JPH0628512B2 - Flyback ringing choke converter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a flyback ringing choke converter (single-stone self-exciting DC-DC converter), and more particularly, to an output voltage of a rigging choke converter having a relatively small capacity. Regarding temperature compensation.

(Prior Art) A conventional ringing choke converter of this type has a third feature.
There is a circuit configuration shown in the figure. In FIG.
IN is the input terminal of the DC power supply before conversion, OU
T is an output terminal of the converted DC power source, TR1 is a switching transistor which is started by a starting current given through a starting resistor R1 and is oscillated and driven at a predetermined oscillation frequency by a positive feedback voltage given to a base, TS Has one end connected to the input terminal IN of the DC power supply,
Further, the primary side winding L1 connected to the collector of the other end switching transistor TR1, the base drive winding L3 for supplying the positive feedback voltage to the base of the switching transistor TR1 via the current limiting resistor R2 and the capacitor C2, And a converter transformer having a secondary winding L2 whose one end is connected to one pole portion (anode) of the rectification diode DI, CC is the output terminal OUT of the DC power source at the other pole portion (cathode) of the rectification diode D1, and the ground , A series circuit composed of a Zener current limiting resistor R3 and a Zener diode D2 having a predetermined Zener voltage connected in series with each other, and TR2 is a series circuit C
The base is connected to the connection portion a between the Zener diode D2 and the Zener current limiting resistor R3 in C, and
It is a control transistor whose collector is connected to the base of the switching transistor TR1. C1 and C3 are smoothing capacitors, respectively.

In the ringing choke converter having such a configuration, when the output voltage Vo appearing at the output terminal OUT becomes large, for example, the Zener diode D
As a result, the Zener current Iz from the transistor 2 increases and the conductivity of the control transistor TR2 increases. As a result, the base current of the switching transistor TR1 decreases, and the output voltage Vo is controlled to decrease, whereby the output voltage Vo decreases. Operates so that is controlled to a constant value. Similarly, when the output voltage Vo decreases, the output voltage Vo is controlled to a constant value.

Since other basic operations of this ringing choke converter are well known, their description will be omitted.

In the ringing choke converter configured as described above, if the ambient temperature is constant, the output voltage Vo can be maintained at a constant value by the above operation without performing temperature compensation. In order to keep the voltage Vo at a constant value, some measure for temperature compensation is necessary.

By the way, the output voltage at the output terminal OUT is Vo, and the base-emitter voltage of the control transistor TR2 is Vb.
When the Zener voltage of the e and Zener eye diode D2 is Vz, the output voltage Vo is expressed by the following equation (1).

Vo = Vbe + Vz (1) Therefore, as is clear from the above equation (1), the temperature characteristic of the output voltage Vo, that is, the change of the output voltage Vo when the ambient temperature rises or falls, depends on the control transistor TR.
Since it is determined by the base-emitter voltage Vbe of 2 and the Zener voltage Vz of the Zener diode D2, the above formula (1) is considered as a temperature compensation measure against a temperature change such as an ambient temperature rise or fall. It is necessary.

(Problems to be Solved by the Invention) However, a Zener diode having a predetermined Zener voltage Vz, generally a Zener voltage Vz of 6 V or more, generally has a positive temperature characteristic, that is, a Zener voltage increases when the ambient temperature rises. Vz increases and its Zener current I
It has a temperature characteristic that z also increases. Therefore, if a Zener diode having a Zener voltage Vz of 6 V or higher is used for a large-capacity ringing choke converter, the temperature compensation can be performed by connecting a temperature compensation diode having a negative temperature characteristic in series with the Zener diode. It can be carried out.

However, when a zener diode having a zener voltage Vz of 6 V or less is used as in a small capacity ringing choke converter, such temperature compensation measure cannot be taken because the temperature characteristic of the zener diode is negative.

