JPH11299223A - Switching power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely prevent overvoltage from being applied to a load, by short- circuiting across terminals and maintaining the short-circuit condition in the case where overvoltage is applied between the terminals. SOLUTION: This switching power unit has a load short circuit detection control circuit 3, which detects a short-circuit between a load overcurrent limiting circuit 2 and a load terminal 6 to interrupt a collector current of a main switching transistor circuit 1 upon load short-circuit, and a Zener diode 8 which absorbs and limits overvoltage applied across a power supply terminal 7 and the load terminal 6. When voltage across the load terminal 6 reaches a Zener voltage value, a resistance value in a yield region inside the Zener diode 8 decreases, so that an over current flows, breaking is instantaneously caused almost without self heating, and a short-circuit condition is generated. In this way, by setting a Zener voltage value of the Zener diode 8 at an overvoltage value or below against a load, applying of the over voltage to the load can be surely avoided.

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, and more particularly, to a switching power supply for protecting a load from overvoltage.

[0002]

2. Description of the Related Art As a conventional switching power supply, there is, for example, one disclosed in Japanese Patent Application No. 8-341536. FIG. 3 is a circuit diagram showing a configuration of the switching power supply device.

As shown in the drawing, this switching power supply device detects a short circuit between a main switching transistor circuit 1, a load excessive current limiting circuit 2, and a load terminal 6, and reduces the collector current of the main switching transistor circuit 1. A load short-circuit detection control circuit 3 for shutting off,
The DC-DC booster circuit includes a pump circuit 4, a three-terminal regulator IC 5, and a power supply terminal 7, and protects the transistors in the main switching transistor circuit 1 from damage due to overcurrent. .

The main switching transistor circuit 1 constitutes a push-pull amplifier circuit including the transistors 11, 12 and the capacitors 15, 16, and the like, and repeats ON / OFF based on an input clock pulse. The anode side of the diode 13 is connected to the base of the transistor 11, and the cathode side of the diode 13 is connected to the power supply terminal 7. The cathode side of the diode 14 is connected to the base of the other transistor 12,
The anode side of the diode 14 is connected to the ground.

The overload current limiting circuit 2 includes a resistor 21,
23, a transistor 22 and the like, the current Ic flowing through the transistor 11 increases,
When the voltage drop at about reaches approximately 0.7 V, a current flows between the collector and the emitter of the transistor 22 and bypasses the base current of the transistor 11.

The load short-circuit detection control circuit 3 is composed of a diode 31 and a resistor 32 whose anode side is connected to the base side of the transistor 22 and whose cathode side is connected to the load terminal 6. ,
12 collector current is cut off.

The power supply terminal 7 is connected to the main switching transistor circuit 1 via the overload current limiting circuit 2 and supplies power required for amplifying a clock pulse input to the main switching transistor circuit 1.

A diode pump circuit 4 and a three-terminal regulator IC 5 are interposed between the load terminal 6 and the amplified output of the main switching transistor circuit 1, so that a DC output voltage approximately twice Vcc is provided. You can get it. This diode pump circuit 4 is a circuit composed of capacitors 41 and 42 and diodes 43 and 44.

Next, the operation of the switching power supply will be described. The collector current of the transistor 11 constituting the main switching transistor circuit 1 increases, and the resistor 2
When the voltage drop due to 1 reaches approximately 0.7 V, a current flows between the collector and the emitter of the transistor 22 and bypasses the base current of the transistor 11. This allows
The collector currents of the transistors 11 and 12 are cut off to protect them from excessive current. On the other hand, if a load short circuit occurs,
Since the cathode side of the diode 31 is grounded,
The diode 31 turns on. Thereby, the collector currents of the transistors 11 and 12 are cut off, and the transistors 11 and 12 are prevented from being damaged.

[0010]

However, according to the conventional switching power supply shown in FIG. 3, when the three-terminal regulator IC 5 is short-circuited between the input and output for some reason, an excessive voltage for the load is applied. There was a problem that it might be done.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a switching power supply that reliably prevents an excessive voltage from being applied to a load.

