JPH0537663Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> The invention is a semi-self-excited switching device in which the main switching element is started by a starting circuit and then the switching operation is continued by a control signal from a control circuit. Regarding switching power supplies, by controlling the on-time width of the starting pulse given to the switching element from the starting circuit by the current flowing through the switching element, the circuit configuration is simple, the number of parts is small, the size is small, and the cost is low. It is possible to obtain a semi-self-excited switching power supply that is inexpensive and has good starting characteristics.

<Prior Art> Various circuit systems for switching power supplies have been known in the past, and one of them is a semi-self-excited switching power supply.
Figure 7 shows a conventional example, in which 1 is a DC power source obtained by rectifying and smoothing commercial AC, 2 is a switching element composed of a power transistor, power MOS FET, etc., and 3 is an oscillation circuit. 4 is a control circuit, 5 is an output rectifying and smoothing circuit, 6 is an auxiliary power supply, 7 is a main transformer, 7 is a starting circuit configured as follows.
1 to 73 are windings of this transformer 7, and 8 is an insulating coupler such as a pulse transformer or a photocoupler.

The starting circuit 3 is composed of an oscillation circuit operated by DC input _Eio . The control circuit 4 has an output terminal 9,
Monitor the DC output V ₀ appearing at 10 and check the DC output
The switching element 2 is controlled in pulse width in a direction in which V ₀ is constant. The output smoothing circuit 5 includes diodes 51, 52, a choke coil 53, and a capacitor 54, and converts the switching output generated at the output winding 72 of the transformer 7 into DC and outputs the DC. The auxiliary power supply 6 includes a winding 73 of a transformer 7, and the voltage induced in the winding 73 is passed through a diode 61 and a capacitor 6.
The DC voltage for operation is supplied to the control circuit 4 by rectification and smoothing by a capacitor input type rectification and smoothing circuit consisting of 2. 63 is a voltage stabilization circuit.

In the conventional semi-self-excited switching power supply described above, the starting circuit 3 first applies a starting pulse having a constant on-time width to the switching element 2 to start it. The activation pulse supplied from the activation circuit 3 to the switching element 2 has an ON width sufficiently smaller than an OFF width. When the switching element 2 is started by the above-mentioned starting pulse, the DC input _Eio applied through the input winding 71 of the transformer 7 is switched, and a switching output is generated from the input winding 71 side of the transformer 7 to the winding 73 side. is taken out. Winding 7
The switching output taken out to the switching element 3 side is a pulse output with a duty substantially equal to the starting pulse supplied from the starting circuit 3 to the switching element 2, and
As shown in FIG. 8, the on-width T _po is sufficiently smaller than the off-width T _pff . This pulse output is rectified by a diode 61, smoothed by a capacitor 62, converted into a DC voltage as shown in FIG. 8, and supplied to the control circuit 4. As a result, the control circuit 4 starts operating. And the control circuit 4
At the point when the starting circuit 3 starts operating, the oscillation operation of the starting circuit 3 is stopped. In the steady operating state after the starting circuit 3 has stopped, the pulse width of the switching element 2 is controlled by the control circuit 4, and the input winding 71 of the transformer 7
The switching element 2 switches the DC input _Eio given through the switching element 2, and the switching output is transferred from the input winding 71 side of the transformer 7 to the output winding 72 side.
It is taken out to the side, rectified and smoothed by the output rectification and smoothing circuit 5, and outputs a stabilized DC output _V0 .

<Problems to be solved by the invention> However, in the above-mentioned conventional switching power supply, the starting circuit 3 is an oscillator that generates a starting pulse with a fixed on-time width, so the circuit configuration becomes complicated and However, there was a problem in that the number of parts increased, which was disadvantageous in efforts to reduce size and cost.

<Means for Solving the Problems> In order to solve the above-mentioned conventional problems, the present invention provides a transformer, a switching element for switching DC input applied through an input winding of the transformer, and a switching element for switching the DC input applied through the input winding of the transformer. The starting circuit includes a starting circuit that starts the device by applying a starting pulse to the switching device, a control circuit that controls the switching device, and an auxiliary power supply that includes a winding of the transformer and supplies operating power to the control circuit. After turning it on and starting it,
In the switching power supply that continues the switching operation based on a control signal from the control circuit, the startup circuit sets the on-time width of the startup pulse to:
The switching device is characterized in that it is a circuit that is controlled by a current flowing through the switching element.

<Function> In the switching power supply according to the present invention, the starting circuit controls the on-time width of the starting pulse by the current flowing through the switching element, and there is no need to accurately determine the on-time width.
Therefore, a switching power supply with a simple circuit configuration, a small number of parts, and a small size and low cost can be obtained.

