JPS644306Y2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a switching type transistor-stabilized DC power supply device for use in VTRs, video cameras, etc.

Prior Art As shown in Figure 1, a conventional ripple voltage detection type transistor stabilized DC power supply (switching regulator) has an input terminal 1 connected to a DC power supply and an output terminal 2 connected to a load. A switching transistor 4 is connected in series to the DC power supply line 3 between them, and the transistor 4 is controlled on/off based on the ripple voltage. To explain this regulator in more detail, a first choke coil 5 is connected in series to the DC power line 3 on the output side of the transistor 4,
The power line 3 is connected to the input side of this chiyoke coil 5.
A rectifier diode 6 is connected in parallel to the power supply line 3 on the output side of the chiyoke coil 5, and a first smoothing capacitor 7 consisting of an electrolytic capacitor is connected in parallel to the power supply line 3 on the output side of the capacitor 7. A second check coil 8 is connected in series, and a second smoothing capacitor 9 is connected in parallel to the power supply line 3 on the output side of the check coil 8. Reference numeral 10 denotes a DC voltage detection circuit for detecting a DC component, which consists of voltage dividing resistors 11 and 12 connected to the output terminal 2, and obtains a DC detection voltage on a line 13 derived from the voltage dividing point. . 14 is a coupling capacitor for ripple detection;
It is connected between one end of the first smoothing capacitor 7 and the line 13 . A common connection line 16 between the DC component detection line 13 and the ripple component detection coupling capacitor 14 is connected to a non-inverting input terminal of the voltage comparator 15, and a reference voltage circuit 17 is connected to its inverting input terminal. The voltage comparator 15
This is a well-known open collector type comparator composed of an IC, which compares a reference voltage and a detection voltage, and outputs a high level when the detection voltage is higher than the reference voltage, and outputs a low level when the voltage is lower. be. The output terminal of this comparator 15 is connected to the base of the transistor 4 via a resistor 18. The power terminal of the comparator 15 is connected to the power line 3, a resistor 19 is connected between the output terminal of the comparator 15 and the power line 3, and a capacitor 20 for speeding up the off-operation is connected in parallel to the resistor 18. is connected. The reference voltage circuit 17 is
Field effect transistor 21 and rectifier diode 22
and Zener diode 23 and voltage dividing resistor 24,2
It consists of 5. The input stage noise removal filter is
Inductance coil 26 and capacitor 27, 2
It consists of 8.

Next, the operation of the regulator shown in FIG. 1 will be explained with reference to FIGS. 2 and 3. In response to the output of the voltage comparator 15, the transistor 4 turns on and off as shown in FIG. After being smoothed by the second smoothing capacitor 7, it is further smoothed by the second smoothing coil 8 and the second smoothing capacitor 9, and a substantially flat DC output voltage with little ripple is obtained at the output terminal 2.
As a result, the DC detection voltage V _DC shown in FIG. 2A is obtained from the voltage detection circuit 10, and the ripple detection coupling capacitor 14 provides the first smoothing capacitor 7.
A ripple component is obtained based on the voltage, and by superimposing these components, a ripple-containing detection voltage V _O shown in FIG. 2A is obtained on line 16. however,
In Figures 2 and 3, the detection voltage and transistor 4
The phase relationship between on and off is shown without considering the operation delay. _The comparator 15 compares _the reference voltage V _R shown in FIG _. controlled. Therefore, as the DC detection voltage V _DC increases, the duty ratio of the switching output of the transistor 4 decreases, and conversely, as the DC detection voltage V _DC decreases, the duty ratio of the switching output of the transistor 4 increases, resulting in a constant Voltage output can be obtained.

Incidentally, the first and second smoothing capacitors 7 and 9 are composed of electrolytic capacitors of, for example, about 100 μF, and their capacitance and ESR (equivalent series resistance) vary significantly depending on changes in ambient temperature. The peak value of the ripple component of the terminal voltage of the first smoothing capacitor 7 is inversely proportional to the inductance value L of the first choke coil 5, and also inversely proportional to the capacitance value C of the first smoothing capacitor 7, so for example, If the temperature rises from the ambient temperature of 25°C and the capacitance of the capacitor 7 decreases, the peak value of the ripple component increases as shown in FIG. 3A, and the switching duty ratio of the transistor 4 decreases. Output voltage decreases. Conversely, when the temperature decreases and the capacitance of the smoothing capacitor 7 increases, the duty ratio increases and the output voltage increases. As a result, in a switching regulator with an output voltage of 5V, the output voltage fluctuates significantly due to changes in ambient temperature, as shown by characteristic line A in FIG.

Purpose of the invention Therefore, the purpose of the present invention is to provide a transistor DC stabilized power supply device that can reduce output voltage fluctuations due to temperature changes.

Structure of the Invention The present invention to achieve the above object includes a switching transistor connected in series to a DC power line between a DC power source and a load, and a switching transistor connected in series to the DC power line at the output side of the transistor. A smoothing device including at least a connected Chi-Yoke coil, a smoothing capacitor connected in parallel to the DC power supply line on the output side of the Chi-Yoke coil, and a rectifier diode connected in parallel to the DC power supply line on the input side of the Chi-Yoke coil. a ripple detection capacitor connected in parallel to the DC power supply line via a resistor between the transistor and the chiyoke coil; and an output voltage detection circuit that detects a DC output voltage at an output stage of the smoothing circuit. , compares a ripple-containing detection voltage obtained by superimposing the DC detection voltage obtained from the output voltage detection circuit and the ripple component obtained from the ripple detection capacitor with a reference voltage, and turns on and off the transistor based on this comparison output. This invention relates to a transistor stabilized DC power supply device comprising a comparison control circuit for off-control.

