JPH05316729A - Controller for power source - Google Patents

Abstract

PURPOSE:To prevent saturation of a transformer at the time of starting a separately-excited flyback type switching power source. CONSTITUTION:When an output of a start/steady switching signal generator 5 is an L level, a triangular wave generator 6 outputs a triangular wave having a low frequency f1 to an inverting input terminal of a comparator 7. Further, a terminal (b) is selected at a switch SW, and a low voltage to be output from a pulse-width limiter 4 is input to a non-inverting input terminal of the comparator 7. Since the triangular wave to be input from the generator 6 to the inverting input terminal of the comparator 7 is extended at a lower part of its waveform (a low voltage part), a pulse having a small ratio of the pulse width to a period with the low frequency f1 is supplied from its output terminal to an FET 9 through a driver 8, and the FET 9 is turned ON/OFF.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply control device suitable for a separately excited flyback type switching power supply.

[0002]

2. Description of the Related Art FIG. 15 is a block diagram showing the configuration of an example of a conventional separately excited flyback type switching power supply. The primary coil L _P of the transformer 2 is connected via a switch 42 in parallel with the power source (DC power source) v _i.
The switch 42 outputs a pulse (PW
ON / OFF corresponding to the M wave), and controls (ON / OFF) the current i _P flowing through the primary coil L _P of the transformer 2.

The secondary coil L _S of the transformer 2 is connected in parallel with a current smoothing capacitor C ₁ via a diode D ₁ . The diode D ₁ is a diode for rectifying the current i _S flowing in the secondary coil L _S of the transformer 2, its anode is connected to one end of the secondary coil L _S of the transformer 2, and its cathode is the capacitor C. It is connected to one end of ₁ .

The control circuit 41 monitors the voltage v _o at the connection point between the diode D ₁ and the capacitor C _1, and turns on / off the switch 42 so that the voltage v _o becomes a predetermined value V.
The pulse width to be changed is output to the switch 42.

In the separately-excited flyback type switching power supply, the period of the pulse for turning on / off the switch 42 is constant, so that the switch 42 is turned on.
By the ON / OFF operation, the frequency of noise (noise due to switching) on the power source becomes only a constant frequency. Therefore, this noise can be easily removed,
It is possible to provide a noise-free voltage (current).

In the separately-excited flyback type switching power supply configured as described above, when the switch 42 is in the ON state, the voltage v _i is applied to both ends of the coil L _P , and i _P = (1 / L _P ) ∫v _i dt = (v _i / L _P ) t A current i _P according to (1) flows, and the current in the transformer 2 (coil L _P
Magnetic flux is generated in the coil and in the coil L _S.

When the switch 42 is turned off, no current flows in the coil L _P , and the magnetic flux generated in the transformer 2 starts to decrease. However, in order to counter the change (decrease) in this magnetic flux, the coil L _S does not. A voltage (back electromotive force) is generated, and in the order of coil L _S → diode D ₁ → capacitor C ₁ → coil L _S , i _S =-(1 / L _S ) ∫ (v _O + v _F ) dt =-( The current i _S according to (v _O + v _F ) / L _S ) t (2) flows. The voltage v _F is the voltage drop in the diode D ₁ and the voltage v _O is the capacitor C
It is the voltage across ₁ .

Therefore, as shown in FIG.
When 2 is ON, the primary coil L _{P of} transformer 2
, A current i _P that increases by v _i / L _P per unit time flows, and when the switch 42 is in the OFF state, the secondary coil L _S of the transformer 2 has (v _O + v _F ) / L per unit time. _P
A current i _S that gradually decreases flows.

The current (ripple current) i _S flowing through the secondary side of the transformer 2 is smoothed by the capacitor C ₁ and supplied to the device connected to the output terminal 10.

[0010]

By the way, since the smoothing capacitor C ₁ has almost no electric charge immediately after the start of the separately excited flyback type switching power supply shown in FIG. 15, that is, when v _O ≈0. Therefore, when the switch 42 is in the OFF state, the coil L
_From the equation (2), the current i _S flowing through _S is i _S = − (v _F / L _S ) t (3). The voltage v _F is about 0.7 V because it is the voltage drop in the diode D ₁ , and therefore the current i
_S hardly decreases during the OFF period of the switch 42.

Therefore, when the switch 42 is turned on again, in the coil L _P , the current i _S flowing through the coil L _S causes the current i corresponding to the magnetic flux generated in the transformer 2 to change to the coil L _P. A large current i _P , which is superimposed on the flowing current due to the voltage v _i being applied to it, flows.

Since the capacitor C ₁ is a smoothing capacitor, its capacitance is large, and therefore it takes time for the capacitor C ₁ to be charged. Therefore, the above operation is repeated during this period (FIG. 17), There has been a problem that a large current i _P flows through the coil L _P , the transformer 2 is saturated, and the device is destroyed.

Therefore, the inductance of the coil L _P is increased to limit the current i _P flowing therethrough, and the transformer 2
There is a method to prevent saturation. However, the coil L
_In order to increase the inductance of _P , the coil L _P must be physically large, which causes a problem of increasing the size of the device.

