Self-oscillated switching power device

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a self-oscillating switching power supply device.

【0002】

[Conventional technology]

Conventionally, a Ringing Choke Converter has been widely used as a self-oscillation type switching power supply device. FIG. 1 is a circuit diagram of a conventional ringing choke converter (hereinafter referred to as RCC). As shown in the figure, the switching transistor Q1 is connected in series to the primary winding N1 of the transformer T, and the phototransistor PT, which is the light receiving element of the photocoupler, is connected to the feedback winding NB of the transformer T. The including control circuit is connected. Further, the control transistor Q2 is connected between the gate and the source of the switching transistor Q1.

【0003】

A rectifying and smoothing circuit consisting of a rectifying diode D3 and a smoothing capacitor C5 is provided across the secondary winding N2 of the transformer T. Further, this rectifying and smoothing output unit is provided with a resistance voltage dividing circuit composed of resistors R9 and R10, a shunt regulator SR, a light emitting diode PD of the photocoupler, and a voltage detection circuit using resistors R8.

【0004】

The operation of the circuit shown in FIG. 1 is as follows. First, when the power is turned on, a voltage is applied to the gate of the switching transistor Q1 via the starting resistor R1 to turn on the switching transistor Q1. As a result, the input power supply voltage is applied to the primary winding N1 of the transformer T, and a voltage having the same polarity as the primary winding N1 is generated in the feedback winding NB. This voltage signal is given as a positive feedback signal to the gate of the switching transistor Q1 via the resistor R2 and the capacitor C2. On the other hand, feedback winding NB A charging current flows through the capacitor C3 via the diode D1, the resistors R3, R5 and the phototransistor PT of the photocoupler due to the electromotive voltage of. When the charging voltage of the capacitor C3 exceeds the forward voltage between the base and the emitter of the control transistor Q2, the control transistor Q2 turns on. As a result, the gate-source voltage of the switching transistor Q1 becomes almost 0, and the switching transistor Q1 is forcibly turned off. At this time, a forward voltage is generated in the secondary winding of the transformer T with respect to the rectifier diode D3, so that the energy stored in the transformer T during the ON period of Q1 is released via the secondary winding N2. Will be done. At this time, the capacitor C3 is reversely charged by the flyback voltage of the feedback winding NB via the resistors R6 and R7 and the diode D2.

【0005】

When the voltage of the capacitor C3 becomes equal to or less than the base-emitter forward voltage of the control transistor Q2, the control transistor Q2 is turned off. When the energy stored in the transformer T is released from the secondary side and the current of the rectifier diode D3 becomes 0, the switching transistor Q1 is turned on again by the kick voltage generated in the feedback winding NB. After that, the above operation is repeated.

【0006】

Here, the output voltage on the load side is detected by the voltage division of the resistors R9 and R10, is applied as the detected voltage and the control voltage for the shunt regulator SR, and the amount of electricity supplied to the light emitting diode PD of the photocoupler changes according to the detected voltage. Let me. As a result, the amount of light received by the phototransistor PT, which is the light receiving element of the photocoupler, changes, and the impedance changes, so that the charging time constant of the capacitor C3 changes. As the output voltage decreases, the charging time constant increases. Therefore, as the output voltage decreases, the time from when the switching transistor Q1 is turned on to when it is forcibly turned off by the control transistor Q2, that is, the switching transistor Q1 The on-time becomes longer, which acts to increase the output voltage. As a result, constant voltage control is performed so that the output voltage becomes constant.

【0007】

[Problems to be Solved by the Invention]

In the conventional RCC type self-oscillation type switching power supply as shown in FIG. 1, it is known that the oscillation frequency f of the switching transistor Q1 changes in substantially inverse proportion to the input power or the output power. This can be expressed in the relationship of the oscillation frequency f with respect to the output power Po as shown in Fig. 2.

