage in the drive winding 9 in a direction to forward bias the main switch 6 as shown in FIG. 7B, and the main switch 6 is kept on.
At the same time, a base current is supplied from the drive winding 9 to the on-time width limiting transistor 53, and this transistor 5
3 is turned on as shown in FIG. As a result, a discharge circuit is formed in accordance with a discharge time constant determined by a circuit including the capacitor 14, the resistor 51, the diode 52, the transistor 53, and the drive winding 9, and the discharge of the drive capacitor 14 is started. Gradually decrease as shown in FIG. The main switch 6 is the sum V9 of the voltage V9 of the driving winding 9 and the voltage V14 of the driving capacitor 14.
+ V14, and the sum voltage V9 + V14 is t
At time 2, when the voltage falls below the threshold value of the main switch 6, the main switch 6 is turned off and the on-time width limiting transistor 53 is also turned off, and the discharging means including the resistor 51, the diode 52 and the transistor 53 is used. The discharge is completed, and the charging of the driving capacitor 14 starts again from the time point t2.

Here, what is important is that t of the main switch 6
The ON time width of 1 to t2 is set so that the input current can be limited to a value lower than the current limit value of the power supply 1. FIG. 7D shows the off-control transistor 2
2 shows the base-emitter voltage and V7 + V24. FIG.
As can be seen from (D), when the main switch 6 is turned on, the base voltage of the transistor 22 also increases with a slope, but before the base voltage reaches the threshold value Vth, the main switch 6 sets the off time width limiting means according to the present invention. Is controlled off.
The maximum ON time width of the main switch 6 is determined by the drive capacitor 1
4, and the input current (average value) Iin of the converter is determined to be lower than the current limit value of the power supply 1 shown in FIG. 3, that is, the maximum current Im. FIG. 8 shows the relationship between the input voltage Vin and the input current Iin of the self-excited flyback converter of FIG. 6 according to the present invention.

Even if the power supply 1 between the power supply terminals 2 and 3 of the converter shown in FIG. 6 has a current limit of Im (39 mA) as shown in FIG. 5, the input current Iin on the converter side is limited to the limit value. When control is performed so that the current Im does not flow, the power supply 1 having the characteristics shown in FIG. 5 can increase the output voltage of the power supply 1, that is, the input voltage Vin of the converter.
In FIG. 8, an input voltage Vin higher than Vb is supplied to the converter, and a voltage Va at point A and a voltage Vc at point C in FIG. 8 can be obtained as the input voltage Vin. If power supply 1 in FIG.
Input voltage Vi when the circuit of FIG. 4 is connected as
n, the input current Iin is at point A in FIG. 8 when the telephone is busy, and at point C when the telephone is on standby.

As is apparent from the above, according to the first embodiment, it is possible to provide a self-excited flyback converter that operates even when a power supply having a current limiting characteristic is connected as the power supply 1.

[0029]

Second Embodiment Next, a converter according to a second embodiment will be described with reference to FIG. However, FIG. 9 and FIG.
In FIG. 12 to FIG. 12, substantially the same parts as those in FIG. The converter shown in FIG. 9 has the same configuration as that of FIG. 6 except that a voltage control circuit including a light emitting diode 19, a phototransistor 21, diodes 25 and 26, and a resistor 27 is omitted from FIG. 6, and a dummy resistor 60 is provided instead. It was done.

The dummy resistor 60 is provided between one end of the smoothing capacitor 12 and the output terminal of the error amplifier 18. Therefore, if the output voltage V0 becomes higher than the reference value, the output voltage level of the error amplifier 18 decreases, the current flowing into the dummy resistor 60 increases, and the output voltage V0 decreases. Conversely, when the output voltage V0 becomes lower than the reference value, the current flowing through the dummy resistor 60 decreases, and the output voltage V0
Becomes higher to return to the reference value. When a constant current source is connected as the power supply 1 of the converter in FIG. 9, the output voltage V0 can be controlled to be constant by the same constant voltage control circuit as in FIG. Can not.
However, if a constant voltage control circuit using the dummy resistor 60 is provided as shown in FIG. 9, the output voltage V0 can be controlled to be constant by controlling the amount of current bypass (equivalently, impedance control), and the input current can be kept constant. Can be.

