JPH04299061A - Power supply - Google Patents

Abstract

PURPOSE:To obtain a totally downsized inexpensive power supply. CONSTITUTION:An AC power supply 1 is connected with a diode bridge 2 having output side connected with a smoothing capacitor 3. A switching element 5 is connected between the smoothing capacitor 3 and a transformer 6. An output rectifying/smoothing circuit 7 is connected with the secondary winding of the transformer 6. An overcurrent detecting circuit 4 comprising a resistor add a capacitor is interposed between the smoothing capacitor 3 and the switching element 5 and the output terminal of the overcurrent detecting circuit 4 is connected with an overcurrent protective circuit 8 which is connected with a PWM control circuit 9. A power supply circuit 10 is connected with the transformer 6 and feeds the PWM control circuit 9 with a working current. An output voltage detecting circuit 12 is connected with the PWM control circuit 9 and an input voltage correcting circuit 13 is connected with the transformer 6 and the PWM control circuit 9.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device which receives power from an AC or DC power supply and supplies a desired stabilized voltage.

0002

2. Description of the Related Art A power supply device is generally provided with an overcurrent protection circuit. FIG. 11 is a block diagram of a conventional power supply device. In FIG. 11, 21 is an AC power source, for example, a commercial power source. The current supplied from this power supply 21 is
The signal is rectified by a diode bridge 22, smoothed by a smoothing capacitor 23, turned on and off intermittently by a switch element 25, and supplied to a transformer 26.

In such a conventional power supply device, when the output current is larger than a predetermined value, that is, when an overcurrent is flowing, the overcurrent detection section 24 detects this, and the overcurrent protection circuit 28 and the pulse A width modulation (hereinafter referred to as PWM) control circuit 29 shortens the time during which the switch element 25 is on, thereby reducing the amount of energy transmitted to the output side of the transformer 26, thereby protecting against overcurrent. In the figure, 2
7 is a smoothing circuit on the output side of the transformer 26, 31 is a feedback photocoupler, and 32 is an output voltage detection circuit.

0004

[Problems to be Solved by the Invention] In the conventional power supply device as described above, the output current is detected by detecting the current flowing to the primary side of the transformer 26, so depending on the voltage of the AC power supply 21, overcurrent may occur. Variations occur in the time it takes for the protection circuit 28 to start operating. This characteristic is shown in Figure 1.
2.

For this reason, in the conventional power supply device as described above, each component must have sufficient capacity so as not to be damaged even if an overcurrent flows until the overcurrent protection circuit 28 starts operating. He was designing the project. As a result, the overall size has increased and the price has also increased.

[0006] The present invention solves the problems as explained in the above-mentioned prior art, and has an overall small size.
The purpose is to obtain an inexpensive power supply device.

[0007]

[Means for Solving the Problems] In order to solve the above problems, the present invention provides an input voltage correction circuit that generates a correction voltage according to the voltage on the secondary side of the transformer, and provides an output voltage of the input voltage correction circuit. was input to the PWM control circuit.

[0008]

[Operation] With the above configuration, the present invention maintains a constant voltage input to the overcurrent protection circuit by the input voltage correction circuit even if the input voltage changes when the output current is the same, and even if the input voltage changes, the PWM The operation start current of the overcurrent protection function of the control circuit can be made constant.

[0009]

Embodiments (Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a power supply device in a first embodiment of the present invention.

Reference numeral 1 indicates an AC power source, for example, a commercial power source. A diode bridge 2 is connected to this AC power supply 1, and a smoothing capacitor 3 is connected to the output side of the diode bridge 2. A switch element 5 is connected between the smoothing capacitor 3 and the transformer 6. 7 is an output side rectifying and smoothing circuit, which is connected to the secondary winding of the transformer 6.

Reference numeral 4 denotes an overcurrent detection circuit, which is composed of a resistor and a capacitor, and is inserted between the smoothing capacitor 3 and the switching element 5, and its output terminal is connected to the overcurrent protection circuit 8. Overcurrent protection circuit 8 is PWM
It is connected to the control circuit 9.

Reference numeral 10 denotes a power supply circuit for the PWM control circuit 9, which is connected to the transformer 6. Reference numeral 12 denotes an output voltage detection circuit, which includes a reference voltage generating means and a comparator. Reference numeral 11 denotes a feedback photocoupler, which is connected to the output voltage detection circuit 12 and the PWM control circuit 9.

