JP3198347B2 - Overcurrent protection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to an overcurrent protection circuit in a multiple output power supply device. Since various electronic circuits require various kinds of stabilized voltages, a multi-output power supply device is used. When an overcurrent flows to an arbitrary load in such a multi-output power supply, it is necessary to drop the output voltage to protect the multi-output power supply from the overcurrent, and a stable and inexpensive configuration is required. Requested.

[0002]

2. Description of the Related Art In a conventional multi-output power supply device, for example, as shown in FIG. 4, a drive signal from a common control unit 41 is transmitted via a drive circuit 48 to a plurality of switching elements (SW) including transistors and the like. In addition to 42-1 to 42-n, a DC current supplied from a DC power supply (not shown) is turned on and off to the primary winding p of the transformers 43-1 to 43-n, and the secondary winding s is turned on. It rectifies the induced voltage and supplies it to the load. In that case, various secondary output voltages can be obtained by selecting the turns ratio between the primary winding p and the secondary winding s. Also, by selecting the output polarity of the rectifier circuit connected to the secondary winding s, a positive or negative voltage can be output.

A case is shown in which a rectifying / smoothing unit 44 is connected to a secondary winding s of a transformer 43-1 and an output voltage or a voltage proportional thereto is applied to a control unit 41 via a feedback circuit 47. Compares the sawtooth signal from the sawtooth signal generator 49 with the feedback signal, outputs a drive signal for controlling the ON period of the switching elements 42-1 to 42-n, and outputs the output voltage of the rectifier / smoothing unit 44. And the output voltage on the secondary side of another transformer is also stabilized. That is, the control unit 41 controls the ON period of each of the switching elements 42-1 to 42-n so as to stabilize the output voltage of the rectifying / smoothing unit 44 provided with the feedback circuit 47.

A case where a magnetic amplification type stabilizer (MA) 45 is connected to the secondary winding s of the transformer 43-n is shown. This magnetic amplification type stabilizer 45 is called a mag amplifier, and As described above, the voltage on the secondary side of the transformer 43-n is stabilized, but the output voltage of the magnetic amplification type stabilizer 45 fluctuates due to load fluctuation. (Not shown) to stabilize the output voltage.

When an overcurrent due to a load short circuit or the like is detected by overcurrent detectors 46-1 to 46-n, and a detection signal of the overcurrent is applied to the controller 41, the controller 41 switches the switching element 42- Control is performed to reduce the output voltage by shortening the on-periods of 1 to 42-n to protect the multiple output power supply device from overcurrent.

The voltages applied to the switching elements 42-1 to 42-n are, for example, as shown in FIG.
The current flowing through the switching elements 42-1 to 42-n changes, for example, as shown in FIG. That is, during the ON period T of the switching elements 42-1 to 42-n, a current flows through the primary winding p of the transformers 43-1 to 43-n, power is supplied to the secondary side, and the magnetic amplification type stable In the section 45, energy is supplied to the load after the saturable reactor is saturated, and T 'corresponds to the ON period.

[0007]

[Problems to be solved by the invention] Magnetic amplification type stabilizer 4
5 is in an overcurrent state, and the overcurrent detection unit 46
When an overcurrent detection signal is applied to the control unit 41 from −n, the control unit 41 performs control to shorten the ON period T, for example, and outputs the output voltage on the secondary side of each of the transformers 43-1 to 43-n. Droop. When the overcurrent state returns to the normal state, the detection signal from the overcurrent detection section 46-n disappears, so that the control section 41 returns the ON period to, for example, T.

In this case, a sudden change in the ON period causes a sudden change in the current flowing through the capacitor in the rectifying / smoothing section 44 and the like.
In some cases, a current in an overcurrent state flows in and is detected by the overcurrent detection unit 46-1 or the like and added to the control unit 41, so that the ON period is further shortened. Since the load is not in an actual overcurrent state, the load returns to the normal state immediately. When the switch returns to the normal state, the on-period returns to T from a period shorter than T ', for example, so that the capacitor of the rectifying / smoothing circuit 44 is returned again. For example, there is a drawback that a large current flows and an overcurrent state occurs, the ON period is shortened, and an oscillation phenomenon is repeated. SUMMARY OF THE INVENTION It is an object of the present invention to enable a stable operation even when a normal state is restored from an overcurrent state.

