JPH04138020A - Switching power supply circuit - Google Patents

Abstract

PURPOSE:To suppress the output voltage at abnormality within the allowable operation voltage of an IC element so as to protect an external load device by equipping it with an output terminal, which outputs DC output voltage, an output voltage monitoring means, which monitors the DC output voltage, and a voltage rise suppressing means. CONSTITUTION:With a solid line 35, if the output voltage rises abnormally at a time to and reaches clamp voltage Vc, a level clamp circuit 31 absorbs the output current of a power source and starts the operation to maintain the output voltage to the clamp voltage, and also sends out a clamp start signal 33 to a timing circuit 32. The timing circuit 32 starts the output of a timing circuit output voltage 39, and the output voltage is increased rectilinearly with the passage of the time until it is restored to the stationary output voltage V0. With a solid line 37, the rise of the timing circuit output voltage 39 stops at a time t1, and in case that the voltage value is below the threshold VTH corresponding to the tolerance TDET of the preset abnormality voltage duration, the output voltage recovers to the stationary output voltage V0.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a switching power supply, and more particularly to a switching power supply circuit having a protection function of detecting overvoltage and stopping the circuit.

[Conventional technology]

In recent years, so-called switching power supplies have been frequently used as power supplies for electronic devices. This switching power supply is usually provided with an overvoltage detection circuit as a protection circuit, and when an overvoltage output is detected, the switching operation is stopped to protect the load device from destruction or malfunction.

FIG. 3 shows a conventional switching power supply circuit. This circuit is provided with a transformer 11 that converts voltage at a predetermined ratio, the primary side of which is connected to an input power source 13 via a high speed switch 12. The high-speed switch 12 is configured to switch the voltage applied from the input power source 13 to the primary side of the transformer 11 at high speed under the control of a control circuit 15 connected to the alarm circuit 14.

On the other hand, on the secondary side of the transformer 110, there is a rectifier diode 16.
A rectifier circuit consisting of a rectifier diode 17 is connected, and a choke coil 18 and a capacitor 19 are connected to both ends of the rectifier diode 17.
A smoothing circuit consisting of is connected. This capacitor 1
A predetermined rectified and smoothed steady voltage is output from both ends of the power supply 9 and applied to the load 21 . Further, an overvoltage detection circuit 22 and a voltage control circuit 23 are connected to this circuit in parallel with the load 21, and the output sides of each are connected to an alarm circuit 14 and a control circuit 15.

The operation of the conventional switching power supply circuit having the above configuration will be explained with reference to FIG.

The secondary voltage converted by the transformer 11 is rectified and smoothed by a rectifier circuit and a smoothing circuit, and appears at both ends of the capacitor 19 as an output voltage. The voltage control circuit 23 monitors the voltage across the capacitor 19, and performs footnoic control on the control circuit 15 so that the voltage is maintained at a predetermined steady output voltage V0.

Here, as shown by a broken line 25 in FIG. 4(a), the output voltage starts to abnormally rise at time t0 due to some circuit abnormality, and the overvoltage detection voltage V is reached at time t1. Suppose it exceeds C. The overvoltage detection circuit 22 detects this and sends a detection signal 27 to the alarm circuit 14. Upon receiving this, the alarm circuit 14 sends the control circuit 1 to the control circuit 1, as shown by the broken line in FIG.
The alarm signal 28 for 5 is changed from the 71 level to the low level. As a result, the control circuit 15 can immediately stop driving the high-speed switch 12 and protect the load 21 from abnormal voltage.

On the other hand, as shown by the solid line 26 in FIG. 2(a), the overvoltage detection voltage V. In the case of a temporary abnormality that does not reach C, the abnormality is not detected and the alarm signal 28 is held at a high level as shown by the solid line in FIG.

