JPH0487516A - Overcurrent protective method and ringing choke converter type switching power supply - Google Patents

Abstract

PURPOSE:To realize an appropriate overcurrent protection independent from power consumption in the secondary circuit by controlling a switching transistor according to the continuous ON time of the driving signal for switching devices such as the switching transistor or a MOSFET. CONSTITUTION:Upon increase of current flowing through a secondary circuit 6 outputting a +5V voltage, width of switching pulse induced in the winding 1 increases proportionally. Peak value of output voltages from integrating circuits 13, 14, 15 increases in proportion to the width of the switching pulse induced in the winding 1. When the overcurrent protective operation current of the secondary circuit 6 outputting +5V voltage is i2, peak value of the output voltages from the integrating circuits 13, 14, 15 is V2. A Zener diode 16 functions at that voltage V2 to turn a thyristor 17 ON and a transistor 18 short-circuits the base of a switching transistor 2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a ringing choke converter type switching power supply, and particularly relates to an overcurrent protection technique thereof.

[Prior Art] For example, as a conventional overcurrent protection technique for a multi-output ringing choke converter type switching power supply, an overcurrent protection circuit described in Japanese Patent Laid-Open No. 181628/1982 is known.

This circuit is provided with a monitoring means for monitoring the output voltage of a circuit other than the secondary circuit stabilized by the constant voltage circuit among the plurality of secondary circuits, and a stop means for stopping the operation of the switching transistor. It has become a
The monitoring means detects an overcurrent in the secondary circuit stabilized by the constant voltage circuit, and when the voltage exceeds a predetermined voltage value, the stopping means stops the operation of the switching transistor to protect the power source from overcurrent. It is something to do.

[Problem to be solved by the invention Wi] By the way, in the conventional multi-output ringing choke converter type switching power supply, the load on the secondary circuit that is not regulated to a constant voltage is not necessarily fixed, but varies depending on the usage conditions, etc. It may change. This variation is particularly noticeable when replacing equipment that receives power from this secondary circuit.

However, in the overcurrent protection circuit according to the prior art, an overcurrent in the secondary circuit stabilized by the constant voltage circuit causes the other two
Since this is intended to detect an increase in the output voltage in the secondary circuit, when the power consumption of the secondary circuit that attempts to detect the increase in output voltage is large, the Even though overcurrent is flowing in the secondary circuit, the output voltage of the secondary circuit that attempts to detect the increase in output voltage does not increase, resulting in a problem that the overcurrent protection circuit does not operate. .

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a ringing choke converter type switching power supply that can appropriately perform overcurrent protection without depending on the power consumption of the secondary side circuit.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides the following features:
The present invention provides an overcurrent protection method for a ringing choke converter type switching power supply, which is characterized by controlling the switching transistor.

Further, in order to achieve the above object, the present invention provides a ringing choke converter type switching power supply equipped with a constant voltage circuit that makes the secondary side circuit constant voltage, which monitors the switching pulse width of the switching transistor drive signal, a monitoring section that instructs to suppress the operation of the switching transistor when the continuous on time of the postal signal exceeds a predetermined value; and a suppressing means that suppresses the operation of the switching transistor in response to the instruction from the monitoring section. To provide a ringing choke converter type switching power supply characterized by the following features.

Note that in this ringing choke converter type switching power supply, the monitoring section includes an integrating circuit that integrates the switching transistor drive signal, and when the integrated value exceeds a predetermined value,
The suppressing means may be configured with a threshold circuit that instructs the suppressing means to suppress the operation of the switching transistor.

Alternatively, the monitoring unit may include a counter that counts the continuous on time of the switching transistor drive signal, and a counted value,
It may also be configured with a detection circuit that instructs the inhibiting means to inhibit the operation of the switching transistor when a predetermined value is exceeded.

Further, the inhibiting means may be a means for stopping the operation of the switching transistor by forcibly turning the switching transistor active signal into an OFF signal.

Alternatively, the suppressing means is also used as a constant voltage circuit. It is also possible to suppress the operation of the switching transistor by lowering the base current of the switching transistor.

Furthermore, a switching MO5FET may be used instead of the switching transistor.

[Function] According to the overcurrent protection method for a ringing choke converter type switching power supply according to the present invention, the continuous on time of the drive signal of the provided switching device, that is,
Since the switching device is controlled according to the energy given to the secondary circuit, overcurrent protection can be performed appropriately regardless of the power consumption of the secondary circuit.