The present invention has been made in view of the above circumstances, and is intended to prevent the device from being destroyed and to make the device compact.

[0015]

According to a first aspect of the present invention, there is provided a power supply control device for a separately excited flyback type switching power supply.
Generating a start / steady switching signal as pulse cycle switching means for switching the current flowing in the secondary coil L _P , for example, switching the cycle of a pulse given to a switching element such as the field effect transistor 9 in two stages at startup and at steady state. vessel 5 (resistor R ₃₁ to R _33, a capacitor C _31, the power source V _R, and the comparator 21 or the resistor R _{4 1,} resistors R _42,, power V _TH, and the comparator 31), the triangular wave generator 6, as well as the comparator 7 It is characterized by being provided.

This power supply control device has a pulse width limiting circuit 4 (resistor R ₂₁ and capacitor C ₂₁ , as pulse width control means for controlling the ratio of the pulse width to the period of the pulse given to the field effect transistor 9 at the time of start-up). Alternatively, the power source V _L ), the switch SW, and the comparator 7 can be further provided.

[0017]

In the power supply control device according to the first aspect, the primary side coil L of the separately excited flyback type switching power supply is provided.
The period of the pulse given to the field effect transistor 9 for switching the current flowing in _P is switched between two stages at the time of startup and the steady state. Therefore, when the separately-excited flyback type switching power supply is activated, it is possible to prevent a large current from flowing through the primary side coil L _P and destroying the device.

When the ratio of the pulse width to the pulse period applied to the field effect transistor 9 is controlled at startup, the device is prevented from being destroyed.

[0019]

1 is a block diagram showing the configuration of an embodiment of a separately excited flyback type switching power supply to which the power supply control device of the present invention is applied. The parts corresponding to those in FIG. 15 are designated by the same reference numerals. Power supply 1
Is a DC power supply (see FIG. 2).
(A)), the output of the AC power supply 12 is the diode D _{11 to} D
Capacitor-input type power supply that performs full-wave rectification with a diode bridge consisting of ₁₄ and smoothes it with a capacitor C ₁₂ (Fig. 2
(B)), or a power factor correction type power supply in which the smoothing capacitor C ₁₂ of the capacitor input type power supply is removed (Fig. 2).
(C)) etc., and the primary coil L of the transformer 2
It is connected in parallel with _P via a field effect transistor (FET) 9 and outputs a DC voltage v _i .

In the DC power supply shown in FIG. 2A, a DC power supply 11 and a bypass capacitor C ₁₁ are connected in parallel, and noise on the DC power supply 11 is removed by the capacitor C ₁₁ and output. It is supposed to be done. In the capacitor input type power supply of FIG. 2B, the noise on the output of the AC power supply 12 is removed by the noise filter 13, and the output of the noise filter 13 is a diode bridge composed of the diodes D _{11 to} D _14. Full-wave rectification is performed, smoothed by the capacitor C ₁₂ , and output. In the power factor correction type power supply of FIG. 2 (c),
The configuration is such that the smoothing capacitor C ₁₂ of the capacitor input type power supply of FIG. 2B is removed, and the power factor of the output is larger than that of the capacitor input type power supply.

[0021] In the diode bridge shown in FIG. 2 (b) or FIG. 2 (c), the anode of the cathode and the diode D ₁₂ of the diode D _11, the cathode of the cathode and the diode D ₁₃ of the diode D _12, a diode D ₁₃ The anode of the diode D _{14 and} the cathode of the diode D ₁₄ , the diode D ₁₄
And the anode of the diode D ₁₁ are connected to each other, and the voltage of the AC power supply 12 is connected to the connection points of the diodes D ₁₁ and D _{12 and} the connection points of the diodes D ₁₃ and D ₁₄ via the noise filter 13. The applied and full-wave rectified output is obtained from the connection point of the diodes D ₁₂ and D _{13 and} the connection point of the diodes D ₁₁ and D ₁₄ .

The FET 9 is a switch 42 in FIG.
The drain is connected to one end of the primary side coil L _P of the transformer 2 and the source is connected to one end of the power supply, and the gate is connected to the drive circuit 8. The FET 9 is turned on / off in response to the drive pulse supplied from the drive circuit 8 to its gate.
Control the current i _p flowing through the coil L _P (ON / OFF)
To do.

The resistors R ₁ and R ₂ are connected in series, and one end of the resistor R ₁ which is not connected to the resistor R ₂ is connected to the connection point between the diode D ₁ and the capacitor C _1. There is. One end of the resistor R ₂ which is not connected to the resistor R ₁ is connected to the ground. Therefore, the series circuit including the resistors R ₁ and R ₂ divides the voltage v _O at the connection point between the diode D ₁ and the capacitor C ₁ .

