JP2001275346A - Power supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize operation under a light-load or no-load condition, without causing low efficiency. SOLUTION: If a load current IL, flowing through output voltage lines 6, 7, decreases under the light-load or unload condition and a voltage level Va of a detection signal detected at an amplifier 23 drops below a fixed value, a transistor 44 is turned on and dummy current flows through a dummy resistor 45. Therefore, even under the light-load or no-load condition, the load current IL corresponding to at least the dummy current passes through to stabilize the operation, where as except when the operation is under the light-load or no-load condition, the transistor 44 is turned off, and the dummy current flowing through the dummy resistor 45 is cut off. Thus low efficiency due to the loss of the dummy resistor 45 can be avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a power supply device for stabilizing operation by flowing a dummy current.

[0002]

Generally, this type of power supply supplies a predetermined DC output voltage generated between output voltage lines to a load, and a dummy resistor is connected between the output voltage lines. Otherwise, the output voltage rises at light load or no load, or the ripple voltage increases, causing a problem that the operation is not stabilized. Also,
When a plurality of power supply units are operated in parallel without a dummy resistor, a certain power supply unit may stop oscillating and enter a standby state due to deterioration of a current balance, particularly at a light load.

[0003] This will be described in detail with reference to FIGS. 4 and 5. In FIG.
Vi and -Vi are input terminals to which a DC input voltage Vin is supplied, and 1 is an inverter composed of a transformer 2 and a MOS FET 3 as a switching element.
By switching the ET3, the DC input voltage Vin is intermittently applied to the primary winding 3A of the transformer 3, and a voltage is induced from the secondary winding 3B. This voltage is rectified and smoothed by the rectifying and smoothing circuit 5, and the output voltage lines 6,
It is supplied as a DC output voltage Vout during the period 7. In addition, +
Vo and -Vo are output terminals at the ends of the output voltage lines 6 and 7, respectively, to which an external load 8 is connected.

On the other hand, as a feedback circuit for stabilizing the DC output voltage Vout between the output voltage lines 6 and 7, an output voltage detection circuit 11 for detecting the DC output voltage Vout, and a voltage detection signal of the voltage detection circuit 11 A comparator 13 for comparing a reference voltage VREF1 supplied to its non-inverting input terminal by a power supply 12, and a MOS type FET 2 of the inverter 1 for supplying a DC output voltage Vout based on the comparison result of the comparator 13.
And a pulse width control circuit 14 for controlling the pulse conduction width of the pulse. When the DC output voltage Vout rises and the voltage level of the voltage detection signal from the output voltage detection circuit 11 rises, the voltage level of the output terminal of the comparator 13 falls, so that the pulse width control circuit 14 The pulse conduction width of the type FET 2 is reduced, and the DC output voltage Vout is reduced.
Conversely, the DC output voltage Vout decreases and the output voltage detection circuit 1
When the voltage level of the voltage detection signal from 1 decreases, the voltage level of the output terminal of the comparator 13 increases, so that the pulse width control circuit 14 increases the pulse conduction width of the MOSFET 2 and increases the DC output voltage Vout. Let it.

