JPH08205532A - Transformer coupling switching power supply device - Google Patents

Abstract

PURPOSE: To lighten the voltage stress of each constituent element, a stabilizer circuit and a load and to prevent the quick deterioration and the burning thereof by forcedly lowering a secondary d.c. power supply voltage to a shelter voltage which is lower than the setting detection overvoltage value of an overvoltage detection element when an overvoltage protection circuit once operates. CONSTITUTION: An overvoltage detection element constituting an overvoltage protection circuit 50 is formed of a plurality of voltage detection elements ZD1, ZD2 connected in series to a secondary d.c. power supply circuit 30 and at the same time a element changeover means for changing over so that a secondary d.c. power supply voltage V2 can be forcedly lowered to a safe voltage which is lower than a setting detection overvoltage by apparently shorting one or more predetermined voltage detection elements (ZD2) on condition that the overvoltage which is higher than a setting detection overvoltage is detected in cooperation with the plurality of voltage detection elements ZD1, ZD2 is provided.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a primary DC power supply circuit and a secondary DC power supply circuit.
The present invention relates to a transformer-coupled switching power supply device which is connected and coupled to a next DC power supply circuit via a transformer and has an overvoltage protection function.

[0002]

2. Description of the Related Art In FIG. 5, a primary DC power supply circuit 10 and a secondary DC power supply circuit 30 are connected and coupled via a transformer 20. The primary DC power supply circuit 10 is an AC power supply 1
1, power switch 12, noise filter 13, rectifier circuit 14, smoothing capacitor C10, switching element 1
5, the switching element 15 is formed including the voltage control element 40, and the switching element 15 includes the primary winding L11 of the transformer 20 and the rectifier circuit 14.
Is connected to the negative electrode circuit Ln. 18 is a current limiting resistor. Further, the control power source (voltage Vc) is the auxiliary winding L
12 is generated, oscillation is generated through the diode D10, and is supplied through the resistor R10.

The secondary DC power supply circuit 30 includes a diode D21 connected to the secondary winding L21 of the transformer 20,
The load 1 is formed by including smoothing capacitors C21 and C22.
00 is connected. A stabilizing circuit 45 inputs a voltage detection signal F for generating and outputting the feedback signal f to a photocoupler (feedback signal generating circuit) 46.

Thus, in such an RCC type self-oscillation type (frequency fluctuation type) transformer coupling type switching power supply device, the voltage control element (transistor) 40 is turned on / off by the feedback signal f based on the voltage detection signal F. Thus, the power energy is supplied from the primary winding L11 to the secondary winding L21 while ON / OFF controlling the switching element 15 using the control power supply (Vc). In the secondary DC power supply circuit 30, the secondary DC power supply V2 is rectified by the diode D21 and smoothed by the smoothing capacitors C21 and C22.
Is generated and supplied to the load 100. The fluctuation of the load 100 is regarded as a fluctuation of the secondary DC power supply voltage V2, and the stabilization circuit 45
And is output to the feedback signal generation circuit (46). As a result, the secondary DC power supply voltage V2 is stabilized.

Therefore, when the load 100 is light,
The current I flowing through the switching element 15 decreases and the oscillation frequency increases. On the other hand, when the load 100 becomes heavy, the current I flowing through the switching element 15 increases and the oscillation frequency decreases. Switching element 1 by voltage control element 40
This is because the ON duty of 5 is constant.

By the way, the secondary DC power supply voltage V2 may become an overvoltage due to a large fluctuation of the load 100 or a failure of the stabilizing circuit 45. If this is left unattended, each component (D21, C21, C22, etc.), stabilizing circuit 45
Or the load 100 is overheated or burned.

Therefore, an overvoltage protection circuit 50 including an overvoltage detection circuit 51 (overvoltage detection element ZD51, resistor R51) and a photocoupler 52 is provided. Overvoltage detection element Z
D51 is composed of a Zener diode, and selectively sets the setting detection overvoltage value to, for example, 25 to 27V with respect to the secondary DC power supply voltage V2 (for example, 24V) at the time of steady load.

Therefore, as shown in FIG. 6, when the overvoltage detection element ZD51 detects that the overvoltage exceeds the set detection overvoltage value, the overvoltage detection signal P is sent to the photocoupler 52.
To enter. Then, the photocoupler 52 generates and outputs an overvoltage protection signal p that is substantially the same as the overvoltage detection signal P,
The overvoltage protection element 53 provided on the primary DC power supply circuit 10 side is turned on. That is, part of the current Ib flowing into the switching element 15 is dropped to the negative electrode circuit Ln side to start the overvoltage protection operation.

