JPH10201235A - Power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply circuit which can output a constant DC voltage regardless of its AC input level. SOLUTION: A power supply circuit is provided with a voltage sensing means R1, R2 for dividing and sensing the output voltage obtained from the rectifying of a commercial power supply voltage by a full-wave diode bridge 2 via a line filter 1, a comparing means 3 for comparing the divided and sensed voltage with a reference voltage Vref, and a switching element 4 connected in series between one terminal of the DC side of the diode bridge 2 and one terminal of a smoothing capacitor 5. The switching element 4 is closed or opened by the comparison output of the comparator 3 to control the duty cycle of the power supply circuit based on its AC input level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply circuit.

[0002]

2. Description of the Related Art A rectifier circuit of a commercial AC power supply of a conventional general switching power supply uses a capacitor input type rectifier circuit as shown in FIG. In the figure, a commercial AC power supply is applied to an AC input terminal of a bridge diode 21 via an AC line filter 20, and after double-wave rectification, smoothed by a capacitor C0 and converted into a DC voltage.

[0003] This type of small AC adapter type switching power supply has a rectification type AC-DC conversion circuit at the subsequent stage.
A switching power supply such as DC-DC is combined to step up / down to a required constant voltage to supply various power supplies, from a tracking type capable of multiple DC outputs, to an AC-DC conversion circuit part For electronic equipment with a built-in DC-DC power supply, it can handle AC input of 100V, 120V, 240V, and can be used in Japan, the United States, Europe, etc. There is a small power supply.

Conventionally, such a switching power supply always has an overcurrent protection function for the purpose of protecting the element against an overload in which the output terminal is short-circuited or exceeds a normal use state of the power supply. It has been incorporated.

However, in a miniaturized power supply device such as an AC adapter, even if the load current is equal to or less than the critical current value at which the overcurrent protection function is started, if the power supply device is continuously used, the power supply device, especially the power semiconductor, There is a risk that the temperature of the winding parts such as the transformer exceeds the rated temperature of the parts, and an overcurrent due to an abnormal temperature rise flows to cause element destruction. As means for avoiding such a risk, an abnormal temperature rise protection circuit as shown in FIG. 16 has been conventionally proposed. In addition,
The switching control operation by the switching FET Q3, the current detection resistor R11, the comparator 101, the latch circuit 102, the oscillation control circuit 103, and the like is not needed now, so the explanation is omitted, and only the necessary protection operation at abnormal temperature rise is explained. I do.

[0006] SCR1 in FIG. 16 is a thyristor.
The resistor R26 and the transistor Q26 are connected to the gate of CR1, and a voltage obtained by dividing the voltage of the constant voltage source Vref4 by the NTC thermistor TH2 and the resistor R27 is applied to the base of Q26. The NTC thermistor TH2 is a resistor having a negative temperature coefficient, and the resistance decreases when the temperature of the thermistor TH2 rises. Accordingly, the transistor Q26 obtained by dividing the constant voltage Vref4 by the thermistor TH2 and the resistor R27.
The voltage applied to the base of the thyristor SCR1 rises as the temperature rises, and when the temperature further rises, the transistor Q26 turns on to supply a trigger current to the gate of the thyristor SCR1. Then, the thyristor SCR1 turns on and the MOS-FET Q3
Is kept at a low level, Q3 turns off, and the switching operation of the power supply stops.

Here, if the divided voltage of Vref4 is, for example, T
By setting the resistance of the resistor R27 and the resistance of the thermistor TH2 so that the voltage for turning on the transistor Q26 when the temperature of H2 reaches 100 ° C. or more, even if the switching power supply is used under continuous overload, the thermistor When the temperature of TH2 reaches 100 ° C., the switching operation stops, and the operation cannot be restored unless the supply of the input voltage is stopped. Thus, the destruction of the constituent elements is prevented by the abnormal temperature rise protection circuit.

[0008]

However, in the conventional example described above, the rectifier circuit of FIG. 15 realizes a rectifier circuit of a commercial AC power supply with a simple structure including the bridge diode 21 and the capacitor C0. In the input type rectifier circuit, the rectified DC voltage is substantially equal to the peak value of the input AC voltage. That is, the rectified DC voltage is about 140 V when AC 100 V is input.

By the way, the switching power supply device is required to be designed to have a wide rated input voltage range from the viewpoint of being compatible with countries around the world. For example, when the destination is common to Japan / North America, the design is performed such that the input voltage range is from AC100V-15% to AC120V + 10%. In this case, the rectification D in the conventional capacitor input type rectifier circuit
The C voltage has a fluctuation range of about DC120V to about DC185V.

Therefore, the DC / DC converter circuit operating after these rectifier circuits is provided with the input DC from the rectifier circuit.
To obtain a constant output voltage for the voltage range, and that the overvoltage protection circuit and overcurrent protection circuit operate normally,
It is required to solve the problems such as improving the yield against the variation in parts during mass production, and as a result, there is a problem that expensive and high-precision parts must be used.

A switching power supply provided with a temperature rise protection circuit as shown in FIG. 16 is an effective means from the viewpoint of ensuring the safety of a product. However, a switching power supply generally has an overcurrent protection circuit. If an abnormal temperature rise protection circuit is provided in the power supply separately from these protection circuits, the number of parts related to the protection circuit increases, and the thyristor S
Since expensive parts such as the CR1 and the NTC thermistor TH2 are required, there is a problem that it is difficult to apply the present invention to a power supply device such as an AC adapter that requires a small size and low cost.