[0005] In addition to the feedback circuit, each of the output terminals + Vo, -Vo of a plurality of independent power supply units A1 to A3 is connected to a common load 8 in parallel operation. Current sharing circuit for equally sharing load currents IL1 to IL3 in power supply units A1 to A3
21 are provided. The current sharing circuit 21 amplifies the voltage generated between both ends of the resistor 22 as a current detector inserted into the output voltage line 7 on the minus side and detects the load currents IL1 to IL3. The amplifier 23 that outputs a signal, the load current IL1 of its own power supply unit A1, and the load current I1 of all power supply units A1 to A3 that operate in parallel.
And a current balance control amplifier 24 for comparing the average value of L1 to IL3 with each other. The amplifier 13 is arranged so that the load currents IL1 to IL3 of all the power supply units A1 to A3 become equal according to the comparison result of the amplifier 24. And a MOS-type FE for each of the power supply units A1 to A3 using the pulse width control circuit 14.
The pulse conduction width of T2 is controlled. In particular, the output terminal of the voltage amplifier 23 is connected to one input terminal of the current balance control amplifier 24 via the resistor 25, and is connected to the current sharing terminal PC via the resistor 26. The connection point with the terminal PC is the current balance control amplifier 24
The output terminal of the amplifier 23 is connected to the non-inverting input terminal of the amplifier 24 via a resistor 25, and is connected to a current sharing terminal PC via a resistor 26. The connection point between 26 and the current sharing terminal PC is an amplifier
24 power supply units A1 to A3 so as to monitor the average value of the load currents IL1 to IL3 of the power supply units A1 to A3 during the parallel operation.
The current sharing terminals PC of A3 are connected to each other. A resistor 15 is connected between the output terminal of the amplifier 24 and the reference power supply 12, and a connection point between the output terminal of the amplifier 24 and the resistor 15 is connected to a non-inverting input terminal of the amplifier 13.
24, the reference voltage VREF1 applied to the inverting input terminal of the amplifier 13 fluctuates, and the power supply unit A1
Is larger than the average value of the load currents IL1 to IL3 of all the power supply units A1 to A3,
In order to reduce L1, the pulse width control circuit 14 is set to the MOS type F.
If the pulse conduction width of the ET2 is reduced and the load current IL1 of the power supply unit A1 of the own device is smaller than the average value of the load currents IL1 to IL3 of all the power supply units A1 to A3, the load current IL1 is increased. The pulse width control circuit 14 is MOS
By increasing the pulse conduction width of the type FET 2, the load currents IL1 to IL3 of all the power supply units A1 to A3 are shared equally. The output terminal of the amplifier 24 and the amplifier 13
A series circuit of a diode 27 and a resistor 28 is connected to the non-inverting input terminal of the amplifier 13 because the reference voltage VREF1 does not change when the voltage of the output terminal of the amplifier 13 becomes L level. belongs to. In addition, each power supply unit A1
-A3 have the same internal configuration.

In the power supply units A1 to A3 provided with the current sharing circuit 21, when the voltage level of the output terminal of the amplifier 23 is Va, the load current IL (IL1 to IL)
As 3) becomes smaller, the voltage level Va also fluctuates linearly and becomes smaller. However, as shown in the graph of FIG.
The offset characteristics and the like of the amplifiers 23 of the power supply units A1 to A3 individually vary, and the variation in the voltage level Va of the output terminal of the amplifier 23 decreases as the load current Il decreases, that is, as no load or light load occurs. large.
Therefore, in the light load state, among the power supply units A1 to A3 operating in parallel, there is a power supply unit (for example, the power supply unit A1) whose oscillation is stopped. In such a situation, if a power supply unit (for example, the power supply unit A2) that supplies the load current IL to the load 8 fails for some reason, the power supply unit A1 whose oscillation has been stopped is difficult to recover. There is.

In order to avoid such a problem, a fixed dummy resistor 31 (see FIG. 4) is provided between the output voltage lines 6 and 7 of each of the power supply units A1 to A3 so that a light load or no load condition is provided. In this case, a constant dummy current may flow through the dummy resistor 31, but in this case, even in a load state where the dummy current is not required, the loss due to the dummy resistor 31 always occurs, and each power supply unit A1 -A3, which leads to a reduction in the efficiency of the entire power supply device.

Therefore, the present invention solves the above problems,
It is an object of the present invention to provide a power supply device capable of stabilizing the operation under a light load or no load without lowering the efficiency.

It is another object of the present invention to provide a power supply device that can respond to any of a plurality of power supply units operating in parallel with each other immediately even if a failure occurs. is there.