The present invention has been made in view of the above, and an object of the present invention is to easily perform temperature compensation even when a Zener diode having a small capacity and a negative temperature characteristic is used.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a switching transistor that is oscillated and driven at a predetermined oscillation frequency by a positive feedback voltage applied to a base, and one end of which is an input terminal of a DC power supply. A primary winding having the other end connected to the collector of the switching transistor, a base drive winding that supplies the positive feedback voltage to the base of the switching transistor, and one end of a rectifying diode. A converter transformer with a secondary winding connected to
A temperature compensating diode having a Zener current limiting resistance and a negative temperature characteristic in which a forward voltage decreases with an increase in temperature, which are connected in series with each other between an output terminal of a DC power source in the other pole portion of the rectifying diode and a ground. And a series circuit composed of a Zener diode having a negative temperature characteristic in which the Zener voltage decreases as the temperature rises, and the Zener current limiting resistor and the temperature compensation diode in the series circuit are connected between the base and the emitter. And a control transistor having a collector connected to the base of the switching transistor.

(Operation) According to this configuration, when the ambient temperature rises, for example, the Zener diode has a negative temperature characteristic, so that the Zener voltage tends to decrease, but the Zener diode is connected in series with the Zener diode. Since the temperature compensating diode connected to has a negative temperature characteristic, its forward voltage decreases as its temperature rises. As a result, the Zener current increases and the Zener voltage increases. for that reason,
The decrease in the Zener voltage of the Zener diode itself is forcibly canceled by the increasing action of the Zener voltage by the temperature compensation diode, and as a result, the output voltage can be maintained at a constant value with respect to the ambient temperature change.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram of a flyback type ringing choke converter according to an embodiment of the present invention, and portions corresponding to those in FIG. 3 are designated by the same reference numerals. And
The ringing choke converter according to the present embodiment has the same configuration with respect to the portion having the same reference numeral as that of the conventional example shown in FIG. 3, and therefore the description of the configuration will be omitted.

The circuit configuration that is characteristic of this embodiment is as follows. That is, the ringing choke converter of this embodiment is
A Zener current limiting resistor R3 between the output terminal OUT of the DC power source at the cathode, which is the other pole of the rectifier diode D1, and the ground, and a temperature compensation diode having a negative temperature characteristic in which the forward voltage Vf decreases with increasing temperature. D3,
It has a series circuit CC composed of a Zener diode D2 having a negative temperature characteristic in which the Zener voltage Vz decreases as the temperature rises.

The Zener current limiting resistor R3 and the temperature compensating diode D3 in this series circuit CC are connected between the base and emitter of the control transistor TR2.

In such a configuration, when the zener current of the zener diode D2 is Iz, the base current of the control transistor TR2 is Iz1, and the forward current of the temperature compensation diode D3 is Iz2, the following equation (2) is established.

Iz = Iz1 + Iz2 (2) Since the current amplification factor of the control transistor TR2 is sufficiently larger than 1, the forward current Iz2 flowing through the temperature compensation diode D3 is sufficiently larger than the base current Iz1 of the control transistor TR2. Therefore, the above equation (2) can be approximated to the following equation (3).

Iz≈Iz2 (3) Further, the base-emitter voltage of the control transistor TR2 is Vbe, and the forward voltage of the temperature compensation diode D3 is Vbe.
f and the resistance value of the zetter current limiting resistor R3 are r3, the following equation (4) is established from the above (3).

Iz = (Vbe-Vf) / r3 (4) Now, when the ambient temperature rises, for example, the Zener diode D2 has a negative temperature characteristic, so the Zener voltage Vz tends to fall. Since the temperature compensating diode D3 has a negative temperature characteristic, its forward voltage Vf is lowered, and as a result, the Zener current Iz of the Zener diode D2 is increased as apparent from the above formula (4). Become. Then, the Zener diode D2 is forced to increase the Zener voltage Vz due to the increase in the Zener current Iz.

As a result, the ambient temperature rises and the Zener diode D2
The voltage drop in the temperature characteristic of the Zener voltage of V is canceled by the forced voltage increase by the temperature compensating diode D3, and the output voltage V _o is maintained at a constant value despite the temperature increase. Will be done.