Further, according to the ringing choke converter type switching power supply according to the present invention, the monitoring unit detects an overcurrent when the continuous on time of the switching transistor drive signal that gives energy to the secondary side circuit exceeds a predetermined value. Judge.

This refers to inhibiting the operation of the switching transistor, and the inhibiting means inhibits the operation of the switching transistor. Therefore, overcurrent protection can be performed appropriately regardless of the power consumption of the secondary circuit.

Further, at this time, the monitoring unit includes an integrating circuit that integrates the switching transistor drive signal and a threshold circuit that instructs the inhibiting means to inhibit the operation of the switching transistor when the integrated value exceeds a predetermined value. With this structure, the monitoring section can be realized with a simple circuit.

Further, the monitoring unit is a counter that counts continuous ON time of the switching transistor drive signal.

If the detection circuit is configured to include a detection circuit that instructs the inhibiting means to inhibit the operation of the switching transistor when the counted value exceeds a predetermined value, more accurate control can be performed.

Further, if the inhibiting means is a means for stopping the operation of the switching transistor by forcibly turning the switching transistor drive signal into an OFF signal, reliable overcurrent protection can be achieved.

For example, sensitive devices such as information processing devices can be protected from overcurrent.

Furthermore, if the suppressing means is a means for suppressing the operation of the switching transistor by lowering the base current of the switching transistor, which is shared with the constant voltage circuit, the circuit can be simplified, and the flexible Can perform current protection operation.

Note that instead of the switching transistor.

The same holds true even when switching MOSFETs are used.

[Example] Hereinafter, a first example of the overcurrent protection circuit according to the present invention will be described.

FIG. 1 shows a multi-output ringing choke converter type switching power supply circuit according to the first embodiment.

In the figure, 1 is the primary winding, 2 is a switching transistor, 5 is a switching transformer, 6 is a secondary side circuit that outputs +5V whose output voltage is stabilized by constant voltage circuits 3 and 4, and 7 is a stabilized output voltage. It is a secondary side circuit that outputs +12V, and is the main part of the Honda ringing choke converter type switching power supply circuit. Note that the winding direction of each winding wire is indicated by a mark in Figure 1.

3.4 is a constant voltage circuit, which controls the switching transistor 2 so as to keep the voltage of the secondary circuit 6 constant.

The monitoring unit 8 includes integration circuits 13, 14, 15, . It is composed of a Zener diode 16 that operates when the peak value of the output voltage of the integrating circuit 13, 14, 15 exceeds a predetermined value.

The stop means 9.18 is constituted by a stop part 9 and a transistor 18 which short-circuits the base of the switching transistor 2 when the thyristor 17 of the stop part 9 is turned on.

The thyristor 17 is turned on when the Zener diode 16 operates.

Diodes 11 and 12 are coupling capacitors 10
An appropriate DC bias voltage is applied to the pulse voltage generated in the winding 11A1 obtained through the winding 19 based on the power from the winding 19. The pulsed voltage to which a DC bias voltage has been applied is supplied to an integrating circuit 13, 14, 15.

The overcurrent protection operation will be explained below.

In FIG. 1, when the current flowing through the secondary circuit 6 that outputs +5V increases, the width of the switching pulse generated in the winding 1 increases in proportion to this current.

This is because the switching transistor 2 is energized for a long time in order to keep the output voltage of the secondary side circuit 6 which outputs +5V constant by the operation of the constant voltage circuit 3.4.

As a result, the peak value of the output voltage of the integrating circuit 13, 14, 15 increases in proportion to the width of the switching pulse generated in the winding 1.

That is, as shown in FIG. 2, the horizontal axis represents the current of the secondary circuit 6 that outputs +5V, and the vertical axis represents the current of the integrator circuits 13, 14, .
When the peak value of the output voltage of 15 is taken, as the current of the secondary side circuit 6 which outputs +5V increases, the integration circuit 13
．． The peak value of the output voltage of 14.15 increases.

Therefore, if the maximum rated current value of the secondary side circuit that outputs +5V is i□, and the peak value of the output voltage of the integrating circuit 13, 14, and 15 is V, then the secondary side circuit that outputs +5■ If the overcurrent protection operating current value of No. 6 is 12, the peak value of the output voltage of the integrating circuits 13, 14, and 15 will be v2.

