KR20040085019A - Circuit for protecting over current - Google Patents

Abstract

PURPOSE: An over current protecting circuit is provided to protect a load circuit from an over current and achieve economic advantages by preventing consumption of current when a load current is normal. CONSTITUTION: A power circuit(2) comprises a DC power unit(21); a condenser(22) charged by the DC voltage output from the DC power unit; and a feed unit(23) for controlling the DC power unit such that the DC power unit does not output DC voltages when the load current flowing along the common contact between the condenser and a load circuit(3) is higher than a predetermined level and the DC power unit outputs DC voltages when the load current is lower than the predetermined level. An over current protecting circuit(1) comprises a judging unit(11) for judging whether the cycle of wave of load voltage generated as a result of power supply of the power circuit is shorter than a predetermined cycle; and a cut-off unit(12) for compulsorily cutting off outputs of the DC power unit when the cycle is shorter than the predetermined cycle.

Description

Overcurrent protection circuit {Circuit for protecting over current}

The present invention relates to an overcurrent protection circuit for a load circuit powered by a power supply circuit.

As a power supply circuit for reducing the power consumption of a load circuit, for example, intermittent energization which continuously supplies electric power in accordance with a load state is performed (for example, refer patent document 1).

6 is a block diagram illustrating a low power consumption power circuit according to a conventional example.

The transformer 51 whose primary side is connected to the AC input is a commercial frequency transformer (hereinafter referred to as a "commercial transformer"), and an AC switch 56 is connected to the primary side of the commercial transformer 51.

The rectifier 52 connected to the secondary side of the commercial transformer 51 converts AC into DC. The voltage converted into DC is smoothed by the capacitor 53 and supplied to the load circuit 3.

The current detection unit 54 detects the magnitude of the load current flowing to the load circuit 3. This detection signal is output to the AC switch control unit 55. The AC switch controller 55 controls the AC switch 56 on / off by the detection signal from the current detector 54.

The auxiliary power supply 57 is a power supply circuit for supplying power to the AC switch 56 and the AC switch control unit 55.

FIG. 7 is a detailed circuit diagram corresponding to the block diagram of FIG. 6.

In the figure, T1 corresponds to the commercial transformer 51 of FIG. The rectifier 52 connected to the secondary side of the commercial transformer 51 converts AC into DC and is constituted by a diode bridge D1. The electrolytic capacitors D2 and D3 and the coil L1 correspond to the capacitor 53. The voltage converted into DC is smoothed by the capacitor 53 and supplied to the load circuit 3.

The photocoupler PC2 corresponds to the current detector 54, and R3 corresponds to the current limiting resistor R. FIG. The transistor Q1 corresponds to the AC switch controller 55.

In addition, the photo triac unit PC1 is composed of a photo triac TR and an LED, and corresponds to the AC switch 56 of FIG. 6. On the other hand, the phototriac unit PC1 is configured to perform on / off operation at the zero cross point of the AC input voltage. That is, the AC switch 56 is turned on when current flows to the LED side of the phototrie TR of FIG. 7, and is turned off when no current flows.

The auxiliary power supply 57 is composed of a capacitor C1 as a reactance element, an electrolytic capacitor C4, and a diode bridge D2. The voltage of the AC input is lowered to the reactance element C1. The voltage drop AC is rectified by the diode bridge D2, and supplies the required DC voltage to the load (voltage supply load) at the rear end. Since the voltage is supplied at the partial pressure due to the reactance element C1 and the voltage supply load, the loss of the DC conversion can be reduced, making it suitable for small power load.

Here, the operation of the low power consumption power supply circuit according to the conventional example illustrated in FIGS. 6 and 7 will be briefly described.