Accordingly, it is an object of the present invention to provide a small-sized switching power supply device capable of making a rectified DC voltage value substantially constant irrespective of the level of an input AC voltage, and a DC / DC converter or the like after a rectifier circuit. It is an object of the present invention to provide a power supply device which can easily design a switching power supply circuit and can be used commonly even for products destined for countries or regions having different power supply voltages.

[0013] Further, the protection circuit for guaranteeing safety is also configured to also serve as a protection circuit such as overcurrent protection.
Eliminates the need for extra-temperature protection circuits and minimizes the cost of components while efficiently performing multiple protection operations, such as overcurrent protection and abnormal temperature rise protection, to improve the safety and reliability of the equipment. An object of the present invention is to provide a power supply circuit for enhancing the power supply.

[0014]

In order to achieve the above object, a configuration for realizing the object of the present invention according to the present invention is connected to a commercial power supply and connected via an AC-DC conversion means. A power supply circuit that outputs a DC voltage by controlling the switching means to always output a DC voltage of a constant magnitude regardless of fluctuations in the AC input. .

According to this configuration, the switching duty of the switching means is controlled by the input AC voltage level, and the input A
Regardless of the C voltage level, the AC-DC converted DC voltage can be kept constant.

According to a second aspect of the present invention, in the power supply circuit according to the first aspect, the AC-DC conversion means connects a commercial power supply to a line. A voltage detecting means for detecting a divided voltage of the output voltage which has been subjected to the double-wave rectification by the bridge diode via the filter;
First comparing means for comparing the reference voltage with the detection voltage;
Switching means connected in series between the DC negative terminal of the bridge diode and the smoothing capacitor is opened and closed by the output of the first comparing means to control the DC output voltage to be constant. In the power supply circuit.

According to this configuration, the rectified output is compared with the first reference voltage by the first comparing means, so that the bridge diode is connected between the negative terminal on the DC side of the bridge diode and the smoothing capacitor, that is, on the negative side of the DC output. By controlling the opening and closing of the switch element, a constant DC voltage defined by the first reference voltage can be output regardless of the input AC voltage level.

According to another specific configuration for realizing the object of the invention according to the present application, in the power supply circuit according to the first aspect, the switch element is connected to a DC side of the bridge diode. A power supply circuit is connected in series between a positive terminal and a smoothing capacitor.

According to this configuration, a constant DC voltage can be obtained in the same manner as in the power supply circuit according to the second aspect, and the switch element is connected to the positive side of the output circuit, so that a circuit that can easily handle a positive output is formed. be able to.

Another specific configuration for realizing the object of the invention according to the present application is the power supply circuit according to the second aspect, wherein the voltage detection circuit includes a voltage dividing resistor. A first comparator using a PNP transistor for comparing a first reference voltage generated by a reference voltage generation circuit with a detection voltage of the voltage detection circuit, and a MOS-FE as a switch element.
T and the output of the comparison circuit is used to
And a switching circuit that controls opening and closing of the power supply circuit.

According to this structure, the DC voltage detected by the voltage dividing resistor and the generated first reference voltage are compared by the comparator, and the MOS-FE of the switch element is output by the comparison output.
Since the switching of T is controlled, a constant DC voltage defined by the generated first reference voltage can be output regardless of the input AC voltage level.

According to another specific configuration for realizing the object of the invention according to the present application, in the power supply circuit according to the second or third aspect, the switching element of the switching means is a MOS element. -A power supply circuit characterized by comprising an FET.

According to this configuration, the gate of the MOS-FET can be efficiently opened and closed by the output voltage of the comparing means.

According to another specific configuration for realizing the object of the invention according to the present application, in the power supply circuit according to the second or third aspect, the voltage detection means includes the bridge. A power supply circuit is characterized in that two or more voltage-dividing resistors are connected between DC output terminals of a diode and a detection voltage is output from a voltage dividing point.

According to this configuration, the DC output voltage of the bridge diode according to the voltage dividing ratio of the voltage dividing resistor can be accurately detected.

According to another specific configuration for realizing the object of the invention according to the present application, as in claim 7, in the power supply circuit according to claim 4, the voltage detection circuit is provided with the bridge diode. In a power supply circuit, two or more voltage dividing resistors are connected between DC output terminals, and a constant voltage diode for limiting an excessive detection voltage is connected in parallel with a voltage dividing output resistor for outputting a detection voltage. .

According to this configuration, the output voltage corresponding to the voltage dividing ratio can be accurately detected, as in the circuit of the sixth aspect.
Unnecessary excessive input can be limited by a constant voltage diode to protect the circuit.

According to another specific configuration for realizing the object of the invention according to the present application, in the power supply circuit according to the second or third aspect, the first comparing means includes A first reference voltage of a certain level is input to an input terminal, and the divided detection voltage is input to a negative input terminal,
The power supply circuit is an operational amplifier-type comparator that conducts a switch element when the detection voltage is smaller than the first reference voltage and the comparison output is at a high level and opens when the comparison output is at a low level.

According to this configuration, by turning on / off the switch element based on the first reference voltage level of the comparator, it is possible to output a constant level DC voltage defined by the first reference voltage. it can.

According to another specific configuration for realizing the object of the invention according to the present application, in the power supply circuit according to the ninth aspect, in the power supply circuit according to the fourth aspect, the first comparator is connected to the bridge diode. A resistor and a constant voltage diode are connected between the DC side output terminals, a capacitor is connected in parallel with the constant voltage diode, and a Zener voltage of the constant voltage diode is connected as a first reference voltage to an emitter of a PNP transistor corresponding to a plus terminal. Then, the divided voltage detection voltage to be compared is connected to the base corresponding to the minus terminal, a resistor is connected between the source of the switching element MOS-FET and the collector of the transistor, and the gate of the MOS-FET is connected to the collector. A comparator configured by a transistor circuit that controls opening and closing of the gate of the MOS-FET by a comparison output. In the power supply circuit.

