JP3534312B2 - Switching power supply - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feedback winding for a transformer.
To perform overcurrent control with the voltage generated in this feedback winding.
The present invention relates to an excitation type switching power supply. 2. Description of the Related Art A self-excited switching power supply having a feedback winding
The source device continues self-oscillation with the voltage generated in the feedback winding
Therefore, it is necessary to add an oscillation circuit composed of IC etc. separately
And can be configured with a simple circuit. For this reason, small and low
In the field of small-capacity switching power supplies because of the price
It is frequently used in Self-excited switching power supply with feedback winding
Various proposals have been made for the device.
For example, JP-A-63-87170 and JP-A-Hei.
The technology described in JP-A-6-178538 is known.
I have. This type of self-excited switching power supply has a primary winding
Wire, secondary winding, feedback winding and, if necessary, control winding.
And a switch for interrupting the current of the primary winding.
A switching transistor and the switching transistor.
Control the positive feedback signal from the feedback winding to the transistor.
A control transistor and the feedback winding or the control
While charging and discharging the electromotive voltage of the winding with a predetermined time constant,
Filling the time constant for giving the control voltage to the control transistor
A discharge circuit. This type of self-excited oscillation type switching power supply device
Wherein the time constant charge / discharge circuit comprises a resistor and a capacitor.
It consists of. The charging of the capacitor is performed by charging the time constant.
The switching transistor is turned off via a discharging circuit.
This is performed by the voltage induced in the feedback winding during the power-on period. Said
The discharging of the capacitor is performed via the time constant charging / discharging circuit.
The feedback winding is provided during the off period of the switching transistor.
This is done with a flyback voltage induced on the line. [0005] The charging and discharging of the capacitor has an input fluctuation.
Or changes in output voltage due to load fluctuations, etc.
I do. The charging voltage of the capacitor is controlled by the control transformer.
Determines the on-timing of the
Controls transistor and outputs to switching power supply
Provides voltage stabilization and overcurrent control. In the above-described self-oscillation type switching power supply,
The control transistor is a bipolar transistor.
It consists of a star. The bipolar transistor has its V
BE generally has a negative temperature characteristic of about −2 mV / ° C.
I have. For this reason, the ambient temperature of the switching power supply increases.
The control transistor is connected to the capacitor.
The battery turns on before charging is sufficiently advanced.
When the ambient temperature of the switching power supply is low,
If the charging voltage does not exceed the specified value, it will not turn on.
You. The ON timing of the control transistor is
Overcurrent point and overcurrent during overcurrent control via switching element
The current curve is controlled. Therefore, switching
The power supply has an overcurrent point during overcurrent control due to temperature fluctuations.
And the overcurrent curve fluctuates. During overcurrent control
The fluctuation of the overcurrent point of
The output voltage is reduced or
Supply power to the load despite the
Problems such as damage may occur. As a means for solving this problem, a negative temperature
The control transistor having characteristics has a positive temperature characteristic.
Combined with a PCT thermistor
It is conceivable to cancel such characteristic fluctuations. Only
However, the PCT thermistor does not have a small element and the price
The problem is that switching power supplies are
There are problems with miniaturization and cost reduction required for
Was. [0008] The object of the present invention is to solve the above-mentioned problems.
The ambient temperature around the switching power supply.
Self-excited switch that can perform accurate overcurrent control even if it fluctuates
The present invention is to provide a power supply device for a vehicle. Means for Solving the Problems The above-mentioned problems are solved.
Therefore, the switching power supply according to the present invention
, A switching element, an output rectifying / smoothing circuit, and a control circuit.
Including roads. The transformer comprises an input winding, an output winding,
And a feedback winding. [0011] The switching element connects the input winding.
The DC voltage supplied through the output winding is intermittent
A voltage is induced in the feedback winding. The feedback winding is connected to the switching element.
