JP2000078838A - Power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform stable current detection without causing delay of temperature compensation, without providing a power unit with an exclusive current detector. SOLUTION: A current detector 11 utilizes the inner resistor of a choke coil 5 and a conductor resistor RCU existing in an output voltage line 22 to connect this choke coil 5 as current detectors. Moreover, the current detector 11 is equipped with compensating resistors R1 and R3 for compensating the temperature property of the conductor resistor RCU. Heat is conducted quickly to the compensating resistors R1 and R3 thermally coupled with a transformer 1 and the coil 5, and the fluctuation caused by the temperature of the conductor resistor RCU can be compensated without delay.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for rectifying and smoothing a voltage induced in a secondary winding of a transformer by a rectifying and smoothing circuit having a choke coil and supplying a predetermined DC output voltage to a load. More particularly, the present invention relates to a power supply device loaded with a current detection circuit that outputs a current detection signal proportional to a load current.

[0002]

Generally, in this type of power supply device, an overcurrent protection circuit is provided to suppress an excessive current of the transformer in an overload state. When a plurality of power supply devices are operated in parallel, it is desired to incorporate a current sharing function for equalizing the load current from each power supply device in terms of reliability. For such an overcurrent protection circuit and a current sharing function, a current detection circuit for monitoring a load current flowing on the secondary side of the transformer is indispensable.

FIG. 4 shows a circuit example of a switching power supply device provided with a conventional current detection circuit. In the figure, reference numeral 1 denotes a transformer for insulating a primary side from a secondary side, and 2 denotes a switching FET which is a switching element forming a series circuit with a primary winding 1A of the transformer.
2, the DC input voltage Vi is intermittently applied to the primary winding 1A of the transformer 1. A well-known rectifying and smoothing circuit 7 composed of diodes 3 and 4, a choke coil 5, and a smoothing capacitor 6 is connected to the secondary winding 1 </ b> B side of the transformer 1. A configuration in which a predetermined DC output voltage Vo is supplied to a load RL connected between output terminals + V and -V by rectifying and smoothing the voltage induced in the secondary winding 1B of the transformer 1 by the rectifying and smoothing circuit 7. It has become. In addition, 8 is a DC output voltage V at no load.
This is a dummy resistor that suppresses the rise of o. Although not shown here, an output voltage detection circuit that monitors the DC output voltage Vo as a feedback loop for stabilizing the DC output voltage Vo, and a detection result from the output voltage detection circuit. A pulse width control circuit for variably controlling the pulse conduction width of the switching FET 2 is provided.

One of the output voltage lines from the secondary winding 1B of the transformer 1 to the load RL is connected to the choke coil 5
And a current detection resistor RS having no temperature characteristic, such as a manganin wire, is connected to the other end of the output voltage line. A current detection circuit 11 is connected between both ends of the current detection resistor RS, and a voltage drop of the current detection resistor RS is detected by the current detection circuit 11 to output a current detection signal proportional to the load current Io. It is supposed to. In this current detection circuit 11,
A filter circuit including a filter resistor 12 and a smoothing capacitor C1 is connected between one end of the current detection resistor RS and the ground line. This filter circuit includes a current detection resistor RS
Is connected as a filter resistor 13 and a smoothing capacitor C2 between the other end and the ground line, and removes a pulsating component generated in the output voltage line.

However, in the above configuration, since the current detection resistor RS, which is a current detector, is connected to the output voltage line, the power consumption by this resistor increases the loss of the power supply device itself and lowers the power efficiency. . In addition, since the dedicated current detection resistor RS is used, the number of components increases, which hinders cost reduction, and is against the space saving of the power supply device.

[0006] On the other hand, Japanese Patent No. 275 proposed by the applicant has been proposed.
Japanese Patent Publication No. 1962 discloses a current detection circuit that detects a voltage drop generated by a secondary winding resistance of a transformer. In this case, although there is an advantage that the dedicated current detection resistor RS is not required, it is necessary to compensate the temperature of the secondary winding resistance of the transformer that generates heat by some method. However, simply incorporating a temperature compensation element such as a thermistor causes a compensation delay between the rapidly changing resistance value of the secondary winding of the transformer and the resistance value of the temperature compensation element, so that stable current detection cannot be performed. Raises concerns.

