JPS627775B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a DC-DC converter with a pseudo load, particularly a DC-DC converter with two outputs, which can obtain stable output regardless of the value of the load connected to each output. This invention relates to a DC-DC converter with a pseudo load that reduces power loss.

Two output windings are provided in the transformer that constitutes the DC-DC converter, and the pulse voltage generated in each output winding is rectified and smoothed to obtain two DC outputs, and one DC output voltage is stabilized. To do so, the DC-DC
Conventionally, a configuration has been used to obtain two stable DC voltages by controlling the switching ratio of the switch elements that make up the converter and providing a series control stabilization circuit to stabilize the other DC output voltages. . Figure 1 is an example of a configuration in which a pseudo load is provided in this type of circuit, where 1 is a DC power supply, 2 is a transformer, and 3 is a transformer.
is a switch element, 4, 5, 15, 16 are rectifiers,
6, 17 are blockage rings, 7, 18 are condesa, 8,
9 is the first output terminal, 10 and 24 are the output loads, 1
1 is a control circuit, 12, 20 is a reference voltage source, 13,
21 is an error amplifier, 14 is a switching control circuit, 19 is a voltage drop element, 22 and 23 are second output terminals, 2
5 is resistance.

The DC power supply 1, the first winding _n1 of the transformer 2, and the switch element 3 using a transistor are connected in series, and the pulse voltage generated by opening and closing the switch element 3 is applied to the first winding n1 of the transformer 2. ₁ , the pulse voltage induced in the second winding _n2 of the transformer 2 is rectified by rectifiers 4 and 5, smoothed by a smoothing circuit composed of a blocking wire 6 and a capacitor 7, and then A first DC output is obtained between the first output terminals 8 and 9 and supplied to the output load 10, and the difference between the DC voltage between the first output terminals 8 and 9 and the voltage of the reference voltage source 12 in the control circuit 11 is A switching control circuit 1 that amplifies the output switching ratio using an error amplifier 13 and varies the output switching ratio according to the output of the error amplifier 13.
By applying the output of 4 to the control terminal, that is, the base electrode of the switch element 3, the switching ratio of the switch element 3 is controlled so that the voltage between the first output terminals 8 and 9 matches the voltage of the reference voltage source 12. is configured to do so. Furthermore, in order to obtain a second output, the pulse voltage induced in the third winding _n3 of the transformer 2 is rectified by rectifiers 15 and 16, and a smoothing circuit consisting of a blocking wire 17 and a capacitor 18 is used. smooth,
Obtaining another DC voltage across the terminals of the capacitor 18,
In order to stabilize the other DC voltage mentioned above, a voltage drop element 19 using a transistor is connected between the second output terminal 22 and the voltage between the second output terminals 22 and 23 and the voltage of the reference voltage source 20. The difference between the two output terminals 22 and 23 is amplified by the error amplifier 21 and applied to the control terminal, that is, the base electrode of the voltage drop element 19, so that the voltage between the second output terminals 22 and 23 is made equal to the voltage of the reference voltage source 20. Controlling the voltage between the terminals of the drop element 19, that is, between the collector and emitter electrodes,
The output load 24 is configured to be supplied with a stable DC voltage.

The circuit shown in FIG. 1 connects the first output terminal 9 and the second output terminal 22 and uses this as the
A stable DC voltage of positive polarity is supplied to the output terminal 8 of , and a stable DC voltage of negative polarity is supplied to the second output terminal 23 .