Conducts the switching element with the voltage induced during the ON period
Bias in the direction. [0013] The output rectifying / smoothing circuit includes a switch.
Rectifies the voltage induced in the output winding during the off period of the switching element
・ Smooth and output. The control circuit includes a time constant charging circuit and a switch.
Switching transistor and charging current shunt circuit
Including. The time constant charging circuit includes a resistor and a capacitor.
And a series circuit, which is connected between both ends of the feedback winding.
You. The switching control transistor includes:
A base is connected to the connection point between the resistor and the capacitor.
Between the collector and the emitter.
Connected to control input side. The charge current shunt circuit is an NTC thermistor.
And shunts the charging current of the capacitor. In the above switching power supply,
The transformer includes an input winding, an output winding, and a feedback winding.
Including. The switching element passes through the input winding
Since the supplied DC voltage is intermittent, the switching
When the device starts to turn on, the input winding
Current begins to flow, and a voltage is applied to the output winding and the feedback winding.
Induce. The feedback winding is used to turn off the switching element.
The switching element is turned on by the voltage induced during the
The switching element is completely biased.
It becomes conductive and the current flowing through the input winding increases. Said
The voltage induced during the ON period of the switching element is
Charge the sensor. Thereafter, the voltage of the capacitor is changed to the switch.
Charged to the threshold voltage of the switching control transistor
Instantaneously turns off the switching control transistor.
And the switching element is turned off. The Sui
When the switching element is turned off, the input winding and the output
The winding and the feedback winding have opposite fly directions.
A back voltage is induced. The flyback voltage is
The ringing voltage
generate. Ringing voltage also occurs in the feedback winding
Triggering the switching element to turn on.
You. Thereafter, self-excited oscillation is continued by this repetition. The output rectifying / smoothing circuit includes a switch.
Rectifies the voltage induced in the output winding during the off period of the switching element
Since the output is smoothed, the DC voltage must be output continuously.
Can be. The control circuit includes a time constant charging circuit.
The time constant charging circuit consists of a series circuit of a resistor and a capacitor.
And is connected between both ends of the feedback winding.
The capacitor returns the feedback during the ON period of the switching element.
The switching element charged with the voltage induced in the winding;
Is discharged by the voltage induced in the feedback winding during the off period.
You. The control circuit may further include a switching control
Including transistors. The switching control transformer
The base of the resistor is a connection between the resistor and the capacitor.
Connected between the collector and emitter
Connected to the control input of the switching element. Because of this,
The voltage of the capacitor is the voltage of the switching control transistor.
When charged to the threshold voltage, the switching control
The transistor is momentarily turned on and the switching element
Turn off the child. [0023] The control circuit may further include a charging current shunting circuit.
including. The charging current shunt circuit includes an NTC thermistor.
And shunts the charging current of the capacitor. This configuration
Is the threshold voltage of the switching control transistor.
To provide a temperature compensation effect. The threshold of the switching control transistor
The value voltage has a negative temperature characteristic. For this reason, the switch
When the ambient temperature of the switching power supply increases, the switch
The threshold voltage of the switching control transistor decreases,
Turns on before the voltage of the capacitor is charged to the initial threshold voltage.
I do. Conversely, if the ambient temperature of the switching power supply
Then, the switching control transistor has a threshold voltage
Rises and the voltage of the capacitor exceeds the initial threshold voltage.
And then turn it on. Generally, the temperature and the resistance of the NTC thermistor
Has an exponential relationship with temperature
The resistance value decreases with the rise. Because of this, switching
When the ambient temperature of the power supply increases, the NTC thermistor
The resistance value decreases and the flow rate of the charging current increases.
To delay the charging of the capacitor. Conversely, switch
When the ambient temperature of the power supply decreases, the NTC
The resistance value of the mister increases, and the partial flow rate of the charging current decreases.