An object of the present invention is to solve the above problems at once, and an object of the present invention is to provide a stable current detection without delay of temperature compensation without providing a dedicated current detector. A power supply device is provided.

[0008]

According to a first aspect of the present invention, there is provided a power supply device comprising: a rectifying and smoothing circuit for rectifying and smoothing a voltage induced in a secondary winding of a transformer; While supplying a predetermined DC output voltage to the load,
The rectifying and smoothing circuit detects a voltage drop generated by an internal resistance of the choke coil and a conductor resistance of the output voltage line connecting the choke coil in a power supply device having a choke coil connected to an output voltage line. And a current detection circuit for outputting a current detection signal proportional to the load current, the current detection circuit being thermally coupled to the transformer or the choke coil to compensate for a temperature characteristic of the conductor resistance. It has a compensating element.

According to the first aspect of the present invention, the internal resistance of the choke coil and the conductor resistance present in the output voltage line connecting the choke coil are used as a current detector, so that the internal resistance of the choke coil and Since the load current is monitored by the voltage drop generated in the conductor resistance of the output voltage line, a dedicated current detector is not required. Therefore, the number of parts can be reduced, the cost can be reduced, and the space of the power supply device can be reduced.

Further, the transformer and the choke coil have a large heat capacity in the power supply device and generate heat quickly when the power supply device operates. Therefore, heat is quickly transmitted to the compensation resistor thermally coupled to the transformer and the choke coil, and it becomes possible to compensate for the fluctuation of the conductor resistance of the output voltage line due to the temperature without delay. Therefore, the current detection circuit can compensate for fluctuations in the resistance value of the conductor resistance due to temperature, and perform stable current detection.

According to a second aspect of the present invention, in order to achieve the above object, a voltage induced in a secondary winding of a transformer is rectified and smoothed by a rectifying and smoothing circuit, and a predetermined DC output is applied to a load. In the power supply device having a choke coil connected to an output voltage line while supplying a voltage, the rectifying and smoothing circuit includes an internal resistance of the choke coil and a conductor resistance of the output voltage line connecting the choke coil. A current detection circuit for detecting a generated voltage drop and outputting a current detection signal proportional to a load current, the current detection circuit being thermally coupled to a bus bar forming the output voltage line, It has a temperature compensating element for compensating the temperature characteristic of the resistor.

According to the configuration of the second aspect, the internal resistance of the choke coil and the conductor resistance existing in the output voltage line connecting the choke coil are used as a current detector, so that the internal resistance of the choke coil and Since the load current is monitored by the voltage drop generated in the conductor resistance of the output voltage line, a dedicated current detector is not required. Therefore, the number of parts can be reduced, the cost can be reduced, and the space of the power supply device can be reduced.

When a current flows through the bus bar, the bus bar generates heat due to the conductor resistance, and the heat is quickly transmitted to the compensation resistor thermally coupled to the bus bar. It is possible to compensate without delay. Therefore, the current detection circuit can compensate for fluctuations in the resistance value of the conductor resistance due to temperature, and perform stable current detection. In the case of a power supply device that outputs a relatively large current, a bus bar is often used as a conductor of the output voltage line. Therefore, particularly in a power supply device for a large current, an existing bus bar can be used without taking any special measures. , Thermal coupling can be easily realized.

[0014]

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 FIG. 4 of the conventional example are denoted by the same reference numerals, and the description of the common parts will be omitted because they are duplicated.

