JP7322807B2 - LOAD CIRCUIT FAILURE DETECTION DEVICE AND LOAD CIRCUIT FAILURE DETECTION METHOD - Google Patents

Description

The present invention relates to a load circuit failure detection device, for example, circuit protection of a DC-DC power supply mounted on a battery forklift, and a load circuit (load device, such as a DC brushless fan) short-circuit failure when supplying power to a load. related to how to detect whether

When supplying power to multiple load circuits from one power supply circuit in a DC-DC converter mounted on a battery forklift, for example,
(1) Power supply to the general control computer (master controller) for the entire vehicle (2) Power supply to other computers (3) Equipped with 3 outputs for power supply to multiple cooling fans There is configuration.

The outputs (2) and (3) are supplied via a high-side switch (for example, MOSFET).

Therefore, for example, if one of the load circuits (3) to which a plurality of cooling fans are connected is short-circuited, simply turning on the high-side switch causes the power supply current (1) to increase to There is a possibility that the power supply current will flow to the shorted fan circuit and the power supply current will not be supplied to the general computer of the entire vehicle. In that case, the function of the entire vehicle is lost.

Therefore, before turning on the high-side switch, it is necessary to check in advance whether the fan circuit is short-circuited (pre-check).

An example of a conventional load short-circuit detection method is shown in FIG. In FIG. 4(a), 200 is a power supply circuit that outputs a DC voltage of 24 V using, for example, a DC-DC converter. A positive output terminal of the power supply circuit 200 is connected to a positive terminal P of a load circuit 202 via a high side switch 201 (for example, FET). Although not shown, the negative output terminal of the power supply circuit 200 is connected to the negative terminal N of the load circuit 202 .

Reference numeral 203 denotes a constant voltage source that outputs a test voltage Vtest for checking short circuits, and its output side is connected to a positive terminal P via a current limiting resistor 204 . A voltage dividing resistor 205 is connected between the positive terminal P and the negative terminal N. FIG.

When the load circuit 202 is, for example, a DC brushless fan, as shown in FIG. , a three-phase bridge circuit 212 of switching elements whose switching is controlled by the control circuit 211 , and a fan motor 213 driven by the output voltage of the three-phase bridge circuit 212 .

When checking the load circuit 202 for a short circuit, the high-side switch 201 is turned off, and the voltage (24 VDC) obtained by dividing the test voltage Vtest of the constant voltage source 203 by the current limiting resistor 204 and the voltage dividing resistor 205 is applied to the positive terminal P, It is applied across the negative terminal N.

If the load side is not short-circuited, the current _IL to the load side will be a value below a certain level, so the voltage at the output voltage terminals (P, N) on the load side will be above a certain level. By detecting the voltage value between the terminals P and N through an insulated analog amplifier (not shown), it can be confirmed that the load circuit 202 is not short-circuited.

Conventionally, a circuit for detecting a drop in the output voltage of a DC-DC converter related to the present invention has been proposed, for example, in Japanese Unexamined Patent Application Publication No. 2002-200013.

JP 2015-300284 A

However, in the case of the circuit shown in FIG. 4, a detection circuit (insulated analog amplifier) is required to detect the voltage Vout between the output terminals (between the positive terminal P and the negative terminal N), and the detection threshold must be clarified. There is

The conditions for load short-circuit check in the circuit of FIG. 4 are as follows. That is, the load resistance RL of the load circuit 202 in FIG. ₄ , the resistance value of the current limiting resistor 204 is R ₁ , the current flowing therethrough is I, the resistance value of the voltage dividing resistor 205 is R ₂ , the current flowing through it is I _R , the load Assuming that the current flowing through the circuit 202 is I _L ,
Vtest=I* _R1 + _R2 * _IR , _R2 * _IR = _RL * _IL , I= _IR + _IL ,
The conditions for load short-circuit check are
Vout=R ₂ ×I _R =Vtest−I×R ₁ <voltage at which the load does not start control operation.

