JPH0747992Y2 - Switching regulator - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to a switching regulator, for example, a P that is used in a power supply device of electronic equipment such as a television receiver or a VTR.
The present invention relates to improvement of a WM (pulse width modulation) type switching regulator.

[Prior Art] Conventionally, a PWM type switching regulator has been adopted as a power supply device for supplying a stable DC power supply in electronic equipment.

This switching regulator is, for example, as shown in FIG. 3, a rectifier circuit (not shown) that rectifies a commercial AC power supply.
Is connected to one end of the primary winding P1 of the transformer T and the resistor R, the switching element 1 such as a transistor is connected in series to the other end of the primary winding P1, and the switching element is connected to the other end of the resistor R. 1 is connected to the power supply point B of the control circuit 3 which outputs the oscillation signal for PWM control, and the other end of the control winding P2 whose one end is grounded is connected to the power supply point of the control circuit 3 via the rectifying diode D1. In addition to connecting to B, a smoothing capacitor C1 is connected between the power supply point B and ground, and a rectifying diode D2 and a smoothing capacitor C2 are connected to the output winding P3 of the transformer T. Had a composition.

The control winding P2 and the output winding P3 of the transformer T are wound so that a flyback voltage (alternating voltage) of opposite phase is induced with respect to the primary winding P1.

In such a switching regulator, when a DC voltage is applied from the rectifier circuit to the point A, that is, the transformer T and the resistor R, a charging current flows through the resistor C to the capacitor C1 and the voltage across the capacitor C1, that is, the power supply point B. Voltage rises.

When the voltage at the power supply point B reaches the oscillation start voltage of the control circuit 3, the control circuit 3 is activated to output the oscillation signal to the switching element 1, and the switching element 1 is driven to supply the power source current flowing to the transformer T. It oscillates by switching.

Therefore, the flyback voltage is induced in the control winding P2 and the output winding P3 of the transformer T, but the flyback voltage induced in the control winding P2 is applied to the diode D1 and the capacitor.
It is rectified and smoothed by C1 and applied to the power supply point B to serve as a drive power source for the control circuit 3.

Moreover, the control circuit 3 outputs the oscillation signal whose pulse width is changed so that the drive power supply level from the control winding P2 is constant, to the switching element 1, and the stable flyback voltage is always output from the output winding P3. Is output.

At the connection point C between the diode D2 and the capacitor C2 connected to the output winding P3 in FIG. 3, the load of the electronic device is connected via a choke coil or the like (not shown).

[Problems to be Solved by the Invention] However, in the switching regulator described above, when the output coil P3 side of the transformer T, for example, the point C is short-circuited to the ground side so that both ends of the capacitor C2 are short-circuited, the output coil As the flyback voltage of P3 decreases, the flyback voltage of the control winding P2 also decreases in proportion to this.

On the other hand, since the control circuit 3 consumes current during the oscillation operation,
As shown in FIG. 4, when the flyback voltage from the control winding P2 decreases, the voltage at the power supply point B decreases, and when the voltage from the oscillation start voltage to the oscillation stop voltage decreases, the oscillation operation of the control circuit 3 stops. .

Then, the current consumption of the control circuit 3 decreases, the charging current again flows from the point A to the capacitor C1 via the resistor R, the voltage at the power supply point B rises, and rises to the oscillation start voltage of the control circuit 3, Oscillation operation is started.

However, the current consumption of the control circuit 3 increases with the start of oscillation, and the flyback voltage level of the control winding P2 is low, so that the voltage at the power supply point B immediately drops to the oscillation stop voltage. The intermittent oscillation state occurs in which oscillation and oscillation stop are repeated.

The oscillation stop period t1 from the oscillation stop voltage to the oscillation start voltage is determined by the time constant of the resistance value of the resistor R and the capacitance value of the capacitor C1, and the oscillation period t2 from the oscillation start voltage to the oscillation stop voltage is the value of the capacitor C1. And the current consumption of the control circuit 3.

Thus, when the output side of the transformer T is short-circuited, overcurrent is generated in the output winding P3 during the oscillation period t2 of the switching element 1.
Depending on the ratio between the oscillation period t2 and the oscillation stop period t1,
Even in the intermittent oscillation state, the components on the load side, such as the diode D2 and the choke coil, may generate heat abnormally, and in extreme cases, the load components may be damaged.

The present invention has been made in order to solve such a conventional drawback. Even if the load side of the transformer is short-circuited and intermittent oscillation occurs, abnormal heat generation of components on the load side can be suppressed and reliable. The purpose is to provide a highly efficient switching regulator.

[Means for Solving the Problem] In order to solve such a problem, the present invention provides a primary side winding, and a secondary side output winding and a control winding for outputting a flyback voltage for output and control. A transformer that has a wire, a contactless switching element that switches the power supply current that flows from the power supply source to the primary winding, and a control circuit that outputs an oscillation signal that controls switching of this switching element. Starts oscillation when the drive voltage is supplied from the power source, outputs the oscillation signal, and outputs the oscillation signal that keeps this voltage constant by the flyback voltage induced in the control winding during the switching operation of the switching element. And a control circuit that operates.