[0009]

The overcurrent protection circuit according to the present invention will be described with reference to FIG. 1. A plurality of switching elements 2-1 to 2-n are controlled by a common control unit 1 to provide a plurality of overcurrent protection circuits. The current flowing in the primary winding of the transformers 3-1 to 3-n is turned on and off, and the rectifying / smoothing unit 4 is connected to at least one secondary winding of the transformers 3-1 to 3-n. A voltage proportional to the output voltage of the rectifying / smoothing unit 4 is fed back to the control unit 1 to stabilize the output voltage, and the other one of the plurality of transformers 3-1 to 3-n A magnetic amplification type stabilizer (MA) 5 is connected to the windings, and overcurrent detection units 6-1 to 6-n for detecting overcurrents flowing through secondary windings of the plurality of transformers 3-1 to 3-n are provided. Primary winding of a transformer having a magnetic amplification type stabilizer 5 connected to a secondary winding A pulse gate circuit 7 for controlling a pulse width of a drive signal from the control unit 1 is connected to a switching element for controlling on / off of a flowing current, and an overcurrent detection unit for detecting an overcurrent flowing to the rectifying / smoothing unit 4 is connected. A detection signal is applied to the control unit 1, and a plurality of switching elements 2-1 to 2-1 are output.
The on-width of 2-n is shortened to control the droop of the output voltage, and a detection signal of an overcurrent detector 6-n for detecting an overcurrent flowing through the magnetic amplification type stabilizer 5 is applied to the pulse gate circuit 7. , So that the pulse width of the drive signal is controlled to be short.

[0010]

By applying a voltage proportional to the output voltage of the rectifying / smoothing unit 4 to the control unit 1 via the feedback circuit 10, the control unit 1 compares the sawtooth wave signal from the sawtooth wave generation unit 9 with Switching elements 2-1 to 2-
A drive signal for turning on and off n is added. The switching element 2-n is connected to the primary winding of the transformer 3-n in which the magnetic amplification type stabilizer 5 is connected to the secondary winding. A drive signal for controlling on and off is applied via.

When the current supplied to the load via the rectifying / smoothing unit 4 is in an overcurrent state, the overcurrent detection unit 6-1
, And a detection signal is added to the control unit 1. Therefore, since the control unit 1 outputs a drive signal for shortening the ON period, each output voltage drops. When the current supplied to the load via the magnetic amplification type stabilizer 5 becomes an overcurrent state, it is detected by the overcurrent detector 6-n, applied to the pulse gate circuit 7, and supplied from the drive circuit 8 to the switching element 2 The pulse width of the drive signal applied to -n is reduced.
When the state returns from the overcurrent state to the normal state, the drive signal from the drive circuit 8 is directly applied from the pulse gate circuit 7 to the switching element 2-n.

Therefore, although the output voltage of the magnetic amplification type stabilizer 5 drops in the overcurrent state, the output voltage of the rectifying and smoothing section 4 does not change suddenly, so that the overcurrent state can be avoided. . Also, even when the output current of the magnetic amplification type stabilizer 5 returns to the normal state, it does not affect the rectifying / smoothing unit 4 side, so that no oscillation phenomenon occurs and the overcurrent protection operation can be stabilized.

[0013]

FIG. 2 is an explanatory view of a main part of an embodiment of the present invention.
11 is a control unit, 12 is a drive circuit, 13 is a switching element (SW), 14 is a transformer, 15 is a rectifying and smoothing circuit, 1
6 is an overcurrent detection unit, 17 is a feedback circuit, 18 is a DC power supply, 19 is a sawtooth wave generation unit, 20 is a pulse gate circuit, 21 is a pulse drive circuit, 22 is an FET (field effect transistor) as a switching element, 23 is a transformer, 24 is a saturable reactor, 25 and 26 are diodes, 27 is an overcurrent detector, 28 is a comparison circuit, 29 and 30
Is a transistor, 31 is a current transformer, 32, 33
Is a diode, R1 to R7 are resistors, and C1 and C2 are capacitors.

The drive circuit 12 includes a transistor, a transformer, and the like, and has a configuration in which a drive signal from the control unit 11 is applied to the switching element 13 and the pulse gate circuit 20.
Various known configurations can be used. Switching element 13, transformer 14, rectifying / smoothing unit 1
5, the configuration including the overcurrent detection unit 16 and the feedback circuit 17 shows the configuration on the rectifying and smoothing unit side similar to the conventional example.

The pulse gate circuit 20 has a comparator 28, a transistor 29 and a resistor R1, and compares the sawtooth signal from the sawtooth generator 19 with the detection signal from the overcurrent detector 27. The comparison is performed by the comparator 28, and the transistor 29 is controlled by the comparison output signal. The pulse drive circuit 21 has a transistor 30 and resistors R2 to R4, drives the FET 22, and controls on / off of the current from the DC power supply 18 to the primary winding of the transformer 23. The overcurrent detector 27 includes a current transformer 31, diodes 32 and 33, resistors R5 to R7, and a capacitor C.
1 and C2 to detect the load current flowing through the primary side of the current transformer 31. The saturable reactor 24 and the diodes 25 and 26 constitute a main part of the magnetic amplification type stabilizer.

