JPH11146635A - Direct current power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect a direct current power supply against overloading and load short-circuiting through a simple circuit. SOLUTION: An n-channel MOS-FET 21 for overcurrent protection which is kept in ON state with a normal load, and brought into OFF state to interrupt an output current supplied to a load 6 when overloading or load short-circuiting occurs is connected between an output capacitor 5 and the load 6. With a normal load, the n-channel MOS-FET 21 is kept in ON state. Therefore, direct current output VOUT of constant voltage output from the output capacitor 5 is supplied to the load 6 through the n-channel MOS-FET 21 by the on/off operation of the MOS-FET 3. If the load 6 is overloaded or short-circuited the n-channel MOS-FET 21 is shifted from ON state to OFF state, and the output current VOUT supplied from the output capacitor 5 to the load 6 is interrupted. For the reason, the direct current power supply can be protected against overloading and load short-circuiting with reliability through a simple circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power supply capable of reliably protecting a power supply from overcurrent with a simple circuit configuration.

[0002]

2. Description of the Related Art A switching element for intermittently converting a DC input of a DC power supply by an on / off operation to convert to a high frequency power, and a DC conversion circuit for converting a high frequency power to a DC output for supplying to a load are provided to the load. 2. Description of the Related Art A DC power supply device that supplies a constant-voltage DC output to a load by controlling on / off of a switching element according to a DC output to be performed has been widely used in power supply circuits of electronic devices and the like. For example, a boost chopper type converter as a conventional DC power supply device shown in FIG. 8 includes a DC power supply 1 such as a battery or a rectifier circuit, a reactor 2 connected in series to both ends of the DC power supply 1, and a MOS-type switching element. FET3,
The output diode 4 and the output capacitor 5 connected in series to both ends of the MOS-FET 3, the load 6 connected to both ends of the output capacitor 5, and the MOS-FET 3 according to the DC output voltage V _OUT supplied to the load 6. and a control circuit 7 for generating an on-off control signal V _G to be applied to the gate terminal of the. In this boost chopper type converter, MO
The DC input current from the DC power supply 1 is intermittently converted by the ON / OFF operation of the S-FET 3 to be converted into high frequency power, and this high frequency power is supplied to the load 6 by the DC conversion circuit including the reactor 2 and the output capacitor 5. Voltage V
Converted to _OUT . A current detecting resistor 8 for detecting an output current I _OUT flowing through the load 6 as a corresponding voltage is connected to a negative line between the output capacitor 5 and the load 6. Control circuit 7, the comparator 10 for comparing the reference voltage V _R1 of the DC output voltage V _OUT of the reference power source 9 for generating a reference voltage V _R1, and the DC output voltage V _OUT and the reference power source 9 to be supplied to the load 6 Output voltage detection circuit 1
Compare 1, reference power source 12 generates a reference voltage V _B2 corresponding to the limit value of the output current I _OUT flowing through the load 6, and a reference voltage V _B2 of the detected voltage and the reference power source 12 of the current detection resistor 8 Overcurrent detection circuit 14 comprising comparator 13
And the comparison output of the comparator 10 of the output voltage detection circuit 11 output through the diode 15 and the diode 16
A PWM (pulse width modulation) signal having a variable pulse width is generated based on a logical sum signal with the comparison output of the comparator 13 of the overcurrent detection circuit 14 output through
MOS-FET a WM signal as an on-off control signal V _G
3 and a PWM signal generating circuit 17 provided to the gate terminal.