Therefore, even if the voltage control by the voltage control element 40 is prioritized and the stabilization circuit 45 fails or the voltage control by the voltage control element 40 becomes impossible, the primary side (1
Since the amount of power supply energy from 0) to the secondary side (30) can be attenuated, it is possible to prevent the secondary DC power supply voltage V2 from rising to an overvoltage that is equal to or higher than the set detection overvoltage value. This also serves as overcurrent protection on the primary DC power supply circuit 10 side.

[0010]

As described above, the overvoltage protection circuit 50 sets the secondary DC power supply voltage V2 to the set detection overvoltage value (25 to 27V) of the overvoltage detection circuit 51 (ZD51).
It is intended to protect the overvoltage by suppressing the runaway rise. In other words, the overvoltage protection circuit 50 [5
1 (ZD51, R51), 52] is performing the overvoltage protection operation, the secondary DC power supply voltage V2 is equal to the rated voltage value (24
V) or higher. Therefore, the voltage stress of each component (D21, C21, C22, etc.), the stabilization circuit 45, the control circuit forming the load 100, and the like is high, which causes rapid deterioration and burnout.

However, when the overvoltage protection circuit 50 once operates, it is difficult to adopt, for example, a configuration in which the power switch 12 is automatically and forcibly turned off because it causes a significant cost increase.

It is an object of the present invention to, once the overvoltage protection circuit operates, forcibly reduce the secondary DC power supply voltage to a save voltage lower than the set detection overvoltage value of the overvoltage detection element,
An object of the present invention is to provide a transformer-coupled switching power supply device that can reduce the voltage stress of each component, the stabilizing circuit, and the load and prevent its rapid deterioration and burnout.

[0013]

According to the present invention, a primary DC power supply circuit including a rectifying circuit, a smoothing capacitor, a switching element and a voltage control element, and a secondary DC power supply circuit including a stabilizing circuit are provided via a transformer. Overvoltage provided on the side of the secondary DC power supply circuit, which is connected and coupled to form a secondary DC power supply by ON / OFF controlling the switching element while applying a feedback signal from the stabilizing circuit to the voltage control element. A switching element is turned on by turning on the overvoltage protection element connected in parallel with the voltage control element on the primary DC power supply circuit side using the overvoltage detection signal that is output when the detection element detects an overvoltage greater than the set detection overvoltage value. In a transformer-coupled switching power supply device having an overvoltage protection circuit formed to be capable of overvoltage protection by attenuating a current flowing into The overvoltage detection element is formed of a plurality of voltage detection elements connected in series to the secondary DC power supply circuit, and it is necessary that the overvoltage of the set detection overvoltage value or more is detected by cooperation of the plurality of voltage detection elements. In addition, there is provided an element switching means for apparently shorting one or more predetermined voltage detection elements to switch the secondary DC power supply voltage to a retract voltage lower than the set detection overvoltage value forcibly. To do.

[0014]

According to the present invention having the above-mentioned structure, when the value of the secondary DC power supply voltage becomes higher than the set detection overvoltage value of the overvoltage protection circuit due to a sudden load change, a failure of the stabilizing circuit, or the like, a plurality of voltages connected in series are provided. The detection elements cooperate to detect this and output an overvoltage detection signal. Then, the overvoltage protection element is turned on to start the overvoltage protection operation of attenuating the current flowing into the switching element. Simultaneously with this, on condition that the overvoltage detection operation is performed, the element switching means switches so as to apparently short-circuit one or more predetermined voltage detection elements.

Then, the level of the overvoltage detection signal rises to further accelerate the damping action of the current flowing into the switching element. Therefore, since the secondary DC power supply voltage droops rapidly to a retract voltage lower than the set detection overvoltage value of the overvoltage detection element, the overvoltage detection operation of the overvoltage detection element stops, but the voltage detection elements other than the apparently shorted voltage detection element are stopped. The operation of detecting the retracted voltage of the remaining voltage detecting element is effective. That is,
Even after the overvoltage detection operation is disabled, an apparent overvoltage detection signal based on the escape voltage detection can be output and held.

Therefore, the secondary DC power supply voltage is clamped to a voltage value equal to or lower than the save voltage value lower than the set detection overvoltage value. Therefore, it is possible to reduce the voltage stress of the stabilizing circuit on the secondary side, each component, and the like, and to prevent their rapid deterioration and burnout.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) As shown in FIG. 1, the present transformer coupling type switching power supply device has the same basic configuration as that of the conventional example (FIG. 5), but the overvoltage detection circuit constituting the overvoltage protection circuit 50 is detected. An element is formed from a plurality (two) of voltage detection elements ZD1 and ZD2 connected in series, and an element switching means 60 is provided, and an overvoltage more than a set detection overvoltage is once detected by the cooperation of the voltage detection elements ZD1 and ZD2. In this case, even if the predetermined voltage detection element ZD2 is apparently short-circuited and the overvoltage detection operation is disabled, the secondary DC power supply voltage V2 is set to the set detection overvoltage value (for example, 2
It is configured so that it can be clamped to a voltage value that is lower than the withdrawal voltage value (for example, 10 V) lower than 7 V.

