JPH01318582A - Light load detector and dc fan abnormality detector - Google Patents

Abstract

PURPOSE:To obtain a light load detector having low power loss by connecting a diode in parallel with a current detection resistor. CONSTITUTION:A parallel circuit of a current detection resistor RS and a diode D is connected between a DC power source E and a load. When the load current is low, the majority of the load current flows through the current detection resistor RS. Consequently, the voltage across the current detection resistor RS produced through the current flowing through the current detection resistor RS is proportional to the load current, and the voltage is compared with a threshold voltage in order to detect a light load. When the load current exceeds a predetermined level, the load current starts to shunt to the diode D, thus maintaining the current flowing through the current detection resistor RS at a constant level. Overload can be detected by comparing the voltage across the diode D with the threshold value. At this time, power loss of the current detection resistor is low.

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD 1 The present invention relates to a device for reporting an abnormality in a relatively light load such as a DC fan, and particularly relates to an improvement for reducing power loss. 2. Description of the Related Art FIG. 5 is a circuit diagram of a conventionally known overload detection circuit. In FIG. 5, a DC power source E is a DC-DC converter, for example, a switching type. The current detection resistor Rs generates a voltage corresponding to the load current I sent from the DC power supply E to the load. The constant voltage source VTH provides a reference voltage, and uses, for example, a Zener diode. The comparator compares the voltage generated by the current detection resistor R with the threshold voltage
When it becomes larger than 1H, an alarm signal for overload is generated. This relationship is given by the following equation. R−I L =V TH (1) The power loss Ps in this case is given by the following equation. P=R−I=V■,·r,H(2)sL Basically, the circuit shown in FIG. 5 can be used as it is as a light load detection circuit. The light load detection circuit is, for example, a DC
This detects when the current is no longer consumed due to a disconnection, etc., in cases such as fans and lighting, which consume a certain amount of current or more under normal conditions.

[Problem to be solved by the invention] Figure 6 is a characteristic diagram of the circuit in Figure 5, which basically consists of (1),
This is a diagram of equation (2). Point A is the light load detection point,
Point B is the overload detection point. When the threshold voltage for light load detection is expressed as V, the following equation holds true and Tl1(A) stands. RI=V (3)s
L (A) T old) Also, the power loss Ps in the current detection resistor RS is maximum at point B (B
(A protection circuit works to prevent overcurrent from flowing beyond this point.)
, this value is given by the following equation. □H(A) L(A)・”L(B)/■L(A)
' 2 (4) = V - I Now, the threshold voltage V is set by the comparator ■11 (
8) There is a lower limit due to requirements such as offset voltage, and the power loss P is 5(B
) L(B) L(A) There is a problem that it will become very large. For example, threshold voltage V =0. IV,■L(A
)TH(A)=0.1^, R=1Ω, I=28, the power s L(B) loss is P5(B)=0. IXO, IX (210°1
) -4W. The present invention has solved these problems, and its first purpose is to provide a light load detection device with low power loss, and its second purpose is to provide a DC fan abnormality detection device using the same. It is about providing. [Means for solving the problem] 2. ) A first invention that achieves the first object includes: a current detection resistor having one end connected to a DC power supply and the other end connected to a load side; and a current detection resistor connected to an end of the current detection resistor on the DC power supply side. a reference voltage source, a first input terminal connected to the load side end of the current detection resistor, and a second input terminal connected to the common side of the base voltage source; A load detection device for a DC power supply including a comparator that compares signals input to a second input terminal and outputs an alarm signal has the following configuration. That is, a diode is provided whose anode side is connected to one end of the current detection resistor and whose cathode side is connected to the other end, and the reference voltage is set lower than the forward voltage of this diode, and the alarm signal is output from the current detection resistor. It is characterized in that it is output when the voltage appearing at is lower than the reference voltage. A second invention for achieving the second object is characterized in that a capacitor is attached to the load side of the current detection resistor and diode, and the load is a speed-controlled DC motor.

[Effect]

Each component of the present invention operates as follows. A diode inserted in parallel with the current sense resistor reduces the power dissipated in the current sense resistor at normal load currents above the reference voltage for light loads. In addition, when attaching such a light load detection device for a DC power supply to a DC fan abnormality detection device, installing a capacitor on the load side will effectively eliminate the ripple component that occurs when the current consumed by the DC fan increases or decreases. will be removed.