In the boost chopper type converter shown in FIG. 8, when the MOS-FET 3 is on,
Current flows through the reactor 2 and the MOS-FET 3 from the
Energy is stored in reactor 2. MOS-FET
When the switch 3 is turned off from the on state, the energy stored in the reactor 2 is released, and the DC output voltage V _OUT is supplied to the load 6 via the output diode 4 and the output capacitor 5. DC output voltage V supplied to the load 6
_OUT is compared with the reference voltage V _R1 of the reference power supply 9 by the comparator 10 of the output voltage detection circuit 11. On the other hand, the output current I _OUT flowing through the load 6 is detected by the current detection resistor 8 as a corresponding voltage, and the
The reference voltage V _B2 of the reference power supply 12
Is compared to Comparator 1 of output voltage detection circuit 11
0 comparison output and comparator 13 of overcurrent detection circuit 14
Are output to the PWM signal generation circuit 17 as OR signals by the diodes 15 and 16, respectively.
When the load 6 is in a normal state, the detection voltage of the current detection resistor 8 is lower than the reference voltage V _B2 of the reference power supply 12, and the comparison output of the comparator 13 of the overcurrent detection circuit 14 becomes low. The output signal of the overcurrent detection circuit 14 is substantially zero.
Becomes Therefore, at the time of a normal load, the pulse width of the PWM signal output from the PWM signal generation circuit 17 is controlled based on the output signal of the output voltage detection circuit 11, and is applied from the control circuit 7 to the gate terminal of the MOS-FET 3. oN width of the on-off control signal V _G is controlled. As a result, according to the DC output voltage V _OUT supplied to the load 6, M
The on / off control of the OS-FET 3 is performed, and a DC output of a constant voltage is supplied to the load 6.

When the load 6 is overloaded or short-circuited, the detection voltage of the current detection resistor 8 becomes higher than the reference voltage V _B2 of the reference power supply 12, so that the comparison output of the comparator 13 of the overcurrent detection circuit 14 It becomes high level, and the overcurrent detection circuit 14 outputs an overcurrent detection signal. Therefore, at the time of overload or load short-circuit, the pulse of the PWM signal output from the PWM signal generation circuit 17 based on the logical sum signal of the output signal of the output voltage detection circuit 11 and the overcurrent detection signal of the overcurrent detection circuit 14 width is narrowed, the oN width of the on-off control signal V _G applied to the gate terminal of the MOS-FET 3 is narrowed from the control circuit 7. With this, MOS-
The ON period of the FET 3 is shortened, and the output current I _OUT flowing through the load 6 is limited to a constant value.

[0005]

By the way, in the boost chopper type converter shown in FIG. 8, even when the MOS-FET 3 is turned off at the time of overload or load short-circuit, the discharge current from the output capacitor 5 causes a relatively large current. The output current I _OUT flows. For this reason, it is difficult to significantly limit the output current I _OUT at the time of overload or load short-circuit. Therefore, when the load 6 is short-circuited in the boost chopper type converter shown in FIG. 8, the output current I _OUT cannot be limited sufficiently, and the excessive current flowing at that time destroys the boost chopper type converter. There was a point.

It is an object of the present invention to provide a DC power supply having a simple circuit configuration and capable of reliably protecting the power supply from overload or load short-circuit.

[0007]

SUMMARY OF THE INVENTION A DC power supply according to the present invention supplies at least one switching element for intermittently converting a DC input of a DC power supply into an RF power by ON / OFF operation, and supplies the RF power to a load. A DC conversion circuit for converting the switching element into a DC output to supply a constant-voltage DC output to the load by controlling ON / OFF of the switching element according to the DC output. In this DC power supply device, a switching element for overcurrent protection is connected between the DC conversion circuit and the load, and the switching element for overcurrent protection keeps an ON state during a normal load and overloads or short-circuits a load. At this time, it is turned off, and the output current supplied to the load is cut off. In another embodiment of the present invention, the DC power supply is a boost converter that supplies a DC output voltage higher than a DC input voltage of the DC power supply to the load, and the overcurrent protection switching element is supplied to the load. When the DC output voltage falls below the DC input voltage of the DC power supply, the power supply is turned off.