According to this configuration, the reference voltage generation circuit is constituted by a circuit in which a resistor and a constant voltage diode are connected in series and a capacitor is connected in parallel to the constant voltage diode, and the zener voltage of the constant voltage diode is set to the first voltage. , The detection voltage from the voltage divider circuit is input to the base of the negative terminal to the emitter of the PNP transistor of the plus terminal as the reference voltage of
Since the switching of the S-FET is controlled, a constant DC defined by the emitter reference voltage regardless of the AC input level
Voltage can be output.

Another configuration for realizing the object of the invention according to the present application is as described in claim 10, wherein the peak current value of the primary circuit is converted into a voltage by the detecting means and detected, and the peak current value is detected by the second comparing means. In a switching type power supply circuit in which an output current is limited by an overcurrent limiting unit based on an output compared with a reference level, a second reference voltage of a second comparing unit for operating the overcurrent limiting unit is set to an internal temperature of the power supply device. And simultaneously performs overcurrent protection and abnormal temperature rise protection for the power supply device based on the second variable reference voltage set by the reference voltage variable setting means. The power supply circuit is characterized by having a multi-abnormality protection means capable of performing the operation.

According to this configuration, when the internal temperature is high, the second
Lowering the reference voltage value of the power supply device, and increasing the second reference voltage value if the internal temperature is low.
The abnormal protection control is performed by varying the reference voltage of the overcurrent protection device so that the current value at which the overcurrent limiter operates varies according to the internal temperature, so the same protection mechanism simultaneously performs overcurrent protection and abnormal temperature rise protection. can do.

A specific configuration for realizing the object of the invention according to the present application is as follows: in the power supply circuit according to claim 10, a primary winding of a step-up transformer for boosting a DC power supply. A switch element connected to the line, a current detection resistor connected in series to the primary side circuit for detecting a signal for overcurrent protection as a voltage between both ends, a level of the detection signal for overcurrent protection, A second comparator for comparing the second reference voltage, and a reference voltage variable for variably setting the second reference voltage of the second comparator using a circuit element having a negative temperature coefficient and following a temperature rise of the power supply device. The second current while variably reducing the peak current value of the circuit and the primary circuit at which the overcurrent protection operation starts following the set value of the reference voltage variable circuit which is variable in response to the temperature rise of the power supply device. In the comparator, the peak current value is The output when exceeding the constant reference value held in the latch circuit stops the switching operation, in the power supply circuit, characterized in that it comprises a multi-failure protection circuit to perform overcurrent protection and abnormal temperature protection at the same time.

According to this configuration, the voltage between both ends of the current detecting resistor connected in series with the switch element is detected and compared with the second reference voltage by the comparator. When the detected voltage exceeds the reference voltage, the switch element is detected. The overcurrent protection mechanism that turns off the
Critical current value for turning off the switch element by changing the setting of the second reference voltage so that the second reference voltage of the comparator can be changed to follow the internal temperature using a circuit element having a negative temperature coefficient Is variably reduced in accordance with the rise in internal temperature, and protection control is performed, so that overcurrent protection and abnormal temperature rise protection can be performed simultaneously in the same circuit.

Another specific structure for realizing the object of the present invention according to the present application is as described in claim 12.
Wherein the circuit element having the negative temperature coefficient is a bipolar transistor having a base-emitter ON voltage that varies proportionally with the junction temperature.

According to this configuration, the base-emitter ON voltage of the bipolar transistor, which changes in proportion to the junction temperature, can be directly set as the second variable reference voltage of the comparator.

Another specific structure for realizing the object of the invention according to the present application is as described in claim 13.
Or the power supply circuit according to 12, wherein the reference voltage variable circuit applies a detection signal detected by the current detection resistor between the base and the emitter of the bipolar transistor, and turns on the base and the emitter of the transistor.
The power supply circuit is a bipolar transistor circuit also serving as a comparator for comparing a voltage as a second variable reference voltage.

According to this configuration, the base-emitter ON voltage of the bipolar transistor, which changes in proportion to the junction temperature, is set as the second variable reference voltage.
A comparator that applies a detection signal between the emitters and compares the detection signal with the second variable reference voltage can be configured.

Another specific structure for realizing the object of the present invention according to the present application is as described in claim 14.
Wherein the circuit element having a negative temperature coefficient is a thermistor having a negative temperature coefficient and a resistance value that changes in proportion to an internal temperature.

According to this configuration, it is possible to set the second variable reference voltage that changes according to the temperature change by using the resistance change due to the negative temperature coefficient of the thermistor.

Another specific structure for realizing the object of the present invention according to the present application is as described in claim 15.
Or the power supply circuit according to 14, wherein the reference voltage variable circuit inputs the detection signal to a base of one side transistor of a differential amplifier type comparator configured by two transistors connected via a common emitter resistor, A second reference voltage for comparison applied to the base of one of the transistors is generated as a second reference voltage that is variable following a temperature rise of a power supply device obtained by dividing a constant voltage source by a thermistor and a resistor. And a power supply circuit.

According to this configuration, it is possible to set the second variable reference voltage that follows the internal temperature by dividing the voltage of the constant voltage source by the resistance and the thermistor whose resistance changes with a negative temperature coefficient. .