Thus, the charging of the capacitor is accelerated. Therefore, the operating temperature of the switching power supply
Range and temperature of the switching control transistor
NTC thermistor with appropriate temperature characteristics in consideration of
Select and combine fixed resistors as necessary
If an electric current shunt circuit is configured,
Fluctuation of on-timing of switching control transistor
Can be compensated for. In the above-described configuration, overload or load short circuit occurs.
When the overcurrent condition occurs, the time constant charging circuit
The switching control transistor with the charging voltage of the capacitor.
Is turned on and the switching element is turned off.
Then, the overcurrent control is performed. In the present invention, the temperature
On the switching control transistor
Switching power supply
Accurate overcurrent control can be performed even if the ambient temperature of the device fluctuates
Self-excited switching power supply can be provided.
You. Other objects, configurations and advantages of the present invention
This will be described in more detail with reference to the accompanying drawings. Drawing
Is merely illustrative. FIG. 1 shows a self-excited switch according to the present invention.
FIG. 3 is an electric circuit diagram showing an embodiment of the switching power supply device.
The self-excited switching power supply shown is for power conversion
Transformer 1, switching element 2, and output rectification smoothing circuit
Including the path 3, the output voltage detection circuit 4, and the control circuit 5.
I have. The transformer 1 has an input winding 11 and an output winding 1
2 and a feedback winding 13. The input winding 11
DC input terminal Ti via the main electrode of switching element 2
n. A DC voltage source E is connected to the DC input terminal Tin.
Continued. The DC voltage source E is an internal element of the present invention.
May be an external element, such as a battery or other direct
Current voltage source or AC voltage to DC through rectifier circuit
Any of the converted voltages can be used. The switching element 2 passes through the input winding 11.
The DC voltage Vin supplied and interrupted is supplied to the output winding 1
2 and the feedback winding 13. Switching
The element 2 switches the supplied DC voltage Vin at a high frequency.
As long as they can be switched, typically a bipolar transistor
And a control electrode such as a field effect transistor.
Conductive elements are used. This embodiment is an N-channel MOS
A field-effect transistor is used. The feedback winding 13 passes through the characteristic improving circuit 6
Connected between the gate and source of the switching element 2,
Switch by the voltage induced during the ON period of the switching element 2
Biasing the gate of the switching element 2 in the conduction direction. Suitable for characteristics
The upper circuit 6 improves the switching characteristics of the switching element 2.
A circuit for increasing the resistance of the capacitor C6 and the resistor R6.
It is configured to include diodes D61 and D62. The gate of the switching element 2 is further activated.
It is connected to an input line via resistors R7 and R8. The output rectifying / smoothing circuit 3 includes a rectifying diode D
3 and a smoothing capacitor C3. Rectification
Diode D3 and smoothing capacitor C3 are connected in series
Then, both ends are connected to the output winding 12. For smoothing
Both ends of the capacitor C3 are connected to the output terminal of the output rectifying and smoothing circuit 3.
Connected to the output terminal Tout of the switching power supply.
Continued. The direction of the rectifier diode D3 is the output winding 1
It becomes forward with respect to the flyback voltage induced in 2
Oriented. With this configuration, the output rectifying flat
The smoothing circuit 3 has an output winding during the off period of the switching element 2.
12 is rectified and smoothed and output. In addition,
Bipolar transistors instead of rectifier diode D3
Switches with control electrodes such as
If a switching element is used, a synchronous rectification type rectifying and smoothing circuit can be configured.
Can be achieved. The output voltage detecting circuit 4 is an output rectifying / smoothing circuit.
3, the output terminal of the switching power supply
Connected to Tout to detect and control output voltage Vout
An output voltage signal is supplied to the circuit 5. In this embodiment, the
Distortor Q4, shunt regulator IC4 and resistor R
Configuration including 41, R42, R43, R44, R45, etc.
Output from the collector of the transistor Q4 to the control circuit 5.
Provides a force voltage signal. The output voltage detection circuit 4 according to the present invention
Although it is not an essential element, a conventionally known circuit may be used as appropriate.
