JP2000287444A - Switching power circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable changeover of an intermittent frequency according to the condition of a load by providing a circuit which obtains an oscillation output from a timer circuit by charging and discharging a capacitor connected to a power line, and changing divided outputs of a frequency divider circuit provided in the timer circuit by a control signal. SOLUTION: A switching power circuit is provided with a timer circuit for forming an intermittent frequency in a stand-by state. In the timer circuit, a charging/discharging circuit performs oscillation by a voltage VD applied from a primary side, if supply of a voltage Vc from the secondary side is interrupted. Then, a frequency dividing circuit 25 divides the frequency of the output of the charging discharging circuit. The output of the dividing circuit 25 is selectively applied to a logic circuit by AND gates 26, 27 and an OR gate 28, which are switching circuit, according to a control circuit CONT3. Consequently, changeover setting of the frequency of intermittent driving to be performed according to the magnitude of the capacity of a load in a standing-by state becomes feasible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply circuit for generating a predetermined power supply voltage on a secondary side of a transformer by switching a current flowing on a primary side of the transformer.

[0002]

2. Description of the Related Art A switching power supply circuit is used as a power supply circuit used for a power supply of an electronic device such as a television or a video tape recorder. In such a switching power supply circuit, an integrated circuit having three to five terminals is used, and a switching transistor for switching the primary side of the transformer and a driving circuit for driving the switching transistor are integrated.

FIG. 5 is a block diagram showing such a switching power supply circuit. The AC power is rectified into DC by the bridge rectifier circuit 1 and supplied to one end of the primary winding of the transformer 2. The other end of the primary winding is connected to the switching drive IC 3. The output of the secondary winding 2a of the transformer 2 is rectified by the diode 4,
The power is supplied to an internal circuit as a main power supply V1 of the electronic device, and is also supplied to a microcomputer 5 for controlling the electronic device via a switch 6. The output of the secondary winding 2b is rectified by the diode 7 and supplied as power to the IC 3 via the phototransistor 8. The phototransistor 8 is used as a feedback signal input for controlling stabilization of the main power supply V1, and is optically coupled to a photodiode 9 connected to the main power supply V1. The secondary winding 2c of the transformer 2 is rectified by the diode 10 and the microcomputer 5 in the standby state of the electronic device.
Is applied to the microcomputer 5 via the switch 6 as the power supply V3.

The IC 3 includes a start circuit 11 for supplying a voltage to each part of the IC 3 to drive the IC 3 when the power is first turned on, and a phototransistor 8 for the IC 3.
Error detection circuit 12 for detecting a signal fed back to the power supply
A timer circuit 13 for determining intermittent feedback for intermittently performing a switching operation in a standby state;
A MOS transistor 14 for switching the primary winding of the transformer 2, an oscillation circuit 16 whose oscillation frequency is switched by a switch 15 whose opening and closing are controlled by a signal from the microcomputer 5, and an error detection circuit for detecting the oscillation output of the oscillation circuit 16 P that performs pulse width modulation based on the output of
It comprises a WM circuit 17 and a logic circuit 18 for applying a pulse-width-modulated signal to the MOS transistor 14 according to the output state of the timer circuit 13.

The operation of FIG. 5 will be described. When no power is supplied, no voltage is generated in the secondary winding 2b of the transformer, and no power supply voltage is supplied to the IC 3, so that the IC 3 does not operate. When the power is turned on for the first time, the voltage rectified by the bridge rectifier circuit 1 is supplied from the primary winding of the transformer 2 to the start circuit 11.
Is supplied to the IC 3 via the. Thereby, the operation of the IC 3 is started, and the oscillation of the oscillation circuit 16 is started. The oscillation frequency of the oscillation circuit 16 at this time is 100 KHz. The error detection circuit 12 at power-on generates an output such that the duty ratio gradually increases, so that the oscillation output is subjected to pulse width modulation in an initial state by the PWM circuit 17. The output of the PWM circuit 17 is applied to the MOS transistor 14 via the logic circuit 18, and the MOS transistor 14 performs the switching operation of the primary winding according to the pulse width modulated signal. As a result, a voltage is generated in each secondary winding of the transformer 2. Thereby, the microcomputer 5 also operates, and the microcomputer 5 operates the emitting diode 9 according to the output signal. Therefore, the phototransistor 8 is turned on, and the voltage of the secondary winding 2b becomes IC3.
Supplied to When a voltage is supplied to the IC 3, the start circuit 11 stops operating and stops supplying power from the primary winding to the inside of the IC 3. Thereby, the normal operation state is maintained.