【0008】

Generally, the lighter the load, the smaller the switching loss per switching, but as shown in Fig. 2, the smaller the output power Po, that is, the lighter the load, the higher the oscillation frequency f and the higher the oscillation frequency f. Indeed, since the number of switching losses generated per unit time increases, the amount of decrease in switching loss is very small even if the load is lightened after all. Therefore, the lighter the load, the lower the efficiency of the power supply device.

【0009】

In order to reduce the switching loss in such a light load state, the circuit constant may be designed so that the oscillation frequency at the rated load is low, but the power supply device can handle a wide range from extremely light load to heavy load. If this is the case, the oscillation frequency f at light load must be relatively high. That is, in general, the oscillation frequency at the rated load is determined by factors such as the magnetic flux density of the transformer and factors such as ripple and noise, and if the oscillation frequency is set too low, the transformer will be saturated.

【0010】

In order to eliminate the above-mentioned inconvenience of the self-oscillation type switching power supply device, conventionally, in the switching power supply device shown in Japanese Patent Application Laid-Open No. 11-235036, a switching signal is input during standby to force the oscillation frequency. By lowering it, the loss during standby is improved. Further, in the switching power supply device of Japanese Patent Application No. 11-09468, the loss during standby is improved by continuously lowering the oscillation frequency from the rated time to the standby time. FIG. 3 shows a frequency characteristic diagram of the switching power supply device shown in Japanese Patent Application Laid-Open No. 11-235036, and FIG. 4 shows a frequency characteristic diagram of the switching power supply device shown in Japanese Patent Application Laid-Open No. 11-09468. There is.

【0011】

[Problems to be Solved by the Invention]

However, each of the above switching power supply devices has the following drawbacks. Japanese Patent Application Laid-Open No. 11-235036 In this switching power supply device, the loss is improved in the standby state, but the RCC operation is performed when the switching signal is in the normal state. Therefore, it is not possible to improve the loss at the time of light load during RCC operation, and it is not possible to solve the problems of increase in input power and heat generation of switching transistors. Alternatively, an operating state in which intermittent oscillation occurs also occurs, and in this case, a problem of an increase in output ripple occurs. If the load is light during RCC operation, for example, there is a print standby state of the printer device.

【0012】

Japanese Patent Application No. 11-09468 In this switching power supply device, the oscillation frequency is automatically lowered when the load is light, but in this case, if the oscillation frequency is lowered too much, the response characteristics of the load are deteriorated. Therefore, the frequency to be lowered needs to be set higher than the frequency in the standby state, and the loss improving effect in the standby state is inferior to the above.

【0013】

An object of the present invention is to control the oscillation frequency to be constantly or slowly lowered at a light load, and to make it possible to greatly reduce the oscillation frequency by a switching signal during standby, thereby deteriorating the response characteristics during RCC operation. The purpose is to prevent the problem and to improve the efficiency during standby.

【0014】

[Means for solving problems]

The present invention is configured as follows in order to solve the above problems.

【0015】

(1) Primary winding N1, secondary winding N2, and feedback winding N_B And the feedback winding N_B It is input to the switching transistor Q1 that oscillates by itself in response to the feedback signal from the primary winding and interrupts the current of the primary winding, the rectifying smoothing circuit connected to the secondary winding, and the switching transistor Q1. The oscillation frequency control circuit includes an oscillation frequency control circuit that extends the off time by controlling the control signal to prevent the switching transistor Q1 from turning on for a predetermined time after the switching transistor Q1 is turned off. When the load current exceeds a certain magnitude, the oscillation frequency decreases as the load becomes heavier. Set to the first operation mode for normal RCC operation, and the load current is a light load of a certain magnitude or less. At times, the oscillation frequency is set to a second operation mode in which the extension control of the off time is performed so that the oscillation frequency becomes constant or slowly decreases as the load current decreases, and further, the oscillation frequency is set. The control circuit includes a switch means, and is characterized in that the switch means is set to a third operation mode in which the oscillation frequency is further lower than that in the second operation mode when the switch means is in a specific state.

