JP2001128453A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To smoothly start a power supply and to stably continue its oscillations irrespective of the largeness of a load at the time of a start-up or in a drooping state that an output electric power becomes large even when starting resistor is made large, in order to extend the cycle of intermittent oscillations. SOLUTION: At a start-up or in a drooping state where an output electric power becomes large, an output voltage-drop detecting circuit part detects that the output voltage of a driving winding L3 is low to turn on a drive current control circuit. Then, a low-voltage power source circuit supplies a start current from a low voltage source that occurs from the output of the driving winding L3 to the gate of a FET through the drive current control circuit, so that sufficient drive current is supplied to the FET and its oscillations are maintained stably, regardless of the size of a load. As a result, starting resistor for extending the cycle of the intermittent oscillations can be made larger, and power consumption at the stand-by time in the intermittent oscillations can be reduced without nonconformities.

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 used for electronic equipment and the like, and more particularly, to a starting circuit of a switching power supply having low power loss.

[0002]

2. Description of the Related Art FIG. 3 shows a configuration example of a DC-DC converter circuit which is a kind of a conventional switching power supply.
Switching power supply (DC-DC converter circuit)
Are a DC power supply V such as a capacitor input type rectifier circuit, an FET (field effect transistor) 1 which is a switching element for generating an intermittent current by switching, and a primary winding L1 and a primary winding L1 of a transformer T for raising and lowering an AC voltage. Next winding L1
Secondary winding L2 and primary winding L1 that are magnetically coupled to opposite polarities.
A drive winding L3 magnetically coupled to the same polarity as above, starting resistors R1 and R2 for starting switching of the FET1, a gate resistor R3 of the FET1, an oscillation capacitor C1, and a rectifying element D for rectifying an AC voltage of the secondary winding L2. And a control circuit for applying a signal for controlling the on-duty of the FET1 in accordance with the DC output voltage Vo supplied to the load Ro, and performing intermittent switching control of the FET1. 10 is provided.

This DC-DC converter circuit is an RCC (ringing choke converter) circuit itself, and uses an induced voltage of a driving winding L3 of a transformer T to generate an FCC.
The ET1 is turned on / off to generate an AC voltage in the primary winding L1 and the secondary winding L2 of the transformer T. And
A DC output of a constant voltage different from the voltage of the DC power supply V is obtained from the AC voltage generated in the secondary winding L2 by a rectifying and smoothing circuit including a rectifying element D and a smoothing capacitor Co.

Here, the circuit in the RCC circuit is started by applying the output voltage of the DC power supply V to the FE through the starting resistor R1.
Charge is applied to the gate of FET1 and the capacitor C1 for oscillation by applying to the gate of T1 and the capacitor C1 for oscillation, and when the gate voltage of FET1 reaches the threshold voltage for driving the FET1, the FET1 starts switching. Then, an intermittent current (switching current) flows through the primary winding L1.

As a result, an AC voltage is generated in the driving winding L3, which supplies an AC current to the gate circuit of the FET1, so that the gate of the FET1 has a period corresponding to a time constant determined by the capacitor C1, the gate resistance R3, and the like. Is applied, and the switching of the FET1 is continued. At this time, the control circuit 10 controls the on-duty of the FET 1 so that the output voltage Vo on the secondary side becomes a constant voltage.

[0006] Today, from the viewpoint of global environmental protection, power saving (Energy Star, Blu-ray) when equipment is in standby mode (light load) is performed.
e Angel) is required, and intermittent oscillation is used for standby power saving technology. This is because the oscillation of the FET 1 is intentionally stopped for a certain period, so that the number of times of switching is reduced and power loss is reduced.

Therefore, when there is no load on the secondary side or when the load is light, in addition to the above-described on-duty control, the control circuit 10 discharges the electric charge accumulated in the gate-source capacitance of the switch FET1 ( (Not shown) is operated to intermittently stop the switching operation of the FET1, so that the FET1 is operated intermittently and the output voltage Vo is kept constant. If this intermittent oscillation (intermittent switching) is not performed, the oscillation frequency of the RCC circuit increases at light load, and the switching loss increases.

FIG. 4 is a diagram showing an oscillation state of the FET1. FIG. 4A shows an oscillation state in a steady state, in which continuous oscillation is performed at 200 KHz. FIG. 4B shows an intermittent oscillation state at a light load, in which intermittent oscillation is performed at a period of 3 KHz.

