JP2003189607A - Switching power supply unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply unit capable of improving the efficiency of power conversion with a simple structure by suppressing loss while a switching device is ON. <P>SOLUTION: This switching power supply unit includes the switching device Q1, and a transformer Tr for supplying energy induced in a secondary winding Ns to a load Z based on DC voltage intermittently supplied to a primary winding Np by the switching device Q1, and comprises control means 19, 20 controlling the switching device Q1 so as to be ON with a signal obtained by reversing counter electromotive force generated at a tertiary winding Nd of the transformer Tr. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a switching power supply device used as a power supply for various electronic devices.

[0002]

2. Description of the Related Art As is well known, there is an example shown in FIG. 9 as a switching power supply device as described above. This Figure 9
The circuit shown in (1) is similar to the circuit described in Japanese Patent Laid-Open No. 2000-287442. Further, FIG. 10 shows operation waveforms of each part of the switching power supply device.

That is, a DC voltage obtained by rectifying a commercial AC power supply is applied to one end of the primary winding Np of the transformer Tr, and a switching circuit driven by the control circuit 11 is applied to the other end of the primary winding Np. The element Q1 is connected.

By driving the switching element Q1 on and off, a DC voltage is intermittently applied to the primary winding Np, so that an AC voltage obtained from the secondary winding Ns of the transformer Tr is converted into a diode D2 and a capacitor C2. The output voltage is supplied to the load Z after being rectified by.

The control circuit 11 is set by the output of the oscillator 12 and reset by the output of the voltage comparator 13.
The output of an FF (Flip Flop) circuit 14 as a bistable circuit is supplied as a control signal to the switching element Q1 via a drive circuit 15.

The voltage comparator 13 includes a switching element Q1.
The output of the current detector 16 that detects the current flowing through the output of the FF circuit 14 is compared with the output of the error amplifier 17 that obtains the difference between the voltage level applied to the load Z and the reference level. There is.

The control circuit 11 includes a transformer Tr.
The DC voltage applied to the primary winding Np is taken into the power supply voltage supplier 18, and the power supply voltage Vcc for driving is obtained by the power supply voltage supplier 18.

By the way, this switching power supply device is
Since the oscillator 12 is connected to the set S side of the FF circuit 14 and the timing for turning on the switching element Q1 is determined, the switching frequency is fixed to the oscillation frequency of the oscillator 12.

That is, at time T1, the oscillator 12 outputs H
When the (High) level pulse is output, the FF circuit 14
Is set and its output Q becomes H level, so that the switching element Q1 is turned on and a drain current flows.

This drain current is a current flowing through the primary winding Np of the transformer Tr, and energy is stored in the transformer Tr during the periods T1 and T2 during which the switching element Q1 is on.

At time T2, when the voltage level output from the current detector 16 becomes higher than the voltage level output from the error amplifier 17, the output of the voltage comparator 13 becomes H level. As a result, the FF circuit 14 is reset,
Since the output Q becomes L (Low) level, the switching element Q1 is turned off.

When the switching element Q1 is turned off, the energy stored in the transformer Tr is transferred to the secondary winding Ns.
Is discharged through the diode D2 from the capacitor C2.

The time T during the release of this energy
At 3, the oscillator 12 outputs a pulse of H level, so that the FF circuit 14 is set and the switching element Q1 is turned on.

However, at this time T3, the transformer T
The current flowing out from the secondary winding Ns of r is not completely zero, that is, the energy of the transformer Tr is not completely zero.

Therefore, at time T3, the switching element Q
When 1 is turned on, the current flowing through the switching element Q1 is not zero at the beginning of the flow, and the energy remaining in the transformer Tr is superimposed.

As described above, in the conventional switching power supply device, since the switching element Q1 cannot be turned on after the energy of the transformer Tr is completely zero, a large loss occurs at the timing when the switching element Q1 is turned on. There is a problem in that the power conversion efficiency is lowered.

[0017]

Therefore, the present invention has been made in consideration of the above circumstances, and it is possible to reduce the loss when the switching element is turned on with a simple structure and promote the efficiency of power conversion. An object is to provide an extremely good switching power supply device.

[0018]

A switching power supply device according to the present invention supplies a primary winding to which a DC voltage is applied by turning on / off a switching element, and energy induced in the primary winding to a load. Having a secondary winding for generating a pulse voltage by a counter electromotive force, a transformer having a tertiary winding for generating a pulse voltage by a back electromotive force, a pulse detector for detecting a pulse voltage generated in the tertiary winding, and an inverter for inverting the pulse voltage And a pulse generating means for outputting an inversion pulse as a control pulse, a change in the output voltage supplied to the load, and a switching element to turn on / off the switching element in response to the control pulse, and the control pulse controls the on-timing of the switching element. And a control means.