Next, in a standby state, that is, in a state where the inside of the electronic device does not require a power supply and only the microcomputer 5 is in an operating state, the microcomputer 5 controls the switch 6 based on the output to control the power supply of the microcomputer 5 itself. Is switched to the power supply from the secondary winding 2c having a small current capacity, and the operation of the light emitting diode 9 is stopped. As a result, the phototransistor 8 is turned off, so that the IC
Since the power supply to the IC 3 is stopped, the power of the IC 3 is supplied from the start circuit 11. At this time, a charging current flows through the capacitor 19 connected to the power supply of the IC 3, and I
The power supply voltage of C3 increases. When the power supply voltage reaches a predetermined level, for example, 5.6 V, the timer circuit 13 stops the power supply from the start circuit 11. Then, a discharge current flows from the capacitor 19, and the power supply voltage decreases. When the voltage of the power supply voltage decreases to a predetermined voltage, for example, 4.7 V, the timer circuit 13 starts power supply from the start circuit 11 again. With such an operation, the 4.7 V and 5.
A triangular wave having an amplitude of 6 V is repeatedly generated. Then, the timer circuit 13 counts the period of the triangular wave, and controls the logic circuit 18 every eight periods, for example, so that the PWM circuit
The output of the circuit 17 is applied to the MOS transistor 14.
The period for controlling the MOS transistor 14 is a discharging period of the capacitor 19, that is, a falling period of the triangular wave.
Further, in the standby state, the microcomputer 5 turns on the switch 6 to switch the oscillation frequency of the oscillation circuit 16 to 20 kHz. Therefore, the MOS transistor 14 is driven at a predetermined interval for a predetermined time at a frequency of 20 KHz. As a result, power consumption in the standby state is reduced.

[0007]

In the intermittent operation of the switching power supply circuit shown in FIG. 5, a switching operation is performed every eight periods, and a voltage is generated in the secondary winding 2C of the transformer during that period. Power is supplied to the microcomputer 5. However, the power supply in the standby state is not limited to the microcomputer 5 alone, and circuits and devices driven by various applications other than the microcomputer can be considered. For example, there are a liquid crystal display device and a fluorescent display tube for displaying time and the like. Therefore, the load capacity in the standby state changes variously depending on these circuits and devices.

However, if the intermittent operation is performed in the standby state in order to reduce the power consumption, a sufficient voltage cannot be supplied depending on the magnitude of the load capacity, which may cause malfunction of the microcomputer 5 or the like. Was.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has a switching element for switching a current flowing through a primary side of a transformer, and a switching frequency signal for the switching element. An oscillation circuit for detecting a feedback signal from a secondary side of the transformer, a pulse width modulation circuit for pulse width modulation of an output of the oscillation circuit based on a detection output of the error detection circuit, and a normal operation. A logic circuit for continuously or intermittently supplying an output of the pulse width modulation circuit to a switching element according to a state and a standby state, and a switching power supply circuit including a timer circuit for generating an intermittent frequency in the standby state, wherein the timer circuit Is the 2
A charging / discharging circuit for performing an oscillating operation by a voltage from the primary side by interrupting a voltage supply from the secondary side, a frequency dividing circuit for dividing the output of the charging / discharging circuit, Is selectively applied to the logic circuit, the intermittent frequency can be switched according to the state of the load.

