JPS6169371A - Flyback type dc/dc converter - Google Patents

Abstract

PURPOSE:To reduce a radiation noise by applying conduction noise absorbing function having small inserting loss to a DC/DC converter, thereby preventing a switching element from damaging by a voltage. CONSTITUTION:A flyback DC/DC converter has the first, second primary windings A1, A2, a transformer T2 having the secondary winding B, a transistor (Tr)Q2 to become a switching element, diodes D2-D3, and a rectifier 12. In this case, a spike voltage absorber made of a series circuit of a capacitor C3 of the prescribed capacity and a low resistor R2 is connected between the primary winding A2 and the anode of a diode D2. Thus, the conduction noise generated when the TrQ2 is switched can be almost absorbed to eliminate the spike voltage.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a flyback type DC-DC converter,
In particular, the present invention relates to a flyback type DC-DC converter belonging to an externally driven type.

[Prior art and its drawbacks]

FIG. 1 is a diagram showing the circuit configuration of a conventional flyback type DC-DC converter belonging to the external drive type as described above. In FIG. 1, a DC voltage E is input from the terminal 51 with the polarity shown in the figure, and! ! The terminal 52 is excited by an externally driven pulse voltage v1. This no J? When the transistor Q1 as a switching element becomes conductive in response to the pulse voltage V1, the current 11 flows through the primary winding 1lT1(A) of the transformer TI and the transistor Ql
Current flows into the negative side of the DC input power supply. At this point.

Inductive energy is stored in the primary winding TI (A) of the transformer T1. When the pulse voltage v1 ends.

The induced energy is transferred to the secondary winding Tl(B
) and is discharged to the rectifier circuit 11. At this time, the output terminal voltage P1 is applied to the primary winding I Tl (A) of the transformer T1.
A voltage determined by E and the primary and secondary winding ratio of the transformer T1 is induced, and this voltage is added to the DC input voltage E, which is applied between the collector and emitter of the transistor Q1. When the discharge of the induced energy in the secondary winding Tl(B) of the transformer T1 ends, the initial state, that is, the voltage I applied between the collector and the emitter of the transistor Q1, the voltage V1, is approximately equal to the DC input voltage E. return to the state.

Thereafter, the terminal 52 is excited by the external driving voltage v1, and the above-described operation process is repeated.

FIG. 2 shows the external drive voltage v1. Current 11 flowing through transistor Q1. The current flowing through the secondary winding TI(B) of the transformer TI and the voltage between the collector and emitter of the transistor Q1 ■1
It is a figure which shows the operation waveform of etc.

In FIG. 2, voltage 11 between the collector and emitter of transistor Q1 produces a spike-like voltage (not shown) at the time point 11 ends. This spike voltage is mainly caused by the leakage inductance existing between the negative winding and the secondary winding of the transformer T. This spike voltage has an extremely large value compared to the input voltage E,
There is a possibility that the voltage may destroy the transistor Q1 as a switching element. As a measure to prevent this, an absorption circuit for the spike-like voltage is constructed. An example of this circuit is the first
As shown in the figure, it is constructed by connecting a series element of a resistor R1 and a capacitor C1 in parallel to a transistor Q1. The spike-shaped voltage shown in the waveform diagram of the voltage v1 of - in FIG. 2 is generated by using the absorption circuit.
This is the residual voltage generated as a result of suppressing the spike voltage. A pulse current corresponding to the switching operation flows through the resistor R1 and the capacitor C1 forming a circuit for absorbing this spike voltage, and heat loss occurs in the resistor R1. When the operating frequency of the DC-DC converter is high, the loss in this absorption circuit increases,
Significantly degrades the efficiency of the DC-DC converter.

It is well known that the switching operation of the transistor Q1 generates an AC voltage via the transformer TI, and the rectifier circuit 11 consisting of the diode DI and the capacitor C2 outputs the DC voltage P1 via the terminal 53. .

As you can see from the above explanation, the conventional flyback type DC
- In DC converters, an absorption circuit containing a resistor and a capacitor is used at the point where direct switching is performed to prevent voltage breakdown of the switching element due to conductive noise generated during switching operation, so the loss in the absorption circuit increases. .

This has the disadvantage of degrading the efficiency of the DC-DC converter.

[Purpose of the invention]

The object of the invention is therefore to obviate the above-mentioned drawbacks.

Provides conductive noise absorption function with low insertion loss.

The object of the present invention is to provide an efficient DC-DC converter that prevents voltage breakdown of switching elements, reduces conduction and radiation noise to the outside, and has high efficiency.

[Structure of the invention]

According to the present invention, an externally driven type fryer converts an input DC voltage into an AC voltage using a transistor circuit and a transformer excited by an external drive/gusrus, and converts this AC voltage into a DC voltage using a rectifier circuit and outputs the DC voltage. Back type DC-DC
In the converter, an end receiving the input DC voltage of the DC-DC converter is connected in series with the first primary winding of the transformer, a resistor and a capacitor, one end is connected to the first -, and the negative terminal is connected to the first primary winding of the transformer. The second primary winding of the i-lance is connected to the hard disk of the spike voltage absorption circuit, and the anode side is the negative electrode side of the second primary winding and the cathode side is the positive electrode of the first primary winding. a first diode whose anode side and cathode side are respectively connected to the positive and negative sides of the second primary winding;
A flyback type DC-DC converter is obtained, which is characterized by having a diode.

〔Example〕

Next, the present invention will be explained in detail.

