JPH0545113Y2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a switching regulator,
In particular, it relates to a switching regulator that is highly efficient.

(Prior art) Switching regulators are used as DC power sources for communication devices that often use DC power sources, and as DC-DC converters for mobile and portable devices that use DC power sources such as dry batteries and storage batteries. Its application fields are wide-ranging.

A switching regulator turns the current flowing through the inductance ON/OFF and extracts the energy stored in the inductance to the output side. In particular, as a self-excited switching regulator,
RCC (Ringing Choke Converter) is used.

This RCC is generally configured as shown in FIG. That is, the primary winding 1 of the transformer 1
A switching transistor Tr1 is connected to a, and an input voltage _V1 is applied to the base of the switching transistor Tr1, and an input voltage _V1 is applied to the base of the switching transistor Tr1 via a resistor 2 and a The voltage of the bias winding 1b of the transformer 1 is applied. A collector of a transistor Tr2 is connected to the base of the switching transistor Tr1, and a phototransistor 6 of a photocoupler 5 is connected to the base of the transistor Tr2 via a resistor R4. On the other hand, the secondary winding 1c of the transformer 1 has the opposite polarity to the primary winding 1a, and the secondary winding 1c includes a diode 7, a smoothing capacitor 8, an amplifier 9, a transistor Tr3,
A photodiode 10 and resistors 11 and 12 of a photocoupler 5 are connected.

This RCC is switching transistor Tr1
By turning ON/OFF, the energy accumulated in the transformer 1 during the ON period of the switching transistor Tr1 is transferred to the switching transistor Tr.
Supplied to the output side during the OFF period of 1. The ON/OFF state of the switching transistor Tr1 is maintained by the bias winding 1b of the transformer 1, and the ON time of the switching transistor Tr1 is controlled by the switching transistor Tr2 using the transistor Tr2.
It is controlled by narrowing down the base current of 1. In other words, the switching transistor Tr
1 turns ON and current flows through the primary winding 1a,
At the same time, a voltage is generated in the bias winding 1b, and 2
A voltage is also generated in the next winding 1c. bias winding 1
The voltage generated at b is the switching transistor
This becomes a positive feedback voltage that makes Tr1 more conductive, but
Since the voltage generated in the secondary winding 1c is applied to the diode 7 in the opposite direction, the voltage generated in the secondary winding 1c of the transformer 1
No current flows through the primary winding 1a, and only the exciting current of the transformer 1 flows through the primary winding 1a. This exciting current becomes V ₁ t/Lp, where Lp is the inductance of the primary winding 1a and time t is, and increases with time t. When the current in the switching transistor Tr1 increases and it becomes impossible for the base current to keep the switching transistor Tr1 saturated,
The switching transistor Tr1 goes out of saturation and the collector-emitter voltage _VCE of the switching transistor Tr1 increases. This V _CE
increases and the voltage of the primary winding 1a of the transformer 1 decreases, the voltage of the bias winding 1b also decreases, and further
V _CE increases. This change is fed back positively and the switching transistor Tr1 is turned off. Also,
As the output voltage _V2 increases, the emitter current of the transistor Tr3 increases by the amplifier 9,
The current flowing through the photodiode 10 of the photocoupler 5 increases, causing the current in the phototransistor 6 to increase. Therefore, the collector current of transistor Tr2 increases, lowering the base current of switching transistor Tr1, and reducing the switching transistor Tr1.
Shorten the ON time of transistor Tr1. As a result, the output voltage decreases and operation becomes stable.

(Problems to be Solved by the Invention) However, in such a conventional switching regulator, the oscillation frequency is inversely proportional to the load current, so the oscillation frequency changes depending on the load. Therefore, when the load is light, especially when there is no load, the oscillation frequency may rise extremely or intermittent oscillation may occur. As a result, there have been problems such as deterioration in reliability, generation of noise, and deterioration in efficiency due to switching loss.

(Purpose of the invention) Therefore, the present invention prevents an extreme increase in the oscillation frequency during light loads by keeping the switching element in the OFF state for a predetermined period of time after the switching element is turned OFF, thereby improving reliability. The purpose is to reduce noise and improve efficiency.

(Structure of the invention) In order to achieve the above object, the invention connects a switching element to the primary side of a transformer with reverse polarity, and
In a switching regulator that connects a rectifying element to the next side and outputs an output to the secondary side by turning ON/OFF the switching element to oscillate, the secondary winding of the transformer is activated after the switching element is in the OFF state. a first state holding means for holding the switching element in the OFF state for a first period of time varying in accordance with the load capacity until the magnetic energy of the wire is released;
a second state holding means for holding the switching element in the OFF state for a predetermined second time period from when the switching element becomes the OFF state, and comparing the first time period and the second time period; When the second time is shorter than the first time, the first state holding means is selected, and when the second time is longer than the first time, the second state holding means is selected. The present invention is characterized in that it is provided with a comparison selection means for selecting.