In the case of a normal load, the switching element for overcurrent protection keeps the ON state, so that the DC output of the constant voltage output from the DC conversion circuit by the ON / OFF operation of the switching element of the power conversion unit. It is supplied to the load through the overcurrent protection switching element. When the load becomes overloaded or short-circuited, the switching element for overcurrent protection changes from the on state to the off state, and the output current supplied from the DC conversion circuit to the load is cut off by the on / off operation of the switching element of the power conversion unit. Is done. As a result, the output current in the overload or load short-circuit state is sufficiently limited, so that the power supply device can be reliably protected from overload or load short-circuit with a simple circuit configuration. In addition, in a boost converter that supplies a DC output voltage higher than the DC input voltage of the DC power supply to the load, the over-current protection is turned off when the DC output voltage supplied to the load falls below the DC input voltage of the DC power supply. If a switching element is provided, the output current can be cut off by detecting a significant drop in the DC output voltage due to an overload or load short-circuit, so that the boost converter can be quickly and reliably protected from overload or load short-circuit. It is possible to do.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a DC power supply according to the present invention is applied to a boost chopper type converter will be described below with reference to FIG. However, in FIG. 1, substantially the same parts as those shown in FIG. 8 are denoted by the same reference numerals, and description thereof will be omitted. As shown in FIG. 1, the boost chopper type converter according to the present embodiment has an N-channel as an overcurrent protection switching element in the positive side line between the output capacitor 5 and the load 6 in the boost chopper type converter shown in FIG. 8. Type MOS-FET 21, the reactor 2 is changed to a two-winding type double winding reactor 22, and the auxiliary winding 22 a of the double winding reactor 22 and an N-channel type MOS-FET 21 are connected.
A rectifying / smoothing circuit including a diode 23 and a capacitor 24 and a series resistor 25 are connected between the gate terminal of the FET 21 and a reference power supply 26 and a comparator 27 between the load 6 and the gate terminal of the N-channel MOS-FET 21. The output current limiting circuit 28 is connected, and the current detecting resistor 8
And an overcurrent detection circuit 14 comprising a reference power supply 12 and a comparator 13 are omitted. Here, the reference power supply 26 constituting the output current limiting circuit 28 has a DC output voltage V
Generates a reference voltage V _R3 corresponding to the lower limit value of the _OUT, the comparator 27 is a DC output voltage V DC output voltage is compared with a reference voltage V _R3 of the _OUT reference power 26 V _{O UT} reference voltage V _R3
The comparison output goes from a high level to a low level when the voltage falls below the threshold. Note that in the present embodiment, N
In order to turn on the channel type MOS-FET 21,
As the load 6, for example, a secondary battery such as a battery is connected. Other configurations are substantially the same as those of the boost chopper type converter shown in FIG.

Next, the operation of the boost chopper type converter shown in FIG. 1 will be described. When the load 6 is normal, since the DC output voltage V _OUT is higher than the reference voltage V _R3 of the reference power supply 26 in the output current limiting circuit 28, the comparator 27 in the output current limiting circuit 28 outputs the N-channel MOS-F
A high level signal is output to the gate terminal of ET21. At this time, by the on / off operation of the MOS-FET 3 of the power conversion unit, the auxiliary winding 22a of the multiple winding reactor 22 is connected to the gate terminal of the N-channel type MOS-FET 21 via the diode 23, the capacitor 24 and the series resistor 25. Since a DC voltage for driving is applied, an N-channel MOS
-The FET 21 keeps the ON state. Therefore, the operation of the main circuit of the boost chopper type converter shown in FIG. 1 at this time is substantially the same as the operation of the boost chopper type converter shown in FIG.

When the load 6 is overloaded or the load 6 is substantially short-circuited and the impedance of the load 6 becomes extremely low, the DC output voltage V _OUT becomes higher than the reference voltage V _R3 of the reference power supply 26 in the output current limiting circuit 28. Will also be lower. For this reason,
The voltage level of the signal output from the comparator 27 in the output current limiting circuit 28 to the gate terminal of the N-channel type MOS-FET 21 changes from a high level to a low level. At this time, the N-channel MOS-FET 21 changes from the on state to the off state, and the output current I _OUT supplied from the output capacitor 5 to the load 6 is cut off. As a result, the output current I _OUT in the overload or load short-circuit state is sufficiently limited, so that the boost chopper type converter can be reliably protected from overload or load short-circuit with a simple circuit configuration. In this embodiment, the N-channel MOS-FE
Since the DC voltage for driving T21 is obtained by rectifying and smoothing the voltage induced in the auxiliary winding 22a of the multiple winding reactor 22, the overcurrent state is detected and the MOS of the power conversion unit is promptly obtained.
-When the FET3 is turned off, the N-channel type MO
The DC voltage for driving the S-FET 21 becomes approximately 0 V, and N
Since the channel type MOS-FET 21 is turned off,
It is possible to more reliably protect the boost chopper type converter from overload or load short circuit.