Can be. The control circuit 5 includes a time constant charging circuit 51,
Constant discharge circuit 52, time constant control circuit 53, switch
Control transistor 54 and charging current shunt circuit 55
It is comprised including. The time constant charging circuit 51 includes a diode D51
And a series circuit of a resistor R510 and a resistor R511.
One end of the series circuit and one end of the capacitor C5 are connected
Be composed. The time constant discharging circuit 52 includes a diode D52
And a series circuit of the resistor R52 and one end of the series circuit.
Connects to one end of a capacitor C5 common to the time constant charging circuit 51.
And a diode D5 in parallel with the capacitor C5.
Are connected. Time constant charging circuit 51 and time constant
The discharge circuit 52 is connected between both ends of the feedback winding 13.
The diode D51 and the diode D52 are opposite to each other.
Connected, diode D51 is forward with respect to charging current
Connected so that Diode D5 is a capacitor
This prevents C5 from being charged in the reverse direction. Time constant charging circuit 51 and time constant charging circuit 52
Can take various forms. For example, diode D5
1 or D52, or
A resistor may be connected in series with the parallel circuit of the diode.
Can be achieved. Time constant charge / discharge circuits 51 and 52 are independent
Although it is not necessary to provide it as
Number can be set individually, and more appropriate control action
Is obtained. The time constant control circuit 53 includes a transistor Q5
3 and its reverse bias preventing diode D53,
Anti-R53 and the main electrode of transistor Q53 is timed
Becomes in parallel with the resistors R510 and R511 of the number charging circuit 51
As described above, the connection is made via the diode D53 and the resistor R53.
Is done. An output voltage signal is input to the control electrode. The time constant control circuit 53 includes an output voltage detection circuit
As in the case of FIG. 4, although not an essential element of the present invention, the output voltage detection
Output circuit 4 and a transistor Q according to the output voltage.
The time constant charging circuit 51
Control the time constant of Form of connection with output voltage detection circuit 4
Configures transistor Q53 with a phototransistor
And a light using a photodiode for the output voltage detection circuit 4.
It may be a combination. The switching control transistor 54 is
It is composed of an NPN transistor whose collector is a diode.
Connected to the gate of the switching element 2 via the node D7.
And the emitter is connected to the source of the switching element 2.
The base is connected to one end of the capacitor C5. Die
Anode D7 is a transistor for switching control of the cathode.
Connected to the collector of the
When C5 is discharged, the switching control transistor 54
Reverse current flows from the base of the
To prevent the switching control transistor 54 from turning on in the reverse direction.
Stop. The charging current shunting circuit 55 is an NTC thermistor.
Including a series circuit of T55 and a resistor R55, a capacitor C
Of the time constant charging circuit 51 so that the charging current of
A connection point between the anti-R510 and the resistor R511 and the capacitor C
5 and the other end. The self-excited switch according to the present embodiment thus constructed
In the switching power supply, a DC power is applied to the input terminal Tin.
When the pressure Vin is applied, the switch is switched via the starting resistor R7.
The gate of the chining element 2 is energized. Switching element
2 starts to turn on, the input winding 11 of the transformer 1
Input current begins to flow through the output winding 12 and the feedback winding 13
To induce a voltage. The voltage induced in the output winding 12 is output rectified flat.
The output is blocked by the diode D3 of the smoothing circuit 3.
No output current flows through the winding 12 and energy is
Is accumulated in The voltage induced in the feedback winding 13 improves the characteristics.
Conduction direction of the gate of the switching element 2 through the circuit 6
Switching element 2 turns on rapidly
And the input current flowing through the input winding 11
Increase with. The voltage induced in the feedback winding 13 is
Sometimes, the diode D51 of the time constant charging circuit 51 and the resistor R
510, a resistor R511, and a time constant control circuit 53.
