JPH0662565A - Stabilized power circuit having overload protective function - Google Patents

Abstract

PURPOSE:To provide a stabilized power circuit having an overload protective function that can ensure the safety of a load circuit by suspending the operation of the power circuit when it is overloaded. CONSTITUTION:A stabilized power circuit having an overload protective function is provided with an input voltage sensing circuit 11 for detecting that an unstabilized power supply is inputted to a power circuit, a delay circuit 12 for delaying the detection signal, and an activating resistor separating circuit 13 for separating an activating resistor from a switching element upon reception of the delayed detection signal. After the power circuit is activated, the activating resistor is immediately separated from the switching element. This makes it impossible to continue self-excitation oscillation in an overloaded state, and the operation of the power circuit is suspended.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a color television receiver,
The present invention relates to a stabilized power supply circuit such as a color display device, and to a self-excited switching power supply circuit having an overload protection function for preventing an overload current due to a failure of a load circuit connected to the stabilized power supply circuit.

[0002]

2. Description of the Related Art Conventionally, in a self-excited switching power supply circuit, a detection resistor is sealed in series with a switching element, and a voltage drop of the detection resistor increases when a load circuit fails and becomes overloaded. A circuit for limiting the ON period is provided to reduce the output voltage, that is, to have the drooping characteristic to reduce the overload current. Such a known example is described in Japanese Utility Model Laid-Open No. 1-127331.

[0003]

In the above-mentioned prior art, although the output voltage drops in the overload state, electric power is supplied to the load circuit, and a large current flows locally depending on the fault state of the load circuit. This can lead to smoking and ignition of parts.

An object of the present invention is to provide a self-excited switching power supply circuit with an overload protection function, which ensures the safety of the load circuit by stopping the operation of the power supply circuit in an overload state.

[0005]

In order to achieve the above object, in the present invention, an input voltage detection circuit for detecting the input of an unstabilized power supply to a power supply circuit, a delay circuit for delaying the detection signal, It is impossible to continue self-excited oscillation in an overload state by providing a startup resistance disconnection circuit that disconnects the startup resistance from the switching element in response to the delayed detection signal, and disconnects the startup resistance from the switching element immediately after the power supply circuit starts. The operation of the power supply circuit is stopped.

[0006]

[Function] When an unregulated power supply is input to the power supply circuit, power is supplied to the switching element via the starting resistance and the switching element is turned on. Thereafter, power is supplied from the feedback winding of the switching transformer and self-oscillation starts. Stabilized power is supplied to the output. On the other hand, the input voltage detection circuit detects the input of the unstabilized power supply, the detection signal passes through the delay circuit, and after the power supply circuit is started, it is transmitted to the start-up resistance cutoff circuit and the start-up resistance from the switching element. Detach.

When a failure occurs in the load circuit and an overload occurs, the output voltage drops due to the drooping characteristic, and the feedback winding voltage drops at the same time, so that power is not supplied from the feedback winding to the switching element. Further, since the starting resistor has already been separated from the switch element, no power is supplied from the unstabilized power supply, and self-sustained pulsation cannot be continued, so that the operation of the power supply circuit is stopped.

[0008]

Embodiments of the present invention will be described below with reference to FIGS.

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

In FIG. 1, 1 is an unregulated power supply, 2 is a switch, 3 is a starting resistor, 4 is a switching transistor which is a switching element, 5 is a switching transformer,
6 is a detection resistor that detects an overload state, 7 is a bias circuit that applies a bias from the return winding N3 of the switching transformer 5 to the switching transistor 4, and 8 is a detection resistor 6
Switching transistor 4 when the voltage drop of
ON period limiting circuit that limits the ON period of the switching transformer, 9 is a rectifying / smoothing circuit that rectifies and smoothes the output of the secondary winding N2 of the switching transformer 5, 10 is a load circuit, and 11 is a non-regulated power supply. An input voltage detection circuit for detection, 12 is a delay circuit that delays the detection signal of the input voltage detection circuit 11 until the power supply circuit is activated, and 13 is a startup resistance disconnection circuit that disconnects the startup resistance from the switching transistor 4.

