JPH0274123A - Overcurrent protective system - Google Patents

Abstract

PURPOSE:To lower rated values of components and to reduce the cost and size by lowering the load voltage when the load current increases over steady current and interrupting the circuit when the maximum load current continues for a predetermined time. CONSTITUTION:A transistor Q is turned ON/OFF by means of switching pulses fed from a pulse width control section 1 so that power fed from a DC power source V is converted into AC power which is then fed to a transformer T and thereafter it is rectified and fed to a load. Primary current of the transformer T is detected through current transformers CT0, CT1. A load voltage lowering means 2 receives the output from the current transformer CT0 and provides a signal to the pulse width control section 1 so that the output voltage is lowered when the current exceeds over a steady level and lowest regular voltage is obtained for the maximum rate current. A switching pulse block means 3 receives output from the current transformer CT1 and blocks switching pulses fed from the pulse width control section 1 when the maximum rated current flows for a predetermined time.

Description

[Detailed Description of the Invention] [Summary] Regarding an overcurrent protection system for a power supply device of an electronic exchange that supplies call current to subscribers, the parts used only need to be able to withstand a small amount of electric power, and the power supply device can be made smaller. Aiming to provide an inexpensive overcurrent protection system, this power supply uses switching pulses with controlled pulse widths from a pulse width controller to turn on and off transistors connected in series with a transformer to keep the load voltage constant. The device detects a current on the primary side of the transformer. A second current transformer is inserted, and the output of the first current transformer is set so that when the load current increases more than the steady current, the load voltage decreases, and when the maximum rated current is reached, the minimum rated voltage is reached. A load voltage reducing means is provided to reduce the pulse width of the switching pulse from the pulse width control section, and the load current becomes the maximum rated current, and the maximum rated current must be supplied to the output of the second current transformer. A switching pulse blocking means is provided for blocking the output of the switching pulse from the pulse width control section after a predetermined time has elapsed.

[Industrial application field]

The present invention relates to an improvement in the overcurrent protection system of a power supply device for supplying communication current to subscribers in an electronic exchange.

When a power supply unit supplies telephone current to a subscriber, the supplied current varies depending on the subscriber's usage of the electronic exchange, but in the case of electronic exchanges, most of the time the operation is in a steady state, and the supplied current is The steady current is approximately 1/2 of the maximum rated current or less.

However, for example, in the event of an earthquake or fire, the call volume increases and the maximum rated current may reach approximately twice the steady current, but the maximum rated current only takes a few seconds.

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

[Conventional technology]

A conventional example will be explained below using figures.

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

The power supply device in FIG. 4 is a DC output voltage stabilized power supply,
To explain this operation, in order to suppress fluctuations in the load voltage, the pulse width of the switching pulse from the pulse width controller 1-1 is controlled, and the pulse width is supplied to the transistor Q, which turns it on and off, and input DC power supply 1. The current flowing through the transformer T,) transistor Q is made into an alternating current, and power is supplied to the secondary side of the transformer T, and the diodes DI, D2 . Chalk L
.

The capacitor C2 converts it into direct current, smoothes it, and supplies power to the load within the standard voltage range.

In this case, in current transformer CTI, 1 of transformer T
Detects the current flowing to the next side, resistor R4゜diode D4
．． Half-wave rectification is performed by resistor R8, and diode D5. The peak voltage is detected by the capacitor C5 and the resistor R7 and inputted to the ten input terminal of the comparator 4.

On the other hand, one input terminal of the comparator 4 has a current transformer C
A reference voltage Vre whose peak voltage value of the current detected by the TI is equal to the peak voltage value at the maximum rated current.
f is addition.

Therefore, when the current detected by the current transformer CTI exceeds the maximum rated current, the output of the comparator 4 becomes H level, blocking the switching pulse output from the pulse width control section 1-1 and stopping the power supply.

Therefore, the load voltage remains constant until the maximum rated current is reached, and when the maximum rated current is exceeded, it suddenly changes to O as shown in FIG. 5 to provide overcurrent protection.

[Problem to be solved by the invention]

However, in the above-described overcurrent protection method, the load voltage remains constant until the maximum rated current is reached, so the output power increases in accordance with the load current.

Therefore, the transformer T and choke L are the parts to be used.
It has a capacity that does not saturate with the power at the maximum rated current at a constant load voltage, and the transistor Q and diodes DI and D2, which are semiconductors, are designed to withstand the power at the maximum rated current at a constant load voltage with a constant temperature rise. .

Therefore, the parts used become larger, and the power supply device also becomes larger and more expensive. In addition, the reliability of the parts used is lower as they withstand greater electric power, so there is a problem of lower reliability.

The present invention aims to provide an overcurrent protection system that allows the use of components that can withstand small amounts of power and that allows the power supply device to be made smaller and cheaper.

[Means to solve the problem]

FIG. 1 is a block diagram of the principle of the present invention.

As shown in FIG. 1, a switching pulse whose pulse width is controlled from a pulse width control unit 1 turns on and off a transistor Q connected in series to the primary side of a transformer T, so that the input DC power supply A first circuit that detects a current between the primary side of the transformer T and the input DC power supply V2O of the power supply device that turns on and off the current of the transformer T and keeps the load voltage on the secondary side of the transformer T constant within the standard voltage range. ．． Insert the second current transformers CTO and CTI.

The output of the first current transformer CTO is
A load that reduces the pulse width of the switching pulse from the pulse width controller 1 so that when the detected current increases more than the steady current of the load current, the load voltage decreases and the minimum rated voltage is reached when the maximum rated current is reached. A voltage reduction means 2 is provided.

In addition, the output of the second current transformer CTl has a pulse width of A switching pulse blocking means 3 is provided for blocking the output of switching pulses from the control section 1.

