JPH0614538A - Power circuit - Google Patents

Abstract

PURPOSE:To materialize the high output and the downsizing of a circuit by turning off a switching element at high speed. CONSTITUTION:In a power circuit, which uses a switching element FET 1 generating a specified current from a power source via a transformer T1, the driving winding L3 of the transformer T1, a resistor R19, and a capacitor C11 are connected in series to the control terminal of a switching element FET so as to drive this switching FED And, it is equipped with a detection resistor R17, which detects the current flowing through switching element FET, transistors Q11 and Q12 for control, which turns off the switching element FET, according to the voltage of the detection resistance R17, a capacitor C12, which generates negative voltage by the induced voltage of the driving winding L3 during the OFF period of the switching element FET a transistor Q13, which controls the quantity of charge of this capacitor C12, and a photocoupler PC.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit which switches a primary side to send a required output to a secondary side, and mainly uses a voltage control element such as MOSFET or IGBT as a switching element. The present invention relates to an exciting flyback power supply circuit.

[0002]

2. Description of the Related Art In a conventional self-excited flyback type switching power supply circuit, an ordinary bipolar transistor, which is a current control element, is generally used as a switching element. That is, a bipolar transistor is connected in series to the primary winding of the transformer, and a control circuit for controlling the ON / OFF of the bipolar transistor is connected to the base of the transformer to switch the primary side. Was sending output.

[0003]

However, since the bipolar transistor has a large switching loss and the control circuit has not been devised such that the bipolar transistor is turned off at a high speed, the loss is not reduced. For this reason, it has been difficult to increase the output and downsize the power supply circuit.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a power supply circuit capable of achieving high output and miniaturization by turning off a switching element at high speed.

[0005]

In order to achieve the above object, the present invention provides a DC power source comprising a primary winding of a transformer having primary, secondary and drive windings, a switching element and a current detection resistor. The control terminal of the switching element is controlled by using the voltage generated in the starting resistance, the voltage induced in the drive winding, and the voltage generated in the current detection resistance, and the switching element is turned on. , Off to induce a voltage in the secondary winding,
In a power supply circuit capable of sending the next output, a capacitor connected to the control terminal of the switching element via a resistor from the drive winding, and a negative voltage induced in the drive winding during the off period of the switching element. A negative voltage generating means to be charged with a current based on the current, a current control means for controlling the charging current to the negative voltage generating means so as to increase in accordance with an increase in the level of the secondary output, and both ends of the capacitor. A switch means is provided which is respectively connected between the negative voltage generating means and short-circuits the capacitor and the negative voltage generating means by a voltage generated in the current detecting resistor (claim 1).

Also, in the power supply circuit according to claim 1,
A diode is connected in parallel to the negative voltage generating means in reverse polarity (claim 2).

Also, in the power supply circuit according to claim 1,
A zener diode is provided between the drive winding and the negative voltage generating means (claim 3).

[0008]

According to the present invention, when the input power supply is connected, a voltage is applied to the control terminal of the switching element via the starting resistor, and the switching element starts to turn on. And
As the current flowing through the switching element increases, the voltage generated across the detection resistor increases, the switching means is turned on, and the switching element is turned off. At this time, since the control terminal of the switching element is short-circuited to the negative voltage of the negative voltage generating means by the switch means, the switching element is turned off at high speed. Further, the negative voltage generated in the negative voltage generating means is controlled by the current control means, and the secondary output of a desired level is obtained.

Further, according to the second aspect of the invention, even when the negative voltage generating means is not in a steady state in which a negative voltage is generated, such as when the power is turned on, the current is switched from the switch means through the diode. Flows and the switching element is turned off.

According to the third aspect of the invention, when the negative voltage generated in the drive winding exceeds the Zener voltage of the Zener diode, the negative voltage generating means is charged, so that the current control means fails. However, this power supply circuit is not destroyed.

[0011]

1 is a circuit diagram showing a first embodiment of a power supply circuit according to the present invention. This power supply circuit includes a drive circuit unit 1, a conversion circuit unit 2, a control circuit unit 3, and a rectifying / smoothing circuit unit 4.