The error amplifier 3 has its inverting input terminal connected to the connection point between the resistors R ₁ and R _2, and its non-inverting input terminal connected to the ground via the power supply V _ref .
The resistor R ₃ has one end connected to the inverting input terminal of the error amplifier 3 and the other end connected to the output terminal of the error amplifier 3, and negatively feeds back the output of the error amplifier 3. Therefore,
The circuit including the error amplifier 3 and the resistor R ₃ has a voltage V _ref
And the voltage v _O amplifies the difference between the voltage divided by the resistors R ₁ and R ₂ .

The switch SW is controlled by the start / steady switching signal generator 5 and is connected to the output terminal of the error amplifier 3 or the terminal a or the terminal b of the pulse width limiting circuit 4. One of them is selected and connected to the non-inverting input terminal of the comparator 7.

The start-up / steady-state switching signal generator 5 comprises resistors R _{31 to} R ₃₃ , a capacitor C ₃₁ , a power supply V _R , and a comparator 21, as shown in FIG. 3, and includes a switch SW and a triangular wave generator 6. Control. The resistors R ₃₁ and R ₃₂ are connected in series, and the connection point is connected to the inverting input terminal of the comparator 21. The resistor R ₃₃ and the capacitor C ₃₁ are connected in series, and the connection point is connected to the non-inverting input terminal of the comparator 21. One end of the resistor R ₃₁ that is not connected to the resistor R ₃₂ or one end of the resistor R ₃₃ that is not connected to the capacitor C ₃₁ is connected to the + terminal of the power supply V _R , respectively. One end of the resistor R ₃₂ that is not connected to the resistor R ₃₁ , one end of the capacitor C ₃₁ that is not connected to the resistor R ₃₃ , or the negative terminal of the power supply V _R is connected to the ground, respectively. ..

The pulse width limiting circuit 4 is composed of a resistor R ₂₁ and a capacitor C ₂₁ , as shown in FIG. 4, for example. One end of the capacitor C ₂₁ is connected to the terminal b of the switch SW, and the other end is connected to the ground. One end of the resistor R ₂₁ is connected to the output terminal of the error amplifier 3, and the other end is connected to the connection point between the terminal b of the switch SW and the capacitor C ₂₁ .

The triangular wave generator 6 is controlled by the start / steady switching signal generator 5 to generate (oscillate) a triangular wave of low frequency f ₁ or a triangular wave of high frequency f ₂ and output it to the inverting input terminal of the comparator 7. To do.

The comparator 7 is a triangular wave generator that receives the output of the error amplifier 3 or the output of the pulse width limiting circuit 4 and its inverting input terminal, which are input to its non-inverting input terminal via the switch SW. Compared with the triangular wave output from 6, if the signal voltage input to the non-inverting input terminal is higher than the signal (triangular wave) voltage input to the inverting input terminal, a predetermined positive voltage (pulse) Is output to the drive circuit 8.

The drive circuit 8 supplies a drive pulse to the gate of the FET 9 in response to the pulse output from the comparator 7.

The power supply V _ref (FIG. 1) and the power supply V
_R (FIG. 3) is designed to generate a voltage when the device starts to operate.

Next, the operation will be described. When the device is activated, the power supply V _ref (FIG. 1) and the power supply V _R (FIG. 3) start to generate voltage. In the start-up / steady-state switching signal generator 5 (FIG. 3), the voltage V _R is equal to the resistance R ₃₁ and the resistance R.
_Applied to ₃₃ . The voltage V _R applied to the resistor R ₃₁ is divided by the resistors R ₃₁ and R ₃₂ and applied to the inverting input terminal of the comparator 21. On the other hand, the resistor R ₃₃ and the capacitor C ₃₁ applied to the non-inverting input terminal of the comparator 21.
The voltage at the connection point of rises slowly due to the delay action of the capacitor C ₃₁ .

That is, the voltage shown in FIG. 5A is applied to the inverting input terminal (point H) and the non-inverting input terminal (point G) of the comparator 21. Therefore, the output of the comparator 21 is at the L level until the predetermined time T ₀ after starting the device, and then becomes the H level (FIG. 5B).

When the output of the start-up / steady-state switching signal generator 5 is at L level (from the time when the apparatus is started to the time T ₀ ) (when the apparatus is started), the triangular wave generator 6 generates a triangular wave of low frequency f ₁ . The output is output to the inverting input terminal of the comparator 7, and the terminal b is selected by the switch SW.
When the output of the start-up / steady-state switching signal generator 5 is at the H level, the triangular wave generator 6 outputs the triangular wave of high frequency f _{2 to} the inverting input terminal of the comparator 7, and the terminal a is selected by the switch SW. To be done.

On the other hand, in the error amplifier 3, the voltage V _ref is applied to its non-inverting input terminal immediately after the device is activated. Immediately after activation of the device to be applied to the inverting input terminal of the error amplifier 3, the voltage v _O is the resistors R ₁ and R ₂ and de-divided voltage, charge to the capacitor C ₁ is almost charged as described above not without because it is almost 0V, in the circuit composed of the error amplifier 3 and the resistor R _3, the voltage V _ref is amplified and output to the switch SW of the terminal a (point a).