In the converter of FIG.
Is not controlled by the voltage control signal, so that it is turned on only depending on the voltage V7 of the current detection resistor 7. If the power supply 1 is configured to supply a constant current in a steady state, the ON time width of the main switch 6 is constant.

The on-time width limiting means comprising the capacitor 14, the resistors 15, 51, the diode 52, and the transistor 53 operates in the same manner as in the first embodiment, and the input of the converter is set to a value lower than the current limit value of the power supply 1. The ON time width of the main switch 6 is limited so as to suppress the current Iin. The ON time width of the main switch 6 determined based on the ON state of the transistor 53 is shorter than the ON time width of the main switch 6 determined based on the transistor 22.

The second embodiment has the same operation and effect as the first embodiment, has the effect of simplifying the constant voltage control circuit, can keep the input current constant, and keeps the output voltage constant. It has the effect that it can be maintained. The converter shown in FIG. 9 is suitable for supplying electric power from the power supply 1 in a constant current supply mode during a call.

[0034]

Third Embodiment A converter according to a third embodiment shown in FIG. 10 corresponds to a converter obtained by adding the dummy circuit shown in FIG. 9 to the converter shown in FIG. That is, the converter of FIG. 10 uses the power supply 1 of the circuit of FIG. 6 as the power supply for the telephone shown in FIG. 4, adds the dummy resistor 60, and turns off the voltage control light emitting diode 19 in the constant current supply mode. A phototransistor 61 is provided.
6 except that a constant current supply mode detection circuit 62 for turning on the power supply in the constant current supply mode is provided.

The dummy resistor 60 has the same purpose as the circuit of FIG. 9 and is connected in series to the phototransistor 61 and the light emitting diode 19. The phototransistor 61 responding to the constant current supply mode is connected to the light emitting diode 19 in parallel. Therefore, when the phototransistor 61 is turned on in the constant current supply mode, the light emitting diode 19 is short-circuited, and the voltage control operation by the light emitting diode 19 is cut off.
Voltage control by 0 starts.

The constant current supply mode detection circuit 62 includes a comparator 63, a reference voltage source 64, and a backflow preventing diode 65.
, A resistor 66 and a light emitting diode 67. One input terminal of the comparator 63 is connected to the second terminal 32 of the power supply 1 via the diode 65, and the other input terminal is connected to the reference voltage source 64. The light emitting diode 67 is connected to the output terminal of the comparator 63 and is optically coupled to the phototransistor 61. Note that one end of the resistor 66 and one end of the reference voltage source 64 are connected to the lower end of the drive winding 9. The lower end of the drive winding 9 is directly connected to the source of the main switch 6 without passing through the current detection resistor 7.

The power supply 1 is the same as that shown in FIG.
The power supply circuit includes a station-side power supply circuit 1a and a converter-side power supply circuit 1b, and selectively takes a constant voltage supply mode and a constant current supply mode. In the constant current supply mode, a positive voltage is obtained at the second terminal 32 as described with reference to FIG. 4, so that the comparator 63 detects this, makes the light emitting diode 67 emit light, and turns on the phototransistor 61.

In this embodiment, when the station side power supply circuit 1a is in the constant voltage supply mode, the phototransistor 61 is kept off, and the constant voltage control by the light emitting diode 19 is performed as in the circuit of FIG. When the station side power supply circuit 1a is in the constant current supply mode, the phototransistor 61 is turned on,
Since the light emitting diode 19 is short-circuited, voltage control is performed by the same dummy resistor 60 as in FIG. Therefore, FIG.
In the converter 0, constant voltage control suitable for the operation mode of the power supply 1 is executed. The ON time width limiting means including the transistor 53 operates in the same manner as in the first and second embodiments, and can obtain the same effect.