The rectifying / smoothing circuit section 4 rectifies and smoothes a commercial AC power source. The conversion circuit unit 2 inputs the rectified DC power to the primary winding L1 of the transformer T1, switches the switching element at a high frequency by turning the switching element on and off, induces a voltage in the secondary winding L2, and outputs the voltage at a predetermined level. To get the output of. The drive circuit unit 1 includes the conversion circuit unit 2
The switching element is driven to perform on / off operation. The control circuit unit 3 detects the output voltage or current from the conversion circuit unit 2 and controls the drive circuit unit 1 so as to maintain a required output.

A rectifying bridge BD and a capacitor C2 are connected to the input terminal through a circuit consisting of a fuse F, a resistor R1 for removing noise and surge, a capacitor C1 and a choke coil LC to rectify and smooth the AC power supply. It is supposed to be done.

The primary winding L1 of the transformer T1, a MOS field effect transistor FET as a switching element, and this field effect transistor FET are provided between the positive electrode and the negative electrode (hereinafter referred to as ground) of the output terminal of the rectifying / smoothing circuit section 4.
A detection resistor R17 for detecting the current flowing through the is connected in series.

The circuit in which the diode D21 is connected in series to the parallel circuit of the capacitor C21 and the resistor R21 is
It improves the characteristics of the current flowing into the primary winding L1 and prevents the reverse current from flowing in.
1 connected in parallel.

The transformer T1 is composed of a primary winding L1, a secondary winding L2 and a drive winding L3, and the current flowing into the primary winding L1 is switched by turning on and off the field effect transistor FET, and as a result. A voltage is induced in the secondary winding L2 and the drive winding L3.

A diode D23 is connected in series to the secondary winding L2, and a capacitor C23 is connected in parallel to the secondary winding L2. The voltage induced in the secondary winding L2 is rectified and smoothed, and the voltage is output from the output terminal. It is designed to supply DC power.

The series circuit of the starting resistors R11, R12 and R13 is for starting the field effect transistor FET by applying a voltage to the gate of the field effect transistor FET. It is connected between the gates of the FETs. Further, a series circuit composed of a capacitor C11, a resistor R19 and a drive winding L3 is connected between the gate of the field effect transistor FET and the ground to form an oscillation circuit. And
The induced voltage of the drive winding L3 is a field effect transistor FET
Is applied to the gate of the field effect transistor FET, and the field effect transistor FET is turned on and off.

The Zener diode Z12 protects the gate of the field effect transistor FET, and has a cathode connected to the gate of the field effect transistor FET and an anode connected to the ground. For the same purpose, a resistor R16 is connected between the source of the field effect transistor FET and the cathode of the Zener diode Z12.

As a result, the field effect transistor FE
A voltage higher than the Zener voltage Vz12 of the Zener diode Z12 is not applied to the gate of T.

The capacitor C12 is a negative voltage generating means that is charged to a negative voltage while the field effect transistor FET is off. A series circuit composed of a diode D11 and a transistor Q13 that charges the capacitor C12 to a negative voltage is a driving winding. It is connected to both ends of L3. A discharging resistor R18 is connected in parallel with the capacitor C12.

A control transistor Q12 for reducing the gate of the field effect transistor FET to the off voltage is provided at both ends of the capacitor C11, and a control transistor for discharging the electric charge accumulated in the capacitor C11 and the electric charge of the gate of the field effect transistor FET. The transistors Q11 are connected to each other.

That is, the control transistor Q11 is
The collector is connected to the connection point between the capacitor C11 and the resistor R19, and the control transistor Q12 is connected to the connection point between the capacitor C11 and the gate of the field effect transistor FET.

The control transistors Q11 and Q12 are also provided.
The base of is connected to the anode of the Zener diode Z11 via resistors R14 and R15, respectively, and its cathode is connected to the source of the field effect transistor FET. Then, the control transistors Q11 and Q
The emitter of 12 is connected to the negative voltage side of the capacitor C12.

A series circuit composed of a Zener diode Z31, a resistor R32 and a light emitting diode of a photocoupler PC is connected between the positive and negative electrodes of the output terminal of this power supply circuit. This circuit constitutes a feedback circuit for output control.

The photocoupler PC is connected in series with the resistor R31 between the ground and the base of the transistor Q13, and controls ON / OFF of the transistor Q13 according to the output level of the power supply circuit. The amount of charge of the capacitor C12 by the voltage induced in the drive winding L3 is controlled based on the on / off state of the transistor Q13.