Another specific configuration for realizing the object of the invention according to the present application is as described in claim 16.
Or, in the power supply circuit according to 11, when the switching operation is stopped by the overcurrent protection and the abnormal temperature protection, perform overcurrent protection having a drooping characteristic of “F”.
The power supply circuit is characterized in that a critical current value at which the overcurrent protection starts is reduced as the internal temperature of the power supply device increases.

According to this configuration, when the overcurrent protection is activated and the operation of the switch element is turned off to cut off the circuit current, a sudden change in current is avoided to form a gently ramp-shaped "F". By cutting off the current, the circuit element can be protected.

[0046]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram of a power supply circuit according to the first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a line filter for removing various noises entering from the outside through a commercial AC power supply line and cutting off noise generated inside the electronic device and radiated to the outside through the power supply line. In many cases, a mutual induction inductor and a capacitor are combined, and a through-type capacitor or the like for blocking high frequency is used as the capacitor. Reference numeral 2 denotes a bridge diode, a rectifying element for arranging four rectifying diodes in each arm to form a bridge, omitting a power transformer, and obtaining a direct current of a double-wave (full-wave) rectified waveform directly from the AC input. It is.

R1 and R2 are voltage-dividing resistors connected between the DC output terminals (indicated by + and-) of the bridge diode 2, and detect the voltage divided at the middle point a as a DC output value. Reference numeral 3 denotes a first comparator of an Op-amp type, which compares the detection voltage from the point a to the-terminal and the Vref of the first reference voltage to the + terminal. Reference numeral 4 denotes a switch element SW1 including a FET, a transistor, and the like connected in series between the DC side-terminal of the bridge diode 2 and the circuit output-. 5 is a smoothing capacitor C1 for averaging the rectified output, and outputs a voltage between both ends.

Next, the operation will be described. The DC voltage that has been double-wave rectified by the bridge diode 2 is divided by a voltage dividing resistor R1.
And R2 are divided by the first comparator (comparator) 3
When the divided voltage at the point a is smaller than the first reference voltage Vref, the comparator output becomes high level, and the switch element SW1 is switched to the first reference voltage Vref. Is made conductive. When the voltage at the point a is higher than the first reference voltage Vref, the comparator output becomes low level, and the switching element SW1 is opened.

FIG. 3 is a waveform diagram of the divided voltage at point a shown in FIG. FIG. 3A shows the case of the maximum of the divided voltage waveform at the point a, and FIG. 3B shows the waveform of the minimum at the point a. 1 reference voltage Vr
In a section smaller than ef, the switch element SW1 is turned on and the voltage of the capacitor C1 becomes Vref × (1 + R1 / R1).
Charged until 2).

When the voltage at the point a is larger than Vref, the switch element SW1 is opened, and the rectified DC voltage across the capacitor C1 is kept constant. Therefore, the capacitor C1
The rectified DC voltage at both ends is Vref × (1 + R1 / R2)
And the first reference voltage Vref is independent of the input voltage.
And the resistances R1 and R2. However, the following conditions must be satisfied when setting the rectified DC voltage.

Vref × (1 + R1 / R2) <Peak value Vpeak (min) of minimum input AC voltage FIG. 4 is a timing chart of opening and closing of the switch element shown in FIG. FIG. 4 shows the voltage waveform after the double-wave rectification by the bridge diode 2, the rectified voltage across the capacitor C1, and
The ON / OFF timing of the switch element SW1 at that time is shown. FIG. 4A shows the timing when the input AC voltage is maximum, and FIG. 4B shows the timing when the input AC voltage is minimum. As can be seen from this timing chart, by controlling the opening / closing duty of the switch element SW1 by the input AC voltage level, the rectified voltage across the capacitor C1 can be kept constant regardless of the AC input.

As described above, according to the present embodiment, AC
Under certain conditions for the voltage Vpeak, a constant DC output determined by the first reference voltage Vref and the voltage dividing resistors R1 and R2 can be obtained regardless of the magnitude of the AC input voltage.

Further, each port of the CPU normally operates in a low active mode, and since the switch element is connected to the negative side of the DC output in this circuit, it is easy to cope with a power supply that requires a negative output of-as an operating voltage.

(Second Embodiment) Next, a second embodiment of the present invention will be described.

FIG. 2 is a configuration diagram of a power supply circuit according to a second embodiment of the present invention. The circuit of FIG. 1 of the previous embodiment;
The configuration different from the circuit shown in FIG.
The only difference is the connection point of 1). In the circuit of FIG. 2, the switch element SW1 is connected in series to the DC terminal + terminal of the bridge diode 2 and the capacitor C1 + terminal. The rest of the configuration is exactly the same as that of the circuit of FIG. 1, and the operation of the circuit is the same as that of the first embodiment, so that the duplicated description will be omitted.

In such a second embodiment,
As in the first embodiment, Vpeak of the AC voltage
Under certain conditions for the value, a constant DC output is obtained.

Further, since the switch element SW1 is connected in series between the + side terminals, it is easy to correspond to a power supply that requires a positive positive output, for example, as a power supply to be supplied to an actuator such as a motor.

(Third Embodiment) Next, a third embodiment of the present invention will be described.