The boost chopper type converter of the embodiment shown in FIG. 1 can be changed. For example, the boost chopper type converter of the embodiment shown in FIG. 2 is different from the boost chopper type converter shown in FIG. 1 in that the positive terminal of the DC power source 1 Channel type MOS-FET21
Diode 29, voltage dividing resistor 30,
An output current limiting circuit 33 comprising an NPN transistor 31 and an NPN transistor 32 is connected. Other configurations are substantially the same as those of the boost chopper type converter shown in FIG. In the boost chopper type converter shown in FIG. 2, when the load 6 is normal, the DC output voltage V _OUT supplied to the load 6 is higher than the DC input voltage V _IN of the DC power supply 1. The diode 29 is reverse-biased and becomes non-conductive. As a result, the NPN transistor 32 in the output current limiting circuit 33 is turned off.
The channel type MOS-FET 21 maintains the ON state.
The load 6 is overloaded or the load 6 is substantially short-circuited,
When the impedance of the load 6 becomes extremely low, the DC output voltage V _OUT becomes lower than the DC input voltage V _IN of the DC power supply 1, so that the diode 29 in the output current limiting circuit 33 is forward-biased and becomes conductive. At this time, a high-level voltage is generated at the voltage dividing point of the voltage dividing resistors 30 and 31 in the output current limiting circuit 33, and the NPN transistor 32 is turned on. In the off state, load 6
Output current I _OUT to be supplied is blocked. Therefore, in the boost chopper type converter of the embodiment shown in FIG. 2, the same overcurrent protection effect as in FIG. 1 can be obtained. Furthermore, in the boost chopper type converter shown in FIG.
Since the output current I _OUT can be cut off quickly by detecting a significant drop in the DC output voltage V _OUT due to an overload or load short circuit, the boost chopper converter can be quickly and reliably protected from overload or load short circuit. Becomes possible.

The boost chopper type converter of the embodiment shown in FIG. 3 includes two MOS-FETs 3, a single-winding type reactor 34 having three intermediate taps 34a, 34b, 34c, and two output diodes 4. Using Figure 1
The power converter of the boost chopper type converter shown in FIG. 1 is changed to a push-pull type circuit configuration. In the boost chopper type converter of the embodiment shown in FIG. 4, the power converter has the same push-pull type circuit configuration as that of the embodiment shown in FIG. 3, but instead of the reactor 34 shown in FIG. An N-channel MOS-FET using a two-winding double winding reactor 35 having a winding 35b
The difference from the circuit of the embodiment shown in FIG. 3 is that the power for driving 21 is obtained from the auxiliary winding 35b of the multiple winding reactor 35. FIG. 5 shows the double winding reactor 22 in the step-up chopper type converter of FIG.
6a and 36b and a transformer 36 having an auxiliary winding 36c, and the main circuit configuration is changed from the secondary winding 36b of the transformer 36 to the load 6 via the output diode 4, the output capacitor 5 and the N-channel type MOS-FET 21. An embodiment of an isolated flyback converter for obtaining a DC output to be supplied is shown. In the isolated flyback converter shown in FIG. 5, a power supply for driving the N-channel MOS-FET 21 is obtained from the auxiliary winding 36c of the transformer 36. In any of the embodiments shown in FIGS. 3 to 5, the overcurrent protection effect when the load 6 is overloaded or short-circuited is substantially the same as that of the embodiment shown in FIG. Almost the same effects as those of the embodiment shown in FIG. 1 can be obtained.

