JP2006180603A - Circuit for correcting voltage drop by line drop - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit and a method for correcting the voltage drop by line drop, which prevent the voltage drop at the end of a load due to the occurrence of the voltage drop by the impedance of load wiring, etc. <P>SOLUTION: In these circuit and method for correcting the line drop, a correction signal by the change of impedance based on the change of a load current is generated by a current detecting resistor provided in one output line on either a positive side or a negative side, and external input voltage is switched, based on the comparative difference from the reference voltage set with a reference voltage setter, and the parameter of current change is added to voltage correction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a line drop voltage drop correction circuit that corrects voltage fluctuation caused by line drop of an output voltage.

  In general, in a DC power supply circuit, an output voltage is controlled to be constant by a voltage detection circuit and a control circuit. Normally, voltage detection is performed at the output terminal of the power supply circuit using voltage dividing resistors R1 and R2 as shown in FIG. 2, but a voltage drop occurs due to impedances L1 and L2 of the load wiring and the like from the output terminal. The voltage drops at the load end.

  Here, the load impedances L1 and L2 are mainly the resistance component of the wiring pattern of the main board, the contact resistance component of the connector, and the like. As illustrated in FIG. 3, this phenomenon becomes more conspicuous as the output voltage is lower and the output current is larger.

Therefore, the present invention detects fluctuations in the load voltage and corrects the fluctuations in the load voltage according to the value of the load current, thereby stabilizing the DC voltage as small as possible with the fluctuations in the load current. It constitutes a power source. As a prior art document of such a line drop supplementary circuit, there is Patent Document 1, and as a technique for changing the reference voltage, there is Patent Document 2 shown in FIG.
Japanese Patent Laid-Open No. 2001-119938 Japanese Utility Model Publication No. 5-23214

  Here, both Patent Document 2 and the present application belong to a similar technical field in that the potential difference generated in the dividing resistor is amplified and fed back to the output voltage detection circuit. Yes.

  The method of using the resistance-divided voltage for control is based on the premise that a stable current flows through these resistors. The reason is that a circuit that generates a reference voltage generally has a high internal impedance and cannot pass a large current. Therefore, there is always a stable potential difference between the two points to which these divided resistors are connected, and it is desirable that this potential difference is sufficiently large with respect to the line drop.

Here, the relationship between the output voltage V ₀ and the reference voltages V _ref and GND in Patent Document 2 shown in FIG. 4 is as shown in FIG. 5, and is between the reference voltage V _ref and the output negative line (GND). A split resistor is inserted in

A power supply circuit in which line drop is regarded as a problem is generally a low voltage circuit such as 1.8V or 1.2V. Therefore, as shown in FIG. 5, the potential difference between V _ref and V ₀ is small and may be equal in some cases. Even in this method, the detection resistor R can be inserted into the V ₀ line. However, as described above, a dividing resistor is inserted between two points having a small potential difference, that is, between V _{0 and} V _ref. It may be difficult to detect accurately.

In general, in the secondary side circuit, the output voltage is the highest potential, and it is necessary to create a power source with another winding or the like in order to create V _ref having a potential higher than V ₀ . For this reason, in the method of Patent Document 2, when the line detection resistor R on the V ₀ side is inserted, it may not be suitable for practical detection due to the above relationship between V ₀ and V _ref .

Furthermore, in the configuration of Patent Document 2, when an input / output minus line such as a non-insulated power source is used as the same potential, a detection resistor cannot be inserted on the minus side. Then, if it is sufficient to put the detection resistor on the plus side, when the difference between V ₀ and V _ref is small as described above, detection becomes difficult due to component errors and the like.