[0010]

According to a first aspect of the present invention, there is provided a power supply device comprising: a series circuit of a dummy load and a switch connected between output voltage lines; A current detection circuit for detecting a load current flowing through a line, and a switch switching circuit for turning on the switch means and flowing a dummy current to the dummy load when a detection level of the load current detected by the current detection circuit becomes a predetermined value or less. And a dummy load circuit comprising:

In this case, when the load current flowing through the output voltage line decreases under a light load or no load, and the detection level of the load current detected by the current detection circuit becomes a certain value or less, a series circuit is formed with the dummy load. The switch means is turned on, and a dummy current flows through the dummy load. As a result, even if the load is light or no load, a load current corresponding to at least the dummy current flows, and the operation of the power supply device is stabilized. Conversely, when the load is other than a light load or no load, the switch means is turned off, and the flow of the dummy current into the dummy load is cut off, so that a reduction in efficiency due to the loss of the dummy load can be avoided.

The power supply according to claim 2 of the present invention is characterized by claim 1
In addition to the configuration described in the above, the switch switching circuit such that the detection level of the load current at which the switch means switches from on to off and the detection level of the load current at which the switch means switches from off to on are different. It is what constituted.

Since the switch switching circuit here has a so-called hysteresis characteristic, for example, when the load current gradually decreases and the load current detection level falls below a certain value, the switch means switches from off to on. Although the dummy current flows through the dummy load after switching, the switch means does not switch from off to on even if the detection level of the load current increases due to the increase in load current accompanying the dummy current. Therefore, it is possible to prevent the switch means from being repeatedly turned on and off frequently.

According to a third aspect of the present invention, there is provided a power supply unit including a plurality of power supply units having the dummy load circuit in addition to the configuration described in the first or second aspect. This power supply unit is connected in parallel to the load, and this power supply unit compares the load current of its own power supply unit with the average value of the load currents of all the power supply units, and distributes the load current in each power supply unit equally. It has a circuit.

Each power supply unit compares the load current of its own power supply unit with the average value of the load currents of all the power supply units, and performs a parallel operation in which the load currents of the power supply units are shared equally. At this time, when the load current decreases at a light load and the detection level of the load current falls below a certain value, the switch means switches from off to on, and a dummy current flows through the dummy load. The state continues. Therefore, even if the power supply unit breaks down, the remaining power supply units continue to operate, so that a desired load current is quickly supplied while balancing the currents of the power supply units. It becomes possible.

According to a fourth aspect of the present invention, there is provided a power supply apparatus comprising:
In addition to the above configuration, the current detection circuit of the dummy load circuit is a current detection circuit of the current sharing circuit that detects a load current of a power supply unit of the own device.

In this case, the current detection circuit of the current sharing circuit also serves as the current detection circuit of the dummy load circuit, so that the circuit configuration can be simplified.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the power supply device according to the present invention will be described below with reference to the accompanying drawings. The same parts as those in the conventional example are denoted by the same reference numerals, and the description of the common parts will be omitted because they are duplicated. FIG. 1 is a circuit diagram schematically showing a configuration relating to the dummy load circuit 41 of the present embodiment. 4, a non-inverting input terminal and an inverting input terminal of an amplifier 23 are connected to both ends of a resistor 22 in the same way as in FIG. Correspond to a current detection circuit that detects a load current IL (IL1 to IL3) flowing through the output voltage line 7. An output terminal of the amplifier 23 is connected to a non-inverting input terminal of a comparator 42 having so-called hysteresis, and a reference power supply 43 is connected to the inverting input terminal of the comparator 42.
Further, the output terminal of the comparator 42 is connected to the switch means NP
Connected to the base of an N-type transistor 44, a series circuit of the transistor 44 and a dummy resistor 45 as a dummy load is
By connecting between the output voltage lines 6 and 7, a dummy load circuit 41 for flowing a dummy current to the dummy resistor 45 only under no load and light load is configured. When the voltage level Va of the detection signal of the load current IL generated at the output terminal of the amplifier 23, that is, the detection level becomes equal to or lower than a predetermined value, the comparator 42 turns on the transistor 44 and causes a dummy current to flow through the dummy resistor 45. It corresponds to a switch switching circuit.

