JP3400216B2 - Power supply - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to relates to a power supply apparatus using <br/> overcurrent detection circuitry.

[0002]

2. Description of the Related Art When an overload condition occurs, an overcurrent detection circuit detects the condition and stops the power supply device, shuts off the load, or limits the current / voltage to prevent the power supply device and / or the load device. Used to protect. In the conventional overcurrent detection circuit, a current detection resistor through which the load current flows is provided to detect the magnitude of the current flowing into the load circuit, and a voltage drop (voltage proportional to the load current) generated in the resistor and a transistor The forward voltage between the base and the emitter is compared, and if the load current becomes excessive, this voltage drop becomes large, and the transistor in question operates (conducts), stopping the power supply, shutting off the load, or overloading the power supply or load. It was designed to generate a signal for current suppression. In this case, since the base-emitter forward voltage of the transistor changes due to changes in ambient temperature, the operating point (overcurrent detection point) of the transistor changes, so set an accurate overcurrent detection threshold value. Was difficult.

Therefore, in order to reduce malfunctions of the overcurrent detection circuit due to changes in the ambient temperature, for example, the actual open flat wire 4-6977 is used.
In JP-A-0, the following measures are taken. The configuration of the overcurrent detection circuit shown in FIG. In FIG. 4 , the output voltage V1 from the power supply device 1 is connected to the load device 3 through the current detecting resistor 2. The current to the load causes a voltage drop in the current detecting resistor 2 and the input voltage of the load device 3 becomes V ₂ .

The power supply output voltage V ₁ is divided by resistors 4 and 5,
The emitter bias voltage V ₃ is obtained, and the voltage V ₂ is applied to the resistors 6 and 6.
The voltage is divided by 7 to obtain the base bias voltage V ₄ . The voltage difference between V ₃ and V ₄ is compared with the forward voltage between the emitter and the base of the transistor 8, and when the voltage difference becomes large, it is determined that an overcurrent has occurred and a collector current is passed (overcurrent detection signal). It operates so as to stop the power supply device 1. In this device, V
_3, the voltage difference V ₄ because any decidable, has the effect of improving the detection accuracy, the emitter-base of the transistor 8 which changes depending on the ambient temperature change - the scan forward voltage, connected to the emitter The temperature characteristics of the diode 9 are corrected. That is, since the emitter bias voltage changes so that the temperature characteristic of the diode 9 cancels the characteristic change of the transistor 8 due to the ambient temperature change, malfunction does not easily occur even if the ambient temperature changes.

[0005] FIG. 5 shows an example of incorporating power supply overcurrent detection circuit shown in FIG. MOS-F connected to the primary winding of the transformer 25 which constitutes a DC / DC converter
The control IC 44 repeatedly turns ON / OFF the ET 24 to chop the primary current.

As a result, output voltages Vo1 and Vo2 are generated. The control IC 44 has its power supply voltage end (capacitor 2
When the voltage of the positive electrode 3) rises from the zero level to a predetermined level or more, the internal circuit is reset (power on / reset), and the above-mentioned MOS-FET 24 is repeatedly turned on / off.
When the phototransistor of the photocoupler 41 becomes conductive (ON) and becomes a negative potential (negative potential of the capacitor 23), the MOS-FET 24 is turned off in response to this, the ON / OFF is stopped, and the power is turned on again. It stays off until it is reset.

When an overcurrent occurs in the load, the current detection transistor 8 operates (conduction: ON) as described above,
Then, the current amplification transistor 40 connected to the transistor 8 is turned on (ON), the light emitting diode of the photocoupler 41 is energized to emit light, and the photocoupler 41 is turned on.
The phototransistor of turns on. In response to this, the control IC 44 turns off the MOS-FET 24 to stop the on / off, and keeps the off until the power is turned on / reset again. That is, the control IC 44
MOS-FET2 for chopper by stopping
4 is stopped and secondary AC output (transformer transformer 25 output)
Is zero, and therefore the secondary DC output (Vo1, Vo2) is also zero.

[0008]

[SUMMARY OF THE INVENTION] The foregoing power supplies (Figure
In 5 ), when the output is short-circuited suddenly, or particularly when the output is short-circuited, the amplifier circuit (40, 41, 4) is used.
Since the voltage used in 5) is obtained from the power supply output line (Vo1) monitored by the overcurrent detection circuit 20, if the voltage drops before the overcurrent protection operation of the circuit 20 (ON of the transistor 8), the amplifier circuit There is a problem that (40, 41, 45) does not operate (transistor 40 does not turn on).