  According to the voltage drop correction circuit by the line drop according to the present invention, the supply current is corrected by the circuit in which the impedance changes based on the change in the load current value of either the positive side or the negative side output line. In this configuration, the voltage at the supply end is kept constant.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. A DC voltage from an appropriate external power supply is applied to the input terminal 1 and input to the switching element 2 such as a MOSFET. A smoothing capacitor C1 is connected between the input terminal 1 and the switching element 2 between the ground potential. A smoothing capacitor C2 is further provided on an output line connecting the choke coil 3 and a current detection resistor R13 described later. The switching element 2 is ON / OFF controlled by the driver 4 and outputs the input DC current by controlling the pulse width. The current flowing from the switching element 2 when ON and the current flowing by the commutation diode 20 when OFF are choked. Combined with the action of the coil 3 and the smoothing capacitor C1, it is rectified and smoothed and output to the output terminal 7 side. Between the choke coil 3 and the output terminal 7, a current detection resistor R13 is inserted in series. A load 19 is connected between the positive output terminal 7 and the negative output terminal 8, and the line resistance from the positive output terminal 7 and the negative output terminal 8 to the load 19 is set to VRL. , VRL ′.

  Further, voltage dividing resistors R11 and R12 connected in series are connected between the current detection resistor R13 and the positive output terminal 7 between the line and the ground. A resistor R8 for outputting a voltage dividing point voltage is provided from an intermediate connection point between the voltage dividing resistors R11 and R12.

  Further, voltage dividing resistors R9 and R10 connected in series are also connected between the output line and the ground on the smoothing capacitor C2 side of the current detection resistor R13. A resistor R6 is also provided to extract a voltage dividing point voltage from an intermediate connection point between these voltage dividing resistors R9 and R10. Here, the resistor R10 is composed of a variable resistor.

  The voltage dividing point voltages extracted by the resistors R6 and R8 are input to the subtraction input and the addition input of the correction amplifier 6, respectively. A feedback resistor R5 for setting an amplification factor is connected between the subtraction input output of the correction amplifier 6 and a voltage dividing resistor R7 is grounded from the addition input.

The output of the correction amplifier 6 is input to the subtraction input of another correction amplifier 5 via the resistor R4, and a predetermined reference voltage V _ref is applied to the addition input of the correction amplifier 5. Furthermore, the output side of the choke coil 3 and the subtraction input of the correction amplifier 5 are connected by a resistor R3.

The output of the correction amplifier 5 is input to the driver 4 that drives the switching element 2 to control the conductivity of the switching element 2. In such a configuration, the voltage dividing resistors R11, R12 and R9, R10 provided at both ends of the current detection resistor R13, the resistors R6, R8 for extracting these voltage dividing point voltages, and the correction amplifier 6 and the voltage dividing resistors thereof R7, feedback resistor R5, and output resistor R4 become a circuit in which the impedance changes in accordance with the change in the load current from the output terminals 7 and 8 (R '), and the positive and negative input values of the correction amplifier 5 match. The correction input V corresponding to the change in impedance with respect to the reference voltage V _ref which is one input of the correction amplifier 5 that feeds back the output to 0 and outputs the control output 5 to the driver 4 that drives the switching element 2. _ref '.

  R10 is a variable resistor, which can adjust the voltage drop adjustment range of the impedance that changes depending on the load current indicated by R '.

  Therefore, the line drop VRL with different load impedances depending on the final product and the voltage correction coefficient for the output current can be adjusted by the adjustment resistor R10.

As for the installation position of R13, it is sufficient to divide the voltage between V _{0 and} GND as described with reference to FIG. 6, and it can be provided between the ground terminals of R10 and R12 which are the negative output lines. There is a degree of freedom in circuit design.

Further, in this embodiment, as shown in FIG. 6, since a resistor is inserted between V _{0 and} GND and a reference voltage is not used for current detection, a sufficiently large voltage difference with respect to the line drop is always secured in the dividing resistor. it can. The detection resistor R can be inserted on either the positive or negative side of the output line.

  In this embodiment, the non-insulated chopper method is used. However, even an insulated circuit using a transformer can be corrected by the same principle, and the current detection is not limited to using a resistor. A configuration for detecting a voltage drop due to the on-resistance of the MOSFET can be used.

  Furthermore, in this embodiment, since the amplification factor of the differential amplifier can be determined only by the feedback resistor, the response to a sudden load change is excellent as compared with the configuration of Patent Document 2.

  The embodiment of the voltage drop correction circuit by line drop, which is an embodiment of the present invention, is as described above. The output current applied to the load is detected, and the output voltage is corrected by the current value to correct the load end. The voltage can be kept constant, and the detection resistor can be grounded on either the positive side or the negative side of the output line, regardless of whether it is an isolated or non-isolated power supply. The voltage response to the output current can be corrected according to the load impedance that varies depending on the product.