【0016】

In the present invention, when the load current exceeds a certain magnitude, the normal operation mode (first operation mode), that is, the normal RCC operation mode is set, and the load current is lighter than a certain magnitude. At the time of load, the standby mode (second operation mode) in which the off-time extension control is performed so that the oscillation frequency becomes constant or slowly decreases as the load current decreases is set. Further, the switching signal by the switch means enables the setting to the standby operation mode (third operation mode) in which the oscillation frequency is further lower than that in the standby mode (second operation mode). In this way, the RCC operation is performed in the normal operation mode, the oscillation frequency is controlled to be constant or slowly reduced in the standby mode, and the oscillation is further lowered by the switch means in the standby operation mode. It can be controlled to frequency. As a result, it is possible to prevent the load response characteristic from deteriorating because the oscillation frequency does not decrease significantly in the standby mode, and prevent an increase in loss by significantly decreasing the oscillation frequency in the standby operation mode. As a result, for example, when this switching power supply device is applied to a printer device, responsiveness is maintained by setting the normal operation mode when printing the printer, the standby mode when the printer is on standby for printing, and the standby operation mode when the power is off. At the same time, it is possible to promote low power consumption of the entire printer device.

【0017】

(2) The oscillation frequency control circuit is used for switching between a capacitor that is charged when the switching transistor Q1 is on and discharged when it is off, and a capacitor that is charged until the charging voltage becomes a constant voltage when the capacitor is discharged. The switch includes a first control transistor Q3 that prohibits the on of the transistor Q1 and a second control transistor Q4 that keeps the first control transistor Q3 off when the switching transistor Q1 is on. The means is characterized in that the constant voltage is made lower in the specific state.

【0018】

In the present invention, when the switching means is put into a specific state (for example, an on state), the operation time of the first control transistor Q3 that prohibits the switching transistor Q1 from being turned on becomes long. As a result, the time for prohibiting the switching transistor Q1 from being turned on is longer, so that the oscillation frequency is lowered. That is, the oscillation frequency decreases in the standby operation mode (third operation mode).

【0019】

(3) The oscillation frequency control circuit is used for switching between a capacitor that is charged when the switching transistor Q1 is on and discharged when it is off, and a charging voltage until the charging voltage becomes a constant voltage when the capacitor is discharged. A first control transistor Q3 that prohibits the on of the transistor Q1, a second control transistor Q4 that keeps the first control transistor Q3 off when the switching transistor Q1 is on, and the first capacitor. It is provided with a discharge circuit that discharges by applying the charging voltage of the above to the control terminal of the switching transistor Q1, and the switch means is provided in the discharge circuit to reduce the amount of discharge in the specific state. To do.

【0020】

In the present invention, a discharge circuit for applying the charge voltage of the first capacitor to the control terminal of the switching transistor Q1 is provided, and the discharge amount can be changed by the switch means. Even with such a configuration, when the switch means is in a specific state, that is, in the standby operation mode, the on-time of the first control transistor Q3 is longer, so that the oscillation frequency is lowered.

【0021】

(4) The switch means is characterized in that it is turned on / off by an external signal.

【0022】

In the present invention, the switch means is turned on / off by an external signal. Therefore, if the external circuit can detect the normal operation mode (first mode), the standby operation mode (second operation mode), and the standby operation mode (third operation mode), these modes can be used. It will be set automatically.

【0023】

(5) A load detecting means for detecting the lightness of the load and a switch switching circuit for switching the switching means so as to enter the third operation mode after a lapse of a predetermined time when the load detecting means detects the light load are provided. It is characterized by that.

【0024】

In the present invention, even if there is a load change from the normal operation mode (first operation mode) to the standby operation mode (third operation mode), the standby operation mode (third operation mode) does not suddenly change. After a lapse of a predetermined time, the standby operation mode (third operation mode) is switched to. As a result, even if a frequent sudden change in load occurs, the responsiveness is not impaired because the operation is performed in the normal operation mode (first operation mode) during this period. On the other hand, switching from the standby operation mode (third operation mode) to the normal operation mode (first operation mode) is performed instantaneously.