The voltage at the terminal a of the switch SW is applied to the resistor R ₂₁ of the pulse width limiting circuit (FIG. 4), this voltage is divided by the resistor R ₂₁ and the capacitor C _21, and the terminal b of the switch SW is applied. It is output to (point B). The voltage output to the terminal b (point B) of the switch SW slowly rises to the output voltage of the error amplifier 3 due to the delay action of the capacitor C ₂₁ (FIG. 6).

Immediately after the start of the apparatus, the triangular wave of the low frequency f ₁ (FIG. 7) output from the triangular wave generator 6 is input to the inverting input terminal (point D) of the comparator 7 as described above. At the non-inverting input terminal (point C), the slowly rising voltage (FIG. 6 or 7) output from the pulse width limiting circuit 4 via the terminal b selected by the switch SW is received. Is being applied.

Therefore, from the output terminal (point E) of the comparator 7, a pulse having a low frequency f ₁ as shown in FIG. 8 in which the ratio of the pulse width to the cycle gradually increases is output to the drive circuit 8.

In the drive circuit 8, the comparator 7
The drive pulse for driving (ON / OFF) the FET 9 corresponding to the pulse output from the FET 9 is
Is supplied to the gate. In the FET 9, its drain and source are turned on / off in response to a drive pulse (FIG. 8) applied to its gate at a low frequency f ₁ and the ratio of the pulse width to the cycle gradually increases.

[0040] When FET9 is in the ON state, the voltage v _i applied by the power source 1 is applied to the both ends of the coil L _P, the current flows i _P in accordance with equation (1), inside the transformer 2 (the coil L _P and Magnetic flux is generated in the coil L _S ).

When the FET 9 is turned off, the coil L
No current flows to the _P, although the magnetic flux generated in the transformer 2 starts to decrease, as against the change of the magnetic flux (reduction), the voltage (counter electromotive force) is generated in the coil L _S, the coil L _S In the order of → diode D ₁ → capacitor C ₁ → coil L _S , the current i _S according to the equation (2) flows.

As described above, since the current smoothing capacitor C ₁ has almost no electric charge immediately after the start-up of the device, the current i _S flowing through the coil L _S when the FET 9 is in the OFF state. , Flows according to the equation (3) in which the voltage v _O in the equation (2) is set to 0,
The drive pulse supplied to the gate of the ET9 has a low frequency f ₁ and a small ratio of the pulse width to the period.
The OFF period of the FET 9 is long, and thus the current i _S is sufficiently reduced during this OFF period.

As the current i _S decreases, this current i _S
There is also reduced magnetic flux that has been generated in the transformer 2 (coil L _S) by flowing through the coil L _S. FET9 again
If There turned ON, in the coil L _P, it is generated in the transformer 2 (coil L _S), a current i corresponding to the fully reduced magnetic flux, voltage v _i of the power supply 1 can take in the coil L _P A current i _P superposed on the current flowing due to

The above operation is repeated until the time T ₀ after starting the device, and the capacitor C ₁ is charged with a predetermined amount of electric charge. The time T ₀ can be changed by changing the value of the resistor R ₃₁ or the resistor R ₃₂ , or the resistor R ₃₃ or the capacitor C _31.
It is set according to the capacity of ₁ .

After a lapse of a predetermined time T ₀ after the start-up of the device, the voltage (point G) of the capacitor C ₃₁ of the start-up / steady-state switching signal generator 5 (FIG. 3) becomes equal to the resistance R ₃₁ and the resistance R ₃₂ . The voltage at the connection point (point H) is exceeded (Fig. 5 (a)), and the comparator 2
1, the output of the start / steady switching signal generator 5 is H
It becomes the level (Fig. 5 (b)).

When the output of the start-up / steady-state switching signal generator 5 becomes the H level, as described above, in the triangular wave generator 6, the triangular wave of the high frequency f ₂ (FIG. 7) is input to the inverting input terminal (point D ) And the terminal a is selected by the switch SW.

In the circuit composed of the error amplifier 3 and the resistor R ₃ , the voltage v _O applied to the inverting input terminal of the error amplifier 3 and corresponding to the charge charged in the capacitor C ₁ at the time of starting the device is the resistor R ₁ And the voltage divided by the resistor R ₂ and the voltage V applied to its non-inverting input terminal
The difference from _ref , that is, the voltage v with respect to a predetermined reference voltage V _REG
The error (error voltage) of _O (FIG. 7) is amplified, and the switch S
It is supplied to the non-inverting input terminal (point C) of the comparator 7 via the terminal a of W.

On the other hand, as described above, in the triangular wave generator 6, the triangular wave of high frequency f ₂ (FIG. 77) is output to the inverting input terminal (point C) of the comparator 7. Therefore, when the output of the start-up / steady-state switching signal generator 5 becomes H level (after the time T ₀ has passed since the device was started),
In the comparator 7, from its output terminal (point E),
A pulse having a high frequency f ₂ as shown in FIG. 8 is output to the drive circuit 8.