The charge / discharge circuit includes a capacitor provided on a power supply line supplied from a secondary side of the transformer, a start circuit for supplying a voltage to the capacitor from a primary side of the transformer, A voltage detecting circuit for detecting the voltage of the line and controlling the operation of the start circuit is provided, and the frequency dividing circuit obtains an intermittent frequency by dividing the output of the voltage detecting circuit.

Further, a switching element for switching a current flowing to a primary side of the transformer, an oscillation circuit for generating a switching frequency signal of the switching element, and an error detection circuit for detecting a feedback signal from a secondary side of the transformer A pulse width modulation circuit that pulse width modulates an output of the oscillation circuit based on a detection output of the error detection circuit;
A logic circuit that continuously or intermittently supplies the output of the pulse width modulation circuit to the switching element according to a normal operation state and a standby state, and a switching power supply circuit including a timer circuit that creates an intermittent frequency in the standby state. The oscillation circuit has a frequency switching circuit whose oscillation frequency is switched by a control signal, and the timer circuit performs an oscillation operation by a voltage from the primary side by cutting off a voltage supply from the secondary side. A divider circuit for dividing the output of the charge / discharge circuit, and a selector circuit for selectively applying the output of the divider circuit to the logic circuit in accordance with the control signal. Can be used also as a switching terminal of the selection circuit, and the number of terminals Increase in which to prevent.

[0012]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. The same parts as those in FIG. 5 are designated by the same reference numerals and their description is omitted.

This embodiment is characterized in that an oscillation output is obtained from a timer circuit 13 by charging / discharging a capacitor C connected to a power supply line Vc.
3 is divided by a control signal CONT
3 is provided.

FIG. 2 shows the start circuit 1 shown in FIG.
1 is a specific circuit block diagram of a timer circuit 13 and a switching circuit 19. FIG. The power line Vc of the IC 3
A capacitor C is connected to the outside. The power supply line Vc is connected to a voltage detection circuit 20 for detecting that the voltage has dropped to 4.7 V and a voltage detection circuit 21 for detecting that the voltage has reached 5.6 V or more. Outputs of the detection circuits 20 and 21 are connected to a reset terminal R and a set terminal R of the flip-flop 22. The output Q of the flip-flop 22 is applied via an inverter 23 to the gate of an N-channel MOS transistor 24 serving as a start circuit. The MOS transistor 24 is provided between the power supply line Vc and the primary winding of the transformer 2, that is, the line VD driven by the switching transistor 14. These circuits form a charge / discharge circuit.

The output Q of the flip-flop 22 is
It is connected to the input of a frequency dividing circuit 25 that constitutes a timer circuit. The outputs Q1, Q2, Q3 of the frequency divider 25 and the output Q of the flip-flop 22 are applied to an AND gate 26,
The output Q1 of the frequency divider 25 and the output of the flip-flop 22 are applied to the AND gate 27. The AND gate 26 is a decoder that detects １ ／ frequency division, and the AND gate 27 is a decoder that detects １ ／ frequency division. Furthermore,
A complementary signal of the control signal CONT3 is applied to the AND gates 26 and 27.
One of the gates 26 and 27 is switched to operate. The outputs of the AND gates 26 and 27 are input to the OR gate 28, and the output of the OR gate 28 is the intermittent frequency signal CL.
It is applied to the logic circuit 18 as K. These AND
The gates 26 and 27 and the OR gate 28 constitute a switching circuit.

Next, the operation in the standby state will be described.
In the standby state, the light receiving transistor 8 is turned off, so that no voltage is supplied from the secondary side of the transformer to the power supply line Vc. As a result, the voltage of the power supply line Vc decreases. When the voltage falls to 4.7 V or less, the output of the voltage detection circuit 20 goes high and the flip-flop 2
2 is reset. Therefore, the output of the inverter 23 becomes “H” level, the MOS transistor 24 is turned on, the primary side voltage VD is supplied to the power supply line Vc, and the capacitor C is charged. The power supply line V
When the voltage of c rises to 6.5 V or more, the voltage detection circuit 2
1 goes high, flip-flop 2
2 is set. Then, the output of the inverter 23 becomes “L” level, so that the MOS transistor 24 is turned off, and the capacitor C is discharged. By repeating this, a triangular wave is generated on the power supply line Vc. The output Q of the flip-flop 22 is a rectangular wave having the same frequency as the triangular wave. The frequency is set to about 10 Hz.