【0025】

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 5 is a circuit diagram of a self-oscillating switching power supply device according to the first embodiment of the present invention.

【0026】

A switching transistor Q1 which is a MOS-FET is connected in series to the primary winding N1 of the transformer T, and the feedback winding NB of the transformer T constitutes a feedback circuit for the switching transistor Q1. A rectifying and smoothing circuit including a rectifying diode D3 and a smoothing capacitor C5 is provided in the secondary winding N2 of the transformer T. Further, the output section of this rectifying and smoothing circuit is provided with a resistance voltage dividing circuit composed of resistors R9 and R10, a shunt regulator SR, and a voltage detection circuit using the light emitting elements PD1 and resistance R8 of the first photocoupler.

【0027】

The difference between the circuit of the present embodiment shown in FIG. 5 and the conventional circuit shown in FIG. 1 is that the oscillation frequency control circuit 1 is provided in the circuit of FIG.

【0028】

The oscillation frequency control circuit 1 turns on the capacitor C41 charged by the voltage vb of the feedback winding NB when the switching transistor Q1 is on, and the switching transistor Q1 when the charging voltage of this capacitor C41 is equal to or higher than a certain voltage. It includes a first control transistor Q3 that is prohibited, and a first control transistor Q4 that is turned on when the voltage vb of the feedback winding NB is generated. The voltage vb of the feedback winding NB charges the capacitor C41 via the diode D42, and this charging voltage is divided by the Zener diode D46, the resistor R41, and the resistor R42, and the voltage across the resistor R42 is the first control. It is applied to the control terminal of the diode Q3. Further, the voltage vb of the feedback winding NB is divided by the series circuit of the diode D43, the Zener diode D44, the resistor R43, and the resistor R44 to the second control transistor Q4, and the voltage vb is generated. Immediately after this, the first control transistor Q3 is turned off. Further, the Zener diode D45 and the switch Q5 are connected in parallel to the Zener diode D46. As will be described later, this switch Q5 is turned on in the standby operation mode, and the relationship of the Zener voltage between the Zener diodes D45 and D46 is that the Zener voltage of D46> the Zener voltage of D45. ..

【0029】

In the switching power supply device of the present embodiment, in the oscillation frequency control circuit 1, the values of each resistance value, diode, etc. are selected so as to operate as follows when the switch Q5 is in the off state.

【0030】

That is, at the rated load, both ends of the resistor R42 so that the first control transistor Q3 is already turned off when the current of the diode D3 of the rectifying smoothing circuit becomes zero and the voltage vb of the feedback winding NB is generated. The voltage is low. Therefore, the first control transistor Q3 controls the switching transistor Q1 so that the switching transistor Q1 is not delayed. In addition, when the load current is a light load of a certain magnitude or less, when the current of the diode D3 becomes zero and the voltage vb of the feedback winding NB is generated, the first control transistor Q3 is turned on thereafter. As shown, the voltage across the resistor R42 appears. However, the first control transistor Q3 is not turned on for a long time, and as a result, the switching transistor Q1 is turned on with a slight delay time. As a result, when the load is light, the oscillation frequency is controlled to be substantially constant or slowly reduced.

【0031】

On the other hand, when the switch Q5 is turned on, the Zener diode D45 is connected in parallel with the Zener diode D46 and the Zener voltage drops, so the voltage across the resistor R42 rises. The time to delay is longer. As a result, when the switch Q5 is turned on under a light load, the oscillation frequency is greatly reduced, and the loss due to switching can be reduced.

【0032】

In the above operation, the oscillation frequency control circuit 1 does not perform extension control of the off time of the switching transistor Q1 by the first control transistor Q3 when the load current exceeds a certain magnitude in the rated load. Set to (first operation mode), and when the load current is light load of a certain magnitude or less, the oscillation frequency becomes constant or slowly decreases as the load current decreases. In addition to setting the standby operation mode (second operation mode) to control the extension of the off time, when the switch Q5 is turned on, the oscillation frequency is further lowered than in the standby operation mode (third operation mode). Operation mode). As a result, the frequency characteristics of the self-oscillating switching power supply shown in FIG. 5 are shown in FIG. In the figure, area A indicates a normal operation mode, B indicates a standby operation mode, C indicates a standby operation mode, a shown for comparison is a characteristic when no measures are taken, and b is a conventional special application. The characteristics of the switching power supply device shown in Japanese Patent Application Laid-Open No. 11-09468 are shown.