When AC power is input, the auxiliary power source 57 composed of the capacitor C1, the electrolytic capacitor C4, and the diode bridge D2 rises, and the DC voltage passes through the resistor R2 to the base of the transistor Q1. It is given as a DC bias. As a result, when the transistor Q1 is turned on, current flows to the LED of the phototrial liquid unit PC1, and the phototrial liquid TR connected to the primary side of the commercial transformer 51 is turned on (on). Initial startup state. When the phototriac unit PC1 is turned on (i.e., the AC switch 56 is turned on), the voltage is supplied to the secondary side of the commercial transformer T1 51, and the output voltage rectified by the diode bridge D1 is Rising while charging the electrolytic capacitors C2 and C3 in the capacitor 53.

When the voltage at the electrolytic capacitors C2 and C3 rises, current begins to flow through the current limiting resistor R3 to the LED of the photocoupler PC2. As a result, the current of the light receiving transistor QR sucks the base current of the transistor Q1 through the resistor R2, and turns off the transistor Q1. Then, the LED current of the phototrial liquid unit PC1 will not flow, and the phototrial liquid TR will be in a non-conductive (off) state.

When the phototrie TR is turned off, the voltage charged in the electrolytic capacitors C2 and C3 starts to discharge. On the other hand, the temporal change of the discharge voltage is determined by the capacity of the load circuit 3 (whether the load is heavy or light). That is, the voltages of the electrolytic capacitors C2 and C3 fall gently when the load is light, and rapidly drop when the load is heavy.

As the discharge voltages of the electrolytic capacitors C2 and C3 fall, the LED current of the port coupler PC2 flowing through the resistor R3 decreases. As a result, the suction amount of the current in the collector of the light receiving side transistor QR also decreases continuously.

Finally, the bias voltage is supplied to the base of the transistor Q1 via the resistor R2 by the DC voltage supplied via the auxiliary power supply 57, and the transistor Q1 is turned on. The current flows to the LED of the port try liquid unit PC1 in the on state of the transistor Q1, turns on the pot try liquid TR, and supplies a voltage to the secondary side of the commercial transformer 51, thereby providing an electrolytic capacitor ( The voltages of the electrolytic capacitors C2 and C3 rise while charging the C2 and C3 again.

The above operation is repeated, i.e., the intermittent energization of the transistor and the charge / discharge of the capacitor cause a wave having a period depending on the time constant of the capacitor or the like to the load current flowing into the load circuit. However, by intermittently energizing the transformer, the power consumption at the load side can be reduced as compared with the case where the transformer is always energized.

Patent Document 1: Japanese Patent Application Laid-Open No. 2001-145354

However, according to the conventional power supply circuit having the structure as described above, since a return portion from the common contact of the capacitor 53 and the load circuit 3 is provided to the primary side of the commercial transformer 51, Fig. 7 When the pot try liquid TR is in an on state (i.e., the AC switch 56 in FIG. 6 is on), the electrolytic capacitors C2 and C3 in FIG. 7 (that is, the capacitor 53 in FIG. 6) When the battery is charged and the phototrile TR is in the off state, the cycle of discharging the electrolytic capacitors C2 and C3 is repeated.

The temporal change of the discharge voltage is determined by the capacity of the load circuit 3. That is, the electrolytic capacitors C2 and C3 discharge slowly when the load is light, and rapidly discharge when the load is heavy. Therefore, when overloaded for some reason, the charge / discharge cycles of the electrolytic capacitors C2 and C3 become faster, and the current supplied to the load circuit 3 becomes an overcurrent.

If the overcurrent continues, damage such as damage to the element on the load side occurs, and there is no countermeasure against such overcurrent.

Accordingly, the present invention has been made in view of the above problem, and when the load current value flowing through the DC power supply unit, the capacitor charged by the DC voltage output from the DC power supply unit, and the common contact between the capacitor and the load circuit is greater than the predetermined value, the direct current is applied. It is an object of the present invention to provide an overcurrent protection circuit for a load circuit that is supplied with power by a power supply circuit having a feedback section for controlling a DC power supply section so as to output a DC voltage when the voltage is not reduced.

1 is a basic block diagram illustrating an overcurrent protection circuit according to the present invention.