Effects of the device According to the above device, the capacitor for detecting ripple voltage is connected in front of the smoothing circuit, so it is possible to detect ripple voltage regardless of the smoothing circuit. And since this ripple detection capacitor does not need to contribute to output smoothing, it can be a ceramic capacitor or the like that has a small capacity and changes little in capacity due to temperature. Therefore, the change in ripple detection voltage due to temperature change is small, and the output voltage fluctuation is also small.

Embodiment Next, a ripple detection type transistor stabilized DC power supply device according to an embodiment of the present invention will be described with reference to FIGS. 4 and 5. However, the components indicated by reference numerals 1 to 28 in FIG. 4 are substantially the same in structure and operation as those indicated by the same reference numerals in FIG. 1, and therefore the explanation thereof will be omitted.

In FIG. 4, a ripple detection capacitor 3 consisting of a magnetic capacitor is connected in parallel to the DC power supply line 3 on the input side of the first choke coil 5 via a resistor 29.
0 is connected, and one end of this capacitor 30 is connected to the line 13 via the coupling capacitor 14. Note that a resistor 31 is connected in series to the line 16. The constants of each circuit element in the circuit of FIG. 4 are as follows. The capacitance of the first and second smoothing capacitors 7 and 9, which are electrolytic capacitors, is 100μF/16V, the inductance of the first chiyoke coil 5 is 220μH, the inductance of the second chiyoke coil 8 is 120μH, and the inductance of the ripple detection capacitor 30 is 220μH. The capacitance is 0.1μF, and the capacitance change rate of this capacitor 30 in the range of -30 to +85℃ is ±15
Within %, the value of resistor 29 is 3600Ω, the value of resistor 31 is
It is 20kΩ.

When the ripple detection circuit is configured as shown in FIG. 4, the ripple component can be detected without being affected by variations in the capacitance of the first smoothing capacitor 7. That is, the rectangular wave voltage obtained by the on/off operation of the transistor 4 is supplied to an RC filter consisting of a resistor 29 and a capacitor 30.
0 terminal voltage becomes a triangular wave, which is superimposed on the DC detection voltage via the coupling capacitor 14, and the first
A ripple-containing detection voltage similar to the circuit shown in the figure can be obtained. Although the capacitance of the capacitor 30 for ripple detection also fluctuates due to temperature changes, this fluctuation is extremely small since it is a small capacitance ceramic capacitor. As a result, in a device with a rated output voltage of 5V, the relationship between ambient temperature and output voltage fluctuation becomes characteristic line B in Figure 5, which is a significant improvement compared to the device in Figure 1, and the target voltage fluctuation range. 40mV (-20℃~+60℃)
can be easily obtained.

Modifications The present invention is not limited to the above-described embodiments, and, for example, the following modifications are possible.

(A) As shown in FIG. 6, a circuit configuration may be adopted in which a resistor 32 of, for example, about 2 kΩ is added between the capacitor 7 and the capacitor 30. The circuit shown in FIG. 6 has the same structure as that shown in FIG. 4 except for the resistor 32.

(B) In the embodiment, the output of the comparator 15 is applied to the base of the switching transistor 4 via the resistor 18, but a control transistor is connected between the base of the switching transistor 4 and the common ground line, and this The base may be controlled by the output of the comparator 15.

(C) One or both of the second choke coil 8 and the second smoothing capacitor 9 in the smoothing circuit may be omitted.

(D) The ripple detection capacitor 30 can be replaced with various capacitors other than those in the embodiment.
However, in order to reliably detect ripples and minimize output voltage fluctuations, the capacitance of the capacitor 30 should be
It is desirable that the value be 1000 pF or more, which is relatively small, and that the rate of change in capacitance from -30 to +85°C be within the range of ±15%.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a conventional stabilized DC power supply device, Fig. 2 is a waveform diagram showing the state of each part in Fig. 1,
Fig. 3 is a waveform diagram showing the state of each part in Fig. 1 when the temperature changes, Fig. 4 is a circuit diagram showing a stabilized DC power supply according to an embodiment of the present invention, and Fig. 5 shows changes in ambient temperature and A characteristic diagram showing the relationship with output voltage fluctuation, and FIG. 6 is a circuit diagram showing a modified example of a stabilized DC power supply device. 1...Input terminal, 2...Output terminal, 3...DC power supply line, 4...Switching transistor,
5...First chiyoke coil, 6...Diode, 7...First smoothing capacitor, 8...Second
9... second smoothing capacitor, 10... DC voltage detection circuit, 14... ripple detection coupling capacitor, 15... voltage comparator, 1
7...Reference voltage circuit, 29...Resistor, 30...Ripple detection capacitor.

Claims (1)

[Claims for Utility Model Registration] A switching transistor connected in series to a DC power supply line between a DC power supply and a load, a chiyoke coil connected in series to the DC power supply line on the output side of the transistor, and the a smoothing circuit including at least a smoothing capacitor connected in parallel to the DC power supply line on the output side of the Chiyork coil, and a rectifier diode connected in parallel to the DC power supply line on the input side of the Chiyork coil; and the transistor. a ripple detection capacitor connected in parallel to the DC power supply line via a resistor between the chiyoke coil; an output voltage detection circuit that detects a DC output voltage at the output stage of the smoothing circuit; and the output voltage detection circuit. a comparison control circuit that compares a ripple-containing detection voltage obtained by superimposing the DC detection voltage obtained from the ripple detection capacitor with a ripple component obtained from the ripple detection capacitor and a reference voltage, and controls on/off the transistor based on this comparison output; A transistor-stabilized DC power supply device consisting of: