JP3459143B2 - Overload protection method for switching converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] TECHNICAL FIELD The present invention relates to various electronic devices.
Switching power supplies and high frequency inverters used
Used in circuits, etc.Switching converter
Overload protection methodAbout. [0002] 2. Description of the Related Art FIG.
Current resonant bridge converterTa1 shows a circuit. Smell this figure
1 is an input voltage source, 2 and 3 are switching elements,
4 is a resonance capacitor. 5 and 6 are resonance inductors
And the resonance inductance 5 is, for example,
Lance leakage inductance or separate inductor
Formed by the inductance
Is formed from the excitation inductance of the main transformer.
Things. 7 is the main transformer as an ideal transformer, 8 and
And 9 are diodes, 14 and 15 are switching elements
16 and 17 are impedance elements, 1
1 is a pulse drive circuit and 10 is an oscillator. [0003] It is to be noted that the capacitance 14 and both ends of each switching element are provided.
And 15 are the parasitic capacitances of switching elements 2 and 3 themselves.
In some cases, the amount may be only
Externally mounted for reduction and measures against radiation and induced noise interference
Capacity is often added. Here, the parasitic capacitance
14 and 1 respectively.
5 is represented. Reference numeral 26 denotes a rectifying / smoothing circuit.
The output of the smoothing circuit 26 is supplied to a load.27Increases the error
Breadboard,28Is a photocoupler, and 21 and 21 'are described later.
Voltage drop detection circuit. In addition, 53
Dance element, 12 is diode, 13 is impedance
A low-pass filter consisting of an element and a capacitor, 54 is
A comparator, 55 is a reference voltage source,29Is a latch circuit
Yes, and these will be described later. [0005] The converter shown in this figureTaIs as follows
Works. That is, switching elements 2 and 3
Is output from the oscillator 10 via the pulse drive circuit 11
Are alternately switched. Input from input voltage source 1
The voltage is alternately switched by switching elements 2 and 3.
Resonance capacitor connected by
4, resonance inductance 5, resonance inductance 6, main
Transformer 7 and the switching element 14
Or 15 the resonance current flows, and the main transformer 7secondary
~ sideOutput an AC voltage. The output is rectified and smoothed by circuit 2
6 rectifies and smoothes the load to provide the desired energy to the load.
It is supplied with energy. The switching elements 2 and 3 have phase inversion.
Since the same operation is repeated, here, the switch
The operation of the switching element 3 will be described. FIG.
FIG. 6 is a diagram showing waveforms of voltage or current at each part in the middle.
You. Immediately after the switching element 2 is turned off
Are the charging current to the capacitor 14 and the discharging current from the capacitor 15.
The flow is divided into the resonance inductance 6 (or the main transformer 7).
Flow) → resonance inductance 5 → resonance capacitor 4 →
It flows on the path of the input voltage source 1 (period a in FIG. 11). The charging of the capacitor 14 and the charging of the capacitor 15
After the discharge is completed, the diode 9 is turned on and the diode 9 is turned on.
Ode 9, resonance inductance 6, resonance inductance
5, via the resonance capacitor 4 and the diode 9
Current flows, and charging of the resonance capacitor 4 is completed (FIG. 1).
1 period b). Thereafter, the switching element 3 is turned on,
From the resonance capacitor 4 to the resonance inductance 5, the resonance
Ductance 6 (and main transformer 7), conducting switch
Discharge from the resonance capacitor 4 via the
This is performed (period c in FIG. 11). During this period c, the rectifying and smoothing circuit 26
The diode included in the transformer conducts and actually outputs the ideal transformer
A power transmission period during which power is supplied to the output side via
The diode becomes non-conductive and the output ideal transformer 7
Power non-transmission period (only the latter half of period c)
Part) and exists. And this time the same behavior
This is performed for the switching element 2, and hereinafter, the
Is repeated. This converter circuit operates as described above.
And as can be seen in the waveforms of each part shown in FIG.
And three modes(Each mode of the periods a, b, and c)of
The combined current waveform of the resonance system
It is clear that zero-cross operation is almost ideally realized.
Call In this converter circuit, the output is
The control of the output voltage is controlled by the operating frequency,
This is done by controlling the vibration frequency. That is,
ConverterPrimary sideThe resonance circuit shown in FIG.
The resonance inductances 5 and 6 and the resonance capacitor
At the resonance frequency determined by the sensor 4
Frequency vs. impedance characteristic
Have. Therefore, the operating frequency must be higher than the resonance frequency.
Operating on the right side of this characteristic curve (upper
Control of the output voltage using this,
Upper sidecontrolCall. Conversely, the operating frequency
Operate as a frequency lower than the resonance frequency, and
Control of output voltage using the left side (lower side) of
You can also do this on the lower sidecontrolCall. In this example, the upper sidecontrolWhat to do
It will be described as. For example, to increase the output voltage,
By lowering the oscillation frequency of the oscillator 10, the resonance circuit
Impedance and increase the current flowing through the resonant circuit
Let it. That is, the main transformer 7Secondary sideGenerated electricity
Pressure is the error amplifier27Is compared with the reference voltage at
The corresponding control signal is the photocoupler28, 30Through
Oscillation of the oscillator 10 is fed back to the oscillator 10
Control is performed so that the frequency becomes lower. On the other hand, the output voltage
Conversely, when lowering, raise the oscillation frequency of the oscillator 10.
Just do it. In other words, the oscillation frequencyNumberBy changing
The desired impedance in the range from A to B shown in FIG.
I'm trying to get In this converter circuit, a load
When an overload condition such as a short circuit occurs,Primary sideCurrent
The protection operation is performed by detecting that the
It has been done. Here, low-side switching
The impedance element 53 connected in series with the element 3
WhatPrimary sideConverts the current flowing through the
After rectification by the ion 12, it passes through the low-pass filter 13.
Is input to the overload protection comparator 54, and the voltage is
If the threshold set by the source 55 is exceeded, the latch
Road29And stops the oscillator 10 by the output
Thus, the protection operation is performed. Now, consider the operation in the overload state.
Then, at the time of overload such as load short circuit,Primary side
The effect of load resistance and operating frequency on impedance
Changes from inductive to capacitive at
Frequency and impedance as shown in FIG. 12 (2).
It becomes a dance characteristic. At this time, the operating frequency is not changed
For this purpose, as shown in FIG.Upper side control
From the areaThe operating frequency is lower than the resonance frequency,
Loose lower sideArea of controlWill be entered.
Once this lower sidecontrolWill be in a state
And the impedance of the system rises, and the output voltage becomes
descend. At this time, the output voltage drops as described above.
Control to lower the oscillation frequency of oscillator 10
Is performed, the output voltage is further reduced.
You. This involves a frequency change during overload.
Oscillation frequency during overload unless protection action is taken
Is fixed to the lowest oscillation frequency determined by the external time constant.
End, and then the original upper sidecontrolWhat is
Different lower sidecontrolMeans that it will continue
I have. A converter shown in the principle diagram of FIG.Ta
Circuit is lower sidecontrolIf you rush into
Is the reverse recovery time of the diode and the
A sharp surge current appears due to the influence of the amount component, etc.
A switching waveform as shown in FIG.
This is a great stress for the switching element. As mentioned above, simplyPrimary sideDetect current
When the method of operating the overload protection circuit is adopted
If the detection is not instantaneous,
To the lower sidecontrolRush into. And if
The threshold for detecting overload operation is somewhat high and oscillation
If there is a delay time before the oscillation stop operation of the
The load protection operation itself may not work. That is,
Lower side due to reversal of impedancecontrolTime
ofPrimary sideSince the current is suppressed, the threshold of the protection circuit
It will not reach it. This is illustrated
As shown in FIG. 10, the current is applied to the impedance element 53.
Therefore, in the case of the method of detecting and converting to the average voltage, it becomes remarkable.
You. As a method of avoiding such inconvenience,
FIG.To 0Voltage drop detection circuit as shown21Is the error
amplifier27Installed in parallel with the
And the impedance reversal phenomenon as a drop in output voltage
When the load is short-circuited, raise the oscillation frequency to resonate the operating frequency.
By making it higher than the frequency,Primary sideExtend the current
There is a method to facilitate detection of an overload condition. That is,
When the power voltage drops, the transformer in the voltage drop detection circuit 21
The transistor conducts, thereby causing the transistor to conduct,
Lights the light emitting diode in the photocoupler to oscillate
Impedance of the phototransistor connected to the device 10
Reduce the oscillation frequency to increase the oscillation frequency.
You. The voltage drop detection circuit 21 is not necessarily
It is not necessary to provide them at the above-mentioned positions.
It may be provided at the position as shown. When the load is short-circuited,
Lower side by increasing the numbercontrolThe transition to
And then increase in response to increasing load current.
The magnitude of the primary current is expressed by the voltage of the impedance element 53.
And the overload protection comparator 54 detects the oscillator 1
0 is set to the oscillation stop state to protect the element and prevent danger.
Is secured. Also,The oscillation frequency shown in FIG.
Higher setting prevents transition to lower side control
For the first method,As a second method,Primary sideElectric
Pulse is detected, and when the value exceeds the threshold, the oscillation frequency
Is higher than the overload resonance frequency,once
~ sideThere is a method to perform protection operation by suppressing the current growth.
You. FIG. 14 shows the transient operation waveform. [0021] However, the first embodiment shown in FIG.
In the first method, the voltage drop detection circuit 21
Since the output voltage is used as its voltage source,
The time until oscillation stops, that is, increase the oscillation frequency
Raise the upper sidecontrolTime to ensure the voltage drops
It becomes shorter as the voltage of the voltage source of the detection circuit 21 decreases.
Cannot maintain its operation. Within that time
When the protection operation is not performed, the upper
-SidecontrolWill be entered. In order to prevent this, the voltage detection circuit shown in FIG.
Shortening the time constant of the low-pass filter 13 makes the operation
The best way to ensure, but if you do
Causes momentary interruptions in the input voltage source and transient increases in the load.
Malfunctions can easily occur. Also this method
Once the lower sidecontrolForcibly prevent entering
When the impedance is forcibly increased for a certain time,
In this way, the switching element
Current loss stress cannot be reduced to zero. Also, an auxiliary power supply is mounted so that the voltage drop always occurs.
A method of backing up the voltage source for the detection circuit 21 is also conceivable.
However, in this case, the configuration of the power supply itself becomes complicated.
It will be. In addition, for example, intermittent
The protection operation can also be maintained by bringing it into oscillation mode.
The same problem remains if the basics are held. On the other hand, according to the second method described above, the low
WorsidecontrolThe switching element itself
The stress can be expelled. But,once
~ sideWhen detecting the current at, of course,
The actual overload current on the output side cannot be detected.
For example, as shown in FIG.
AtPrimary sideNumber of turnsSecondary sideOverwhelmingly more than the number of turns
Now, even ifPrimary sideEven if the current is suppressed to a certain value,
Secondary sideA considerable amount of current will flow through the winding,
There is a risk of fire. In order to prevent this,Secondary sideDirect current detection
Need to send out and provide feedback. However,
When using a multi-winding transformer,
The problem that the circuit becomes complicated and the number of parts increases
There is. Therefore, the overload condition is detected and detected at the peak current.
To protect the switching element from stress.
If the protection action continues for a certain period of time
Ideally, some way of acting like a stop
is there. Therefore, the present invention provides an overload condition,
Do not apply stress to the switching element,
The protection of the whole circuit, such as the smoke
Switching converter overpower protection circuit
It is intended to provide. [0027] [MEANS FOR SOLVING THE PROBLEMS] To achieve the above object
In the present invention,Overload protection in switching converter
The protection method is to drive the oscillator circuit and the output of the oscillator circuit.
Switching element, and the switching element
The secondary side is driven and the output is supplied from the secondary side to the load.
And a resonance circuit provided in connection with the transformer.
Therefore, the resonance frequency in the normal operation state is
Lower than the operating frequency range of
As an impedance to the current flowing to the primary side of the
And a voltage flowing through the switching element.
Overcurrent detection means to detect whether the current exceeds a predetermined threshold
And an oscillating circuit according to an output of the overcurrent detecting circuit.
A switch having oscillation condition changing means for changing the oscillation condition.
