JP2004007939A - Switching power source having output short-circuit protective circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an element for constituting a switching power source from burning out at the time of load short-circuit. <P>SOLUTION: The switching power source includes a DC switching element between an output terminal of a rectifying and smoothing circuit and an output terminal connected to the load. The switching power source also includes a second diode for connecting an input side or an output terminal of the rectifying and smoothing circuit to a control element of the switching element for controlling the operation of the DC switching element to forward bias, and a third diode for conducting the output terminal of the rectifying and smoothing circuit to the output terminal to connect the output terminal of the circuit to the output terminal. If a short-circuit state of the load is released, the DC switching element returns to the normal operation making it turn on. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a circuit configuration of a switching power supply, and more particularly to an automatic return switching power supply having a circuit protection function at the time of a load short circuit and capable of automatically returning.
[0002]
[Prior art]
The circuit shown in FIG. 3 is often used as a step-up switching power supply. This voltage induced in the inductance element L ₀ is rectified by the diode D ₀ by off of the main switching element Q _0, is intended to obtain a DC output is smoothed by the capacitor C _2. Such a switching power supply is often used because it can provide a boosting function with a simple configuration and can be reduced in cost.
[0003]
However, since the switching power supply as shown in FIG. 3 does not have the output short-circuit protection function, there is a problem in that if the output is short-circuited, the coil L ₀ , the main switching element Q ₀ , the rectifier diode D _{0 and the} like will be damaged. Occurs. That is, the input _{V IN} terminal → coil _{L 0} in the absence of substantially resistance, a rectifier diode _{D 0,} the flow in the order of the output _{V O} terminal → GND terminal, is Sonsho like coil elements _{L 0} and the rectifier diode _{D 0} There was a possibility.
[0004]
The circuit shown in FIG. 4 is often used as a boost type separately-excited switching power supply. This voltage induced in the inductance element L ₁ is rectified by the diode D ₀ by off of the main switching element Q _0, is intended to obtain a DC output is smoothed by the capacitor C _2.
[0005]
The PWM controller in FIG. 4 has a main function of controlling the switching pulse width so that the output voltage is maintained at a predetermined value even when the input voltage or the load fluctuates. Further, when the output terminal is short-circuited to GND for some reason, it generally has a protection function to protect the switching power supply from burning.
[0006]
However, the operation of the protection function, by 100% Ofudeyutei pulse output signal of the PWM controller is used a method of off the main switching element 100% Deyutei the on-off operation of the Q _0. However, while in the circuit configuration between the indicated such input and output terminals are not insulated in Figure 4 even PWM controller to output a signal of 100% Ofudeyutei, GND terminal V _O from the input terminal V _IN is shorted It becomes.
[0007]
That is, the flow in the order of approximately input in the absence of the resistor V _IN terminal → the coil L ₁ → rectifier diode D _{0 →} output V _O terminal → GND terminal, is Sonsho like coil element L ₁ and the rectifier diode D ₀ And it was not enough as a protection function.
[0008]
[Problems to be solved by the invention]
The present invention provides a switching power supply that prevents a circuit element from burning when a load is short-circuited by adding a function of cutting off a current between input and output terminals when the load is short-circuited. Another object of the present invention is to provide a switching power supply capable of returning to a normal operation when the load short-circuit state is released.
[0009]
[Means for Solving the Problems]
According to the present invention, a DC switch function is added to the output terminal side, and when the load is short-circuited, this DC switch function is operated to cut off between the input and output. When the short-circuit state is released, the cut-off state is changed to the conductive state. By returning, the above problem is solved.
[0010]
That is, in a switching power supply that rectifies and smoothes energy stored in an inductance element by turning on and off a main switching element and obtains a DC output, the output terminal of a regulated input side or a rectifying and smoothing circuit and an output terminal connected to a load. A second diode for providing a positive bias by connecting an output terminal of the rectifying / smoothing circuit to a control terminal of a switching element for controlling the operation of the DC switching element, and an output of the rectifying / smoothing circuit; It is characterized by having a third diode that connects the end and the output terminal by conduction.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
The basic operation of the switching power supply provided with the output short-circuit protection circuit according to the present invention is as follows.
In a normal operation state, a small part of the output current of the rectifying and smoothing circuit is used to generate a bias state that turns on the DC switch element.
Conversely, when a load short circuit occurs, the current from the rectifying and smoothing circuit used to generate a bias state that turns on the DC switch element in a normal operation state generates a bias state that turns off the DC switch element. Can be turned into a current path.