Zener diode 16 operates at this voltage v2 and turns on thyristor 17.

By turning on the thyristor 17, the transistor 1
8 shorts the base of switching transistor 2.

Therefore, the switching transistor 2 stops operating and stops sending energy to the secondary circuit 6.7, thereby being protected from overcurrent.

By the way, the resistor and capacitor in the detection section 9 are provided to give a delay to the gate signal of the thyristor 17 so that the switching transistor 2 can start without any trouble when starting up the power supply circuit.

In addition, according to this circuit, since an appropriate DC bias voltage is added to the switching pulse voltage generated in the winding 1 by the coupling capacitor 10 and the diodes 11 and 12, this is achieved regardless of the Zener voltage of the Zener diode 16. can do.

Furthermore, by using diodes, such as the Zener diode 16 and the thyristor 17, which have temperature characteristics that compensate for temperature fluctuations, as the diodes 11 and 12, it is possible to eliminate operational fluctuations due to temperature increases in the circuit.

Further, by adjusting the variable resistor 14 of the integrating circuits 13, 14, 15, it is possible to absorb variations in the operating point of the overcurrent protection circuit caused by manufacturing variations in the Zener diode 16, the switching transformer 5, etc.

Next, a second embodiment of the overcurrent protection circuit according to the present invention will be described.

FIG. 3 shows a multi-output culling chain converter type switching power supply circuit according to a second embodiment.

As shown in the figure, the power supply circuit according to the second embodiment has a configuration in which a switching MOSFET 23 is used in place of the switching transistor 2 in the power supply circuit according to the first embodiment.

Furthermore, when the stop unit 9 and the thyristor 17 are turned on, the stop means 9.18 in the first embodiment is switched on.
It is composed of a resistor 24 and a diode 25 that stop the operation of the OSFET 23.

Even with such a configuration, the same effects as in the first embodiment can be obtained.

Next, a third embodiment of the overcurrent protection circuit according to the present invention will be described.

FIG. 4 shows a multi-output ringing choke converter type switching power supply circuit according to the third embodiment.

As shown in the figure, in the power supply circuit according to the present embodiment, the monitoring unit 8 converts the level of the pulse voltage generated in the winding 1, and during the ON period of the switching transistor, the signal level p
A signal level converter 26 (see FIG. 5) that outputs "pH" to the reset terminal of the counter 20. A counter 20 that counts the number of clocks from the oscillator 21 input within the t1 period of the pulse voltage generated in the winding 1. , an oscillator 2 that oscillates a clock having a period sufficiently smaller than the period of the pulse voltage.
1 and a detector 22 that detects when the count output from the counter 20 reaches a predetermined value and outputs a signal to the stop section 9.

The other configurations are the same as the power supply circuit according to the first embodiment (see FIG. 1).

The operation will be explained below.

In FIG. 4, when the current flowing through the secondary circuit 6 that outputs +5V increases, as described above.

The switching pulse width generated in the winding 1 increases in proportion to this current.

Therefore, the t1 period of the specific power of the signal level converter 26 input to the reset terminal of the counter 20 is extended, and the operating time of the counter 20 is also lengthened, so that the maximum value counted by the counter 20 is also increased.

That is, as shown in FIG. 6, the horizontal axis represents the current of the secondary circuit 6 that outputs +5V, and the vertical axis represents the number of clock counts of the counter 20, and the maximum rating of the secondary circuit 6 that outputs +5V is calculated. When the current is i, and the count number of the counter 20 is m.

If the overcurrent protection operation of the secondary side circuit 6 that outputs +5V and the current value is 12, the count number of the counter 20 will be n.

Here, the detector 22 detects that the output of the counter 20 has reached n, and turns on the thyristor 17.

This stops the operation of the switching transistor 2 and stops sending energy to the secondary circuit 6.7.

As described above, in the third embodiment, since the switching pulse width generated in the winding 1 is monitored using a clock with a small period, the accuracy can be improved by using a highly accurate and stable oscillator 21. A highly stable overcurrent protection circuit can be realized.

In the third embodiment, the t1 period of the output of the signal level converter 26 is monitored, but a pulse signal corresponding to the rise of the pulse voltage shown in FIG. 7 is generated from the output of the signal level converter 26, and By inputting this to the reset terminal of the counter 20, the signal level converter 26 output 11+1. The length of the period -Δt may also be monitored. That is, when the current flowing through the secondary circuit 6 that outputs +5V increases, the pulse width t becomes the pulse period t.
This is because it increases with □+t2.