An overload protection method for a switching converter,
The overcurrent detection means allows the current to flow through the switching element.
Detecting whether the current flowing exceeds a predetermined threshold, and
When the current flowing through the switching element exceeds a predetermined threshold
The oscillation condition changing means. Circuit operation
The frequency is increased, and the operating frequency of the oscillation circuit is high.
Is measured, and the operating frequency of the oscillation circuit is measured.
If the time during which the high number continues is longer than a certain time
In this case, the oscillation circuit is interposed by the oscillation condition changing means.
Intermittent oscillation state, and the intermittent oscillation state of the oscillation circuit continues.
The intermittent oscillation state of the oscillation circuit is measured.
If the duration time exceeds a certain time, the oscillation
Stop the oscillation of the oscillation circuit by the condition changing meansAlso
It is. Therefore, according to the present invention, the resonance converter
ーTaOr bridge convertorTaLoad short circuit in the circuit
Which overloadFlowing to the switching elementCurrentPredetermined threshold
Whether the value has been exceededDetectAnd the switching element
If the flowing current exceeds a predetermined threshold, the oscillation
The operating frequency of the oscillation circuit is increased by the condition changing means,
When the operating frequency of the oscillation circuit remains high
And the operating frequency of the oscillation circuit remains high.
If the duration time exceeds a certain time, the oscillation
The oscillation circuit is set to an intermittent oscillation state by a condition changing means,
Measure the time during which the intermittent oscillation state of the oscillation circuit continues
The time during which the intermittent oscillation state of the oscillation circuit continues is
If the predetermined time is exceeded, the oscillation condition changing means
Stop the oscillation of the oscillation circuitBy the primary side
Small number of turns, which is difficult with the current detection non-intermittent operation protection circuit method
Smoke protection of the winding can be performed at the same time. Above
Safer and protects the entire circuit even under overload conditions
Is done. [0029] FIG. 1 shows a switching capacitor according to the present invention.
It is a figure showing a 1st embodiment of a barter. This figure
In order to avoid complication, in FIG.
The same components as those in the circuit are given the same numbers and detailed
Detailed description is omitted and the output voltage is controlled to a constant voltage.
Error amplifier 27 and photocoupler 28 for controlling
Oscillation frequency control circuit consisting of
I have. In this figure, 52 is a resonance capacitor, 5
3 is an impedance element, 54 is a comparator, 55 is
Reference voltage source, 56 is overcurrent time measurement circuit, 57 is intermittent
An oscillation circuit 58 is an intermittent time measurement circuit. This time
In the path, the resonance capacitors 4 and 52
It is a circuit having two resonant capacitors of
As in the circuit of FIG. 10 described above, one resonance capacitor
4 may be used. Now, the switching constructed as described above will be described.
In the converter, the switching element 2 is conducting.
When the current flows from the input voltage source 1 to the switching element 2,
The parallel circuit of the resonance inductance 6 and the transformer 7
Conductance 5, resonance capacitor 4, impedance element
1 and flows back to the input voltage source 1 through the
At point (a), a voltage as shown in FIG. 2A is generated.
When the switching element 3 is conductive, the current is equal to the input voltage.
From the pressure source 1 to the resonance capacitor 52, the resonance inductance
5, parallel circuit of resonance inductance 6 and transformer 7,
It enters through the switching element 3 and the impedance element 53.
It flows on the path returning to the force-voltage source 1, and the point (a) in FIG.
A voltage as shown in FIG. Here, a large current is generated due to an overload or a load short circuit.
When flowing, the current is shown in FIG. 2 (A) or (B).
Detected by the impedance element 53 as shown in FIG.
The output of the comparator 54 is compared with the reference voltage source 55 and
Thus, a signal as shown in FIG. 2C is generated.In addition,
Impedance element 53, comparator 54, reference voltage source 5
5 constitutes an overpower protection circuit. FIG. 2C shows the result of the comparator 54.
When the output signal goes high, the output of the oscillator 10
The signal is inverted. As a result, the driving circuit 11
And one of the conducting switching elements 2 or 3
Open and immediately afterwards the other switching element 3 or 2
Is output. That
Thereafter, a voltage higher than the reference voltage 55 is similarly detected.