According to the above configuration, the transformer 3
Since the switching element is controlled to the on state by the signal that reverses the back electromotive force generated in the next winding, the switching element is turned on only when the transformer energy is zero, so the configuration is simple. It is possible to reduce loss when the switching element is turned on and promote efficiency in power conversion.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows the switching power supply device described in this embodiment with the same parts as in FIG. Also, in FIG.
The operation waveform of each part of this switching power supply device is shown.

That is, instead of the output signal of the oscillator 12, the voltage generated in the tertiary winding Nd of the transformer Tr is detected by the pulse detector 19, and the detected pulse is inverted by the inverter 20. , FF circuit 14 is set.

Further, from the voltage comparator 13 to the FF circuit 1
When the signal for resetting 4 is output, the inverter 2
The output of 0 is bypassed via the switch 21 to the ground end as the reference potential point. This surely resets the FF circuit 14.

In the above structure, the current on the secondary side of the transformer Tr charges the capacitor C2 from the secondary winding Ns via the diode D2 while the switching element Q1 is off, and the load Z Supply the output voltage to.

The current flowing through the diode D2 is the time T
When finished with 1, each winding Np, Ns, N of the transformer Tr
Since a counter electromotive force is generated in d, the voltage of the tertiary winding Nd of the transformer Tr changes from H level to L level.

The pulse voltage generated in the tertiary winding Nd is detected by the pulse detector 19 and supplied to the inverter 20. The inverter 20 changes its output from L level to H level when the input changes from H level to L level.

The output of the inverter 20 is the set (S) input of the FF circuit 14. Therefore, the FF circuit 1
In No. 4, when the set input changes from L level to H level, the output Q also changes from L level to H level.

As a result, the switching element Q1 is controlled from the off state to the on state via the drive circuit 15. That is, the switching element Q1 is turned on at time T1 when the current of the secondary winding Ns of the transformer Tr ends.

During the period T1 to T2 during which the switching element Q1 is turned on, a current flows through the primary winding Np of the transformer Tr to be charged with energy.

Load Z connected to the secondary side of transformer Tr
When charging is completed up to the energy consumed by, the output voltage level of the current detector 16 becomes higher than the output voltage level of the error amplifier 17, and the output of the voltage comparator 13 changes from L level to H level.

The output of the voltage comparator 13 is the FF circuit 1.
4 reset (R) input, so FF circuit 1
4 is reset, and its output Q becomes L level.

At the same time, the output of the voltage comparator 13 is the switch 2
1 is controlled, the switch 21 is closed at time T2, the output of the inverter 20 is forced to the L level, and the FF circuit 14
The set input of is also at the L level. Therefore, at time T2, the switching element Q1 is surely turned off.

When the switching element Q1 is turned off, the energy stored in the primary winding Np of the transformer Tr charges the capacitor C2 from the secondary winding Ns of the transformer Tr via the diode D2.

At time T3 when the current flowing through the diode D2 ends, a counter electromotive force is generated in the tertiary winding Nd of the transformer Tr, so that the switching element Q1 is turned on again as described above. As described above, the switching element Q1 is repeatedly turned on and off to transfer energy.

According to the above embodiment, the transformer T
The state in which the energy of the secondary winding Ns of r is zero (transformer T
Since the switching element Q1 is turned on only when the energy of r is zero), it is possible to almost eliminate the loss when the switching element Q1 is turned on (zero current switch).

That is, the switching frequency fluctuates due to the fluctuation of the load Z and the fluctuation of the input voltage, and the current flowing through the switching element Q1 always rises from zero. Therefore, there is almost no loss when the switching element Q1 is turned on, and efficiency can be improved.

Further, by attaching the switch 21 which opens and closes depending on the presence or absence of the reset pulse of the FF circuit 14 to the output of the inverter 20, the switching element Q1 can be surely turned off and the switching element can be turned off. The transition of Q1 to the off state can be promoted.

FIG. 3 shows the details of the current detector 16. In this case, the connection terminal 16a is connected to the drain of the switching element Q1, and the connection terminal 16b is connected to the non-inverting input terminal (+) of the voltage comparator 13.

The connection terminal 16a is connected to the connection terminal 16b via the resistor R1 and is also grounded via the resistor R2. In addition, the resistor R1 and the connection terminal 16
The connection point with B is grounded via a capacitor C4.