2 is a basic block diagram showing an overcurrent protection circuit according to a variation of the present invention.

3 is a block diagram illustrating an overcurrent protection circuit according to an embodiment of the present invention.

4 is a detailed circuit diagram corresponding to the block diagram of FIG. 3.

5 is a time chart of each partial waveform in the circuit diagram of FIG.

(a) is the load voltage detected at the common contact between the electric field capacitor C3 and the load circuit 3,

(b) is the LED current flowing through the LED in the photo coupler (PC2),

(c) denotes an output signal of the current detection unit 54,

(d) is the current setting pulse,

(e) indicates current abnormality detection signal,

(f) is the latch output,

(g) shows an output signal of the AC switch controller 55

6 is a block diagram illustrating a low power consumption power supply circuit according to a conventional example;

FIG. 7 is a detailed circuit diagram corresponding to the block diagram of FIG. 6.

* Explanation of symbols for main parts of the drawings

1: overcurrent protection circuit 2: power supply circuit

3: load circuit 4: AC power supply

11: determination means 12: blocking means

21: DC power supply 22,53: capacitor

23: return part 24: trance

25 switch 26,52 rectifier

31: current abnormality detection part 32: latch

51: commercial transformer 54: current detector

55: AC switch control unit 56: AC switch

57: auxiliary power

In order to realize the above object, according to the present invention, when the load current value flowing through the DC power supply unit, the capacitor charged by the DC voltage output from the DC power supply unit, and the common contact between the capacitor and the load circuit is greater than a predetermined value, the DC voltage In the case of supplying power to the load circuit using a power supply circuit having a feedback section for controlling the DC power supply unit so as to output a DC voltage when it is small, first, inevitably occurs in the configuration of such a power supply circuit. Observe the period of the wave of the load voltage. When it is determined that the period of the wave of the load voltage is shorter than the predetermined period, the output of the DC power supply unit is cut off to protect the load circuit from overcurrent.

As described above, the period of the wave of the load voltage is due to the intermittent energization of the transformer and the repetition of charging and discharging of the capacitor. If the load is overloaded due to any cause, the discharge cycle of the capacitor is accelerated, so the period of the wave is also shortened. The present invention is characterized by determining whether or not an overcurrent has occurred in the load current according to the period of the wave of the load voltage. When it is determined that an overcurrent has occurred, the DC power output is cut off.

1 is a basic block diagram showing an overcurrent protection circuit according to the present invention.

According to the present invention, the load current value flowing through a common contact between the DC power supply unit 21, the capacitor 22 charged by the DC voltage output from the DC power supply unit 21, and the capacitor 22 and the load circuit 3 The load supplied with power by the power supply circuit 2 provided with the feedback part 23 which controls the said DC power supply part 21 so that it may output DC voltage when it becomes small when this value becomes larger than this predetermined value. The overcurrent protection circuit 1 for the circuit 3 is

Judging means 11 for judging whether or not the period of the wave of the load voltage generated as a result of the power supply of the power supply circuit 2 is shorter than a predetermined period;

When it is determined by the determining means 11 that it is shorter than the predetermined period, it is provided with a blocking means 12 for forcibly interrupting the output of the DC power supply unit 21 because a current abnormality occurs.

On the other hand, as a modification of the present invention, the DC power supply unit 21 may be realized using an AC power supply and a rectifier. 2 is a basic block diagram illustrating an overcurrent protection circuit according to a modification of the present invention.

As shown in FIG. 2, the switch 25 connected between the AC power supply part 4 and the primary side of the transformer 24, the rectifier 26 connected to the secondary side of the transformer 24, and the said rectifier 26 Switch when the load current value flowing through the common contact between the capacitor 22 and the capacitor 22 and the load circuit 3 that is charged by the DC voltage output from The overcurrent protection circuit 1 for the load circuit 3 supplied with the power by the power supply circuit 2 having the feedback section 23 for controlling 25 is:

Judging means 11 for judging whether or not the period of the wave of the load voltage generated as a result of the power supply of the power supply circuit 2 is shorter than a predetermined period;

When it is determined by the determining means 11 that it is shorter than the predetermined period, the blocking means 12 is provided to forcibly turn off the switch 25 because a current abnormality has occurred.