Next, the operation of the power supply circuit configured as described above will be described. When the input power source is connected, the capacitor C11 is passed through the starting resistors R11, R12, R13.
Are charged, so that a voltage is applied to the gate of the field effect transistor FET,
Starts to turn on. Therefore, a current flows through the primary winding L1 to induce a feedback voltage in the drive winding L3, and this induced voltage rises with a time constant determined by the drive winding L3, the resistor R19, and the capacitor C11, and the field effect transistor FET Of the gate voltage Vg of the field effect transistor FET
The current Is flowing from the source of the source increases.

On the other hand, the current Is flowing from the source of the field effect transistor FET increases as the induced voltage of the drive winding L3 rises, and the voltage Vs generated in the detection resistor R17 rises.

Here, the voltage across the capacitor C12 is Vc, and the zener voltage of the zener diode Z11 is Vz1.
1. Let Vbe be the voltage between the base and emitter of the control transistors Q11 and Q12.
When the source current Is of ET begins to flow, Vs + Vc ≦ Vz11 + Vbe, but when the source current Is increases and becomes Vs + Vc> Vz11 + Vbe, the Zener diode Z11 is turned on.

By this turning on, the base current is supplied,
Both the control transistors Q11 and Q12 are turned on, and the gate voltage of the field effect transistor FET is the capacitor C1.
To a negative voltage of 2.

At this time, the charge of the capacitor C12 is discharged by the control transistor Q11 to remove the charge of the gate of the field effect transistor FET together with the control transistor Q12, so that the field effect transistor FET is turned off at high speed. It

After this, the starting resistors R11, R12, R13
A voltage is again applied to the gate of the field effect transistor FET through the field effect transistor FET, and the field effect transistor FET is turned on. That is, the field effect transistor FET repeats switching, and this switching causes the secondary winding L2.
Electric power is induced in and rectified to obtain a DC power supply.

As described above, since the capacitor C12 reverse biases the gate of the field effect transistor FET, the larger the negative voltage Vc of the capacitor C12, the faster the field effect transistor FET is turned off and the switching loss is reduced. You can

The control transistors Q11 and Q12 are also provided.
Causes the field effect transistor FET to be turned off even faster, thus reducing the switching loss and thus
The heat generation of the field effect transistor FET is suppressed, the size is small, and a low-cost power supply circuit can be realized.

When the output voltage of the DC power supply obtained by the above operation exceeds the Zener voltage of the Zener diode Z31, the photocoupler PC is driven, the base current is supplied to the transistor Q13, and the transistor Q13 is turned on. , The capacitor C12 is charged, and the output voltage is suppressed.

When the negative voltage Vc of the capacitor C12 is increased to Vc> Vz11 + Vbe, the field effect transistor FET can be completely cut off and oscillation can be stopped. Therefore, by controlling this negative voltage, it is possible to cope with a minute output.

Next, a second embodiment of the power supply circuit according to the present invention will be described. FIG. 2 shows a second power supply circuit according to the present invention.
It is a circuit diagram which shows an Example. The same parts as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the second embodiment, the diode D12 is connected in parallel with the capacitor C12 in the circuit of the first embodiment. The cathode of the diode D12 is connected to the ground so as to have the opposite polarity.

In this way, the control transistor Q11,
By connecting the emitter of Q12 to the ground via the diode D12, the electric field can be generated even when the capacitor C12 is not charged, that is, when the capacitor C12 is charged and becomes a steady state, such as when the power is turned on. The on-time of the effect transistor FET becomes long, a large current flows, and there is no risk of the circuit being destroyed, and the reliability of the circuit can be improved.

Further, by disposing the diode D12, it is possible to prevent the circuit from being broken even if the capacitor C12 is opened.

Next, a third embodiment of the power supply circuit according to the present invention will be described. FIG. 3 shows a third power supply circuit according to the present invention.
It is a circuit diagram which shows an Example. The same parts as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the third embodiment, the charging Zener diode Z13 is connected in parallel with the transistor Q13 in the circuit of the first embodiment. The cathode of the charging Zener diode Z13 is connected to the collector side of the transistor Q13.