【Example】

The present invention will be explained below using the drawings. FIG. 1 is a configuration block diagram showing an embodiment of the first invention. In FIG. 1, parts having the same functions as those in FIG. 5 are given the same reference numerals and their explanations will be omitted. In the figure,
The diode D is connected in parallel with the current detection resistor Rs, and its anode side is on the DC power supply E side and its cathode is on the load side. Compared to the forward voltage V of this diode D, the threshold #
The L voltage VTH should be low. The comparator outputs a light load abnormality signal when the voltage appearing on the current detection resistor Rs falls below the threshold voltage 1H. The operation of the device configured in this manner will be described next. Second
The figure is a characteristic diagram of the circuit of FIG. 1. Each case will be explained below. (1) Near point A At point A, the load current corresponds to the threshold voltage VTH for light load detection, and is, for example, 0. It has reached IV purity. This voltage acts on the current detection resistor Rs and the diode D, and the forward voltage VF of the diode D is usually 0.7V.
The diode is in the off state. As a result, the current flowing through the diode D becomes several IA or less, and most of the load current flows through the current detection resistor R3. Therefore, the potential difference between the two current detection resistors Rs generated by the current IR flowing through the current detection resistor Rs is the load current ■,
By comparing this with the threshold voltage 1H, it becomes possible to detect a light load. (10 When the forward voltage V of the diode D and the potential difference between both ends of the nearby current detection resistor Rs become about 0.3 V, the load current 1
1 starts to be shunted to diode D, and when it reaches about 0.7V, diode D turns on and most of the current flows to diode D (■). The current (18) flowing through the current detection resistor Rs becomes constant, and the potential difference across the current detection resistor Rs never exceeds the forward voltage VF of the diode D. @ Near point B Point B is the operating point of the overload detection circuit provided independently of the light load detection circuit. The power loss Rs(B) of the current detection resistor Rs near this point is given by the following equation. R5(B)=VF7RS
Addition of (S) improves the score to 4 by -+0.49-, an order of magnitude. Next, the case where the device shown in FIG. 1 is used as a DC fan will be explained. FIG. 3 is a configuration block diagram showing an embodiment of the second invention. A speed-controlled DC fan is connected as a load. A capacitor C is installed between the load side and the common side of the current detection resistor Rs. The operation of the device configured in this manner will be described next. Fourth
The figure is a waveform diagram explaining the operation of the device shown in Figure 3, where the vertical axis is the load current I, the horizontal axis is time, and the Tenryu flow case and the small current case are shown side by side. As shown in the figure, when the speed of the DC fan is controlled, the load current It fluctuates widely and the ripple component becomes extremely large. In a small current region (where the voltage appearing on the current detection resistor R3 is about the forward voltage 2), the current detection resistor Rs and the capacitor C constitute a filter, and the ripple component is greatly reduced. In a large current region (load current 1 turns on diode D), the load current I flows through diode D, so capacitor C does not constitute a filter, so it has no effect in removing the tool. Since the ripple content ((AC component)/(DC component)) is originally small, the burden on TA (PI) can be reduced. [Effects of the Invention] As explained above, according to the present invention, the following can be achieved. ■ The current detection resistor Rs detects light loads, and by adding the diode D, it is possible to realize a light load detection device for a DC power supply that suppresses loss during heavy loads. ■ Speed-controlled DC fan When applied to, in addition to the effect (2), by installing the capacitor C, it is possible to realize a DC fan abnormality detection device with reduced ripple.

[Brief explanation of the drawing]

FIG. 1 is a configuration block diagram showing an embodiment of the first invention;
Fig. 2 is a characteristic diagram of the circuit shown in Fig. 1, Fig. 3 is a configuration block diagram showing an embodiment of the second invention, Fig. 4 is a characteristic diagram of the circuit shown in Fig. 3, and Fig. 5 is a conventional device. FIG. 6 is a characteristic diagram of the circuit shown in FIG. D...Diode, E...DC power supply, ■...Load current, Rs...Current detection resistor, v1□...Threshold voltage (reference voltage).

Claims (2)

[Claims] (1) A current detection resistor with one end connected to a DC power supply and the other end connected to the load side, a reference voltage source connected to the DC power supply side end of this current detection resistor, and a load side of this current detection resistor. A first input terminal is connected to the end of the reference voltage source, and a second input terminal is connected to the common side of the reference voltage source, and an alarm is generated by comparing the signals input to the first and second input terminals. A comparator that outputs a signal; and a diode having an anode connected to one end of the current detection resistor and a cathode connected to the other end, and a forward voltage of this diode. In contrast, the reference voltage is lowered, and the alarm signal is output when the voltage appearing at the current detection resistor becomes lower than the reference voltage. (2) A DC fan abnormality characterized in that a capacitor is attached to the load side of the current detection resistor and the diode in the light load detection device for a DC power supply according to claim 1, and the load is a speed-controlled DC motor. Detection device.