JPS5935564A - Power converter - Google Patents

Abstract

PURPOSE:To reduce the switching loss of a main transistor by controlling the On and OFF of a rectifier with the logic product output of the ON output of a load side voltage detecting means and the ON output of a rise detecting delay circuit. CONSTITUTION:The rise of a voltage of an exciting direction which is induced in the secondary coil N2 of a trnasformer 4 is detected by a delay circuit 11, and the output of the delay circuit 11 rises in delay by the time longer than the rising time of a main transistor 1 from the detected time. Since an input which is connected to the output side of a control circuit 8 of two inputs of a logic circuit 12 has already risen by the ON output of the control circuit 8, a rectifying transistor 2 and a circulating transistor 3 are respectively conducted and interrupted simultaneously when the output of the delay circuit 11 has risen. Consequently, no conducting switching loss is produced at the main transistor 1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power converter equipped with an on/off rectifier in a load circuit, and more specifically, it is used for a power supply with a low output voltage and a large current. 1 is a circuit diagram showing a conventional example of this type of power converter. In the figure, 1 is the main transistor for switching, 2 is the rectifier transistor (in this case, it is shown in the form of FBT, but is not limited to this), and 3 is the current transistor (same as (F'ET)). 4 is a transformer, 5 is a main power supply, 6 is an excitation current circulation diode, 7 is a smoothing filter, 8 is a control circuit, 9
is a drive circuit, 10 is a load, and rectifier transistor 2
, each control terminal (gate terminal q) of the freewheeling transistor 3
is directly connected to the secondary winding N2 of the transformer 4.

Next, an outline of the circuit operation will be explained. The control circuit 8 is a load 10
The drive circuit 9 detects the load voltage supplied to the main transistor, generates an on/off output according to its magnitude, and outputs it to the drive circuit 9. The drive circuit 9 operates according to the on/off output from the control circuit 8, and 1 and thereby control the load voltage to a constant value. Now, if the main transistor 1 is turned on, voltage is applied from the main power supply 5 to the primary winding N1, and as a result, the secondary winding N2 A positive voltage is generated on the e-port side. Then Y
The voltage on the gate G side of transistor 2 becomes higher than the voltage on the source S side, and transistor 2 becomes conductive.
Current flows from the e-port side of the secondary winding MN2 through the smoothing filter 7, the load 10, the first rectifying transistor 2, and the other side of the secondary winding N2. In this way, power is supplied to the load 10. At this time, the coil in the smoothing filter 7 is excited and can be considered as a current source. The transformer 4 is in a state where its excitation inductance is excited and stores energy. In this state, it is assumed that the main transistor 1 is now turned off. Then, in transformer 4, 1
The stored energy generates a winding voltage (flyback voltage) in a direction that does not reduce the current that had previously flowed through each winding. This flyback voltage Since the voltage is negative and the other side is positive, the rectifying transistor 2 is turned off and the circulating transistor 3 is turned on instead.The current flowing through the coil in the O smoothing filter 7 is transferred to the capacitor and the load 10. , and circulates through the circulating transistor 3. A circulating current also flows through a closed circuit formed by the tertiary winding Na, the main power source 5, and the diode 6, and surplus energy is returned from the transformer 4 to the power source 5.

Next, the main transistor 1 is turned on again, and the same operation is repeated.

Now, in the circuit operation described above, the main transistor 1 is
When the drive circuit 9 starts to shift from the OFF state to the ON state due to the drive action of the drive circuit 9 due to the ON output of the control circuit 8, at the same time, the secondary winding MN2 of the transformer 4 is activated as described above. As shown in FIG.
Next, the current flowing through both windings iFj NIP N2 begins to increase.

That is, if we focus on the emitter and collector, which are the controlled terminals of the main transistor 1, in the conduction transition state before the voltage between the emitter and collector drops sufficiently and the transistor 1 reaches a completely conductive state, these collector and collector Current will begin to flow through the emitter. Therefore, in the main transistor 1, a conduction switching loss corresponding to the power loss (represented by the product of the collector-emitter voltage and the current flowing therethrough) in the conduction M transition state occurs.

Next, when the main transistor 1 begins to shift from the on state to the off state under the action of the drive circuit 9 due to the off output of the control circuit 8, at the same time, the leakage inductance and excitation inductance of the transformer 4 are accumulated. The energy generates a voltage in each winding of the transformer 4 in the de-energizing direction. That is, focusing on the emitter and collector, which are the controlled terminals of the main transistor 1, when the current passing between the emitter and collector is sufficiently reduced and the current passing between the emitter and collector decreases enough to reach the OFF state, in the cutoff transition state, the current between the emitter and collector is A voltage will be applied to. Therefore, the main transistor 1 has a power loss (
(product of collector-emitter voltage and current flowing there)
A cut-off switching loss corresponding to .

As described above, the conventional power converter has the disadvantage that the main transistor 1 suffers a switching loss which is the sum of the conduction switching loss and the cutoff switching loss, resulting in poor efficiency.

The present invention has been made to eliminate the drawbacks in the prior art as described above, and therefore, the purpose of the present invention is to:
An object of the present invention is to provide a power conversion device that makes it possible to significantly reduce switching loss in a main transistor.

The main point of the configuration of the present invention is that a DC power supply and a main switching transistor are connected in series to the primary winding of a transformer, and the transformer t
A load circuit is connected to the secondary winding of the transformer through at least an on-off rectifier, and the switching of the main transistor is controlled according to the load (i[voltage] detected by the load n voltage detection means. In a power conversion device configured to supply DC voltage to a load circuit, a rise detection delay that detects the rise of the first voltage in the secondary winding, delays it for a certain period of time after detection, and then generates the detected output. A circuit is provided, and the ON/OFF control of the preceding 8 rectifying elements is performed by the AND output of the ON output of the load side voltage detection means and the ON output of the rise detection delay circuit.