In addition, in the third embodiment, as shown in the second embodiment, a switching MOSFET 23 is used instead of the switching transistor 2, or the stop means is constituted by a stop section 9, a resistor 24, and a diode 25. (See Figure 3).

Alternatively, the stopping means may be omitted and the switching pulse width control function provided in the constant voltage circuit 3 may be used. In other words, the detector 22 notifies the constant voltage circuit 3 of the detection result. In response to this notification, the constant voltage circuit 3 may suppress the ON time of the switch transistor in the same manner as in the case where the overvoltage notification is received from the constant voltage circuit 4.

Furthermore, each of the above embodiments has been explained using a multi-output ringing choke converter type switching power supply circuit as an example.
This can be achieved in the same way with one output instead of the Taro power.

As described above, according to each of the embodiments, the energy given to the regulated secondary circuit is monitored based on the pulse width of the immobility signal of the switching transformer, and thereby overcurrent is detected. , the overcurrent protection operation can be performed appropriately regardless of the power consumption of the secondary side @path.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a ringing choke converter type switching power supply that can appropriately perform overcurrent protection regardless of the power consumption of the secondary circuit.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of a multi-output ringing choke converter type switching power supply according to the first embodiment of the present invention, and FIG. 2 is an explanatory diagram showing the operating principle of the overcurrent protection circuit according to the first embodiment. FIG. 3 is a circuit diagram showing the configuration of a multi-output ringing choke converter type switching power supply according to a second embodiment of the present invention, and FIG. 4 is a circuit diagram showing the configuration of a multi-output ringing choke converter type switching power supply according to a third embodiment of the present invention. The circuit diagrams showing the configuration, FIGS. 5, 6, and 7 are explanatory diagrams showing the operation of the overcurrent protection circuit according to the third embodiment. 2... Switching transistor, 3.4... Constant voltage circuit, 5... Switching transformer, 6, 7...
Secondary side circuit, 8... Monitoring section, 9... Stopping section, 17.
...Thyristor, 18...Transistor, 23...
Switching MO5FET. Applicant: Hitachi, Ltd. (and 1 other person)

Claims (1)

[Claims] 1. An overcurrent protection method for a ringing choke converter type switching power supply, which comprises controlling a switching device according to the continuous ON time of a drive signal for the switching device provided. 2. A ringing choke converter type switching power supply equipped with a constant voltage circuit that makes the secondary side circuit constant voltage, which monitors the switching pulse width of the switching transistor drive signal and maintains the continuous on time of the drive signal to a predetermined value. A ringing choke converter type switching device comprising: a monitoring section that instructs to suppress the operation of the switching transistor when the voltage exceeds the limit; and a suppressing means that suppresses the operation of the switching transistor in accordance with the instruction from the monitoring section. power supply. 3. The ringing choke converter type switching power supply according to claim 2, wherein the monitoring section includes an integrating circuit that integrates the switching transistor drive signal, and a switching transistor that acts as the inhibiting means when the integrated value exceeds a predetermined value. A ringing choke converter type switching power supply comprising a threshold circuit that instructs to suppress the operation of the ringing choke converter. 4. The ringing choke converter type switching power supply according to claim 2, wherein the monitoring unit includes a counter that counts the continuous ON time of the switching transistor drive signal, and a counter that counts the continuous ON time of the switching transistor drive signal, and a counter that counts the continuous ON time of the switching transistor drive signal, and A ringing choke converter type switching power supply, comprising a detection circuit that instructs the means to suppress the operation of a switching transistor. 5. The ringing choke converter type switching power supply according to claim 2, 3 or 4, wherein the inhibiting means is means for stopping the operation of the switching transistor by forcibly turning off the switching transistor drive signal. A ringing choke converter type switching power supply characterized by: 6. The ringing choke converter type switching power supply according to claim 2, 3 or 4, wherein the suppressing means suppresses the operation of the switching transistor by lowering the base current of the switching transistor, which is shared with the constant voltage circuit. A ringing choke converter type switching power supply characterized in that: 7. The ringing choke converter type switching power supply according to claim 2, 3, 4, 5 or 6, characterized in that a switching MOSFET is used in place of the switching transistor.