The above-mentioned dummy load circuit 41 is connected to each power supply unit A
It is provided for each of 1 to A3. Especially dummy load circuit
The resistor 22 and the amplifier 23 included in the current detection circuit 41 also serve as the current detection circuit of the current sharing circuit 21 described above. The other configuration is the same as that of the conventional example shown in FIG.

FIG. 2 shows an embodiment of the circuit shown in FIG. In the figure, reference numerals 51 to 53 denote resistors for determining the amplification factor of the amplifier 23. A resistor 51 is connected between one end of the resistor 22 and an inverting input terminal of the amplifier 23.
A resistor 52 is connected between the non-inverting input terminal of 23 and the amplifier.
A resistor 53 is connected between the inverting input terminal and the output terminal. Further, resistors 54 and 55 for voltage division are connected between the output terminal of the amplifier 23 and the output voltage line 7, and the voltage level of the output terminal of the amplifier 23 is appropriately divided. The comparator 42 having the hysteresis specifically includes a base connected to a resistor 54,
An NPN transistor 56 grounded to a connection point 55 and an emitter connected to the output voltage line 7, a connection point between the collector of the transistor 56 and the base of the transistor 44, and an operation voltage line for generating a predetermined operation voltage VCC. A resistor 57 connected between the base of the transistor 56 and the transistor 44
And a resistor 58 for determining the hysteresis characteristics connected between the collector 58 and the collector of the transistor. Further here,
A dummy resistor 45 is configured by connecting a pair of resistors 45A and 45B in parallel.

Next, the operation of the above configuration will be described with reference to the graph of FIG. 3 shows the relationship between the voltage level Va of the output terminal of the amplifier 23 and the load current IL (IL1 to IL3), and the portion indicated by the dotted line does not include the dummy resistor 45 described later. The characteristics of the case are shown.

In the dummy load circuit 41, when a voltage is generated across the resistor 22 by the load current IL flowing through the output voltage line 7, this voltage is amplified by the amplifier 23,
A detection signal of the load current IL is output from the output terminal of the amplifier 23. This detection signal is compared with the reference voltage VREF2 of the reference power supply 43 by the comparator 42. If the voltage level Va of the detection signal is lower than the voltage value at light load or no load, the comparator 42 The output terminal goes to H (high) level, the transistor 44 turns on, and a dummy current flows through the dummy resistor 45. On the other hand, the voltage level Va of the detection signal
When the voltage exceeds the voltage value at the time of light load or no load, the transistor 42 is turned off to prevent the dummy current from flowing into the dummy resistor 45. Therefore, as shown in FIG. 3, in the no-load and light-load regions, the load current IL increases by the amount of the dummy current flowing, and in other regions, the load current IL changes without the dummy resistor 45. As described above, by supplying the load current IL to the output voltage line 7 only when the load is light or no load, the operation of each of the power supply units A1 to A3 is stabilized, and in the state where the dummy current is not required, This can be cut off by the transistor 44 to avoid a decrease in efficiency.

Also, due to the hysteresis of the amplifier 42, the load current IL gradually decreases, and the voltage level Va at which the transistor 44 switches from on to off is different from the voltage level Va at which the switch means switches from off to on. ing. The reason is, for example, when the load current IL gradually decreases and the voltage level Va falls below a certain voltage value, the transistor 44 is turned on and a dummy current flows through the dummy resistor 45. This is because when the voltage level Va rises due to the increase in IL, the transistor 44 is turned off, the dummy current is cut off again, and the on / off of the transistor 44 is not repeated. This can prevent the transistor 44 from being frequently turned on and off.

