JPH06303727A - Input low voltage protective circuit - Google Patents

Abstract

PURPOSE:To realize a hysteresis function for providing a difference between a no-load time and a load time by commonly using an input switch placed at front and rear stages of input switches at two input points of a resistor network. CONSTITUTION:A protective circuit turns OFF an input switch S1 when a battery B1 is connected between input terminals 1 and 2 even if there is a stabilized DC power source for operating a load L1 connected between input terminals 3 and 4. Accordingly, when the battery B1 is connected between the terminals 1 and 2, power is not supplied from an input 12 to a resistor network, and hence a voltage is input to an inverting input terminal of a voltage comparator CP1. On the other hand, an output voltage of a reference voltage Vr1 is input to a non-inverting input end of the comparator CP1, an input low voltage protective circuit becomes a state for deciding an input switch switching voltage at the time of no load, starts to compare a high voltage with a low voltage, the comparator CP1 and the switch S1 do not turn ON if the battery output voltage becomes higher than the switching voltage but maintains a no load state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention aims to protect the input power supply, its power supply line, and the load circuit from various problems that occur when the output voltage of the input power supply drops. The present invention relates to an input low voltage protection circuit that is large and is highly effective in the case of an unregulated DC input power supply that requires limiting the minimum output voltage.

[0002]

2. Description of the Related Art Conventionally, many techniques concerning input low voltage protection have mainly aimed to control charge / discharge in a power input circuit using a battery as a supporting power source.

In the embodiment of FIG. 3, a switch F1 connecting the battery B2 and the load L2, a switch Q1 controlling the switch F1, a voltage comparator CP2 controlling the switch Q1, and a reference power source Vr2 for voltage comparison. And resistance R1
A hysteresis function is realized by 1, R12 and R13. The hysteresis operation will be described below.

Load L2 using battery B2 as an input power source
When the voltage Vb of the battery B2 becomes lower than the voltage V12 set by the following equation, the switch F1 is opened and the discharge of the battery B2 is stopped.

V12 = Vref2 (1 + R11 / R12) In the above equation, the output voltage of the reference power supply Vr2 is Vref2.

However, at this point, the battery B2 is removed and V
When b is naturally recovered to a voltage higher than V12 and then mounted again, the output of the voltage comparator CP2 is OFF, so Q1 and F1 are turned ON, and the battery B2 restarts discharging. Further, when a stabilized DC power supply with an output voltage of V12 or higher is connected to the input terminal A, if the DC power supply is removed after the battery B2 similar to the above is connected, the battery B2 will likewise restart discharging. . When this discharge restart is repeated, the over-discharge of the battery B2 becomes deeper. This is the first drawback of the prior art.

On the other hand, when the Vb of the battery B2 fully charged by the DC power supply is higher than the voltage Vh2 set by the following equation, the battery B2 starts supporting when the DC power supply is removed.

Vh2 = Vref2 {1 + R11 (R12 + R13) / R12 · R13} Next, the overload protection function is constituted by the transistors Q2 and Q3 and the resistors R15, R16 and R17. The operation will be described below.

As the load current increases, the potential difference across R15 increases. This potential difference is applied between the emitter and the base of Q2, and above a certain potential difference, the resistance between the emitter and collector of Q2 decreases and the potential at the connection point of R16 and R17 rises. Therefore, at a certain potential or higher, Q3 is O
N to lower the base potential of Q1 and turn off Q1 and F1 to suppress overcurrent.

However, if F1 is turned off and the load current disappears, the operation of each of the above parts is restored and F1 is turned on again, so that F1 cannot be kept off. This is the second drawback.

[0011]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art with a smaller number of parts than the above-mentioned conventional examples.
It is an object of the present invention to provide an input low voltage protection circuit that is more effective for an unstabilized DC input power source in which the output voltage has a large load dependency and the output minimum voltage must be limited.

For example, as shown in FIG. 4, the output voltage of the battery increases as the load current decreases due to the influence of the internal resistance even if the charged amount is the same. Therefore, to prevent the deep discharge of the battery,
Regarding the continuous voltage of the battery output, a hysteresis having the characteristics shown in Fig. 5 not only during charging and discharging, but also during no load (when the load is stopped) and during load (when the load is operating). It is necessary to add a function. The first object of the present invention is to realize this function with fewer components than the conventional example and at the same time add an overload protection characteristic.