Hereinafter, the present invention will be explained in detail based on embodiments.

1 and 2 are diagrams showing an embodiment of the present invention, which is applied to an RCC (Ringing Choke Converter).

In FIG. 1, T is a transformer, and the transformer T
The polarity is reversed as shown in the figure. The primary winding Ta of the transformer T is equipped with an enhancement type N-channel field effect transistor (FET) as a switching element.
Q1 is connected and an input voltage Vi is applied, and the voltage of the primary winding Ta, that is, the drain voltage V _D of the field effect transistor Q1 is input to the base of the transistor Q2 via the resistor R1 and the capacitor C1. ing. transistor Q
The collector of the transistor Q2 is connected to the gate G of the field effect transistor Q1, and the gate G of the field effect transistor Q1 is connected to the collectors of the transistor Q3 and the transistor Q4. A resistor R2 is connected to the gate G of the field effect transistor Q1.
A predetermined voltage _Vcc is applied through the field effect transistor Q1, and a current detection resistor R3 is connected to the source S of the field effect transistor Q1. The current _ID of the field effect transistor Q1 is detected as a voltage drop across the resistor R3, and this voltage drop, that is, the source potential _Vs of the field effect transistor Q1 is input to the positive terminal of the comparator CO1. Comparator CO
The negative terminal of 1 has a voltage value obtained by dividing the current of transistor Q5 by resistors R4 and R5 and converting it into a voltage.
Vb is input and comparator CO1 is Vs
>Vb, a high level signal is output to the base of the transistor Q4 via the resistor R6, and is also output to the base of the transistor Q6 via the resistor R7. A predetermined voltage _Vcc is supplied to the base of the transistor Q5 via a resistor R8, and
The phototransistor PT of the photocoupler PC is connected. A predetermined voltage _Vcc is supplied to the collector of the transistor Q6 via resistors R9 and R10, and a capacitor C2 is connected to the collector.
A predetermined voltage is applied to capacitor C2 through resistor R9.
A charging current flows from _Vcc , and this charging voltage _Vc is input to the negative terminal of the comparator CO2. Also, the charge on capacitor C2 is transferred to transistor Q6.
When it is ON, it is discharged through the resistor R10 and the transistor Q6, and the voltage Vc of the capacitor C2 drops to zero. A comparison voltage Ve obtained by dividing the predetermined voltage _Vcc by resistors R11 and R12 is input to the positive terminal of the comparator CO2.
CO2 outputs a high level signal to the base of transistor Q3 when Ve>Vc.

On the other hand, a diode D and a capacitor C are connected to the secondary winding Tb of the transformer T, and the secondary output voltage V _p is detected by a feedback amplifier IC. That is, a voltage obtained by dividing the output voltage V _p by resistors R13 and R14 is input to the positive terminal of the feedback amplifier IC, and a reference voltage V _ref is input to the negative terminal of the feedback amplifier IC. feedback amplifier ic
detects the difference between the output voltage V _p and the reference voltage V _ref and amplifies this value to drive the transistor Q7. A light emitting diode LD of the photocoupler PC is connected to this transistor Q7, and a current proportional to the output voltage V _p is supplied to the light emitting diode LD. Therefore, the phototransistor PT
The current increases in accordance with the output voltage _Vp , and the current of the transistor Q5 decreases, lowering the voltage Vb.

Note that the capacitor C1, resistor R1, and transistor Q2 keep the field effect transistor Q1 active until the magnetic energy of the secondary winding Ta is released.
The resistors R7, R9, R10, R11, and R
12, capacitor C2, transistor Q3, Q
6. The comparator CO2 constitutes a second state holding means 22 that holds the transistor Q1 in the OFF state for a predetermined period of time after the field effect transistor Q1 turns OFF, and the
1, R12, capacitor C2, transistor Q
6. The comparator CO2 selects the first state holding means 21 if it is longer than a predetermined time from when the field effect transistor Q1 is turned off;
Comparison and selection means 23 is configured to select the second state holding means 22 if the time is shorter than the predetermined time.

Next, the circuit operation will be explained with reference to the waveform diagram of each part shown in FIG. In addition, the left side of FIG. 2 shows when the load is large (during large load), and the right side shows when the load is small (during small load).

When transistors Q2, Q3, and Q4 are OFF,
The gate G of the field effect transistor Q1 is connected to the resistor R2.
is charged up by a predetermined voltage _Vcc through
When the potential of the gate G reaches the threshold voltage of the field effect transistor Q1, it turns ON and current flows.
_ID begins to flow. This current _ID is approximately equal to the input current Ii flowing through the primary winding Ta of the transformer T, and is given by the following equation, where Lp is the inductance of the primary winding Ta and t is the time.

