JPH03183362A - Ringing choke converter - Google Patents

Abstract

PURPOSE:To prevent a transistor from being conducted earlier than resetting of a transformer by additionally providing a diode and a capacitor thereby suppressing base potential rise during OFF interval of a switching transistor without sacrifice of starting characteristic. CONSTITUTION:A diode D3 and a capacitor C3 are additionally provided. Current flowing in from a resistor R1 is shunted to the capacitor C1 side and the capacitor C3 side thus retarding voltage rise of the capacitor C1 correspondingly. Potential rise at the joint of R1 and D3 is also low because the capacitor C3 is charged reversely with the current from the resistor R1 being fed by the voltage of L3 upon turn OFF of a transistor Q1. Since the transistor Q1 is sustained in perfect OFF state for a longer time, the transistor Q1 can be conducted at a time point when the voltages of all windings go to zero after perfect reset of the transformer T.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in a ringing choke converter, which is a type of self-excited DC-DC converter.

(Prior Art) FIG. 3 shows the main part configuration of a typical conventional ringing choke converter. A switching transistor Q1 is inserted into one line connecting the primary winding L1 of the transformer T and the input terminal.

A starting resistor R1 is connected between the positive side of the input terminal and the base of the transistor Ql. Secondary winding L of transformer T
On the 2 side, there is a rectifier diode D2 and a smoothing capacitor C2.
is connected, and a load RL is connected to both ends of the capacitor C2. Furthermore, a diode D1 and a resistor R2 are connected in series in the forward direction of the base current between one end of the base drive winding L3 of the transformer T and the base of the transistor Q1, and a speed-up capacitor C1 is connected in parallel to the diode D1. ing.

As is well known, this ringing choke converter operates as follows.

When a current flows through the starting resistor R1 to the base of the transistor Q1, the transistor Q1 becomes conductive, and as a result, a voltage is applied to the primary winding L1 of the transformer T, and at the same time, a voltage is also generated in the base drive winding L3. . This voltage becomes a positive feedback voltage that further makes transistor Q1 conductive, and transistor Q1 is rapidly turned on. Here, the voltage of the secondary winding L2 is applied to the diode D2 in the opposite direction, so no current flows through the secondary winding L2. Therefore, the current flowing through the primary winding L1 is only the excitation current of the transformer, and magnetic energy is accumulated in the transformer T.

This exciting current increases in proportion to time, and the transistor Q
When the collector current of Q1 increases and it becomes impossible for the base current to maintain the saturation of Ql, the transistor Q1 goes out of saturation and the collector-emitter voltage V. I! increases.

(2) When o5 increases and the voltage of the primary winding L1 decreases, the voltage of the base drive winding L3 also decreases, further increasing VCE. Since this change is fed back positively, transistor Q1 is quickly turned off. When transistor Q1 turns off, the energy stored in transformer T is transferred to the output side, diode D2 becomes conductive, and current flows to load RL. When all the energy stored in the transformer is transferred to the output side, the current in diode D2 becomes zero, and at that moment the voltage in each winding of transformer T becomes zero, and transistor Q
1 becomes conductive again due to the base current supplied through the resistor R1 and the base current due to the discharge of the capacitor C1,
The change to the conductive state is fed back positively and the device is rapidly turned on again. FIG. 4 shows the waveforms of the collector-emitter voltage Vc and collector current IC in the above operation.

(Problems to be Solved by the Invention) In the conventional circuit shown in FIG. 3, when the transistor Q1 is turned off, a voltage that reverse biases the transistor Q1 is generated in the base drive winding L3, and Charging current i flows in a manner that draws in the accumulated charge on the base side of Q1. Further, when the off-state of the transistor Q1 continues, a current i flows through the path of resistor R1-resistor R2-capacitor C1, and the voltage across C1 gradually increases. The charging voltage of the capacitor C1 increases the base potential of the transistor Q1 in the forward direction.
The control is working so that the off period of
In some cases, before all the energy stored in the transformer T is transferred to the secondary winding L2 side and the voltage of each winding of the transformer T becomes zero (before the transformer T is reset),
A base current may flow into the transistor Q1, causing Ql to become conductive. In the waveform of the collector current IC in Figure 4, the dotted line is due to conduction before the reset of the transformer T.
1 conducts unnecessarily and collector current ■. If this happens, the efficiency of the converter will be significantly reduced.