Here, due to the disconnection of the light emitting diode of the photocoupler PC, the opening of the transistor Q13, etc.
When a state occurs in which the induced voltage of the drive winding L3 does not charge the capacitor C12 via the transistor Q13,
The negative voltage Vc of the capacitor C12 becomes smaller, and along with this, the output voltage on the secondary side increases and becomes dangerous.

At this time, when the drive winding L3 is opened, the induced voltage becomes high, and the Zener diode Z13 is turned on by the increased induced voltage to negatively charge the capacitor C12, so that the output voltage is suppressed. To be done.

The voltage induced in the secondary winding L2 is
Drive winding L3 during the off period of the field effect transistor FET
Since it is proportional to the voltage induced in the power source, the Zener voltage of the charging Zener diode Z13 may be selected so that the output of the power supply circuit is slightly above the required level.

As described above, the charging Zener diode Z
13 is connected in parallel to the transistor Q13,
There is no risk of circuit breakdown or accidents such as electric shock due to excessive output voltage.

In each of the above-described embodiments, the MOS type field effect transistor FET is used as the switching element, but it is also applicable to an IGBT which is a kind of voltage control element, and a normal bipolar element which is a current control element. It can also be applied to a transistor.

[0048]

According to the present invention, the DC power source is
It is supplied to the series circuit consisting of the primary winding of the transformer having the secondary and drive windings, the switching element and the current detection resistance, and is generated in the starting resistance generated voltage, the voltage induced in the drive winding and the current detection resistance. In the power supply circuit that controls the control terminal of the switching element by using the voltage to turn on and off the switching element to induce a voltage in the secondary winding and send a secondary output, A capacitor connected from the drive winding through a resistor to the control terminal of the switching element, and a negative voltage generating means that is charged with a current based on a negative voltage induced in the drive winding during the OFF period of the switching element. And current control means for controlling the charging current to the negative voltage generation means so as to increase in accordance with the rise in the level of the secondary output,
Since both ends of the capacitor and the negative voltage generating means are respectively connected, and the switch means for short-circuiting the capacitor and the negative voltage generating means by the voltage generated in the current detection resistor is provided, the switching element can be operated at high speed. Since it can be turned off, heat generation of the switching element can be suppressed, and a small-sized, inexpensive, large-capacity power supply circuit can be realized.

Further, since the diode is connected in parallel with the negative voltage generating means in the opposite polarity, the switching element can be turned off by the switch means even before the steady state in which the negative voltage is generated in the negative voltage generating means. it can.

Further, since the Zener diode is provided between the drive winding and the negative voltage generating means, even if the current control means fails, the negative voltage generating means is charged to the negative voltage and the secondary output is suppressed. be able to.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a power supply circuit according to the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the power supply circuit according to the present invention.

FIG. 3 is a circuit diagram showing a third embodiment of the power supply circuit according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 drive circuit unit 2 conversion circuit unit 3 control circuit unit 4 rectifying / smoothing circuit unit C12 capacitor (negative voltage generating means) L3 drive windings R11 to R13 start-up resistor R17 detection resistor Q11, Q12 control transistor Z13 charging Zener diode

Claims (3)

[Claims] 1. A DC power supply is supplied to a series circuit including a primary winding of a transformer having primary, secondary and drive windings, a switching element and a current detection resistor, and a voltage generated by a starting resistor, the drive winding. A voltage is induced in the secondary winding by controlling the control terminal of the switching element by using the voltage induced in the wire and the voltage generated in the current detection resistor to turn on and off the switching element. Two
In a power supply circuit capable of sending the next output, a capacitor connected to the control terminal of the switching element via a resistor from the drive winding, and a negative voltage induced in the drive winding during the off period of the switching element. A negative voltage generating means to be charged with a current based on the current, a current control means for controlling the charging current to the negative voltage generating means so as to increase in accordance with an increase in the level of the secondary output, and both ends of the capacitor. A power supply circuit comprising: switching means that is respectively connected between the negative voltage generating means and short-circuits the capacitor and the negative voltage generating means by a voltage generated in the current detecting resistor. 2. The power supply circuit according to claim 1, wherein a diode is connected in parallel with the negative voltage generating means in a reverse polarity. 3. The power supply circuit according to claim 1, wherein a zener diode is provided between the drive winding and the negative voltage generating means.