FIG. 4 shows the details of the pulse detector 19. In this case, the connection terminal 19a is connected to the connection point between the tertiary winding Nd of the transformer Tr and the diode D1,
The connection terminal 19b is connected to the input terminal of the inverter 20.

The connection terminal 19a is connected to the diode D
3 in the forward direction and then grounded via resistors R3 and R4 in series. The connection point of the resistors R3 and R4 is connected to the connection terminal 19b and is grounded via the capacitor C5.

FIG. 5 shows the details of the error amplifier 17. In this case, the connection terminal 17a is connected to the connection point between the diode D2 and the capacitor C2,
b, that is, the collector of the phototransistor Q2 forming the light receiving element of the photocoupler 17c is the diode D1.
Connected to the connection point of the capacitor C3 and the connection terminal 17
d is connected to the inverting input terminal (−) of the voltage comparator 13.

The connection terminal 17a has resistors R6 and R
7 is grounded in series, and is connected to the cathode of the constant voltage diode D5 via the resistor R5 and the light emitting diode D4 forming the light emitting element of the photocoupler 17c in the forward direction. The anode of the constant voltage diode D5 is grounded, and the control terminals are resistors R6 and R5.
7 connection points.

The emitter of the phototransistor Q2 is grounded via the resistor R9 and is also connected to the inverting input terminal (-) of the operational amplifier OP1 via the resistor R8. The non-inverting input terminal (+) of this operational amplifier OP1
Is grounded via a constant voltage source E.

Further, a resistor R10 is connected between the inverting input terminal (-) and the output terminal of the operational amplifier OP1. The output end of the operational amplifier OP1 is connected to the connection terminal 17b via the resistor R11 after passing through the diode D6 in the forward direction. The connection point between the resistor R11 and the connection terminal 17b is grounded via the resistor R12 and is also grounded via the constant voltage diode D7 in the reverse direction.

FIG. 6 shows a modification of the above embodiment. In this modification, the output of the inverter 20 is supplied to the reset (R) input of the FF circuit 14, and the voltage comparator 13
Is supplied to the set (S) input of the FF circuit 14,
The inverting output Q of the F circuit 14 controls the switching element Q1.

FIG. 7 shows still another modification of the above-described embodiment, and FIG. 8 shows operation waveforms of respective parts in this modification. That is, the pulse fall delay circuit 22 is connected between the pulse detector 19 and the inverter 20.

In most switching power supply devices, when the switching element is turned off, the drain voltage of the switching element rapidly rises to increase the loss. Therefore, this is prevented by the snubber capacitor Cs.

However, the above-mentioned switching element Q
When 1 is turned on, the energy charged in the snubber capacitor Cs is discharged, and the loss increases.

In the modification shown in FIG. 7, a pulse fall delay circuit 22 is provided to minimize this loss. That is, when the secondary current of the transformer Tr ends, the inductance Lp of the primary winding Np of the transformer Tr
A resonance phenomenon occurs between the snubber capacitor Cs and the snubber capacitor Cs.
This resonance voltage becomes the drain voltage of the switching element Q1.

The output of the pulse detector 19 is supplied to the inverter 20 for the time Td from the end of the current flowing through the secondary side of the transformer Tr until the resonance voltage reaches the minimum level. It is delayed by the pulse fall delay circuit 22.

This delay time Td can be obtained in advance by the equation Td = π (Lp × Cs) ^1/2 .

As a result, the switching element Q1 can be turned on at the time when the energy charged in the snubber capacitor Cs becomes the minimum, so that the loss can be minimized.

In the above embodiment, a digital IC (Integrated Circuit) is used to control the switching power supply, and a self-exciting flyback converter type power supply circuit is provided with a simple configuration without using the oscillator 12, and the efficiency is also improved. This is an improvement over the conventional self-excited flyback converter type power supply using the oscillator 12.

The present invention is not limited to the above-mentioned embodiments, but can be variously modified and implemented without departing from the scope of the invention.

[0055]

As described above in detail, according to the present invention,
It is possible to provide an extremely good switching power supply device capable of reducing loss when the switching element is turned on with a simple configuration and promoting efficiency of power conversion.

[Brief description of drawings]

FIG. 1 is a block configuration diagram shown to explain an embodiment of the present invention.

FIG. 2 is a diagram shown for explaining an operation waveform of each unit in the same embodiment.

FIG. 3 is a circuit configuration diagram shown for explaining the details of the current detector in the same embodiment.

FIG. 4 is a circuit configuration diagram shown for explaining details of the pulse generator in the embodiment.