To avoid this problem, increase the value of resistor R1, increase the capacitance of capacitor C1, and
All you have to do is increase the charging time constant.

However, with this measure, the startup characteristics deteriorate, and startup becomes impossible, especially at low temperatures where the current amplification factor of transistor Q1 is small.

This invention was made in view of the above-mentioned conventional problems, and its purpose is to suppress the rise in base potential during the off period of the switching transistor without impairing the startup characteristics, so that the transistor conducts more quickly than in the reset state of the transformer. The purpose is to prevent the situation from occurring.

(Means for Solving the Problem) A ringing choke converter according to the present invention includes a transistor connected between input terminals in series with the primary winding of a transformer, and a transistor connected between one of the input terminals and the base of the transistor. A resistor R connected in series and forward to the base current
1 and a diode D3, and a diode D1 and a resistor R connected in series and forward to the base current between the base drive winding of the transformer and the base of the transistor.
2, a capacitor C1 connected in parallel to the diode D1-, and a capacitor C3 connected between the connection point between the resistor R1 and the diode D3 and the emitter of the transistor.

(Function) When the transistor Q1 is off, the current flowing through the resistor R1 is shunted to the capacitor C1 and capacitor C2, and the rise in the base potential of the transistor Q1 is slowed down.

(Embodiment) FIG. 1 shows the configuration of a ringing choke converter according to an embodiment of the present invention. This configuration is obtained by adding a diode D3 and a capacitor C3 to the conventional circuit shown in FIG. 3, and the other configurations are the same as those shown in FIG. Although its basic operation is the same as described above, the addition of diode D3 and capacitor C3 causes the following differences in operation and effect.

When transistor Q1 is turned off, a voltage is generated in base drive winding L3 that reverse biases transistor Q1. At this time, a charging current i flows through the capacitor C1 in a manner that the accumulated charge on the heath side of the transistor Q1 is extracted. Also, depending on the voltage of the base drive winding L3, C3→D3→R
Current also instantaneously flows through the loop 2→C2→L3. After that, if the off state of transistor Q1 continues further,
While current flows through the R1-C5 path, R1-D
Current also flows through the path 3-R2-CI-L3. In other words, the current flowing from the resistor R1 is shunted to the capacitor C1 side and the capacitor C3 side, and the rise in the voltage of the capacitor C1 is delayed accordingly. Furthermore, since the capacitor C3 was charged in the opposite direction to the current from R] when the transistor Q1 was turned off, especially by the voltage of L3, the potential at the connection point between R1 and D3 did not rise much. As a result, transistor Q
] is kept completely off for a longer time, and the transformer T
The transistor Q1 becomes conductive when the voltage across each winding becomes zero after the voltage is completely reset.

Figure 2 shows the ringing choke converter in Figure 1 with transistor Q2, capacitor C4, and Zener diode D4.
, an overcurrent protection circuit 10 consisting of a resistor R3 is added, and the main points of the present invention are a diode D3 and a capacitor C.
The effect of adding 3 is the same as in FIG.

(Effects of the Invention) As explained in detail above, according to the present invention, by simply adding a diode and a capacitor to the conventional circuit configuration, the switching transistor can be reliably operated until the transformer is completely reset. Furthermore, due to the improvements of the present invention, the starting characteristics are not impaired, the device starts well even in low temperature conditions, and always operates stably even when the negative GI fluctuates greatly.

[Brief Description of the Drawings] Figure 1 is a circuit diagram of a ringing choke converter according to an embodiment of the present invention, Figure 2 is a circuit diagram of the embodiment of Figure 1 with an overcurrent protection circuit added, and Figure 3 is a circuit diagram of a ringing choke converter according to an embodiment of the present invention. 4 is a circuit diagram of a conventional ringing choke converter/7, and FIG. 4 is a waveform diagram showing the basic operation of the ringing choke converter/7 and problems with the conventional ringing choke converter. 10... Overcurrent protection circuit

Claims (1)

[Claims] a transistor connected between input terminals in series with the primary winding of the transformer; a resistor R1 and a diode D3 connected in series with the base current in a forward direction between one of the input terminals and the base of the transistor; a diode D1 and a resistor R2 connected in series to the base current between the base drive winding of the transformer and the base of the transistor, a capacitor C1 connected in parallel to the diode D1, and the resistor R1. A ringing choke converter comprising a capacitor C3 connected between the connection point of the diode D3 and the emitter of the transistor.