When a voltage above a certain level is applied to the load circuit 202, for example, in a DC brushless fan, when the voltage reaches the voltage at which the control circuit 211 starts operating, the consumption current (I _L ) increases, resulting in an erroneous short circuit. may be detected. Therefore, the current consumption (I _L ) must be taken into consideration when designing the current limiting resistor 204 (R ₁ ) and the voltage dividing resistor 205 (R ₂ ). Therefore, the design of the current limiting resistor 204 (R ₁ ) and the voltage dividing resistor 205 (R ₂ ) becomes complicated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a load circuit failure detection device capable of reliably detecting a failure such as a short circuit in a load circuit that operates at a voltage equal to or higher than a set voltage.

The load circuit failure detection device according to claim 1 for solving the above problems,
a first switch connected between a positive terminal of a DC power supply and a positive terminal of a load that operates at a set voltage or higher and whose negative terminal is connected to the negative terminal of the DC power supply;
a second switch, a resistor, a Zener diode whose Zener voltage is set to be less than the starting voltage of the load, and a photocoupler, which are sequentially connected in series between the positive terminal and the negative terminal of the DC power supply;
a diode having an anode connected to the common junction of said resistor and a Zener diode, and a cathode connected to the positive end of said load;
The normality/abnormality of the load is determined based on the on/off operation of the photocoupler when the first switch is turned off and the second switch is turned on.

The load circuit failure detection device according to claim 2 is the load circuit failure detection device according to claim 1,
The load operating above the set voltage is a fan.

The load circuit failure detection method according to claim 3,
a first switch connected between a positive terminal of a DC power supply and a positive terminal of a load that operates at a set voltage or higher and whose negative terminal is connected to the negative terminal of the DC power supply;
a second switch, a resistor, a Zener diode whose Zener voltage is set to be less than the starting voltage of the load, and a photocoupler, which are sequentially connected in series between the positive terminal and the negative terminal of the DC power supply;
a diode having an anode connected to the common junction of said resistor and a Zener diode, and a cathode connected to the positive end of said load;
a control step of turning off the first switch and turning on the second switch;
and determining whether the load is normal/abnormal based on the ON/OFF operation of the photocoupler during execution of the control step.

According to the present invention, it is possible to reliably detect a failure such as a short circuit in a load circuit that operates at a voltage equal to or higher than a set voltage. Also, for a load circuit whose current consumption varies depending on the magnitude of the voltage, the short-circuit check circuit can be designed regardless of the current value of the load circuit. Further, since analog voltage detection is not required, an insulated analog amplifier or the like is not required, and the circuit configuration is simplified.

1 is an overall configuration diagram according to an embodiment of the present invention; FIG. FIG. 2 is a circuit diagram of a main part of FIG. 1; Fig. 3 shows the relationship between the operating voltage and current of a DC brushless fan, where (a) is an explanatory diagram of measured values of the operating voltage and current, and (b) is an input current/voltage characteristic diagram. The block diagram of the conventional load short circuit detection apparatus.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiment examples. FIG. 1 shows the configuration of a DC-DC converter mounted on a battery forklift and a load circuit connected thereto. In FIG. 1, 100 is a J24 power supply circuit that outputs a voltage of 24 V DC, and 101 is an inverse conversion unit in which switching elements 101a to 101d are single-phase bridge-connected between the positive and negative terminals of a DC voltage source (not shown). be.

The switching elements 101a and 101b are on/off controlled by the gate driver IC102, and the switching elements 101c and 101d are on/off controlled by the gate driver IC103.

The AC output of the inverse converter 101 is supplied via a transformer 104 to a forward converter 105 in which diodes 105a to 105d are bridge-connected and converted into a direct current.

The DC output of the forward converter 105 is waveform-shaped by a filter composed of a reactor 106 and a capacitor 107, and a 24V DC power supply (J24V) is obtained at the positive terminal of the capacitor 107. FIG.

108 is a current sensor (CS1) that detects the current output from the reactor 106, and 109 is a J24 overcurrent detection circuit that detects overcurrent from the current detected by the current sensor 108. FIG.