The power supply device of this embodiment is a forward type switching power supply device as in the prior art, but the choke coil 5 constituting the rectifying / smoothing circuit 7 is not one output voltage line 21 but the other output voltage line. 22 is inserted and connected. In order to detect a voltage drop between the conductor resistance RCU existing in the output voltage line 22 and the internal resistance (not shown) of the choke coil 5, a current is detected between a series circuit of the choke coil 5 and the conductor resistance RCU. Circuit 11 is connected. The choke coil 5 may be connected to one output voltage line 21 as in the conventional example, or the rectifying and smoothing circuit 7 may be used.
May be a full-wave rectification system, and the choke coils 5 may be connected to both output voltage lines 21 and 22, respectively. In particular, if the current detection circuit 11 detects the voltage drop between the internal resistance of the choke coil 5 connected to both output voltage lines 21 and 22 and the conductor resistance RCU of each output voltage line 21 and 22, There is an advantage that an error in current detection is reduced.

The configuration of the current detection circuit 11 will be described.
Reference numerals 1 and R3 denote compensation resistors for compensating that the resistance value of the conductor resistor RCU changes due to a temperature rise during energization. One end of the compensation resistor R1 is connected to the connection point between the choke coil 5 and the diode 4, and the resistor R2
And grounded capacitor C1 and T-type filter circuit
23. The other compensating resistor R3 has one end connected to the output terminal -V whose ground is grounded.
4 and the grounded capacitor C2 constitute a T-type filter circuit 24. The pair of filter circuits 23 and 24 is configured to remove a pulsating component generated in the output voltage line 22. Note that the compensation resistor R3
Is connected to the output terminal -V because the conductor resistance RCU
This is to make it possible to detect as large a voltage drop as possible. The compensation resistors R1 and R3 correspond to a temperature compensating element such as a thermistor for compensating the temperature characteristic of the conductor resistor RCU. However, by using a part of the filter circuits 23 and 24, the circuit configuration is simplified. I have.

Reference numerals 31 and 32 denote differential amplifiers connected to the output sides of the filter circuits 23 and 24, respectively. One differential amplifier 31
Is an NPN transistor having one end of the resistor R2 and a base connected to the output terminal of the differential amplifier 31.
33 emitters are connected. The inverting input terminal of the differential amplifier 32 is connected to one end of the resistor R4 and the emitter of an NPN transistor 34 whose base is connected to the output terminal of the differential amplifier 32. And these differential amplifiers 31,
All 32 non-inverting input terminals are grounded. Also, the transistor 3 on the output side of each differential amplifier 31, 32
A pair of PNP transistors 35 and 34 having bases connected to each other and an emitter connected to the operating voltage VS line are connected to each other.
Connected to 36. Specifically, the collector of the transistor 33 is connected to the collector of the transistor 35, and the collector of the transistor 34 is connected to the base and the collector of the transistor 36. And these differential amplifiers 3
1 and 32 and transistors 33 to 36, filter circuit 2
3 or conductor resistance RCU output from filter circuit 24
From the detection currents + In and -In, which depend on the voltage drop between the voltage and the internal resistance of the choke coil 5, the AC component is cut to extract only the DC component and send it to the current sense amplifier 41 at the subsequent stage.

A current detection signal VCS proportional to the load current Io
The current sense amplifier 41 that outputs 0 is connected to the collector of the transistor 33 and the transistor
A connection point with the collector of 35 is connected, and a capacitor 42 and a variable resistor RCS for changing the amplification factor are connected between the inverting input terminal and the output terminal. In addition, the current sense amplifier 41
A reference power supply 43 having a predetermined voltage value Vref is connected between the non-inverting input terminal and the ground line.

FIG. 2 shows a partial structure of the power supply device in this embodiment. In the figure, reference numeral 51 denotes a metal core substrate on which electronic components of the power supply device are mounted, and a conductive pattern 54 is formed on a surface of a metal substrate 52 made of aluminum or the like and having excellent thermal conductivity via an insulating layer 53. It is composed. The compensation resistors R1 and R3 are soldered and fixed at predetermined positions of the conductive pattern 54 (soldering portions are not shown). Near the compensation resistors R1 and R3, heat generation is most remarkable as a power supply device. The transformer 1 and the choke coil 5 are fixed by soldering. When the transformer 1 and the choke coil 5 generate heat, the metal core substrate
The metal substrate 52 constituting 51 conducts heat, and the resistance values of the compensation resistors R1 and R3 in the vicinity change quickly. That is,
The compensation resistors R1 and R3 are thermally coupled to the transformer 1 and the choke coil 5 by being mounted on the common metal core substrate 51.

