JPH03186908A - Switching power source - Google Patents

Abstract

PURPOSE:To protect a load-side by fluctuating the value of an overcurrent point in accordance with the fluctuation of the load-side and stopping the switching operation of a switching means when the value of a current which a smoothing means outputs reaches the value of the overcurrent point. CONSTITUTION:When the value of a load current I0 exceeds the value of a rated current on the load-side, an output lack voltage detection circuit 3 detects it and the output of a comparator IC 3 is set to 'low', whereby the operation of a transistor Q2 is stopped. Thus, the operation of a switching transistor Q1 is stopped. When the value of a load current I0 exceeds the overcurrent point Va, the output of the comparator IC 3 is set to 'low' and the operation of the switching transistor Q1 is stopped by an output from an amplifier IC 4. Thus, an overcurrent can securely be detected at the time of shorting in a load-side terminal and the load-side can be protected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a switching power supply employed in office automation equipment.

(Prior Art) In recent years, switching power supplies that meet the needs of office automation equipment and the like, which have advantages such as small size and light weight, have come to occupy the mainstream of these electronic devices.

FIG. 3 shows an example of such a switching power supply, which is composed of a power supply circuit 1, a voltage control circuit 2, an output undervoltage detection circuit 3, and an overcurrent detection circuit 4.

Then, the power supplied from the DC voltage source E1 is turned on and off by the switching transistor Q1, and then supplied to the primary coil of the transformer TI.

The intermittent operation of the switching transistor Ql at this time is controlled by the voltage control circuit 2.

That is, the load current 1o is monitored, and the voltage applied to the base of the switching transistor Q1 is controlled via the transistor Q2 so that the value of the load current 1o does not exceed the rated current value.

- Is the power supplied to the next coil transformed by transformer TI and rectifier diode CI? I, negative after rectification by CR2 and smoothing by a smoothing circuit consisting of choke coil Ll and smoothing capacitor CI? It is output to the IIT side.

At this time, the load current output to the negative -1j side is 10
It is.

However, if the value of the negative current 1o exceeds the rated current value of the negative (+) I side, the output undervoltage detection circuit 3 detects it and sets the output of the comparator IC3 to "Low". By stopping the operation of the transistor Q2, the operation of the switching transistor Q1 is stopped.

In addition, if the value of the current 1o exceeds the overcurrent J,1, the output from the amplifier IC4 sets the output of the comparator IC3 to "1,ow" in the same way as in item 1 above, and the switching transistor Ql The operation of J1 is stopped.

By the way, in a switching power supply with such a configuration, the above-mentioned overcurrent point is generally set higher than the rated current value, so even if a current occurs at the terminal on the negative t;i side, the overcurrent Unless a current that exceeds the point flows, overcurrent cannot be detected.

In other words, when negative -11 current 1o is supplied to the load side at an extremely small value compared to the rated current, negative 11i? A short circuit may occur at the side terminal, so that even if a short circuit current flows, it may not exceed the value of the short circuit current or the value of the overcurrent point.

Therefore, if such a situation occurs, not only will it be impossible to detect the overcurrent, but the electronic components and the like that make up the circuit on the negative 61f side will be destroyed.

(Problem to be solved by the invention) In this way, in the conventional dual switching source,
In particular, when the load current io is converted to the rated current and is supplied to the load side at an extremely small value, a short circuit occurs at the end of the load side, resulting in a short circuit 71? Even if current flows, it may not exceed the value of the short circuit current or the value of the overcurrent point.

Therefore, if such a situation occurs, not only will it be impossible to detect the overcurrent, but the electronic components forming the negative 41 (+111 circuit) will be destroyed.

The present invention is like this! The purpose is to provide an overcurrent detection circuit that can reliably detect overcurrent and protect the load side even in the event of a short circuit at the negative 6:J side terminal. shall be.