The switching element that is conducting again is opened and
The released switching element becomes conductive. Below,
The above operation is continued. FIGS. 2D and 2E show the peak currents.
With flow detectionSaidSwitch when the overpower protection circuit is activated
6 is a waveform of a current flowing through the tinching elements 2 and 3. This
Such an operation is caused when the overcurrent
By detecting the current value, the switching element
Is open, the conduction period of the other switching element
This instantly increases the operating frequency of the circuit
It is supposed to be. Next, an overcurrent time measuring circuit 56, an intermittent oscillation
Circuit 57 and the operation of the intermittent oscillation time measuring circuit 58.
The intermittent oscillation operation explanatory diagram shown in FIG. 3 and the intermittent oscillation operation shown in FIG.
This will be described with reference to an explanatory diagram of the oscillation time measuring circuit. That is, switching is performed as shown in FIG.
When an overcurrent flows to element 3 or 2, the overcurrent time measurement
The constant circuit 56 is controlled by the voltage at the point (b) in FIG.
Is detected, and an overcurrent continues to flow in the circuit for the time T0.
It is determined whether or not it has been activated. Then, the overcurrent occurs during the time T0.
Over current when it is detected that
The intermittent oscillation circuit 56 has an intermittent oscillation as shown in FIG.
Outputs a signal to the intermittent oscillation circuit 57 to operate the circuit intermittently.
State. Further, as shown in FIG.
Intermittent time measurement when intermittent oscillation state lasts for time T3
The circuit 58 detects this and detects the situation shown in FIG.
Outputs a signal to completely stop the oscillation of the switching element
You. Due to the above operation, an overcurrent has flowed.
When the operating frequency is instantaneously increased,
When a certain period of time has passed, intermittent oscillation starts and the switch
The stress of the switching element. Furthermore, its intermittent oscillation
When the state exceeds a certain time, oscillation of the switching element
Completely shuts down and switches and other circuits
The whole is protected. FIG. 5 shows the first embodiment shown in FIG.
FIG. In this figure, FIG.
Detailed description of the same components with the same reference numerals
Is omitted. 59 is an overcurrent time measuring circuit 5 in FIG.
6 and the intermittent oscillation circuit 57.
You. 60 and 64 are buffers, 61 is a diode,
62 is a resistor and 63 is a capacitor.
4 constitutes a pulse generator 86. The operation of the circuit shown in FIG.
7 showing voltage waveforms at points (c) to (h) in FIG.
It will be described using FIG. (L) in FIG.Flow to switching element
BeGenerated in the impedance element 53 according to the current
Indicates the voltage, and when this voltage is input,
Road 86 is a figure7The pulse that lasts for a certain time shown in (c)
generate. This pulse width is determined by the resistor 62 and the capacitor 63
Can be set arbitrarily by the value of
Set to a pulse width of time T4 which is several times longer than the oscillation cycle of the circuit
Keep it. By doing so, the error shown in FIG.
Pulse generation times corresponding to the currents L1, L2, L3,.
Indicated by (M), (N) and (O) by road 86
A pulse signal of such a width T4 is generated, and an overcurrent signal is generated.
When continuous, the output (c) of the pulse generation circuit 86
The signal is a continuous signal as shown in (P). Now, a large current flows through the main circuit,
A voltage higher than the reference voltage 55 is generated in the sensing element 53.
And a pulse signal is output from the comparator 54.
As described above, the output signal of the oscillator 10 is inverted and becomes conductive.
Switching element is open and the open switch
The switching element is turned on. At the same time, pulse generation
A pulse signal having a predetermined time width t4 is output from the circuit 86.
(C) is output. (E) voltage is usually high level
Therefore, the AND gate 65
Goes high, enabling current source 66 to
The charging of the capacitor 68 is started. When overcurrent is continuously detected,
As shown in (c), a continuous signal is generated.
Signal (D) increases the voltage of the capacitor 68
Go. This overcurrent signal continues for an arbitrary set time T0.
