JPH06225533A - Dc-dc converter - Google Patents

Abstract

(57) [Summary] [Purpose] To reliably start a self-excited oscillation type Royer circuit in a short time. [Structure] The Royer circuit includes a pair of transistors Q ₁ and Q ₂ connected in series to both windings N _p1 and N _p2 of the transformer T with the center tap of the primary winding N _p as a boundary. Prepare The respective windings N _p1 and N _p2 and the transistors Q ₁ and Q
_A DC input Vin is applied to both ends of the series circuit with ₂ . The voltage induced in the feedback windings N _f1 and N _f2 provided in the transformer T is _{supplied to} the respective transistors Q via the oscillation capacitor C _2.
Apply positive feedback to ₁ and Q ₂ . As a result, the transistors Q ₁ and Q ₂ are alternately turned on and off. Different DC bias is applied to the transistors Q ₁ and Q ₂ by the resistors R ₁ and R ₂ . As a result, when the DC input Vin is applied, the transistor Q ₁ is turned on first, and any of the transistors Q ₁ and Q ₂ is turned on.
Also prevents the state of turning on in a halfway state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC-DC converter which obtains a DC output from an output obtained by temporarily converting a DC input into an AC by using a self-oscillation type Royer circuit.

[0002]

2. Description of the Related Art DC using a self-oscillation type Royer circuit
A DC converter is shown in FIG. In this DC-DC converter, the DC input Vin is used as a power source, the two transistors Q ₁ and Q ₂ are alternately turned on and off, and a current is passed through the primary winding N _p of the transformer T in the positive and negative directions. , An AC output is generated in the secondary winding N _s of the transformer T, and the AC output is rectified or rectified and smoothed to obtain a DC output which is voltage converted.

Self-oscillation type that converts DC input into AC output
Royer circuit, so-called push-pull configuration Invar
In the circuit, the primary winding N of the transformer T_pAnd secondary winding N
_sThe one with an intermediate tap is used as. Less than
Of the primary winding N in FIG._pThe upper winding of
N_p1, Lower winding N_p2Similarly, the secondary winding N_sof
The upper winding is N_s1, Lower winding N_s2Call. 1
Next winding N_pUpper winding N_p1Is the secondary winding N_sUpper winding N
_s1Electromagnetically coupled with primary winding N_pLower winding N _p2Is secondary
Winding N_sThe lower winding is NN_s2Is electromagnetically coupled with. It
In addition, the transformer T has two tertiary windings
Transistor Q₁, Q₂Feedback volume to apply positive feedback to each
It is used as a line. The transistor Q₁Corresponds to
N feedback winding_f1Called transistor Q₂Corresponding to
Feedback winding N_f2Call.

A specific configuration will be described. A smoothing capacitor C ₀ is connected to both ends of the DC input Vin. The DC input Vin is applied to the center tap of the primary winding N _p of the transformer T, and the transistors Q ₁ and Q ₂ are DC input via the windings N _p1 and N _p2 of the primary winding N _p , respectively. It is connected to both ends of Vin. Feedback windings N _f1 and N _f2 are respectively connected between the base and emitter of the transistors Q ₁ and Q ₂ via an oscillation capacitor C ₂ . This capacitor C _2
Forms an oscillating circuit together with each of the feedback windings N _f1 and N _f2 . A diode D is connected across the capacitor C _2.
A base resistor R _b is connected in parallel via ₁ . A DC input Vin is applied to a connection point between the capacitor C ₂ and the feedback windings N _f1 and N _f2 via a bias resistor R _g to apply a DC bias to the transistors Q ₁ and Q ₂ .

This Royer circuit operates as follows.
When the DC input Vin is applied, a DC bias is applied to the transistors Q ₁ and Q ₂ via the bias resistor R _g . At this time, the transistors Q ₁ and Q ₂ have the current amplification factor H
The one with high fe turns on first. For example, if the transistor Q ₁ is turned on _first , a current flows through the winding N _p1 by turning on the transistor Q ₁ . When the current flows through the winding N _p1 as described above, the transistor Q is _fed to the feedback winding N _f1.
A voltage that biases ₁ in the forward direction is induced, and positive feedback is applied to the transistor Q ₁ . As a result, the transistor Q
The on-state of ₁ goes deeper and reaches saturation quickly. Then, when the on-state of the transistor Q ₁ reaches a saturation state, a voltage for reverse-biasing the transistor Q ₁ is induced in the feedback winding N _f1, and the transistor Q ₁ is turned off.

[0006] In this way the transistor Q ₂ is turned off, turn it takes a DC bias to the transistor Q ₂ from Baiau resistor R _g, the transistor Q ₂ is turned on, operates in the same manner as the transistor Q ₁ described above, the saturation Turn off after reaching. After that, the transistors Q ₁ and Q ₂ are alternately turned on and off by repeating the above operation while the DC input Vin is applied. A voltage is induced in the secondary windings N _s1 and N _s2 by turning on and off the transistors Q ₁ and Q ₂ , and a voltage conversion output is obtained from the voltage.

[0007]

By the way, in the above-mentioned self-oscillation type Royer circuit, the transistor which is turned on first when the DC voltage Vin is applied has a high DC amplification factor Hfe. However, the two transistors Q ₁ ,
When there is almost no difference in the DC amplification factor Hfe of Q ₂ , both transistors Q ₁ and Q ₂ are turned on halfway. In such a case, there occurs a state where the Royer circuit does not start up properly, that is, a state where oscillation does not start properly. Even if it starts up successfully, there is a problem that it takes time to reach a complete oscillating state because the transistors Q ₁ and Q ₂ oscillate in an insufficient on state at the initial stage of starting. In other words, there is a problem that it takes time for the Royer circuit to rise because neither of the transistors Q ₁ and Q ₂ is surely turned on first.