The same applies to the case where the ambient temperature decreases, and the description thereof will be omitted.

FIG. 2 is a circuit diagram of a flyback ringing choke converter according to another embodiment of the present invention, and the portions corresponding to those in FIG. 1 are designated by the same reference numerals. The embodiment of FIG. 2 is characterized in that the collector of another control transistor TR3 is connected to the base of the control transistor TR2, the emitter of the control transistor TR3 is connected to the cathode of the rectifying diode D1, and The anode of the temperature compensation diode D3 in the series circuit CC is connected to the cathode of the rectification diode D1, and the Zener current limiting resistor R is connected to the cathode of the temperature compensation diode D3.
3 and the Zener diode D2 are connected, and the base of the control transistor TR3 is connected to the connection portion b between the Zener current limiting resistor R3 and the cathode of the Zener diode D2.

In the ringing Kyoke converter of FIG. 2 having such a configuration, the basic operation is the same as that of FIG. 1, but by providing another control transistor TR3 in addition to the control transistor TR2, the switching transistor TR1 is provided. The control amount is increased to prevent the stability of the output voltage Vo from decreasing due to the temperature compensation diode D3.

(Effect) As is apparent from the above description, according to the present invention,
A Zener current control resistor between the output terminal of the DC power supply at the other pole of the rectifier diode and ground, a temperature compensation diode with negative temperature characteristics in which the forward voltage decreases with increasing temperature, and a Zener voltage with increasing temperature. Since a series circuit composed of a Zener diode having a negative temperature characteristic that decreases and a Zener current limiting resistor and a temperature compensation diode in the series circuit are connected between the base and emitter of the control transistor, For example, when the ambient temperature rises, the Zener diode has a negative temperature characteristic, so the Zener voltage tends to decrease.However, the temperature compensation diode connected in series with the Zener diode Due to its negative temperature characteristic, its forward voltage decreases with increasing temperature. Results Zener current increases, the decrease in the Zener diode Zener voltage of itself negative temperature characteristic of the zener diode is offset by the amount of increase in the forced zener voltage due to temperature compensation diode is canceled. As a result, in the ringing choke converter of the present invention, even if a Zener diode having a negative temperature characteristic is used for a small capacity, temperature compensation can be easily performed so as to keep the output voltage constant with respect to temperature changes in the surroundings. it can.

[Brief description of drawings]

1 and 2 relate to an embodiment of the present invention, FIG. 1 is a circuit diagram of a flyback type ringing choke converter according to the embodiment, and FIG. 2 is a ringing choke converter according to another embodiment. It is a circuit diagram. FIG. 3 is a circuit diagram of a ringing choke converter according to a conventional example. IN ... input terminal, OUT ... output terminal, TS ... converter transformer, TR1 ... switching transistor, TR2. TR3 ... Control transistor, CC ... Series circuit, D2 ... Zener diode, D3 ... Temperature compensation diode, R3 ... Zener current limiting resistor.

Claims (1)

[Claims] 1. A switching transistor driven to oscillate at a predetermined oscillation frequency by a positive feedback voltage applied to a base, one end of which is connected to a DC current input terminal and the other end of which is connected to a collector of the switching transistor. A primary side winding, a base drive winding that supplies the positive feedback voltage to the base of the switching transistor, and a converter transformer including a secondary side winding whose one end is connected to one pole of a rectifying diode, A Zener current limiting resistor connected in series between the output terminal of the DC power source at the other pole of the rectifying diode and the ground, and a temperature compensation diode having a negative temperature characteristic in which the forward voltage decreases with increasing temperature; Series consisting of a Zener diode with negative temperature characteristics that the Zener voltage decreases with increasing temperature And a control transistor in which the Zener current limiting resistor and the temperature compensation diode in the series circuit are connected between the base and the emitter, and the collector is connected to the base of the switching transistor. Flyback ringing choke converter.