In each of the embodiments shown in FIGS. 1 to 5, an N-channel MOS-type switching element is used as an overcurrent protection switching element.
Although the FET is used, a P-channel type MOS-FET can also be used. For example, the boost chopper type converter of the embodiment shown in FIG.
Channel-type MOS-FET 21 is replaced with P-channel type MOS-F
ET37, a series resistor 38 is connected between the gate terminal of the P-channel type MOS-FET 37 and the negative output line, and the output terminal of the comparator 27 of the output current limiting circuit 28 is connected to the positive output line. Voltage dividing resistors 39 and 40 between
, A PNP transistor 41 is connected between the source terminal and the gate terminal of the P-channel MOS-FET 37, and the base terminal of the PNP transistor 41 is connected to the voltage dividing points of the voltage dividing resistors 39 and 40. It is. In the boost chopper type converter of the embodiment shown in FIG. 6, the comparator 27 in the output current limiting circuit 28 at the time of normal load.
Outputs a high-level signal, and a voltage is generated at the voltage dividing points of the voltage dividing resistors 39 and 40. At this time, the PNP transistor 41 is turned on, and the P-channel MOS-FET
Since 37 maintains the ON state, the operation of the main circuit of the boost chopper converter shown in FIG. 6 at this time is substantially the same as the operation of the boost chopper converter shown in FIG. 1 at the time of a normal load. Further, when an overload or a load short-circuit occurs, a low-level signal is output from the comparator 27 in the output current limiting circuit 28 and the PNP transistor 41 is turned off, so that the gate terminal of the P-channel MOS-FET 37 is connected in series. It goes to the ground potential through the resistor 38. At this time, the P-channel MOS-FET 37 is turned off, and the output current I _OUT supplied from the output capacitor 5 to the load 6 is cut off. Therefore, also in the boost chopper type converter of the embodiment shown in FIG. 6, the same overcurrent protection effect as in FIG. 1 can be obtained.

In the embodiment shown in FIGS. 1 to 6, by way of example, a secondary battery such as a battery is connected to the converter output terminal as the load 6, and the N-channel type M
The OS-FET 21 or the P-channel type MOS-FET 37 is turned on. In these embodiments, when the secondary battery such as a battery is connected to the converter output terminal with the polarity reversed, an N-channel MOS
-Since the FET 21 or the P-channel type MOS-FET 37 remains in the off state, it is possible to protect the converter from reverse connection of a battery or the like. However, in the embodiment shown in FIGS. 1 to 6, when the load 6 is not connected to the converter output terminal, the N-channel MOS-FE
Since the T21 or P-channel type MOS-FET 37 cannot be turned on, the converter cannot be operated. For this reason, for example, in the boost chopper converter of the embodiment shown in FIG. 7, in the boost chopper converter shown in FIG. 6, the voltage dividing resistors 42 and 43 are connected between the positive and negative output lines, A starting resistor 44 is connected between the voltage dividing points 42 and 43 and the positive output line, a series resistor 45 is connected in series with the reference power source 26 in the output current limiting circuit 28, and the reference power source 26 and the series Resistance 45
And a non-inverting input terminal of the comparator 27 in the output current limiting circuit 28 is connected to a voltage dividing point of the voltage dividing resistors 42 and 43. In the boost chopper type converter shown in FIG. 7, a voltage is generated at the voltage dividing points of the voltage dividing resistors 42 and 43 via the starting resistor 44 at the time of starting, and a high level signal is output from the comparator 27 of the output current limiting circuit 28. PNP transistor 41
Is turned on, and the P-channel type MOS-FET 37 is turned on. Therefore, since the P-channel type MOS-FET 37 can be turned on at the time of startup, the boost converter can be operated even when the load 6 is not connected to the converter output terminal. The operation of the boost chopper type converter shown in FIG. 7 at the time of normal load and at the time of overload or load short circuit is substantially the same as that shown in FIG.

The embodiments of the present invention are not limited to the above embodiments, and various modifications are possible. For example, FIG.
Also, in the embodiment shown in FIG. 7, the embodiment in which the N-channel type MOS-FET 21 in the step-up chopper type converter of FIG. 1 is changed to the P-channel type MOS-FET 37 is shown. In the above, the same change as described above is possible. In the embodiment shown in FIG. 5, the non-insulated boost chopper converter shown in FIG. 1 is changed to an insulated flyback converter. However, a forward bridge, a half bridge bridge, a full bridge bridge or the like is used. It is also possible to change to another type of isolated converter. In each of the above embodiments, a mode in which a MOS-FET is used as a switching element has been described. However, other switching elements such as a bipolar transistor and a junction field effect transistor (J-FET) can be used. Further, it is easily understood that the present invention can be applied to other DC power supply devices such as a buck converter, a buck-boost converter, and a polarity inversion converter without being limited to the boost converter.