The start-up time in the intermittent oscillation operation state when the load is light or no load depends on the resistance value of the start-up resistor R1. That is, the period of the intermittent oscillation based on the resistance value of the starting resistor R1 (the period when the switch FET1 is off).
Changes. If the starting resistor R1 is large, only a small starting current flows through R1, and the gate of the switch FET1 slowly reaches the threshold voltage, so that the starting time is prolonged, and therefore the period of the intermittent oscillation is prolonged. This allows
The period of the intermittent oscillation becomes longer, the number of times of switching is reduced, and the loss during standby is reduced.

[0010]

In the conventional switching power supply device as described above, if the start-up resistor R1 is increased to increase the intermittent oscillation cycle in order to reduce the loss during standby, the start-up time of the device is reduced. , Starting resistance R
Since 1 is large, the gate charging current of FET1 becomes small, and it becomes difficult to continue oscillation of the device. In particular, when the input DC voltage V is low and the resistance value of the load Ro is small (the output power is large), oscillation cannot be continued. Further, when the output current is large at the time of drooping and the output voltage is lowered, there is a problem that oscillation cannot be maintained.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems. An object of the present invention is to increase the starting resistance in order to lengthen the period of intermittent oscillation, regardless of the size of the load. An object of the present invention is to provide a switching power supply device that can smoothly start up a device and continue oscillation, and can stably continue oscillation even in a drooping state when output power becomes large.

[0012]

To achieve the above object, the present invention is characterized in that a DC power supply, a switching element for switching a DC current supplied from the DC power supply, and a DC power supply. A starting resistor for supplying a starting current for driving the switching element to a control terminal of the switching element, and a transformer through which a switching current obtained by the switching element flows through a primary winding;
A control circuit that controls switching of the switching element based on an output voltage output from a secondary winding of the transformer; and a control voltage generated from an output of a tertiary winding of the transformer to a control terminal of the switching element. A supply circuit, a low voltage generating circuit for generating a low voltage lower than the voltage of the DC power supply from an output of the tertiary winding of the transformer, and an output voltage of the tertiary winding of the transformer being equal to or lower than a predetermined voltage. A voltage detection circuit for detecting whether the output voltage of the tertiary winding of the transformer has become equal to or less than a predetermined voltage. A drive current control circuit for supplying a control terminal of the switching element.

A feature of the invention according to claim 2 is that an intermittent oscillation circuit is provided which is controlled by the control circuit to intermittently oscillate the switching element.

According to a third aspect of the present invention, the low voltage generating circuit is
A low voltage lower than the voltage of the DC power supply is generated from an output of a winding obtained by adding a tertiary winding of the transformer or a separately provided winding.

According to a fourth aspect of the present invention, the low voltage generating circuit is
A first rectifying and smoothing output terminal of the tertiary winding of the transformer T
Rectifier and a first smoothing capacitor, and a second rectifier and a second smoothing capacitor for rectifying and smoothing the output from the first rectifier and the first smoothing capacitor.

According to a fifth aspect of the present invention, in the voltage detecting circuit, a third rectifying element and a third smoothing capacitor for rectifying and smoothing an output terminal of a tertiary winding of the transformer, and a terminal of the third smoothing capacitor A resistor for averaging the voltage, a constant voltage diode for detecting that the terminal voltage of the resistor has become a constant voltage, and turned on and off by the constant voltage diode,
A first transistor for controlling the operation of the drive current control circuit.

According to a sixth aspect of the present invention, the driving current control circuit includes an adjusting resistor for adjusting a starting current supplied to the gate of the switching element, and a current flowing to the gate of the switching element controlled by the first transistor. And a protection diode for the second transistor.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a schematic configuration of a switching power supply according to an embodiment of the present invention.
However, the same parts as those in the conventional example will be described with the same reference numerals. A switching power supply (RCC) includes a DC power supply V such as a capacitor input type rectifier circuit, a switching element FET1 that switches and generates an intermittent current,
A transformer T for raising and lowering the AC voltage, a primary winding L1 of the transformer T, a secondary winding L2 magnetically coupled in a polarity opposite to that of the primary winding L1 of the transformer T, and the same as the primary winding L1 of the transformer T From the drive winding L3 magnetically coupled to the polarity, the starting resistors R1 and R2 for starting the switching of the FET1, the gate resistor R3 of the FET1, the oscillation capacitor C1, the rectifying element D for rectifying the secondary-side AC voltage, and the rectifying element D A control circuit 10 for performing on-duty control and intermittent switching control of the FET 1 according to a DC output voltage Vo supplied to a load Ro, a smoothing capacitor Co for smoothing a rectified voltage, and a voltage source lower than the voltage of the DC power supply V Low voltage voltage source circuit section 20, output voltage drop detection circuit section 30 for detecting a drop in output voltage, and low voltage voltage source circuit section 20 and output voltage drop detection circuit section 30 Connected to FET1 of drive current for controlling the driving current control circuit unit 40 and the FET1 gate, it has an intermittent oscillation circuit 50 to discharge the charge accumulated in the source capacitance.