According to the present invention, it is possible to provide an overcurrent protection circuit for a load circuit supplied with power by an intermittent output of a DC power supply unit or an intermittent energization of a transformer and repetition of charging and discharging of a capacitor.

(Example)

As an embodiment of the present invention, a case where an overcurrent protection circuit is connected to the low power consumption power circuit shown in Figs. 6 and 7 described above will be described.

3 is a block diagram illustrating an overcurrent protection circuit according to an embodiment of the present invention.

The overcurrent protection circuit 1 according to the present embodiment is connected to the low power consumption power circuit described with reference to FIG. 6, and from the load current value detected by the current detection unit 54, a current abnormality, that is, a current abnormality that detects an overcurrent The detection part 31 is provided, and the latch 32 which latches the detection signal output when a current abnormality is detected is provided. The driving power of the current abnormality detection unit 31 and the latch 32 is supplied from the auxiliary power supply 57.

4 is a detailed circuit diagram corresponding to the block diagram of FIG. 3.

The current abnormality detecting unit 31 includes a low power consumption CMOS monomulti IC IC11 and an AND circuit IC12. The CMOS mono-multi IC IC11 uses a falling edge of the output of the current detector 54 to detect an abnormality of a current, and a duty ratio that depends on the time constants of the resistor R13 and the capacitor C12. Outputs the current abnormal setting pulse with the through port (Q). The AND circuit IC12 adds the output of the CMOS mono-multi IC IC11 and the collector signal of the light-receiving transistor QR of the photocoupler PC2 corresponding to the current detector 54 to output to the latch 32. .

The latch 32 is composed of transistors Q11, Q12, Q13 and Q14, resistors R14, R15, R16, R17, R18 and R19 and a capacitor C13. In the state where the overcurrent input pulse has not yet been input, that is, the output of the current abnormality detection unit 31 is at the L level, all the transistors Q11, Q12, Q13 and Q14 are turned off and the load current is normal. Suppresses the power consumption of the overcurrent protection circuit.

On the other hand, the output voltage from the diode bridge D2 is supplied to the current abnormality detection unit 31 and the latch 32 as drive power.

Next, the operation of the overcurrent protection circuit according to the present embodiment illustrated in FIGS. 3 and 4 will be described.

5 is a time chart of each partial waveform in the circuit diagram of FIG. 4, (a) is a load voltage detected at a common contact between the electric field capacitor C3 and the load circuit 3, and (b) is a photocoupler PC2. LED current flowing through the LED inside, (c) is the output signal of the current detection unit 54, (d) is the current abnormal setting pulse, (e) the current abnormal detection signal, (f) the latch output, (g) is AC The output signal of the switch control part 55 is shown. The waveforms shown in Figs. 5 (a) to 5 (g) correspond to the square shapes at the points (a) to (g) shown in Fig. 4.

When the AC power is turned on, the DC voltage rectified in the diode bridge D2 is given as a direct current bias to the base of the transistor Q1 via the resistor R2. Then, the transistor Q1 is turned on (see Fig. 5G), and current flows through the LED of the phototriac unit PC1. As a result, the phototrial solution TR of the phototrial liquid unit PC1 is turned on. By turning on the phototrile TR, an alternating current voltage is applied to the primary side of the commercial transformer T1, and a voltage is induced to the secondary side. The induced voltage on the secondary side of the commercial transformer T1 is rectified by the diode bridge D1, and the electrolytic capacitors C2 and C3 are gradually charged by the output voltage of the diode bridge D1 (FIG. 5A). ) Reference). When the voltage at the electrolytic capacitors C2 and C3 rises, current begins to flow through the current limiting resistor R3 to the LED of the photocoupler PC2 (see FIG. 5B). As a result, the collector of the light receiving transistor QR sucks the base current of the transistor Q1 through the resistor R2, and turns off the transistor Q1 (see Fig. 5G). The waveform of each part in the series of operations of the above initial state is shown in period (a) of FIG.