[0017]

According to the present invention, the output current supplied to the load can be cut off when the load is overloaded or short-circuited, and the output current can be sufficiently limited. Therefore, a switching element for overcurrent protection is added to the output side. With this simple circuit configuration, the DC power supply can be reliably protected from overload or load short-circuit. Therefore, an excessive current does not flow at the time of overload or load short circuit, and it is possible to prevent the DC power supply device from being destroyed due to the overcurrent.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram of a DC power supply device showing an embodiment of the present invention.

FIG. 2 is an electric circuit diagram of a DC power supply device showing another embodiment of the present invention.

FIG. 3 is an electric circuit diagram showing a first modified embodiment of the circuit of FIG. 1;

FIG. 4 is an electric circuit diagram showing a second modified embodiment of the circuit of FIG. 1;

FIG. 5 is an electric circuit diagram showing a third modified embodiment of the circuit of FIG. 1;

FIG. 6 is an electric circuit diagram showing a fourth modified embodiment of the circuit of FIG. 1;

FIG. 7 is an electric circuit diagram showing a fifth modified embodiment of the circuit of FIG. 1;

FIG. 8 is an electric circuit diagram showing a conventional DC power supply device.

[Explanation of Codes] . . DC power supply, 2. . . Reactor, 2. . . MO
3. S-FET (switching element); . . Output diode, 5. . . Output capacitor, 6. . . load,
7. . . Control circuit, 8. . . 8. current detection resistor; . .
Reference power supply, 10. . . Comparator, 11. . . 11. output voltage detection circuit; . . Reference power supply, 13. . . Comparator, 14. . . Overcurrent detection circuit, 15, 16. . . Diode, 17. . . 21. PWM signal generation circuit . .
12. N-channel MOS-FET (switching element for overcurrent protection); . . Double winding reactor, 22a. . .
Auxiliary winding, 23. . . Diode, 24. . . Capacitor, 25. . . Series resistance, 26. . . Reference power supply, 2
7. . . Comparator, 28. . . Output current limiting circuit,
29. . . Diodes, 30, 31. . . Voltage dividing resistor, 3
2. . . NPN transistor, 33. . . Output current limiting circuit, 34. . . Reactor, 34a, 34b, 34
c. . . Middle tap, 35. . . Double winding reactor, 3
5a. . . Middle tap, 35b. . . Auxiliary winding, 3
6. . . Transformer, 36a. . . Primary winding, 36b. . .
Secondary winding, 36c. . . Auxiliary winding, 37. . . 38. P-channel type MOS-FET (switching element for overcurrent protection), . . Series resistance, 39, 40. . . Voltage dividing resistor, 41. . . PNP transistor, 42, 4
3. . . Voltage dividing resistor, 44. . . Starting resistor, 45. . .
Series resistance, 46. . . Capacitor

Claims (2)

[Claims] 1. A power supply comprising: at least one switching element for intermittently converting a DC input of a DC power supply by an on / off operation to convert to a high frequency power; and a DC conversion circuit for converting the high frequency power to a DC output to be supplied to a load. A DC power supply that supplies a constant-voltage DC output to the load by controlling on / off of the switching element in accordance with the DC output; switching for overcurrent protection between the DC conversion circuit and the load; DC power supply device, wherein the switching element for overcurrent protection keeps the on state at the time of normal load and turns off at the time of overload or short circuit of the load to cut off the output current supplied to the load. . 2. The DC power supply device is a boost converter that supplies a DC output voltage higher than a DC input voltage of the DC power supply to the load, and the overcurrent protection switching element is a DC output voltage supplied to the load. 2. The DC power supply according to claim 1, wherein the DC power supply is turned off when the voltage of the DC power supply falls below the DC input voltage of the DC power supply.