JPH05308774A - Power unit - Google Patents

Abstract

PURPOSE:To miniaturize a circuit at large and lower the cost by reducing the margin of rating on parts to the output rated current of each element. CONSTITUTION:Though the detection ingredients of the pulse current on input side detected by an overcurrent detector 7 gets on lower level, the higher the voltage on input side to a transformer 4 becomes, by the pulse width control which narrows the conductivity width of a switch element 5 more by PWMIC 27, the higher the voltage on input side to a transformer 4 becomes, an overcurrent protective input voltage compensating circuit 21 compensates the detection ingredients by the overcurrent detector 7 by supplying the input terminal A of the PWMIC 27 being an overcurrent protective circuit 8 with the voltage proportionate to the voltage on input side. Since the PWMIC 27 performs protective operation of the power source by controlling the input element 5 after detecting the excessiveness of the pulse current on input side, based on this compensated input voltage, it becomes constant without the current on output side of a transformer enlarging more at the start of operation of an overcurrent protective means, the higher the voltage on input side becomes, as before.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention switches PWM current (pulse width control) while switching DC current on the input side.
In addition, the present invention relates to a power supply device of a switching regulator type that transfers electric power on the input side to an output side via a transformer to obtain an arbitrary stabilized DC voltage.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing the configuration of a conventional switching regulator type power supply device. In FIG. 6, both ends of the AC input power source 1 are diode bridges 2
Is connected to both ends of the smoothing capacitor 3 via the, and the input AC voltage of the AC input power source 1 is rectified by the diode bridge 2 and then smoothed by the smoothing capacitor 3 to obtain a DC voltage. One end of the smoothing capacitor 3 is connected to the primary winding of the transformer 4 and further to the switch element 5, and a DC voltage is switched by the switch element 5 through the primary winding of the transformer 4 and PWM control is performed. The electric power on the input side is transmitted to the output side via the, and a pulse voltage is obtained on the secondary winding of the transformer 4. Both ends of the secondary winding of the transformer 4 are connected to a rectifying / smoothing unit 6, and the pulse voltage on the output side is rectified / smoothed by a rectifying / smoothing unit 6 including a diode and a smoothing capacitor to generate an arbitrary stabilized DC voltage V ₀ . obtain.

An overcurrent detector 7 connected in series with the switch element 5 is connected to the other end of the smoothing capacitor 3,
The input side pulse current flowing through the switch element 5 is detected.
The overcurrent protection circuit 8 connected to the overcurrent detection unit 7 is connected to the PWM control circuit 9 connected to the gate of the switch element 5, and the input side pulse current becomes excessive based on the detection component by the overcurrent detection unit 7. After detecting that, the switch element 5 is controlled via the PWM control circuit 9 to perform an operation for protecting the power supply device from overcurrent. This PWM control circuit 9
Is supplied by the PWM control circuit power supply unit 10.
11 is a feedback phototransistor coupler, and 12
Is an output voltage detection unit error amplification unit.

With the above structure, first, the PWM control will be explained. As shown in FIG. 7, when the input voltage to the transformer 4 is high, the PWM control circuit 9 narrows the conduction width of the switch element 5, and thereby the overcurrent is suppressed. As the input voltage to the current protection circuit 8, a low voltage is input via the overcurrent detection unit 7.
Further, when the input voltage to the transformer 4 is low or when the load current on the output side is large, the PWM control circuit 9 causes the switch element 5 to
The width of conduction is increased, so that the input voltage to the overcurrent protection circuit 8 becomes high.

Next, for the overcurrent protection operation, the output side current is simulated through the transformer 4 in a pseudo smoothing capacitor 3
Is converted into a pulse current flowing through the transformer 4 and the switch element 5 and detected by the overcurrent detection unit 7, and when the input voltage to the overcurrent protection circuit 8 which is the detection component exceeds a predetermined value,
The switch element 5 is turned off via the PWM control circuit 9, and when it falls below a predetermined value, the switch element 5 is turned on via the PWM control circuit 9 to perform an intermittent operation to reduce the amount of energy transfer to the output side of the transformer 4. , Overcurrent protection was on.

[0006]

However, in the above-mentioned conventional configuration, since the output side current is pseudo-detected by the input side pulse current, when the operation of the overcurrent protection circuit 8 is started due to the voltage change on the input side. Change occurs in the output current and the characteristic becomes as shown in FIG. That is, when the input voltage to the transformer 4 is low, the transformer output current at the start of the operation of the overcurrent protection circuit 8 is small, and the higher the input voltage to the transformer 4, the transformer output at the start of the operation of the overcurrent protection circuit 8. The current becomes large. Therefore, in order to prevent each element of the power supply device from being destroyed until the overcurrent protection circuit 8 performs the protective operation, a large margin of component rating must be taken with respect to the output rated current of each element. This led to an increase in the size and cost of the entire circuit.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a power supply device capable of reducing the size of the entire circuit and reducing the cost by reducing the margin of the component rating with respect to the output rated current. To do.

