JP2614056B2 - DC / DC converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] Regarding a DC / DC converter used for a communication device or the like, a high-voltage output can be obtained without increasing the shape of a transformer and further reducing the efficiency of voltage conversion. DC
In order to provide a DC / DC converter, the DC power supply 10 and the switch means 30 are connected in series with respect to the primary winding of the transformer and between the secondary winding of the transformer,
A first DC smoothing circuit 60 in which a parallel circuit of a series connection of a choke coil L1 and a capacitor C1 and a commutation diode D2 is connected in series with the rectifier diode D1, and a commutation diode D4 with respect to the rectifier diode D3 A second DC smoothing circuit 70 in which a series connection of a series connection of a capacitor C2 and a choke coil L2 is connected in series is connected in parallel, and a connection point of the choke coil L1 and the capacitor C1 and a commutation diode D4 A load 40 is connected between the capacitor C2 and the connection point of the capacitor C2, and an adjustment voltage of a resistor R in parallel with the load controls on / off of the switch means via a control circuit.

[Industrial applications]

The present invention relates to an improvement of a DC / DC converter used for a communication device or the like.

In some cases, a high voltage is required for the output of the DC / DC converter. In this case, it is desirable that the transformer used is not enlarged and the efficiency of voltage conversion is not further reduced.

[Conventional technology]

 FIG. 2 is a circuit diagram of a conventional DC / DC converter.

In FIG. 2, a DC power supply 1 (the voltage is Ei)
Is connected to the terminal a of the winding Np on the primary side of the transformer 2, the terminal b of the transformer 2 is connected to the collector of the switch means 3 such as an npn transistor, and the emitter of the switch means 3 is connected to the DC power supply 1 To the load side.

A DC smoothing circuit 6 including a rectifier diode D1, a commutation diode D2, a choke coil L1, and a capacitor C1 is connected to both ends of a winding Ns1 on the secondary side of the transformer 2. The resistor R and the load 4 are connected in parallel to the output of the DC smoothing circuit 6. Then, for example, a terminal at the middle point f of the resistor R is applied to the control circuit 5 and its output is applied to the base of the switch means 3.

 The operation principle of the circuit shown in FIG. 2 will be described below.

In the above circuit, if the voltage across the load 4 is Eo,
The voltage at the terminal f at the resistor R is Eo / 2. This voltage is applied to one of the inputs of the operational amplifier 5-1 in the control circuit 5, and the other input is applied with a reference voltage Vref set to 1/2 of the voltage value to be output to the load, and Eo / 2 and the reference voltage Find the voltage difference from Vref. This is added to a voltage / frequency conversion circuit (hereinafter referred to as V / f) 5-2, and a pulse having a repetition frequency corresponding to the difference voltage (pulse width is constant) is output. By adding this to the switch means 3, the load voltage is controlled to be constant by changing the switching cycle of the switch means 3.

When the switch means 3 is on, the winding on the primary side of the transformer 2
A current flows through Np, a current also flows through the secondary winding Ns1, and a voltage is generated at both ends of the winding Ns1, a current flows through the rectifier diode D1 and the load 4 via the choke coil L1, and the capacitor C1 is charged. .

On the other hand, when the switching means 3 is off, no current flows through the winding Np on the primary side of the transformer 2 via the switching means 3. When the switch means 3 is turned off, electromagnetic energy is accumulated in the primary and secondary windings of the transformer.
No current flows due to the electromagnetic energy of the winding Na1 on the secondary side of the transformer 2. This is because the rectifier diode D1 is in the opposite direction to the back electromotive force of the winding Ns1.

However, when the switch means 3 is turned on, the choke coil L1
The electromagnetic energy is accumulated in the choke coil L1 by the current flowing through the choke coil L1, and when the switch means 3 is turned off, the capacitor C1 and the commutation diode D2
, The capacitor C1 is charged and supplies a DC voltage to the load 4.

The voltage Eo supplied to the load 4 depends on the switching means 3
Assuming that the cycle of the pulse generated by turning on / off is T, the on time is Ton, and D = Ton / Ton + Toff = Ton / T, the DC power supply voltage Ei
On the other hand, the output voltage Eo is as follows.

Eo = Ns1 / Np ・ Ei ・ D When the switch means 3 is off, a back electromotive force is generated between the terminals a and b and between the terminals a and c due to the electromagnetic energy accumulated in the winding on the primary side of the transformer 2. Electromagnetic energy stored in the winding between the terminals a and b causes a current to flow through the DC power supply 1, the diode D5 and the windings c and a to charge the DC power supply, thereby reducing waste of electromagnetic energy.