To charge the capacitor C5. After that, the voltage of the capacitor C5 is switched
Up to the threshold voltage of the switching control transistor 54
And the switching control transistor 54 is turned on.
To short-circuit the control input side of the switching element 2. This result
As a result, the switching element 2 is turned off and the input winding 1
1, output winding 12 and feedback winding 13
Generates a flyback voltage in the reverse direction. Flyback voltage generated at output winding 12
Is rectified and smoothed by the output rectifying and smoothing circuit 3, and the output terminal
The DC output voltage Vout is output to the child Tout. Return winding
The flyback voltage generated on line 13 is
52 is connected through a resistor R52 and a diode D52.
The charge of the sensor C5 is discharged. At this time, the diode
Since D5 is turned on, the capacitor C5 is charged in the reverse direction.
It will not be done. Thereafter, the flyback voltage is
The ringing voltage
generate. Ringing voltage also occurs in feedback winding 13
And the switching element 2 starts to turn on.
Give injuries. Thereafter, self-sustained pulsation continues by this repetition,
DC output voltage Vout is continuously output to the input terminal Tout
I do. The output voltage detection circuit 4 outputs the output voltage Vout
And supplies an output voltage signal to the control circuit 5. Concrete
Specifically, when the output voltage Vout is high, the transistor Q4
The base is deeply biased and the transistor Q4
Output voltage signal with high potential level
I do. When the output voltage Vout is low, the transistor Q4
Source is biased shallowly and the impedance of transistor Q4 is
The dance becomes high and an output voltage signal of low potential level is output.
You. The output voltage signal is controlled by a time constant control circuit constituting the control circuit 5.
It is supplied to the base of transistor Q53 in path 53. Therefore, in the control circuit 5, the output voltage
When Vout is high, the impedance of transistor Q53 is
And the time constant of the time constant charging circuit 51 is small.
The capacitor C5 is charged in a short time,
The ON timing of the switching control transistor 54
Hasten. Conversely, if the output voltage Vout is low,
Q53 impedance increases, time constant charging circuit
Since the time constant of 51 is controlled largely, the capacitor C5
Is slowly charged and the switching control transistor
The ON timing of 54 is delayed. Therefore, the switching element 2 outputs the output voltage
If Vout is high, the ON period is shortened and the output voltage drops
On the contrary, if the output voltage Vout is low,
The ON period becomes longer and the output voltage is controlled to increase.
Stabilizes the output voltage Vout. Also, an overcurrent or a short circuit of the load causes an overcurrent.
When the output voltage Vout drops to the
The impedance of the transistor Q53 becomes infinite. Conde
The sensor C5 is slowly charged by the time constant of the time constant charging circuit 51.
However, the threshold value of the switching control transistor 54
When charging is completed, the switching control transistor 54
Turn on. Therefore, the ON period of the switching element 2
Is limited by a certain value and shifts to the off period, and the output voltage rises
Do not rise. In the off period of the switching element 2,
The capacitor C5 is a feedback winding via the time constant discharging circuit 52.
The charge is discharged by the flyback voltage induced in
You. The flyback voltage is proportional to the output voltage Vout
Therefore, the discharge amount of the capacitor C5 is very small.
You. Therefore, during the next ON period, the capacitor
C5 is charged slowly by the time constant of the time constant charging circuit 51.
Immediately, the switching control transistor 54
Charged to the threshold value, the switching control transistor 5
4 is turned on. Therefore, the switching element 2 is turned on.
The period is controlled to be shorter, and the output voltage Vout is reduced.
And the overcurrent control is performed. Next, the switching system which is a feature of the present invention will be described.
Of the threshold voltage caused by the temperature fluctuation of the control transistor 54
The fluctuation will be described. Transistor for switching control
Base of the data 54. Emitter voltage VBE is a negative temperature characteristic
Have. Therefore, around the switching power supply
When the temperature rises, the switching control transistor 5
4 indicates that the voltage of the capacitor C5 has been charged to the initial threshold voltage.