[0039]

Fourth Embodiment FIG. 11 shows a fourth embodiment in which the output winding 8 of FIG. 6 is omitted, and a smoothing capacitor 12 is connected in parallel to the drive winding 9 via a diode 11. It has the same configuration as that of FIG. As shown in FIG.
The same effect as the converter of FIG. The drive winding 9 shown in FIG.
May be omitted, and the output winding 8 may be used also as the drive winding.

[0040]

Fifth Embodiment A converter according to a fifth embodiment shown in FIG. 12 omits the output winding 8 from FIG.
Are connected in parallel to the main switch 6 via a diode 11 in the same configuration as in FIG. The converter of FIG. 12 is a boost converter that can obtain an output of the sum of the voltage of the power supply 1 and the voltage of the main winding 5 when the main switch 6 is turned off. In the converter of FIG. 12, the same effect as in FIG. 6 can be obtained.

[0041]

[Modifications] The present invention is not limited to the above-described embodiment, and for example, the following modifications are possible. (1) Also in the circuits of FIGS. 11 and 12, the power supply 1 and the constant voltage control means can be configured like the circuits of FIGS. 9 and 10. (2) The main switch 6 can be replaced with another semiconductor switch such as a bipolar transistor. (3) The transistors 21 and 22 can be replaced with semiconductor switches such as FETs. (4) The charging resistor and the discharging resistor can be individually provided without using the resistor 51 for both the charging time constant and the discharging time constant.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a conventional flyback type converter.

FIG. 2 is a waveform diagram showing a state of each unit in FIG.

FIG. 3 is a diagram showing a relationship between an input voltage and an input current when the power supply in FIG. 1 is used as a voltage source.

FIG. 4 is a circuit diagram showing a telephone power supply having a current limiting characteristic.

FIG. 5 is a characteristic diagram showing a relationship between a current and a voltage of a power supply having a current limiting characteristic.

FIG. 6 is a circuit diagram showing a flyback type converter according to the first embodiment.

FIG. 7 is a waveform diagram showing a state of each unit in FIG. 6;

FIG. 8 is a diagram showing a relationship between an input voltage and an input current of a comparator when the current in FIG. 6 has current limiting characteristics.

FIG. 9 is a circuit diagram illustrating a converter according to a second embodiment.

FIG. 10 is a circuit diagram illustrating a converter according to a third embodiment.

FIG. 11 is a circuit diagram showing a converter according to a fourth embodiment.

FIG. 12 is a circuit diagram showing a converter according to a fifth embodiment.

[Explanation of symbols]

 Reference Signs List 6 Main switch 7 Current detection resistor 9 Drive winding 21 On-time width limiting transistor 22 Off-control transistor 26 Dummy resistor

Claims (10)