Then, as shown in FIG. 7, the voltage of the capacitor 68 becomes
Upper threshold of comparator 70 with hysteresis
When the voltage reaches Vth-1, the output of the comparator 70
(E) is inverted to low level. This allows
Thus, the intermittent oscillation operation starts. That is, the output voltage of the comparator 70
When (e) goes low, the AND gate 91You
And 92Output is both low level,
The switching elements 2 and 3 are both open, causing intermittent oscillation.
The vibration stop period T1 starts. At this time, the potential of (e) becomes low.
And the output of the AND gate 65 becomes low,
Since the flow source 66 stops, the electric charge of the capacitor 68 becomes a resistance.
Discharge through 69, the potential (d) of the capacitor 68 is low
Down. The potential (d) of the capacitor 68 decreases.
And the lower threshold voltage Vt of the hysteresis comparator 70
When the voltage reaches h-2, the output voltage of the comparator 70 (e)
Goes high, enabling AND gates 91 and 92 again
Drive signal is supplied to the switching elements 2 and 3
And the operation of the main circuit is resumed.
Then, the charging of the capacitor 68 by the overcurrent signal starts again.
Is done. Thus, charging and discharging of the capacitor 68 is repeated.
The repetition maintains intermittent oscillation. On the other hand, this overcurrent operation is performed for an arbitrary set time T.
When it is less than 0, it operates as follows. Conden
The potential (d) of the hysteresis comparator 70 is
Before reaching the threshold voltage Vth-1, the overcurrent state is released.
And the output from the comparator 54 is not output.
Is continued for more than T4 hours shown in FIG.
The output (C) of the source generation circuit 86 goes low. this
As a result, the output of the AND gate 65 goes low,
The charging of the sensor 68 is stopped. At the same time,
Data 72 goes high and the output of NAND gate 75 goes high.
The force (f) becomes low level and the diode 67 conducts.
Thus, the charge (d) of the capacitor 68 is rapidly discharged. In this discharging operation, the intermittent oscillation operation is opened.
After the start, the main circuit is turned off (T1 period).
During (interval), the output potential (e) of the comparator 70 is low.
Therefore, the voltage at the point (f) which is the output of the NAND gate 75 is
Becomes high, and discharge through the diode 67 stops.
It will not be done. By the above series of operations,
Intermittent oscillation only when overcurrent signal continues for T0 period
State, and overcharge for a period shorter than T0
Malfunctions due to current flow are prevented. Next, the intermittent oscillation time measuring circuit shown in FIG.
The operation of 58 is described below. The intermittent oscillation starts
And the potential (e) of the output of the comparator 70 becomes low.
RS flip-flop 7 via inverter 76
8 is set and the output of the RS flip-flop 78 is
The current source 79 is enabled, and the capacitor 80 is charged.
Be started. Then, as shown in FIG.
After the lapse of the set time T3, the voltage of the capacitor 80 becomes
When the threshold voltage Vth-3 by the quasi-voltage source 82 is reached,
RS flip-flop by the output signal from the
84 is set and inverted as shown in FIG.
The output signal goes low. This signal is
Applied to the gates 91 and 92, thereby switching
The drive signals of the elements 2 and 3 are prohibited, and the operation of the main circuit is
Stopped completely. Also, this operation releases the overcurrent state.
Is released by generating a low signal at (f).
It is. With the above operation, the overcurrent state continues and intermittent
When oscillation continues for an arbitrary set time T3, the circuit is maintained.
The operation of the main circuit is completely stopped for protection.
ing. In the above description, the upper sideSystem
YourWas explained as an example, but the lower sideSystem
YourCan be applied in exactly the same way for
It is clear that. However, in this case,
When the overcurrent state occurs, the oscillation frequency of the oscillation circuit 10
It is necessary to control it to be low. In the above description, the overload condition
Protection by hardware using electronic circuits
An example has been shown, but it is not limited to this.
Software using a microcomputer
, A similar process can be executed. in this case
Compared to the case of hardware
Pressure and various times can be easily set and changed.
Swell. FIG. 8 shows an example of the block diagram. In FIG. 8, the same components as those in FIG.
The same numbers are given and the detailed description is omitted. 100
Is a single-chip microcomputer with an internal
Built-in peripheral circuits such as A / D converter and timer
You. 101 is a single-chip microcomputer 10
0 analog input port.
