JP2808286B2 - Power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] Regarding an overcurrent protection method of a power supply for supplying a call current to a subscriber of an electronic exchange, components to be used may withstand a small amount of power, and the power supply may be downsized. A transistor connected in series between the input DC power supply (V) and the primary side of the transformer (T) is provided with a pulse from the pulse width control unit (1) for the purpose of providing an inexpensive overcurrent protection method. In a power supply device for controlling the current from an input DC power supply (V) by turning on and off by a switching pulse whose width is controlled and supplying a load voltage to a secondary side of the transformer (T), the primary of the transformer (T) The first and second current transformers (CT0, CT1) for detecting a current are inserted between the input side and the input DC power supply (V), and the current is detected at the output of the first current transformer (CT0). When the current is The pulse width control unit maintains a constant load voltage until a constant steady current corresponding to the use state, and decreases the load voltage when the current exceeds the steady current. A load voltage lowering means (2) for reducing the pulse width of the switching pulse from (1) is provided. The detected current becomes the maximum rated current of the load current at the output of the second current transformer (CT1). A switching pulse blocking means for maintaining a minimum rated voltage within a predetermined time during which a maximum rated current must be supplied, and blocking output of a switching pulse from the pulse width control unit (1) after a predetermined time has elapsed; (3) is provided.

[Industrial applications]

The present invention relates to an improvement of an overcurrent protection method of a power supply for supplying a call current to a subscriber of an electronic exchange.

When supplying the call current to the subscriber from the power supply,
The supply current changes depending on the state of the subscriber's use of the electronic exchange. However, in the case of the electronic exchange, most of the operation in the steady state is performed, and the supply current is less than about 1/2 of the maximum rated current.

However, for example, when an earthquake or a fire occurs, the call volume increases and the maximum rated current may be about twice the steady-state current. However, the time for the maximum rated current is several seconds.

As an overcurrent protection method for the power supply device in such a use state, it is desirable that the used parts of the power supply device can be downsized.

[Conventional technology]

 Hereinafter, a conventional example will be described with reference to the drawings.

FIG. 4 is a circuit diagram of a main part of an overcurrent protection method of a conventional power supply device, and FIG. 5 is a characteristic diagram with respect to an overcurrent in the case of FIG.

The power supply device shown in FIG. 4 is a DC output voltage stabilized power supply. To explain the operation, the pulse width of the switching pulse from the pulse width control unit 1-1 is controlled in order to suppress the fluctuation of the load voltage. And provided to transistor Q,
Turns on and off, and makes the current flowing through the input DC power supply V1, transformer T, transistor Q an alternating current, supplies power to the secondary side of the transformer T, and smoothes the load by turning the diode D1, D2, choke L, and capacitor C2 into direct current. Is supplied within the specified voltage range.

In this case, in the current transformer CT1, 1 of the transformer T1 is used.
The current flowing to the next side is detected, and the resistor R4, diode D4,
Half-wave rectified by R8, diode D5, capacitor C5, resistor R7
Detects the peak voltage, and inputs it to the + input terminal of the comparator 4.

On the other hand, the negative input terminal of the comparator 4 has a current transformer
The reference voltage Vref, which is a voltage at which the peak voltage value of the current detected by CT1 is equal to the peak voltage value at the time of the maximum rated current, is added.

Therefore, when the current detected by the current transformer CT1 exceeds the maximum rated current, the output of the comparator 4 becomes H level, and the switching pulse output from the pulse width control unit 1-1 is blocked to stop the power supply.

Therefore, the load voltage is constant until the maximum rated current is reached, and when the load voltage exceeds the maximum rated current, the load voltage suddenly becomes zero as shown in FIG.
And performs overcurrent protection.

[Problems to be solved by the invention]

However, in the above overcurrent protection method, the output power increases according to the load current because the load voltage is constant until the maximum rated current is reached.