13 is an input voltage correction circuit, which includes a diode, a resistor, and a capacitor, and includes a transformer 6 and a PWM
It is connected to the control circuit 9.

FIG. 5 is a more specific example of the above block diagram. The PWM control circuit 9 is formed in an integrated circuit together with the overcurrent protection circuit 8, and the input voltage correction circuit 13 is formed in a PWM integrated circuit (hereinafter referred to as PWMIC).
It is connected to the overcurrent protection input terminal 8' of the WM control circuit 9.

The operation of the power supply device according to the first embodiment of the present invention will be explained below. A current supplied from an AC power supply 1 is rectified by a diode bridge 2 and smoothed by a smoothing capacitor 3. Then, it passes through the overcurrent detection circuit 4, is intermittently turned on and off by the switch element 5, becomes a pulse state, and is supplied to the transformer 6.

The current supplied to the transformer 6 is converted into voltage therein, then rectified by the output side rectifier circuit 7, and output. At this time, the output voltage of the overcurrent detection circuit 4 is transmitted to the overcurrent protection input terminal 8' of the PWM control circuit 9, and the PWM control circuit 9 controls the on time of the switch element 5 so that the output voltage becomes a predetermined value. be done.

The overcurrent protection operation when the output current is constant will be explained. When the voltage on the secondary side of the transformer 6 increases, this is detected by the output voltage detection circuit 12 and transmitted to the PWMIC. Further, the negative voltage generated by the input voltage correction circuit 13 is transmitted to the overcurrent protection input terminal 8'.

The overcurrent protection operation when the output current is constant will now be explained with reference to FIG. In FIG. 6, a is the waveform of the pulse current passing through the overcurrent detection circuit 4, b is the voltage waveform of the overcurrent detection circuit 4, c is the voltage waveform input from the overcurrent detection circuit 4 to the PWM control circuit 9, and d is the waveform of the pulse current passing through the overcurrent detection circuit 4. The voltage waveform e input from the input voltage correction circuit 13 to the PWM control circuit 9 is the sum of waveforms c and d.

As can be seen from FIG. 6, the input voltage correction circuit 13 inputs a voltage proportional to the voltage of the power supply 1 to the PWM control circuit 9, so that the operation start time of the PWM control circuit 9 can be made constant. .

As a result, as shown in FIG. 2, the output voltage of the overcurrent protection circuit 8 becomes constant with respect to the input voltage, and the margin of component ratings can be reduced.

FIG. 3 shows the characteristics of the difference in the input voltage to the overcurrent detection circuit 4 with respect to the voltage of the power supply 1 when the output currents are the same. From Figure 3, even when the output current is the same,
It can be seen that if the voltage of the power supply 1 is different, the input voltage of the overcurrent protection circuit 8 is different.

FIG. 2 shows a characteristic in which the overcurrent protection voltage becomes constant if a voltage proportional to the voltage of the power supply 1 is applied to the voltage input to the overcurrent protection circuit 8.

(Embodiment 2) A second embodiment of the present invention will be described below. FIG. 7 is a block diagram of a power supply device in a second embodiment of the present invention.

[0024] Here, the same parts as in the first embodiment of the present invention described above are given the same numerals and their explanations are omitted.

Reference numeral 14 denotes a detection winding provided on the transformer 6. The input voltage correction circuit 13 is connected to the detection winding 14.

When the voltage on the secondary side of the transformer 6 increases,
The voltage of the detection winding 14 also increases, and the input voltage correction circuit 13
The absolute value of the negative voltage generated by this increases, and the voltage is transmitted to the overcurrent protection input terminal 8'.

As can be seen from FIG. 7, the input voltage correction circuit 13 inputs a voltage proportional to the voltage of the power supply 1 to the PWM control circuit 9, so that the operation start time of the PWM control circuit 9 can be made constant. .

(Embodiment 3) A third embodiment of the present invention will be described below. FIG. 8 is a block diagram of a power supply device in a third embodiment of the present invention.

[0029] Here, the same parts as in the first embodiment of the present invention described above are given the same numerals and their explanations are omitted. Input voltage correction circuit 13 is connected to winding 15 .