In the drive circuit 8, the comparator 7
The drive pulse for driving (ON / OFF) the FET 9 corresponding to the pulse output from the FET 9 is
Is supplied to the gate. A drive pulse of high frequency f ₂ applied to the gate of FET 9 (FIG. 8)
Corresponding to, the drain and the source are turned on / off.

[0050] When FET9 is in the ON state, the voltage v _i applied by the power source 1 is applied to the both ends of the coil L _P, the current flows i _P in accordance with equation (1), inside the transformer 2 (the coil L _P and Magnetic flux is generated in the coil L _S ).

When the FET 9 is turned off, the coil L
No current flows to the _P, although the magnetic flux generated in the transformer 2 starts to decrease, as against the change of the magnetic flux (reduction), the voltage (counter electromotive force) is generated in the coil L _S, the coil L _S In the order of → diode D ₁ → capacitor C ₁ → coil L _S , the current i _S according to the equation (2) flows.

As described above, when the FET 9 is in the ON state as shown in FIG. 16, the primary coil L _P of the transformer 2 has a current i _{P that} increases by v _i / L _P per unit time. And the FET 9 is in the OFF state, the secondary coil L _S of the transformer 2 receives (v _O +
v _F) / L _P by decreasing current i _S flows.

The current (ripple current) i _S flowing through the secondary side of the transformer 2 is smoothed by the capacitor C ₁ and supplied to the device connected to the output terminal 10.

When a heavy load (a heavy load device) is connected to the output terminal 10, a large amount of current flows through the load, and the voltage v _O across the capacitor C ₁ drops. Then, the voltage corresponding to the voltage v _O input to the inverting input terminal of the error amplifier 3 via the resistor R ₁ drops, so that the error amplifier 3 causes the comparator 7 via the switch SW.
The voltage output to the non-inverting input terminal (point C) becomes high. On the other hand, the triangular wave output from the triangular wave generator 6 to the inverting input terminal (point D) of the comparator 7 has a sharp upper portion (high voltage portion), so the comparator 7
At the high frequency f ₂ , a pulse having a large ratio of pulse width to the cycle is output from the output terminal of the drive circuit 8
Is output to. In the drive circuit 8, the drive pulse for driving (ON / OFF) the FET 9 corresponding to the pulse output from the comparator 7 is the FET
The FET 9 is turned on / off between its drain and source in response to a drive pulse having a high frequency f ₂ and a large pulse width ratio to the cycle, which is supplied to the gate of the FET 9.

[0055] Accordingly, since the time current i _P flows in the coil L _P increases, capacitor C current i _S flowing through the coil L _S increases, dropped by a heavy load is connected to the output terminal 10 The voltage v _O across ₁ rises.

When a light load (apparatus having a light load) is connected to the output terminal 10, almost no current flows through the load, so the voltage v _O across the capacitor C ₁ is reduced.
Rises. Then, the voltage corresponding to the voltage v _O inputted to the inverting input terminal of the error amplifier 3 via a resistor R ₁ is raised, from the error amplifier 3, the non-inverting input terminal (point of the comparator 7 via a switch SW The voltage output to C) is low. On the other hand, the triangular wave output from the triangular wave generator 6 to the inverting input terminal (point D) of the comparator 7 is
Since the lower part of the waveform (the part where the voltage is low) is widened, in the comparator 7, a pulse having a high frequency f ₂ and a small ratio of the pulse width to the cycle is output from the output terminal to the drive circuit 8. In the drive circuit 8, a drive pulse for driving (ON / OFF) the FET 9 corresponding to the pulse output from the comparator 7 is supplied to the gate of the FET 9,
At 9, the high frequency f applied to its gate
_{In 2} , corresponding to the drive pulse whose ratio of the pulse width to the cycle is small, the drain and source are ON / OF.
F will be done.

[0057] Thus, since the time current i _P flows in the coil L _P becomes shorter, the capacitor C which current i _S flowing through the coil L _S is reduced, and increased by the light load is connected to the output terminal 10 The voltage v _O across ₁ drops.

Next, FIG. 9 is a block diagram showing the configuration of a second embodiment of a separately excited flyback type switching power supply to which the power supply control device of the present invention is applied. 1 or 15
The same reference numerals are given to the portions corresponding to the case of. The resistors R ₄₁ and R ₄₂ are connected in series, and one end of the resistor R ₄₁ which is not connected to the resistor R ₄₂ is connected to a connection point between the resistor R ₁ and the capacitor C ₁ . One end of the resistor R ₄₂ which is not connected to the resistor R ₁ is connected to the ground. Thus, the series circuit composed of the resistor R _{4 1} and the resistor R ₄₂ is dividing the voltage v _O across the capacitor C _1. The connection point between the resistors R ₄₁ and R ₄₂ is connected to the non-inverting input terminal of the comparator 31, and the inverting input terminal of the comparator 31 is connected to the ground via the power supply V _TH .