[0008]

In order to solve the above-mentioned problems, the power supply device of the present invention switches a direct current on the input side with a switch element, and the conduction width of the switch element increases as the voltage on the input side increases. Is a switching regulator type power supply device for controlling the pulse width so as to narrow the input side and transmitting the electric power on the input side to the output side through a transformer to obtain an arbitrary stabilized DC voltage, and the input flowing through the switch element. Overcurrent detecting means for detecting a positive component of the side pulse current, and after detecting an excessive amount of the input side pulse current on the basis of the detected component by the overcurrent detecting means, controlling the switch element to perform a power protection operation. The current protection means and the input side so that the current on the output side at the start of the protection operation of the overcurrent protection means becomes constant even if the voltage on the input side changes. It is obtained by a overcurrent protection input voltage correction means for correcting the detected components by supplying a voltage proportional to the pressure.

[0009]

With the above configuration, the detection component of the input side pulse current detected by the overcurrent detection means by the pulse width control that narrows the conduction width of the switch element as the input side voltage increases becomes lower as the input side voltage increases. However, the overcurrent protection input voltage correction means corrects the detection component by supplying a voltage proportional to the voltage on the input side, and based on this corrected input voltage, the overcurrent protection means causes the input side pulse current to become excessive. After detecting, the switch element is controlled to perform the power protection operation.
The output side current at the start of operation of the overcurrent protection means does not become larger as the input side voltage becomes higher as in the past, but it becomes constant, and the margin of the component rating for the output rated current of each component is small. Therefore, it is possible to reduce the size and cost of the entire circuit.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. It should be noted that the same effects as those of the conventional example are given the same reference numerals and the description thereof will be omitted.

FIG. 1 is a block diagram showing the configuration of a switching regulator type power supply device showing an embodiment of the present invention. In FIG. 1, an overcurrent protection input voltage correction circuit 21
Is composed of a series circuit of resistors 22 and 23 connected to both ends of the smoothing capacitor 3, the connection point of these resistors 22 and 23 is connected to the input voltage terminal of the overcurrent protection circuit 8, and the overcurrent detection unit 7
After detecting the excessive input side pulse current on the basis of the detection component by, the output current at the start of operation of the overcurrent protection circuit 8 that operates to protect each element of the power supply device changes the input voltage to the transformer 4. Even if it is constant, a voltage proportional to the input voltage is supplied to correct the detection component of the overcurrent detection unit 7.

FIG. 2 is a circuit diagram showing a specific configuration of the power supply device shown in FIG. In FIG. 2, a resistor 24 is interposed between the switch element 5 and the diode bridge 2, and the connection point between the resistor 24 and the switch element 5 is connected to the input voltage terminal A of the overcurrent protection circuit 8 via the resistor 25. The connection point between the resistor 24 and the diode bridge 2 is connected to the input voltage terminal A of the overcurrent protection circuit 8 via the capacitor 26. The resistors 24 and 25 and the capacitor 26 described above constitute the overcurrent detection unit 7, which detects the positive component of the input side pulse current.
Further, the PWMIC 27 having both functions is used for the overcurrent protection circuit 8 and the PWM control circuit 9.

With the above structure, the AC input voltage Vi supplied from the AC input power supply 1 is rectified by the diode bridge 2, smoothed by the smoothing capacitor 3, and converted into a DC voltage. Then, the direct current is supplied to the primary winding of the transformer 4, and the switching operation of the switch element 5 causes the input element side of the transformer 4 to pass from the primary winding of the transformer 4 to the switch element 5 and to the overcurrent detection section 7. Pulse current flows. Further, on the output side of the transformer 4, an arbitrary stabilized DC voltage is obtained from the secondary winding of the transformer 4 via the output side rectifying / smoothing section 6.

Here, the overcurrent detection unit 7 performs a current-voltage conversion on the pulse current flowing through the switch element 5 with the resistor 24, and inputs it to the input voltage terminal A of the overcurrent protection circuit 8 via the resistor 25. When the input voltage value exceeds a predetermined threshold value, the overcurrent protection circuit 8 operates. The PWM control circuit 10 turns off the switch element 5 when the threshold value is exceeded and turns on the switch element 5 when the threshold value is exceeded, thereby reducing the energy transfer amount to the output side of the transformer 4 to reduce the overcurrent. I am protecting.