The same parts as those in the conventional example (FIG. 5) are designated by the same reference numerals, and the description thereof will be simplified or omitted.

In FIG. 1, the overvoltage detecting element which constitutes the overvoltage detecting circuit 51 together with the resistor R51 is formed of a plurality (two) of voltage detecting elements (Zener diodes) ZD1 and ZD2 connected in series. In the case of the conventional example (FIG. 5), the limit voltage of one overvoltage detection element (zener diode) ZD51 is set to be equal to the set detection overvoltage value, for example, 27 V, whereas in the case of this embodiment, the voltage detection element ZD1. Is 10 V and the limit voltage of the voltage detection element ZD2 is 17 V.

Therefore, both voltage detecting elements ZD1 and ZD
By the cooperation of 2 and the resistor R51, it is possible to detect the overvoltage of the set detection overvoltage value (27V) or more and to output the overvoltage detection signal P. Here, if one or more voltage detection elements ZD2 are apparently short-circuited, the remaining voltage detection element ZD1 and the resistor R51 cooperate with each other to cause an apparent overvoltage detection signal P with a voltage value equal to or higher than the save voltage (10V). Can be output.

The element switching means is a magnetic force operation switch 62.
And a switching element (transistor) 61 whose collector is connected to its coil 62C and whose base is connected to the upstream side of the resistor R51.

Therefore, the two voltage detecting elements ZD1,
When the detection voltage Vd corresponding to the set detection overvoltage value (27V) is detected by the cooperation of ZD2, the transistor (61).
Turns on and excites the coil 62C, so switch 62
When S is turned on, a zener diode (Z
D2) can be apparently short-circuited.

To turn off the transistor (61), the power switch 12 may be turned off once.

In the first embodiment having such a configuration, the stabilized secondary DC power supply voltage V2 at the time of steady load is stabilized and controlled to, for example, 24V as shown in FIG. In addition,
When the load 100 is light, the oscillation frequency on the primary side is high, and when the load 100 is heavy, the oscillation control is performed at a low oscillation frequency.

Here, when the value of the secondary DC power supply voltage V2 becomes equal to or higher than the set detection overvoltage value (27V) due to the failure of the stabilizing circuit 45 or the sudden change or short circuit of the load 100, the overvoltage protection circuit 50 operates. That is, the two voltage detection elements ZD1 and ZD1 forming the overvoltage detection element
Since D2 cooperates to perform the overvoltage detection operation (ON), a part of the overvoltage detection signal (current) P flows through the resistor R51. Therefore, since the detection signal Vd, that is, the base voltage rises and the transistor 6L is turned on, the overvoltage protection signal p is generated and output from the photocoupler 52 forming the overvoltage protection circuit 50 to the overvoltage protection element 53.

Then, the overvoltage protection element 53 is turned on, and part of the current Ib flowing into the switching element 15 is dropped into the negative electrode circuit Ln. Therefore, the primary side (10)
From the secondary side (30) is reduced, the secondary DC power supply voltage V2 is set to the set detection overvoltage value (27
V).

When the transistor (61) is turned on, the coil 62C turns on the switch 62S. That is, the element switching means 60 operates and one voltage detection element ZD
Apparently make 2 short. Therefore, the detection signal Vd
, The apparent overvoltage detection signal (current) P flowing to the photocoupler 52 through the transistor (61) increases by the voltage difference (17V = 27-10).

Therefore, the overvoltage protection element 53 increases the amount of current (Ib) dropped in the negative electrode circuit Ln, so that the electric power energy supplied through the transformer 20 is extremely reduced. That is, the secondary DC power supply voltage V2 can be rapidly reduced. The settling point is equal to or lower than the save voltage value (10 V) corresponding to the limit voltage (10 V) of the voltage detection element ZD1.

Therefore, the stabilizing circuit 45, each component (D
(21, C21, C22, etc.) and the voltage stress of the control circuit forming the load 100 can be minimized, and their rapid deterioration and burnout can be reliably prevented.

According to the first embodiment, however, the overvoltage detecting element is formed by the plurality of voltage detecting elements ZD1 and ZD2 connected in series to the secondary DC power supply circuit 30, and the element switching means 60 is provided. Overvoltage detection element (ZD
1, ZD2) once performs an overvoltage detection operation, a predetermined voltage detection element (ZD2) is apparently short-circuited to switch to the voltage forced drop operation state, and even if the overvoltage detection operation is disabled, the secondary Since the DC power supply voltage V2 can be clamped to a voltage value that is lower than the set detection overvoltage value (for example, 27V) and is equal to or lower than the save voltage value (for example, 10V), the stabilizing circuit 45 and each component (D2).
1, C21, C22, etc.) and the voltage stress of the control circuit forming the load 100, etc. can be minimized, and their rapid deterioration and burnout can be reliably prevented.

