JPH0649112Y2 - DC power supply - Google Patents

Description

[Detailed Description of the Invention] Industrial field of application The present invention relates to a DC power supply device and has an output disconnection protection function using overcurrent characteristics (regulation characteristics such as foldback characteristics and drooping characteristics). Moreover, this function is intended to prevent the switch from malfunctioning during an instantaneous power failure.

2. Description of the Related Art A conventional DC power supply device, as shown in FIG. 2, uses an overcurrent characteristic of a switching power supply circuit to provide an electronic switch circuit having a function of disconnecting and protecting an output when an output short circuit (or an excessive current of a load) occurs. Was used.

In FIG. 2, 22 is the secondary winding of the output transformer connected to the primary side inverter of the switching power supply, 23 and 24 are diodes, 24 and 30 are capacitors, 2526, 29, 31 and 32 are resistors, 27 and 28 are transistors, 33 is a Zener diode, 35 is an output terminal, 36 is a signal terminal for an electronic switch, 37 is a ground terminal, and 38 is an external switch.

In the operation of this circuit, when the external switch 38 is turned on, the charge of the capacitor 24 is charged in the capacitor 30 through the resistors 25 and 29, so that this charging current flows through the transistor 28 as a base current, turning on the transistor 28. When the transistor 28 is turned on, a current flows through the resistor 26 and the transistor 27 is turned on, so that the voltage of the capacitor 24 appears at the output terminal 35. Since the capacitor voltage is higher than the Zener voltage, a current flows through the Zener diode 33, and this current becomes the base current of the transistor 28, and the transistor 28
And 27 remain ON.

Then when the output is shorted (or overcurrent),
Due to the overcurrent characteristic of the switching power supply circuit as shown in FIG. 4, the voltage of the capacitor 24 drops and at the same time the output terminal 35
Since the voltage (output voltage) also decreases, when the output voltage V ₀ becomes equal to or lower than the Zener voltage V ₂ , the current does not flow through the Zener diode 33, and the transistor 28 is turned off. When the transistor 28 is turned off, no current flows through the resistor 26, so the transistor 27 is turned off to disconnect and protect the load.
The conventional circuit (Fig. 2) has a capacitor 30 connected to the transistor 28 unless the external switch 38 is turned off or the power input switch is turned off and the voltage of the capacitor 24 becomes zero after disconnection. Since no charge is discharged, the turned off transistor 28 cannot be turned on again and the electronic switch, ie the transistor 27, remains switched off.

Problems to be Solved by the Invention In the conventional switching power supply, since the electronic switch circuit operates as described above, an instantaneous power failure occurs, the switching power supply stops oscillating, and the voltage V ₀ decreases as shown in Fig. 3, and Zener voltage V ₂ (point)
Electronic switch (ie transistor 2
7) is turned off, and immediately after that, the switching power supply starts oscillating by restarting the power supply, that is, the primary side inverter starts operating, the voltage of the smoothing capacitor 24 rises, and even if the voltage returns to the original voltage, the capacitor 30 for starting Since the electric charge of is not discharged, the charging current does not flow and the transistor 27 continues to be in the OFF state.

If there is a short power failure, the circuit in Fig. 2 has a drawback that the protection circuit malfunctions and the output remains off.

Means for Solving Problems The present invention solves the above-mentioned problems. Even if there is an instantaneous power failure, the protection circuit of the switch circuit malfunctions and the output is turned off.
It is configured so as not to

That is, the first diode 3 is connected to one end of the secondary winding 1 of the output transformer connected to the primary side inverter of the switching power supply unit, and the other end of the diode 3 and the secondary winding 1 of the output transformer are connected. The first capacitor 5 is connected between the other ends, and the first diode 3 and the first capacitor 5 are connected.
A first transistor 8 having a disconnection function for output short circuit or overcurrent protection connected between a connection point of the output terminal 18 and the output terminal 18, and a second transistor 11 for turning on or off the first transistor 8. Comprises a second transistor 11
Is activated by the charging current of the activation capacitor 13 when the external switch 21 connected between the other end of the secondary winding 1 of the output transformer and the emitter terminal 19 of the second transistor 11 is turned on, and When the output voltage drops when the first transistor 8 is turned on, the output terminal 18 and the second transistor 11
The Zener diode 16 connected between the bases of the second transistor 11 and the first transistor 8
In the DC power supply that turns off the
A series circuit consisting of a second diode 2 and a first resistor 4 connected to a connection point between one end of the secondary winding 1 and the first diode 3 and the other end of the secondary winding 1 of the output transformer are discharged. The second resistor 12 and the starting capacitor 13 are connected in series at the connection point with the resistor 6 to form the second transistor.
The DC power supply device is characterized in that it is connected to the base terminal of 11 and discharges the electric charge of the starting capacitor 13 through the discharge resistor 6 at the same time when the oscillation of the switching power supply unit is stopped.