Turn on before being turned on. Conversely, around the switching power supply
When the temperature decreases, the switching control transistor 5
4 is whether the voltage of the capacitor C5 exceeds the initial threshold voltage
Will be turned on. Transistor for switching control
The ON timing of the switch 54 is the ON period of the switching element 2.
Influence in between. FIG. 3 shows a switching control transistor.
54 and the maximum ON period T of the switching element 2
FIG. 9 is a diagram showing a relationship with on (max), and
This is shown in comparison with the presence / absence of a current dividing circuit. Max on
The period Ton (max) refers to the in-state of the transistor Q53.
Charge of capacitor C5 when the impedance reaches infinity
Means the ON period of the switching element 2 determined by the charging time.
I taste. If there is no charging current shunting circuit, FIG.
As shown by the broken line, the switching control transistor
When the temperature at 54 is low, the maximum
The switching period Ton (max) is controlled to be long,
As the temperature of the control transistor 54 increases,
The maximum on-period Ton (max) of the switching element 2 is
Controlled short. This is a switching control transistor.
If the temperature of the star 54 is low, overcurrent control is performed even if the rated load is exceeded.
Is not performed, and the temperature of the switching control transistor
If the temperature is too high, overcurrent control will be activated below the rated load
It means that the pressure drops. On the other hand, the charging current shunt circuit of the present embodiment
In the case of having a switch, as shown by a solid line in FIG.
Switch against the temperature fluctuation of the switching control transistor 54.
Fluctuation width of the maximum ON period Ton (max) of the switching element 2
Is small. That is, the charging current shunt circuit 55 of the present embodiment
Includes an NTC thermistor T55 and a capacitor C5.
Divides the charging current. NTC thermistor T55
If the ambient temperature around the
To reduce the flow rate of the charging current,
Since the charging is quickened, the switching control transistor 5
4 turns on earlier and there is no charging current shunt circuit 55.
In comparison, the maximum ON period Ton (m
ax) is shortened. Conversely, the ambient temperature of the switching power supply
As the temperature increases, the resistance of the NTC thermistor T55 decreases.
And increase the flow rate of the charging current to charge the capacitor C5.
The switching control transistor 5
4 is delayed, compared with the case where the charging current shunt circuit 55 is not provided.
In comparison, the maximum ON period Ton (ma
x) is lengthened. Therefore, the switching element for the temperature fluctuation
The fluctuation width of the maximum ON period Ton (max) of the child 2 is reduced.
can do. This is the switching control transformer.
In response to temperature fluctuations of the
Accurate overcurrent control is performed with small fluctuation range of current point
Means that. As described above, in this embodiment, due to the temperature fluctuation,
Of the switching control transistor
Switching fluctuations.
Even if the ambient temperature of the power supply fluctuates, accurate overcurrent control is performed.
Can provide a self-excited switching power supply
You. In this embodiment, the time constant charging circuit 51 and the time constant
The discharge circuit 52 and the discharge circuit 52 are provided individually.
To prevent the capacitor C5 from being charged in the reverse direction.
Mode D5. This configuration is a constant
There is an advantage that calculation becomes easy and an optimal design can be performed. Ma
The diode D7 is a switching control transistor.
To prevent the power switch 54 from being turned on in the reverse direction. Transistor reverse
It is difficult to grasp the value of the current flowing due to
Through the switching control transistor 54
The above-described configuration is used because no discharge path is formed.
Accordingly, the charging and discharging of the capacitor C5 can be performed accurately. FIG. 2 shows a self-excited switching according to the present invention.
FIG. 4 is an electric circuit diagram showing another embodiment of the power supply device,
Example applied to a self-excited switching power supply
I have. In the figure, the same components as those shown in FIG.