FIGS. 3A and 3B are explanatory diagrams of the operation of the embodiment of the present invention. FIG. 3A shows an example of a drive signal, FIG. 3B shows an example of an input signal of the comparator 28, and FIG. 3C shows an example of an output signal of the pulse gate circuit 20. Show. As described above, the comparator 28 compares the sawtooth signal (solid line) with the detection signal (chain line) from the overcurrent detection unit 27, and detects the detection signal from the overcurrent detection unit 27. Is proportional to the load current, and thus becomes a low level detection signal in a normal state. Therefore, the output signal of the comparator 27 becomes "0" for almost one cycle of the sawtooth signal, and the transistor 29 is turned on during the "0" period, and the drive signal from the drive circuit 12 is directly used as the pulse drive circuit. 21 to the gate of the FET 22. That is, in the normal state, on / off control of the switching elements on the rectifying / smoothing section side and the magnetic amplification type stabilizing section side is performed as in the conventional example, and output voltage stabilization control is performed.

When the load current rises to an overcurrent state,
Since the detection signal from the overcurrent detection unit 27 rises as indicated by the chain line on the right side of FIG. 3B, the “0” period of the output signal of the comparator 28 of the pulse gate circuit 20 becomes shorter, Therefore, the pulse width of the drive signal from the drive circuit 12 is reduced to a length according to the ON period of the transistor 29 and is applied to the pulse drive circuit 21. Thereby,
Even when the drive signal applied from the drive circuit 12 to the pulse gate circuit 20 is as shown in FIG. 3A, the drive signal as shown on the right side of FIG. The period is shortened. That is, when the load current supplied via the magnetic amplification type stabilizer becomes an overcurrent state, the on / off control of the switching element on the rectifying / smoothing unit side is normal, but the magnetic amplification type stabilizer is not used. In only the switching element on the side, the ON period is shortened and the output voltage droops. When the normal state is restored from the overcurrent state, the pulse gate circuit 20 is driven by the drive circuit 12.
Is applied to the gate of the FET 22 via the pulse drive circuit 21 as it is. Therefore, since there is no sudden change in the output voltage on the rectifying / smoothing section side, no current flows into the capacitor or the like in an overcurrent state, and the oscillation phenomenon can be prevented.

[0018]

As described above, according to the present invention, when an overcurrent is detected by the overcurrent detector 6-n on the side of the magnetic amplification type stabilizer 5 in the multi-output power supply device, the pulse gate circuit 7 is activated. By controlling the driving circuit 8, the switching element 2-n
In this case, the output voltage is drooped by shortening the pulse width of the drive signal applied to the rectifying / smoothing unit 4. At that time, the control of the output voltage on the rectifying / smoothing unit 4 side is the same as in the normal state. No overcurrent occurs due to this. That is, even though the characteristics of the rectifying / smoothing unit 4 and the magnetic amplifier-type stabilizer 5 are different, even when the magnetic-amplifier-type stabilizer 5 enters an overcurrent state or returns to a normal state, The rectifying and smoothing unit 4 has an advantage that stable operation can be continued.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is an explanatory view of a main part of an embodiment of the present invention.

FIG. 3 is an operation explanatory diagram of the embodiment of the present invention.

FIG. 4 is an explanatory diagram of a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 control unit 2-1 to 2-n switching element 3-1 to 3-n transformer 4 rectifying and smoothing unit 5 magnetic amplification type stabilizing unit (MA) 6-1 to 6-n overcurrent detection unit 7 pulse gate circuit 8 driving Circuit 9 Sawtooth wave generator 10 Feedback circuit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 3/28 H02H 7/20

Claims (1)

(57) [Claims] An electric current flowing through primary windings of a plurality of transformers (3-1 to 3-n) by controlling a plurality of switching elements (2-1 to 2-n) by a common control unit (1). Is turned on and off, a rectifying / smoothing unit (4) is connected to at least one secondary winding of the plurality of transformers (3-1 to 3-n), and an output voltage of the rectifying / smoothing unit (4) is output. Is fed back to the control unit (1) to stabilize the output voltage, and the plurality of transformers (3-1 to 3-
n), a magnetic amplification type stabilizer (5) is connected to another secondary winding, and the plurality of transformers (3-1 to 3-
n) In a multi-output power supply device provided with overcurrent detection units (6-1 to 6-n) for detecting an overcurrent flowing through the secondary winding, the magnetic amplification type stabilizing unit (5) is A pulse gate circuit (7) for controlling a pulse width of a drive signal from the control unit (1) is connected to a switching element for controlling on / off of a current flowing in a primary winding of a transformer connected to the winding, A detection signal of an overcurrent detection unit for detecting an overcurrent flowing through the rectifying / smoothing unit (4) is applied to the control unit (1) to shorten the ON width of the plurality of switching elements (2-1 to 2-n). And the droop control of the output voltage is performed, and a detection signal of an overcurrent detection unit for detecting an overcurrent flowing in the magnetic amplification type stabilizing unit (5) is applied to the pulse gate circuit (7). The pulse width is controlled to be shorter. Current protection circuit.