The circuit composed of the resistors R ₄₁ , R ₄₂ , the power supply V _TH and the comparator 31 corresponds to the start / steady state switching signal generator 5 of FIG. 1, and when the output of the comparator 31 is L level. At the time of starting the apparatus, the triangular wave generator 6 outputs the triangular wave of the low frequency f _{1 to} the inverting input terminal of the comparator 7, and the switch SW selects the terminal b. When the output of the comparator 31 is at the H level, the triangular wave generator 6 outputs the triangular wave of the high frequency f _{2 to} the inverting input terminal of the comparator 7, and the switch SW selects the terminal a.

The terminal b of the switch SW is connected to the ground via the power supply V _L. In addition, the power supply V _L is as shown in FIG.
It corresponds to the pulse width limiting circuit 4.

Next, the operation will be described. Immediately after starting the device, as described above, the capacitor C ₁ is hardly charged, and the voltage v _O is almost 0V. Therefore, the voltage v _O is
_The voltage divided by the resistor ₄₁ and the resistor R ₄₂ (FIG. 10) is also almost 0V, and almost 0V is applied to the non-inverting input terminal (point I) of the comparator 31. On the other hand, since the voltage (positive voltage) V _TH is applied to the inverting input terminal (point J) of the comparator 31, its output becomes L level (FIG. 14).

Therefore, immediately after the start-up of the apparatus, the triangular wave generator 6 outputs the triangular wave of the low frequency f _{1 to} the inverting input terminal of the comparator 7, and the switch SW selects the terminal b.

When the terminal b (point B) is selected by the switch SW, the voltage V _L (FIG. 11 or FIG. 12) is applied to the non-inverting input terminal (point C) of the comparator 7. Further, the inverting input terminal (point D) of the comparator 7 receives the triangular wave of the low frequency f ₁ output from the triangular wave generator 6 (FIG. 12), so the output terminal of the comparator 7 (point E). Therefore, a pulse having a low frequency f ₁ and a small ratio of the pulse width to the cycle is output to the drive circuit 8 as shown in FIG.

In the drive circuit 8, the comparator 7
The drive pulse for driving (ON / OFF) the FET 9 corresponding to the pulse output from the FET 9 is
Is supplied to the gate. In the FET 9, in response to a drive pulse (FIG. 13) having a low frequency f ₁ and a small ratio of the pulse width to the cycle, which is applied to the gate of the FET 9,
The drain and the source are turned on / off.

[0065] When FET9 is in the ON state, the voltage v _i applied by the power source 1 is applied to the both ends of the coil L _P, the current flows i _P in accordance with equation (1), inside the transformer 2 (the coil L _P and Magnetic flux is generated in the coil L _S ).

When the FET 9 is turned off, the coil L
No current flows to the _P, although the magnetic flux generated in the transformer 2 starts to decrease, as against the change of the magnetic flux (reduction), the voltage (counter electromotive force) is generated in the coil L _S, the coil L _S In the order of → diode D ₁ → capacitor C ₁ → coil L _S , the current i _S according to the equation (2) flows.

As described above, since the current smoothing capacitor C ₁ is not charged immediately after the device is started, the current i _S flowing through the coil L _S when the FET 9 is in the OFF state is as follows. a v _O in the equation (2) 0
The drive pulse supplied to the gate of the FET 9 has a low frequency f ₁ and a ratio of the pulse width to the period is small.
The FF period is long, so the current i _S is sufficiently reduced during this OFF period.

As the current i _S decreases, this current i _S
There is also reduced magnetic flux that has been generated in the transformer 2 (coil L _S) by flowing through the coil L _S. FET9 again
If There turned ON, in the coil L _P, it is generated in the transformer 2 (coil L _S), a current i corresponding to the fully reduced magnetic flux, voltage v _i of the power supply 1 can take in the coil L _P A current i _P superposed on the current flowing due to

After the device is activated, the above operation is repeated,
The capacitor C ₁ is gradually charged. Therefore, the voltage v _O across the capacitor C ₁ rises and the resistance R ₄₁
The voltage at the connection point between the resistor R ₄₂ and the resistor R ₄₂ , that is, the voltage applied to the non-inverting input terminal (point I) of the comparator 31 exceeds the voltage V _TH applied to its inverting input terminal (point J) (see FIG. 10), the output of the comparator 31 becomes H level (FIG. 14).

When the output of the comparator 31 becomes H level, the triangular wave generator 6 outputs the triangular wave of high frequency f ₂ (FIG. 12) to the inverting input terminal (point D) of the comparator 7 and the switch SW. The terminal a is selected.

Here, the voltage at the terminal a of the switch SW, that is, the output voltage of the error amplifier 3, is the same as in the case of FIG. 1, the voltage V _ref and the voltage v _O corresponding to the charge charged in the capacitor C _1. Is the difference between the voltage divided by the resistors R ₁ and R ₂ , that is, the error (error voltage) of the voltage v _O with respect to the predetermined reference voltage V _REG is amplified (FIG. 6 or FIG. 11). ..