[0012]

In order to achieve the above object, the present invention, as a first aspect, drives at least one switching element to apply a predetermined voltage between terminals to which a load is connected. In the switching power supply device to be applied, when an overvoltage equal to or greater than a predetermined voltage value is applied between the terminals, an overvoltage protection means for short-circuiting the terminals and maintaining the short-circuit state is provided. A switching power supply device is provided.

According to a second aspect of the present invention, a predetermined signal is input to and driven by at least one switching element to achieve the above object. In a switching power supply device for applying a voltage of over, excessive current limiting means for limiting the amount of current supplied to the switching element to a predetermined current value or less, and an overvoltage of a predetermined voltage value or more is applied between terminals. The present invention provides a switching power supply device characterized by comprising overvoltage protection means for short-circuiting between the terminals in such a case. In the above configuration, when the overvoltage protection unit short-circuits the terminals, it is desirable that the overcurrent limiting unit limits the amount of current supplied to the switching element.

Further, according to a third aspect of the present invention, a predetermined signal is input to at least one switching element to drive the at least one switching element so that a predetermined voltage is applied between terminals to which a load is connected. In a switching power supply device that applies a voltage of not more than a predetermined current value to a switching element, an excessive current cutoff unit that cuts off the supply of current to the switching element, When an overvoltage of
A switching power supply device comprising an overvoltage protection means for short-circuiting between terminals. In the above configuration, when the overvoltage protection unit short-circuits the terminals, it is preferable that the supply of the current to the switching element is cut off by the excessive current cutoff unit.

Further, in order to achieve the above object, according to a fourth aspect of the present invention, by inputting a predetermined signal to at least one switching element and driving the switching element, at least one switching element is connected between terminals to which a load is connected. In a switching power supply for applying a predetermined voltage, an excessive current limiting means for limiting the magnitude of a current supplied to the switching element to a predetermined first current value or less, and a second predetermined current for the switching element. Excessive current interrupting means for interrupting the supply of current to the switching element when a current greater than the current value is supplied, and short-circuiting between the terminals when an overvoltage greater than a predetermined voltage value is applied between the terminals A switching power supply device provided with overvoltage protection means is provided. In the above configuration, when the overvoltage protection means short-circuits the terminals, it is desirable to limit the magnitude of the current supplied to the switching element by the excessive current limiting means, and the overvoltage protection means short-circuits the terminals. In this case, it is desirable that the supply of the current to the switching element be interrupted by the excessive current interrupting means.

In the above second, third or fourth aspect of the present invention, it is desirable that the overvoltage protection means maintain a short-circuit state between the terminals after an overvoltage is applied between the terminals.

Further, in any of the above aspects of the present invention, it is desirable that the overvoltage protection means is a Zener diode.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

[First Embodiment] FIG. 1 is a circuit diagram showing a configuration of a switching power supply according to a first embodiment. 3 are denoted by the same reference numerals as in FIG. 3 and will not be described repeatedly. However, the switching power supply of the first embodiment includes a main switching transistor circuit 1 and a load current. An overload current limiting circuit 2 for detecting an increase and limiting the collector current of the main switching transistor circuit 1; and a circuit for detecting a short circuit between the load terminals 6 and cutting off the collector current of the main switching transistor circuit 1 when the load is shorted. A configuration including a load short-circuit detection control circuit 3, a diode pump circuit 4, a three-terminal regulator IC 5, a power supply terminal 7, and a Zener diode 8 for limiting absorption of an overvoltage applied between the load terminals 6. Has become.

Next, the operation of the switching power supply will be described. Collector current IC corresponding to load current for transistors 11 and 12 of main switching transistor circuit 1
Flows, a voltage drop of IC · Rp occurs in the current detecting resistor 21 (resistance value Rp).