Furthermore, since the on-time width of the starting pulse is controlled by the current flowing through the switching element, a self-control effect is added to the current flowing through the switching element, resulting in a primary-side current suppression effect at the time of starting. It will be done.

<Embodiment> FIG. 1 is an electrical circuit connection diagram of a switching power supply according to the present invention. In the figure, the same reference numerals as in FIG. 7 indicate the same components. The starting circuit 3 is configured as a circuit that controls the on-time width of the starting pulse to be applied to the control electrode G of the switching element 2 using the current I flowing through the main circuit DS of the switching element 2. In the embodiment, circuits 31 to 33 that turn on the switching element 2
and circuits 34 and 35 that turn on the switching element 2 by the circuits 31 to 33 and then turn off the switching element 2 when the current I of the switching element 2 reaches a predetermined value.

Circuits 31 to 3 that turn on the switching element 2
3 is a resistor 31 charged by the DC input E _io
and a time constant circuit consisting of a capacitor 32, and a terminal voltage of the capacitor 32 that constitutes this time constant circuit.
The circuit 33 becomes conductive when V ₂ reaches a predetermined value to forward bias the switching element 2.

Circuits 34 and 3 that turn off the switching element 2
5 is a current detection element 34 that is connected in series to the main circuits S and D of the switching element 2;
and a three-terminal control element 35 connected to the control electrode G and controlled by a signal given from the current detection element 34.

At startup, as shown in Figure 6a, when the DC power supply 1 is turned on at the time of to, the terminal voltage _V2 of the capacitor 32 changes to Figure 6a according to the time constant determined by the resistor 31 and the capacitor 32. It rises as shown. And the terminal voltage of capacitor 32
When V ₂ reaches the set value V ₂₁ at time t ₁ , the circuit 33 becomes conductive and a voltage as shown in FIG. 6b appears at its output.
V ₃ occurs. This voltage V ₃ biases the control electrode G of the switching element 2 in the forward direction,
Switching element 2 is turned on.

By turning on the switching element 2,
A current I as shown in FIG. 6c flows through the main circuits S and D, and the winding 7
Output is taken out on the 3rd side. The output taken out to the winding 73 side is rectified by a diode 61, and then smoothed by a capacitor 62 and converted into a DC voltage _V1 .
Supplied to the control circuit 4.

Current I flowing through the main circuit of switching element 2
increases with time, as shown in Figure 6c. When the current I reaches a predetermined value I ₁ at time t ₂ , it is detected by the current detection element 34 , the three-terminal control element 35 is made conductive by the detection signal given from the current detection element 34 , and the switching element 2 is turned on. The voltage _V3 applied to the control electrode G drops rapidly as shown in FIG. 6b, and the switching element 2 is turned off. In the end _, for the control electrode _{G of} the switching element 2, as shown in FIG. pulse is given,
This activates the switching element 2.

As described above, the starting circuit 3 according to the present invention is configured to control the on-time width _Tpo of the starting pulse by the current I flowing through the switching element 2, and to accurately control the on-time width _Tpo . There is no need to specify. Therefore, the circuit configuration is simple, the number of parts is small, and a switching power supply that is small and inexpensive can be obtained.

Moreover, since the on-time width T _po of the starting pulse is controlled by the current I flowing through the switching element 2, a self-control effect is added to the current I flowing through the switching element 2, and the peak of the primary current at the time of starting is reduced. The value is suppressed, and a small capacity switching element 2 can be used.

After the control circuit 4 starts operating as described above, the pulse width of the switching element 2 is controlled by the control circuit 4, and the DC input _Eio applied through the input winding 71 of the transformer 7 is applied to the switching element 2.
The switching output is taken out from the input winding 71 side of the transformer 7 to the output winding 72 side, rectified and smoothed by the output rectification and smoothing circuit 5, and a stabilized DC output V ₀ is output. do.

FIG. 2 is a circuit diagram showing a more specific embodiment of the switching power supply according to the present invention, in which a circuit 33 for forward biasing the switching element 2 is connected in series with the control electrode G of the switching element 2, and a time constant circuit 3 is connected in series to the control electrode G of the switching element 2.
It is constructed of a two-terminal trigger element that becomes conductive when the terminal voltage V ₂ of terminals 1 and 32 reaches a predetermined value V ₂₁ (see FIG. 6a). Further, the current detection element 34 is composed of a resistor, and the three-terminal control element 35 is composed of a thyristor.

