JPS61254074A - Power source - Google Patents

Abstract

PURPOSE:To reduce the number of parts as a whole by turning OFF the first current controller when the terminal voltage of a capacitor becomes the prescribed value, and using the terminal voltage as a drive power source of a controller. CONSTITUTION:A DC input Ein is switched through the primary coil Np of an inverter transformer T1 by an FETQ2 to obtain the prescribed output voltage V0 from the secondary coil Ns. The FETQ2 is controlled at its duty ratio by a controller (CONT) through a photocoupler PC to maintain the voltage V0 at the prescribed value. In this case, the power source of the controller is composed of the first, second current controllers Q3, Q4, and a capacitor C1, and the second current controller Q4 is operated by a trigger element D1 at the stage that the terminal voltage of the capacitor C1 arrives at the prescribed value to turn OFF the first controller Q3 to use the terminal voltage of the capacitor C1 as a drive power source. The capacitor C1 is also charged by the bias coil NB of the transformer T2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention particularly relates to a power supply device used in electronic devices such as personal computers and word processors.

[Technical Background of the Invention] In recent years, battery-powered burner computers and word processors have been developed. A so-called switching power supply device is installed, which is configured to transform the voltage and further rectify it to obtain a stabilized direct current at a predetermined level.

FIG. 3 is a block diagram showing an example of the configuration of this switching power supply device (hereinafter referred to as SR).

In the same figure, E in is the input DC current, C1 is the smoothing capacitor, TI is the inverter transformer, NP sNs are the primary and secondary coils of the inverter transformer Tff, and Q
+ is a power transistor that performs switching, T2 is a drive transformer, N1 and N2 are drive transformers T2
, C0NT is a control circuit that controls the switching operation of power transistor Q1, Dll is a rectifying diode on the secondary side, CF is a smoothing capacitor, A is an error amplifier, and R++ to R+s are voltage dividing resistors. , Dz is a Zener diode that generates a reference voltage, R1
4 indicates a resistor for supplying the bias current. In this SR, the output of the error amplifier A connected to the secondary side is input to the control circuit C0NT, and the control circuit C0NT is inputted to the control circuit C0NT.
0NT is power transition.

The output voltage Vo is controlled to be constant by controlling the 0N10FF time ratio (duty ratio) of the star Q1.

. The part indicated by the dotted line in the figure is the control circuit C.
Auxiliary power supply circuit (hereinafter referred to as AUX PS-ALlxiliary) for supplying a stabilized drive voltage to 0NT
R8 is a bias resistor, T3 is an inverter transformer,
N^, NO and Nc are the primary coil, bias coil and secondary coil, Q^ is the switching transistor, C0NT-8 is a control circuit that controls the operation of the switching transistor Q^, D^ is the diode on the primary side, DB indicates a rectifying diode on the secondary side, and C^ indicates a smoothing capacitor on the secondary side.

In the power supply device as described above, when the input DC E in is first applied, the control circuit C0NT-8 is operated through the bias resistor R8, and the transistor Q^ is roughly operated to start switching.

Then, a stabilized voltage Vcc is generated on the secondary side of the inverter transformer T3, and this voltage operates the control circuit C0NT. Then, the power transistor Q1 is turned on via the drive transformer T2, and the main switching operation is opened.

As a result, the input DC E in is transmitted as AC to the secondary coil of the inverter transformer 〒1, and the DC output voltage V
o.

On the other hand, the output voltage Vo is the reference voltage (
zener voltage of Dz), and the output voltage of error amplifier A is generated such that these errors are O volts.

This output voltage enters the 3rd pin of the control circuit C0NT, and a signal for controlling the switching duty ratio of the power transistor 19Q1 is created in the control circuit C0NT, and is used as a drive signal from the 2nd pin of the control circuit C0NT. taken out.

And, ゛This drive signal is the drive transformer T'z
is applied to the base of power transistor Q+ via
Transistor Q1 performs switching with a duty ratio that stabilizes output voltage Vo.

[Problems with the background art] However, the conventional
:SR is AUX PS is inverter transformer T3,
It consists of diodes D^, DB, smoothing capacitor C^, control circuit C0NT-B, etc., so the number of parts is large and the configuration is complicated.

For this reason, there is a problem in that especially in a small capacity SR, the size of the AUXPS becomes relatively large and the manufacturing cost becomes high.