Therefore, when the output of the comparator 31 becomes H level, the error amplifier 3 shown in FIG. 11 (FIG. 6) is connected to the non-inverting input terminal of the comparator 7 via the switch SW.
Output voltage is input, and the triangular wave (FIG. 12) of high frequency f ₂ is input to its inverting input terminal.

Then, in the comparator 7, as shown in FIG.
A pulse having a high frequency f ₂ and a large ratio of the pulse width to the cycle is output to the drive circuit 8. In the drive circuit 8, a drive pulse corresponding to the pulse output from the comparator 7 for driving (ON / OFF) the FET 9 is supplied to the gate of the FET 9. In the FET 9, its drain and source are turned on / off in response to a drive pulse (FIG. 13) applied to its gate at a high frequency f ₂ and having a large ratio of pulse width to period.

[0074] When FET9 is in the ON state, the voltage v _i applied by the power source 1 is applied to the both ends of the coil L _P, the current flows i _P in accordance with equation (1), inside the transformer 2 (the coil L _P and Magnetic flux is generated in the coil L _S ).

When the FET 9 is turned off, the coil L
No current flows to the _P, although the magnetic flux generated in the transformer 2 starts to decrease, as against the change of the magnetic flux (reduction), the voltage (counter electromotive force) is generated in the coil L _S, the coil L _S In the order of → diode D ₁ → capacitor C ₁ → coil L _S , the current i _S according to the equation (2) flows.

As described above, when the FET 9 is in the ON state as shown in FIG. 16, the primary coil L _P of the transformer 2 has a current i _{P which} increases by v _i / L _P per unit time. And the FET 9 is in the OFF state, the secondary coil L _S of the transformer 2 receives (v _O +
v _F) / L _P by decreasing current i _S flows.

The current (ripple current) i _S flowing through the secondary side of the transformer 2 is smoothed by the capacitor C ₁ and supplied to the device connected to the output terminal 10.

The operation of controlling the change of the voltage v _O to a constant value in accordance with the load of the device connected to the output terminal 10 is the same as in the case of FIG.

As described above, the period of the pulse given to the field effect transistor 9 for switching the current flowing in the primary side coil L _P of the separately excited flyback type switching power supply and the ratio of the pulse width to the period are defined as those at the time of starting. Since it has been set to switch to two stages with a constant time, when starting the separately excited flyback type switching power supply,
It is prevented that a large current flows through the primary coil L _P and the device is destroyed.

[0080]

According to the power supply control device of the first aspect of the present invention, the cycle of the pulse applied to the switching element for switching the current flowing through the primary side coil of the separately excited flyback type switching power supply is set at the start-up time and the steady-state time. Switch to two steps. Therefore, when the separately-excited flyback type switching power supply is started up, it is possible to prevent a large current from flowing through the primary coil of the switching power supply and destroying the device.

According to the power supply control device of the second aspect,
At the time of start-up, the ratio of the pulse width to the pulse period given to the switching element is controlled, so that the device is prevented from being destroyed.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a separately excited flyback type switching power supply to which a power supply control device of the present invention is applied.

2 is a circuit diagram showing a more detailed configuration of the power supply 1 of FIG.

3 is a more detailed circuit diagram of the start / steady state switching signal generator 5 of FIG.

FIG. 4 is a more detailed circuit diagram of a pulse width limiting circuit 4 of FIG.

5 is a waveform diagram of a voltage input and a voltage output to the comparator 21 of FIG.

6 is a waveform diagram of voltages at terminals a and b of the switch SW of FIG.

7 is a waveform diagram of a voltage input to the comparator 7 in FIG.

8 is a waveform diagram of a voltage output from the comparator 7 of FIG.

FIG. 9 is a block diagram showing the configuration of a second embodiment of a separately excited flyback type switching power supply to which the power supply control device of the present invention is applied.

10 is a waveform diagram of a voltage input to the comparator 31 of FIG.

11 is a waveform diagram of voltages at terminals a and b of the switch SW of FIG.

12 is a waveform diagram of a voltage input to the comparator 7 of FIG.

13 is a waveform diagram of a voltage output from the comparator 7 of FIG.

14 is a waveform diagram of a voltage output from the comparator 31 of FIG.

FIG. 15 is a block diagram showing a configuration of an example of a conventional separately excited flyback type switching power supply.

[16] Figure 1, in the steady state of the separately excited flyback type switching power supply of FIG. 9 or FIG. 15, the coil L _P
3 is a waveform diagram of a current flowing through a coil L _S and a coil L _S.

17 is a waveform diagram of currents flowing through the coil L _P and the coil L _S when the separately excited flyback type switching power supply shown in FIG. 15 is started.

