JPH01318543A - Dc-dc conversion type power circuit - Google Patents

Abstract

PURPOSE:To restart a DC-DC converter stably and automatically by providing a stoppage circuit to stop the operation of the DC-DC converter for a predetermined time when sudden voltage drop is detected in an output capacitor. CONSTITUTION:A DC-DC converter 14 adds a stoppage circuit 12 to a normal DC-DC converter 4. The DC input voltage from an input terminal 2 is charged to an output capacitor 5 as the designated voltage with the DC-DC converter 4. This voltage is then converted into AC voltage of a specified frequency with an inverter circuit 6 and the current is fed to a load equipment 10 from an output terminal 8. When the sudden voltage drop of this output capacitor 5 is detected by the stoppage circuit 12, the operation of the converter 4 is stopped for the predetermined period of time. When the converter 4 is restarted during this period, a soft start circuit will work and the converter 4 is gradually charged with the output capacitor 5 and no rush current will flow. As a result, the load equipment 10 can be started without regard to the order of putting the power switch to work.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a direct current/direct current conversion type power supply circuit (DC/DC converter).

[Prior Art] As an application example of a DC-DC converter, a DC (direct current) voltage from a power source such as a battery is converted to a desired DC voltage, and the DC voltage is converted to AC (alternating current) by a DC/AC inverter circuit. There is a so-called DC-AC inverter that converts voltage into voltage. Electronic devices such as oscilloscopes use AC
Although it is generally driven by a power supply, a DC power drive method using a battery or the like is preferable for measurements in places without commercial power supply equipment or measurements that require insulation from an AC power supply. This type of AC-driven electronic equipment is
A DC-AC inverter is used to drive the C power source.

FIG. 3 is a block diagram when a conventional DC-AC inverter is connected to an AC-driven load device. DC-A
The C inverter 3 converts the DC voltage of the battery etc. to a desired D.
A place for converting to C voltage m D C/DC converter 4,
The inverter circuit 6 converts DC voltage into AC voltage.

The DC-DC converter 4 has an output capacitor 5 and is configured such that the voltage stored in the output capacitor 5 is converted into an AC output voltage by an inverter circuit 6. To use this DC-AC inverter 3, first,
After turning on the power switch of the load device 10,
Turn on the power switch of C inverter 3. Then, D
The soft start circuit in the C-DC converter 4 operates to gradually charge the output capacitor 5, and the ACN pressure output to the output terminal 8 also gradually rises. This output voltage gradually charges an input capacitor (not shown) in the power input circuit of the load device 10, and when the voltage value of this input capacitor reaches a predetermined value, the load device 10 is started.

However, before turning on the power switch of the load device 10,
When the power switch of the DC-AC inverter 3 is turned on and then the power switch of the load device 10 is turned on, the DC
-While the output capacitor 5 of the DC converter 4 is fully charged, the input capacitor of the load device 10 is not fully charged, so the input capacitor is rapidly charged and an inrush current is generated. As a result, DC-DC
The output capacitor 5 of the converter 4 is rapidly discharged and the voltage drops rapidly. On the other hand, the input capacitor of the load device 10 is also discharged by the power supply starting circuit (not shown) of the load device, resulting in a voltage drop.

The control circuit in the DC=DC converter 4 tries to compensate the voltage of the output capacitor 5, but the electric charge charged in the output capacitor 5 is overloaded and flows into the input capacitor of the load device 10 as a rush current one after another. It becomes a load state and cannot recover to the specified operating voltage. Unless this overload condition is resolved or the operation of the DC-DC converter is stopped, an excessive rush current will continue to flow due to the voltage drop of the output capacitor 5, which may cause burnout of circuit components. There was a problem. In such cases, conventional DC
-The AC inverter was configured to generate an alarm and interrupt the circuit. At this time, the user is DC-
After turning off the power switch of the AC inverter, it was necessary to turn it on again according to a predetermined procedure.

[Problems to be Solved by the Invention] The above problems are caused by a sudden drop in the voltage of the output capacitor 5 of the DC-DC converter 4.
If the capacitance of the output capacitor 5 is made sufficiently large (for example, 10 times or more) compared to the input capacitor of the load device 10, this problem can be solved. However, unnecessarily increasing the capacitance of the output capacitor 5 is undesirable because it increases the size of the device. Furthermore, recent electronic devices equipped with a microprocessor (MPU) often store information such as measurement results and measurement mode settings in memory. In this case, the design is generally such that the latest measurement and setting information is retained even when the power switch is turned off; There is also a risk that the MPU may run out of control due to abnormal operation of the reset circuit due to a momentary interruption of power supply, etc., and this information may be lost.