When the transistor Q1 is turned off, the LED current of the phototrial liquid unit PC1 does not flow, and the phototrial liquid TR is turned off. When the phototrie TR is turned off, the voltage charged in the electrolytic capacitors C2 and C3 starts to discharge (see FIG. 5A). The waveform of each part in the above series of operations is shown by period (b) of FIG.

As the discharge voltages of the electrolytic capacitors C2 and C3 drop, the LED current of the photocoupler PC2 flowing through the resistor R3 decreases (see FIG. 5B). As a result, the suction amount of the current in the collector of the light receiving side transistor QR also decreases continuously. Finally, the bias voltage is supplied to the base of the transistor Q1 via the resistor R2 by the DC voltage supplied via the auxiliary power supply 57 (see FIG. 5C). Is turned on (see FIG. 5G). When the transistor Q1 is turned on, a current flows in the LED of the phototrial liquid unit PC1, the phototrial liquid TR is turned on, and a voltage is supplied to the secondary side of the commercial transformer 51, and the electrolytic capacitors C2 and While charging C3) again, the voltages of the electrolytic capacitors C2 and C3 rise (see Fig. 5A). The waveform of each part in the above series of operations is shown by period (c) of FIG.

Thereafter, if no abnormality occurs in the load current, a wave having the period (b) and (c) described above as one cycle occurs.

In this embodiment, in order to detect whether or not the period of the wave of the load voltage is shorter than normal, a current abnormal setting pulse having a predetermined period as shown in Fig. 5D is generated.

Specifically, the CMOS monomulti (IC) IC11 is generated so that the current abnormal setting pulse rises at the falling edge of the output of the current detector 54. This current anomaly setting pulse has a duty ratio which depends on the time constant between the resistor R1 and the capacitor C12 connected to the CMOS monomulti (IC) IC11. That is, the length of the period (wh) of the H level of the current abnormal setting pulse when the load current is normal (see Fig. 5 (d)) depends on the time constant determined by the resistor R13 and the capacitor C12. . The period (h) of the H level of the current abnormality setting pulse depending on this time constant is set shorter than the period (b).

If an abnormality occurs in the load current, that is, an overcurrent occurs, the charge / discharge cycles of the electrolytic capacitors C2 and C3 become faster as described above, so that the period of the wave of the load voltage becomes shorter than normal (FIG. 5 ( a) to (c)). In the embodiment shown in FIG. 5, when the collector signal of the light receiving-side transistor QR of the photocoupler PC2 corresponding to the current detection unit 54 is normal, the pulse rises again after the period b from the fall of the pulse. When there is an error in the load current, the pulse rises after a short period (d) elapsed from the period (b) (see (c) of FIG. 5). As described above, the current abnormal setting pulse rises at the lower phase edge of the output of the current detector 54, and therefore, when the load current is abnormal, the falling edge of the output of the current detector 54 is renewed even if it is in the middle of the period (wh). As a reference, since the current abnormal setting pulse in the next cycle rises, the H level is maintained for a longer time. Therefore, as shown in Fig. 5D, the duration of the H level of the current abnormality setting pulse is a period longer than the period m.

From the above, it can be seen that in the present embodiment, simply adjusting the period (wh) of the H level of the current error setting pulse when the load current is normal, it is possible to easily set the detectable current error level, that is, the magnitude of the overcurrent. have. On the other hand, for example, by realizing the resistor R13 as a variable resistor, it is possible to more easily set the level above the detectable current, that is, the magnitude of the overcurrent.