In this embodiment, the terminal voltage of capacitor 32
When V ₂ reaches the set value V ₂₁ , the two-terminal trigger element 3
3 becomes conductive, the control electrode G of the switching element 2 is biased in the forward direction, and the switching element 2 is turned on. When the switching element 2 is turned on and the current I flowing through its main circuits S and D reaches a predetermined value _I1 , the terminal voltage of the current detection resistor 34 changes to the gate voltage of the thyristor 35. A voltage is applied between the cathodes, the thyristor 35 becomes conductive, and the switching element 2 is turned off. The thyristor 35 continues to be turned on until its main circuit current becomes equal to or less than the holding current, and during that time, the switching element 2 remains in the off state. When the main circuit current becomes equal to or less than the holding current, the thyristor is turned off and reset.

FIG. 3 is a circuit diagram of the main parts of yet another embodiment of the switching power supply according to the present invention. In this embodiment, the circuit 33 for forward biasing the switching element 2 includes a three-terminal control element 33 such as a transistor connected in series with the control electrode G of the switching element 2.
1, a transistor 332 that makes the three-terminal control element 331 conductive when the terminal voltage V ₂ of the capacitor 32 forming the time constant circuit reaches the set value V ₂₁ ;
Zener diode 333, resistor 334, 335
It is configured with a circuit consisting of:

FIG. 4 shows a circuit diagram of essential parts in yet another embodiment. In this embodiment, the current detection element 3
4 consists of a current transformer, whose primary winding 3
41 is connected in series with the main circuits S and D of the switching element 2, and the secondary winding 342 is connected to the three-terminal control element 35.
It is connected to the control electrode of No. 1 via a diode 352.

FIG. 5 shows another embodiment of the switching element according to the present invention. Reference numeral 11 denotes a delay circuit that delays power supply to the control circuit 4 until the output voltage of the auxiliary power supply 6 rises to a predetermined value. Delay circuit 11
is a switch element _Q1 consisting of a transistor etc. that is connected in series to the output line of the auxiliary power supply 6, and a switch element Q1 that is connected when the output voltage of the auxiliary power supply 6 reaches a predetermined value.
A first circuit 111 that turns on Q ₁ and a second circuit 112 that keeps switch element Q ₁ in an on state.
Equipped with.

The switch element _Q1 is composed of a transistor, whose collector is connected to the positive line of the auxiliary power supply 6, its emitter is connected to the control circuit 4, and its base is connected to the negative line via a Zener diode _Dz . be.

The first circuit 111 includes a transistor _Q2 ,
The emitter is connected to the output terminal of the auxiliary power supply 6, and the collector is connected to the switch element through the resistor _R1 .
A resistor _R2 is connected between the emitter and base of the transistor _Q2 , and the base is connected to the negative line of _the auxiliary power supply 6 via a resistor _R3 .

The second circuit 112 includes a transistor _Q3 ;
The collector of this transistor Q ₃ is connected to the base of transistor Q ₂ via a resistor R ₄ , and
The emitter is connected to the negative line of the auxiliary power supply 6. The base of transistor _Q3 is connected to the output terminal of switch element _Q1 via resistor _R5 .
Also the base of transistor _Q3 . A resistor _R6 is connected between the emitters.

At startup, the output taken out to the winding 73 side is rectified by the diode 61, and the capacitor 62 is charged by the rectified output. The charging voltage of the capacitor 62 increases according to the time constant from the time when the rectified voltage is applied. While the charging voltage V _c of the capacitor 62 is low, the transistor Q ₂ and the transistor Q ₁ are off, and no voltage is applied to the control circuit 4.

Next, the charging voltage V _c of the capacitor 62 increases,
When the bias voltage determined by resistor R ₂ and resistor R ₃ reaches a voltage at which transistor Q ₂ is turned on, transistor Q ₂ is turned on, and subsequently switch element Q ₁ is turned on. As a result, the voltage V ₁ is applied to the control circuit 4, and the control circuit 4 starts operating.

As described above, no voltage is applied to the control circuit 4 during the charging period of the capacitor 62.
Therefore, the voltage of the capacitor 62 drops less by ΔV _s than in the conventional example, as shown in FIG. 8A. Therefore, power consumption at startup is reduced. As a result, in combination with the primary side current suppression effect by the starting circuit 3, a switching power supply with low power consumption can be realized. Further, since there is no need to increase the starting power by increasing the pulse width or frequency of the starting pulse, the leakage voltage appearing between the output terminals 9 and 10 is also reduced.