[Explanation of symbols]

 1 power supply 2 transformer 3 error amplifier 4 pulse width limiting circuit 5 start / steady switching signal generator 6 triangular wave generator 7 comparator 8 drive circuit 9 field effect transistor (FET) 11 DC power supply 12 AC power supply 13 noise filter 21, 31 comparator 41 Control circuit 42 switch

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[Procedure amendment]

[Submission date] September 8, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0002

[Correction method] Change

[Correction content]

[0002]

2. Description of the Related Art FIG. 15 is a block diagram showing the configuration of an example of a conventional separately excited flyback type switching power supply. The primary coil L _P of the transformer 2 is connected via a switch 42 in parallel with the power source (DC power source) v _i.
Switch 42, the output pulses of the control circuit 41 (PW
ON / OFF corresponding to the M wave), and controls (ON / OFF) the current i _P flowing through the primary coil L _P of the transformer 2.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction content]

[0006] In another exciting flyback type switching power supply configured as described above, when the switch 42 is in the ON state, a voltage is applied v _i across the coil L _P, the coil L _P
Inclination .DELTA.i _P of the current flowing in the _{Δi P = d ((1 /} L P) ∫v i dt) / dt = (v i / L P) current i _P in accordance with the flow (1), trans within 2 ( Coil L _P
Magnetic flux is generated in the coil and in the coil L _S.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

When the switch 42 is turned off, the current stops flowing through the coil L _P , and the magnetic flux generated in the transformer 2 starts to decrease. However, the coil L _S should be opposed to the change (reduction) of this magnetic flux. voltage (counter electromotive force) is generated in the coil L _S → diode D ₁ → in the order of the capacitor C ₁ → coil L _S, the inclination .DELTA.i _S of the current flowing through the coil L _S is _{Δi S = d (- (1} / L _S ) ∫ (v _O + v _F ) dt) / dt = − ((v _O + v _F ) / L _S ) . The current i _S according to (2) flows. The voltage v _F is the voltage drop in the diode D ₁ and the voltage v _O is the capacitor C
It is the voltage across ₁ .

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

In the DC power supply of FIG. 2A, the DC power supply 11 and the bypass capacitor C ₁₁ are connected in parallel, and the noise on the DC power supply 11 is removed by the capacitor C ₁₁ and output. It is supposed to be done.
In the capacitor input type power supply of FIG. 2 (b),
The noise on the output of the AC power supply 12 is removed by the noise filter 13, and the output of the noise filter 13 is full-wave rectified by the diode bridge composed of the diodes D _{11 to} D ₁₄ and smoothed by the capacitor C ₁₂ and output. It is supposed to be done. In the power factor correction type power supply of FIG. 2 (c), the configuration is such that the smoothing capacitor C ₁₂ of the capacitor input type power supply of FIG. 2 (b) is removed . The power factor is getting bigger.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0043

[Correction method] Change

[Correction content]

[0043] with a current i _S is decreased, the current i _S is also reduced magnetic flux that has been generated in the transformer 2 (coil L _S) by flowing through the coil L _S. FET again
When 9 is turned ON, in the coil L _P, is generated in the transformer 2 (coil L _S), a current i corresponding to the fully reduced magnetic flux, voltage v _i of the power supply 1 is applied to the coil L _P As a result, the current i _P superimposed on the flowing current flows. In this case, the superimposed current is small enough,
By repeating ON / OFF of the current i _P ,
It becomes a large current and the transformer 2 is never saturated.

[Procedure Amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0058

[Correction method] Change

[Correction content]

Next, FIG. 9 shows a second embodiment of a separately excited flyback type switching power supply to which the power supply control device of the present invention is applied.
It is a block diagram which shows the structure of an Example. 1 or FIG.
The same reference numerals are given to the portions corresponding to the case in FIG. The resistors R ₄₁ and R ₄₂ are connected in series, and one end of the resistor R ₄₁ which is not connected to the resistor R ₄₂ is connected to a connection point between the resistor R ₁ and the capacitor C ₁ . One end of the resistor R ₄₂ , which is not connected to the resistor R _41, is connected to the ground. Therefore, the series circuit composed of the resistor R ₄₁ and the resistor R ₄₂ divides the voltage v _O across the capacitor C ₁ . The connection point between the resistor R ₄₁ and the resistor R ₄₂ is
It is connected to the non-inverting input terminal of the comparator 31,
The inverting input terminal of the comparator 31 is connected to the ground via the power supply V _TH .

[Procedure Amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0068

[Correction method] Change

[Correction content]

As the current i _S decreases, the current i _S also flows through the coil L _S , so that the magnetic flux generated in the transformer 2 (coil L _S ) also decreases. FET again
When 9 is turned ON, in the coil L _P, is generated in the transformer 2 (coil L _S), a current i corresponding to the fully reduced magnetic flux, voltage v _i of the power supply 1 is applied to the coil L _P As a result, the current i _P superimposed on the flowing current flows. In this case, the superimposed current is small enough,
By repeating ON / OFF of the current i _P ,
It becomes a large current and the transformer 2 is never saturated.

Claims (2)

[Claims] 1. A pulse cycle switching means for switching a cycle of a pulse given to a switching element for switching a current flowing through a primary side coil of a separately excited flyback type switching power supply between two stages at startup and at steady time. Power control device characterized by. 2. The power supply control device according to claim 1, further comprising pulse width control means for controlling a ratio of a width of the pulse to a cycle of the pulse given to the switching element at the time of starting.