[Problem to be solved by the invention]

In this way, in the conventional switching power supply circuit, the overvoltage detection voltage V. When C was detected, the power was immediately shut off. Therefore, from the viewpoint of preventing malfunction, it is necessary to have sufficient noise margin and level margin, so the overvoltage detection voltage V. C is 120% of the steady output voltage V0
It was set to a certain extent. For example, the steady output voltage V. is 5
In case of V, overvoltage detection voltage V. . is set to about 6V, so if the abnormal output voltage is less than this value, it will not be detected and the output will continue.

On the other hand, ICs used in electronic devices as external loads (
The allowable operating voltage of an integrated circuit (integrated circuit) element is usually plus or minus 5%, and the upper limit is 5.25V for a rated voltage of 5V. Therefore, conventionally, a voltage higher than this permissible voltage may be applied to these ICs, which may cause erroneous signal transmission or
There is a drawback that malfunction or destructive operation such as latch-up may occur.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a switching power supply circuit that can protect an external load device by suppressing the output voltage during an abnormality to within the allowable operating voltage of an IC element.

[Means to solve the problem]

The invention according to claim 1 provides: (i) an output terminal that outputs a DC output voltage created and shaped by a power conversion transformer, a high-speed switch, a rectifier circuit, and a smoothing circuit; an output voltage monitoring means for monitoring a DC output voltage; and (iii) when the output voltage monitoring means detects a threshold voltage set slightly higher than the steady output voltage, absorbs the output current to suppress a voltage rise. The switching power supply circuit is provided with a voltage rise suppressing means.

In the invention according to claim 1, when the output voltage output from the output terminal of the switching power supply circuit reaches a threshold voltage slightly higher than the steady output voltage, the output current is absorbed and the voltage is increased beyond that level. shall be suppressed.

In the invention according to claim 2, (i) a high-speed switch that switches at high speed the voltage applied to the primary side of a power conversion transformer that converts power at a predetermined power ratio; and (ii) a secondary switch of the power conversion transformer. (m) A voltage shaping circuit that rectifies, smoothes, and shapes the voltage output from the side, and (m) when the output voltage shaped by this voltage shaping circuit exceeds a certain voltage set slightly higher than the steady output voltage. , a level clamp circuit that absorbs the output current and suppresses the rise in voltage level, (lv) a measurement circuit that measures the continuous operation time of this level clamp circuit, and (v) a level clamp circuit that this measurement circuit measures. The switching power supply circuit is provided with a switching stop means for stopping the switching operation of the high-speed switch when the continuous operation time reaches a predetermined time.

In the invention as claimed in claim 2, when the output voltage exceeds a certain voltage, the output voltage suppression operation by the level clamp circuit is started, and when this operation continues for a predetermined period of time, the switching operation of the high-speed switch is stopped. That's it.

〔Example〕

The present invention will be described in detail with reference to Examples below.

FIG. 1 shows a switching power supply circuit in one embodiment of the present invention. In this figure, the conventional example (Fig. 3)
The same parts are given the same reference numerals, and the explanation will be omitted as appropriate.

This switching power supply circuit is provided with a level clamp circuit 31 instead of the overvoltage detection circuit 220 in FIG.
Its output is connected to the alarm circuit 14 via a timing circuit 32.

The other configurations are the same as in FIG. 3.

The operation of the switching power supply circuit configured as above will be explained with reference to FIG. The normal operation of this circuit is the same as that of the conventional example. That is, the secondary voltage converted by the transformer 11 is rectified and smoothed by a rectifier circuit and a smoothing circuit, and appears as an output voltage across the capacitor 19. The voltage control circuit 23 monitors the voltage across the capacitor 19, and performs feedback control on the control circuit 15 so that the voltage is maintained at a predetermined steady output voltage v0.

Here, as shown by the solid line 35 in FIG. 2(a), when the output voltage abnormally increases at time t0 and reaches the clamp voltage Ve due to some circuit abnormality, the level clamp circuit 31
absorbs the output current of the power supply and clamps the output voltage to V
At the same time, a clamp start signal 33 is sent to the timing circuit 32. Upon receiving this, the timing circuit 32 outputs a timing circuit output voltage 39
(b in the same figure) starts outputting, and then the output voltage (a in the same figure)
is the steady output voltage V. increase linearly over time until it returns to . As shown by a solid line 37 in FIG. 2(b), the rise in the timing circuit output voltage 39 stops at time tl, and the voltage value at this time is a threshold value corresponding to a preset allowable value TDET of abnormal voltage duration. vT,! In the following cases, the output voltage is the steady output voltage V. to return to.