[Problems to be solved by the invention]

However, in the above-described DC / DC converter, when it is desired to obtain a high voltage for the load, the number of windings on the secondary side of the transformer must be increased. As a result, the shape of the transformer becomes large and the distributed capacitance of the coil increases. There is a problem in that current flows through the distributed capacitance, switching loss increases, and voltage conversion efficiency decreases.

Therefore, an object of the present invention is to realize a DC / DC converter that can obtain a high-voltage output without increasing the shape of the transformer of the present invention and without lowering the efficiency of voltage conversion.

[Means for solving the problem]

The above object is achieved by a DC power supply as shown in FIG.
1 of a transformer in which 10 and switch means 30 are connected in series
For the next winding, between the secondary windings of the transformer, for the rectifier diode D1, the first DC smoothing in which a parallel connection of a choke coil L1 and a capacitor C1 and a commutation diode D2 are connected in series A circuit 60 and a second DC smoothing circuit 70 in which a series connection of a commutation diode D4 and a capacitor C2 and a parallel circuit of a choke coil L2 are connected in series to the rectifier diode D3 are connected in parallel. Load 40 is connected between the connection point of coil L1 and capacitor C1 and the connection point of commutation diode D4 and capacitor C2.
Is connected, and the adjustment voltage at the resistor R in parallel with the load controls the on / off of the switch means via the control circuit.

[Action]

In the present invention, when the switch means 30 is turned on, the rectifier diode D is generated by the electromotive force induced in the secondary winding Ns2 of the transformer 20.
1, a current flows through the choke coil L1, the load 40 and the capacitor C2, and a charging current also flows from the choke coil L1 to the capacitor C1.

Further, a current flows from the winding Ns2 to the rectifier diode D3 and the choke coil L2.

On the other hand, when the switch means 30 is turned on, the choke coil L1 and
Electromagnetic energy is accumulated in L2, and the electromotive force generated by the electromagnetic energy acts when the switch means 30 is turned off.

That is, a current flows through the capacitor C1 and the commutation diode D2 due to the electromotive force generated in the choke coil L1, and the capacitor C1 is charged.

Further, current flows through the capacitor C2 and the commutation diode D4 due to the electromotive force generated in the choke coil L2, and the capacitor C2 is charged.

Then, the charging voltages of the capacitors C1 and C2 are connected in series and supplied to the load 40, and the discharge current is supplied to the load.

In this case, the output voltage supplied to the load is Eo, the repetition period of the pulse generated by turning on / off the switch means 30 is T, the on time is Ton, and D = Ton / T. It becomes like.

Eo = Ns2 / Np.Ei.D (2-D) / 1-D As is apparent from this equation, the value of D sequentially changes by changing the on / off cycle from the completely off state of the switch means. However, this allows the voltage of Eo to be controlled over a wide range from OV.

For example, when the Ns2 / Np ratio is set to 1, which is the same as the conventional example, and D = 0.5, an output voltage three times that of the conventional circuit can be obtained.

Note that the electromagnetic energy accumulated in the secondary winding Ns2 when the switch 30 is turned on is equal to the electromagnetic energy when the switch 30 is turned off.
1. The reason why the second direct current smoothing circuit is not affected at all is that the electromotive force induced in Ns2 is opposite to the rectifier diodes D1 and D3.

However, the electromagnetic energy stored in the primary winding Np is used for charging the DC power supply 1 when the switch means 30 is turned off, as in the case of FIG.

〔Example〕

FIG. 1 is a circuit diagram of a DC / DC converter according to an embodiment of the present invention.

In FIG. 1, both ends of the winding Ns2 on the secondary side of the transformer 20
A second DC smoothing circuit 70 comprising a rectifier diode D3, a commutation diode D4, a choke coil L2 and a capacitor C2 is connected between d and e in parallel with the first DC smoothing circuit 60. It differs from the conventional example shown in FIG. 2 in that a load is connected between them.

The operations of the control circuit 50 and the switch means 30, for example, an npnTr, are the same as in the conventional example.

 The main points of the circuit operation will be described below.