Next, the output voltage of the battery drops,
With the hysteresis function or the overload protection feature that realizes the first problem above, if the battery goes into a no-load state, it realizes a function to maintain the no-load (load stop) state even if the battery voltage rises. This is the second object of the present invention.

[0014]

An input switch located between an input power supply and a load for connecting and disconnecting the input power supply and the load, a reference power supply for voltage comparison, and one of the reference power supply. A voltage comparator that controls the opening and closing of the input switch as an input, a resistor network that divides the voltage of the input power supply to generate the other input of the voltage comparator, and a resistor network that is located after the input switch and the resistor network. And a diode for preventing backflow from the load, the resistance network has two input points respectively in front of and behind the input switch, and realizes a hysteresis function by sharing the input switch. It has means for adding overload protection characteristics.

Further, the load is composed of a DC voltage converter, a voltage detector, a bistable oscillator and a system, and when the voltage of the input power source is lowered and the input switch is opened once, the system normally controls the system. The voltage detector provided for use detects the output voltage drop of the DC voltage converter, and causes the bistable oscillator powered by the input power source and the output of the DC voltage converter to function, It has means for stopping the voltage converter. Here, it is not necessary to newly install the voltage detector dedicated to the above problem.

[0016]

The input low-voltage protection circuit of the present invention has the above-described structure, regardless of the presence or absence of the stabilized DC power supply for load operation.
Even if an unregulated input power source is connected, the input switch is initially O
It is FF. Therefore, there is no power supply to the resistance network from the one placed in the latter stage of the input switch among the inputs of the resistance network, and therefore the resistance network determines the input switch opening / closing voltage when there is no load together with the reference power supply and the voltage comparator. Put in a state. At this time, if the voltage of the input power supply is not higher than the switching voltage, the input switch will not turn on,
The input power supply remains unloaded. If the input voltage is higher than the switching voltage, the input switch is turned on, and the input power source is in the load state.

Next, in the load state, power is supplied to the input of the resistor network placed after the input switch, so that the resistor network sets the input switch opening / closing voltage at the time of load together with the reference power source and the voltage comparator. Ready to go. Here, since the input switch opening / closing voltage can be set higher in the no-load state than in the load state, the hysteresis function can be easily realized. further,
As the load current flowing through the input switch increases, the voltage drop in the output stage of the input switch due to the internal resistance of the input switch gradually increases, so that the open / close voltage of the input switch gradually increases and the input switch is turned off. In this way, the overload protection characteristic against the overload current is added.

As described above, the input switch is turned off,
However, the output voltage of the input power supply in the no-load state is restored to the voltage at the time of no load if the power supply has a large load dependency. When the recovery voltage exceeds the input switch opening / closing voltage when there is no load, the input switch turns on again.
Then, it is under load. The situation of repeating this ON-OFF becomes a problem in terms of protection of the input power supply and the load,
When the input power source is in a no-load state, the function of maintaining the state is required, and this is realized by means of the voltage detector and the bistable oscillator in the above configuration. When the voltage of the input power supply is lowered and the input switch is opened once, the voltage detector detects a decrease in the output voltage of the DC voltage converter and outputs the input power supply and the output of the DC voltage converter. The bistable oscillator used as a power source is made to function and the DC voltage converter is stopped. In this way, the unloaded state is maintained.

[0019]

1 shows a first embodiment of the present invention and FIG. 2 shows a second embodiment of the present invention. In these examples, a battery was used as a DC input power source in which the output voltage had a large load dependency and the output minimum voltage had to be limited.

First, the operation of the input low voltage protection circuit in FIG. 1 will be described. Connected between input terminals 3 and 4 and load L
Even if there is a stabilized DC power supply for driving the battery 1, the backflow prevention diode D1 prevents the current from flowing into the input low voltage protection circuit. When there is no connection between 1 and 2, the input switch S1 is off.
Therefore, when the battery B1 is connected between the input terminals 1 and 2, the input switch S among the inputs 11 and 12 of the resistance network including the resistances R1, R2, R3, R4 and R5.
Since there is no power supply to the resistor network from the input 12 placed at the rear stage of 1, the resistor network sets the battery output voltage to Vb and applies the voltage Vh represented by the following formula to the inverting input terminal of the voltage comparator CP1. input.