Reference numeral 110 denotes a J24 overvoltage detection circuit that detects whether or not the potential of the positive terminal of the capacitor 107 is overvoltage.

Capacitors C115 and C116 are connected in series between the positive terminal and the negative terminal of the capacitor 107 (the negative terminal of the forward converter 105).

The positive terminal (J24V output terminal) of the capacitor 107 is connected to the positive terminal (terminal number 2) of the terminal (connector) P1 for power supply to the master controller (computer for controlling the entire vehicle), and the voltage control circuit 121 and the high side switch 122 to the positive electrode (terminal number 4) of the terminal P2 for power supply to a computer other than the master controller. The negative terminal of the capacitor 107 is connected to the negative terminal P1 (terminal number 7) and the terminal P2 negative terminal (terminal number 10).

Also, the positive terminal (J24V output terminal) of the capacitor 107 is connected to the positive terminals of the terminals P11 to P13 for supplying power to the cooling fans FAN1 to FAN3 via the high side switches TR16, TR18, TR20 (first switch). (terminal numbers 3, 5, 6). The negative terminal of the capacitor 107 is connected to the negative terminals of the terminals P11 to P13 (terminal numbers 1, 9 and 8).

The cooling fans FAN1 to FAN3 connected to the terminals P11 to P13 are composed of DC brushless fans, for example.

A fan short-circuit detection circuit 300 of the present invention is connected to the load circuit consisting of the high-side switches TR16, TR18, TR20 and terminals P11 to P13. The fan short-circuit detection circuit 300 includes a high-side switch TR42 (second switch) connected in series between the positive terminal of the capacitor 107 (J24V output terminal) and the ground (negative potential of the J24V power supply), and a current limiter. A resistor R371, a voltage limiting Zener diode ZD34, a photocoupler U51, and an anode are connected to a common connection point of the resistor R371 and the Zener diode ZD34, and a cathode is connected to a common connection point of the positive electrodes of the high-side switch TR16 and the terminal P11. a diode D65 whose anode is connected to the common connection point of the resistor R371 and the Zener diode ZD34 and whose cathode is connected to the common connection point of the positive electrodes of the high-side switch TR18 and the terminal P12; A diode D66 connected to a common connection point of the diodes ZD34 and having a cathode connected to a common connection point of the positive electrodes of the high-side switch TR20 and the terminal P13 is provided.

The high side switches TR42, TR16, TR18, and TR20 are composed of MOSFETs, for example.

In FIG. 1, if the minimum operating voltage of the device connected to the load is clear, for example, the cooling fan connected to terminals P11 to P13 operates at a rated voltage of 24 V DC, operates with a microcomputer or brushless drive In the case of a DC brushless fan using an IC, even if a voltage of about 5V is supplied, it will not operate normally due to insufficient voltage. Therefore, the current value supplied to the DC brushless fan circuit is zero or extremely low.

The fan short-circuit detection circuit 300 utilizes this characteristic, and when a voltage that does not operate normally is supplied to the load and a current value exceeding a certain value flows, it is determined that the circuit is abnormal such as a short circuit. do.

For example, to check the short circuit of the DC brushless fan connected to the terminal P11, the high side switch TR16 is turned off and TR42 is turned on. Supply voltage. At that time, if there is no load short circuit, the current value flowing through the terminal P11 is small, and if there is a load short circuit, the current value is large. Normality/abnormality is determined based on the operating state of the photocoupler U51, which is turned on or off according to the magnitude of this current value.

Next, a detailed circuit of the fan short-circuit detection circuit 300 will be described with reference to FIG. In FIG. 2, a circuit for controlling ON/OFF of the high-side switches TR42, TR16, TR18, and TR20 of FIG. 1 is added, and the same parts as those in FIG.

2, the capacitor 107 in FIG. 1 is replaced with capacitors C111 and C212 connected in parallel, and the positive terminals of these capacitors C111 and C212 are denoted as "J24 output", and the positive and negative terminals of the J24 output are shown. Resistors R164 and R352 are connected in parallel therebetween, and the load circuit on the side of terminals P1 and P2 in FIG.