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a circuit diagram showing one embodiment of the present invention.

In the figure, 1 to 10 are the same as in FIG. 1, 11 is a delay circuit, and 12 is a logic circuit. The delay circuit 11 controls the addition r7E in the secondary winding N2 of the transformer 4.
A zero logic circuit 12 that detects the rising time of the winding voltage in the J7m direction (voltage with positive side) and generates the detected force after a certain period of time has elapsed from this detection time is connected to the output of the control circuit 8. It has the function of using the output of the delay circuit 11 as an input, driving the rectifying transistor 2 with the AND output of these two inputs, and driving the circulating transistor 3 with the negative output of this AND. The delay time in the delay circuit 11 is set longer than the rise time, which is defined as the time from when the main transistor 1 starts conducting until it reaches a sufficiently conductive state, that is, the time required to pass through the conductive transition state.

Now, when the output of the control circuit 8 turns on and reaches a level that should turn on the main transistor 1, the main transistor 1 begins to conduct due to the driving action of the drive circuit 9. At this time, the rise of the voltage in the excitation direction induced in the secondary winding N2 of the transformer 4 is detected by the delay circuit 11, and the delay circuit 11 is delayed from this detection time by a time equal to or more than the rising time of the main transistor l. 11 output rises.

Of the two inputs of the logic circuit 12, the input connected to the output side of the control circuit 8 has already risen due to the ON output of the control circuit 8. Therefore, at the same time as the output of the delay circuit 11 rises, the rectifier transistor 2 , the freewheeling transistor 3 becomes conductive and cut off, respectively, and at this point the primary and secondary windings of the transformer 4 N1 t
Current flows through N2.

If we look at the above operation focusing on the emitter and collector, which are the controlled terminals of the main transistor 1, we can see that after the voltage between the emitter and collector drops sufficiently and becomes conductive, it passes through the emitter and collector. Current will flow. Therefore, no conduction switcher loss occurs in the main transistor l.

Next, when the output of the control circuit 8 becomes an OFF output and reaches a level that requires cutting off the main transistor 1, the output of the logic circuit 12 that receives this output is immediately reversed, and the rectifying transistor 2 and the circulating transistor 3 into the cutoff state and conduction state, respectively. Therefore, the current flowing through the secondary winding N2 of the transformer 4 is cut off, and the current flowing through the primary winding N1 immediately decreases to the excitation current value. Meanwhile, the drive circuit 9
At the same time, when the output of the control circuit 8 reaches a level at which the main transistor 1 should be disconnected, the emitter and cap, which are the control terminals of the main transistor 1, are connected to the M ljJ FIE load in order to disconnect the main transistor 1. aspirate. Main transistor 1 stores this)! The conductive state is maintained for the accumulation time until the charge attraction ends, and then the transition to the cut-off state begins. At this point, a voltage in the de-excitation direction due to the excitation energy is generated in each winding of the transformer 4 for the first time. That is, at the same time that the output of the control circuit 8 reaches a level that requires the main transistor 1 to be cut off, the output of the transformer 4 is turned off.
The current flowing through the next winding N1 is reduced to the excitation current, and a voltage in the de-excitation direction is generated in each winding of the transformation R34 after a delay of the storage time of the main transistor 1 from this point.

If we look at this operation by focusing on the emitter and collector, which are the controlled terminals of the main transistor 1, we can see that a voltage is applied between the emitter and collector after the current flowing through the emitter and collector has sufficiently decreased. become. Therefore, the cut-off loss in the main transistor 1 is extremely small compared to the conventional one.

As explained above, according to the present invention, among the switching losses of the main transistor, conduction switching losses are eliminated and cut-off switching losses are reduced, so that the switching losses of the main transistor are extremely reduced, and the amount of heat generated by the main transistor is reduced. It becomes less. Therefore, the heat dissipation mechanism conventionally required for heat dissipation can be made smaller, and this gravity conversion device has the advantage of being able to be made smaller and lighter.

In addition, in the present invention, the rectifying transistor is cut off at the same time that the output of the control circuit reaches a level that should cut off the main transistor, and the current on the secondary side is cut off. The effect of accumulation time is no longer included. Therefore, there is also the advantage that the design of this power conversion device becomes easy.

Although the above description has been made for the case where there is one main transistor, it goes without saying that the present invention can be applied to any circuit configuration as long as it is a power conversion device equipped with a rectifier circuit using a transistor.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional power conversion device, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. Description of symbols 1... Main transistor, 2... Rectifying transistor, 3... Freewheeling transistor, 4
...Transformer, 5...Main power supply, 6...
... Rectifier for circulation, 7 ... Smoothing filter, 8
... Control circuit, 9 ... Drive circuit, 10
...Load, 11...Delay circuit, 12.
...Logic circuit agent Patent attorney Akio Namiki Patent attorney Kiyoshi Matsuzaki

Claims (1)

[Claims] 1) Connect the DC power supply and the main switching transistor in series to the primary winding of the transformer, connect the load circuit to the secondary winding of the transformer through at least an on/off rectifier, and In a power conversion device configured to supply DC voltage to a load circuit by controlling switching of the main transistor according to a load side voltage detected by a voltage detection means, a rise in voltage at the secondary winding is detected. , a rise detection delay circuit is provided which generates the detection output after a certain time delay after detection, and the output of the rectifier is determined by the AND output of the ON output of the load side voltage detection means and the ON output of the rise detection delay circuit. A power conversion device characterized by performing on/off control.