JPH0530734A - Dc switching power supply - Google Patents

Abstract

PURPOSE:To provide a DC switching power supply which can perform appropriate overcurrent protection depending on the type of load, operating conditions, and the like. CONSTITUTION:A CPU 10 selects a load 16 to be driven depending on the operating mode of machine and provides the load 16 with a control signal. The CPU 10 also reads out an offset value corresponding to each operation mode from a table in a ROM 15 or RAM 14 storing the offset values of overcurrent detection level and delivers thus read out offset value through an interface circuit 7 to an overcurrent detecting circuit I. Consequently, the overcurrent detection level of the overcurrent detection circuit I is regulated according to the operating mode of machine resulting in an overcurrent protection suitable for the load.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching type DC power supply device, and more particularly to overcurrent protection thereof.

[0002]

2. Description of the Related Art Conventionally, a switching type power supply has been used as a power supply device for various electronic devices. In particular, as a DC power supply, the switching method is widely adopted because of its advantages of small size, light weight and high efficiency. Figure 5
It is a circuit diagram of the conventional switching type DC power supply device which has an output stabilization circuit. In FIG. 5, reference numerals 1 and 2 denote input power supply terminals, the input power supply terminals 1 and 2 are connected to the input capacitor C1, and further connected to the primary winding N1 of T1 via the resistor R1 and the switching transistor Q1. There is. The secondary winding N2 of the transformer T1 is led to a smoothing capacitor C2 via a rectifying diode Q3. The smoothed output by this filter circuit is output terminals 4, 5
Is supplied to a load (not shown).

In order to detect the output voltage to the load, an output voltage detection circuit 6 is connected in parallel with the load connected to the output terminals 4 and 5. The detected value is fed back to the control circuit including the PWM (Pulse width modulation) circuit 3 via the photocoupler Q4.

The photocoupler Q4 outputs the fed back detection voltage to the PWM circuit 3, and the PWM circuit 3 controls the switching duty ratio or frequency of the drive pulse given to the base of the switching transistor Q1 according to the detected value.

In this way, the switching transistor Q1 is driven by the output of the PWM circuit 3, and the voltages at the output terminals 4 and 5 are stabilized to a predetermined value.

As a protection function, the resistance R1 detects the current of the switching transistor Q1.

Next, the operation of overcurrent protection in the circuit of FIG. 5 will be described.

When a DC power supply is connected to the input power supply terminals 1 and 2, the voltage application to the primary winding N1 of the transformer T1 is interrupted by the switching transistor Q1. The AC output generated by the intermittent switching transistor Q1 is insulated and transformed by the transformer T1.

The insulated and transformed AC output is rectified by the diode Q3. Rectified output is smoothing capacitor C2
After being smoothed by, it is supplied to the load from the output terminals 6 and 7.

When the load becomes heavy and the current of the switching transistor Q1 increases, the voltage generated in the resistor R1 also increases, and when the threshold value for overcurrent detection set by the resistors R4 and R5 is exceeded, the output of the comparator Q2 is inverted. PW
A signal is output to the M circuit 3, and the PWM circuit 3 stops pulse output by this signal. This operation is performed for each pulse.

[0011]

However, in the conventional example shown in FIG. 5, in consideration of a load having a smaller average current than the peak current value, such as a motor load, the overcurrent is adjusted according to the peak current value. When the threshold value for detection is set, there is a problem that the overcurrent cannot be properly detected in the case of another load having a large average current, and the peak current causes continuous operation, resulting in abnormal overheating of the power supply device. Further, this is also a problem that the abnormal state of the load is continued and the load is imposed on the load.
Furthermore, in order to prevent abnormal overheating of the power supply device, it is necessary to increase the heat capacity of the heat sink or to add an overheat protection circuit, which causes problems such as an increase in the size of the power supply and an increase in cost. There is.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a switching type DC power supply device capable of performing appropriate overcurrent protection in accordance with the type of load and operating conditions. is there.

[0013]

In order to achieve the above object, the present invention provides a switching type DC power supply device with the following (1),
It is configured as in (2).

(1) A switching type DC power supply device for converting an alternating current generated by intermittently connecting a DC input with a switching element into a direct current and supplying the same to a load, the current detecting means for detecting a current of the switching element; Threshold setting means for setting a threshold for overcurrent detection of the switching element, offset means for offsetting the threshold according to the type of the load, operating condition, etc., and output and offset of the current detection means And a control means for controlling the switching operation of the switching element according to the comparison signal.

(2) In addition to the offset means, a load current detecting means for detecting an average value of the load current is provided, and the offset by the output of the load current detecting means is used together.
The switching type DC power supply device described.

[0016]

With the configurations (1) and (2) described above, the threshold value for overcurrent detection is offset according to the type of load and the operating condition, and the appropriate overcurrent protection according to the type of load and the operating condition is provided. Done.

According to the configuration of (2), even if an abnormality occurs in the offset means, normal overcurrent protection is performed by the offset by the load current detection means.

[0018]

EXAMPLES The present invention will be described in detail below with reference to examples.
The same parts as those in the conventional example described above are designated by the same reference numerals, and detailed description thereof will be omitted.