FIG. 2 shows characteristics showing the operation in FIG. 1, where the horizontal axis shows the output current _I1 flowing to the output load, and the vertical axis shows the switching ratio D of the switch element 3 and the first output terminals 8, 9.
₁ , the voltage V ₂ ' between the terminals of the capacitor 18, and the voltage V ₂ between the second output terminals 22 and 23. When the output current _I1 is large, excitation current accumulates in the blocking wire 6 through the rectifier 4 while the switch element 3 is conducting, and the excitation current accumulated in the blocking wire 6 due to the cutoff of the switch element 3 The current is commutated to the rectifier 5 and continues to flow, and the switch element 3 becomes conductive again, so that the excitation current is not completely discharged through the rectifier 5 to the capacitor 7 and the output load 10. Therefore, even if the output current I ₁ is gradually reduced, the switching ratio D of the main switch is approximately equal to the peak value of the pulse voltage induced in the second winding n ₂ of the transformer 2 and the peak value of the pulse voltage induced in the second winding n 2 of the transformer 2. The voltage ratio between 9 and 9 remains almost constant. When the output current I ₁ approaches zero, the first
The control circuit 11 maintains the output voltage V ₁ constant.
controls the switching ratio D of the switch element 3 so as to approach zero. The boundary between the state where the switching ratio D changes and the state where the switching ratio D is approximately constant (the second
In the figure, the output current I _{1 (} I _c ) is the switch element 3
This is the case when the discharge of the excitation current from the blocking coil 6 is completed at the time when the current changes from cutoff to conduction. When the first output current I ₁ is greater than or equal to I _c , the voltage V ₂ ' between the terminals of the capacitor 18 is large enough to allow the voltage drop element ₁₉ to operate sufficiently; I
If the value is less than _c , the switching ratio D of the switch element 3 becomes small as described above, so that when a desired current is supplied to the output load 24, the voltage V ₂ ' between the terminals of the capacitor 18 decreases. At this time, since the potential at the input end (collector electrode) of the voltage drop element 19 falls below the potential of the reference voltage source 20, the second output terminals 22, 2
The voltage V ₂ between the two terminals cannot be maintained at a predetermined constant value, and the voltage V ₂ decreases. Output loads 10 and 24
The voltage V ₁ between the first output terminals 8 and 9 and the voltage between the second output terminals 22 and 23
In order to keep V ₂ constant, a resistor 25 is connected in parallel with the capacitor 7, which normally serves as a pseudo load equivalent to flowing a current that is apparently higher than the output current I _c from the first output terminals 8 and 9. However, since the resistor R always consumes a current greater than the current I _c , the switch element 3 and the rectifiers 4 and 5 are required to be capable of passing a large current as power loss increases.

In order to solve these drawbacks, the present invention reduces power loss by passing current through the pseudo load only when the current supplied to the output load 10 decreases, and will be described in detail with reference to the drawings below. do.

FIG. 3 shows a DC--
This is an example of a DC converter, where 30 is a pseudo load circuit, 31 is a resistor, 32 is a transistor, and 33
is a reference voltage source, 34 is a voltage comparator, and a resistor 31 and a transistor 32 are connected between the first output terminals 8 and 9.
are connected in series, and the voltage comparator 34 is a voltage drop element for stabilizing the voltage of the reference voltage source 33 and the second output with respect to the potential of the first output terminal 9 or the second output terminal 22. 19, and if the voltage at the input end of the voltage drop element 19 is smaller than the voltage of the reference voltage source 33, the output of the voltage comparator 34 becomes a high potential and the transistor 32 is Connected for conduction. If the voltage of the reference voltage source 33 is selected to be higher than the input-output voltage at which the voltage drop element 19 can operate normally, that is, the collector-emitter voltage, then
The current flowing through the output load 10 decreases and the control circuit 1
1, when the switching ratio D of the switch element 3 decreases and the voltage between the terminals of the capacitor 18 decreases,
The voltage between the input and output of the voltage drop element 19 is the reference voltage source 3
When the voltage drops below 3, the transistor 32 is made conductive through the voltage comparator 34 to flow a pseudo load current, and the switching ratio D of the switch element 3 is operated through the control circuit 11 so that it does not fall below a certain value. 19 operates normally under all conditions of the output load 10, and the output terminals 22, 2
A stabilized voltage is obtained between 3 and 3.

FIG. 4 shows another configuration example of the pseudo load circuit 30, in which 40 is a transistor, and 41 and 42 are resistors. Terminal A is connected to the first output terminal 8, and terminal B is connected to the first output terminal 8.
The terminal C is connected to the output terminal 9 of the voltage drop element 19, the base electrode of the transistor 40 is connected to the terminal C through the resistor 41, the emitter electrode of the transistor 40 is connected to the terminal B, and the terminal C is connected to the input terminal of the voltage drop element 19.
The collector electrode of the transistor 32 is connected to the base electrode of the transistor 32, and is also connected to the terminal A through the resistor 42. If the potential at terminal C with respect to the potential at terminal B is higher than the base-emitter voltage required to make transistor 40 conductive, transistor 40 becomes conductive and transistor 32 is cut off, so no pseudo load current flows and the voltage decreases. Falling element 19
When the input/output voltage of the transistor 40 becomes lower than the base-emitter voltage, the transistor 40 is cut off, and the transistor 32 becomes conductive, causing a pseudo load current to flow through the resistor 31. In this case, the voltage of the reference voltage source 33 shown in FIG. 3 corresponds to the base-emitter voltage.
Further, the resistor 31 is inserted for the purpose of limiting the pseudo load current, but naturally it must have a value that allows a current greater than the output current I _c shown in FIG. 2 to flow.

FIG. 5 shows still another configuration example of the pseudo load circuit 30, in which 50 is a resistor, 51 is a capacitor, and the collector electrode of the transistor 40 and the transistor 3
A resistor 50 is connected between the base electrode of the transistor 32 and the collector electrode of the transistor 32, and a capacitor 51 is connected between the base electrode and the collector electrode of the transistor 32.