[0012]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention. The circuit from the input terminal _VIN to the connection point to the series resistors R ₅ and R ₆ is the same as the conventional circuit shown in FIG. Connected to the inductance element L main switching element Q ₀ in series with _0, resistance is alternately turned on and the auxiliary transistor connected to the input terminal via the by to obtain the oscillation operation.
[0013]
In the switching power supply according to the present invention, PNP transistor Q ₁ is connected as a direct current switching element and the detection resistor R _s between the output terminal V _O. Between the input V _IN and the transistor Q ₂ base connected through a resistor R ₁ and a diode D _2, the emitter of the transistor Q ₂ is grounded, connected to the base of the transistor Q ₁ through the collector resistor R ₃ Have been. The output terminal _{V O} and the input terminal _{V IN} is connected through a resistor _{R 1} and a diode _{D 1.} Connection point between the emitter of the resistor R _S and the transistor Q ₁ is connected to the base of the transistor Q _3, the emitter of the transistor Q ₃ are the input side of the resistor R _S, the collector is connected to the base of the transistor Q _1.
[0014]
Next, the operation of this circuit will be described.
[0015]
(1) In the initial state, the load is normal and the switching power supply operates normally, but thereafter, the operation input voltage _VIN when the load is short-circuited for some reason is supplied, and the conventional switching power supply unit (see FIG. 2) ) Starts operation, a predetermined output voltage is output to a terminal V ₀ ′ corresponding to a conventional output terminal. On the other _hand, the base of the transistor _{Q 2} by the application of _{V IN R 1,} positive bias current through the diode _{D 2} is the transistor _{Q 2} is turned on to flow into.
[0016]
By on of the transistor Q _2, since the base current path of the transistor Q ₁ is to open, the transistor Q ₁ is also turned on, is approximately equal to a predetermined output voltage V _{O 'is} output to the load side end V _0, the power to the load Is supplied.
[0017]
Thereafter, when the load-side end for any reason is short-circuited, R _1, D ₂ a current which has been flowing into the base of the transistor Q ₂ through not directed to the diode D _2, short-circuited via the diode D ₁ Start to flow into the road. Therefore, the transistor Q ₂ is turned off, since the cut off the base current path of the transistor Q _1, the transistor Q ₁ is turned off. As a result, the existing current path from the input terminal to the output terminal is cut off, so that the elements constituting the switching power supply are prevented from being damaged.
[0018]
(2) Operation when the output terminal is short-circuited from the initial state When the input voltage _VIN is applied, the conventional switching power supply unit shown in FIG. 3 normally starts up, and a predetermined voltage is applied to the terminal V ₀ ′. Output voltage is output. However, the current passing through the resistor R ₁ is again flows into the short-circuit path through the diode D _1, it does not flow to the diode D _2. Therefore, the transistor Q ₂ in the same manner as described above is not turned on, the transistor Q ₁ is also not turned on, the output voltage is cut off by the transistor Q _1. This protects the switching power supply.
[0019]
A short-circuit state is canceled during operation, the current passing through the resistor R ₁ is flowed to the diode D ₁ but not the diode D ₂ starts the same operation as the original (1), the transistor Q ₁ is turned-on by a predetermined An output voltage is obtained. As a result, the switching power supply automatically returns.
[0020]
The resistor R _s and the transistor Q ₃ constituting the constant current power supply can be omitted depending on the specification, and one end of the resistor R ₁ may be connected to the terminal _VO ′ instead of _VIN . Although the above-described example shows a self-excited switching power supply, the present invention can be applied to a separately-excited switching power supply. Further, the I _CEO reduction resistor R _{4 of} the transistor Q ₁ may be omitted depending on the specification.
[0021]
FIG. 2 is a circuit diagram showing another embodiment of the present invention. The circuit from the input side to the connection point to the series resistors R ₁ and R ₂ is the same as the conventional circuit shown in FIG.
[0022]
In the switching power supply according to the present invention, PNP transistor Q ₂ is connected as a direct current switching element between the output terminal V _O. Between the base of the emitter side of the transistor _{Q 3} of the transistor _{Q 2} is connected through the resistor _{R 4} and the diode _{D 3,} the emitter of the transistor _{Q 3} are the input _{V IN,} the transistor Q the collector through a resistor _{R 5 2} is connected to the base.
[0023]
Next, the operation of this circuit will be described.