[Structure of the Invention] (One Stage for Solving the Problems) In order to achieve the objective ``L'', the overcurrent detection circuit of the present invention includes a switching means for intermittent input voltage, and a switching means for intermittent input voltage. a smoothing means for smoothing the voltage transformed by the transforming means and outputting it to the load side; and a smoothing means for changing the value of the overcurrent point according to fluctuations on the load side. and control means for controlling the switching means to stop the switching operation when the value of the current outputted by the controller reaches the overcurrent point value.

(Function) In the overcurrent detection circuit of the present invention, when the switching means intermittents the input voltage, the sudden pressure means transforms the f voltage interrupted by the switching means, and further transforms the voltage transformed by the smoothing means or the sudden pressure means. is smoothed and output to the load side.

At this time, if a current exceeding the overcurrent point value is attempted to be output to the load side due to fluctuations on the load side, the control means changes the overcurrent point value according to the fluctuations on the load side. - The switching operation of the switching means is stopped when the value of the current output by the doping stage reaches the overcurrent point value.

Therefore, since the value of the overcurrent point is varied in accordance with load fluctuations, overcurrent can be reliably detected even when a short circuit occurs at the end of the load at a light load.

(Example) Hereinafter, details of an example of the present invention will be described based on the drawings.

FIG. 1 shows a switching power supply showing an embodiment of the present invention.

As shown in the figure, the switching power supply includes a power supply circuit 1,
It is composed of a voltage control circuit 2, an output undervoltage detection circuit 3, and an overcurrent detection circuit 4A.

The four power supply circuits 1 include a DC voltage source Ct (jt), a transformer Tl that transforms the supplied energy and transmits it to the secondary side,
l-A switching transistor Q1 and a transformer T which intermittent the energy supplied to the primary coil of the lance T1.
Rectifier diode CI to rectify the 7G pressure generated in the secondary coil of 1? l, CI? 2, choke coil, 1
A smoothing circuit including a smoothing capacitor C1 is provided.

Voltage control] 111 path 2 includes an amplifier 3: ICI, which is connected to the secondary output end side of power supply 4 paths through a resistor 171.
Amplification 9: A comparator IC3 is connected to the output side of the ICI via a diode CR3, and a transformer connected to the output side of the comparator I03 is connected to the output side of the ICI. Intermittent!・Langister Q
2 are provided.

Output undervoltage detection []l[path 3 has power supply inlet path 1. A comparator I02 is connected to the secondary output side of the comparator IC2, and the output side of the comparator IC2 is connected between the output side of the comparator I03 and the base side of the transistor Q2.

The overcurrent detection circuit 4A includes a transformer T3 provided on the primary side of the power supply circuit 1, and a diode C1 connected to the transformer T3.
? A non-inverting input voltage (+) is connected to the non-inverting input voltage (+) through the resistor 1?51?6, which is connected to the inverting input voltage (=) of the widening device IC4 and divides the reference voltage Vz4, and a load. A capacitor C2 that holds the voltage before the fluctuation in the fluctuation 11S,
Diode CI that lowers the overcurrent point Va when the load current io is smaller than the rated current value on the load side? 6, and the output side of this 1-radiator 1c4 is a diode C1?
4 between the amplifier IC+ and the comparator 103.

The overcurrent detection circuit 4 having such a configuration operates as follows.

First, the voltage control circuit 2 controls the intermittent operation of the switching transistor Q1, thereby outputting a negative 6:f current 1o.

Then, the power supplied from the DC voltage source is turned on and off by the switching transistor Q1, and then is fed to the primary coil of the transformer T1.

The intermittent operation of the switching transistor Q1 at this time is controlled by the voltage control circuit 2.

That is, the load current IQ is monitored, and the voltage applied to the terminal of the switching transistor Q1 is controlled via the transistor Q2 so that the load current IQ does not exceed the zero value or the rated current value.

-The power supplied to the next coil is transformed by a transformer ]'l and rectifier diode CI? I, CI? 2 and smoothed by a smoothing circuit consisting of a choke coil Ll and a smoothing capacitor CI, and then output to the negative '67f side.

The load current output to the load side at this time is IQ.