(Embodiment 1) FIG. 1 is a block diagram of a "switching type DC power supply device" which is Embodiment 1. In FIG. As shown in the figure, the power supply device of this embodiment is connected to the overcurrent detection circuit of the conventional power supply device through the interface circuit 7 (I / O port 13, conversion circuit 12, photocoupler 11).
The CPU 10 of the device body 8 is connected. A storage device (ROM 15, RAM 14) in which each control information is stored is connected to the CPU 10 on the device body side. The CPU 10 selects a load to be driven in accordance with the operation mode of the device 8 and outputs a control signal to the load 16, and each operation from a table storing the offset value of the overcurrent detection level in the ROM 15 or the RAM 14. The offset value according to the mode is read and output to the overcurrent detection circuit I via the interface circuit 7. The interface circuit 7 adjusts the overcurrent detection threshold value of the overcurrent detection circuit I so as to match the data set by the CPU 10, and outputs it to the overcurrent detection circuit I. As a result, the overcurrent detection level of the overcurrent detection circuit I is adjusted according to the operation mode of the device, and appropriate overcurrent protection suitable for the load is performed. The transistor part of the photocoupler 11 is used as a variable resistor.

Therefore, when the CPU 10 drives a motor load or the like, the overcurrent detection level of the overcurrent detection circuit I, that is, the threshold value is raised as shown in FIG. 2A so that the peak current can flow. When driving other loads, the overcurrent detection level of the overcurrent detection circuit I is lowered to limit the overcurrent, as shown in FIG.

The overcurrent is limited by raising or lowering the overcurrent detection level according to the operating condition of the load.

As described above, according to this embodiment, the current can be limited according to the type of load and the operating condition, and problems such as abnormal overheating of the switching transistor Q1 and destruction of the load can be avoided.

(Second Embodiment) FIG. 3 is a block diagram of the second embodiment. As shown in the figure, the circuit configuration of the second embodiment is the same as that of the first embodiment. As a current detecting means, a resistor is used in the first embodiment to detect the pulse current of the switching transistor Q1, but in the present embodiment, a current transformer is used. Only the part using T2 is different.

That is, the primary pulse current is transformed by the current transformer T2 and converted into a voltage by the terminating resistor R6.
After being rectified by the diode Q6, it is input to the comparator Q2.

The subsequent operation is the same as that of the first embodiment.

(Third Embodiment) FIG. 4 is a block diagram of the third embodiment. As shown in FIG. 4, the circuit configuration of the third embodiment has a resistor R8 and an output current detection circuit 9 on the secondary side of the circuit of the first embodiment.
In addition, a photocoupler Q5 is added, and a part in which an overcurrent detection circuit II, an AND circuit 17, and an OR circuit 18 are added to the primary side is different.

The output current detection circuit 9 is the CPU of the first embodiment.
It has the same function as, and is composed of an operational amplifier, a transistor, etc., and outputs a voltage proportional to the average value of the output current generated in the resistor R8. This output is photocoupler Q5
The offset value for the overcurrent detection circuit II is output via. As a result, the overcurrent detection circuit II performs the same operation as when it receives the output from the CPU, and this output and the CPU 1
After the AND operation with the inverted value of the value of the overcurrent detection circuit I by the output from the 0 side is performed by the AND circuit 17, the OR operation of the operation result and the value of the overcurrent detection circuit I is performed by the OR circuit 1.
8 and supplies to the PWM circuit 3.

With the above configuration, an abnormality occurs on the CPU 10 side.
Alternatively, even if an abnormality occurs in the control signal of the CPU 10 and the output of the comparator Q6 does not become "H", "H" is supplied to the AND circuit 17 via the inverter 19 and the current detection circuit 9 on the secondary side Since the output is supplied to the PWM circuit 3 via the AND circuit 17 and the OR circuit 18, normal overcurrent protection can be performed.

Although each of the above embodiments is of the flyback type, the present invention is not limited to this and can be applied to a forward type or push-pull type switching type DC power supply device.
Moreover, although a transistor is used as the switching element,
Other elements such as FET and GTO can also be used.

[0030]

As described above, according to the present invention,
In the power supply of electronic equipment, etc. equipped with a CPU, the configuration is such that the overcurrent detection level is offset by the output from the CPU in accordance with the type of load and the operating condition.
Appropriate overcurrent protection can be performed according to the type of load and operating conditions, and it is now possible to design the heat sink, transformer, switching element, etc. with the average current, which had to be designed with the peak current. In addition, the device can be downsized and the price can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of a first embodiment.

FIG. 2 is an explanatory diagram of the first embodiment.

FIG. 3 is a block diagram of a second embodiment.

FIG. 4 is a block diagram of a third embodiment.

FIG. 5 is a circuit diagram of a conventional example.

[Explanation of symbols]

3 PWM circuit 10 CPU Q1 switching transistor R1, R3, R5 resistance

Claims (2)

[Claims] 1. A switching type DC power supply device for converting an alternating current generated by intermittently inputting a direct current by a switching element into a direct current and supplying it to a load, the current detecting means detecting a current of the switching element, and the switching. Threshold setting means for setting the threshold of overcurrent detection of the element,
An offset means for offsetting the threshold value according to the type of the load, the operating condition, etc. is compared with the output of the current detection means and the offset threshold value, and the switching operation of the switching element is controlled by the comparison signal. A switching type DC power supply device comprising: 2. A switching type according to claim 1, further comprising a load current detecting means for detecting an average value of the load current, in addition to the offset means, and using an offset by an output of the load current detecting means in combination. DC power supply.