JPS6226246B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an overcurrent detection control circuit for a power supply device, which reduces power loss in the detection circuit.
The purpose is to obtain an efficient power supply device.

The detection control circuit for overcurrent due to overload or shorting of a power supply device such as a switching regulator or a series regulator is an output circuit as shown in Figure 1, taking a pulse control switching regulator as an example. A detection resistor R1 is inserted at an appropriate position, and the voltage across the transistors Q2,
A type of circuit in which current limiting operation is performed by turning on Q3 is generally known. However, transistor Q
Approximately 0.7V (in the case of a silicon transistor) is required to turn on R1, so if the output of the power supply is low voltage and large current, the proportion of power loss due to voltage drop across resistor R1 will be extremely large, and the power supply This will result in a significant drop in efficiency as a device. For example, in the case of a power supply with an output voltage of 5V, approximately 12% of the power is consumed by this detection resistor R1, and the efficiency of the power supply decreases to 88% due to the loss in this detection section alone.

The overcurrent detection circuit of the present invention has extremely reduced power loss in the detection section, and will be explained below with reference to the drawings. First, as shown in FIG. 2, a peak detection and holding circuit 3, a proportional amplifier 4, and a Schmitt trigger circuit 5, the square wave power source 1 is repeatedly turned on and off at a period of T seconds as shown in FIG. 3a, and the duty ratio is approximately 50: Generate 50 square waves. This square wave is transmitted from the A and B ends of the detection coil section 2 to the resistor R.
2 to the first winding 6. A second winding 8 for passing the current to be detected is wound around the magnetic core 7 of the detection coil section 2, or the second winding 8 is simply passed through the magnetic core 7 to connect it to the first winding 6. A connection has been made. The magnetic core 7 may have a toroidal shape as shown in the figure, or may have a core shape such as EI type or UI type.

Now, when a square wave as shown in FIG. 3a is applied from the square wave power source 1 to the detection coil section 2, the square wave has a differential effect due to the inductance L of the first winding 6 and the resistor R2. receive. Here L/R2≪T
If a constant is selected in advance, C of the detection coil section 2,
At the D end, a differential voltage waveform as shown in FIG. 3b appears. However, as the DC current I _DC flowing through the second winding 8 wound around the magnetic core 7 increases, the peak value V _pp of this differential voltage waveform gradually decreases as shown in FIG. However, until the magnetic core 7 is saturated, I _DC and V _pp have a substantially linear relationship as shown in FIG. 4a. Therefore, the overcurrent detection level I' _DC is set to an appropriate level in this straight line part, and the overcurrent control signal voltage V _p is calculated from the peak voltage value V' _pp at that time.
The overcurrent detection circuit of the present invention extracts _p and operates the current control circuit.

From the peak voltage value V' _pp to the overcurrent control signal voltage V _p
Various methods can be considered for processing _p , but the method shown in Figure 2 detects and holds the peak value of the differential voltage waveform appearing at the C and D terminals in the peak detection and holding circuit 3, and then increases the peak value. The input impedance is amplified by the proportional amplifier 4, and the level is detected by the Schmitt trigger circuit 5, so that the overcurrent control signal voltage _Vpp is generated at the overcurrent detection level I' _DC , as shown in Fig. 4b. This is an example of a circuit.

FIG. 5 shows an embodiment in which the present detection circuit is applied to a switching regulator for pulse width control, in which the magnetic core 7 of the detection coil section 2 is connected to the DC output circuit's choke coil 9 and the smoothing capacitor C2. A line inserted between them and through which the detected current I _DC flows passes through (or is wound around) the magnetic core 7 as the aforementioned second winding 8 . Then, the magnetic core 7 has a first
A winding 6 is wound thereon, and when a square wave is supplied thereto from the square wave power source 1 through the resistor R2, a peak voltage value V _pp corresponding to the detected current appears at the C and D terminals as described above. Therefore, this peak voltage value _Vpp is passed through a peak voltage detection and holding circuit 3, a proportional amplifier 4, and a Schmitt trigger circuit 5 to obtain an overcurrent control signal voltage _Vpp , and this output is connected to a diode D.
2 to the connection point 10 with voltage dividing resistors R3 and R4 connected in parallel to the output terminal of the regulator, and led to the pulse width control circuit 11 to generate the reference voltage V _RE
The current is limited by operating the switching transistor Q1 according to the level compared with _F and controlling the pulse width.

Note that this detection circuit requires the square wave power source 1, but since the switching regulator already has a built-in square wave power source, it goes without saying that its output can be used.

The present invention detects overcurrent by simply passing the DC output line through which the current to be detected flows as the second winding 8 to the magnetic core 7, or by winding a minute inductance wound a few times. Since this is carried out in the detection section, the power loss in the detection part is extremely small, and therefore a highly efficient power supply device can be obtained.

In addition, in the circuit of the present invention, there is almost no voltage drop in the detection section, so the difference between the input side voltage and the output side voltage is small, and even if the input side voltage decreases, the necessary output voltage can be extracted. I can do it. Particularly in the case of a regulator of a portable device that uses a battery on the input side, there is an advantage that a predetermined voltage can be extracted until the end even if the battery voltage drops.

Furthermore, in this detection circuit, the detection part and control part are electrically separated, so there is no restriction on the installation location of the detection part, and overcurrent detection can be performed at any position in the output circuit where DC current flows. There are also features that allow you to

As described above, the overcurrent detection circuit of the present invention has the above-mentioned features as well as extremely low power loss, and is extremely excellent as an overcurrent detection circuit for a current device.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a power supply device having a conventional overcurrent detection circuit, and FIG. 2 is a circuit diagram showing a detection circuit of the present invention. FIG. 3 is an explanatory diagram showing the operating waveforms of FIG. 2,
A shows the output waveform of the square wave power supply, and b, c, and d show the peak voltage waveforms appearing at the CD end in Fig. 2. Figure 4a shows the direct current I _DC and the peak voltage value V _P-
Graph _b is a graph showing the relationship between DC current I _DC and overcurrent control signal voltage V _OP . FIG. 5 is a circuit diagram showing an embodiment in which the detection circuit of the present invention is applied to a switching regulator. Q1...Switching transistor, D1...
Flywheel diode, C1, C2... Smoothing capacitor, R1... Detection resistor, 2... Detection coil section, 3... Peak detection holding circuit, 4... Proportional amplifier, 5... Schmitt trigger circuit, 7... Magnetic core, 11...Pulse width control circuit.

Claims (1)

[Claims] 1. A first winding wound around a magnetic core to generate a detection voltage, and a second winding wound around the same magnetic core a few times or simply passed through the magnetic core for passing the current to be detected. a detection coil section configured with a winding, a square wave power supply, and a peak voltage detection control signal generation circuit, and supplies a square wave from the square wave power supply to both ends of the first winding via a resistor. At the same time, a current to be detected is passed through the second winding, and the peak voltage value of the differential waveform of the voltage induced at the end of the first winding is extracted as an overcurrent control signal through a peak voltage detection control signal generation circuit. , an overcurrent detection circuit characterized in that overcurrent is controlled using this control signal. 2. The overcurrent detection circuit according to claim 1, wherein the peak voltage detection control signal generation circuit comprises a peak voltage detection and holding circuit, a proportional amplifier, and a Schmitt trigger circuit.