FIG. 3 is a diagram showing the configuration of an embodiment of the present invention. In FIG. 3, this flyback type DC-DC converter has a first primary winding ym T2(A1), a second primary winding T2(A2), and a secondary winding T2(B). A rectifier circuit 12 is provided which includes a run T2, a transistor Q2 acting as a switching element, a capacitor C3, a resistor R2, a diode D2, a diode D3, a diode D4, and a capacitor C4.

A DC voltage E is input from the terminal 54 with the polarity shown in the figure. The external drive terminal 55 is excited by the external driving voltage v2. When the transistor Q2 as a switching element becomes conductive due to this excitation, a current of 1
3 is winding T2 (A1') of the primary winding of transformer T2
And by the electromotive force induced in T2 (A2) when transistor Q2 is energized, -order winding T2 (A1) and T2 (A2)
If the windings of the diode D3 are equal, the voltage v3 between the cathode and the anode of the diode D3 will be approximately twice the voltage E1.

When the pulse voltage v2 is terminated, the current 13 that flows through the transistor Q2 becomes zero, and the secondary winding T of the transformer T2
The current 14 of 2(B) begins to flow rapidly, decreases with a constant slope, and reaches zero. During this time, voltage v2, which is the sum of the voltage induced from the secondary winding T2 (B) of the transformer T2 to the first primary winding T2 (A1) and the DC input voltage E1, is applied between the collector and emitter of the transistor Q2. . After this, the voltages v2 and v3 are in the initial state, that is, the voltage E
, returns to a state equal to . Thereafter, the terminal 55 is periodically excited by the externally driven pulse voltage v2, and the above-described operation process is repeated.

FIG. 4 shows the pulse voltage v2 of the external drive during the operation progress as described above. Current i3. flowing through transistor Q2. Current 14 flowing through the secondary winding of transformer T2 + transistor Q
2 is a diagram showing operating waveforms of a voltage V2 between the collector and emitter of the diode D3 and a voltage v3 between the cathode and anode of the diode D3.

In this waveform diagram, if we look at the voltage v2 between the collector and emitter of the transistor Q2.

At the time when the current i3 ends, there is a potential condition where a spike-like voltage occurs, as in the case of the conventional example. However, in this embodiment, a series circuit consisting of a capacitor C3 of a predetermined capacity and a low resistance R2 is connected between the -order winding T2 (A2) and the connection point with the anode of the diode D2. /, a) Most of the conductive noise generated during switching operation is absorbed and no spike voltage is generated as shown in FIG. A resistor R2 connected in series with the capacitor C3 connects the capacitor C3 and the negative winding T.
2(A1) and 'r2(A2), and acts as a damper for the series resonant circuit formed by the DC input power source.
Since the movement of charge in the series circuit consisting of R2 and low resistance R2 is only due to the leakage inductance,
The value of the resistor R2 can be set to a small value according to the circuit characteristics, so the loss in this part is very small.

As mentioned above, an alternating current voltage is generated on the secondary side via the transformer T2 due to the switching operation by the external drive pulse voltage on the negative side 1, and a predetermined direct current voltage P2 is generated by the rectifier circuit 2 via the terminal 56. The output is the same as before.

〔Effect of the invention〕

The present invention substantially absorbs conduction noise exceeding twice the supply voltage generated through switching operation on the negative side, prevents voltage breakdown of the switching element, reduces conduction and radiation noise to the outside, and also has the following features: - There is an effect that the conversion efficiency can be improved when the operating frequency of the DC converter is high.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing an example of the configuration of a conventional flyback type DC-DC converter, Figure 2 is a waveform diagram of each part of the circuit in Figure 1, and Figure 3 is a diagram showing the configuration of an embodiment of the present invention. The circuit diagram shown in FIG. 4 is a waveform diagram of each part of the circuit of FIG. 3. Explanation of symbols: 11 and 12 are rectifier circuits, 51 to 56 are terminals, Ql and Q2 are transistors as switching elements, Tl and T2 are transformers, TI(A). T2(A1) and T2(A2) are the negative windings, Tl(
B) and T2 (B), the secondary windings IV1 and v2 are each supplied with an external drive pulse voltage. S ・S -Go 5 Ward () C) (1) LLI LLI
θVn Pulse of Tato part 41

Claims (1)

[Claims] 1. Converting an input DC voltage to an AC voltage using a transistor circuit and a transformer excited by an external drive pulse,
In an externally driven flyback DC-DC converter that converts this AC voltage into a DC voltage using a rectifier circuit and outputs the DC voltage, one end of the AC is connected to the negative side of the terminal from a terminal that receives the input DC voltage of the DC-DC converter. The transistor circuit connected to the terminal and the first circuit of the transformer whose circuit configuration up to generation of voltage is such that the positive terminal side is connected to the positive terminal of the terminal and the negative terminal side is connected to the other end side of the transistor circuit. a spike-like voltage absorption circuit consisting of a primary winding, a resistor and a capacitor connected in series, one end of which is connected to the negative pole side of the first primary winding, and a positive pole side of the circuit connected to one end of the transistor circuit; a second primary winding of the transformer whose negative pole side is connected to the other end of the spike voltage absorption circuit, an anode wire connected to the negative pole side of the second primary winding, and a cathode wire connected to the first It has a first diode connected to the positive electrode side of the primary winding, and a second diode whose anode side and cathode side are respectively connected to the positive electrode side and the negative electrode side of the second primary winding. A flyback type DC-DC converter characterized by the following.