As in the operation of the pseudo load circuit described above, when the current flowing through the output load 10 is small, a pseudo load current flows through the resistor 31 and the transistor 32, and the operation of maintaining the voltage across the terminals of the capacitor 18 above a certain value is carried out through the control circuit 11. First output terminal 8, 9
In addition to the negative feedback control system that keeps the voltage between A second negative feedback control system is configured in which the switching ratio D of the switch element 3 is controlled by the control circuit 11 through the circuit. In order to stably operate the power supply circuit constituted by the double negative feedback control system, it is necessary to reduce the response characteristics of the pseudo load circuit as necessary. In FIG. 5, a well-known Miller integral operation is performed using a resistor 50 and a capacitor 51 in a transistor 32, and the other operations are exactly the same as in FIG.
By appropriately selecting the value 1, extremely stable operation can be obtained.

As explained above, according to the present invention, the transformer 2 constituting the DC-DC converter in which the first output voltage is stabilized is provided with the third winding, and the voltage induced in the third winding is In a power supply circuit that rectifies and smoothes a pulse voltage and obtains a second stabilized output voltage through a series control stabilization circuit, a series circuit of a resistor 31 and a transistor 32 is connected between the first output terminals,
Voltage drop element 1 constituting the series control stabilization circuit
A reference voltage source 33 having a voltage higher than the voltage between the input and output of the voltage drop element 19 necessary for normal operation of the voltage drop element 19 is provided, and the voltage of the reference voltage source 33 and the voltage at the input end of the voltage drop element 19 are set to a voltage. By comparing with the comparator 34 and controlling the transistor 32, the second output terminal 2 is
A stable second output voltage can be obtained between 2 and 23, and the pseudo load current flowing through the resistor 31 and the transistor 32 is reduced when the input terminal voltage of the voltage drop element 19 is about to drop below a predetermined value. only,
That is, since the current flows only when the current flowing through the output load 10 falls below I _c , power loss is reduced compared to a conventional DC-DC converter having a pseudo load. Furthermore, the DC with pseudo load according to the present invention
- In the DC converter, a pseudo load current flows according to the input terminal voltage of the voltage drop element 19, so
For example, even if the inductance of the blockage wire changes for some reason and the value of I _c shown in FIG. . On the other hand, in the conventional configuration shown in FIG. 1, the resistor 25 is required to have a resistance value that allows an extra pseudo load current to flow, taking into account manufacturing deviations or deviations during use of the inductance of the above-mentioned blockage wire, for example. This results in more power loss. Further, in the case of the present invention, more power loss is reduced and the switch element 3,
There is an advantage that the current capacity of the rectifiers 4 and 5 is also small.

[Brief explanation of the drawing]

Fig. 1 is a circuit example of a conventional DC-DC converter with a pseudo load, Fig. 2 is a characteristic diagram for explaining the operation of Fig. 1, and Fig. 3 is a DC-DC converter with a pseudo load according to the present invention. One embodiment, FIG. 4 is an example of the configuration of the pseudo load circuit in FIG. 3, and FIG.
The figure shows another example of the configuration of the pseudo load circuit in FIG. 3. 1... DC power supply, 2... Transformer, 3... Switch element, 4, 5, 15, 16... Rectifier, 6, 1
7... Blocking wire, 7, 18, 51... Capacitor, 8, 9... First output terminal, 10, 24...
Output load, 11...Control circuit, 12, 20, 33
... Reference voltage source, 13, 21 ... Error amplifier, 1
4... Opening/closing control circuit, 19... Voltage drop element, 2
2, 23...second output terminal, 25, 31, 4
1, 42, 50...Resistor, 30...Pseudo load circuit, 32, 40...Transistor, 34...Voltage comparator.

Claims (1)

[Claims] 1 A DC power source, the first winding of the transformer, and a switch element are connected in series, and the pulse voltage generated in the second winding of the transformer is rectified and smoothed by opening and closing of the switch element. The first output is stabilized by comparing the voltage of the first output with a desired reference voltage and controlling the switching ratio of the switch element, and the pulse voltage generated in the third winding of the transformer is stabilized. The DC voltage obtained by rectifying and smoothing is input to a series control stabilizing circuit to obtain a second output stabilized as the output of the series control stabilizing circuit.
In a DC stabilized power supply that obtains two stabilized outputs, a positive pole and a negative pole, by connecting the terminals on each side of the output and the second output to form a common ground,
A series circuit of a resistor and a transistor is connected to the first output, and a second reference voltage higher than the lowest voltage drop value at which the series control stabilization circuit can operate normally is input to the series control stabilization circuit. A DC-DC converter having a pseudo load, characterized in that the transistor is controlled by comparing the voltage at the terminal.