JPH035929Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a DC stabilized power supply device.
In particular, it concerns the overcurrent protection circuit.

In order to prevent damage to the load and power supply due to overcurrent flowing into the load, a DC stabilized power supply is generally equipped with an overcurrent protection circuit to prevent current exceeding a certain value from flowing.

On the other hand, the drive currents of printers, motor drives, and capacitors are not constant; as shown in Figure 1, they temporarily show a high current (peak current) value I _P and most of the rest of the time they show a low current (minimum current). current) value _IM . Therefore, its average current I _a is low.

By the way, if such printers, motor drives, capacitors, etc. are driven by a power supply device equipped with an overcurrent protection circuit that operates at a current higher than the average current, it becomes impossible to supply the necessary peak current. For this reason, conventionally, a discharging capacitor is provided on the output side of a power supply device, and even if an overcurrent protection circuit operates when a peak current is supplied, the peak current is supplied by the discharging current of the discharging capacitor. However, the discharge capacitor becomes large, making it unsuitable for small devices.

On the other hand, if the overcurrent protection setting value is set higher than the peak current value _IP , it is possible to supply the peak current.
Circuit elements such as transistors in the power supply device must be large in order to handle large currents, which has the disadvantage of increasing the size and cost of the device, and also has the disadvantage that the response of the heat-sensitive element is slow.

The purpose of the present invention is to eliminate these drawbacks and provide a small, inexpensive overcurrent protection circuit for a DC stabilized power supply that can supply peak current while keeping the overcurrent setting low. .

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.

Referring to Figure 2, output line ₁ of the power supply
Insert an overcurrent detection resistor R ₁ in the middle of the circuit, and connect a series circuit of resistors R ₂ and R ₃ in parallel with it. The operational amplifier 1 generates an output when the voltage across the resistor R ₁ and therefore the voltage across the series resistors R ₂ and R ₃ exceeds a certain value ΔV. on the other hand,
Operational amplifier 2 converts the voltage across resistor R ₁ to resistor R ₂ ,
The voltage divided by _R3 , that is, the voltage across resistor _R2 , is applied, and when this input voltage ΔV is exceeded, an output is generated. Both outputs are supplied to the control circuit 3 of the power supply, which controls the transistor T _r1 and transformer T
Controls the secondary side output of Note that the resistances R ₁ , R ₂ ,
By adjusting R ₃ and ΔV of the operational amplifier, when the output current of the power supply device exceeds the minimum current I _M mentioned above, operational amplifier 1 will generate the output, and when the peak current exceeds the peak current I _P , operational amplifier 2 will output the output current. Allow this to occur.

Connect a resistor R ₄ and a capacitor C in parallel to the output of the operational amplifier 1, and set the time constant of the series resistor R ₅ , parallel resistor R ₄ , and capacitor C to the duration of the peak current mentioned above (Fig. 1, t _P ). Set above. Thus,
The output of the operational amplifier 1 is not applied to the control circuit T _r until a certain period of time t _P has elapsed after generation.

According to the circuit shown in Fig. 2, assuming that the current shown in Fig. 1 is supplied from this power supply to the load, if the peak current I _P flows into the output line, the operational amplifier 1 will not operate. generates output, but
Operational amplifier 2 produces no output. However, since time constant circuits R ₄ , R ₅ , and C are connected to the output of operational amplifier 1, the time t _P determined by the time constant
During this period, its output is not applied to the control circuit 3, and t _P
After this time, the current is applied to the control circuit 3 for the first time, and based on the control, the current on the output line becomes _IM . That is, as shown in FIG. 3, the power supply output current is controlled after the peak current occurs. This means that the required peak current is supplied. On the other hand, when a current exceeding the peak current value I _P flows, operational amplifiers 1 and 2 operate, and the output of operational amplifier 2 operates the control circuit 3 to maintain the power supply output current at _IP . After a period of time t _P has elapsed, the output of the operational amplifier 1 is input to the control circuit 3, so that the DC output current is controlled to I _M. In this case as well, changes as shown in FIG. 3 are shown.

According to the above configuration, the flow of a DC output current exceeding I _P is reliably prevented, and even if the current exceeds I _M , it is limited to the instant t _P.
While it is possible to supply the peak current I _P necessary for the load, it is also possible to use circuit elements such as small transistors with low capacitance, which has the advantage of miniaturizing the device and reducing costs. A reduction in power consumption is realized, and a DC power supply device having an overcurrent protection circuit that does not require a heat-sensitive element is obtained. This is suitable as a power supply device for printers, motor drives, capacitors, etc.

It is clear that if two resistors R ₆ and R ₇ are connected in series and inserted into the power supply output line as overcurrent detection resistors, as shown in Figure 4, they can also be used as voltage dividing resistors. Probably.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an example of a change in current to be supplied to a load, Fig. 2 is a diagram showing an example of an embodiment of the present invention, and Fig. 3 is a diagram for explaining the operation of the embodiment of Fig. 2. FIG. 4 is a diagram showing the main part of a modification. I _P ... Peak current, I _M ... Minimum current, R ₁ ... Overcurrent detection resistor, R ₂ , R ₃ ... Voltage dividing resistor, 1, 2
...Operation amplifier, 3...Control circuit, R ₄ , R ₅ ...
Resistor, C... Capacitor, T _r ... Transistor,
R ₆ , R ₇ ... Resistance for overcurrent detection and voltage division.

Claims (1)

[Scope of utility model registration request] A resistor is inserted into the output line of the DC stabilized power supply, the error voltage of the voltage across the resistor from the reference voltage is detected, and the output current of the DC stabilized power supply is controlled using the error voltage. In the overcurrent protection circuit of the power supply device, first and second error voltage detectors are provided to detect the error voltage, and the voltage detected by the resistor is input to the first error voltage detector. The detected voltage is divided and inputted to the second error voltage detector, and the detected voltage is input to the second error voltage detector.
The output side of the error voltage detector is equipped with a circuit that blocks its output for a certain period of time, thereby allowing large current output for only the certain period of time while providing overcurrent protection. Current protection circuit.