When the voltage on the secondary side of the transformer 6 increases,
The voltage of the winding 15 also increases, and the absolute value of the negative voltage generated by the input voltage correction circuit 13 increases, and this voltage is transmitted to the overcurrent protection terminal 8'.

The overcurrent protection operation when the output current is constant will now be explained with reference to FIG. In FIG. 9, a is the waveform of the pulse current passing through the overcurrent detection circuit 4, b is the voltage waveform of the overcurrent detection circuit 4, c is the voltage waveform input to the PWM control circuit 9 by the overcurrent detection circuit, and d is the input The voltage waveform e input from the voltage correction circuit 13 to the PWM control circuit 9 is the sum of waveforms c and d.

As can be seen from FIG. 9, the input voltage correction circuit 13 inputs a voltage proportional to the voltage of the power supply 1 to the PWM control circuit 9, so that the operation start time of the PWM control circuit 9 can be made constant. .

(Embodiment 4) A fourth embodiment of the present invention will be described below. FIG. 10 is a block diagram of a power supply device in a fourth embodiment of the present invention.

[0034] Here, the same parts as those in the first embodiment of the present invention described above are given the same numbers, and the description thereof will be omitted.

16 is a detection winding provided on the transformer 6. The input voltage correction circuit 13 is connected to the detection winding 16. In this embodiment, the winding direction of the detection winding 16 is opposite to that of the second embodiment, and the direction of the diode of the input voltage correction circuit 13 is opposite.

When the voltage on the secondary side of the transformer 6 increases,
The voltage of the detection winding 16 also increases, and the input voltage correction circuit 13
The absolute value of the negative voltage generated by this increases, and the voltage is transmitted to the overcurrent protection input terminal 8'. Therefore, the input voltage correction circuit 13 inputs a voltage proportional to the voltage of the power supply 1 to the PWM control circuit 9.
The operation start time can be made constant.

[0037]

Effects of the Invention The present invention provides a correction voltage generation circuit that generates a correction voltage according to the voltage on the secondary side of the transformer, and inputs the output voltage of the correction voltage generation circuit to the PWM control circuit. Overcurrent protection can be performed according to the voltage on the secondary side of the transformer as well as the current flowing to the next side, and the starting current for overcurrent protection operation of the PWM control circuit can be kept constant even if the input voltage changes. Therefore, it is not necessary to design each component with sufficient capacity, and it is possible to obtain a power supply device that is overall compact and inexpensive.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a first embodiment of a power supply device of the present invention.

[
Figure 2: Characteristic diagram showing the relationship of output current to the same power supply voltage

[Figure 3] Waveform diagram showing the relationship of output current to the same power supply voltage

[Figure 4] Waveform diagram showing the relationship of output current to the same power supply voltage

FIG. 5 is a block diagram of the first embodiment of the power supply device of the present invention.

[
Figure 6: Waveform diagram showing voltage and current at each part

[Figure 7
] Block diagram of a second embodiment of the power supply device of the present invention

[Figure 8]
Block diagram of the third embodiment of the power supply device of the present invention

[Figure 9] Waveform diagram showing voltage and current at each part

FIG. 10 is a block diagram of a fourth embodiment of the power supply device of the present invention.

[Figure 11] Block diagram of a conventional power supply device

[Figure 12] Characteristic diagram showing the relationship of output current to the same power supply voltage

[Explanation of symbols]

1 AC power supply 2 Diode bridge 3 Smoothing capacitor 4 Overcurrent detection circuit 5 Switch element 6　Trans 7 Output side rectification and smoothing circuit 8 Overcurrent protection circuit 9 PWM control circuit 10 Power supply circuit 11 Return photo coupler 12 Output voltage detection circuit 13 Input voltage correction circuit

Claims (1)

[Claims] 1. A switching element that switches current supplied from a power source, and an on/off state of this switching element.
A control circuit that controls the off time, an overcurrent protection circuit that detects the current pulsed by the switching element and operates when the current exceeds a predetermined value, and a voltage control circuit that controls the voltage of the current pulsed by the switching element. What is claimed is: 1. A power supply device comprising a voltage conversion means for converting the voltage, and a correction circuit for correcting a detected value of the overcurrent protection circuit according to a voltage on a secondary side of the voltage conversion means.