The same components are denoted by the same reference numerals. Illustrated Self-Excited Switching Power Supply
Is a power conversion transformer 1, a switching element 2,
Output rectifying / smoothing circuit 3, output voltage detecting circuit 4, control circuit
It includes a path 5 and a level shift circuit 7. Power conversion
Transformer 1 and output rectifying / smoothing circuit 3 are shown in FIG.
The configuration is the same as that of the embodiment described above, and the description is omitted. The switching element 2 is an NPN type bipolar transistor.
It is composed of a transistor. Switching element 2
Is connected to the input winding 11 of the transformer 1 and
Is connected to the DC input terminal Tin, and the base is
The feedback winding 1 via the shift circuit 7 and the characteristic improving circuit 6
3 is connected. The level shift circuit 7 includes a diode D7
1, D72 and a capacitor C7. Daioh
The capacitors D71 and D72 are connected in parallel with the capacitor C7.
Connected, diode D71 is in the opposite direction to the base current
Diode D72 is forward with respect to the base current.
It is oriented to The output voltage detection circuit 4 includes resistors R41, R4
2, R45, shunt regulator IC4, photocap
La PC4. Photo coupler PC4 is photo
Including diode PD4 and phototransistor PT4
In. The photodiode PD4 is a shunt regulator
Data IC4 in series with the output terminal Tout.
Connected. The resistors R41 and R42 are connected in series.
Connected between the output terminals Tout and the output voltage Vout
Divided voltage to the control terminal of shunt regulator IC4
Supply. The phototransistor PT4 has its collector
The stable voltage VCC on the input side is supplied to the
Optically coupled to diode PD4, output voltage signal to emitter
Generate The output voltage signal is applied to a resistor connected to the emitter.
It is supplied to the control circuit 5 via the anti-R45. Photo tiger
The transistor PT4 supplies a stable voltage on the input side to its collector.
The collector potential is kept constant,
Pulse-shaped abnormal current caused by stray capacitance between collectors
Flow can be prevented. Output voltage detection circuit 4 of the present embodiment
Converts the output voltage signal to the output terminal Tou with the above-described configuration.
It is electrically insulated from t. The control circuit 5 includes a time constant charging circuit 51,
Constant control circuit 53 and switching control transistor
54 and a charging current shunting circuit 55. The time constant charging circuit 51 also serves as a discharging circuit.
And A series circuit of a resistor R510 and a resistor R511;
One end of the series circuit is connected to one end of the capacitor C5.
It is composed. The time constant charging circuit 51 includes the feedback winding 13
Is connected between both ends. The time constant control circuit 53 operates in the actual
The control electrode of the transistor Q53 has the same configuration as that of the embodiment.
Receives an output voltage signal. The switching control transistor 54 is
It is composed of an NPN transistor whose collector is a diode.
Switch D7 through the mode D7 and the level shift circuit 7.
Connected to the base of switching element 2 and the emitter is switched
Connected to the emitter of element 2. Switching control
The base of the transistor 54 is the same as that of the embodiment shown in FIG.
The capacitor C5 is connected to one end. The level shift circuit 7 is a bipolar transistor.
The threshold voltage of the transistor is higher than the threshold voltage of the field-effect transistor.
Circuit for switching control.
When the transistor 54 is turned on, the switching element 2
It works to make sure it is turned off. Charge Current Dividing Circuit 55 and Other Configurations
Has the same configuration as the embodiment shown in FIG. The self-excited switch according to the present embodiment thus constructed
In the switching power supply, a DC power is applied to the input terminal Tin.
When the pressure Vin is applied, the starting resistance R7 and the level shift
The base of the switching element 2 via the circuit 7
Electric current flows. Switching element 2 starts to turn on
Then, the input current starts flowing through the input winding 11 of the transformer 1.
Therefore, a voltage is induced in the output winding 12 and the feedback winding 13. The voltage induced in the feedback winding 13 improves the characteristics.
A switching element via a circuit 6 and a level shift circuit 7
Since the base of element 2 is biased in the conducting direction, the switch
The switching element 2 is rapidly turned on and flows to the input winding 11.