FIG. 5 is a configuration diagram of a power supply circuit according to the third embodiment of the present invention. In the circuit shown in FIG. 5, the voltage dividing resistors R1 and R2 are connected between the DC output terminals of the bridge diode 2, and the constant voltage diode ZD1 is connected in parallel with one of the R2. Connected to the base. In FIG. 1, the comparator constituted by the Op amplifier 3 is constituted by a PNP transistor Q2, R3 and a constant voltage diode ZD2 are connected between the DC output terminals of the bridge diode 2, and a stabilizing capacitor is connected to the constant voltage diode ZD2. C2 is connected in parallel to form a reference voltage generation circuit that uses the Zener voltage of the constant voltage diode ZD2 as a first reference voltage, and is connected to the emitter of Q2.

A resistor R4 is connected between the collector of Q2 and the DC-terminal of the bridge diode 2, and a switching element Q4 is connected in series between the -terminal of the resistor 4 and the -side of the capacitor C1.
As 1, the MOS-FET is connected, and the gate of the MOS-FET is connected to the collector of the transistor Q2. Other configurations are the same as those in FIG.

Next, the operation will be described. The voltage at point a obtained by dividing the rectified output of the bridge diode 2 by R1 and R2 is applied to the base of the transistor Q2. In the constant voltage diode ZD1 connected in parallel with the resistor R2, when the input AC voltage is large, the signal level divided by R1 and R2 also becomes large, and an excessive reverse voltage is applied between the base and the emitter of the transistor Q2 to cause junction breakdown. This is for preventing the occurrence of the voltage, and the voltage at the point a is limited by ZD1.

A first reference voltage equal to the zener voltage of the constant voltage diode ZD2 is generated by a reference voltage generating circuit including the resistor 3, the constant voltage diode ZD2 and the capacitor C2, and applied to the emitter of Q2.

The operation of the PNP transistor Q2 is turned on when the voltage at point a becomes lower than the first reference voltage Vref (emitter potential), as in the timing chart shown in FIG.
Then, when it becomes high, it is turned off and operates as a comparator, and the base operates as a negative terminal and the emitter operates as a positive terminal.

When the transistor Q2 is turned on, a collector current flows through the resistor 4, a voltage of VGS = 1c × R4 is applied between the gate and the source of the switch element MOS-FET, and the MOS-FET is turned on. Also, the transistor Q
When 2 is turned off, the voltage VGS between the gate and the source of the MOS-FET becomes 0, and the MOS-FET is turned off. As a result, the switching duty of the switching element MOS-FET is controlled by the input AC voltage level, and the rectified DC voltage between the capacitors C1 can be kept constant.

As described above, according to the third embodiment,
Under the same conditions as in the first embodiment, a constant DC output can be obtained regardless of the AC input, and the reference voltage generation circuit and the comparator are composed of a single PNP transistor. Thus, the cost of parts can be reduced.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described.

FIG. 6 is a configuration diagram of a power supply circuit according to a fourth embodiment of the present invention. The circuit in FIG. 6 is a power supply circuit that steps up and down the DC-DC voltage of the output DC voltage of the circuits shown in FIGS. 1 to 3 by a flyback converter type switching power supply.

In FIG. 6, Vin is an input DC voltage,
Q3 is a switching element MOS-FET, R10 is a bias resistor for supplying a gate voltage of Q3, T is an insulating transformer of a switching power supply, D1 is a secondary side rectifier diode, C
3 is a secondary side rectifying capacitor, Vo is an output DC voltage, R
11 is a detection resistor for detecting the current of the primary circuit, Vref1
Is a second reference voltage source, which is a second variable reference voltage having a negative temperature coefficient and being variably set following a rise in temperature.

10 is a second comparator for comparing the voltage across R11 with the second reference voltage Vref1, and 11 is the second comparator 1
And a latch circuit 103 for latching and holding the output of 0.
This is an oscillation control circuit that controls ON / OFF of the S-FET. Reference numeral 12 denotes a multi-abnormality protection circuit (multi-abnormality protection means) capable of simultaneously performing overcurrent protection and abnormal temperature rise protection, which will be described in further detail in the fifth and sixth embodiments described later. R11, Vref1, comparator 10, It comprises a latch circuit 11.

FIG. 9 is a timing chart of the multi-failure protection circuit shown in FIG. FIG. 10 is a diagram showing a temperature characteristic of the second reference voltage source shown in FIG. FIG. 11 is a diagram showing the relationship between the operating time and the internal temperature of the power supply circuit shown in FIG. FIG. 12 is an explanatory diagram of the “figure” drooping characteristic of the power supply circuit shown in FIG.

Next, the operation will be described. The switching element Q1 is turned ON / O by the oscillation control circuit 103.
When the switch power supply for flip-flop operates, a triangular wave current flows through the primary circuit, and both ends of the resistor 11 are shown in FIG. 9A at an internal temperature of 25 ° C. and FIG. 9B at an internal temperature of 75 ° C. A detection waveform occurs. This signal is input to the + terminal of the comparator 10. On the other hand, the second reference voltage Vref1 input to the minus terminal of the second comparator 10 is an element having a negative temperature coefficient as shown in FIG. Here, if the second reference voltage when the internal temperature of the power supply device is 25 ° C. is Vref (a), and the second reference voltage when the internal temperature is 75 ° C. is Vref (b), FIG. In the operation waveform at an internal temperature of 25 ° C., the peak value of the detection waveform of R11 is Vref1 (a).
Is exceeded, the output of the comparator 10 becomes high level, and at this timing, the output of the latch circuit 11 is held at high level. When the latch output is high, the MOS-FET of Q3 is turned off and the switching operation stops. At the same time, the rectification stage switch element SW
1 may be turned off by the OFF signal.