Therefore, an object of the present invention is to provide a DC/DC conversion type power supply circuit (DC-DC converter) that can always automatically restart even if a sudden overload condition occurs by adding a minimum number of circuits. The goal is to provide the following.

Another object of the present invention is to provide a load device equipped with an MPU.
It is an object of the present invention to provide a C-DC converter suitable for a power supply circuit that enables reliable restart of an MPU.

[Means and effects for solving the problem] When the DC-DC converter of the present invention detects a sudden drop in the voltage of the output capacitor, the DC-DC converter of the present invention
It has a stop circuit that stops the operation of the DC converter. During this predetermined period of stoppage, the output capacitor of the DC-DC converter and the input capacitor of the load device are completely discharged.

Thereafter, the DC-DC converter is restarted.

As a result, the voltage of the output capacitor gradually rises,
Power is also gradually supplied to the input capacitor of the load device connected to the output terminal. Therefore, even if an overload condition occurs, the load equipment can be reliably restarted by automatically restarting the DC-DC converter after stopping its operation for a predetermined period of time.

In the power supply circuit that supplies power to load equipment equipped with an MPU, unstable power supply operation or short-term interruption of the power supply is caused by the MP
This will cause U to go out of control. In order to reliably operate the reset circuit added to the MPU, a stop time of about 1 second, for example, is set as the predetermined stop time of the stop circuit. As a result, the power supply circuit of the present invention has a built-in M
Since runaway of the PU can be avoided and the load equipment can be restarted as if nothing had happened, there is no risk of information loss due to runaway of the MPU.

[Embodiment] FIG. 1 is a block diagram of an embodiment of a DC-AC inverter using a DC-DC converter according to the present invention.

Circuit elements corresponding to FIG. 3 are given the same reference numerals. The DC-DC converter 14 of the present invention is different from the conventional DC-DC converter 14.
- It has a configuration in which a stop circuit 12 is added to the DC converter 4. The other configurations are the same as those in FIG. 3. The DC input voltage supplied from input terminal 2 is DC-DC
The converter 4 charges the output capacitor 5 to a predetermined voltage, and this voltage is converted by the inverter circuit 6 into an AC voltage of a predetermined frequency and supplied to the load equipment 10 from the output terminal 8. If you first turn on the power switch of the load device 10 and then turn on the power switch of the DC-AC innomator 3, the soft start circuit of the DC-DC converter 4 will work as in the conventional case, and the AC output current will gradually rise. by the input capacitor of the load device 10 (not shown)
is gradually charged, and when the voltage of this input capacitor reaches a predetermined value, the load device 10 is started. Next, first turn on the power switch of the inverter 3, and then turn on the load device 10.
When the power switch of the DC-DC converter 4 is turned on, the output capacitor 5 of the DC-DC converter 4 is connected to the load device 10 when it is fully charged, so a rush current flows into the input capacitor of the load device 10, which is not charged at all. As a result, the voltage of the output capacitor 5 drops rapidly. When the stop circuit 12 detects this sudden voltage drop of the output capacitor 5, the D
The operation of the C-DC converter 4 is stopped for a predetermined period. During this period, the charges in the output capacitor 5 of the DC-DC converter 4 and the input capacitor of the load device 10 are completely discharged, so when the DC-DC converter 4 is started up again, the soft start circuit is activated. Since the output capacitor 5 is gradually charged and the input capacitor of the load device 10 is gradually charged by the AC output current that gradually rises, no inrush current flows. As a result, load equipment 1
The load equipment 10 can be started regardless of the order in which the power switches of the DC-AC inverter 3 and the DC-AC inverter 3 are turned on. That is, by stopping the operation of the DC-DC converter 4 for a predetermined period, the DC-AC inverter 3 and the load device 10 can always be restarted from the initial state. Since only a simple stop circuit 12 is added without increasing the capacity of the output capacitor 5, it is extremely easy to downsize the device.