In FIG. 2, U50 is a photocoupler for driving the high side switch TR42. The emitter (terminal 3) of the phototransistor on the secondary side of the photocoupler U50 is grounded (the negative potential of the J24 output), and the collector (terminal 4) is connected to the positive terminals of the capacitors C111 and C212 through the resistors 368 and R367. (J24 output), and the common connection point of the resistors R367 and R368 is connected to the gate of the high side switch TR42.

When the potential of the FANCheck terminal connected to the terminal 2 of the photocoupler U50 is lowered to a potential at which the primary diode can conduct, the primary diode conducts and the phototransistor turns on. The high-side switch TR42 is turned on by the applied potential.

Conversely, by increasing the potential of the FANCheck terminal to a potential at which the primary-side diode does not conduct, the phototransistor is turned off and the high-side switch TR42 is controlled to be off.

A resistor R372 is connected in parallel with the primary diode of the photocoupler U51 connected between the anode of the Zener diode ZD34 and the ground (negative potential of the output J24).

The Zener voltage of the Zener diode ZD34 is selected to a voltage at which the circuit of the cooling fan (DC brushless fan) connected to the terminals P11 to P13 does not operate reliably. This selection is made by experimentally measuring the starting voltage (voltage at which current begins to flow) and current of the DC brushless fan (actual fan) shown in FIG.

Fig. 3(a) shows the measured values of the current and voltage when the limiter current is about 1/10 of the rated current of 0.89 A and the applied voltage is about 7 V or less to the measured fan rated at 24 VDC. , and FIG. 3(b) shows its input current/voltage characteristics.

According to FIG. 3, it is clear that current does not flow in the fan circuit if the applied voltage is less than DC 7.4V. 1V was selected.

For example, when checking the short circuit of the DC brushless fan on the terminal P11 side, if the high side switch TR16 connected to the terminal P11 is turned off and TR42 is turned on, if the load side is normal (not short-circuited), the Zener diode ZD34 becomes 5.1 V or higher, the Zener diode ZD34 becomes conductive, current flows through the primary diode of the photocoupler U51, the secondary phototransistor turns on, and the collector of the phototransistor (terminal 4) becomes LOW. level, and a FAN short-circuit detection signal (LOW) is transmitted to the digital input port of the CPU.

U39 is a photocoupler for driving the high side switch TR16. A resistor R186 and a resistor R187 are connected in series between the 5V control power supply terminal provided on the primary diode side of the photocoupler U39 and the FAN1 OUTEN terminal, and the anode and cathode (terminals 1 and 2) of the primary diode are connected in series. ) are connected to both ends of a resistor R186, the emitter (terminal 3) of the phototransistor on the secondary side of the photocoupler U39 is grounded, and the collector (terminal 4) is connected to the capacitors C111, C111, C111 through a resistor R184. The common connection point of resistors R184 and R185 is connected to the gate of high-side switch TR16, and capacitor C132 is connected in parallel with resistor R184.

When the potential of the FAN1OUTEN terminal connected to the terminal 2 side of the photocoupler U39 is lowered to a potential at which the primary diode can conduct, the primary diode conducts and the phototransistor turns on. The high-side switch TR16 is turned on by the voltage-divided potential.

Conversely, by increasing the potential of the FAN1 OUTEN terminal to a potential at which the primary diode is not conductive, the phototransistor is turned off and the high-side switch TR16 is controlled to be off.

U40 is a photocoupler for driving the high side switch TR18. A resistor R191 and a resistor R192 are connected in series between the 5V control power supply terminal provided on the primary diode side of the photocoupler U40 and the FAN2OUTEN terminal, and the anode and cathode (terminals 1 and 2) of the primary diode are connected in series. ) are connected to both ends of a resistor R191, the emitter (terminal 3) of the phototransistor on the secondary side of the photocoupler U40 is grounded, and the collector (terminal 4) is connected to the capacitors C111, C111, C111 through a resistor R189 through a resistor 190 and a resistor R189. The common connection point of the resistors R189 and R190 is connected to the gate of the high side switch TR18 A capacitor C133 is connected in parallel to the resistor R189.