Vb = (1 + R1 / R2 ′) V−h R2 ′ = R2 (R3 + R5) / (R2 + R3 + R5) On the other hand, the output voltage Vref1 of the reference voltage Vr1 is input to the non-inverting input terminal of the voltage comparator CP1 and the present invention is realized. The input low voltage protection circuit of the input switch switching voltage Vh1
Then, the voltage comparator CP1 becomes
And the comparison of Vref1 are started. At this time, if the battery output voltage Vb is not higher than the switching voltage Vh1 represented by the following equation, the voltage comparator CP1 and the input switch S
1 does not turn on, and the input low voltage protection circuit of the present invention maintains the unloaded state.

Vh1 = (1 + R1 / R2 ′) Vref1 R2 ′ = R2 (R3 + R5) / (R2 + R3 + R5) If Vb is higher than Vh1, the voltage comparator C
P1 and the input switch S1 are turned on, and the battery B1 is in a load state. In load condition, input switch S
Since power is supplied to the input 12 of the resistor network placed after 1, the resistor network inputs the voltage V-1 represented by the following equation to the inverting input terminal of the voltage comparator CP1.

Vb = (1 + R1 / R2) V-1 + {(1 + R4 / R5) V-1-Vb + (Vsd + Vf)} / RR = R1R5 / (R3R4 + R4R5 + R5R3) where Vsd is the potential difference between the input and output of the switch S1, Vf is the forward voltage of the diode D1.

Therefore, the input low voltage protection circuit of the present invention is
The state in which the input switch opening / closing voltage V11 at the time of load is determined is entered, and the voltage comparator CP1 starts the high-low comparison of V-1 and Vref1. When the battery B1 continues to operate the load L1 and the battery output voltage Vb becomes lower than the switching voltage V11 represented by the following formula, the voltage comparator CP1 and the input switch S1 are turned off, and the input low voltage protection of the present invention is performed. The circuit is in an unloaded state.

V11 = (1 + R1 / R2) Vref1 + {(1 + R4 / R5) Vref1-V11 + (Vsd + Vf)} / R ... (1) R = R1R5 / (R3R4 + R4R5 + R5R3); where the above load is applied. When the input switch opening / closing voltage V11 is set, the resistance value is set so as to satisfy the condition of R1 / R2 = R4 / R5, and Vsd and Vf are ignored, the following formula is obtained.

V11 = (1 + R1 / R2) Vref1 As described above, the open / close voltage of the input switch S1 can be set higher in the no load condition than in the load condition. Figure 5
A hysteresis function having the characteristics shown in can be realized.

Further, as the load current flowing through the input switch S1 and the diode D1 increases, the voltage drop due to the internal resistance of the input switch S1 and the diode D1 gradually increases, so that the Vsd and Vf cannot be ignored. Therefore, the input switch opening / closing voltage V of the above equation (1)
11 gradually increases and turns off the input switch S1.

As described above, the input low voltage protection circuit of the present invention is added with the overload protection characteristic against the overload current.

Here, as shown in FIG. 4, in an unregulated input power source having a large load dependency such as a battery, the input switch is turned off due to the end of discharge or overload during load operation, but there is no load state. In this case, the output voltage of the input power supply recovers to the voltage when there is no load. Then, when the recovery voltage exceeds the input switch opening / closing voltage Vh1 when there is no load, the input switch is turned on again and the load state is entered. This situation in which the input switch repeatedly turns on and off poses a problem in terms of protection of the input power source and the load, such as deepening the discharge depth of the battery and not holding load disconnection at the time of load short circuit. Therefore, when the input power supply changes from the loaded state to the unloaded state, the function of maintaining the unloaded state is required. Further, as shown in FIG. 4, the input power supply having a large load dependency has almost no difference in the output steady-state voltage when it is in the no-load state regardless of whether it can be used or not. It is difficult to judge.