When the switch element _Q1 is turned on, a drive is applied from its output side to the transistor _Q3 via the resistor _R5 , and the transistor _Q3 is turned on. As a result, resistor R ₄ is connected in parallel with resistor R ₃ , and the first
The bias point of the transistor _Q2 constituting the circuit 111 becomes deeper. Therefore, even if the charging voltage V _c of the capacitor 62 decreases, the transistor Q ₂ and the switch element Q ₁ maintain the on state, and the voltage V ₁ is stabilized using the Zener voltage of the Zener diode D _z as a reference value. is supplied to the control circuit 4.

During the above-described circuit operation, when the switching element 2 starts its original switching operation in response to a control signal supplied from the control circuit 4, it enters a steady operation state.

<Effects of the Invention> As described above, the present invention includes a starting circuit that controls the on-time width of the starting pulse by the current flowing through the switching element, so it is necessary to accurately determine the on-time width. Therefore, it is possible to provide a semi-self-excited switching power supply that has a simple circuit configuration, requires a small number of parts, and is small and inexpensive.

[Brief explanation of the drawing]

Fig. 1 is an electric circuit connection diagram of a switching power supply according to the present invention, Fig. 2 is an electric circuit diagram in another embodiment, Fig. 3 is an electric circuit diagram of the main parts in another embodiment, and Fig. 4 5 is an electric circuit diagram of the main part in yet another embodiment, FIG. 6 is a waveform diagram explaining the operation of the switching power supply according to the present invention, and FIG. FIG. 7 is an electric circuit connection diagram of a conventional switching power supply, and FIG. 8 is a waveform diagram of a starting pulse that similarly explains the problem. 1...DC power supply, 2...Switching element, 3
...Start circuit, 31...Resistor, 32...Capacitor, 33...Circuit for forward biasing the switching element, 34, 35...Circuit for turning off the switching element, 4...Control circuit, 5...Output rectification and smoothing Circuit, 6... Auxiliary power supply, 7... Transformer, 71...
Input winding, 72...output winding, 73...auxiliary power supply winding.

Claims (1)

[Claims for Utility Model Registration] (1) A transformer, a switching element for switching DC input applied through an input winding of the transformer, a starting circuit for starting the switching element by applying a starting pulse to the switching element, a control circuit for controlling a switching element; and an auxiliary power source that includes a winding of the transformer and supplies operating power to the control circuit; 1. A switching power supply that continues a switching operation by switching, wherein the starting circuit is a circuit that controls the on-time width of the starting pulse by a current flowing through the switching element. (2) The starting circuit includes a circuit that turns on the switching element, and a circuit that turns on the switching element by the circuit and then turns off the switching element when the current of the switching element reaches a predetermined value. The switching power supply according to claim 1, characterized in that the switching power supply is equipped with a circuit for causing the switching to occur. (3) The circuit that turns on the switching element includes a time constant circuit that is charged by the DC input, and conducts when the charging voltage of this time constant circuit reaches a predetermined value to turn on the switching element. 2. The switching power supply according to claim 2, further comprising a biasing circuit. (4) The circuit that forward biases the switching element is configured with a two-terminal trigger element that is connected in series with the control electrode of the switching element and becomes conductive when the charging voltage of the time constant circuit reaches a predetermined value. A switching power supply according to claim 3 of the utility model registration claim, characterized in that: (5) The circuit that forward biases the switching element includes a three-terminal control element whose main circuit is connected in series with the control electrode of the switching element, and a three-terminal control element whose main circuit is connected in series with the control electrode of the switching element, and a three-terminal control element whose main circuit is connected in series with the control electrode of the switching element, and when the charging voltage of the time constant circuit reaches a predetermined value. 3. The switching power supply according to claim 3, which is characterized by comprising a circuit for making the terminal control element conductive. (6) The circuit for turning off the switching element is controlled by a current detection element connected in series with the main circuit of the switching element, and a signal connected to a control electrode of the switching element and supplied from the current detection element. A switching power supply according to claim 2, claim 3, claim 4, or claim 5, characterized in that the switching power supply comprises a terminal control element. (7) The switching power supply according to claim 6, wherein the current detection element is a resistor. (8) The switching power supply according to claim 6, wherein the current detection element is a current transformer. (9) The utility model registration request is characterized in that the auxiliary power source has a circuit between it and the control circuit that delays power supply to the control circuit until the output voltage rises to a predetermined value. Switching power supply described in scope 1. (10) The circuit for delaying power supply to the control circuit includes a switch element connected in series to the output line of the auxiliary power supply, and a switch element that activates the switch element when the output voltage of the auxiliary power supply reaches a predetermined value. The switching power supply according to claim 9, which is a registered utility model and is characterized by comprising a first circuit that turns on the switch element and a second circuit that holds the switch element in the on state.