ID=Vi/Lpt Therefore, the current of field effect transistor Q1
_ID increases with time t, as shown in FIG. 2b. The current value of this current _ID is detected as a voltage drop by resistor R3, and compared with voltage Vb by comparator CO1. Voltage Vb is a voltage value obtained by dividing the current of transistor Q5 by resistors R4 and R5 and converting it into a voltage, and the current value of transistor Q5 increases or decreases in inverse proportion to the current value of photo transistor PT. The current value of the photo transistor PT increases or decreases in proportion to the amount of light from the light emitting diode LD.
The amount of light from the light emitting diode LD is determined by the current value supplied to the light emitting diode LD. This current value is controlled by the feedback amplifier IC to a value corresponding to the magnitude of the output voltage V _p . That is, the feedback amplifier
The IC compares the output voltage V _p with the reference voltage V _ref and outputs a voltage corresponding to the difference to the transistor Q7 to control the current of the transistor Q7 flowing to the light emitting diode LD. Therefore, when the output voltage V _p increases, the current value of the photocoupler PC increases (the resistance value of the photo transistor PT decreases), the current value of the transistor Q5 decreases, and the reference voltage Vb of the comparator CO1 decreases. Set. As a result, the current value I _D of the field effect transistor Q1 for the comparator CO1 to output a high level signal
becomes lower, and the ON time of the field effect transistor Q1 becomes shorter.

Conversely, when the output voltage V _p decreases, the current in the photocoupler PC decreases (the resistance value of the photo transistor PT increases), the current in the transistor Q5 increases, and the reference voltage Vb of the comparator CO1 is set high. Therefore, the field effect transistor Q
1's N time T _ON becomes longer, and the current I _D of the field effect transistor Q1 increases.

After the field effect transistor Q1 is turned on, the current of the field effect transistor Q1 increases and Vs>Vb
Then, transistor Q4 turns on, and the gate-source voltage of field effect transistor Q1 increases.
As shown in FIG. 2g, V _GS becomes 0 [V] and the field effect transistor Q1 is turned off. The ON time of the field effect transistor Q1 is from when the field effect transistor Q1 is turned ON until it is turned OFF due to the ON of the transistor Q4.

In this way, the field effect transistor Q1
Since OFF is performed by comparator CO1, switching speed is fast and switching loss is small. Further, since the field effect transistor Q1 is used as a switching element, not only switching loss is reduced, but storage time is eliminated, and switching operation does not become intermittent even under light loads.

When field effect transistor Q1 turns off, field effect transistor Q
The drain voltage V _D of 1 is, as shown in Figure 2a,
The input voltage increases above Vi. This change in the drain voltage V _D of field effect transistor Q1 is transmitted to the base of transistor Q2 via capacitor C1 and resistor R1, transistor Q2 is turned on, the output of comparator CO1 is changed to low level, and transistor Q4 is turned off. The field effect transistor Q1 is kept OFF even after being reset to OFF. That is, the field effect transistor Q1
When it turns OFF, Vs decreases and comparator CO1
The output of the transistor Q4 is switched to a low level as shown in FIG. 2d, and the transistor Q4 is reset to OFF. However, at this time, transistor Q2
The gate of the field effect transistor Q1 is grounded, and the field effect transistor Q1 is kept in the OFF state.

In this way, field effect transistor Q1 is turned on.
When the field effect transistor Q1 is switched from OFF to OFF, the magnetic energy accumulated in the transformer T during the ON time T _ON of the field effect transistor Q1 is
During the OFF period T _OFF, it is supplied to the output side through the diode D. That is, the field effect transistor Q
1 turns OFF, the voltage of the bias winding Tb becomes positive on the winding start side, so the diode D becomes conductive, and the ON time T _ON of the field effect transistor Q1 decreases.
The energy stored in the transformer T is fed through the diode D to the output side. The output current I _p at this time is the primary current I _D as shown in Figure 2c.
When this output current I _p (magnetic energy of the secondary winding) is released, the voltage of the primary winding Ta of the transformer T, that is, the drain voltage
V _D decreases from a value higher than the input voltage Vi to about the magnitude of the input voltage Vi, as shown in FIG. 2a.
Due to this decrease in drain voltage V _D , transistor Q2 turns OFF, and at this time, transistor Q
3 is OFF, the charge up of the gate G of the field effect transistor Q1 starts from this point, and the state returns to the initial state. That is, the transistor Q2 of the first state holding means 21 is connected to the transistor Q2 of the transformer T.
Until the magnetic energy of the next winding Tb is released, it is turned ON and the field effect transistor Q1, which is a switching element, is kept in the OFF state.