When the switch means 30 is turned on in the circuit of FIG. 1, a current flows through the winding Np on the primary side of the transformer 20 and the winding Ns on the secondary side.
Current also flows through 2. The current in the winding Ns2 is divided into two at the terminal d, and one current i1 is supplied to the first DC smoothing circuit.
In 60, the current flows through the rectifier diode D1, the choke coil L1, the load 40, the resistor R, and the capacitor C2 in the second DC smoothing circuit 70, and a current is supplied to the load and the capacitor C2 is also charged.

Further, the current branches from the choke coil L1 to the capacitor C1, and C1 is charged.

The current i2 branched at the other terminal d is supplied from the terminal d to the rectifier diode D3 and the choke coil L in the second DC smoothing circuit 70.
Flow into the loop formed by 2.

On the other hand, when the switch means 30 is off, no current flows through the switch means 30 to the winding Np on the primary side of the transformer 20.

However, when the switch means 30 is on, the choke coils L1, L
Electromagnetic energy is accumulated in each of the two, and when the switch means 30 is turned off, a current flows in a loop formed by the capacitor C1 and the commutation diode D2 due to the back electromotive force generated in this L1, and the capacitor C1 is charged. The capacitor C2 and commutation diode D4 are generated by the back electromotive force generated in L2.
A current flows in the loop formed by the above, and the capacitor C2 is charged. The charges charged in the capacitors C1 and C2 are discharged in series via the resistor R / load 40.

As a result, by repeating the ON / OFF operation of the switch means 30, a DC voltage equal to the sum of the voltages of the capacitors C1 and CD by the current of the DC smoothing circuits 60 and 70 is supplied to the load 40.

The output voltage Eo supplied to the load 40 is represented by T, the repetition period of a pulse generated by turning on / off the switch means 30, Ton the on time, the voltage of the capacitor C1 to Vc1, and the voltage of the capacitor C2 to Vc2. Then, Vc1 and Vc2 are as follows.

Vc1 = Ns2 / Np · Ei · D Vc2 = Ns2 / Np · Ei · D / 1−D Therefore, the output voltage Eo is Eo = Vc1 + Vc2 = Ns2 / Np · Ei · D + Ns2 / Np · Ei · D / 1−D = Ns2 / Np ・ Ei ・ D (2-D) / 1-D.

For example, if D = 0.5 and the winding ratio Ns1 / Np is 1, which is the same as the conventional example, the value of Eo (1) = 0.5Ei in the conventional example is Eo (2) = 1.5Ei in the embodiment of the present invention. Becomes As a result, Eo (2) / Eo (1) = 3 and DC / DC according to the present invention.
The converter can obtain three times the output voltage of the conventional example.

〔The invention's effect〕

As described above, in the DC / DC converter according to the present invention, a high-voltage output can be obtained without increasing the shape of the transformer and further reducing the efficiency of voltage conversion.

[Brief description of the drawings]

 FIG. 1 is a circuit diagram of a DC / DC converter according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a DC / DC converter of a conventional example. In the figure, 1,10 is a DC power supply, 2,20 is a transformer, 3,30 is a switch means, 4,40 is a load, 5,50 is a control circuit, D1 and D3 are rectifier diodes, and D2 and D4 are commutation diodes. , C1 and C2 are capacitors, L1 and L2 are choke coils, Np is a primary winding, Ns2 is a secondary winding, Ei is a DC power supply voltage, and Eo is an output voltage.

Continuation of the front page (56) References JP-A-62-225164 (JP, A) JP-A-56-107784 (JP, A) JP-A-53-8724 (JP, A) JP-A-50-156654 (JP, A) , A) Japanese Utility Model Showa 59-75786 (JP, U) Japanese Utility Model Showa 55-170890 (JP, U)

Claims (1)

(57) [Claims] A DC power supply 10 and a switch means 30 are connected in series with a primary winding of a transformer. Between a secondary winding of the transformer, a rectifier diode D1, a choke coil L1 and a capacitor C1 are connected in series. A first DC smoothing circuit 60 in which a connection and a parallel circuit of a commutation diode D2 are connected in series; and a parallel circuit of a series connection of a commutation diode D4 and a capacitor C2 and a choke coil L2 for a rectifier diode D3. Are connected in series with a second DC smoothing circuit 70, and a load 40 is connected between a connection point of the choke coil L1 and the capacitor C1 and a connection point of the commutation diode D4 and the capacitor C2. A DC / DC converter characterized in that a regulated voltage in a resistor R in parallel with a load controls on / off of switch means via a control circuit.