Here, another modified example relating to "thermal coupling" is shown in FIG. Reference numeral 61 denotes a metal bus bar constituting the DC voltage line 21 or the DC voltage line 22. Using an adhesive 62 having good thermal conductivity on this bus bar 61,
The compensation resistors R1 and R3 are bonded. Since the bus bar 61 has the conductor resistance RCU as described above, it generates heat when a current flows through the bus bar 61, and the resistance values of the compensation resistors R1 and R3 change quickly due to the heat conduction of the bus bar 61 and the adhesive 62. In this case, compensation resistors R1 and R3 are thermally coupled to bus bars 61 forming output voltage lines 21 and 22.

Next, the operation of the above configuration will be described. By switching the switching FET 2, the DC input voltage Vi is intermittently applied to the primary winding 1A of the transformer 1, and a voltage is induced in the secondary winding 1B. This voltage is rectified and smoothed by the rectifying and smoothing circuit 7, and a predetermined DC output voltage Vo is supplied to the load RL connected between the output terminals + V and -V. The above operation is the same as the conventional example.

The current detection circuit 11 detects a voltage drop between the internal resistance of the choke coil 5 and the conductor resistance RCU of the output voltage line 22, and monitors the load current Io flowing through the load RL. Specifically, when the switching FET 2 is on, the diode 3 conducts while the diode 4 becomes non-conductive, and energy is stored in the choke coil 5. The voltage at the connection point between 5 and the diode 4 decreases. Therefore, the potential of the inverting input terminal of the differential amplifier 31 is
It becomes lower than the potential of the 32 inverting input terminal. Conversely, when the switching FET 2 is off, the diode 3 is turned off, whereas the diode 4 is turned on and the energy stored in the choke coil 5 is released to the load RL. Choke coil 5 than -V
And the voltage at the connection point of the diode 4 becomes higher. Therefore, the potential of the inverting input terminal of the differential amplifier 31 is
It becomes higher than the potential of the 32 inverting input terminal. Differential amplifier 3
1, 32 and transistors 33 to 36 are switching FEs.
A filter circuit 23 generated with the switching of T2,
The AC voltage generated between both ends of the choke coil 5 is cut from the input side voltage of 24, and only the voltage drop between the conductor resistance RCU and the internal resistance of the choke coil 5 is taken out. Supply to input terminal. The current sense amplifier 41 amplifies the signal of this voltage drop with a predetermined amplification factor, and outputs a current detection signal (V
CS0) is output to the outside of the current detection circuit 11. This output result is used, for example, for overcurrent protection of the load RL.

On the other hand, as the switching FET 2 performs the switching operation, a current flows through the conductor resistance RCU to generate heat, and the resistance value changes with the temperature rise. In this case, in the configuration shown in FIG. 2, the transformer 1 and the choke coil 5 also generate heat during the operation of the power supply device, but this heat is transmitted to the metal substrate 52 of the metal core substrate 51, and the compensation resistors R1, R3
, The resistance values of the compensation resistors R1 and R3 change quickly so as to compensate for fluctuations in the resistance value of the conductor resistor RCU. Further, in the configuration of FIG. 3, when a current flows through the bus bar 61 during operation of the power supply device, the bus bar 61 is controlled by the conductor resistance RCU.
However, the heat is transmitted to the bus bar 61 and the adhesive 62 and reaches the compensation resistors R1 and R3.
1, the resistance value of R3 changes quickly so as to compensate for the fluctuation of the resistance value of the conductor resistance RCU. Therefore, in any case, the current detection circuit 11 can compensate for the fluctuation of the resistance value of the conductor resistance RCU due to the temperature, and perform stable current detection. In particular, it is necessary to thermally couple the transformer 1, the choke coil 5 or the bus bar 61, which generates heat quickly during operation of the power supply device and has a large heat capacity in the power supply device, to the compensation resistors R1 and R3. Even if the compensation resistors R1 and R3 are mounted on the circuit board,
Since heat is not quickly transmitted to the compensation resistors R1 and R3, the change in the resistance values of the compensation resistors R1 and R3 does not follow the change in the resistance value of the conductor resistor RCU.