Next, the operation when the power supply units A1 to A3 having the dummy load circuit 41 are operated in parallel will be described. When the load state becomes light and the load currents IL1 to IL3 of the power supply units A1 to A3 decrease, the transistor 44 of the dummy load circuit 41 is turned on as described above, and the dummy current 45 is supplied to the dummy load 45 in each of the power supply units A1 to A3. Flows in. Accordingly, the output voltage lines 7 of the power supply units A1 to A3 are connected to the load currents IL1 to IL3 even when the load is light.
Flows, and the oscillation of the individual power supply units A1 to A3, that is, the operation state continues. Here, even if a certain power supply unit (for example, the power supply unit A2) fails for some reason and the supply of the load current IL2 from the power supply unit A2 stops, the remaining power supply units A1 and A3 correspond at least to the dummy current. Since the load currents IL1 and IL3 flowing through the power supply units A1 and A3 continue to operate, the desired load current I1
L1 and IL3 can be supplied.

As described above, in this embodiment, the dummy resistor 45, which is a dummy load connected between the output voltage lines 6 and 7,
And a series circuit of a transistor 44 serving as a switch means,
A resistor 22 and an amplifier 23 as a current detection circuit for detecting a load current IL flowing through the output voltage line 7;
When the detection level of the load current IL detected by the amplifier 23, that is, the voltage level Va of the detection signal becomes equal to or less than a predetermined value, the transistor 44 is turned on and the comparator 42 as a switch switching circuit for flowing a dummy current to the dummy resistor 45 is output. Dummy load circuit 41 is provided.

In this case, when the load current IL flowing through the output voltage lines 6 and 7 decreases under a light load or no load, and the voltage level Va of the detection signal detected by the resistor 22 and the amplifier 23 falls below a certain value, The transistor 44 which forms a series circuit with the dummy resistor 45 is turned on, and the dummy resistor 45 is turned on.
A dummy current flows through 45. As a result, even in a light load or no load state, a load current IL corresponding to at least the dummy current flows, and the operation of the power supply unit and the power supply device as a whole is stabilized. On the other hand, when the load is not a light load or no load, the transistor 44 is turned off and the flow of the dummy current into the dummy resistor 45 is cut off, so that a reduction in efficiency due to the loss of the dummy resistor 45 can be avoided.

The comparator 42 according to the present embodiment includes a transistor
Voltage level V of detection signal at which 44 switches from on to off
a, and the voltage level Va of the detection signal at which the transistor 44 switches from off to on is configured to be different. That is, since the comparator 42 has a so-called hysteresis characteristic, for example, the load current IL gradually decreases,
When the voltage level Va of the detection signal from 23 falls below a certain value, the transistor 44 switches from off to on, and a dummy current flows through the dummy resistor 45. Even if the voltage level Va increases, the transistor 44 does not switch from off to on. Therefore, it is possible to prevent the transistor 44 from being repeatedly turned on and off.

In this embodiment, a plurality of power supply units A1 to A3 having a dummy load circuit 41 are connected in parallel to a load, and the power supply units A1 to A3 are all connected to the load current of the power supply unit A1 of the own device. And a current sharing circuit 21 for equally sharing the load currents IL1 to IL3 in the power supply units A1 to A3 by comparing the average value of the load currents IL1 to IL3 of the power supply units A1 to A3.

In this case, each of the power supply units A1 to A3
The load current IL1 of the own power supply unit A1 is compared with the average value of the load currents IL1 to IL3 of all the power supply units A1 to A3, and the load currents IL1 to IL3 of the respective power supply units A1 to A3 are shared equally. Parallel operation. At this time, when the load current IL1 to IL3 decreases at a light load and the voltage level Va of the detection signal falls below a certain value, the transistor 44 switches from off to on and the dummy current flows through the dummy resistor 45. Power supply units A1 to A
The operation state of No. 3 continues. Therefore, even if the power supply unit A2 fails, the remaining power supply units A
Since the operating states of the power supply units A1 and A3 continue, the desired load currents IL1 and IL3 can be quickly supplied while maintaining the current balance between the power supply units A1 and A3.