However, if the load current exceeds the value of 0 or the value of the rated current on the negative 61f side, the output undervoltage detection circuit 3 detects it and sets the output of the comparator 1c3 to "1., o v By stopping the operation of the transistor Q2, the operation of the switching transistor Ql is stopped.

In addition, when the value of the negative 6:f current 1o exceeds the overcurrent point Va, the output of the comparator IC3 is set to "Low" by the output from the seven-stage amplifier IC4, and the operation of the switching transistor Ql is stopped. let

At this time, the maximum value of the overcurrent point Va is determined by dividing the reference voltage Vz4 by a resistor of 1 to 5.17 [i]. Also, at this time, due to short-term load changes,
The state before the fluctuation is maintained by the capacitor C2.

In other words, when the load current is supplied to the load side at a small value relative to 1o or a constant 1% to 1% current, the voltage generated at the resistor R7 is lowered by the current I/transformer T3 and the resistor 1 to 4. Therefore, the overcurrent point V
The value of a decreases.

On the other hand, when the negative dl current 1o exceeds the rated current, the resistance 1?
The voltage generated at 7 also increases, and this voltage or overcurrent point Va
When approaching the value of , the diode CI? [i is no longer conductive.

Therefore, when the voltage generated across the resistors 1 to 7 reaches the value of the overcurrent point Va, the output of the comparator 1c3 becomes ``Low'' due to the output from the amplifier IC4, and this causes switching. The operation of transistor Q1 stops.

In this way, in this embodiment, the overcurrent point Va
Since the value of is varied, overcurrent can be reliably detected even if a short circuit occurs at the end of the load side during light load.

FIG. 2 shows another example of a large cell in which the configuration of the overcurrent detection circuit 4A of the switching power supply shown in FIG. 1 is changed. Note that parts common to those in FIG. 1 are denoted by the same reference numerals and redundant explanations will be omitted.

That is, the configuration of the overcurrent detection circuit 4B in this embodiment is such that there is a resistor 1 on the non-inverting input voltage (+) side of the amplifier 1c4.
1 (9 width device IC5
is connected, and the current Is flowing through the secondary side of the power supply circuit 1 is manually applied to the inverting input voltage (-) side of this one-slot extractor 1c5.

When the current 1s flowing through the secondary side exceeds the rated current, the voltage generated across the resistor R7 also increases, and when this voltage approaches the value of the overcurrent point Va, the diode 1 CI? fi or no longer conductive.

Furthermore, (when the voltage generated in the civil resistor R7 reaches the value of the overcurrent point Va), the output of the comparator I03 becomes "1.OW" due to the output from the t19 amplifier IC4, as shown in a double series. As a result, the operation of the switching transistor Q1 is stopped I'.

Therefore, in this embodiment, the current flowing through the secondary side is 1
It is possible to reliably detect overcurrent based on s.

[Effects of the Invention] As described above, according to the switching power supply of the present invention, it is possible to reliably detect overcurrent even when the terminal on the load side is running, and to protect the negative 6f side.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing one embodiment of the switching power supply of the present invention, Fig. 2 is a circuit diagram showing another embodiment in which the configuration of the overcurrent detection circuit of Fig. 1 is changed, and Fig. 3 is a circuit diagram showing an embodiment of the switching power supply of the present invention. FIG. 2 is a circuit diagram showing a switching power supply. 1... Power supply circuit, 2... Voltage Fll11 # circuit,
3... Output lower] 2 Constant voltage detection l! il path, 4A, 4B... Overcurrent detection port path, TI, 1'2. T3...Trans, Ql,
Q2...transistor, ICI, lc4...amplifier, lc2, IC3/comparator, CRI-CR8/
...Diode, Va...Overcurrent point.

Claims (1)

[Claims] (1) A switching means for intermittent input voltage, a transformation means for transforming the voltage intermittent by the switching means, a smoothing means for smoothing the voltage transformed by the transformation means and outputting it to the load side, and the load. control so as to vary the value of the overcurrent point in accordance with fluctuations in the side, and to stop the switching operation of the switching means when the value of the current output by the smoothing means reaches the value of the overcurrent point. A switching power supply characterized by comprising a control means for controlling.