The second reference voltage Vref1 is variable depending on the internal temperature, and is equal to the internal temperature of 75 ° C. shown in FIG.
The second reference voltage at the time of Vref1 (b) <Vref1
(A) Therefore, at 75 ° C., the switching operation stops at a lower level (CLM current value) than at 25 ° C.

Next, the relationship between the peak value of the triangular wave current of the primary circuit and the output DC current of the switching power supply will be described. The output current value Io can be expressed by the following equation particularly in the ringing choke converter among the power supply circuits having the configuration as shown in FIG.

Io = １ ／ × Ipp / (Vo / Vin + Ns / Np) (1) where Ipp is the peak current value of the primary side circuit, Ns is the number of turns of the secondary winding of the transformer T, Np Is the number of turns of the primary winding of the transformer T. The internal loss of the power supply is not taken into account. From this relational expression, it can be seen that the output current Io is proportional to the peak current value Ipp of the primary circuit.

FIG. 12 shows the relationship between the output current and the voltage at an internal temperature of 25 ° C. and at a temperature of 75 ° C. based on the above relationship. When the switching operation is stopped by the operation, the overcurrent protection having the drooping characteristic of "F" is provided. In this way, control is performed so as to avoid occurrence of an abnormal surge due to a transient phenomenon. Therefore, in this power supply circuit, FIG.
As shown in FIG. 3, the critical current value (C
The LM current value decreases from the solid line to the dotted line as the internal temperature increases.

As described above, according to the fourth embodiment,
In the power supply device of the present invention, in a use state (maximum rating) in which the electronic device as a load operates normally, the resistance value of the resistor R11 and the second variable reference voltage Vre are set so that the overcurrent protection does not operate.
Set the f1 voltage value and temperature coefficient. If the internal temperature rises abnormally due to continuous use in abnormal operating conditions exceeding the maximum rating, overcurrent protection will be performed without exceeding the maximum operating temperature of the components. In order to operate, the operating point (CLM current value) of the overcurrent protection circuit has a negative temperature characteristic so that it can be variably reduced in accordance with the rise of the internal temperature, so that the overcurrent protection and the abnormal temperature rise protection are performed. It can be implemented simultaneously in the same circuit.

As a result, as shown in the rise characteristic diagram of the internal temperature with respect to the operating time in FIG. 11, the maximum attained temperature (saturation temperature) increases as the load current value actually increases, but there is a certain point. If you operate continuously with the load current value or more,
It was confirmed that the overcurrent protection was activated and the internal temperature was reduced.

(Fifth Embodiment) FIG. 7 shows a fifth embodiment of the present invention.
FIG. 3 is a configuration diagram of a power supply circuit according to the embodiment. FIG. 13 is a diagram illustrating an example of the temperature characteristics of the transistor illustrated in FIG. FIG. 14 is a diagram showing the relationship between the temperature of the transistor shown in FIG. 7 and the CLM current value.

FIG. 7 shows the configuration of the multi-abnormality protection circuit 12. In FIG. 7, Q4 is a bipolar transistor and constitutes a comparator (also a second comparator). Q5, Q
6, R12 and C4 constitute a latch circuit. The base-emitter ON voltage of Q4 is used for the negative temperature coefficient of this circuit.

Next, the operation will be described. The base of the transistor Q4 is set by the triangular wave current flowing through R11.
Voltage VBE = I × R11 is applied between the emitters.
The collector current Ic flows through Q4 according to this voltage. Here, the base-emitter voltage for generating the collector current required to trigger the latch circuits of Q5 and Q6 is VB
If E (on), the peak current Ipp of the primary side circuit
When Ipp> VBE (on) / R11 (2), the latch circuits of Q5 and Q6 operate and the MOS-F
ET switching stops and overcurrent protection is activated. The output current value Io at this time is expressed by equation (1).

It is known that the ON voltage VBE (on) of the bipolar transistor Q4 changes depending on the junction temperature of the transistor, and generally has a temperature characteristic of -2 mV / ° C. This characteristic is the characteristic shown in FIG.
Here, the ON voltage at 25 ° C. is 0.7 V.
That is, the second reference voltage Vr of Q4 operating as a comparator
ef is the base-emitter ON voltage, and the second reference voltage is variably set in accordance with the rise of the internal temperature. As a result, the CLM current value for which the overcurrent protection is performed decreases as the internal temperature increases.

FIG. 14 shows, as a result, an example in which the relationship between the CLM current value and the internal temperature obtained by the circuit shown in FIG. 2 also shows how the error between the plots is small.

According to the fifth embodiment,
The configuration is such that the overcurrent protection and the abnormal temperature rise protection can be simultaneously performed by setting the second variable reference voltage and using the comparator with a simple transistor circuit, so that the same abnormal protection as that of the fourth embodiment is performed. The effect can be maintained, and the number of parts can be significantly reduced and the cost can be reduced.

(Sixth Embodiment) FIG. 8 shows a sixth embodiment of the present invention.
FIG. 3 is a configuration diagram of a power supply circuit according to the embodiment. FIG. 8 is also an example of the multi-error protection circuit 12, and the transistor Q
4, a differential amplifier type comparator (second) constituted by Q7 and a common emitter resistor R13, and a constant voltage source Vref5 are divided by a resistor R14 and an NTC thermistor TH1, and the temperature is increased by a negative temperature characteristic. A circuit for generating a second variable reference voltage Vref1 to be variably followed and applied to the base of Q7, transistors Q5 and 6 and resistor R12 and capacitor C
The multi-failure protection circuit 12 is constituted by the latch circuit 4.