The current abnormal setting pulse (refer to FIG. 5D) output from the port Q of the CMOS mono-multi IC IC11 is connected to the current detector 54 by the AND circuit IC12. And the collector signal of the light-receiving side transistor QR (see Fig. 5C). That is, the AND circuit IC12 outputs only the 'H' period of the input. The resulting waveform is shown in Fig. 5E.

The operation result of the AND circuit IC12 is input to the latch 32.

As described above, each of the transistors Q11, Q12, Q13 and Q14 in the latch 32 is in a state where the output of the current abnormality detection unit 31 is at an L level, i. Therefore, the power consumption of the overcurrent protection circuit in this state is very small.

At this time, when overcurrent occurs and the output of the overcurrent detector 31 becomes H level, the transistor Q12 is turned on.

Then, since the bases of the transistors Q11 and Q13 are at the L level, the transistors Q11 and Q13 are turned on.

As a result, the transistor Q14 is turned on because its base is H level. As a result, the current output from the diode bridge D2 flows through the collector-emitter of the resistor R2 and the transistor Q14.

Then, the transistor Q1 is turned off (see FIG. 5G), so that the current of the LED of the phototrial liquid unit PC1 does not flow, so the phototrial liquid TR is turned off. When the phototrie TR is off, no AC voltage is applied to the primary side of the commercial transformer T1, and no voltage is induced to the secondary side. As a result, the output of the DC voltage by the diode bridge D1 is cut off, and the load circuit 3 is protected from overcurrent. On the other hand, since the transistor Q11 is in the ON state, the base of the transistor Q12 is maintained at the H level, and the latch state by the latch 32 is established. That is, since the state is maintained when the overcurrent is detected and the overcurrent protection operation is activated, the load circuit is not affected by this overcurrent.

As described above, when the load current value flowing through the surface DC power supply unit, the capacitor charged by the DC voltage output from the DC power supply unit, and the common contact between the capacitor and the load circuit is greater than the predetermined value, the DC voltage is decreased. An overcurrent protection circuit which protects the load circuit from overcurrent can be realized for a load circuit supplied with power by a power supply circuit having a feedback section for controlling the DC power supply section so as to output a DC voltage when the voltage is reduced.

On the other hand, the current abnormality level that can be detected can be easily set by adjusting the duty ratio of the current abnormality setting pulse when the load current is normal.

In addition, the overcurrent protection circuit according to the present invention is economical because almost no current is consumed when the load current is normal. Therefore, it is especially suitable for the overcurrent protection circuit in standby power supply circuits, such as a remote control, for example.

Claims (3)

When the load current value flowing through the DC power supply unit, the capacitor charged by the DC voltage output from the DC power supply unit, and the common contact between the capacitor and the load circuit is larger than a predetermined value, the DC voltage is not outputted. An overcurrent protection circuit for a load circuit supplied with power by a power supply circuit having a feedback unit for controlling the DC power supply unit to output a voltage, Judging means for judging whether or not the period of the wave of the load voltage generated as a result of the power supply of the power supply circuit is shorter than a predetermined period; And an interruption means for forcibly interrupting the output of the DC power supply unit if a current abnormality occurs when the determination means determines that the predetermined period is shorter than the predetermined period. A switch connected between the AC power supply and the primary side of the transformer, a rectifier connected to the secondary side of the transformer, a capacitor charged by a DC voltage output from the rectifier, and a common contact between the capacitor and the load circuit. As an overcurrent protection circuit for a load circuit supplied with power by a power supply circuit having a feedback section for controlling the switch to turn OFF when the load current flowing in the current value exceeds a predetermined value, and to be ON when the load current value is larger than the predetermined value. , Judging means for judging whether or not the period of the wave of the load voltage generated as a result of the power supply of the power supply circuit is shorter than a predetermined period; And an interrupting means for forcibly turning off the switch if a current abnormality has occurred when it is determined by the determining means to be shorter than the predetermined period. The method according to claim 1 or 2, And the determining means includes setting means for setting the predetermined period.