When the potential of the FAN2OUTEN terminal connected to the terminal 2 side of the photocoupler U40 is lowered to a potential at which the primary diode can conduct, the primary diode conducts and the phototransistor turns on. The high-side switch TR18 is turned on by the voltage-divided potential.

Conversely, by increasing the potential of the FAN2OUTEN terminal to a potential at which the primary side diode does not conduct, the phototransistor is turned off and the high side switch TR18 is controlled to be off.

U41 is a photocoupler for driving the high side switch TR20. A resistor R196 and a resistor R197 are connected in series between the 5V control power supply terminal provided on the primary diode side of the photocoupler U41 and the FAN3OUTEN terminal, and the anode and cathode (terminals 1 and 2) of the primary diode are connected in series. ) are connected to both ends of a resistor R196, the emitter (terminal 3) of the phototransistor on the secondary side of the photocoupler U41 is grounded, and the collector (terminal 4) is connected to the capacitors C111, C111, C111 through a resistor R194 through a resistor 195 and a resistor R194. The common connection point of resistors R194 and R195 is connected to the gate of high-side switch TR20, and capacitor C134 is connected in parallel with resistor R194.

When the potential of the FAN3OUTEN terminal connected to the terminal 2 side of the photocoupler U41 is lowered to a potential at which the primary diode can conduct, the primary diode conducts and the phototransistor turns on. The high-side switch TR20 is turned on by the voltage-divided potential.

Conversely, by increasing the potential of the FAN3 OUTEN terminal to a potential at which the primary side diode does not conduct, the phototransistor is turned off and the high side switch TR20 is controlled to be off.

Assuming that the steady-state ON voltages of the primary diodes in the high-side switch TR42 and the photocoupler U51 are both 0 V, the current I flowing through the resistor R371 (resistance value=330Ω) when the high-side switch TR42 and the photocoupler U51 are ON is ,
I=(24V-5.1V)/330Ω (1)
(assuming there is no short circuit in the load circuit).

This current I is set to a value sufficient to turn on the photocoupler U51. In other words, the resistance value of 330 Ω of the resistor R371 is designed based on the rated output voltage of 24 V, the Zener voltage of the Zener diode ZD34 of 5.1 V, and the current that can be turned on by the photocoupler U51 (generally described in the data sheet of the photocoupler). It will be.

2 may be replaced with mechanical switches such as relays.

Next, the short circuit check procedure will be described.
(1) Initially, the high-side switches TR16, TR18, and TR20 are all turned off.
(2) Turn on the primary diode of the photocoupler U50 to turn on the high side switch TR42.
(3) Power is sent (energized) from the J24 output to the high-side switch TR42→resistor R371→diodes D64, D65, D66→each of the terminals P11 to P13.

Hereinafter, the operations when there is no load short-circuit are described in (4) to (6), and the operations when there is a load short-circuit are described in (7) to (9).
(4) As a result of energization, when there is no load short-circuit, the current flowing from the J24 output to the output terminal side is small, so the potential of the cathode terminal of the Zener diode ZD34 ≈ the Zener voltage of 5.1 V, and the Zener diode ZD34 is conduct. As a result, most of the current flowing through the resistor R371 flows from the Zener diode ZD34 to the primary diode of the photocoupler U51.
(5) The phototransistor on the secondary side of the photocoupler U51 is turned on, and the FAN short-circuit detection signal (LOW signal) at the terminal 4 of the photocoupler U51 notifies the CPU that the operation is normal.
(6) Turn off the high-side switch TR42 to end the load short-circuit check. At the same time, the high-side switches TR16, TR18, and TR20 corresponding to the required output terminal are turned on to supply each load circuit with a DC 24V voltage, which is the rated voltage of the DC brushless fan.
(7) As a result of the energization in (3) above, if there is a load short-circuit, a large amount of current flows out to the output side, so the potential of the cathode terminal of the Zener diode ZD34≈0V (potential of the negative electrode of the output of J24). As a result, Zener diode ZD34 does not conduct. Therefore, the current does not flow from the Zener diode ZD34 to the primary diode of the photocoupler U51.
(8) As a result, the phototransistor on the secondary side of the photocoupler U51 remains in the OFF state, so that the abnormality is notified to the CPU by the FAN short-circuit detection signal (High signal) at the terminal 4 of the photocoupler U51.
(9) An error is issued, and the high-side switches TR16, TR18, TR20 corresponding to the requested output terminals are not turned on. At the same time, the high side switch TR42 is turned off to end the load short-circuit check. Since high side switches TR16, TR18, TR20 and TR42 are off, no power is supplied to the load circuit.
(10) If one of the plurality of cooling fans FAN1 to FAN3 is already outputting, even if a new output is added, it is possible to check in the same sequence as above.