[Objective of the invention] The present invention solves the problems of conventional SR.
This is an AU that generates a drive voltage for a control circuit that controls switching elements.
'x Aims to provide SR with simplified PS configuration
□.゛ [Overview of Kojimei] ゛゛ That is, the SR of the present invention includes an inverter transformer having a primary coil, a secondary coil, and a bias coil magnetically coupled to the primary coil, and an input flowing to the primary coil. a switching element that converts direct current to alternating current; a capacitor that is charged by a current induced in the bias coil; a first current control element that applies the input direct current to the capacitor during operation; and this first current control element. a bias resistor, a second current control element that bypasses the bias current of the first current control element during operation and turns off the first current control element, and a terminal voltage of the capacitor reaches a certain value. At this stage, a trigger element operates the second current control element, and a terminal voltage of the capacitor is used as a driving power source, and the switching operation of the switching element is controlled so as to stabilize the current induced in the secondary coil. It is characterized by comprising a control circuit that performs the following operations.

[Embodiments of the Invention] Hereinafter, details of embodiments of the present invention will be described based on the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, and parts common to those in FIG. 3 are given the same reference numerals.

Note that although the SR of this embodiment uses an FET that operates at low voltage as a switching element, the circuit configuration remains the same even if a power transistor is used as in the conventional SR.

In the figure, E in is an input DC current, T1 is an inverter transformer, Np and Ns are its primary and secondary coils, No is a bias coil magnetically coupled to the primary coil NP, Q2 is an FET that performs switching, and C1 is a capacitor charged by the current induced in the bias coil NO of the inverter transformer T1, Q3 is a current control transistor that applies input DC to the capacitor C1 during operation, and R1 is a bias inserted in the baseline of the transistor Q3. Resistor Q4 is a transistor that bypasses the base current of transistor Q3 during operation, DL is a Zener diode as a trigger element that turns on transistor Q4 when the terminal voltage of capacitor C1 reaches a certain value Vcc, C0NT is FET Q2 This shows a control circuit that controls the duty ratio.

Also, A is an error amplifier connected to the secondary coil N8, and PC
shows a photocoupler consisting of a photodiode PD and a phototransistor PT, which insulates this error amplifier A from the primary side.

In the figure, D2 indicates a diode inserted between the bias coil Nb and the capacitor C1, and R2 indicates a current limiting resistor of the photodiode PD.

The emitter of the phototransistor PT is connected to the third bin of the control circuit C0NT, and the input DC E i
n is divided by resistors R3 and R4 and connected to the fifth bin of the control circuit C0NT, and the voltage dropped by the resistor R6 connected to the drain of the FET Q2 is input to the fourth bin of the control circuit C0NT. Further, the terminal voltage of the capacitor C1 is connected as a driving voltage to the first bin of the control circuit C0NT, and the gate of the FET Q2 is connected to the second bin of the control circuit C0NT.

Next, the operation of this circuit will be explained.

First, when the input DC current E in rises, a bias current flows through the resistor R1 to the base of the transistor Q3, turning on the transistor Q3. Then, a current obtained by multiplying the current increase rate hpE of the transistor Q3 by the bias current flows as the collector current of the transistor Q3, and the current increases by the bias current.
Charge 1. The terminal voltage Vcc of this capacitor C1 becomes the drive voltage of the control circuit C0NT, and the control circuit C0NT operates. Then, (Nb /NO)E t in the bias coil Nb of the inverter transformer T1
A voltage of n is induced. When the terminal voltage Vcc of the capacitor C1 reaches the Zener voltage of the Zener diode D1, the Zener diode D1 becomes conductive and the transistor Q4 is turned on.

Then, when transistor Q4 turns on, transistor Q
The base voltage of Q3 is bypassed and transistor Q3 is
Become FF.

From then on, the capacitor C1 is charged exclusively by the induced voltage of the bias coil Nb, and the control circuit C1 is charged exclusively by the induced voltage of the bias coil Nb.
A driving voltage is stably supplied to 0NT.

Note that in the above, the output voltage Vo from the secondary coil Ns
is fed back to the 3rd pin of the control circuit C0NT via the error amplifier A and the photocoupler PC, and the control circuit CON King is thereby fed back to the FETQ2
The output voltage Vo is always kept at a constant value.

On the other hand, the input DC E in is divided by resistors R3 and R4,
It enters pin 5 of the control circuit C0NT and is used for feedforward control. This feedforward control is performed in order to speed up the response and improve the quality of control by controlling the duty ratio of FET Q2 in accordance with changes in the input voltage, compared to feedback control of the output voltage Vo.

If overcurrent flows through FETQ2, resistor R6
This is detected by the control circuit C0NT.
The control voltage is input to pin No. In this case also FE
The duty ratio of TQ2 is limited and overcurrent is suppressed.