FIG. 5 is a circuit configuration diagram shown for explaining details of the error amplifier according to the first embodiment.

FIG. 6 is a block configuration diagram shown for explaining a modified example of the same embodiment.

FIG. 7 is a block configuration diagram shown for explaining another modification of the embodiment.

FIG. 8 is a diagram shown for explaining an operation waveform of each unit in the other modified example.

FIG. 9 is a block diagram showing a conventional switching power supply device.

FIG. 10 is a diagram for explaining operation waveforms of respective parts of the conventional device.

[Explanation of symbols]

11 ... Control circuit, 12 ... Oscillator, 13 ... voltage comparator, 14 ... FF circuit, 15 ... Drive circuit, 16 ... current detector, 17 ... Error amplifier, 18 ... power supply voltage supply, 19 ... Pulse detector, 20 ... Inverter, 21 ... Switch, 22 ... Pulse falling delay circuit.

Claims (9)

[Claims] 1. A primary winding to which a DC voltage is applied by turning on / off a switching element, a secondary winding for supplying energy induced in the primary winding to a load, and a pulse generated by a back electromotive force. A transformer having a tertiary winding that generates a voltage, a pulse detector that detects a pulse voltage generated in the tertiary winding, and an inverter that inverts the pulse voltage, and the inversion pulse is used as a control pulse. And a control means for turning on / off the switching element in response to a change in the output voltage supplied to the load and the control pulse, and controlling the on-timing of the switching element by the control pulse. A switching power supply device characterized in that 2. The control means is configured to generate a first pulse in response to a change in the output voltage, the first pulse and the control pulse being input, and the first pulse and the control pulse. A bistable circuit whose output state is changed in response to the input of the bistable circuit, and driving means for turning on the switching element during the control pulse period by using the output from the bistable circuit. The switching power supply device according to claim 1, which is characterized in that. 3. The switching power supply device according to claim 1, wherein the control means includes delay means for delaying the pulse voltage from the pulse detector for a predetermined time and supplying the delayed pulse voltage to the inverter. . 4. The control means comprises means for controlling the output state of the control pulse from the inverter by using the first pulse to promote the switching of the switching element to the off state. The switching power supply device according to claim 2, wherein 5. The promoting means comprises a switch connected between an output end of the inverter and a reference potential point, the switch being conductive in response to the first pulse. Switching power supply. 6. The bistable circuit is a flip-flop circuit having a set input terminal and a reset input terminal,
A control pulse from the inverter is supplied to the set input terminal, the first pulse is supplied to the reset input terminal, and an output signal for controlling ON / OFF of the switching element is obtained from a non-inverting output terminal. The switching power supply device according to claim 2, which is characterized in that. 7. The bistable circuit is a flip-flop circuit having a set input terminal and a reset input terminal,
The control pulse from the inverter is supplied to the reset input terminal, the first pulse is supplied to the set input terminal, and an output signal for controlling on / off of the switching element is obtained from an inverting output terminal. Claim 2
The switching power supply described. 8. A primary winding to which a DC voltage is applied by turning on / off a switching element, a secondary winding for supplying energy induced in the primary winding to a load, and a pulse generated by a back electromotive force. A transformer having a tertiary winding that generates a voltage, a pulse detector that detects a pulse voltage generated in the tertiary winding, and an inverter that inverts the pulse voltage, and the inversion pulse is used as a control pulse. A pulse generating means for outputting, a means for generating a first pulse in response to a change in the output voltage supplied to the load, the first pulse and the control pulse are input, and the first pulse and the control A bistable circuit whose output state changes in response to the input of a pulse, and an output from the bistable circuit is used to control ON / OFF of the switching element, and the switching element is switched during the control pulse period. Switching power supply apparatus characterized by comprising; and a on-state and forms drive means quenching element. 9. A primary winding to which a DC voltage is applied by turning on / off a switching element, a secondary winding for supplying energy induced in the primary winding to a load, and a pulse generated by a back electromotive force. A transformer having a tertiary winding for generating a voltage, a pulse detector for detecting a pulse voltage generated in the tertiary winding, a delay means for delaying the pulse voltage from the pulse detector for a predetermined time, and the delay Pulse generator for inverting the pulse voltage delayed by the means, outputting the inverted pulse as a control pulse, and generating a first pulse in response to a change in the output voltage supplied to the load. Means, a bistable circuit for receiving the first pulse and the control pulse, and changing an output state in response to the input of the first pulse and the control pulse; Switching power supply of the switching element on-off controlled by using the output, and characterized by being provided with said switching element in the ON state and makes driving means to said control pulse duration.