[Claims] A first DC power supply terminal connected to a DC power supply configured to supply DC power with a means for restricting a supply current from increasing beyond a predetermined limit value; A main winding having one end connected to the first DC power supply terminal, first and second main terminals, and a control terminal, wherein the first main terminal is the other end of the main winding; A main switch having the second main terminal connected to the second DC power supply terminal; storing energy in the main winding during an ON period of the main switch; An output circuit for supplying DC power to a load including a rectifying diode for discharging the stored energy of the main winding and a smoothing capacitor for smoothing a rectified output of the diode; and an electromagnetically coupled to the main winding. And one end of the main switch is A drive winding connected to the control terminal and having the other end connected to the second main terminal and having a polarity determined to drive the main switch in a positive feedback manner; and controlling the output voltage of the smoothing capacitor to be constant. Voltage control circuit, and the main switch so that a current flowing through the first and second DC power supply terminals can be limited to a value lower than the predetermined limit value of a supply current of the DC power supply. A flyback type DC converter comprising an on-time width limiting means for restricting an on-time width of the power supply. 2. The on-time width limiting means includes: a driving capacitor connected between one end of the driving winding and a control terminal of the main switch; and a control terminal of the main switch that turns on the main switch. Charging means for gradually charging the driving capacitor in a direction in which a voltage in the direction of applying the voltage can be applied; and starting discharging of the capacitor in synchronization with turning on of the main switch, for driving the main switch. 2. The DC converter according to claim 1, further comprising discharging means for gradually lowering a charging voltage of the capacitor. 3. The on-time width limiter includes: a drive capacitor connected between one end of the drive winding and a control terminal of the main switch; and one end of the drive capacitor on the main switch side of the drive capacitor. A first resistor connected to a terminal; an on-time width limiting switch connected between the other end of the first resistor and the other end of the drive winding; and a first DC power supply terminal. A second resistor connected between the other end of the first resistor and a voltage generated in the drive winding for driving the main switch to turn on, the on-time width limiting switch; 2. A DC converter according to claim 1, further comprising: means for controlling the ON state of the DC converter. 4. The constant voltage control circuit, comprising: a current detection resistor connected between the second main terminal of the main switch and the second DC power supply terminal; a control terminal of the main switch; An off control switch connected between the other end of the drive winding, an off control resistor connected between a main switch side terminal of the current detection resistor and a control terminal of the off control switch, A voltage control capacitor connected in parallel to the control resistor, a control element connected between one end of the drive winding and a control terminal of the off control switch, and a reference voltage source for constant voltage control. An output voltage detecting means for detecting a voltage of the smoothing capacitor; and a voltage control signal corresponding to a difference between the voltage detected by the output voltage detecting means and a reference voltage of the reference voltage source, to control the control element. Voltage system DC converter according to claim 1 or 2 or 3, wherein the composed of the signal forming means. 5. The constant voltage control circuit includes: a reference voltage source for constant voltage control; output voltage detection means for detecting a voltage of the smoothing capacitor; and a voltage detected by the output voltage detection means and the reference voltage. A difference signal forming means for forming a signal corresponding to a difference from a reference voltage of a source, and a dummy resistor connected between one end of the smoothing capacitor and an output terminal of the difference signal forming means. The DC converter according to claim 1, 2, 3, or 4. 6. A DC power supply connected to the first and second DC power supply terminals, comprising: a voltage / current source that selectively takes a constant voltage supply mode with a current limit and a constant current supply mode; Connecting the first terminal to one end of the voltage / current source and connecting the second terminal to the other end of the voltage / current source in the constant voltage supply mode; In the supply mode, the first
Switching means for connecting a first terminal to the other end of the voltage / current source and connecting the second terminal to one end of the voltage / current source; and a full-wave rectifier circuit connected to the first and second terminals. Wherein the output terminals of the full-wave rectifier circuit are the first and second
The DC converter according to claim 1, wherein the DC converter is configured to be connected to a DC power supply terminal. 7. A DC power supply connected to the first and second DC power supply terminals, comprising: a voltage / current source that selectively takes a constant voltage supply mode with a current limit and a constant current supply mode; Connecting the first terminal to one end of the voltage / current source and connecting the second terminal to the other end of the voltage / current source in the constant voltage supply mode; In the supply mode, the first
Switching means for connecting a first terminal to the other end of the voltage / current source and connecting the second terminal to one end of the voltage / current source; and a full-wave rectifier circuit connected to the first and second terminals. Wherein the output terminals of the full-wave rectifier circuit are the first and second
Or is configured to function as first and second DC power supply terminals, wherein the constant voltage control circuit controls an ON time width of the main switch to output the output. The voltage can be controlled to be constant and the current flowing through a dummy resistor connected in parallel to the smoothing capacitor is controlled so that the output voltage can be controlled to be constant. Means is provided for obtaining a signal capable of distinguishing between the constant current supply mode and the constant voltage supply mode, and the dummy resistor is provided in the constant current supply mode based on the distinguished signal. Means for setting a constant voltage control state by controlling the ON time width of the main switch in the constant voltage supply mode. Claim 1 or 2 or 3 DC converter wherein Rukoto. 8. The output circuit has an output winding electromagnetically coupled to the main winding, and the smoothing capacitor is connected in parallel to the output winding via the diode. The DC converter according to claim 1. 9. The DC converter according to claim 1, wherein the smoothing capacitor is connected at least partially in parallel to the drive winding via the diode. 10. The DC converter according to claim 1, wherein the smoothing capacitor is connected in parallel to the main switch via the diode.