JP2008289308A - Overcurrent detection circuit and electronic device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply circuit optimizing an overcurrent detection threshold in accordance with a load by switching the overcurrent detection threshold from a load-side in accordance with a structure of the load such as a type of the load or the number of loads without changing a DC power supply circuit in an overcurrent protection function of the DC power supply circuit. <P>SOLUTION: A switch element 37, a resistor R3c and a resistor R3b are arranged inside the DC power supply circuit 3. Wiring of a point B is taken to outside the DC power supply circuit 3, and it is connected to A of a load 4. Thus, voltage Vc obtained by feeding back a difference between both end potentials of the current detection resistor R1 can be varied from A of the load 4. Consequently, the overcurrent detection threshold of the DC power supply circuit 3 can be varied from the load-side. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to overcurrent detection and overcurrent protection of a DC power supply circuit.

  In general, as one of the methods for protecting the output overcurrent of a DC power supply circuit, a current detection resistor is provided at the output section, the current value is detected as a voltage value by this resistor, and this detection voltage and the power supply circuit are set in advance. A method is known in which overcurrent detection and overcurrent protection are performed by controlling or stopping a switching operation when the detected voltage exceeds the threshold voltage by comparing the detected threshold voltage. A typical example is shown in FIG. A typical example of a power supply device using this method is the DC-DC converter disclosed in Non-Patent Document 1.

  In these power supply circuits or DC-DC converters, threshold values are set and fixed in the power supply circuit or in the DC-DC converter. Therefore, the overcurrent detection value is determined by the power supply circuit or DC-DC converter regardless of the load. It is a fixed value.

  Patent Document 1 discloses an overcurrent control circuit for a power supply device that is characterized by switching control at the time of overcurrent detection. Similarly, the overcurrent detection value on the power supply device side is a fixed value.

JP-A-6-86454 C & D Technologies Inc. “DC-DC Converter Application Note AN-001-PS”

  However, when such a power supply circuit or power supply device having a fixed overcurrent detection threshold in the power supply circuit is used for an electronic device such as a computer, the electronic device such as a computer generally has a kind and number of loads such as a CPU. In order to support these multiple load configurations with a single type of power supply and hardware such as a chassis, the overcurrent detection value and output current capability of the power supply may vary depending on the load depending on the load configuration. In some cases, the overcurrent protection function cannot be optimized.

  In addition, it is conceivable to realize a variable function of the detection value using a microcomputer or the like, but since software is part of the protection function, it may be necessary to add a stronger protection function by hardware. is there.

  On the other hand, when the power supply device is optimized for each load configuration, the types of power supply devices to be prepared increase, which is disadvantageous in terms of cost and operation.

  The present invention provides a current detection resistor for detecting a DC output current at a DC output portion of a power supply circuit, an amplifier circuit for amplifying a potential difference generated when a current flows through the current detection resistor, and an output of the amplifier circuit Overvoltage protection of DC output by controlling or stopping the switching operation by the voltage dividing circuit that divides the voltage, the detection circuit that detects that the divided voltage exceeds the reference voltage, and the output of this detection circuit A circuit having a function is characterized in that the overcurrent detection value can be switched from the outside of the power supply circuit by connecting the voltage dividing circuit to the outside of the power supply circuit.

  According to the present invention, the overcurrent detection value can be transferred to the load side only by preparing a very simple connection circuit such as pull-up or pull-down connection on the load side without changing the overcurrent detection circuit of the power supply circuit or power supply device. The overcurrent detection value of the power supply circuit or the power supply device can be optimized according to the load configuration.

  Hereinafter, embodiments of the present invention will be described in detail using examples.

  FIG. 1 is a diagram of an electronic device using the DC power supply circuit according to the first embodiment of the present invention.

  In FIG. 1, reference numeral 1 denotes an electronic device including an AC / DC converter 2, a load 4, and a DC power supply circuit 3 connected to the load 4. The AC / DC converter 2 receives an AC input AC and converts it into a DC output. The DC power supply circuit 3 receives a DC output of the AC / DC converter 2, a PWM circuit 31 that performs PWM (pulse width modulation) on this input, and a rectifying / smoothing circuit 32 that rectifies and smooths the output of the PWM circuit 31. The output voltage is converted, and a direct current is supplied to the load 4 through the current detection resistor R1. The load 4 is, for example, a CPU in a computer or a mother board on which a CPU is mounted.

  The amplifier 33 detects and amplifies a potential difference between both ends of R1 generated when a direct current flows through the current detection resistor R1, and divides the output of the amplifier 33 by the voltage dividing resistor R3a and the voltage dividing resistor R3b. The divided voltage Vc and the voltage Vref of the reference voltage source 36 are input to the comparator 34. The comparator 34 compares the voltage Vc with the voltage Vref, outputs an H level when the voltage Vc becomes larger than the voltage Vref, and inputs it to the PWM / ON / OFF control circuit 35. The PWM / ON / OFF circuit 35 The PWM operation is controlled or stopped by detecting this H level input. With the above operation, output overcurrent protection of the DC power supply circuit 3 is performed.