The transistor 2 of the overload current limiting circuit 2
Reference numeral 2 denotes a transistor for detecting this voltage drop. The base-emitter voltage (VB
While E) is less than about 0.7V, the transistor 22
Is off, but when the load current increases and the voltage drop (= IC · Rp) by the resistor 21 reaches approximately 0.7 V or more, the transistor 22 is turned on. As a result, the transistor 22 bypasses the base current of the transistor 11.

In this state, a feedback loop is formed between transistor 11 and transistor 22 to maintain a constant current operation.
The collector current of No. 2 is limited to a constant collector current even if the load current increases, and the collector loss can be suppressed within the rated value.

On the other hand, the load short-circuit detection control circuit 3 connects the anode side of the diode 31 to the base of the transistor 22 and connects the cathode side to the load terminal 6.
A load short circuit is detected. Here, when the switching power supply is operating normally, the diode 3
Since the potential on the cathode side of 1 is sufficiently higher than the potential on the anode side, the diode 31 is off. If a load short circuit occurs in this state, the cathode side of the diode 31 is grounded, and the diode 31 is turned on. Therefore, the transistor 22 is also turned on, and the base current of the transistor 11 is bypassed to the power supply terminal 7 side. As a result, the collector currents of the transistors 11 and 12 are cut off, and the transistors 11 and 12 are prevented from being destroyed. This state is maintained until the load short circuit is released. When the load short circuit is released, the cut-off state of the collector currents of the transistors 11 and 12 is released, and the operation returns to the normal operation.

The Zener diode 8 provided between the load terminals 6 does not include a current limiting resistor in series, unlike the normal use method for the power output load terminal. When the voltage between the load terminals 6 reaches the Zener voltage value, the resistance value in the breakdown region inside the Zener diode 8 decreases. From these facts, when the voltage between the load terminals 6 reaches the Zener voltage value, an overcurrent is likely to flow, and is destroyed instantaneously with almost no self-heating, resulting in a short circuit state.
In order to utilize this, only the Zener diode 8 is provided between the load terminals 6. Therefore, by setting the Zener voltage value of the Zener diode 8 to be equal to or less than the voltage value which is an overvoltage for the load, the overvoltage is applied to the load by the function of the Zener diode 8 even if the input / output terminals of the three-terminal regulator 5 are short-circuited. Can be reliably avoided. Since the application of the overvoltage to the load is prevented by the Zener diode 8, there is an effect that it can be realized with a low-cost and simple configuration, and an effect that it is easy to apply to an existing switching power supply device.

The cathode side of the diode 31 is connected to the Zener diode 8. Therefore, when the Zener diode 8 is short-circuited, the diode 31 is turned on, and the load short-circuit detection control circuit 3 and the excessive load current limiting circuit 2 are operated to cut off the collector currents (IC) of the transistors 11 and 12. Thus, when the Zener diode 8 is short-circuited, even if an excessive voltage is applied to the power supply terminal 7, an excessive current flows through the circuit elements such as the transistors 11 and 12 to prevent the circuit elements from being damaged.

[Second Embodiment] FIG. 1 is a circuit diagram showing a configuration of a switching power supply according to a second embodiment of the present invention. In the second embodiment, the switching power supply of the first embodiment is further provided with a zener diode 9 between the input terminal line Vo of the three-terminal regulator IC 5 and the ground, a load terminal 6 and the input terminal line Vo.
The diodes 10 are further added between them.

With such a circuit configuration, when a short circuit occurs between the input terminal of the three-terminal regulator IC 5 and the ground, the diode 10 is turned on, and the diode 31 is also turned on. , And the circuit elements such as the transistors 11 and 12 can be protected.
Also, the input terminal line Vo of the three-terminal regulator IC5
When an overvoltage exceeding the steady voltage is applied to the power supply, the Zener diode 9 is short-circuited and the diode 10 is turned on, so that the load and other circuit elements can be similarly protected from the overvoltage.