【0033】

Further, FIGS. 7A to 7C are waveform diagrams of the main parts in each mode of the normal operation mode, the standby operation mode, and the standby operation mode. In these figures, vb is the output voltage of the feedback winding NB, vgs is the voltage between the gate and source of the switching transistor Q1, and vc2 is between the gate of the first switching transistor Q1 and the feedback winding Nb. The voltage across the capacitor C2 connected to is shown. As shown in FIG. 7 (C), in the normal operation mode, there is no pause period from immediately after the RCC operation is performed and the load current becomes zero until the switching transistor Q1 is turned on. Further, in the standby operation mode shown in FIG. 7B, the oscillation frequency becomes small to some extent because there is a slight pause period. Further, in the standby operation mode shown in FIG. 7 (C), the oscillation frequency is greatly reduced because the pause period is set to be considerably long.

【0034】

FIG. 8 shows a circuit diagram of a self-oscillating switching power supply device according to a second embodiment of the present invention. The difference between this switching power supply and the switching power supply shown in FIG. 5 is that instead of the Zener diode D45 and the switch Q5, a discharge circuit 2 that discharges by applying the charging voltage of the capacitor C41 to the gate of the switching transistor Q1 is installed. This is the point provided. In this discharge circuit 2, a resistor R45 is connected in series with the diode D45, and a series circuit of the resistor R46 and the switch Q5 is connected in parallel with the resistor R45.

【0035】

In the above circuit, when the switch Q5 is on, the amount of discharge from the capacitor C41 increases. Therefore, at the rated load, the first control transistor Q3 is turned off before the current of the diode D3 becomes zero, so that the switching transistor Q1 is turned on without a delay time. Further, at the time of light load, since the first control transistor Q3 is in the ON state even if the current of the diode D3 becomes zero, the switching transistor Q1 is turned on with a slight delay time. Therefore, when the switch Q5 is on, the normal operation mode is set when the load is rated, and the standby operation mode is set when the load is light. Further, when the switch Q5 is off, the amount of discharge from the capacitor 41 is small, so that the first control transistor Q3 keeps on even if the current of the diode D3 becomes zero. Therefore, the delay time becomes longer than when the switch Q5 is on, and the switching frequency decreases. The frequency characteristics of the self-oscillating switching power supply device of this embodiment are as shown in FIG. 6, and the waveform diagrams are also the same as those shown in FIGS. 7 (A) to 7 (C). ..

【0036】

Since the electric charge of the capacitor C41 is supplied to the capacitor C2 during the delay time by the oscillation frequency control circuit 1, the attenuation factor of the voltage difference between the terminals of the capacitor C2 when the switching transistor Q1 is turned on / off becomes small. Therefore, even if the delay time becomes very long, the switching transistor Q1 is surely turned on, so that the delay time can be set to an arbitrary length.

【0037】

FIG. 9 is a circuit diagram of a self-oscillating switching power supply device according to a third embodiment of the present invention.

【0038】

The difference between this self-oscillating switching power supply and the self-oscillating switching power supply shown in FIG. 8 is that the switch Q5 in FIG. 8 is replaced with the phototransistor PT2 of the photocoupler, and the photodiode PD2 on the light emitting side of the photocoupler is replaced. Is connected to the external remote signal input terminal REM.

【0039】

With such a configuration, the phototransistor PT2 can be turned on simply by inputting a remote signal to the remote signal input terminal REM. Therefore, if the remote signal input terminal REM is configured to input the "H" signal in the normal operation mode and the standby operation mode, and the "L" signal is input to the same terminal in the standby operation mode, The operation mode can be set easily.