Further, in the present embodiment, the resistor 22 and the amplifier 23, which are current detection circuits of the dummy load circuit 21, use the current detection circuit 41 for detecting the load currents IL1 to IL3 of the power supply units A1 to A3 of the own device. Used as a circuit. That is, the current detection circuit of the current sharing circuit 41 is
Since the current detection circuit is also used, the circuit configuration can be simplified.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention. For example, in the present embodiment, a transistor is used as a switch for forming a series circuit with the dummy load. However, for example, a field switch such as a MOSFET may be used. Alternatively, the current detector (the resistor 22) may be inserted and connected to the output voltage line 6 on the positive side instead of the output voltage line 7 on the negative side.

[0032]

According to a first aspect of the present invention, there is provided a power supply device comprising: a series circuit of a dummy load connected between output voltage lines and switch means; and a current detection circuit for detecting a load current flowing through the output voltage line. A switch switching circuit that turns on the switch means and causes a dummy current to flow to the dummy load when a detection level of the load current detected by the current detection circuit is equal to or less than a predetermined value. In addition, it is possible to provide a power supply device capable of stabilizing the operation under a light load or no load without lowering the efficiency.

The power supply according to claim 2 of the present invention is characterized by claim 1
In addition to the configuration described in the above, the switch switching circuit such that the detection level of the load current at which the switch means switches from on to off and the detection level of the load current at which the switch means switches from off to on are different. It is possible to prevent the switch means from being repeatedly turned on and off frequently.

According to a third aspect of the present invention, there is provided a power supply device comprising:
Or, in addition to the configuration described in 2, a plurality of power supply units including the dummy load circuit are connected in parallel to a load, and the power supply unit has a load current of its own power supply unit,
Compare with the average value of the load current of all power supply units,
It is equipped with a current sharing circuit that equally shares the load current in each power supply unit, so that even if one of a plurality of power supply units operating in parallel fails, another power supply unit can immediately respond. It becomes possible.

According to a fourth aspect of the present invention, there is provided a power supply according to the third aspect.
In addition to the configuration described in, characterized in that the current detection circuit of the dummy load circuit is a current detection circuit of the current sharing circuit that detects the load current of the power supply unit of its own,
In this case, the circuit configuration can be simplified by using both the current detection circuit of the current sharing circuit and the current detection circuit of the dummy load circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a power supply device according to an embodiment of the present invention, particularly around a dummy load circuit.

FIG. 2 is a circuit diagram showing a specific example of the dummy load circuit.

FIG. 3 is a graph showing a relationship between a voltage level Va of an output terminal of the amplifier and a load current IL.

FIG. 4 is a circuit diagram of a power supply device showing a conventional example.

FIG. 5 is a graph showing a relationship between a voltage level Va of an output terminal of an amplifier and a load current IL for each power supply unit.

[Explanation of symbols]

 A1 to A3 Power supply unit 6, 7 Output voltage line 21 Current sharing circuit 22 Resistance (current detection circuit) 23 Amplifier (current detection circuit) 41 Dummy load circuit 42 Comparator (switch switching circuit) 44 Transistor (switch means) 45 Dummy resistance (Dummy load)

Claims (4)

[Claims] 1. A series circuit of a dummy load and switch means connected between output voltage lines, a current detection circuit for detecting a load current flowing through the output voltage line, and a load current detected by the current detection circuit. A power supply device comprising: a dummy load circuit including a switch switching circuit that turns on the switch means and causes a dummy current to flow to the dummy load when the detection level becomes equal to or lower than a predetermined value. 2. The switch switching circuit according to claim 1, wherein a detection level of a load current at which the switch means switches from on to off is different from a detection level of a load current at which the switch means switches from off to on. The power supply device according to claim 1, wherein: 3. A plurality of power supply units each including the dummy load circuit are connected in parallel to a load, and the power supply unit determines a load current of its own power supply unit and an average value of load currents of all the power supply units. 3. The power supply device according to claim 1, further comprising a current sharing circuit for equally sharing a load current in each power supply unit. 4. The current detection circuit of the dummy load circuit,
The power supply device according to claim 3, wherein the power supply device is a current detection circuit of the current sharing circuit that detects a load current of a power supply unit of the own device.