In FIG. 1, when the switch 2 is turned on, a current flows from the unstabilized power source 1 to the switching transistor 4 via the starting resistor 3 to turn on the switching transistor 4. After that, the feedback winding N3 of the switching transformer 5
A bias is applied to the switching transistor 4 via the bias circuit 7, self-excited oscillation starts, an output appears in the secondary winding N2 of the switching transformer 5, rectifying and smoothing is performed by the rectifying and smoothing circuit 9, and a stabilized voltage is supplied to the load 10. To be done. On the other hand, when the switch 2 is turned on, the input voltage detection circuit 11 detects that the unstabilized power supply 1 is input, the detection signal passes through the delay circuit 12, and after the power supply circuit is activated, the activation resistance disconnection circuit 13 and the starting resistor 3 is disconnected from the switching transistor 4. When the load becomes abnormal and becomes overloaded, the voltage drop of the detection resistor 6 increases, and the ON period limiting circuit 8 operates to limit the ON period of the switching transistor 4 and reduce the output voltage. Since the voltage of the feedback winding N3 also decreases at the same time as the output voltage decreases, the bias is not applied to the switching transistor 4, and since the starting resistor 3 is already disconnected, the bias is not applied from the unstabilized power supply 1 and self-excited. The oscillation stops and the load circuit 10 is no longer supplied with power.

FIG. 2 shows a voltage obtained by rectifying and smoothing an AC power source as an unstabilized power source shown in FIG. 1, and also shows the input voltage detection circuit 11, the delay circuit 12, and the starting resistor disconnecting circuit 13 shown in FIG. 1 as a concrete example. It is a circuit diagram which applied to the circuit which stabilizes the direct current of the alternating current power supply in an Example.

In FIG. 2, the same functions as those in FIG. 1 are designated by the same reference numerals, and the difference from FIG.
Is an AC power supply, 15 is a bridge rectifying diode, 16 is a smoothing capacitor, 17 and 18 are input voltage detecting resistors, 19 is a delay capacitor, 20 is a discharging diode for the capacitor 19, 21 is an input voltage detecting zener diode, 22
Is a transistor for disconnecting the starting resistance, and 23 is a diode for disconnecting the starting resistance.

In FIG. 2, when the switch 2 is turned on, the midpoint voltage of the resistors 17 and 18 gradually rises due to the charge accumulation effect of the capacitor 19, and when the zener voltage of the zener diode 21 is exceeded, the transistor 22 is turned on and the starting resistor 3 is formed. The midpoint potential of the diode 23 is set to zero volt, and the starting resistor is disconnected from the switching transistor 4. The start-up operation of the power supply circuit and the power supply stop operation in the overload state are as described in FIG.

[0015]

According to the present invention, the operation of the power supply circuit is stopped in the overload state and the power supply to the load is stopped, so that the load circuit can be safely protected.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing an embodiment in which an AC power supply is applied to a circuit for stabilizing DC.

[Explanation of symbols]

1 ... Unregulated power supply, 2 ... Switch, 3 ... Startup resistance, 4 ...
Switching transistor, 5 ... Switching transformer, 6 ... Detection resistor, 7 ... Bias circuit, 8 ... ON period limiting circuit, 9 ... Rectifying / smoothing circuit, 10 ... Load circuit, 11 ... Input voltage detecting circuit, 12 ... Delay circuit, 13 ... Starting resistance disconnection circuit, 14 ... AC power supply, 15 ... Bridge rectifying diode, 16 ... Smoothing capacitor, 17 ... Input voltage detection resistance,
18 ... Input voltage detection resistance, 19 ... Capacitor, 20 ... Diode, 21 ... Zener diode, 22 ... Transistor, 23 ... Diode.

Claims (1)

[Claims] 1. An electric power supplied from an unregulated power source to a primary winding of a switching transformer is switched by a switching element to obtain a stabilized voltage at a secondary winding of the switching transformer, and an overload state is detected. In a self-excited switching power supply circuit having a drooping characteristic that lowers an output voltage, a detection unit that detects that the unstabilized power supply is input, a delay unit that delays the detection signal until the power supply circuit is activated, A starting resistance disconnecting means is provided for disconnecting a starting resistance for applying a starting power to the switching element from the switching element in response to the delay detection signal. A stabilized power supply circuit with an overload protection function that stops the operation of the circuit.