Here, the low-voltage voltage source circuit section 20 generates a DC voltage lower than the voltage of the DC power supply V from the voltage generated across the drive winding L3 of the transformer T. The output voltage drop detection circuit unit 30 monitors a voltage proportional to the magnitude of the output voltage generated at both ends of the drive winding L3, and detects an output low voltage. When the output voltage drop detection circuit unit 30 detects an output low voltage at the time of start-up, drooping, or the like, the drive current control circuit unit 40 applies a low voltage source generated by the low voltage voltage source circuit unit 20 to the gate of the FET 1. Supply charging current.

However, the low-voltage voltage source circuit section 20 corresponds to a low-voltage generation circuit described in the claims, the output voltage drop detection circuit section 30 corresponds to a voltage detection circuit in the claims, and a drive current control circuit. The unit 40 corresponds to a driving current control circuit described in the claims.

FIG. 2 is a circuit diagram showing a detailed example of the switching power supply device shown in FIG. Low voltage voltage source circuit 2
Reference numeral 0 denotes a rectifying element D1 and a smoothing capacitor C2 for rectifying and smoothing the output terminal voltage of the drive winding L3 of the transformer T, and a rectifying element D2 and a smoothing capacitor C3 for rectifying and smoothing the output from the rectifying element D1 and the smoothing capacitor C2. ing.

The output voltage drop detection circuit section 30 detects a rectifying element D3 for rectifying and smoothing the output terminal voltage of the drive winding L3, a smoothing capacitor C4, a resistor R4 for averaging the terminal voltage of the smoothing capacitor C4, and a constant voltage. Constant voltage diode Dz1, bias resistor R of constant voltage diode Dz1
5, a transistor Q1 for controlling ON / OFF of the transistor Q2, and a protection resistor R6 of the transistor Q1.

The drive current control circuit section 40 includes a starting current adjusting resistor R7 to the gate of the FET1, a transistor Q2 for stopping supply of current to the gate of the FET1, and a transistor Q2.
2 and a protection diode D4 for the transistor Q2.

The other parts are the same as those of the circuit of FIG.

Next, the operation of this embodiment will be described. When the output voltage of the DC power supply V is applied to the switching power supply device, the switch FET1
When a charging current for charging the gate charge flows into the gate of the switch, the gate voltage rises, and when the gate voltage reaches the threshold value, the switch FET1 is turned on to start oscillation.

Switch FET1 OFF (non-conducting state)
Is performed by applying a drive signal to the gate of the control circuit 10 so that the DC output voltage Vo supplied to the load Ro becomes a constant voltage.

At this time, when the switch FET1 is turned off, the energy stored in the transformer T causes
The smoothing capacitor C2 of the low-voltage voltage source circuit section 20 is charged via the rectifying element D1 to a voltage proportional to the turns ratio of the windings L2 and L3 of the output voltage Vo. In addition, switch FET
When 1 is in the conducting state, the smoothing capacitor C3 is connected to the rectifying element D2 by the sum of the induced voltage of the winding L3 (voltage proportional to the windings L1 and L3) and the terminal voltage of the smoothing capacitor C2.
Is charged through.

When switch FET1 is off,
The smoothing capacitor C4 of the output voltage drop detection circuit unit 30 is charged to a voltage proportional to the turn ratio of the windings L2 and L3 of the output voltage Vo.

When the device starts oscillating as described above, the constant voltage diode Dz1 does not conduct because the charging voltage of the smoothing capacitor C4 is low, and the base current of the transistor Q1 is supplied because it does not conduct. In a non-conductive state. Therefore, a base current flows through the transistor Q2 of the drive current control circuit 40, and the transistor Q2 is in a conductive state. As a result, a charging current for charging the gate-source capacitance of the FET 1 flows through the resistor R7, the transistor Q2, and the diode D4 by the charging voltage of the smoothing capacitor C3 of the low-voltage voltage source circuit section 20.