On the other hand, the second state holding means 22 is a comparator.
When the trigger pulse shown in Figure 2 d is input from CO1, transistor Q6 turns on and the charge in capacitor C2 is transferred to resistor R10 and transistor Q6.
is discharged through the capacitor C2, i.e. the negative input voltage Vc of the comparator CO2.
becomes zero, as shown in FIG. 2e. after that,
Transistor Q6 turns OFF when the pulse of comparator CO1 becomes low level, and from the time transistor Q6 turns OFF, capacitor C
2, charging is started via resistor R9. Therefore, the voltage Vc of the capacitor C2 increases with time, as shown in FIG. 2e, and for a predetermined time Tc until Vc>Ve, the output of the comparator CO2 becomes as shown in FIG. 2f. As such, it maintains a high level. Thereafter, when Vc>Ve, the output of the comparator CO2 becomes low level, and the transistor Q3 is turned off. As a result, the second state holding means 22 causes the comparator CO1 to output a trigger pulse and turn off the field effect transistor Q1.
After that, Tc transistor Q3 is turned on for a predetermined period of time.
Therefore, the gate of field effect transistor Q1 is grounded, and field effect transistor Q1 is
Keep in OFF state.

However, as described above, the first state holding means 2 remains in the state after the field effect transistor Q1 is turned off until the energy of the secondary winding Tb is released.
It is maintained in the OFF state from 1, but this 1st
It is maintained in the OFF state by the state holding means 21.
As shown in Figure 2c, the OFF time Te changes depending on the amount of energy stored in the secondary winding Tb during the ON time of the field effect transistor Q1. It is long as shown in FIG. 2, and becomes shorter as the load becomes smaller as shown on the right side of FIG. The comparison selection means 23 causes the first state holding means 21 to turn off the field effect transistor Q1.
The time Te for holding the state is the second state holding means 2
2, if it is longer than the predetermined time Tc for holding the OFF state (Te≧Tc), the first state holding means 2
1 is selected, and the oscillation period of this switching regulator, that is, the oscillation frequency, is the OFF time Te.
Depends on. However, by the comparison selection means 23,
The first state holding means 21 is a field effect transistor Q
1 is held in the OFF state for a predetermined period of time Te is held in the OFF state by the second state holding means 22.
If it becomes shorter than Tc (Te<Tc), the second state holding means 22 is selected and the transistor Q3 is
Since it is ON during the OFF time Tc, the field effect transistor Q1 is in the OFF state during the OFF time Tc, and the time that the field effect transistor Q1 is OFF is a delay time Td (Td) from the OFF time Te to the OFF time Tc. = Tc - Te). Therefore, the oscillation frequency of the switching regulator depends on the OFF time Tc, and it is possible to prevent intermittent oscillation or an extreme increase in the generated frequency during light loads.

As a result, noise generation in the switching regulator can be reduced and the oscillation frequency band of the noise can be lowered, thereby improving the efficiency and reliability of the switching regulator.

Note that in the above embodiment, the capacitor C2
By appropriately selecting the capacity of , the OFF time Tc of the second state holding means 22 can be set.

(Effects) According to the present invention, it is possible to prevent the extreme increase in the oscillation frequency of the switching regulator when the load is light, thereby reducing noise, lowering the noise generation frequency band, improving efficiency, and improving reliability. can be improved.

[Brief explanation of the drawing]

1 and 2 are diagrams showing an embodiment of the switching regulator of the present invention. FIG. 1 is a circuit diagram thereof, and FIG. 2 is a waveform diagram of each part showing its operation. FIG. 3 shows the circuit of a conventional switching regulator. 21...First state holding means, 22...Second state holding means, 23...Comparison selection means, Q1...Field effect transistor, T...Transformer, Ta...Primary winding, Tb...Bias winding.

Claims (1)

[Scope of utility model registration request] In a switching regulator, a switching element is connected to the primary side of a transformer of opposite polarity, a rectifying element is connected to the secondary side, and output is taken out to the secondary side by turning the switching element ON/OFF to oscillate. , a first for holding the switching element in the OFF state for a first period of time varying in accordance with the load capacitance after the switching element is in the OFF state until the magnetic energy of the secondary winding of the transformer is released; a state holding means, and a state holding means that maintains the switching element for a predetermined second period of time from when the switching element becomes OFF.
A second state holding means that maintains the OFF state, compares the first time and the second time, and if the second time is shorter than the first time,
When the first state holding means is selected and the second time is longer than the first time, the second state holding means is selected.
A switching regulator comprising: a comparison selection means for selecting a state holding means.