Moreover, the switching regulator of the present invention is characterized in that it has a delay circuit that delays the supply of the drive voltage from the power supply source to the control circuit when the flyback voltage level of the control winding is lowered and the oscillation of the control circuit is stopped. There is.

[Operation] In the present invention equipped with the above-mentioned means, when a drive voltage is supplied from the power supply source to the control circuit at the time of start-up, oscillation is started and an oscillation signal is output to the switching element. The flyback voltage is induced in the output winding and the control winding by switching the power supply current flowing in the primary winding, and the control circuit outputs the oscillation signal to the switching element by using this flyback voltage as the drive voltage. Is obtained from the output winding.

When the load on the output winding side of the transformer T is short-circuited or the like, the flyback voltage of the control winding and the output winding also decreases, and the oscillation operation of the control circuit is stopped.
A drive voltage is supplied from the power supply source to the control circuit in the same way as at startup, and oscillation starts, but this drive voltage is applied to the control circuit with a delay by the delay circuit, which delays the start of oscillation of the control circuit and causes oscillation. The interval to the period becomes longer.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. In addition,
The same parts as those in the conventional example are designated by the same reference numerals.

FIG. 1 is a circuit diagram showing an embodiment of a switching regulator according to the present invention.

In the figure, a bridge-type rectifying circuit (power supply source) 7 for full-wave rectifying the commercial AC power supply 5 is connected to an input point A, and a DC power supply smoothed by a smoothing capacitor C3 is supplied. The point A is connected to one end of the primary winding P1 which is the primary winding of the transformer T and the resistor R.

The other end of the resistor R is connected to the power supply point B of the control circuit 3 via the diode D3 connected in the forward direction.

The control circuit 3 changes the duty ratio of the oscillation signal at a rectified and smoothed flyback voltage level, which will be described later, and changes the duty ratio of the oscillation signal so that the flyback voltage level becomes constant. Is output to. That is, the control circuit 3 is PW
This is a circuit for M control.

The other end of the primary winding P1 is grounded via a switching element 1 including, for example, a power transistor,
This switching element 1 is switched by an oscillation signal from the control circuit 3 to turn ON / OFF the power supply current flowing through the primary winding P1.

The transformer T is wound not only on the primary winding P1 but also on the opposite side of the primary winding P1 so that a positive flyback voltage is generated during the OFF period after a current flows through the primary winding P1. Line P3
And a control winding P2.

A diode D2 is connected in the forward direction to one end of the output winding P3, and a smoothing capacitor C2 is connected between the cathode side of the diode D2 and the other end of the output winding P3, and the diode D2 and the capacitor C2 are connected. A load component is connected to a connection point C between the load component and.

The control winding P2 of the transformer T is for inducing a flyback voltage for control, and is connected to the power supply point B of the control circuit 3 through a diode D1 which is grounded at one end and forwardly connected to the other end. A smoothing capacitor C1 is connected between the power supply point B and the ground, and the induced flyback voltage is rectified and smoothed and supplied to the control circuit 3.

The collector of the NPN transistor Q whose base is grounded is connected to the connection point between the resistor R and the diode D3 via the resistor R1, and the emitter is connected to the other end of the control winding P2 via the diode D4 connected in the forward direction. It is connected to the connection point of diode D1.

A capacitor C4 is connected between the emitter of the transistor Q and the ground, and these form a delay circuit 9. The operation of the delay circuit 9 will be described later.

Next, the operation of the switching regulator according to the present invention will be described.

When the DC voltage that is full-wave rectified by the rectifier circuit 7 and smoothed by the capacitor C3 is applied to the primary winding P1 and the resistor R of the transformer T via the point A, the resistor R and the diode D3 are
A charging current flows through the capacitor C1 via the capacitor C1 and the voltage at the power supply point B of the control circuit 3 rises.

As shown in FIG. 2, when the voltage at the power supply point B reaches the oscillation start voltage, the control circuit 3 starts oscillation and outputs an oscillation signal to the switching element 1.

The switching element 1 oscillates by switching the current flowing through the transformer T with the oscillation signal.

Therefore, a flyback voltage is induced in the control winding P2 of the transformer T, the flyback voltage is rectified and smoothed by the diode D1 and the capacitor C1 and applied to the power supply point B, and the control circuit 3 receives the control voltage from the control winding P2. The oscillation signal is oscillated by the flyback voltage and the oscillation signal whose pulse width is changed so that the flyback voltage level becomes constant is output to the switching element 1, and a stable output voltage is always output from the output winding P3.

Therefore, a stable DC voltage rectified and smoothed by the diode D2 and the capacitor C2 is supplied to the load.