Next, the operation will be described. A voltage is applied between the base and the emitter by a triangular wave current flowing through R11 to one transistor Q4 of the differential amplifier, and Vref1 that changes according to the internal temperature is applied to the other transistor Q7 by a thermistor TH1.
And the input of Q7 is the comparator output. Now Vre
When the detection input to Q4 becomes larger than f1, the comparison output becomes high, and is held by the latch circuits of Q5 and 6 to turn off the switching of the switching element Q3. Temperature rise protection can be implemented simultaneously.

As described above, according to the sixth embodiment,
By setting Vref1 to maintain the same abnormality protection effect as that of the fourth embodiment and accurately follow the internal temperature, overcurrent protection that more accurately follows the internal temperature rise becomes possible.

(Other Embodiments) In the present invention, a power supply circuit using a combination of a bridge diode rectifier circuit that does not use a power transformer and a flyback type DC-DC converter has been described. The rectifier circuit is a rectifier circuit using a transformer, a rectifier element using various rectifiers such as a thyristor in addition to a diode as the rectifier element. Of course, all rectification methods such as those of the other methods are included.

Further, in the present invention, a flyback type DC-DC converter is taken as an example of the switching power supply circuit of the subsequent stage, but other types of DC-DC converters such as a ringing choke type and a dual type are also included. Needless to say, the present invention can be applied to all switching power supplies such as various switching regulators, up converters, down converters, tracking regulators, etc., which are other switching power supplies. It goes without saying that various combinations with the above-described various rectifiers are possible, and the case where a battery is used for the input DC power supply is also within the applicable range.

Also, as for the housing, when only the rectification stage in the form of an AC adapter and a single housing type is used, or when the housing includes a switching power supply adapted to the required DC voltage on the device side, the rectifier and the switching power supply unit are connected. It can be applied to any variation of power supply circuit, such as when housing each separately, when rectifying unit and switching power supply circuit are built in the device, when rectifying unit uses AC adapter to incorporate switching power supply circuit into the device, etc. Of course, it is.

[0091]

As described above, according to the first to ninth aspects of the present invention, the first comparison circuit compares the rectified output of the rectifier circuit using the bridge diode with the set first reference voltage. And a switch element for averaging the DC output by opening and closing control by the output of the comparator,
The rectified DC voltage value can be made substantially constant regardless of the input AC voltage level, and the DC-D
This makes it easy to design a switching power supply circuit such as a C converter, and can be used commonly for products destined for countries or regions with different power supply voltages.

According to the tenth to sixteenth aspects of the present invention, in order to ensure the safety of the switching power supply circuit,
The detection voltage at both ends of the current detection resistor of the next circuit is compared with the reference value, and when the detection voltage exceeds the reference value, the switch element is turned off.
F to variably set a second reference voltage set in the second comparator of the overcurrent protection circuit that stops the switching operation by following a rise in internal temperature using a circuit element having a negative temperature characteristic; A multi-failure protection circuit is provided to control the CLM current value that activates the overcurrent protection so as to decrease as the internal temperature rises. The overcurrent protection and the abnormal temperature rise protection are simultaneously and efficiently performed by a simple circuit configuration while minimizing the component cost without providing the components, thereby improving the safety and reliability of the device.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a power supply circuit according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a power supply circuit according to a second embodiment of the present invention.

FIG. 3 is a waveform diagram of a divided voltage at point a shown in FIG.

4 is an opening / closing timing chart of the switch element shown in FIG.

FIG. 5 is a configuration diagram of a power supply circuit according to a third embodiment of the present invention.

FIG. 6 is a configuration diagram of a power supply circuit according to a fourth embodiment of the present invention.

FIG. 7 is a configuration diagram of a power supply circuit according to a fifth embodiment of the present invention.

FIG. 8 is a configuration diagram of a power supply circuit according to a sixth embodiment of the present invention.

FIG. 9 is a timing chart of the multi-error protection circuit shown in FIG. 6;

10 is a diagram showing a temperature characteristic of the reference voltage source shown in FIG.

11 is a diagram showing a relationship between an operation time and an internal temperature of the power supply circuit shown in FIG.

FIG. 12 is an explanatory diagram of a “figure shape” drooping characteristic of the power supply circuit shown in FIG. 6;

13 illustrates an example of a temperature characteristic of the transistor illustrated in FIG. 7;

FIG. 14 is a diagram showing a relationship between the temperature of the transistor shown in FIG. 7 and a CLM current value.

FIG. 15 is a configuration diagram of a conventional rectifier circuit.

FIG. 16 is a configuration diagram of a conventional abnormal temperature rise protection circuit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 line filter 2 bridge diode 3 first comparator 4 switch element SW1 5 smoothing capacitor C1 10 second comparator 11 latch circuit 12 multi-error protection circuit Q1, Q3 switch element MOS-FET R1, R2 voltage dividing resistor R11 detection resistor Vref Reference voltage Vref1 Variable reference voltage

Claims (16)