【0040】

FIG. 10 shows a circuit diagram of a self-oscillating switching power supply device according to a fourth embodiment of the present invention.

【0041】

The difference between this self-oscillating switching power supply and the self-oscillating switching power supply shown in FIG. 9 is that the resistor R50 for detecting the lightness of the load and the resistor R50 in series with the diode D3. A switch switching circuit 3 for controlling on / off of the phototransistor PT2 based on the voltage across the ends is provided.

【0042】

The switch switching circuit 3 includes two comparators, COMP-1 and COMP-2. COMP-1 detects the voltage across the resistor R50 and detects whether it is a rated load or a light load. At the rated load, the output of COMP-1 is grounded because the voltage across the resistor R50 is large. Also, when the load is light, the output of COMP-1 is in the open state. COMP-2 compares the reference voltage Vref with the charging voltage charged in the capacitor C11, and turns off the photodiode PD2 when the charging voltage of the capacitor C11 exceeds the reference voltage Vref. When the photodiode PD2 is turned on, the phototransistor PT2 is turned off and the standby operation mode is set. That is, the above switch changeover circuit 3 operates as follows.

【0043】

Normal operation mode Standby operation mode When the output current decreases, the output of COMP-1 becomes open, and the voltage of the capacitor C11 of the CR time constant circuit consisting of the resistor R15 and the capacitor C11 begins to rise. When this voltage exceeds the reference voltage Vref, the output of COMP-2 becomes L, the photodiode PD2 turns off, and the standby operation mode is entered.

【0044】

Standby operation mode Normal operation mode When the load becomes heavy and the output current increases, the output of COMP-1 becomes grounded, and the voltage of the capacitor C11 of the CR time constant circuit decreases immediately. When this voltage falls below the reference voltage Vref, the output of COMP-2 becomes "H", the photodiode PD2 turns on, and the normal operation mode is entered.

【0045】

By the above operation, even if the rated load is changed to a light load, the mode does not shift for the time determined by the time constant of the CR time constant circuit. Further, when the load is changed from the light load to the rated load, the mode shifts from the standby operation mode to the normal operation mode instantly. Therefore, when the load suddenly changes frequently, the operation is always performed in the normal operation mode, and the responsiveness is improved. Further, since the switching from the standby operation mode to the normal operation mode is instantaneous, the problem of responsiveness does not occur.

【0046】

[Effect of the invention]

According to the present invention, by controlling the oscillation frequency to decrease constantly or slowly at a light load, it is possible to avoid increasing the frequency at a light load, improve the efficiency of the RCC at a light load, and improve the output ripple. In addition, the switching means can significantly improve the efficiency at the time of light load.

【0047】

In addition, the switch switching circuit can automatically switch the mode, and when a light load is detected, it is controlled to switch to the third operation mode after a lapse of a predetermined time. Therefore, normal operation occurs when the load suddenly changes frequently. It will operate in the mode, and it is possible to prevent the responsiveness from becoming poor.

[Simple explanation of drawings]

[Figure 1]

Circuit diagram of a conventional self-excited switching power supply [Figure 2]

Frequency characteristic diagram of the switching power supply [Fig. 3]

Frequency characteristic diagram of the conventional improved self-oscillation type switching power supply [Fig. 4]

Frequency characteristic diagram of other conventional improved self-oscillation type switching power supply [Fig. 5]

Circuit diagram of the self-oscillation type switching power supply device according to the first embodiment of the present invention. [Fig. 6]

Frequency characteristic diagram of the switching power supply [Fig. 7]

Waveform diagram of the main part of the switching power supply [Fig. 8]

Circuit diagram of the self-oscillation type switching power supply device according to the second embodiment of the present invention. [Fig. 9]

Circuit diagram of the self-oscillation type switching power supply device according to the third embodiment of the present invention. [Fig. 10]

Circuit diagram of the self-oscillation type switching power supply device according to the fourth embodiment of the present invention. [Explanation of symbols]

1-Oscillation frequency control circuit C41-Capacitor Q5-Switch