[0009] The present invention is directed to purpose an overcurrent protection function to provide a high power device.

[0010]

The first power supply device of the present invention, in order to solve the problems]
The mode (FIGS. 1 and 2 ) is such that a rectifying bridge (22) for converting an alternating current into a direct current, a transformer (25), and a conduction loop between the primary coil of the transformer and the rectifying bridge (22). Power supply circuit (1) including inserted switching means (24) and control means (44) for turning off the energization loop by the switching means in response to an overcurrent detection signal; output of the power supply circuit An overcurrent detection circuit (20) that includes a resistor (2) through which a current flows and that detects an overcurrent based on the potential difference between the power supply circuit side potential and the load side potential of the resistor, and generates an overcurrent signal; And a power supply device comprising amplification means (40, 41, 45) for giving an overcurrent detection signal obtained by amplifying an overcurrent signal to the control means (44), wherein the power supply voltage of the amplification means (40, 41, 45) The power output line monitored by the overcurrent detection circuit (20)
It is characterized in that it is connected to a line (Vo2) that gives a required voltage, which is different from (Vo1).

Further, the power supply device according to the second aspect of the present invention (FIG. 3 )
Is a rectifying bridge (22) for converting an alternating current into a direct current, a transformer (25), a primary coil of the transformer and the rectifying bridge.
Switching means (2) inserted in the energizing loop between (22)
4), control means (44) for turning off the energization loop by the switching means in response to the overcurrent detection signal, and transformer 2
The rectifier (26, 27) connected to the next winding, the choke coil (30) for smoothing the rectified output, and the anode are the choke.
Power supply circuit including a diode (44) connected to the rectifier side of the coil coil, and a capacitor (47) connected to the cathode of the diode and the other side of the choke coil.
(1); Includes a resistor (2) through which an output current of the power supply circuit flows, and detects an overcurrent based on a potential difference between the power supply circuit side potential and the load side potential of the resistor to generate an overcurrent signal An overcurrent detection circuit (20) for amplifying the overcurrent signal, and an amplification means for giving an overcurrent detection signal obtained by amplifying the overcurrent signal to the control means (44), the power supply voltage application terminal of which is the diode (44). Amplification means (40, 41, 45) connected to the cathode.

In order to facilitate understanding, the reference numerals of the corresponding elements or corresponding matters of the embodiments shown in the drawings and described later are added in parentheses for reference.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION An overcurrent detection circuit (20) for a power supply device of the present invention comprises a current detection resistor (2), a current detection transistor (8), and a base-emitter of the transistor (8). Bias means (9) for canceling forward voltage temperature change by diode forward voltage temperature change, and current detection setting means
Equipped with (4,5). Further, the amplification means includes an amplification transistor (40), a thyristor (48) or a triac.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0015]

Embodiments- First Embodiment-FIG. 1 shows an embodiment of a power supply circuit according to the present invention. In FIG. 1 , an AC power source 21 is rectified by a rectifying diode bridge 22 and smoothed by a smoothing capacitor 23 to generate a direct current (first
To the next). This direct current (first order) output circuit has M
The OS-FET 24 and the primary side of the transformer 25 for transformation are connected in series. The MOS-FET 24 is a control IC 4
4 is repeatedly turned ON / OFF. Control IC4
4 is of the same functions as those used in the conventional example shown in FIG. Repeated ON / OFF of MOS-FET24
When turned off, an AC voltage (secondary AC) is generated in one coil on the secondary side of the transformer 25. The alternating current is converted into direct current (secondary) by the diodes 26 and 27, and the choke coil 30 and the capacitor 32 smooth the pulsating direct current to a constant level. This constant level direct current is passed through the resistor 2
Further, the output is smoothed by the capacitor 42. This is the first output circuit. DC output voltage Vo1 of this circuit
Is monitored by the voltage detection circuit 43.
The voltage detection circuit 43 gives a feedback signal indicating the detection voltage Vo1 to the control IC 44, and the control IC 44 sets the MO so that the detection voltage Vo1 matches the set value (target value).
The ON duty of the S-FET 24 is adjusted.

An AC voltage (secondary AC) is also generated in the other coil on the secondary side of the transformer 25. This alternating current is converted into direct current (secondary) by the diodes 28 and 29, and the cho
The coil 31 and the capacitor 33 smooth the pulsating direct current to a constant level. This constant level DC is output. This is the second output circuit 50.