[Claims] 1. A power supply circuit connected to a commercial power supply and outputting a DC voltage via an AC-DC conversion means, wherein a switching means is controlled to always output a DC voltage of a constant magnitude irrespective of AC input fluctuations. A power supply circuit, comprising: 2. The power supply circuit according to claim 1, wherein the AC-DC converter includes a voltage detector that detects an output voltage obtained by performing a double-wave rectification of a commercial power supply with a bridge diode via a line filter; A first comparing means for comparing the reference voltage with the detected voltage, and a switch element connected in series between the DC negative terminal of the bridge diode and the smoothing capacitor, which is opened and closed by the output of the first comparing means. A power supply circuit comprising switching means for controlling an output voltage to be constant. 3. The power supply circuit according to claim 1, wherein the AC-DC conversion means includes a voltage detection means for detecting a divided voltage of an output voltage obtained by dual-wave rectifying a commercial power supply with a bridge diode via a line filter; And a first comparing means for comparing the reference voltage with the detection voltage, and the switch element is connected in series between a DC-side positive terminal of the bridge diode and a smoothing capacitor. 4. The power supply circuit according to claim 2, wherein a PNP transistor that compares a voltage detection circuit formed by a voltage dividing resistor with a first reference voltage generated by a reference voltage generation circuit and a detection voltage of the voltage detection circuit. A power supply circuit, comprising: a first comparator using a MOS-FET as a switch element; and switching means for controlling opening and closing of the MOS-FET by an output of the first comparison circuit. 5. The power supply circuit according to claim 2, wherein the switching element of the switching means is a MOS-F.
A power supply circuit comprising ET. 6. The power supply circuit according to claim 2, wherein the voltage detecting means connects two or more voltage dividing resistors between the DC output terminals of the bridge diode and outputs a detection voltage from a voltage dividing point. A power supply circuit characterized by: 7. The power supply circuit according to claim 4, wherein the voltage detection circuit is connected to two or more voltage dividing resistors between the DC output terminals of the bridge diode and outputs a detection voltage. A power supply circuit in which a constant voltage diode for limiting an excessive detection output is connected in parallel. 8. The power supply circuit according to claim 2, wherein said first comparing means includes a first input voltage having a constant level applied to a positive input terminal and a divided voltage applied to a negative input terminal. A comparator circuit of an operational amplifier type that inputs a switching element when the detection voltage is lower than the first reference voltage and the comparison output is at a high level, and opens when the comparison element is at a low level. . 9. The power supply circuit according to claim 4, wherein the first comparator connects a resistor and a constant voltage diode between the DC side output terminals of the bridge diode, and further connects a capacitor in parallel with the constant voltage diode. As a result, the Zener voltage of the constant voltage diode is connected as a first reference voltage to the emitter of the PNP transistor corresponding to the plus terminal, and the divided voltage detection voltage to be compared is set to the PN corresponding to the minus terminal.
Connected to the base of a P-transistor, the MOS-FET
A resistor is connected between the source of the MOS-FET and the collector of the transistor, and the gate of the MOS-FET is connected to the collector, and a comparator circuit is used to control the opening and closing of the gate of the MOS-FET by a comparison output. A power supply circuit, characterized in that: 10. A peak current value of a primary circuit is converted into a voltage by a detecting means and detected, and an output current is limited by an overcurrent limiting means based on an output compared with a second reference voltage by a second comparing means. In a switching type power supply circuit, a reference voltage variable setting means for variably generating and setting a second reference voltage of a second comparing means for operating an overcurrent limiting means in accordance with an internal temperature of a power supply device; A power supply circuit comprising: a multi-abnormality protection unit capable of simultaneously executing overcurrent protection and abnormal temperature rise protection of a power supply device based on a second variable reference voltage set by a variable setting unit. 11. The power supply circuit according to claim 10, wherein
A switching element connected to the primary winding of the step-up transformer for boosting the DC power supply; a current detecting resistor connected in series to the primary winding to detect a signal for overcurrent protection as a voltage across both ends; A second comparator for comparing a level of the detection signal for overcurrent protection with a second reference voltage, and a second comparator for following a temperature rise of the power supply device by using a circuit element having a negative temperature coefficient. A reference voltage variable circuit for variably setting a second reference voltage of the power supply, and a reference voltage variable circuit for varying a peak current value of a primary circuit in which an overcurrent protection operation is started in response to a temperature rise of a power supply device. The output when the peak current value exceeds the set reference value in the second comparator is held by a latch circuit to stop the switching operation while variably reducing the current value according to the set value, and the switching operation is stopped. Run protection simultaneously Power supply circuit, characterized in that it comprises a multi-failure protection circuit. 12. The power supply circuit according to claim 11,
The power supply circuit according to claim 1, wherein the circuit element having the negative temperature coefficient is a bipolar transistor having a base-emitter ON voltage that changes in proportion to a junction temperature. 13. The power supply circuit according to claim 11, wherein said reference voltage variable circuit applies a detection signal detected by said current detection resistor between a base and an emitter of said bipolar transistor, and wherein said transistor is a transistor. A bipolar transistor circuit which also serves as a comparator for comparing the base-emitter ON voltage as a second variable reference voltage. 14. The power supply circuit according to claim 11, wherein
The power supply circuit, wherein the circuit element having a negative temperature coefficient is a thermistor having a negative temperature coefficient and a resistance value that changes in proportion to an internal temperature. 15. The power supply circuit according to claim 11, wherein said reference voltage variable circuit is provided at a base of a one-side transistor of a differential amplifier type comparator composed of two transistors connected via a common emitter resistor. The detection signal is input, and a second reference voltage for comparison applied to the base of one of the transistors is made variable by following a temperature rise of a power supply device obtained by dividing a constant voltage source by a thermistor and a resistor. A power supply circuit, which is a circuit that generates a second reference voltage. 16. The power supply circuit according to claim 10, wherein when the switching operation is stopped by the overcurrent protection and the abnormal temperature protection, the overcurrent protection having a drooping characteristic of “F” is performed. A power supply circuit characterized in that a peak critical current value at which overcurrent protection starts is reduced as the internal temperature of the power supply device rises.