The frequency dividing circuit 25 is a circuit for counting the rise of the output Q of the flip-flop 22. When the counted output "Q3, Q2, Q1" becomes "111", AND operation is performed.
The gate 26 outputs “H” from the output Q of the flip-flop 22.
During the level period, that is, during the period when the MOS transistor 24 is off, an “H” level signal is output. Therefore,
It becomes 1/8 frequency-divided output. On the other hand, when the count output Q1 becomes "1", the AND gate 27 turns on the flip-flop 22.
Output a signal at the "H" level during the "H" level of the output Q. Which of the AND gate outputs is selected is selected by the control signal CONT3. Control signal CON
If T3 is "H" and a bell, AND gate 26
出力, that is, the intermittent frequency of 1.25 Hz is selected, and when the control signal CONT3 is at the “L” level, the 1/2 frequency output of the AND gate 27, that is, the intermittent frequency of 5 Hz is selected. Selected.

As described above, in the standby state, the frequency of the intermittent operation for intermittently switching the MOS transistor 14 is switched by the control signal CONT3 from the outside.

On the other hand, in the standby state, the oscillation frequency of the oscillation circuit 16 can be selected. That is, the oscillation frequency of the oscillation circuit 16 is set to 10 by the control signal CONT2.
It is also possible to select 0 KHz and 20 KHz.

Therefore, in the standby state, the intermittent frequencies are 1.25 Hz and 5 Hz in accordance with the state of the load.
And the oscillation frequency of the oscillation circuit 16 can be set in combination with one of 100 kHz and 20 kHz.

FIG. 3 is a block diagram showing a second embodiment of the present invention. The difference from the embodiment of FIG. 1 is that a switch 1 for switching the oscillation frequency of the oscillation circuit 16 is provided.
5 is that the control signal CONT3 of the frequency division number switching circuit 19 is obtained from the terminal to which the terminal 5 is connected. That is, in the normal operation state, the control signal CONT2 from the microcomputer 5 is at the “L” level, and the switch 15 is opened. At this time, the oscillation circuit 16 oscillates at an oscillation frequency of 100 KHz.

On the other hand, in the standby state, as described above, the phototransistor 8 is turned off to operate the timer circuit 13 and start oscillation at 10 Hz.
At this time, when the control signal CONT2 from the microcomputer 5 is at the “L” level, the switch 15 is open, and the frequency switching terminal of the oscillation circuit 16 is pulled up to the “H” level. At this time, the oscillation frequency of the oscillation circuit 16 is 100 KHz. Switching circuit 1
9 is also at the “H” level. Therefore, the switching circuit 19 outputs a 1/8 frequency-divided output, that is, an intermittent frequency of 1.25 Hz. In this state, the intermittent frequency is 1.25 Hz and the oscillation frequency is 100K.
Hz operating state.

When the microcomputer 5 sets the control signal CONT2 to "H" level in the standby state, the switch 15 is closed, and the frequency switching terminal of the oscillation circuit 16 is lowered to "L" level. As a result, the oscillation frequency of the oscillation circuit 16 becomes 20 KHz. Further, the switching circuit 19 outputs a 1/2 frequency divided output, that is, an intermittent frequency of 5 Hz. In this state, the intermittent frequency is 5 Hz and the oscillation frequency is 20 KHz.

As described above, according to the embodiment of FIG. 3, two types of standby operation states can be selected by the control signal applied to the frequency switching terminal of the oscillation circuit 16, and the special switching circuit 19 as shown in FIG. A terminal for controlling is unnecessary.