FIG. 2 is a circuit diagram of one embodiment of the DC-DC converter of the present invention. The DC current input from the input terminal 2 charges the capacitor 24 on the primary side of the transformer 23 via the fuse 20 and the switch 22. The DC voltage charged in this capacitor 24 is converted to AC by the oscillation of a switching FET (field effect transistor) 26.
It is transmitted to the secondary side of the transformer 23. A control IC (integrated circuit) 30 that controls switching of the FET 26 is a μPC494 type manufactured by NEC Corporation, which is well known as a control IC for a so-called switching regulator. This control IC 30 is composed of a triangular wave oscillator, two comparators, two error amplifiers, five standard voltage sources, etc., and the circuit configuration and operation are well known to those skilled in the art, so detailed explanations will be provided. Explanation will be omitted. The AC current supplied to the secondary side of the transformer 23 is rectified by two rectifying diodes 32, smoothed by a choke coil 34 and an LC filter of an output capacitor 5, and a DC output is supplied to an output terminal 35. The output terminal 35 is connected to the anode of a light emitting diode 42 in an optocoupler 40 through a series circuit of a resistor 36 and two Zener diodes 38. Photo coupler 40
The emitter of the transistor 44 inside is connected to the first terminal of the control IC 30 via the resistor 46, and
It is grounded via 8. Control from output terminal 35■C3
The output voltage is fed back through the feedback path from 0 to the 1st terminal, and the oscillation of the FET 26 is controlled by pulse width control, so that the voltage of the output capacitor 5 is held constant. For example, if the voltage of the output capacitor 5 rises above a predetermined voltage, the potential of the control IC 30 also rises, and the 1
The width of the control pulse output from the No. 0 terminal becomes narrower, which acts to lower the voltage of the output capacitor 5. Conversely, if the output voltage decreases, it acts to increase the voltage of the output capacitor 5 and controls the output voltage to a constant value.

A parallel circuit 50 of a capacitor and a resistor between the No. 1 terminal of the IC 30 and ground is provided to remove noise from the photocoupler 4o and stabilize the operation. A voltage obtained by dividing the input voltage Vc on the primary side by resistors 52 and 54 is supplied to the 16th terminal via an inverting amplifier 56. this is,
When the input voltage Vc falls below a predetermined voltage, the voltage at the 16th terminal is increased, and the control pulse from the 10th terminal is stopped to stop the operation of the circuit. The output terminal of inverting amplifier 56 is connected to the base of transistor 60 via resistor 58. The emitter of transistor 60 is grounded,
The collector is connected to the base of transistor 62.

The emitter of transistor 62 is also grounded, the collector is connected to input voltage source Vc through resistors 64 and 66, and the junction of resistors 64 and 66 is connected to the base of transistor 68. A transistor 68 whose emitter is connected to the input voltage source VC and whose collector is connected to the 12th terminal which is the power input terminal of the control IC 30 supplies operating power to the control IC 30 . If the power supply voltage Vc further decreases,
The output of inverting amplifier 56 rises, turning on transistor 60 and turning off transistors 62 and 68, cutting off the power supply to the control IC. This prevents the circuit from burning out due to excessive current caused by voltage drop. Furthermore, the base of the transistor 60 and the input power supply Vc
A series circuit of a resistor 70 and a Zener diode 72 is inserted between them. When Vc rises above the zener voltage of the diode 72, the transistor 60 is turned on and the power supply to the control IC 30 is cut off in the same manner as described above. A parallel circuit 74 of a capacitor and a resistor connected to terminals 5 and 6 of the control IC 30 is used to set the oscillation frequency of the built-in oscillator, which in this embodiment is approximately 5QKHz.
has been adjusted to. A capacitor 76 and a resistor 78 inserted between the connection point of terminals 14 and 15 and the ground are a circuit for controlling a so-called soft start. The connection point between the capacitor 76 and the resistor 78 is connected to the No. 4 terminal. The 14th terminal is a 5V reference voltage source for the control IC, and the capacitor 76 is gradually charged from the time the power switch 22 is turned on, and the voltage at the 4th terminal is gradually lowered due to changes in the charging current to perform a soft start. Execute the action. The capacitor 80 connected to terminal 14 is 5V.
This is for stabilizing the reference power supply. Diodes 82 and 84 connect capacitor 7 when input power supply Vc is cut off.
This is for rapidly discharging the charge No. 6. This discharge current flows through resistors 86, 88 and 90 to ground. Transistor 92, whose collector and emitter are connected between the gate and source of FET 26, has its base connected to the connection point of resistors 88 and 90. Since the No. 10 terminal that drives the gate of the FET 26 via the oscillation prevention resistor 94 and the No. 8 terminal that drives the base of the transistor 92 via the resistor 88 generate control pulses of opposite phase,
The FET 26 and the transistor 92 are alternately turned on and off. As a result, when the FET 26 is off, the transistor 92 is turned on, rapidly discharging the charge in the gate capacitance, and shortening the turn-off time of the FET 26. Furthermore, FET2
A resistor 96 between the gate and source of FET 6 is for protection of FET 26.