Therefore, the alarm signal 28 is kept at a high level, as shown by the solid line in FIG. 2C, and the circuit is not stopped.

On the other hand, when the timing circuit output voltage 39 reaches the threshold value VTH at time t2, as shown by the broken line 38 in FIG. 2(B), the alarm circuit 14 detects this and , a cell that changes the alarm signal 28 from high level to low level.

As a result, the control circuit 15 stops driving the high-speed switch 12 and turns off the output, thereby protecting the load 21 from abnormal voltage.

In this way, in this embodiment, since the noise margin is not taken into consideration, the value of the clamp voltage VC as the protection voltage can be set to a small value, for example, about 105 to 110% of the steady output voltage V0. Therefore, there is no risk of causing troubles such as erroneous signal transmission, malfunction, or latch-up to the load 21. Further, by setting the allowable time T''n!t for continuous operation of the level clamp circuit 31 to be as short as necessary, excessive power consumption can be suppressed.

〔Effect of the invention〕

As explained above, according to the invention set forth in claim 1, when the output voltage reaches the threshold voltage, the output current is absorbed to suppress the voltage rise. Therefore, there is no need to set the threshold voltage to a large value, and the threshold voltage as a protection voltage can be set below the allowable voltage required by the external load. Therefore, there is an effect that abnormal voltage and external noise can be cut and stable power supply can be performed without adversely affecting the load equipment such as malfunction or destruction of the IC due to the application of a voltage higher than the allowable voltage.

Further, according to the second aspect of the invention, the switching operation of the high-speed switch is stopped when the output voltage suppression operation by the level clamp circuit continues for a predetermined period of time. By setting this, the amount of heat generated due to excess power consumption can be minimized, and the effect is that it is possible to configure a small, high-power power source.

[Brief explanation of the drawing]

1 and 2 are for explaining one embodiment of the present invention, of which FIG. 1 is a block diagram showing a switching power supply circuit, and FIG. 2 is a block diagram for explaining the operation of the switching power supply circuit. FIG. 3 is a block diagram showing a conventional switching power supply circuit, and FIG. 4 is a timing diagram for explaining the operation of the conventional switching power supply circuit. 11...Transformer, 12...High speed switch, 13...Input power supply, 14...Alarm circuit, 15...
・Control circuit, 23... Voltage control circuit, 31... Level clamp circuit, 39...
・Timing circuit.

Claims (1)

[Claims] 1. An output terminal that outputs a DC output voltage created and shaped by a power conversion transformer, a high-speed switch, a rectifier circuit, and a smoothing circuit, and a monitor that monitors the DC output voltage output from this output terminal. The present invention includes an output voltage monitoring means, and a voltage rise suppressing means for absorbing an output current and suppressing a voltage rise when the output voltage monitoring means detects a threshold voltage set slightly higher than a steady output voltage. A switching power supply circuit featuring: 2. A high-speed switch that rapidly switches the voltage applied to the primary side of a power conversion transformer that converts power at a predetermined power ratio, and a high-speed switch that rectifies and smoothes the voltage output from the secondary side of the power conversion transformer. When the output voltage shaped by this voltage shaping circuit exceeds a certain voltage set slightly higher than the steady output voltage, it absorbs the output current and suppresses the rise in voltage level. a level clamp circuit that measures the continuous operation time of the level clamp circuit; a measurement circuit that measures the continuous operation time of the level clamp circuit; and a measurement circuit that stops the switching operation of the high-speed switch when the continuous operation time of the level clamp circuit measured by this measurement circuit reaches a predetermined time. A switching power supply circuit comprising switching stop means.