  Here, the wiring on one side of the voltage dividing resistor R 3 b is taken out of the DC power supply circuit 3 and connected to A of the load 4. Depending on the type of load, A prepares an open-circuit shown in A (part 1), a pull-down connection shown in A (part 2), or a pull-down connection via a resistor RA shown in A (part 3). Thus, the voltage Vc can be varied from the load side according to the load. That the voltage Vc can be varied, that is, the overcurrent detection threshold of the DC power supply circuit 3 can be varied.

  That is, the overcurrent detection value of the DC power supply circuit 3 can be varied from the load side according to the load without changing the DC power supply circuit 3.

  FIG. 2 is a diagram of an electronic device using the DC power supply circuit according to the second embodiment of the present invention. The same reference numerals as those in FIG. 1 indicate the same parts.

  The difference from FIG. 1 is that the wiring on one side of the voltage dividing resistor R3b is not directly output to the outside of the DC power supply circuit 3, but is connected inside the DC power supply circuit 3 via a switch element 37 such as an FET. To do. Further, for driving the switch element 37, a resistor R3c and a resistor R3d connected from the control circuit power supply Vcc are connected to a drive terminal of a switch element such as a gate terminal, for example. Further, the middle point B of the resistors R3c and R3d is taken out of the DC power supply circuit 3 and connected to A of the load 4.

  Here, when A is A (part 1), the switch element 37 is turned ON, and when A is A (part 2), the switch element 37 is turned OFF. As a result, the voltage Vc varies.

  That is, the overcurrent detection value of the DC power supply circuit 3 can be varied from the load side according to the load without changing the DC power supply circuit 3.

  In the second embodiment, the voltage dividing resistor R3b is not directly exposed to the outside of the DC power supply circuit. Therefore, the voltage Vc is not directly affected by the wiring resistance or the impedance on the load side. As compared with the above, there is an effect that the accuracy of the overcurrent detection threshold can be stably obtained.

  FIG. 3 is a diagram of an electronic device using the DC power supply circuit according to the third embodiment of the present invention. The third embodiment is an example in which a multi-output power supply circuit is configured using the DC power supply circuit of the second embodiment. Note that the same reference numerals as those in FIG. 2 indicate the same parts, and constitute a first output power supply circuit.

  In FIG. 3, a PWM circuit 41, a rectifying / smoothing circuit 42, a current detection resistor R2, an amplifier 43, a comparator 44, and a PWM / ON / OFF control circuit 45 connected in parallel to the input of the PWM circuit 31 are sequentially The second output power supply circuit is configured with functions similar to those of 31, 32, R1, 33, 34, and 35 in FIG. The voltage dividing resistors R4a and R4b determine the overcurrent detection threshold of the second output power supply circuit. Here, R4b is connected to the inside of the DC power supply circuit 300, and therefore, the second output power supply The Vc4 of the circuit is a fixed value regardless of the load. A common reference voltage Vref is input to the non-inverting input terminals of the comparator 34 and the comparator 44. As in the second embodiment, Vc3 of the first output power supply circuit can be varied from the load side according to the load.

  In other words, in this method, Vc3 on the feedback side is changed instead of changing the reference voltage side. Therefore, in the multi-output power supply circuit, the reference voltage source is shared, but only to a specific output power supply circuit side. Thus, the overcurrent detection threshold can be varied from the load side according to the load.

  The technology according to the present invention can be applied to any power supply circuit or power supply device having a DC output function, such as a DC-DC converter, an on-board power supply circuit, an on-board power supply module, an AC-DC converter, and a front-end power supply unit.

It is a block diagram of the electronic device by Example 1 of this invention. It is a block diagram of the electronic device by Example 2 of this invention. It is a block diagram of the electronic device by Example 3 of this invention. It is a figure of the typical example of the electronic apparatus using the conventional overcurrent detection circuit.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electronic device, 2 ... AC-DC converter, 3 ... DC power supply circuit, 4 ... Load, 31 ... PWM circuit, 32 ... Rectification smoothing circuit, 33 ... Amplifier, 34 ... Comparator, 35 ... PWM ON / OFF control Circuit: 36: Reference voltage source 37: Switch element 41: PWM circuit 42: Rectification smoothing circuit 43: Amplifier 44: Comparator 45: PWM ON / OFF control circuit 300: DC power supply circuit R1 A current detection resistor, R2 ... a current detection resistor, R3a ... a resistor, R3b ... a resistor, R4a ... a resistor, R4b ... a resistor, RA ... a resistor.

Claims (3)

  In a DC power supply circuit, a current detection resistor for detecting a DC output current, an amplifier circuit for amplifying a potential difference generated by current flowing through the current detection resistor, and a voltage dividing circuit for dividing the output voltage of the amplifier circuit In a circuit having a detection circuit that detects that the divided voltage exceeds the reference voltage, and a DC output overcurrent protection function by controlling or stopping the switching operation by the output of the detection circuit, A DC power supply circuit comprising a function capable of switching an overcurrent detection value from outside the power supply circuit by connecting the voltage dividing circuit to the outside of the power supply circuit.   A power supply apparatus using the DC power supply circuit according to claim 1.   An electronic apparatus using the DC power supply circuit according to claim 1.

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