Here, an example of the applied circuit constants in FIG. 1 is shown. Compensation resistors R1 and R3 are 1 kΩ, resistors R2 and R4
Is 100Ω, the variable resistance RCS is 150kΩ, the conductor resistance RCU of the output voltage line 22 is 0.2mΩ, and the voltage value Vref of the reference power supply 43 is 1.
When the load current is 100 A under the condition of 265 V, the voltage ΔVCSO generated at the collectors of the transistors 33 and 35 is obtained by the following equation (1).

[0025]

(Equation 1)

Then, the voltage VCSO generated at the output terminal of the current sense amplifier 41 is obtained by the following equation (2).

[0027]

(Equation 2)

As described above, according to the present embodiment, the voltage induced in the secondary winding 1B of the transformer 1 is rectified and smoothed by the rectifying and smoothing circuit 7, and the predetermined DC output voltage Vo is applied to the load RL.
And a rectifying / smoothing circuit 7 for controlling the internal resistance of the choke coil 5 and the conductor resistance of the output voltage line 22 connecting the choke coil 5 in the power supply device having the choke coil 5 connected to the output voltage line 22. A current detection circuit 11 for detecting a voltage drop generated by the RCU and outputting a current detection signal VCSO proportional to the load current Io, which is thermally coupled to the transformer 1 or the choke coil 5 In addition, compensation resistors R1 and R3, which are temperature compensation elements for compensating the temperature characteristics of the conductor resistor RCU, are provided.

With such a configuration, the choke coil 5
By using the internal resistance of the choke coil 5 and the conductor resistance RCU existing in the output voltage line 22 connecting the choke coil 5 as a current detector, the internal resistance of the choke coil 5 and the conductor resistance RCU of the output voltage line 22 are generated. Since the load current Io is monitored by the voltage drop, a dedicated current detector becomes unnecessary. Therefore, the number of parts can be reduced, the cost can be reduced, and the space of the power supply device can be reduced.

The transformer 1 and the choke coil 5 are
It has a large heat capacity in the power supply device, and generates heat quickly when the power supply device operates. Therefore, heat is quickly transmitted to the compensation resistors R1 and R3 thermally coupled to the transformer 1 and the choke coil 5, and the conductor resistance R of the output voltage line 22 is increased.
Fluctuations due to the temperature of the CU can be compensated without delay. Therefore, the current detection circuit 11 can compensate for fluctuations in the resistance value of the conductor resistance RCU due to temperature, and perform stable current detection. Note that the compensation resistors R1 and R3 may be thermally coupled to either the transformer 1 or the choke coil 5.

Further, as an effect on the embodiment, in this embodiment, the thermal coupling between the compensation resistors R1 and R3 and the transformer 1 or the choke coil 5 is common to the metal core substrate 51.
This is achieved by disposing the compensation resistors R1 and R3 and the transformer 1 or the choke coil 5 close to each other. Therefore, in a power supply device in which electronic components are mounted on the metal core substrate 51 and assembled, thermal coupling can be easily realized without taking special measures.

As shown in FIG. 3, the compensation resistors R1,
R3 may be thermally coupled to bus bar 61 forming output voltage lines 21 and 22. Also in this case, when a current flows through the bus bar 61, the bus resistance is determined by the conductor resistance RCU.
61 generates heat, and the compensation resistor R is thermally coupled to the bus bar 61.
Since heat is quickly transmitted to R1 and R3, the output voltage line
It is possible to compensate for the fluctuation of the 22 conductor resistors RCU due to temperature without delay. Therefore, the current detection circuit 11 can compensate for fluctuations in the resistance value of the conductor resistance RCU due to temperature, and perform stable current detection.