In this embodiment, the overcurrent detection circuit 20 is connected to the first output circuit. This overcurrent detection circuit 2
The output of the current detection transistor 8 of 0 is applied to the base of the current amplification transistor 40. Capacitor 45
Is for smoothing. The collector of the current amplifying transistor 40 is supplied with a voltage (Vcc) from the second output circuit 50 of another system via the light emitting diode of the photocoupler 41.
Is getting

During normal operation, the current detection transistor 8
Is OFF, therefore the current amplification transistor 40 is also OFF, the light emitting diode of the photocoupler 41 does not emit light, the phototransistor is OFF, and a negative potential (device ground) is not applied to the control IC 44. .

However, when an overcurrent, a load short circuit or a short circuit start occurs, the current detection transistor 8 is turned on, the current amplification transistor 40 connected to another system line (50 output line) is turned on, and the photocoupler is turned on. The light emitting diode of 41 emits light to turn on the phototransistor, and a negative potential (apparatus ground) is applied to the control IC 44 from the photocoupler 41. In response to this, the control IC 44 turns off the MOS-FET 24 and stops ON / OFF. The power supply voltage (the positive voltage of the capacitor 23) is 0
The control IC 44 turns off the MOS-FET 24 until the power is turned on / reset after the voltage rises above the predetermined level.
To continue. Therefore, the DC chopper operation by the MOS-FET 24 stops, the AC output (secondary) on the secondary side of the transformer 25 disappears, and the DC (secondary) output also disappears, so the output stops. Since the power source of the control IC 44 itself is obtained from the primary DC, the control function is not impaired even when an overcurrent or the like occurs.

As described above, even when the DC output voltage Vo1 suddenly drops due to the overcurrent, the amplifier circuit voltage is obtained from the separate system line (output circuit 50), so that the power cutoff function is lost. Without fail, overcurrent protection is reliably performed.

Second Embodiment FIG. 2 shows an example in which a thyristor (or triac) 48 is used instead of the current amplification transistor 40 in an overcurrent signal amplification circuit used in a power supply device. The operation of FIG. 2 is almost the same as that of FIG. 1 , but a thyristor (or triac) 48 is used instead of the current amplifying transistor 40, and the current detecting transistor 8 is turned on to temporarily turn on the thyristor (or triac) 48. When the gate (G) signal is input to the thyristor (or triac) 48, the photocoupler 41 is turned on because the thyristor (or triac) 48 is kept on (latched) until the energization level becomes substantially zero. Since the ON / OFF control of the MOS-FET 24 of the control IC 44 is stopped, the power supply device stops the output. Other configurations and operations are the same as those in the first embodiment, and the description thereof will be omitted.

Third Embodiment FIG. 3 shows a mode in which the power supply voltage of the current amplification transistor 40 is obtained in the upstream stage of the first output circuit. The embodiment of FIG. 3 is also a embodiment and generally similar construction and operation of the FIG. 1, the light emitting diode of the current amplifying transistor 40 and the photo-coupler 41 in FIG. 3 - de power supply voltage (Vcc) is,
Immediately after direct-current (secondary) full-wave rectification, that is, obtained by branching from the connection point of the rectifying diodes 26 and 27 and the smoothing choke coil 30. The diode 44 is for rectification,
The capacitor 47 is for smoothing the power supply voltage (Vcc).

With this circuit configuration, even if the output voltage Vo1 drops significantly due to a short circuit or the like in the load circuit, the power is diverted from the upstream side of the current detection resistor 2 and the choke coil 30. Is obtained, the power supply voltage (Vc
c) can be secured, and the current amplification transistor 4
It is certain that the overcurrent protection operation of the cutoff circuit composed of 0 and the photocoupler 41 is performed. The other structure and operation are the same as those in the first embodiment, and the description thereof will be omitted.

