JPS61254073A - Power source - Google Patents

Abstract

PURPOSE:To reduce the number of parts by operating a current control element at the stage that the terminal voltage of the first capacitor arrives at the prescribed value to move the charge to the second capacitor as a drive source of a controller. CONSTITUTION:A DC input Ein is switched through the primary coil Np of an inverter transformer T1 by an FETQ3 to obtain the desired output voltage V0 from the secondary coil Ns of the transformer T1. The duty ratio of the FETQ3 is controlled by a controller (CONT). In this case, the power source of the controller is composed of the first capacitor C1 charged by the voltage Ein, a current controller Q4 operated by a trigger element D5 at the state that the terminal voltage arrives at the prescribed value, and the second capacitor C2 charged by the output of the element Q4 and the bias coil NB of the transformer T1, and the terminal voltage of the capacitor C2 is supplied as a drive power source.

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 1 In recent years, battery-powered personal computers and word processors have been developed. A so-called switching power supply device is installed, which is configured to transform and rectify direct current 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, Ct is the smoothing capacitor, T1 is the inverter transformer, NP%Ns is the primary and secondary coils of the inverter transformer T1, Ql is the power transistor that performs switching, T2 is the drive transformer, Nt , N2 is drive transformer T2
, C0NT is a control circuit that controls the switching operation of power transistor Q1, C++ is a rectifying diode on the secondary side, CF is a smoothing capacitor, A is an error amplifier, and R11 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 C
0NT controls the 0N10FF time ratio (duty ratio) of the power transistor Q1, thereby performing IIJIll to keep the output voltage Vo constant.

The part indicated by the dotted line in the figure is the control circuit C0N.
Auxiliary power supply circuit (hereinafter referred to as ALIX PS-Auxil + ary
p over s up + y), and R
e is a bias resistor, T3 is an inverter transformer, N^,
NB and Nc are their primary coils, bias coils and secondary coils, Q^ is a switching transistor, C0
NT-8 is a control circuit that controls the operation of the switching transistor Q^, D^ is a diode on the primary side, D
B 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 Ein is first applied, the control circuit C0NT-8 operates through the bias resistor R8, and the transistor Q^ also operates 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 started.

As a result, the input direct current E in is transmitted as alternating current to the secondary coil of the inverter transformer T1, and is taken out as a direct current output voltage Vo via the rectifying diode Drti13 and the smoothing capacitor Cp.

On the other hand, the output voltage Vo is the reference voltage (
02 Zener voltage), and the output voltage of error amplifier A is generated such that these errors become 0 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 Q1 is generated within the control circuit C0NT, and is taken out as a drive signal from the 21st pin of the control circuit C0NT.

And this drive signal is a drive transformer.

The voltage is applied to the base of the power transistor Q1 via T2, and the transistor Q1 performs switching with a duty ratio that stabilizes the output voltage Vo.

[Problems with Background Art] However, the conventional SR configured as described above has
Since AUX PS is composed of inverter transformer T3, diodes O^, DB, smoothing capacitor C^, control circuit C0NT-B, etc., 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 dimensions of the ALIXPS are relatively large (and the manufacturing cost is also high).

[Objective of the Invention] The present invention has been made to solve the problems of the conventional SR, and is an SR in which the configuration of the AUX PS that generates the drive voltage of the control circuit that controls the switching elements is simplified. The purpose is to provide

[Summary of the Invention] 1″″’ Honshu 11 (7) S R!・1st order 04″・2I
.

an inverter transformer having a coil and a bias fill magnetically coupled to the primary coil, and a switching element that converts input direct current flowing through the primary coil to alternating current;
A first capacitor charged by the input DC current, a second capacitor charged by the current induced in the bias coil, and a charge accumulated in the first capacitor during operation is transferred to the second capacitor. a trigger element that operates the current control element when the terminal voltage of the first capacitor reaches a certain value; and a trigger element that drives the terminal voltage of the second capacitor.
It is characterized by comprising an iR source and a control circuit that controls the switching operation of the switching element so as to stabilize the current induced in the secondary coil.

Embodiments of the present invention] Details of embodiments of the present invention will be described below based on the drawings.

The stain is from fJd company.

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 same figure, E in is the input DC current, C1 is the smoothing capacitor °, T1 is the inverter transformer, N P %N
8 is the primary and secondary coils of the inverter transformer T1;
Na is a bias coil magnetically coupled to the primary coil Np, C3 is an FET for switching, C+ is a capacitor charged by the input DC, and C2 is charged by the current induced in the bias coil Nθ of the inverter transformer T1. C4 is a current control transistor, D5 is a diac as a trigger element that turns on transistor Q4 when the terminal voltage of capacitor C1 reaches a certain value, and C0NT is a control circuit that controls the duty ratio of FETC3. It shows.

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

In the figure, 04 indicates a Zener diode connected to both ends of the capacitor C2, and R+s 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 in is voltage-divided by resistors R7 and R8 to the control circuit C0N.
The voltage drop due to the resistor R6 connected to the 5th bin of T and the drain of the FET is controlled by the control circuit C0NT.
is input into the 4th bin. Further, the terminal voltage of the capacitor C2 is connected as a driving voltage to the first bin of the control circuit C0NT, and the gate of FETC3 is connected to the second bin of the control circuit C0NT.

Next, the operation of this circuit will be explained.

First, when the incoming DC current E in rises, the capacitor C1 is charged through the resistor R1. Also, the voltage of capacitor C1 is the breakover voltage Ve (2
When φ increases to a value equal to the sum of the base-emitter voltage of transistor Q4), diac D5 turns on. In this case, the diac D5 has the same function as a combination of a Zener diode and a thyristor, and the impedance between terminals A and B after the diac D5 is turned on becomes very small. Therefore, when the diac D5 is turned on, the base current of the transistor Q4 rapidly flows through the resistor R2, and the transistor Q4 is turned on. Note that C3 is a capacitor for speeding up the transistor Q4.

Then, when transistor Q4 turns on, the charge stored in capacitor C1 moves to capacitor C2. At this point, let the voltage of capacitor C1 be vl, and the terminal voltage of each capacitor C1 and C2 after discharge be v2,
Ignoring the voltage drop across transistor Q4 and diode D2, first, V+-Ve (breakover voltage of diac D5).

At this time, assuming that the charge of each capacitor is conserved, C1V1-(CI+02)V2 holds true.

Therefore, rV2=01/(C1+02)Vl.

Coco rC1-2, 2μFs C2= 2.2μFs V
When it is t-26■, it is V2-13V.

This voltage v2 enters the first pin of the control circuit C0NT, and the control circuit C0NT starts operating. In addition, in the above, the zener voltage Vz of the zener diode D4
is 12V.

And FET from pin 2 of control circuit C0NT
A voltage is generated that turns on Qs.

Generally, the gaiter source voltage Vcs (ON) required to keep the FETGjs in the ON state is around 10 volts.

When FETQs is roughly turned on, the input DC Ein is applied to the primary coil NP of the inverter transformer T+, and the bias coil N8 of the inverter transformer T1 receives (
A voltage of Ne/Np)·E- is induced. This voltage is
Capacitor C2 is charged through the path D3→R4→C2, but the voltage Vcc of capacitor C2 is
A constant value of 12 volts is maintained by the Zener voltage (12 volts) of D.

Therefore, from now on, capacitor C2 from capacitor C1
Even if no charge is supplied to the control circuit C0NT, as long as the FET Qs performs the switching operation, the drive power necessary for the operation of the control circuit C0NT is supplied from the bias coil Na.

Note that in the above, the output voltage Vo from the secondary coil N8
is fed back to the third bin of the control circuit C0NT via the error amplifier A and the photocoupler PC, and the control circuit CON■ is thereby fed back to the FETQ+
The output voltage Vo is always kept at a constant value.

On the other hand, the input DC EIn is divided by resistors R7 and R11,
It enters the 5th bin of the control circuit C0NT and is used for feedforward control. This r feedforward control allows the FET to
By controlling the duty ratio of Qs, the output voltage V
This is done to speed up the response and improve the quality of control compared to the feedback control of o.

If an overcurrent flows through FETQs, the resistor Rs
This is detected by 1. Control circuit C0NT
Control in the 4th bin of i! ! It is input as pressure. In this case as well, the duty ratio of FETQs is limited and overcurrent is suppressed.

In addition, in the above, R word-410 is Ω, 01m2, 2uF
, Ein -100V, the charging time τ of the capacitor C1 is r+ -Ct R1Jim ・1/ (1
-V+ /Ein)■1(Sec).

Also, the loss in R1 is P, assuming Ein -154V.
,, -(154)' / 470k -0,05(
W). From this, it can be seen that the loss in the bias resistor R1 is extremely small.

As explained above, in the SR of this embodiment, the voltage Vcc to be supplied to the control circuit C0NT is generated without using a DG/DC converter, so the number of parts is reduced, and as a result, the manufacturing cost is reduced, and the device can be easily Overall dimensions become smaller.

Furthermore, since the charging voltage of the capacitor C1 can be increased, the capacitance of the capacitor C1 can be reduced. Note that this allows the resistor R1 to be made larger, thereby reducing power loss in the resistor R1.