Effect The present invention has the above-described configuration, and when the oscillation of the switching power supply section on the primary side of the output transformer is stopped instantaneously, the voltage is not applied to the starting capacitor from the diode connected to the secondary side of the output transformer. Is discharged through the discharge resistor. Therefore, the charging current can flow to the starting capacitor during re-feeding, so that the second transistor is turned on again, the base current of the first transistor is passed, and the first transistor is turned on to turn off the output during re-feeding. Has the effect of preventing

Embodiment An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a circuit diagram of a main part of the DC power supply device. The secondary winding 1 of the output transformer connected to the primary side converter of the switching power supply unit connects the second diode 2 and the first resistor 4 and the resistance. Connected to the starting capacitor 13 of the second transistor 11 via the device 12, 3 is a first diode, 17 is a second diode, 5 is a first capacitor, 7
Is a second capacitor, both of which are for smoothing. 6 is a discharge resistor, 9, 10, 12, 14, 15 are resistors, 8 is a first transistor, 16 is a zener diode, 18 is an output terminal, 19
Is the signal terminal of the external switch, that is, the second transistor
11 is an emitter terminal, 20 is a ground terminal, and 21 is an external switch. In this case, even if a sufficient voltage is applied to the smoothing capacitor 5, since the voltage is not applied from the diode 2 to the starting capacitor 13 at the same time as the oscillation of the switching power supply unit is stopped, the electric charge of the starting capacitor 13 is a resistor.
It is discharged through 12 and the discharge resistor 6. If the charge of the starting capacitor 13 is exhausted, the charging current can flow at the time of re-power supply, so that the second transistor 11 can be turned on again and the first transistor 8 can be turned on.

Effects of the Invention As described above, the DC power supply device of the present invention is an industrial one in which a malfunction circuit at the moment of a power failure is prevented by adding an inexpensive circuit to the circuit having the disconnection function for the conventional output short circuit protection. And the practical value is enormous.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of a main part of an embodiment of a DC power supply device according to the present invention, and FIG. 2 is a circuit diagram of a main part of a conventional DC power supply device.
FIG. 3 is an output voltage-current characteristic diagram of the DC power supply device, and FIG. 4 is a voltage-time characteristic diagram of each part of the DC power supply device comparing the present invention with the conventional one. 1: Secondary winding of output transformer 2: Second diode 3: First diode 4: First resistor 5: First capacitor 6: Discharge resistor 8: First transistor 11: Second Transistor 12: Second resistor 13: Starting capacitor 16: Zener diode 18: Output terminal 19: Second transistor emitter terminal 21: External switch

Claims (1)

[Scope of utility model registration request] 1. A first diode is connected to one end of a secondary winding of an output transformer connected to a primary side inverter of a switching power supply unit, and the other end of the diode is connected to the other end of the secondary winding of the output transformer. Connect the first capacitor between the ends,
A first transistor connected between the connection point of the first diode and the first capacitor and the output terminal and having a disconnection function for output short circuit or overcurrent protection and the first transistor is turned on or off. And a second transistor for turning on an external switch connected between the other end of the secondary winding of the output transformer and the emitter terminal of the second transistor. When the output voltage drops due to the start-up of the charging current and turning on the first transistor, the output terminal and the second
In the DC power supply device for turning off the second transistor and the first transistor by the Zener diode connected between the bases of the transistors, the connection is made to the connection point between one end of the secondary winding of the output transformer and the first diode. A second resistor and the starting capacitor are connected in series at a connection point between a series circuit including a second diode and a first resistor and a discharge resistor connected to the other end of the secondary winding of the output transformer. Then, the DC power supply device is connected to the base terminal of the second transistor, and at the same time as the oscillation of the switching power supply unit is stopped, the charge of the starting capacitor is discharged through the discharge resistor.