  Further, since the amplification factor of the amplifier is defined only by the negative feedback resistor, the fluctuation of the output voltage is high in response to the fluctuation of the load current shown in FIG. Compared to the configuration of the conventional example shown in FIG. 4, it is less affected by load current fluctuations.

The figure which shows the Example of the voltage drop correction circuit by a line drop of the Example of this invention. The block diagram of the prior art example which used the voltage dividing resistor for the output terminal. The graph which shows the relationship between output current, load end voltage, and line drop. The block diagram of the line drop correction circuit of a prior art. The figure which shows the relationship between the insertion position of the division resistance in the prior art example of FIG. The figure which shows the relationship between the voltage dividing resistor insertion position and potential difference of the Example of this invention. The wave form diagram of the voltage response with respect to load current fluctuation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Input terminal 2 Switching element 3 Choke coil 4 Driver 5 Correction amplifier 6 Correction amplifier 7, 8 Output terminal 9, 10 Line drop resistance 11 Load 12 Smoothing capacitor R3, R4, R5, R6, R7, R8 Resistance R9, R10 , R11, R12 Voltage _dividing resistor V _ref reference voltage

Claims (4)

In the voltage drop correction circuit by line drop that detects the fluctuation of DC output voltage and feeds back to the voltage control circuit to stabilize the output voltage,
A current detection resistor inserted in series in either the positive side or negative side output line to detect the output current in the output line;
Two sets of voltage dividing resistors each including two resistors provided between both ends of the current detection resistor and either the negative side or the positive side output line, and connected in series,
A differential amplifier having a negative feedback resistor, wherein each of the divided voltages from the voltage dividing points of the two voltage dividing resistors is inputted to perform a difference calculation and generate a correction signal;
A voltage drop correction circuit for controlling the voltage control circuit by performing a difference operation with a predetermined reference voltage supplied to the voltage control circuit using a correction signal output from the difference amplifier circuit. Voltage drop correction by line drop that detects fluctuation of DC output voltage with voltage dividing resistor and feeds back error signal of this detected value and reference value to control circuit via error amplifier to stabilize output voltage In the circuit
A correction current generator that is inserted in series in either the positive or negative output line and includes a current detection resistor that detects the output current in the output line, and the impedance changes according to the output current detection value. A voltage drop correction circuit using a line drop that generates a correction current and feeds back to the control circuit to stabilize the output voltage.   An input terminal to which a predetermined external DC voltage is applied, a switching element connected to the input terminal, a choke coil connected to the switching element, and either the positive side or the negative side downstream from the choke coil A current detection resistor connected to the output line, a positive or negative output terminal connected to the current detection resistor, and a connection between the input terminal and the switching element and the ground. A differential amplifier having two sets of voltage dividing resistors and a negative feedback resistor provided between the smoothing capacitor and the negative or positive output line from both ends of the current detection resistor. The difference amplifier that inputs two voltage detection values from the voltage dividing points of the two sets of voltage dividing resistors and outputs a difference comparison value, and the difference comparison value of the difference amplifier are input from the reference setter. Reference voltage and Input and difference comparison, line drop voltage drop correction circuit for controlling the power driver. The DC voltage supplied to the input terminal is chopped by the switching element, smoothed by the smoothing capacitor, supplied from the output terminal to the load, and the voltage dividing resistor connected to either the positive or negative output terminal The detected voltage fluctuation value is compared with the output current value detected by the current detection resistor inserted between the smoothing capacitor and the output terminal to generate a correction signal and control the driver of the switching element. In the control method of the voltage drop correction circuit by the line drop for correcting the output voltage,
The output current of either the positive side or the negative side of the output line is detected, and a compensation value based on the impedance fluctuation of the voltage dividing circuit due to the detected current is generated by a differential amplifier that defines an amplification factor with a negative feedback resistor, A control method of a voltage drop correction circuit by line drop, wherein the driver is controlled by calculating a difference with a predetermined reference voltage with the generated compensation value.

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