Capacitor 98 and resistor 10 connected between the emitter of transistor 44 in optocoupler 40 and ground.
0, and a resistor 102 inserted between these connection points and the 5V power supply constitute a differential circuit 103. The output terminal of this differentiating circuit 103 is connected to the clock terminal of a monostable multivibrator 104. The width of the output pulse of this monostable multi-bi break 104 is determined by the capacitor 106 and resistor 108, and is adjusted to about 1 second in this embodiment. Multi vibrator 104
The output terminal of is connected to the collector of transistor 60 via resistor 110.

When the voltage of the output capacitor 5 suddenly decreases, the emitter voltage of the transistor 44 in the photocoupler 40 also decreases rapidly, and this voltage change is sent as a negative direction pulse to the monostable multivibrator 104 via the differentiating circuit 103. It will be done. In response to this input pulse, the multivibrator 104 changes its output terminal from a "high" state to a "low" state, maintains the "low" state for approximately one second, and then returns to the "high" state. When the output of multivibrator 104 becomes "low", transistors 62 and 68 are both turned off, and the supply of power supply voltage to control IC 30 is cut off. As a result, the operation of the DC-DC converter is stopped, the charges in the output capacitor 5 and the soft start capacitor 76 are completely discharged, and the entire circuit returns to its initial state. When the output of monostable multivibrator 104 returns to the "high" state approximately one second later, transistors 62 and 68 are turned on and power supply to control IC 30 is resumed.

Therefore, the output capacitor 5 is gradually charged with electric charge by the function of the soft start circuit, so that sudden discharge of the output capacitor 5 due to rush current can be avoided. Furthermore, since a stable restart can be performed after a stop period of about 1 second, there is no risk of MPU runaway in devices equipped with an MPU.

Although the DC-DC converter according to the present invention has been described above based on one embodiment, the present invention is not limited to the embodiment described herein, and various modifications, changes, and applications can be made as necessary. It is clear to those skilled in the art that For example, to stop the operation of the DC-DC converter, in addition to stopping the power supply to the control IC 30, the capacitor 76 may be temporarily shorted, or the transistor 90 may be shorted to short the gate and source of the FET 20. A control signal may also be given. Since only a stop circuit is added, the circuit configuration and control method of the DC-DC converter may be of any type.

With the exception of the inverter circuit of this embodiment, it is possible to automatically restart by canceling a temporary sudden overload state, and various applications are possible as a C power source. Since the stop period of the stop circuit can be easily and freely adjusted, it can be easily used for various load devices. Furthermore, if the overload condition is not a temporary cause, when the number of consecutive operations of the stop circuit reaches a predetermined number of times, the operation of the DC/DC converter is completely stopped,
It may be configured to issue an alarm or turn on a warning light.

[Effects of the Invention] According to the DC-DC converter of the present invention, by simply providing a stop circuit that stops the operation of the DC-DC converter for a predetermined period of time when a sudden voltage drop of the output capacitor is detected, instantaneous damage to the load equipment can be prevented. It is possible to release the overload condition caused by inrush current and restart automatically. Furthermore, even if the voltage of the output capacitor suddenly drops due to a momentary interruption due to chattering of the power switch or a poor contact of the DC input power source, stable restart can be automatically performed. Therefore, since the circuit configuration is extremely simple, it can be easily miniaturized, the device can be protected from excessive current, and the trouble of turning on the power switch again can be saved. Also, MPU
By appropriately setting a stop time long enough to ensure the operation of the reset circuit of the MPU for a load device equipped with the MPU, runaway of the MPU can be easily prevented and loss of stored information can be avoided.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an application example of one embodiment of the present invention, Fig. 2 is a circuit diagram of one embodiment of the present invention, and Fig. 3 is a connection between a conventional DC-AC inverter and load equipment. It is a block diagram showing a state. 4: DC-DC converter 5: Output capacitor 12: Stop circuit

Claims (1)

[Claims] In a DC/DC conversion type power supply circuit that receives DC input voltage and outputs DC voltage to an output capacitor, when a sudden drop in the voltage of the output capacitor is detected, the operation of the DC/DC conversion type power supply circuit is stopped for a predetermined period of time. A DC/DC conversion type power supply circuit characterized by comprising a stop circuit for stopping the power.