Therefore, the transformer T and the choke L
Shall have a capacity that does not saturate with power at the maximum rated current at a constant load voltage, and transistors Q and diodes D1 and D2 that are semiconductors shall withstand the power at the maximum rated current at a load voltage with a constant temperature rise. And

Therefore, the components used are large, and the power supply device is large and expensive. In addition, since the reliability of components used is lower as the components withstand higher power, there is a problem of low reliability.

An object of the present invention is to provide an overcurrent protection system that can withstand a small amount of electric power and that can reduce the size and cost of a power supply device.

[Means for solving the problem]

The object of the present invention is to connect a transistor connected in series between an input DC power supply (V) and a primary side of a transformer (T) to a pulse width control unit (1) as shown in the principle block diagram of FIG. ), The current from the input DC power supply (V) is turned on / off by turning on / off by a switching pulse having a controlled pulse width from (1), and a load voltage is supplied to the secondary side of the transformer (T). T) Insert first and second current transformers (CT0, CT1) for detecting current between the primary side of T) and the input DC power supply (V), and output the first current transformer (CT0). When the current to be detected maintains a constant load voltage until a constant current corresponding to the steady use state of the load, the load voltage decreases when the current exceeds the steady current, and when the maximum rated current is reached, the minimum specification Voltage A load voltage lowering means (2) for reducing the pulse width of the switching pulse from the pulse width controller (1), and the output of the second current transformer (CT1) is a load current , The minimum rated voltage is maintained within a predetermined time during which the maximum rated current must be supplied, and after a lapse of the predetermined time, the output of the switching pulse from the pulse width control unit (1) is changed. The present invention is achieved by a power supply device provided with a switching pulse blocking means (3) for blocking.

(Operation)

According to the present invention, the load voltage lowering means 2 lowers the load voltage when the load current is higher than the steady current, makes the load voltage lower when the load current reaches the maximum rated current, and the switching pulse blocking means 3 When the load current reaches the maximum rated current and a predetermined time of several seconds at which the maximum rated current has to be supplied has elapsed, the output of the switching pulse from the pulse width control unit 1 is stopped and the supply of power is stopped.

Therefore, the transformer T and the chokes need not be saturated at the maximum rated current and the power of the minimum rated voltage, and the semiconductors such as the transistor Q have a temperature rise of about 1 / the maximum rated current at the minimum rated voltage. If it can withstand the power in the case of the steady-state current of 2, it can withstand the power in the case of the steady-state current because the maximum rated current flows for several seconds.The parts can be made small, and the power supply unit can be small and inexpensive. Becomes

Also, the parts to be used need to withstand a smaller amount of power than in the past, so that the reliability is improved.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a circuit diagram of a main part of the overcurrent protection system of the power supply device according to the embodiment of the present invention, and FIG. 3 is a characteristic diagram with respect to the overcurrent in the case of FIG.

The difference between FIG. 2 and FIG. 4 is that two current transformers CT0 and CT1 are provided, and when the current detected by the current transformer CT0 exceeds a steady value which is a steady state current value of the load current. When the output voltage is lowered and reaches the maximum rated current, it becomes the minimum rated voltage. When the current detected by the current transformer CT1 reaches the maximum rated current of the load current and continues for several seconds, the switching pulse output from the pulse width control unit 1 is output. That is, the power supply is stopped.

Hereinafter, the operation of FIG. 2 will be described focusing on this different point.

In the steady state, a voltage + V from the auxiliary power supply is applied to the base of the transistor Q1 via the resistor R6, the transistor Q1 is on, and the resistor R2 is short-circuited.

Therefore, the current detected by the current transformer CT0 is
Half-wave rectification is performed by the resistor R3, the diode D3, the resistor R1, and the capacitor C3, and the generated voltage is applied to the pulse width control unit 1.

In this case, the value of the resistor R1 is selected, the voltage input to the pulse width control unit 1 is adjusted, and when the load current exceeds a steady value,
As shown in FIG. 3, the pulse width of the switching pulse output from the pulse width control unit 1 is reduced so that the output voltage is lowered and becomes the minimum rated voltage when the maximum rated current is reached.