Further, during the forward period of the control winding P2, a negative voltage is generated across the capacitor C4 due to the current flowing from the side of the capacitor C4 to the diode D4, and this negative voltage causes the transistor Q to operate ON and the resistor R The flowing current flows through the transistor Q into the capacitor C4.

Here, for some reason, C on the output side of the transformer T is
When the point is short-circuited to the ground side, the flyback voltage of the output winding P3 decreases and the control winding is proportional to this.
The flyback voltage of P2 also drops.

Even if the flyback voltage from the control winding P2 drops, the driving current is not supplied from the diode D1 because the transistor Q is ON, and the voltage at the power supply point B stops oscillating as shown in FIG. The voltage drops to the voltage and the oscillation operation of the control circuit 3 stops.

And when this oscillation is stopped, the transistor Q is still ON.
Since this is the state, the current flowing from the point A through the resistor R flows through the transistor Q to the capacitor C4,
Increase the terminal voltage of C4.

The voltage at which this terminal voltage turns off the transistor Q, which varies depending on the transistor, rises to, for example, about -0.7V, the transistor turns off, and the current flowing from the point A through the resistor R flows to the capacitor C1 via the diode D3.
The voltage at the power supply point B rises.

When the voltage at the power supply point B reaches the oscillation start voltage, the control circuit 3 starts oscillation again and causes the switching element 1 to oscillate.

That is, the delay circuit 9 including the transistor Q, the diode D4, and the capacitor C4 delays the supply of the drive voltage of the control circuit 3 to the power supply point B via the resistor R.

However, while the oscillation is started, the capacitor C4 is charged again and the transistor Q is turned on. However, since the current consumption of the control circuit 3 increases and the flyback voltage of the control winding P2 is low, the voltage at the power supply point B is Immediately, it drops to the oscillation stop voltage, and thereafter intermittent oscillation as shown in FIG. 2 is repeated.

In this way, in the switching regulator of the present invention, when the load side is short-circuited, intermittent oscillation occurs as in the conventional example.
While the oscillation period t2 does not change, an ON state period of the transistor Q of the delay circuit 9 occurs after the control circuit 3 stops oscillation until the voltage at the power supply point B starts to rise, and the oscillation stop period
t1 becomes longer.

Therefore, the interval between the oscillation periods t2 becomes longer, the average loss of the load components is reduced, and abnormal heat generation can be suppressed.

In the present invention, the configuration of the delay circuit 9 described above is arbitrary, in short, a delay function of delaying the supply of the drive voltage from the power supply source to the control circuit 3 when the flyback voltage of the control winding P2 falls below a predetermined level. Any circuit having

[Advantages of the Invention] As described above, the present invention switches a transformer having a primary winding, a secondary output winding, and a control winding, and a power supply current flowing from the power supply source to the primary winding. And a control circuit for controlling the switching of the switching element.The control circuit starts oscillation by supplying a driving voltage from a power supply source at the time of startup and outputs an oscillation signal, and thereafter, the control winding. In a switching regulator formed to output an oscillating signal by a flyback voltage induced in a coil, a delay that delays the supply of the drive voltage from the power supply source to the control circuit when the flyback voltage level of the control winding drops Since the circuit is provided, even if the load side becomes short-circuited and intermittent oscillation occurs, from oscillation stop to oscillation start The oscillation stop period can be extended for a long time.

Therefore, even if the oscillation period is the same as that of the conventional configuration, the average loss of components on the load side is reduced, abnormal heat generation of the load components can be suppressed, and reliability is enhanced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a switching regulator according to the present invention, FIG. 2 is a waveform diagram explaining the operation of the switching regulator of FIG. 1, and FIG. 3 is a circuit diagram showing a conventional switching regulator. FIG. 4 is a waveform diagram showing the operation of the switching regulator of FIG. 1 ... Switching element, 3 ... Control circuit, 5 ... Power supply source (commercial AC power supply), 7 ... Rectifier circuit, 9 ... Delay circuit, C1-C4 ... Capacitor, D1-D4 ... Diode,
P1 …… Primary winding, P2 …… Control winding, P3 …… Output winding,
Q: Transistor, R ... Resistor, T ... Transformer.

Claims (1)

[Scope of utility model registration request] 1. A transformer having a primary side winding, a secondary side output winding for outputting an output and control flyback voltage, and a control winding, and a power supply source flowing to the primary side winding. A contactless switching element that switches a power supply current, and a control circuit that outputs an oscillation signal that controls switching of this switching element.At the time of startup, the drive voltage from the power supply source starts oscillation and outputs the oscillation signal. A control circuit that outputs the oscillation signal such that the flyback voltage induced in the control winding keeps this voltage constant during the switching operation of the switching element; In a switching regulator that obtains an output voltage from the output winding, A switching regulator having a delay circuit that delays the supply of a drive voltage from the power supply source to the control circuit when the oscillation voltage of the control circuit is stopped due to a decrease in the idle voltage level.