Input current increases over time. Feedback winding 1
3 is simultaneously applied to the resistance of the time constant charging circuit 51.
Via the anti-R510, R511 and the time constant control circuit 53
To charge the capacitor C5. Thereafter, the voltage of the capacitor C5 is switched
Up to the threshold voltage of the switching control transistor 54
And the switching control transistor 54 is turned on.
You. At this time, the bipolar shifter 7
Switching element 2 composed of transistors
I can do it. When the switching element 2 is turned off, the input winding
To the wire 11, the output winding 12, and the feedback winding 13.
A flyback voltage is generated in the opposite direction. afterwards,
The flyback voltage depends on the disappearance of the flyback energy.
Both drop and generate a ringing voltage. Ringin
The switching voltage is also generated in the feedback winding 13 and the switching element
2 gives the opportunity to start turn-on. Thereafter, self-sustained pulsation continues by repeating this,
A DC voltage is continuously output to the input terminal Tout. The operation of the output voltage detection circuit 4 is based on the output voltage signal
Is electrically insulated from the output terminal Tout.
This is the same as the embodiment shown in FIG. The operation of the control circuit 5 is as follows.
Embodiment shown in FIG. 1 except that the discharge circuit is also used.
The charge current shunt circuit 55 is caused by temperature fluctuation.
Of switching control transistor 55
To compensate for fluctuations in For this reason, the self-excited switching of this embodiment
The power supply has a fluctuating ambient temperature around the switching power supply.
However, accurate overcurrent control can be performed. The present invention has been described with reference to the preferred embodiments.
Although the contents have been described in detail, the present invention is not limited thereto.
If you are a person skilled in the art,
It is possible to conceive various modifications based on
It is obvious. As described above, according to the present invention, the switch
Even if the ambient temperature of the switching power supply fluctuates,
To provide a self-excited switching power supply that can control the flow
be able to.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an electric circuit diagram showing an embodiment of a self-excited switching power supply according to the present invention. FIG. 2 is an electric circuit diagram showing another embodiment of the self-excited switching power supply device according to the present invention. FIG. 3 shows a temperature T of the switching control transistor 54;
a and the maximum ON period Ton (ma
FIG. 7 is a diagram showing a relationship with (x). [Description of Signs] 1 Transformer 11 Input winding 12 Output winding 13 Feedback winding 2 Switching element 3 Output rectification smoothing circuit 5 Control circuit 51 Time constant charging circuit 54 Switching control transistor 55 Charging current shunt circuit R51 Resistor C5 Capacitor T55 NTC thermistor

Claims (1)

(57) Claims 1. A switching power supply device that includes a transformer, a switching element, an output rectifying / smoothing circuit, and a control circuit, and that performs a self-excited oscillation operation. Includes an input winding, an output winding, and a feedback winding, wherein the switching element interrupts a DC voltage supplied through the input winding and applies a voltage to the output winding and the feedback winding. The feedback winding biases the switching element in a conduction direction with a voltage induced during an ON period of the switching element, and the output rectifying / smoothing circuit applies a voltage to the output winding during an OFF period of the switching element. The induced voltage is rectified and smoothed and output. The control circuit includes a time constant charging circuit, a switching control transistor, and a charging current shunt circuit. The time constant charging circuit includes a resistor and a capacitor. The switching control transistor is connected between both ends of the feedback winding, the base of the switching control transistor is connected to a connection point between the resistor and the capacitor, and the collector and the emitter of the switching element are connected between the collector and the emitter. Connected to a control input side, the charging current shunt circuit includes an NTC thermistor, and the NTC thermistor is provided in parallel with the series circuit.
Charge current to the capacitor when ambient temperature is low
Volume and the ambient temperature is high.
A switching power supply unit that shunts a charging current of the capacitor so that a charging current amount decreases .