The present invention has been made in view of the above points, and an object of the present invention is to provide a DC-DC converter capable of reliably rising in a short time.

[0009]

In order to achieve the above object, the present invention provides a bias means for applying different DC bias to transistors and turning ON one of the transistors first when a DC input is applied. There is.

[0010]

The present invention has the above-mentioned configuration,
When a DC input is applied, a certain transistor is always turned on first to prevent any transistor from being turned on in a halfway state. As a result, the push-pull inverter circuit is reliably stabilized and oscillation is started, and the DC-DC converter is surely started in a short time.

[0011]

FIG. 1 shows an embodiment of the present invention. This embodiment has a basic configuration similar to that described with reference to FIG. 2, and operates in the same manner as described with reference to FIG. Therefore, the same components are denoted by the same reference numerals, duplicate description is omitted, and only the characteristic points of the present embodiment will be described in the following description.

In this embodiment, the resistor R ₁ is connected between the positive electrode of the DC input Vin and the base of the transistor Q ₁ , and the resistor R ₂ is connected between the base of the transistor Q ₂ and the negative electrode of the DC input Vin. The transistor Q ₁ to the transistor Q ₂
It is configured to apply a DC bias larger than that. This ensures that the transistor Q is always applied when the DC input Vin is applied.
_{The 1} is turned on _first . In this way, the DC amplification factor Hfe of the _two transistors Q ₁ and Q ₂ is
Even if there is almost no difference in
_It is possible to prevent the state where ₁ and Q ₂ are turned on halfway, and it is possible to reliably start up the self-oscillation type Royer circuit in a short time.

By the way, in this way apply a large DC bias of the transistor Q _1, the base of the parasitic capacitance is charged by the counter electromotive voltage generated in the feedback winding N _f1 at from ON to OFF of the transistor Q _1, the transistor Q ₁ There is a problem that the responsiveness of becomes worse. Therefore, a capacitor C ₁ is connected between the base of the transistor Q ₁ and the negative electrode of the DC input Vin so that the counter electromotive voltage is absorbed by the capacitor C ₁ to improve the response of the transistor Q _1. . In addition,
The capacitor C ₁ also has a function of maintaining the base voltage of the transistor Q ₁ when the direct current input Vin is applied and stabilizing the rising of the transistor Q ₁ .

Each constant in FIG. 1 may be set by the following equation. _{R g ≦ (Vin-Vbe)} × Hfe (min) / 2 · Ic R g of dissipation ≧ 2 × (Vin-Vbe) 2 / R g R b ≦ (Vf -Vbe-Vd 1) × Hfe (min) Permissible loss of / 2 · Ic R _b ≧ 2 × (Vf −Vbe−Vd ₁ ) ² / R _b R ₁ ≧ Vbe × Hfe _(min) /0.05×Ic R ₂ ≦ Vbe × Hfe _(max) /0.2 × Ic Lower limit of R ₂ Vbe / R ₂ + Ic / Hfe _(min) ≤ (Vf-Vbe) / R _b
Therefore, R ₂ ≧ Vbe / {(Vf-Vbe) / _Rb- Ic / Hfe _(min) } where Vbe is the base-emitter voltage of the transistor, Ic is the collector current, and Vd ₁ is the order of the diode D ₁ . The directional voltage, Vf, is the induced voltage in the feedback winding.

[0015]

As described above, according to the present invention, the bias means for applying different DC bias to the transistors and turning on one of the transistors first when the DC input is applied is provided. Sometimes it is possible to always turn on a fixed transistor first and prevent any of the transistors from turning on halfway, so it is possible to reliably stabilize the push-pull inverter circuit and start oscillation. Therefore, the DC-DC converter can be started up reliably in a short time.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional example.

[Explanation of symbols]

T transformer N _p primary winding N _p1 , N _p2 winding part N _S secondary winding N _f1 , N _f2 feedback winding Q ₁ , Q ₂ transistor C ₂ capacitor R ₁ , R ₂ resistance Vin DC input

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[Procedure amendment]

[Submission date] July 5, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction content]

In this way, the transistorQ ₁ Turns off
And this time, transistor Q₂ToInduced in the feedback winding N _f2
Depending on the voltageDC bias is applied and transistor Q₂
Turns on, and the transistor Q described above₁Works the same as
Turns off after reaching saturation. After that, DC input Vin
By repeating the above operation while the
Transistor Q₁, Q₂Turns on and off alternately.
This transistor Q₁, Q ₂Secondary by turning on and off
Winding N_s1, N_s2Voltage is induced in the
Obtain the replacement output.

Claims (1)

[Claims] 1. A pair of transistors connected in series to both of the respective winding parts with an intermediate tap of the primary winding of the transformer as a boundary, and a series circuit of the respective winding parts and the transistor. A DC input is applied to both ends, and a voltage induced in a feedback winding provided in the transformer is positively fed back to each transistor through an oscillation capacitor, and the transistors are alternately turned on and off to turn the secondary winding of the transformer. DC-DC having a push-pull inverter circuit for obtaining an output obtained by converting a DC input into an AC line, and obtaining a DC output from an output obtained by once converting the DC input into an AC using this inverter circuit
A DC-DC converter, characterized in that, in the converter, different biases are applied to the transistors, and biasing means is provided for turning on one of the transistors first when a DC input is applied.