In the case of a power supply device that outputs a relatively large current (for example, 100 A), the bus bar 61 is often used as a conductor of the output voltage lines 21 and 22. The thermal coupling can be easily realized using the existing bus bar 61 without taking any special measures.

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, “thermal coupling” is not limited to the structure shown in the present embodiment, but the point is that the temperature compensation element can sufficiently respond to a change in the resistance value of the conductor resistance due to the temperature. Just do it. Although the switching power supply device is described in the embodiments, the present invention can be applied to any power supply device including a current detection circuit.

[0035]

According to the power supply device of the present invention, a voltage induced in a secondary winding of a transformer is rectified and smoothed by a rectifying and smoothing circuit to supply a predetermined DC output voltage to a load. The rectifying and smoothing circuit detects a voltage drop generated by an internal resistance of the choke coil and a conductor resistance of the output voltage line connecting the choke coil in a power supply device having a choke coil connected to an output voltage line. And a current detection circuit that outputs a current detection signal proportional to the load current.
A temperature compensation element that thermally couples with the transformer or the choke coil and compensates for the temperature characteristic of the conductor resistance is provided, and a temperature compensation delay occurs without providing a dedicated current detector. And a power supply device capable of performing stable current detection.

According to a second aspect of the present invention, in the power supply device, a voltage induced in a secondary winding of the transformer is rectified and smoothed by a rectifying and smoothing circuit to supply a predetermined DC output voltage to a load. The rectifying and smoothing circuit detects a voltage drop generated by an internal resistance of the choke coil and a conductor resistance of the output voltage line connecting the choke coil in a power supply device having a choke coil connected to an output voltage line. And a current detection circuit that outputs a current detection signal proportional to the load current, and the current detection circuit is thermally coupled to a bus bar that forms the output voltage line to compensate for the temperature characteristics of the conductor resistance. Temperature compensation element, and a stable current detection can be performed without delay of temperature compensation without providing a dedicated current detector. It is possible to provide a power supply. Also,
In this case, in particular, in a power supply device for a large current, thermal coupling can be easily realized by using an existing bus bar without taking special measures.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a power supply device showing one embodiment of the present invention.

FIG. 2 is a sectional view showing a part of the power supply device.

FIG. 3 is a perspective view of a main part showing a modification of the above.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transformer 5 Choke coil 7 Rectifying smoothing circuit 11 Current detection circuit 21, 22 Output voltage line 61 Bus bar RL Load R1, R3 Compensation resistance (temperature compensation element)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H730 AA14 BB23 DD04 EE02 EE08 EE10 EE51 FD31 FD38 XX03 XX15 XX23 XX35 ZZ07 ZZ11

Claims (2)

[Claims] 1. A rectifying and smoothing circuit rectifies and smoothes a voltage induced in a secondary winding of a transformer to supply a predetermined DC output voltage to a load, and the rectifying and smoothing circuit is connected to an output voltage line. In a power supply device having a choke coil, a voltage drop caused by an internal resistance of the choke coil and a conductor resistance of the output voltage line connecting the choke coil is detected, and a current detection signal proportional to a load current is detected. A power supply device, comprising: a current detection circuit that outputs a current; and the current detection circuit includes a temperature compensation element that is thermally coupled to the transformer or the choke coil to compensate for a temperature characteristic of the conductor resistance. . 2. A rectifying and smoothing circuit rectifies and smoothes a voltage induced in a secondary winding of a transformer to supply a predetermined DC output voltage to a load, and the rectifying and smoothing circuit is connected to an output voltage line. In a power supply device having a choke coil, a voltage drop caused by an internal resistance of the choke coil and a conductor resistance of the output voltage line connecting the choke coil is detected, and a current detection signal proportional to a load current is detected. An output current detection circuit, wherein the current detection circuit includes a temperature compensation element thermally coupled to a bus bar constituting the output voltage line to compensate for a temperature characteristic of the conductor resistance. Power supply.