The analog signal to be output is A in the microcomputer 100.
It is converted to a digital signal by a / D converter. 102 is
Output port.
Is applied to the pulse drive circuit 11 to control its operation.
It is being controlled. 103 is an output port
And the signal output from the output port 103 is
Applied to the vibrator 10 to control its oscillation frequency and the like.
Used for FIG. 9 shows the operation of the microcomputer 100.
9 is a flowchart illustrating an outline of a process to be executed.
When the process is started, first, in step S110,
From the analog input port 101 to the impedance element
The voltage generated at both ends of the circuit 53 is captured, and the voltage is
/ D conversion, and whether the value exceeds a predetermined reference value
Is determined. If the determination result is NO, the input
Voltage from the port 101 to determine whether an overcurrent has occurred.
Repeat the judgment. Now, an overcurrent state occurs, and step S1
If the result of the determination in step 10 is YES, step 11
1 to output the oscillation frequency of the oscillator 10 from the output port 103.
Output a control signal to switch the number to a higher frequency,
The oscillation frequency of the oscillator 10 is increased. Next,
The process proceeds to step 112, and the overcurrent state is set for a predetermined time (T0).
It is determined whether or not the above is continued. Overcurrent condition
If T0 has not elapsed since the last
12 is executed to determine whether or not the time T0 has elapsed. What
If the overcurrent state has been eliminated, go to step 110.
Return. The overcurrent state continues for the time T0 or more, and
If the determination result of step 112 is YES,
Proceed to 113. In this step 113, the output port
For example, when the pulse drive circuit 11 is
The level period is T1 time and the low level period is T2 time
Output an intermittent oscillation control signal. Pulse drive circuit 11
Indicates that the control signal from the microcomputer 100 is high.
When the signal is at the level, the signal output from the oscillator 10 is switched.
Operates so as not to be applied to the switching elements 2 and 3,
It is configured to be applied as a drive signal when the level is
As a result, the switching element 2 and T1
And 3 are stopped and then operated for T2 hours.
Below, it becomes the intermittent operation mode which repeats this. Note that this
In the meantime, when the overcurrent state disappears,
Return to 10. Next, the routine proceeds to step 114, where the intermittent oscillation is performed.
It is determined whether or not a predetermined time (T3) has elapsed since the state was entered.
judge. If the result of this determination is NO, step 1 is repeated.
Step 14 is executed. On the other hand, when this determination result is YES
Goes to step 115 and outputs from output port 102
A high level signal is applied to the pulse drive circuit 11 to switch
The operations of the switching elements 2 and 3 are stopped. Note that this
If the overcurrent state disappears during the
Execute. As described above, by software processing,
As described with reference to FIGS.
The operating frequency is instantaneously increased when the
If the state exceeds a certain period of time, it will start intermittent oscillation and
When the intermittent oscillation state exceeds a certain time, the switch
Stop the switching element completely by stopping the oscillation of the switching element.
First, the entire circuit can be protected. [0057] According to the present invention, a resonant converter is provided.TaOr bridge convertor
TaIn a circuit, the main current
Instantaneously open the switching element by detecting the
To prevent switching element stress.
Can be. Also, the upper sidecontrolType converterTaIn
The operating frequency to increase the resonance impedance.
Comb can protect excess power supply to the load. further,
The switching stress of the switching element can be expelled,
In addition, it is necessary to stably protect the entire circuit, such as smoke smoke protection.