[For production]

According to the present invention, the load voltage reducing means 2 reduces the load voltage when the load current increases more than the steady current, so that when the maximum rated current is reached, the minimum rated voltage is reached, and the switching pulse is blocked. By means of means 3, when the load current reaches the maximum rated current and a predetermined time of several seconds has elapsed during which the maximum rated current must be supplied, the output of the switching pulse from the pulse width control section 1 is blocked and the supply of power is stopped. Stop.

Therefore, the transformer T and chokes need not be saturated with power at the maximum rated current and the minimum rated voltage, and the temperature rise of semiconductors such as the transistor Q is approximately 1/1/1 of the maximum rated current at the minimum rated voltage. As long as it can withstand the power in the case of steady current (2), it can withstand even if the maximum rated current flows for several seconds, so it is sufficient to withstand the power in the case of steady current, and the parts can be made smaller, and the power supply device can also be made smaller and cheaper. becomes.

In addition, reliability is improved because the parts used need only be able to withstand less electric power than in the past.

〔Example〕

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

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.

The difference between Fig. 2 and Fig. 4 is that two current transformers, CTO and CTI, are provided, and the current transformer CTO
When the current detected by the current transformer exceeds a steady-state value, which is the steady-state current value of the load current, the output voltage is lowered so that when the maximum rated current is reached, the minimum rated voltage is reached, and the current transformer C
The point is that when the current detected by the TI reaches the maximum rated current of the load current and continues for several seconds, the switching pulse output from the pulse width controller 1-1 is blocked and the power supply is stopped.

The operation of FIG. 2 will be explained below, focusing on this different point.

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

Therefore, the current detected by the current transformer CTO is
Resistor R3, diode D3. Resistor R1゜Capacitor C3
The voltage is half-wave rectified at , and the resulting voltage is applied to the pulse width control section I.

In this case, by selecting the value of the resistor R1, the pulse width controller 1-
The pulse width controller 1-1 adjusts the voltage input to the pulse width controller 1-1, and when the load current exceeds a steady value, the output voltage is lowered as shown in FIG.
1, the pulse width of the switching pulse to be outputted is made smaller.

Also, the output of the current transformer CTI is connected to the resistor R4, diode D4. Half-wave rectification is performed by resistor R8, and diode D5. The peak voltage is detected by the capacitor C5 and the resistor R7 and inputted to the ten input terminal of the comparator 4.

Also, as in the past, one input terminal of the comparator 4 has the peak voltage value of the current detected by the current transformer CTI.
Since the reference voltage Vref, which is a voltage equal to the peak voltage value at the maximum rated current of the load current, is added, when the current detected by the current transformer CTI exceeds the maximum rated current, the output of the comparator 4 goes to H level. Then, after a few seconds of being applied to a time constant circuit consisting of resistor R5 and capacitor C4, the voltage of capacitor C4 reaches H level 7.

This l(level) is applied to one terminal of the comparator 5 to which the reference voltage Vref is applied to the input terminal of the comparator 5.
The output becomes L level, and the transistor Ql is turned off.

Then, the output of the current transformer CTO is the resistor R1, R
The voltage across the resistors R1 and R2 rises, blocking the output of the switching pulse from the pulse width controller 1 and stopping the power supply.

In this way, the transformer T and choker can be made of a material that does not saturate with the power of the minimum rated voltage and maximum rated current.
Also, the transistor Q is a semiconductor.

As for the temperature rise of the diodes DI and D2, if they can withstand the power of the steady current value at the minimum rated voltage, they can withstand even if the maximum rated current flows for several seconds, so they should be able to withstand the above power (, The parts can be made smaller, and the power supply device can also be made smaller and cheaper.

In addition, reliability is improved because the parts need only withstand less electric power.

〔Effect of the invention〕

As described in detail above, according to the present invention, parts can be made smaller, the power supply device can be made smaller and cheaper, and reliability can be improved.

[Brief explanation of the drawing]

Fig. 1 is a principle block diagram of the present invention, Fig. 2 is a circuit diagram of the 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 for overcurrent in the case of Fig. 2. , 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 for overcurrent in the case of FIG. 4. In the figure, 1.1-1 is a pulse width control unit, 2 is a load voltage reduction means, 3 is a switching pulse blocking means, 4.5 is a comparator, Vl is a human input DC power supply, 01 to C5 are capacitors, CTO, CTI is a current transformer, T is a transformer, Q and Ql are transistors, D1 to D5 are diodes, L is a choke, and R1 to R8 are resistors. Wed/departure! ] f4tr) Principle 1072 Figure 7 Figure 2 Figure 2. Pa L (Nimura Suuga ÷ 1, raw m

Claims (1)

[Claims] The transistor (Q) connected in series to the primary side of the transformer (T) is turned on and off by a switching pulse whose pulse width is controlled from the pulse width control unit (1), and the input The primary side of the transformer (T) and the input DC of a power supply device that turns on and off the current from the DC power supply (V1) and keeps the load voltage on the secondary side of the transformer (T) constant within the standard voltage range. First and second current transformers (CT0, CT1) for detecting current are inserted between the power supply (V1), and the output of the first current transformer (CT0) is such that the current to be detected is at the steady state of the load current. Load voltage reducing means (2) for reducing the pulse width of the switching pulse from the pulse width controller (1) so that the load voltage decreases when the current increases more than the current, and the minimum rated voltage is reached when the maximum rated current is reached. and the output of the second current transformer (CT1) is such that the current to be detected becomes the maximum rated current of the load current, and after a predetermined period of time during which the maximum rated current must be supplied, the pulse width changes. An overcurrent protection system characterized in that a switching pulse blocking means (3) is provided for blocking the output of switching pulses from a control section (1).