Therefore, at the time of the above-mentioned startup, a charging current is supplied to the gate of the FET 1 from the low-voltage voltage source circuit section 20 through the drive current control circuit section 40 in addition to the path of the startup resistor R1. As a result, the charging current for charging the capacitance between the gate and the source of the FET 1 is large, and even in a transient state at the start of oscillation with a heavy load (large output power), the FET 1
1 oscillation (switching) can be maintained.

Thereafter, when the oscillation of the FET 1 becomes stable and steady, and the charging voltage of the smoothing capacitor C4 rises and exceeds a predetermined voltage, the constant voltage diode Dz1 conducts,
As a result, the base current of the transistor Q1 is supplied, and the transistor Q1 is turned on.
One base current is drawn through transistor Q1. As a result, the transistor Q2 becomes non-conductive, so that the FET 1
The operation of supplying the charging current of the capacitance between the gate and the source is stopped. Thereafter, charging of the capacitance between the gate and the source of the FET 1 is continuously supplied from the resistor R1 and the winding L3.

By the way, during the period when the load Ro is no load or light load, the control circuit 10 operates the intermittent oscillation circuit 50 to intermittently pull out the charging current between the gate and the source of the FET 1, so that the switching operation of the FET 1 is performed. Is intermittently stopped to cause the FET 1 to perform an intermittent switching operation and keep the output voltage Vo constant.

In this intermittent oscillation state, the charging between the gate and the source of the FET 1 is mainly a charging current by the starting resistor R1 having a large resistance value, so that the intermittent switching operation with a long intermittent oscillation cycle (starting time) is performed. Become. Further, when the load Ro becomes heavy (output power becomes large) and becomes a drooping state, the charging voltage of the smoothing capacitor C4 becomes low in conjunction with the drop of the output voltage Vo.

Thus, when the charging voltage of the smoothing capacitor C4 becomes lower than a predetermined value, the constant voltage diode Dz1 becomes non-conductive, and the transistor Q1 becomes non-conductive.
For this reason, the transistor Q2 is turned on, and the charging current of the capacitance between the gate and the source of the FET 1 by the charging voltage of the smoothing capacitor C3 flows, so that the FET 1 can maintain the oscillation.

However, as described above, during the normal operation and the intermittent switching operation of the FET1, the starting current for charging the gate-source capacitance of the FET1 from the low-voltage voltage source circuit section 20 stops, and the starting resistance R1 is reduced. It is large and the current flowing through it is small, so it has low loss.

After all, in this switching power supply,
(1) In the case of a drooping state due to heavy load, at the time of startup, the path of the resistor R1, the path of the transistor Q2, and the driving winding L3
A current for charging the capacitance between the gate and the source of the FET 1 is supplied from the path. Normally, a current for charging the gate-source capacitance of the FET 1 is supplied from the path of the resistor R1 and the path of the drive winding L3.

(2) In the case of a light load, a current for charging the capacitance between the gate and the source of the FET 1 is supplied from the path of the resistor R1 and the path of the drive winding L3.

According to the present embodiment, even when the starting resistance R1 is large, the driving current control circuit section 40 operates in the low voltage / voltage source circuit section 20 at the time of starting or in a drooping state when the output power becomes large. By supplying a current from the low-voltage power supply to the gate of the FET1 and charging the capacitance between the gate and the source of the FET1, a sufficient drive current is supplied to the FET1, so that the oscillation can be stably maintained.

Therefore, by increasing the starting resistance R1, the FE
The period of the intermittent oscillation of T1 can be made longer,
1, the power consumption during standby can be reduced without inconvenience, and the device can be power-saving.

The drive current control circuit section 40 is provided with the FET 1
In the steady operation and the intermittent switching operation, the starting current from the low-voltage voltage source circuit section 20 to the FET 1 is stopped. Therefore, even if the starting resistor R1 is large, the current flowing therethrough is small, so that the loss due to this resistor is low. However, power consumption is not increased.

The embodiment of the present invention is not limited to the above-described embodiment, and various changes can be made. For example,
The low voltage voltage source circuit section 20 may be configured with another circuit that generates a DC voltage. In addition, the low voltage voltage source circuit section 2
A low voltage can be generated even if the end of the driving winding L3 wound on the input side of 0 or another winding end is connected.

Further, for example, the self-excited oscillation using the drive winding L3 for the drive signal of the FET 1 can be changed to the separately excited oscillation by the control circuit 10.