As described above, in the present invention, based on the on/off operation of the photocoupler U51 when the high-side switches TR16, TR18, and TR20 are turned off and the high-side switch TR42 is turned on, the normality/abnormality of the load (whether or not the load is short-circuited) is detected. ) is determined.

Note that the load of the present invention may be replaced with a device that operates at a predetermined voltage (set voltage) or higher (that is, a device through which current flows at a predetermined voltage or higher) instead of the cooling fan.

As described above, according to this embodiment, it is possible to reliably detect a failure such as a short circuit in a load circuit that operates at a voltage equal to or higher than the set voltage. Further, the design of a short-circuit check circuit for a load circuit whose current consumption fluctuates according to the magnitude of the voltage can be performed based on the above equation (1), which is not related to the current value of the load circuit. Easy to design.

In addition, analog voltage detection (the voltage Vout across the voltage dividing resistor 205 is detected in FIG. 4 of the conventional example) is unnecessary, so an insulated analog amplifier or the like is unnecessary, and the circuit is simple.

In addition, when one of the plurality of cooling fans (FAN1 to FAN3) is already outputting, even when adding a new output, it is possible to check in the same sequence as above.

100... J24 power supply circuit 10I... Inverse converter 102, 103... Gate driver IC
DESCRIPTION OF SYMBOLS 104... Transformer 105... Forward conversion part 106... Reactor 107... Capacitor 108... Current sensor 300... FAN short circuit detection circuit D65, D65, D66... Diode TR16, TR18, TR20, TR42... High side switch U39, U40, U41, U50, U51... Photocoupler R371, R372... Resistor ZD34... Zener diode P11 to P13... Terminal (connector)
FAN1 to FAN3... Cooling fans

Claims (3)

a first switch connected between a positive terminal of a DC power supply and a positive terminal of a load that operates at a set voltage or higher and whose negative terminal is connected to the negative terminal of the DC power supply;
a second switch, a resistor, a Zener diode whose Zener voltage is set to be less than the starting voltage of the load, and a photocoupler, which are sequentially connected in series between the positive terminal and the negative terminal of the DC power supply;
a diode having an anode connected to the common junction of said resistor and a Zener diode, and a cathode connected to the positive end of said load;
A load circuit failure detection device, wherein normality/abnormality of the load is determined based on an on/off operation of a photocoupler when the first switch is turned off and the second switch is turned on. 2. The load circuit failure detection device according to claim 1, wherein the load that operates at the set voltage or higher is a fan. a first switch connected between a positive terminal of a DC power supply and a positive terminal of a load that operates at a set voltage or higher and whose negative terminal is connected to the negative terminal of the DC power supply;
a second switch, a resistor, a Zener diode whose Zener voltage is set to be less than the starting voltage of the load, and a photocoupler, which are sequentially connected in series between the positive terminal and the negative terminal of the DC power supply;
a diode having an anode connected to the common junction of said resistor and a Zener diode, and a cathode connected to the positive end of said load;
a control step of turning off the first switch and turning on the second switch;
and determining normality/abnormality of the load based on ON/OFF operation of a photocoupler during execution of the control step.

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