Therefore, it is necessary to detect the abnormality at the moment when the load state shifts to the no-load state and maintain the protection state.
It is the input low voltage protection circuit of the present invention having the configuration shown in FIG. 2 that realizes the above function. The operation of FIG. 2 will be described below.

As shown in FIG. 2, the load L1 shown in FIG.
Receives the power from the battery B1 via the input switch S1 and detects the output voltage drop of the DC voltage converter 22 and the DC voltage converter 22 for generating the voltage to be supplied to the system 25 as the device, and detects the output voltage to the system 25. A voltage detector 23 provided for notifying, and a bistable oscillator 2 provided for holding an operation stop of the system 25 at the time of abnormality.
It is composed of 4.

When the input switch S1 built in the input low voltage protection circuit 21 is opened during load operation,
The input and output voltages of the DC voltage converter 22 drop. The voltage detector 23 detects the voltage drop before the output of the DC voltage converter 22 disappears, causes the bistable oscillator 24 to function, and stops the output of the DC voltage converter 22. here,
Since the bistable oscillator 24 uses the output of the input switch and the output of the DC voltage converter 22 as a power source, power is supplied from the DC voltage converter 22 to the bistable oscillator 24 at the moment when the input switch is opened once. , DC voltage converter 22
When the output voltage of the battery B1 in the no-load state is rapidly recovered at the moment when the output of the battery is stopped, and the recovered voltage exceeds the input switch opening / closing voltage Vh1 at the time of no load, the input switch S1 is turned on again, and the battery B1 From the bistable oscillator 24. Therefore, the power of the bistable oscillator 24 is not lost, and the input low voltage protection circuit of the present invention protects the protection state even after the DC voltage converter 22 is stopped. Here, the voltage detector 23 is usually the system 2
It is deployed for control of No. 5.

[0033]

The present invention solves the problems of the prior art by sharing the conventional parts or the existing parts with less parts than the above conventional example or without adding new parts.
It not only prevents over-discharge of the supporting battery, but also easily realizes low voltage protection for all unregulated DC input power sources that have a large load dependency and need to limit the minimum output voltage. That is, even when the stabilized DC power supply or the supporting battery is attached or detached, the battery is prevented from being over-discharged, and the protection against low voltage due to discharge termination or overload of all unstabilized DC input power supplies such as batteries. (EN) Provided is an inexpensive input low voltage protection circuit which realizes and maintains the unloaded state of the input power supply.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an input low voltage protection circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of an input low voltage protection circuit according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a conventional input low voltage protection circuit.

FIG. 4 is a load characteristic diagram of an unregulated DC input power supply.

[Figure 5] Input switch hysteresis function operating characteristic diagram

[Explanation of symbols]

 1, 2 Unregulated DC power supply input terminal 3, 4 Stabilized DC power supply input terminal 21 Input low voltage protection circuit 22 DC voltage converter 23 Voltage detector 24 Bistable oscillator 25 System

Claims (2)

[Claims] 1. An input switch located between an input power supply and a load for connecting and disconnecting a power supply line from the input power supply to the load, a reference power supply for voltage comparison, and one of the reference power supply. A voltage comparator that controls opening and closing of the input switch as an input, and a resistor network that divides the voltage of the input power supply to generate the other input of the voltage comparator,
The input switch and a diode located after the resistor network to prevent backflow from the load,
In the resistance network, two input points are placed in front of and behind each of the input switches, and the input switches are shared so that the input switches should be opened and closed between load operation and load stop. Input low-voltage protection circuit that realizes a hysteresis function that makes the power supply voltage different and at the same time adds overload protection characteristics. 2. The load is a DC voltage converter, a voltage detector,
It consists of a bistable oscillator and a system, and when the voltage of the input power supply in the previous section drops and the input switch in the previous section opens one time,
The voltage detector detects a decrease in the output voltage of the DC voltage converter, causes the bistable oscillator powered by the input power supply and the output of the DC voltage converter to function, and stops the DC voltage converter. The input low voltage protection circuit according to claim 1, further comprising means.