Furthermore, since the power loss in the control circuit C0NT is reduced, there is little decrease in efficiency even when applied to a small capacity SR.

Note that the present invention is not limited to the above-mentioned embodiment. For example, if the polarity of the bias coil Nθ is reversed,
During the period when the secondary side diode Dot is on, the capacitor C2 can be charged through the diode D3.

In this case, the voltage induced in the bias coil N8 is (No/Ng)Vo, but since Vo is constant, the voltage of the bias coil Na is also constant. Therefore, since the charging voltage to capacitor C2 is also constant, resistor R4 and Zener diode D4 can be omitted.
The efficiency of the control circuit C-ONT can be further improved.

Further, in the above embodiment, the diac D5 is used as the trigger element connected to the base of the transistor Q4, but a silicon unilateral switch (StJ
S), silicon pirate switch (SBS), etc. can also be used. Note that these also have a function equivalent to a combination of a Zener diode and a thyristor.

Note that when a combination of a Zener diode and a thyristor is used as a trigger element, one with a Zener voltage of about 40 volts is selected.

Furthermore, in the above-mentioned embodiments, the case where the present invention was applied to a flyback converter was explained, but the present invention can also be applied to a forward converter, a half-bridge converter, etc.
It can be similarly applied to other SRs.

Furthermore, the control circuit C in the embodiment described above
The ON king is a control circuit that controls the duty ratio of the switching transistor, that is, pulse width (PWM) control, but the control circuit may also be a control circuit that controls the frequency of the switching transistor.

FIG. 2 is a circuit diagram showing the configuration of essential parts of another embodiment of the present invention. This diagram is an excerpt of the resistor R1, transistor 02, diode D2, capacitor C2, bias coil Ne, diode D3, and resistor R4 in FIG.

The difference from the circuit shown in FIG. 1 is that the capacitor C1 is
The point is that the discharge start voltage is defined by the Zener diode D5 connected to the base of the transistor Q2.

According to this, when the voltage of the capacitor C1 increases and the Zener diode D5 becomes conductive, the charge of the capacitor C+ moves to the capacitor C2.

This allows the voltage of the capacitor C2 to be maintained approximately at the Zener voltage of the Zener diode D5.

In this case, after the main switching has started,
Capacitor C from bias coil N8 through resistor R4
2 is supplied with charge. The voltage of the capacitor C2 is suppressed to the Zener voltage of the Zener diode D5, and the excess current charges the capacitor C+ through the diode DI.

And when the voltage of capacitor C2 becomes high,
Excess charge flows into the Zener diode D5 through the path C2→collector of Q2→base of Q2→D5. Therefore, under normal operating conditions, it is possible to keep the voltage Vcc generated across the capacitor C2 lower than the Zener voltage of the Zener diode D5, thereby reducing power loss in the Zener diode D5.

[Effects of the Invention] As explained above, the SR of the present invention includes an inverter transformer having a primary coil, a secondary coil, and a bias coil, a switching element that converts input DC flowing into the 11th coil to AC, and an input A first capacitor that is charged by direct current, a second capacitor that is charged by a current induced in the bias coil, and a current that transfers the charge stored in the first capacitor to the second capacitor during operation. When the terminal voltage of the control element and the first capacitor reaches a certain value, the current control element is operated using the terminal voltage of the element and the second capacitor as a driving power source, and the current is induced in the secondary coil. Since it includes a control circuit that controls the switching operation of the switching element to stabilize the current, a constant voltage can be supplied to the control circuit with a simple circuit configuration, and the number of parts as a whole is small.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the structure of one embodiment of the present invention, FIG. 2 is a block diagram showing the structure of another embodiment of the invention, and FIG. 3 is a block diagram showing the structure of a conventional power supply device. be. T1...Inverter transformer NO...Bias coil Q+, C2, C4...Transistor Q3...・
・・・・・・・・・FETR1～R+s・・・Resistance C+, C2・・・Capacitor D+～D3・・・Diode D4・・・・・・・・・−・・...Zena diode D
*, Os...Diac PC......Photocoupler A.
・・・・・・・・・・・・・・・Error amplifier C0N
T... River... Control circuit applicant Toshiba Corporation Patent attorney Sa Suyama - Figure 1 Figure 2

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 first capacitor that is charged, a second capacitor that is charged by a current induced in the bias coil, and a charge accumulated in the first capacitor during operation is transferred to the second capacitor.
a current control element to be moved to the capacitor, a trigger element to operate the current control element when the terminal voltage of the first capacitor reaches a certain value, and a terminal voltage of the second capacitor as a driving power source. , a control circuit that controls the switching operation of the switching element so as to stabilize the current induced in the secondary coil. (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 diac. (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.