At this time, if the output current (load) is the same,
Overcurrent protection circuit 8 depending on the level of input voltage to the transformer 4
The difference in the input voltage to the input voltage terminal A of the above is shown in FIG. Figure 3
As shown in, even if the output current is the same, if the input voltage to the transformer 4 is different, the input voltage to the input voltage terminal A of the overcurrent protection circuit 8 is different. This is because the switch element 5 is PWM-controlled by the PWM control circuit 10 and narrows the conduction width of the switch element 5 when the input voltage to the transformer 4 is high.
This is because it works to widen the conduction width of the switch element 5 when the input voltage to the transformer 4 is low. Here, if a voltage proportional to the input voltage to the transformer 4 is applied to the overcurrent protection circuit input voltage and corrected by the overcurrent protection circuit input voltage correction circuit 21, if the output current of the transformer 4 is the same, the voltage is transferred to the transformer 4. Even if the input voltage is different, the input voltage of the overcurrent protection circuit becomes the same, and therefore the transformer output current at the start of the operation of the overcurrent protection circuit with respect to the input voltage also becomes constant.

FIG. 4 shows a waveform diagram of each main part of the power supply device of FIG. 1, a of FIG. 4 is a pulse current waveform of the input part of the transformer 4, b of FIG. 4 is a voltage waveform of the overcurrent detection part 7, 4c shows the input voltage terminal A of the overcurrent protection circuit 8 from the overcurrent detection unit 7.
4 is a voltage waveform input to the input voltage terminal A of the overcurrent protection circuit 8 from the overcurrent protection circuit input voltage correction circuit 21.
4 is a total voltage waveform obtained by adding the voltage waveforms of c of FIG. 4 and d of FIG. Figure 4
As shown in, the current protection input voltage correction circuit 21 inputs a voltage proportional to the DC voltage obtained by rectifying and smoothing the AC input voltage Vi to the input voltage terminal A of the overcurrent protection circuit 8 to input voltage to the transformer 4. The voltage input to the overcurrent protection circuit 8 can be made constant regardless of whether the current is high or low, and thus the transformer output current at the start of the overcurrent protection operation can be made constant.

Therefore, as shown in FIG. 5, since the transformer output current at the start of the overcurrent protection operation can be made constant regardless of the input voltage to the transformer 4, the overcurrent protection circuit 8
It is possible to reduce the margin of the component rating with respect to the output rated current in order to prevent each element of the power supply device from being broken until the protection operation is performed, and thus it is possible to reduce the size and cost of the entire circuit.

[0018]

As described above, according to the present invention, by providing the overcurrent protection input voltage correction means, the change in the transformer output current at the start of the overcurrent protection operation due to the high and low of the input voltage can be eliminated with a simple structure. Therefore, it is possible to reduce the margin of the component rating with respect to the output rated current, and it is possible to reduce the size and cost of the entire circuit.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a switching regulator type power supply device showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a specific configuration of the power supply device shown in FIG.

FIG. 3 is a pulse current waveform and an overcurrent protection circuit input voltage waveform diagram with respect to the level of the input voltage in the power supply device of FIG.

FIG. 4 is a waveform diagram of each main part of the power supply device of FIG.

5 is a characteristic diagram of a transformer output current at the start of operation of an overcurrent protection circuit with respect to an AC input voltage in the power supply device of FIG.

FIG. 6 is a block diagram showing a configuration of a conventional switching regulator type power supply device.

7 is a pulse current waveform and an overcurrent protection circuit input voltage waveform diagram for high and low input voltages in the power supply device of FIG.

8 is a characteristic diagram of a transformer output current at the start of operation of an overcurrent protection circuit with respect to an AC input voltage in the power supply device of FIG.

[Explanation of symbols]

 1 AC input power supply 2 Diode bridge 3 Smoothing capacitor 4 Transformer 5 Switch element 6 Rectification smoothing part 7 Overcurrent detection part 8 Overcurrent protection circuit 9 PWM control circuit 21 Overcurrent protection input voltage correction circuit 22, 23, 24, 25 Resistance 26 Capacitor 27 PWMIC

Claims (1)

[Claims] 1. A direct current on the input side is switched by a switch element, and a pulse width is controlled so that the conduction width of the switch element is narrowed as the voltage on the input side is higher, and the electric power on the input side is converted to a transformer. A switching regulator type power supply device for transmitting an arbitrary stabilized DC voltage via an output side via an overcurrent detection means for detecting a positive component of an input side pulse current flowing in the switch element, and the overcurrent. After detecting an excess of the input side pulse current based on the detection component by the detection means, an overcurrent protection means for controlling the switching element to perform a power supply protection operation, and the overcurrent even if the input side voltage changes. Overcurrent protection for correcting the detection component by supplying a voltage proportional to the voltage on the input side so that the current on the output side at the start of the protection operation of the protection means becomes constant Power supply and a power voltage correction means.