FIG. 4 is a specific circuit example of the oscillation circuit 16. In the figure, N channel MOSs 30 and 31 have their gates connected to each other to form a current mirror circuit. The drains of the N-channel MOSs 30 and 31 each have a P
Channel MOSs 32 and 33 are connected, and a P-channel MO
The sources of S32 and S33 are commonly connected to the drain of a P-channel MOS 34 whose source is connected to the power supply Vdd. A capacitor 35 is connected between the drain of the N-channel MOS 30 and the ground.
Connected to. The reference voltage Vref1 and the reference voltage Vref2 are applied to the comparison circuit 36. The output of the comparison circuit 36 is applied to the inverter 37. The inverter 37
Is applied to the inverter 38. Then, the output of the inverter 38 is taken out as the oscillation output OSCOUT. The output of the inverter 37 is a P-channel M
OS32 gate, the output of inverter 38 is P
The voltage is applied to the gate of the channel MOS 33.

The gate of the P-channel MOS 34 is
Connected to the gate of P-channel MOS 39, it forms a current mirror circuit. An N-channel MOS 40 is connected between the P-channel MOS 39 and the ground, and a circuit in which an N-channel MOS 41 and an N-channel MOS 42 are connected in series is provided. Further, N-channel MOSs 40 and 4
The 1 and N-channel MOS 44 have their gates connected in common to form a current mirror circuit. Where MOS 40 and M
The OS 44 has the same size, and the transistor size of the MOS 41 is, for example, in a relationship of 1: 4. The N-channel MOS 44 has a gate connected to the bias voltage Vbias and a P-channel MOS 45 serving as a constant current source. The gate of N-channel MOS 42 is connected to frequency switching terminal 46 and to power supply Vdd by pull-up resistor 47. The frequency switching terminal 46 has
The switch SW2 shown in FIG. 1 is connected.

Next, the oscillation operation will be described. When the terminal voltage of the capacitor 35 is smaller than the reference voltage Vref1, the output of the comparison circuit 36 is at "H" level, the output of the inverter 37 is at "L" level, and the output of the inverter 38 is at "H" level. Therefore, the MOS 32 is on, M
The OS 33 is turned off, and the MOS 30 and the MOS 31 are also turned off. As a result, the current Ia flowing through the MOS 34
Flows into the capacitor 35, and the terminal voltage of the capacitor 35 increases. The terminal voltage of the capacitor 35 is equal to the reference voltage Vr.
When it becomes larger than ef1, the output of the comparison circuit 36 becomes “L”.
Level. Then, the MOS 32 is turned off, and the MOS 33
And the MOSs 30 and 31 are turned on, so that the MOS 3
4 flows through the MOSs 33 and 31.
Therefore, the discharge current from the capacitor 35 flows through the MOS 30, and the terminal voltage of the capacitor 35 decreases. When the terminal voltage of the capacitor becomes lower than the reference voltage Vref2, the output of the comparison circuit 36 becomes “H” level. By performing the same operation as described above, the terminal voltage of the capacitor 35 has a triangular waveform that repeats charging and discharging.

On the other hand, when the signal applied to the frequency switching terminal 46 is at "H" level, the MOS 42 is turned on.
The current flowing through the MOS 39 is a combined current of the MOS 40 and the MOS 41. The current flowing through the MOS 34 due to this current is Ia, and the oscillation frequency in this case is 100
KHz. Next, when an “L” level signal is applied to the frequency switching terminal 46, the MOS 42 is turned off, so that the current flowing through the MOS 39 is only the current flowing through the MOS 40. That is, it is 1/5 of the above case.
Therefore, in this case, the current flowing through the MOS 34 is also 1 /
5 and the charging / discharging current Ia of the capacitor 35 becomes 1/5, so that the oscillation frequency of the oscillation circuit becomes 20 KHz.

As described above, the oscillation frequency of the oscillation circuit is switched by the signal applied to the frequency switching terminal 46. This frequency switching terminal 46 is also used as a control signal CONT3 of the switching circuit 19.

[0030]

As described above, according to the present invention, the frequency of the intermittent drive can be switched according to the magnitude of the load capacity in the standby state, so that the power consumption can be reduced. , A stable voltage can be supplied to the secondary side. As a result, the application range of the switching power supply is expanded, and versatility is improved.