(1) load is operating transistor to Q ₁ when normal when turned on and off, at both ends of the capacitor C ₂ resistors R _1, R ₂ predetermined DC voltage appears set in. Then, the resistance R _4, positive bias current flows through the diode D ₃ between the base and emitter of the transistor Q _3, between the collector and the emitter of the transistor Q ₃ are turned on. When the transistor Q ₃ is turned on, since the base current path of the transistor Q ₂ is opened, the collector-emitter of the transistor Q ₂ is also turned on, the output terminal V _O a predetermined output voltage is output.
[0024]
(2) Operation when output terminal is short-circuited after operation under normal load state In the above-mentioned normal operation, current flows from resistor R _{4 to} diode D ₃ and transistor Q ₃ is turned on. There When short circuit for some reason, the current passing through the R ₄ is not directed to the diode D _3, so flows into GND via the diode D _2. Therefore, the base-emitter of the transistor Q ₃ are reverse biased by V _IN, the collector-emitter of the transistor Q ₃ are turned off, since the cut off the base current path of the transistor Q _2, the transistor Q ₂ collector-emitter Turn off for a while. As a result, the existing current path from the input terminal to the output terminal is cut off, so that the elements constituting the switching power supply are prevented from burning.
[0025]
(3) Start the transistor Q ₀ is a switching operation by receiving a pulse signal from the operation PWM controller when the left V _IN output is short-circuited is turned on, but appears predetermined output voltage on the capacitor C ₂ the current passing through the resistor _{R 4} is again because the flow into the diode _{D 2} → GND, is blocked similarly output voltage by the transistor _{Q 2} and (2).
[0026]
When the short-circuit condition during operation is released, the resistor R ₄ a current passing through the flow to no diode D ₃ in the diode D ₂ starts the same operation as (1), the transistor Q ₂ is turned on a predetermined output voltage Is obtained.
[0027]
Although the above example shows a separately-excited switching power supply, the present invention can be applied to a self-excited switching power supply. Further, the inductance element may be replaced with a transformer instead of a single-turn coil. Furthermore, the above example the diode D ₃ is not required by the input specification. Incidentally, the insertion position of the diode _{D 3} may be the emitter · GND of the transistor _{Q 3.}
[0028]
【The invention's effect】
According to the present invention, by adding the function of cutting off the current between the input and output terminals when the load is short-circuited, it is possible to prevent the circuit element from burning when the load is short-circuited. Further, when the load short-circuit state is released, the normal operation can be automatically restored, and the power supply does not need to be turned off or turned on again.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an embodiment of the present invention. FIG. 2 is a circuit diagram showing another embodiment of the present invention. FIG. 3 is a circuit diagram showing a conventional switching power supply. FIG. Circuit diagram [Description of symbols]
Q ₀ : Main switching element (transistor)
D ₀ : Rectifying diode C ₂ : Smoothing capacitors Q _{1 to} Q ₃ : Transistors D _{1 to} D ₃ : Diodes R _{1 to} R ₆ : Resistance

Claims (3)

In a switching power supply that rectifies and smoothes energy stored in an inductance element by turning on and off a main switching element to obtain a DC output,
A DC switch element between the output terminal of the rectifying and smoothing circuit and the output terminal connected to the load,
A second diode for connecting the input terminal or the output terminal of the rectifying / smoothing circuit to the control terminal of the switching element for controlling the operation of the DC switch element and positively biasing the output terminal; And a third diode connected by conducting the current. A switching power supply comprising an output short-circuit protection circuit. In a switching power supply that rectifies and smoothes energy stored in an inductance element by turning on and off a main switching element to obtain a DC output,
A DC switch element between the output terminal of the rectifying and smoothing circuit and the output terminal connected to the load,
A second diode for connecting the input terminal or the output terminal of the rectifying / smoothing circuit to the control terminal of the switching element for controlling the operation of the DC switch element and positively biasing the output terminal; And a third diode for conducting and connecting
In a normal state, the switching element is positively biased by the second diode to turn on the DC switching element, and when the load is short-circuited, the third diode rectifies and conducts the output of the smoothing circuit to the output terminal to connect the switching element. Reverse bias to turn off the DC switch element,
A switching power supply comprising an output short-circuit protection circuit. 3. A switching power supply having an output short-circuit protection circuit according to claim 2, wherein when the load short-circuit state is released, the DC switch element is turned on to return to a normal operation.

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