In the SR of this embodiment, when the input DC Ein is -100V, the base current of the transistor Q3 is 0.111 A when the resistance is R+-IMΩ, and the current amplification factor of the transistor Q3 is hpi-100, the base current of the transistor Q3 is It becomes 10+e A.

And for capacitor c+-ioμF, capacitor C
It takes 121 seconds to boost the terminal voltage of 1 to 12V required for driving the control circuit C0NT.

Here, when the input DC current Ein is -154V and the current amplification factor hpε-300 of the transistor Q3, the peak power consumption of the transistor Q2 is 6.5W.

However, since the transistor Q2 is turned off when the terminal voltage of the capacitor C1 reaches 12V, the power loss in the transistor Q2 is extremely small.

On the other hand, the power consumption in resistor R1 during steady state is Einm154
In the case of V, R+ -IMΩ, it is about 0.025W. Therefore, the SR of this embodiment has the following characteristics: ■ The power loss generated in the AUX PS of the control circuit C0NT is small. ■ The AUX PS is miniaturized. ■ The number of parts of the ALIX PS is reduced. ■ The efficiency does not decrease much even in the case of a small container. exhibits.

Note that the present invention is not limited to the above-mentioned embodiment. For example, if the polarity of the bias coil Ne is reversed,
Capacitor C1 can be charged while FET Q2 is OFF.

Further, in the above embodiment, the Zener diode D1 is used as the tri-element connected to the base of the transistor Q4, but a thyristor S can also be used as shown in FIG. In this case, the anode of the thyristor is connected to the base side of transistor Q3, and the cathode is
Connect to the ground line of V, and roughly connect capacitor C2 between the anode of Zener diode D1 and the ground line.
Interpose.

Further, in the embodiments described above, the case where the present invention is applied to a flyback converter has been described, but the present invention can be similarly applied to other SRs such as a forward converter and a half-bridge converter.

In addition, the control circuit C in the embodiment described briefly above
0NT is a control circuit that controls the duty ratio of the switching transistor, that is, controls the pulse width (PWM), but the control circuit may also be a control circuit that controls the frequency of the switching transistor.

[Effects of the Invention] As explained above, in the present invention, S R is a primary coil,
An inverter transformer has a secondary coil and a bias coil magnetically coupled to the primary coil, and converts the input direct current flowing through the primary coil into alternating current.
a capacitor that is charged by a current; a first current control element that applies input DC to the capacitor during operation; a bias resistor of this first current control element;
a second current control element that bypasses the bias current of the current control element and turns off the first current control element; and operates the second current control element when the terminal voltage of the capacitor reaches a certain value. It is equipped with a trigger element and a control circuit that uses the terminal voltage of the capacitor as a driving power source and controls the switching operation of the switching element to stabilize the current induced in the secondary coil, so it can be controlled with a simple circuit configuration. A constant voltage can be supplied to the circuit, and the total number of components is small.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of one embodiment of the present invention, FIG. 2 is a circuit diagram showing the configuration of another embodiment of the present invention, and FIG. 3 is a circuit diagram showing the configuration of a conventional power supply device. be. T1...Inverter transformer Na...Bias coil Q+, Q3, Q4...Transistor Q2...・・・・・・・・・・・・FETR+”R+
s...Resistor CI, C2... Capacitor D1... Zener diode D2... Diode P.C.
・・・・・・・・・・・・・・・Photocabra A・・・・
・・・・・・・・・・・・Error amplifier C0NT・・
...Control circuit applicant Toshiba Corporation Patent attorney Sa Suyama - Figure 1 Figure 2 Figure 3

Claims (4)

[Claims] (1) An inverter transformer having a primary coil, a secondary coil, and a bias coil magnetically coupled to the primary coil; a switching element that converts input DC flowing through the primary coil into AC; a capacitor charged by an induced current; a first current control element that applies the input direct current to the capacitor during operation; a bias resistor of the first current control element; and a first current control element during operation. a second current control element that bypasses the bias current of the element and turns off the first current control element, and operates the second current control element when the terminal voltage of the capacitor reaches a certain value. It is characterized by comprising a trigger element and a control circuit that uses the terminal voltage of the capacitor as a driving power source and controls the switching operation of the switching element so as to stabilize the current induced in the secondary coil. power supply. (2) The power supply device according to claim 1, wherein the switching element is a FET. (3) The power supply device according to claim 1 or 2, wherein the trigger element is a Zener diode. (4) The power supply device according to any one of claims 1 to 3, wherein the control of the switching element by the control circuit is pulse width control.