The effects of each embodiment described above are summarized as follows. (1) In the power supply device of the present invention (FIGS. 1, 2, 3), 5
Compared with the conventional circuit shown in FIG. 1, by obtaining the power supply voltage (Vcc) of the interruption circuit composed of the current amplification transistor 20 and the photocoupler 21 used in the protection circuit from the power supply of another system, the output short circuit and the output short circuit start are performed. Even in the event of an abnormality such as the above, it is possible to solve the problem that the cutoff circuit does not operate due to a decrease in the power supply voltage (Vcc), and a reliable overcurrent protection operation can be performed. ( 2 ) In the power supply device of the present invention (FIG. 2 ), by using a thyristor (or triac) 28 instead of the current amplification transistor 20 used in the protection circuit,
Once a signal is applied to the gate (G) due to the occurrence of an overcurrent, the state is latched, and the photocoupler 21 is operated to operate the control IC, so that the power supply can be surely stopped. ( 3 ) In the power supply device of the present invention (FIG. 3 ), the power supply voltage (Vcc) of the interruption circuit composed of the current amplification transistor 20 and the photocoupler 21 used in the protection circuit is set to the direct current (2).
By branching immediately after the output of the rectifying diode in (next) and obtaining the voltage (Vcc) from another circuit, the power supply voltage can be secured even in the event of an output short circuit or an output short circuit start. It is possible to solve the problem that the protection circuit does not operate due to the decrease, and it is possible to perform a reliable overcurrent protection operation.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a first embodiment which is one of the power supply devices of the present invention.

FIG. 2 is an electric circuit diagram showing a second embodiment which is one of the power supply devices of the present invention.

FIG. 3 is an electric circuit diagram showing a third embodiment which is one of the power supply devices of the present invention.

FIG. 4 is an electric circuit diagram showing one of conventional overcurrent detection circuits.

FIG. 5 is an electric circuit diagram showing one of conventional power supply devices.

[Explanation of symbols]

1: Power supply circuit 2: Resistor for current detection 3: Load device 4-7: Resistor for voltage division 8: Transistor for current detection 9: Diode for temperature correction 10: Resistor for voltage division 11: Resistor for current limitation 12: Zener diode 20: Overcurrent detection circuit 21: AC power supply 22: Rectifying bridge 23: Smoothing capacitor 24: MOS-FET 25: Transformers 26 to 29: Diodes 30, 31: Choke coils 32, 33: Smoothing capacitor 40: Current amplification transistor 41: Photocoupler 42: Smoothing capacitor 43: Voltage detection circuit 4: Control IC 45: Smoothing capacitor 46: Diode 47: Smoothing capacitor 48: Thyristor (or triac) 50: Second output circuit P : Package

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01R 19/165 G01R 19/32 H02H 3/08 G05F 1 / 56,320 H02M 7/48 H02M 3/00

Claims (4)

(57) [Claims] 1. A rectifying bridge for converting an alternating current into a direct current,
A transformer, a switching means inserted in an energizing loop between the primary coil of the transformer and the rectifying bridge, and the energizing loop is turned off by the switching means in response to an overcurrent detection signal. A power supply circuit including control means; including a resistor through which an output current of the power supply circuit flows, and detecting an overcurrent based on a potential difference between a potential on the power supply circuit side of the resistor and a potential on the load side to generate an overcurrent signal An overcurrent detecting circuit for amplifying an overcurrent signal, and an amplifying means for giving an overcurrent detecting signal obtained by amplifying the overcurrent signal to the control means. A power supply device characterized in that it is connected to a line that provides a required voltage, which is different from the power output line to be monitored. 2. A rectifying bridge for converting an alternating current into a direct current,
Transformer, switching means inserted in the energization loop between the primary coil of the transformer and the rectifying bridge, control means for turning off the energization loop by the switching means in response to an overcurrent detection signal A rectifier connected to the secondary winding of the transformer, a choke coil for smoothing the rectified output of the rectifier, a diode having an anode connected to the rectifier side of the choke coil, and the diode. Power supply circuit including a cathode and a capacitor connected to the other side of the choke coil; a potential of the power supply circuit side and a load side potential of the resistor including a resistor through which an output current of the power supply circuit flows. An overcurrent detection circuit for detecting an overcurrent based on a potential difference between the overcurrent detection circuit and an overcurrent detection circuit; and an amplifying means for giving an overcurrent detection signal obtained by amplifying the overcurrent signal to the control means. Voltage application end the diode - de of cathode - amplification means connected to the de; power device comprising a. 3. The power supply device according to claim 1 , wherein the amplification means includes a current amplification transistor, a thyristor or a triac. 4. An overcurrent detection circuit comprising a current detection transistor in which a potential at one end of the resistor is applied to a base and a potential at the other end is applied to an emitter, and a forward direction between a base and an emitter of the current detection transistor. diode to cancel the temperature change of the voltage at the temperature change of the forward voltage - comprises a biasing means including de, means for setting the overcurrent detection threshold of the current detection transistor, according to claim 1, claim 2 or claim The power supply device according to item 3 .