The element switching means 60 includes one magnetic force operation switch 62 and one switching element (transistor) 61.
Since it is formed from, the structure is simple and the cost is low. Therefore, for example, the power switch 12 on the side of the primary DC power supply circuit 10 is automatically forced by the overvoltage detection and O
It is easy to implement and highly practical with respect to measures such as FF.

(Second Embodiment) In the second embodiment, as shown in FIG. 3, the element switching means 60 includes two transistors 63 and 6.
4 and a resistor R65.

Therefore, in the case of the second embodiment, the same operational effect as in the case of the first embodiment can be obtained, and
Furthermore, cost reduction can be achieved and stable operation for a long period can be guaranteed.

(Third Embodiment) This third embodiment is shown in FIG. The overvoltage detection element is composed of four voltage detection elements ZD1.
To ZD4 and three element switching means 60
A to 60C and which element switching means 60A to 60C
A selection means 70 for selecting whether to use is provided.

The limit voltage of each of the voltage detecting elements ZD1 to ZD4 is set to 7V, the set detection overvoltage value is set to 28V, and the save voltage values can be selected from 21V, 14V and 7V.

Thus, in the case of the third embodiment, the same operational effect as in the case of the first embodiment can be obtained.
Further, the applicability to the load 100 can be remarkably expanded. For example, the secondary DC power supply of only the control circuit (100) can be continuously output.

[0037]

According to the present invention, the overvoltage detecting element is formed of a plurality of voltage detecting elements connected in series to the secondary DC power supply circuit, and the element switching means is provided so that the overvoltage detecting element once performs the overvoltage detecting operation. In this case, a predetermined voltage detection element is apparently short-circuited to switch to the voltage forced drop operation state, and even when the overvoltage detection operation is disabled, the secondary DC power supply voltage is set to a save voltage lower than the detection overvoltage value. Since it is configured to be clamped to a voltage value below the specified value, the voltage stress of the stabilizing circuit, each component and the control circuit that forms the load can be minimized, and their rapid deterioration and burnout can be reliably prevented. it can.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a timing chart for explaining the operation.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a third embodiment of the present invention.

FIG. 5 is a circuit diagram for explaining a conventional example.

FIG. 6 is likewise a timing chart for explaining the operation.

[Explanation of symbols]

 10 Primary DC Power Supply Circuit C10 Smoothing Capacitor 11 AC Power Supply 12 Power Switch 13 Noise Filter 14 Rectifier Circuit Ln Negative Electrode 15 Switching Element I Current Ib Inflow Current 20 Transformer L12 Auxiliary Winding 30 Secondary DC Power Supply Circuit 40 Voltage Control Element 45 Stable Circuit F F Overvoltage detection signal 46 Photocoupler f Feedback signal 50 Overvoltage protection circuit 51 Overvoltage detection circuit ZD1, ZD2 Voltage detection element (overvoltage detection element) R51 Resistance P Overvoltage detection signal 52 Photocoupler p Overvoltage protection signal 53 Overvoltage protection element 60 Element switching Means 61 Transistor 62 Magnetic force operation switch 62C Coil 62S switch 63, 64 Transistor 100 Load

Claims (1)

[Claims] 1. A primary DC power supply circuit including a rectifying circuit, a smoothing capacitor, a switching element, and a voltage control element, and a secondary DC power supply circuit including a stabilizing circuit are connected and coupled via a transformer, and a stabilizing circuit is connected. It is formed so as to generate a secondary DC power source by ON / OFF controlling the switching element while applying a feedback signal to the voltage control element, and an overvoltage detection element provided on the side of the secondary DC power supply circuit sets the detected overvoltage value or more. Using the overvoltage detection signal that is output when the overvoltage is detected, the overvoltage protection element connected in parallel with the voltage control element on the primary DC power supply circuit side is turned on to attenuate the current flowing into the switching element. In the transformer-coupled switching power supply device including an overvoltage protection circuit formed to be capable of overvoltage protection by: And forming a plurality of voltage detecting element connected in series to the next DC power supply circuit, overvoltage than the setting detecting overvoltage value by cooperation of a plurality of voltage detecting elements predetermined on condition that the detected 1
A transformer-coupled switching power supply characterized by comprising an element switching means for apparently short-circuiting the above voltage detection element to switch the secondary DC power supply voltage so that the secondary DC power supply voltage can be forcibly lowered to a retract voltage lower than the set detection overvoltage value. apparatus.