In the standby state, when the display is performed by the display device or when the display is turned off, the power supply can be controlled in accordance with the load state on the secondary side by switching the intermittent drive frequency. Therefore, power consumption can be reduced efficiently.

Further, the signal applied to the frequency switching terminal of the oscillation circuit can be used for switching the intermittent frequency without specially providing a terminal for the signal for controlling the switching of the intermittent frequency, so that the number of terminals is not increased. The function can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit block showing a specific example of the block shown in FIG. 1;

FIG. 3 is a block diagram showing a second embodiment of the present invention.

FIG. 4 is a specific circuit diagram of an oscillation circuit.

FIG. 5 is a block diagram showing a conventional example.

[Description of Signs] 1 Bridge rectifier circuit 2 Transformer 3 IC 4, 7, 10 Diode 5 Microcomputer 6, 15 Switch 8 Phototransistor 9 Light emitting diode 11 Start circuit 12 Error detection circuit 13 Timer circuit 14 Switching transistor 16 Oscillation circuit 17 Pulse width Modulation circuit 18 Logic circuit 19 Switching circuit 20, 21 Voltage detection circuit 22 Flip-flop 23 Inverter 24 N-channel MOS transistor 25 Divider circuit 26, 27 AND gate 28 OR gate

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Norifumi Ikeda 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Hiroshi Iizuka 2-chome Keihanhondori, Moriguchi-shi, Osaka No.5 Sanyo Electric Co., Ltd. F-term (reference) 5G065 AA01 BA02 DA06 DA07 EA06 FA02 GA07 HA01 HA12 HA16 JA01 JA07 LA01 MA07 MA10 NA01 NA09 5H730 AA14 BB21 BB57 CC01 DD04 EE02 EE73 FF06 FF09 FF19 FG05 FG07 V01

Claims (3)

[Claims] 1. A switching element for switching a current flowing to a primary side of a transformer, an oscillation circuit for generating a switching frequency signal of the switching element, and an error detection circuit for detecting a feedback signal from a secondary side of the transformer. A pulse width modulation circuit that performs pulse width modulation on an output of the oscillation circuit based on a detection output of the error detection circuit; and a switching element that continuously or intermittently outputs the output of the pulse width modulation circuit depending on a normal operation state and a standby state. And a switching power supply circuit comprising a timer circuit for creating the intermittent frequency in the standby state, wherein the timer circuit is configured to supply a voltage from the primary side by cutting off a voltage supply from the secondary side. A charge / discharge circuit for performing an oscillating operation, a frequency divider for dividing the output of the charge / discharge circuit, and a control signal A switching circuit for selectively applying an output of the frequency dividing circuit to the logic circuit according to a signal. 2. A charge / discharge circuit comprising: a capacitor provided on a power supply line supplied from a secondary side of the transformer; a start circuit for supplying a voltage to the capacitor from a primary side of the transformer; 2. The switching power supply circuit according to claim 1, further comprising a voltage detection circuit that detects a voltage of a line and controls an operation of the start circuit, wherein the frequency division circuit divides an output of the voltage detection circuit. 3. A switching element for switching a current flowing to a primary side of a transformer, an oscillation circuit for generating a switching frequency signal of the switching element, and an error detection circuit for detecting a feedback signal from a secondary side of the transformer. A pulse width modulation circuit that performs pulse width modulation on an output of the oscillation circuit based on a detection output of the error detection circuit; and a switching element that continuously or intermittently outputs the output of the pulse width modulation circuit depending on a normal operation state and a standby state. In a switching power supply circuit including a logic circuit that supplies a clock signal and a timer circuit that creates an intermittent frequency in the standby state, the oscillation circuit includes a frequency switching circuit that switches a transmission frequency by a control signal, and the timer circuit includes: , By shutting off the voltage supply from the secondary side, A charge / discharge circuit that performs an oscillating operation by a voltage from the side, a frequency divider that divides the output of the charge / discharge circuit, and a selection that selectively applies the output of the frequency divider to the logic circuit according to the control signal. A switching power supply circuit comprising a circuit.