In the above embodiment, the MOS-FET (MOS field effect transistor) is used as a switching element. However, a J-FET (junction field effect transistor), a bipolar transistor or an IGBT is used. Other switching elements such as (insulated gate transistors) can also be used.

Further, although the device of the above embodiment performs an intermittent oscillation operation, the present invention is applied to a device that does not perform the intermittent oscillation operation, and performs stable startup and oscillation even under heavy load. be able to.

[0045]

As described above in detail, according to the switching power supply of the present invention, even if the starting resistance is increased in order to lengthen the period of the intermittent oscillation, the device can be smoothly operated regardless of the magnitude of the load. It is possible to start up and continue oscillating, and to stably oscillate even in a drooping state when the output power becomes large. Therefore, by increasing the starting resistance, the period of the switching element during intermittent oscillation can be made longer, and the power consumption of the switching element during standby can be reduced without inconvenience.

[Brief description of the drawings]

FIG. 1 is a circuit showing a schematic configuration of an embodiment of a switching power supply device of the present invention.

FIG. 2 is a circuit diagram showing a detailed example of the switching power supply device shown in FIG.

FIG. 3 is a circuit diagram showing a configuration example of a conventional switching power supply device.

FIG. 4 is a diagram showing an oscillation state of the FET shown in FIG. 3;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 FET 10 control circuit 20 low-voltage voltage source circuit section 30 output voltage drop detection circuit section 40 drive current control circuit section 50 intermittent oscillation circuit C1 oscillation capacitor Co, C2 to C4 smoothing capacitor D, D1 to D3 rectifying element D4 protection diode Dz1 Constant voltage diode L1 Primary winding L2 Secondary winding L3 Drive winding Ro Load R1, R2 Starting resistance R3 Gate resistance R4 Averaging resistance R7 Starting current adjusting resistance Q1, Q2 Transistor T transformer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasuhiro Suzuki 3-6-3 Kitano, Niiza-shi, Saitama F-term (reference) in Sanken Electric Co., Ltd. 5H730 AA14 BB43 BB55 DD04 EE02 EE07 FD01 FD24 VV01

Claims (6)

[Claims] A switching element for switching a DC current supplied from the DC power supply; a starting resistor for supplying a starting current for driving the switching element from the DC power supply to a control terminal of the switching element; A transformer in which a switching current obtained by the switching element flows through a primary winding; a control circuit that controls switching of the switching element based on an output voltage output from a secondary winding of the transformer; A drive circuit that supplies a control voltage generated from an output of a tertiary winding to a control terminal of the switching element; and a low voltage generator that generates a low voltage lower than a voltage of the DC power supply from an output of the tertiary winding of the transformer. A circuit for detecting whether an output voltage of the tertiary winding of the transformer has become equal to or lower than a predetermined voltage. A detection circuit, when the voltage detection circuit detects that the output voltage of the tertiary winding of the transformer has become equal to or lower than a predetermined voltage, the starting current from the low voltage generation circuit is supplied to the control terminal of the switching element. A switching power supply device comprising: a drive current control circuit for supplying the switching power supply; 2. The switching power supply according to claim 1, further comprising an intermittent oscillation circuit controlled by the control circuit to intermittently oscillate the switching element. 3. The low voltage generation circuit generates a low voltage lower than the voltage of the DC power supply from an output of a winding obtained by adding a tertiary winding of the transformer or a separately provided winding. The switching power supply according to claim 1 or 2, wherein 4. The low-voltage generating circuit includes:
A first rectifying element and a first smoothing capacitor for rectifying and smoothing the output terminal of the tertiary winding; a second rectifying element for rectifying and smoothing the output from the first rectifying element and the first smoothing capacitor; 4. The apparatus according to claim 1, further comprising a second smoothing capacitor.
The switching power supply device according to any one of the above. 5. The voltage detecting circuit according to claim 3, wherein
A third rectifying element for rectifying and smoothing the output end of the next winding;
A resistor for averaging the terminal voltage of the third smoothing capacitor; a constant voltage diode for detecting that the terminal voltage of the resistor has become a constant voltage; and a constant voltage diode that is turned on and off by the constant voltage diode. The switching power supply device according to any one of claims 1 to 4, further comprising: a first transistor that controls an operation of the drive current control circuit. 6. The drive current control circuit, comprising: an adjustment resistor for adjusting a starting current supplied to a gate of the switching element; and a supply of current to a gate of the switching element controlled by the first transistor. The switching power supply according to any one of claims 1 to 5, further comprising: a second transistor; and a protection diode for the second transistor.