The output of the current transformer CT1 is
4, Diode D4, half-wave rectification by resistor R8, diode D5,
The peak voltage is detected by the capacitor C5 and the resistor R7 and input to the + input terminal of the comparator 4.

As in the conventional case, the peak voltage value of the current detected by the current transformer CT1 is supplied to the-input terminal of the comparator 4.
Since the reference voltage Vref, which is the voltage equal to the peak voltage value at the maximum rated current of the load current, is added, if the current detected by the current transformer CT1 exceeds the maximum rated current,
The output of the comparator 4 becomes H level, and the resistor R5 and the capacitor C
After a few seconds, the capacitor C is added to the time constant circuit consisting of
The voltage of 4 becomes H level.

This H level is applied to the-terminal of the comparator 5 to which the reference voltage Vref is applied to the + input terminal, and the output of the comparator 5 becomes L because the H level is higher in potential than the reference voltage Vref.
Level, and the transistor Q1 is turned off.

Then, the output of the current transformer CT0 is terminated by the series circuit of the resistors R1 and R2, and the voltage across the resistors R1 and R2 increases.
The output of the switching pulse from the pulse width control unit 1 is stopped, and the supply of power is stopped.

In this way, the transformer T and the choke L need not be saturated at the maximum rated current at the minimum rated voltage, and the temperature rise of the transistor Q and the diodes D1 and D2, which are semiconductors, can be reduced by the steady current at the minimum rated voltage. If it can withstand the power of the value, it can withstand the maximum rated current flowing for several seconds, so that it can withstand the above-mentioned power, the components can be downsized, and the current device can be downsized and inexpensive.

In addition, since the components need only withstand a small amount of power, the reliability is improved.

〔The invention's effect〕

As described above in detail, according to the present invention, the components can be downsized, the power supply device can be reduced in size and cost, and the reliability can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of the principle of the present invention, FIG. 2 is a circuit diagram of a main part of an overcurrent protection system of a power supply device according to an embodiment of the present invention, and FIG. 3 is a characteristic diagram for overcurrent in the case of FIG. FIG. 4 is a circuit diagram of a main part of an overcurrent protection system of a conventional power supply device, and FIG. 5 is a characteristic diagram with respect to an overcurrent in the case of FIG. In the figure, 1,1-1 is a pulse width control unit, 2 is a load voltage lowering means, 3 is a switching pulse blocking means, 4,5 are comparators, V and V1 are input DC power supplies, C1 to C5 are capacitors, CT0 , CT1 is a current transformer, T is a transformer, Q and Q1 are transistors, D1 to D5 are diodes, L is a choke, and R1 to R8 are resistors.

Claims (1)

(57) [Claims] An input DC power supply (V) and a transformer (T) 1
A transistor connected in series with the next side is turned on / off by a switching pulse having a controlled pulse width from the pulse width control unit (1), thereby turning on / off the current from the input DC power supply (V), and thereby setting a transformer ( A power supply device for supplying a load voltage to a secondary side of the transformer (T), wherein a first and a second current transformer (A) detect a current between the primary side of the transformer (T) and the input DC power supply (V). CT
0, CT1), and the output of the first current transformer (CT0) maintains a constant load voltage until the detected current reaches a constant steady current corresponding to a steady use state of the load. When the load voltage decreases, the load voltage decreases. When the maximum rated current is reached, the load voltage lowering means (2) for reducing the pulse width of the switching pulse from the pulse width control unit (1) so that the minimum rated voltage is obtained. The detected current becomes the maximum rated current of the load current, and the minimum rated voltage is maintained within a predetermined time when the maximum rated current must be supplied to the output of the second current transformer (CT1). And a switching pulse blocking means (3) for blocking the output of the switching pulse from the pulse width control section (1) when a predetermined time has elapsed.