When the input terminal of the three-terminal regulator IC 5 is grounded, the load 10 has a long time constant on the load side. It also acts as protection to prevent reverse voltage (reverse bias) applied between them.

In the first and second embodiments,
Although the load short-circuit detection control circuit 3 and the overload current limit circuit 2 are operated in conjunction with the short-circuit of the Zener diode 8, they do not always have to be linked. Also, it is not always necessary to provide these. As described above, the present invention can be variously modified.

[0030]

As described above, according to the switching power supply of the present invention, when an overvoltage exceeding a predetermined voltage value is applied between the terminals, the terminals are short-circuited and the short-circuit state is reduced. Since the overvoltage protection means that is maintained is provided, it is possible to reliably prevent an excessive voltage from being applied to the load.

When at least one of the excessive current limiting means and the excessive current cutoff means is further provided, the switching element can be protected from excessive current.

[Brief description of the drawings]

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

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

FIG. 3 is a circuit diagram showing a configuration of a conventional switching power supply device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main switching transistor circuit 2 Load excess current limiting circuit 3 Load short circuit detection control circuit 4 Diode / pump circuit 5 Three-terminal regulator IC 6 Load terminal 7 Power supply terminal 8 Zener diode 9 Zener diode 10 Diode 11 Transistor 12 Transistor 13 Diode 14 Diode 15 Capacitor 16 Capacitor 21 Resistor 22 Transistor 23 Resistor 31 Diode 32 Resistor 41 Capacitor 42 Capacitor 43 Diode 44 Diode 61 Capacitor

Claims (8)

[Claims] 1. A switching power supply device for applying a predetermined voltage between terminals to which a load is connected by driving at least one switching element, wherein an overvoltage equal to or greater than a predetermined voltage value is applied between the terminals. In such a case, there is provided an overvoltage protection means for short-circuiting the terminals and maintaining the short-circuit state. 2. A switching power supply for applying a predetermined voltage between terminals to which a load is connected by inputting and driving a predetermined signal to at least one switching element, wherein a current supplied to the switching element is provided. Overcurrent limiting means for limiting the magnitude of the current to not more than a predetermined current value, and overvoltage protection means for short-circuiting the terminals when an overvoltage of not less than a predetermined voltage value is applied between the terminals. A switching power supply device characterized in that: 3. A switching power supply for applying a predetermined voltage between terminals to which a load is connected by inputting a predetermined signal to at least one switching element and driving the switching element, wherein a predetermined current is supplied to the switching element. An excess current cutoff means for interrupting the supply of current to the switching element when a current equal to or greater than a value is supplied, and when an overvoltage equal to or greater than a predetermined voltage value is applied between the terminals, A switching power supply device comprising: overvoltage protection means for short-circuiting. 4. A switching power supply for applying a predetermined voltage between terminals to which a load is connected by inputting and driving a predetermined signal to at least one switching element, wherein a current supplied to the switching element is provided. Excessive current limiting means for limiting the magnitude of the current to a predetermined first current value or less, and when a current equal to or more than a predetermined second current value is supplied to the switching element, A switching power supply comprising: an excessive current interrupting unit that interrupts the supply of current; and an overvoltage protection unit that short-circuits the terminals when an overvoltage greater than a predetermined voltage value is applied between the terminals. apparatus. 5. The circuit according to claim 2, wherein when the overvoltage protection circuit short-circuits the terminals, the overcurrent limiting circuit limits the amount of current supplied to the switching element. A switching power supply device according to claim 1. 6. The method according to claim 3, wherein when the overvoltage protection means short-circuits between the terminals, the supply of current to the switching element is cut off by the excessive current cutoff means. Switching power supply. 7. The switching device according to claim 2, wherein the overvoltage protection unit maintains a short-circuit state between the terminals after the overvoltage is applied between the terminals. Power supply. 8. The method according to claim 1, wherein said overvoltage protection means is a Zener diode.
A switching power supply device according to the item.