Can be.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a first embodiment of the present invention. FIG. 2 is an explanatory diagram of an operation of an overpower protection circuit based on peak current detection. FIG. 3 is a diagram for explaining an intermittent oscillation operation. FIG. 4 is an explanatory diagram of an intermittent oscillation operation time measurement circuit. FIG. 5 is a detailed circuit diagram of the first embodiment. FIG. 6 is a diagram for explaining the operation of the detailed circuit in FIG. 5; FIG. 7 is a diagram for explaining the operation of the detailed circuit in FIG. 5; FIG. 8 is a diagram for explaining a second embodiment of the present invention. FIG. 9 is a diagram illustrating a flowchart of a process according to the second embodiment of the present invention. FIG. 10 is a diagram showing an example of a conventional configuration. 11 is a diagram showing waveforms at various parts in FIG. FIG. 12 is a diagram illustrating a relationship between input impedance and frequency. FIG. 13 is a diagram showing waveforms at various portions in a conventional method. FIG. 14 is a diagram showing waveforms at various parts in the lower side control . [Description of Signs] 1 Input DC voltage source 2, 3 Main switching element 4, 52 Resonance capacitor 5, 6 Resonance inductance 8, 9 Diode 10 Oscillator 11 Pulse drive circuit 13 Low-pass filter 14, 15 Switching element end capacitance 16, 17 Impedance Element 21 Voltage drop detection circuit 26 Rectifier smoothing circuit 27 Load 53 Impedance element 54, 83 Comparator 55, 71, 82 Reference voltage source 56 Overcurrent time measurement circuit 57 Intermittent oscillation circuit 58 Intermittent oscillation time measurement circuit 59 Overcurrent time measurement and intermittent Oscillator circuits 60, 64 Buffers 61, 67, 85 Diodes 62, 69, 73, 81 Resistors 63, 68, 74, 80 Capacitors 65, 91, 92 AND gate 66, 79 Current source 70 Hysteresis comparators 72, 76, 77 Inverter 75 NA D gate 78 and 84 RS flip-flop 86 the pulse generator 90 frequency divider 100 the microcomputer 101 analog input port 102 and 103 output ports

──────────────────────────────────────────────────続 き Continuing on the front page (51) Int.Cl. ⁷ Identification code FI H02M 7/48 H02M 7/48 P (72) Inventor Haruo Watanabe 2-2-1 Otemachi, Chiyoda-ku, Tokyo Shin-Otemachi Building Shindengen Kogyo Co., Ltd. (72) Inventor Takeshi Keni 2-2-1 Otemachi, Chiyoda-ku, Tokyo Shin-Otemachi Building Shindengen Kogyo Co., Ltd. (72) Inventor Kenji Horiguchi Chiyoda-ku, Tokyo (2-1) Shinden Otemachi Building Shindengen Kogyo Co., Ltd. (72) Inventor Yoshinori Kobayashi Shinden Otemachi Building Shindengenkogyo Co., Ltd. 2-56, Otemachi, Chiyoda-ku, Tokyo References JP-A-7-194113 (JP, A) JP-A-7-1433741 (JP, A) JP-A-7-163143 (JP, A) JP-A-7-31130 (JP, A) 7-46828 (JP, A) (58) Survey The field (Int.Cl. ^7, DB name) H02M 3/28 H02H 3/093 H02M 3/335 H02M 7/48

Claims (1)

(57) [Claims 1] An oscillator circuit and a drive circuit based on an output of the oscillator circuit.
A switching element to be operated, and the switching element
The primary side is driven and the output is supplied to the load from the secondary side
Transformer and resonance circuit provided in connection with the transformer
Wherein the resonance frequency in a normal operation state is the oscillation frequency.
It is set lower than the operating frequency range of the circuit,
Impedance with respect to the current flowing on the primary side of the transformer
Resonance means acting as a
Overcurrent to detect whether the current flowing exceeds a predetermined threshold
Detecting means, and oscillating according to an output of the overcurrent detecting circuit.
Oscillation condition changing means for changing the oscillation condition of the circuit.
Overload protection method for switching converters
Thus, the overcurrent detection means allows the switching element to flow.
Detecting whether the current flowing through the switching element exceeds a predetermined threshold.
The oscillation circuit is changed by the oscillation condition changing means.
The operating frequency of the oscillator circuit is high, and the operating frequency of the oscillation circuit is high.
The oscillation frequency is high and the operating frequency of the oscillation circuit is high.
If the time exceeds a certain time, the oscillation condition changing means
The intermittent oscillation state of the oscillation circuit, and measures the time during which the intermittent oscillation state of the oscillation circuit is continued.
The time during which the intermittent oscillation state of the oscillation circuit continues is constant.
If the time has been exceeded, the oscillation condition changing means
Switching converter that stops oscillation of the oscillator circuit
Overload protection method.