JPS591422Y2 - DC/DC converter - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a DC/DC converter that can maintain an output voltage for a long time during a power outage or the like.

BACKGROUND ART In a power supply device used in a computer or the like, it is necessary to maintain an output voltage for a certain period of time in the event of a power outage or the like in order to protect stored contents, programs, and the like.

Conventionally, in order to lengthen such voltage holding time, D
Many methods have been used to increase the capacitance of the input capacitor of the C/DC converter to lengthen the time it takes for the output voltage to decay to the lower limit value.

However, the capacitance of a capacitor is proportional to its volume, and in order to increase the capacitance, the volume increases, and the proportion of the volume occupied by the capacitor in the power supply device increases, making it impossible to downsize the device. This caused some design inconveniences.

Furthermore, if the capacity of the input capacitor is increased, the duration of the rush current that flows when the power is turned on becomes longer, which adversely affects the power-on characteristics.

The present invention eliminates the drawbacks of the conventional device as described above, and provides a DC/DC converter that can extend the voltage holding time without increasing the volume occupied by the capacitor, and does not adversely affect the power-on characteristics. The purpose is to realize this with a simple configuration.

FIG. 1 shows the configuration of an embodiment of the DC/DC converter of the present invention.

In the figure, Ein is a DC power supply, C1 and C2 are capacitors, SW1 and SW2 are switching circuits, and CON is a switching circuit SW1. In the drive circuit of SW2, T is a transformer, REC is a rectifying and smoothing circuit, and L is a load.

The capacitors C1 and C2 are each a switching circuit S
W1. The primary windings N, , N2 of the transformer T via SW2
It is connected to the.

The output signal Sd of the drive circuit COH is applied to the switching circuits SWl and SW2, and they are driven synchronously.

Note that the capacitor C2 is provided to lengthen the voltage holding time.

The operation of the DC/DC converter of the present invention configured as described above is as follows.

The voltage charged in the human-powered capacitor C1 is switched on and off by the switching circuit SW1, and then the transformer T and the rectifying and smoothing circuit R
It is supplied to the load via EC.

Here, a voltage Z □·Ein l is induced in the other primary winding N2 of the transformer T, but if the terminal voltage of the capacitor C2 is lower than this, the voltage is induced in the capacitor C2 via the switching circuit SW2. Charging is performed.

Therefore, the capacitor C2 is always charged with a certain voltage, which is balanced with the induced voltage of the primary winding N2.

Now, if the DC power source Ein is no longer applied due to a power outage or other cause, the power supply device will operate using the charging voltage of capacitors C1 and C2, and power will be supplied to the load from capacitors C1 and C2. Become.

At this time, the secondary winding N2 of the transformer T is connected to the capacitor C2.
The voltage induced on the side becomes , which is the same voltage as before the power outage.

In this way, from the moment the power goes out, backup is performed by capacitors C1 and C2, and the output voltage gradually attenuates, but the voltage holding time until the output voltage reaches its lower limit value is stored in capacitors C1 and C2. It corresponds to the amount of energy.

Next, consider the influence of capacitor C2 on voltage holding time.

Now, to make it easier to think about it, if the capacitance of capacitors C1 and C2 is C1 (C2), then capacitor C2 is called capacitor C
When connected in parallel with 1, the stored energy Eg1
becomes .

Further, as shown in FIG. 1, when the capacitor C2 is connected via the primary winding N2 and the switching circuit SW2, the energy Eg2 stored is as follows.

Here, when the volume of the capacitor is constant, its capacitance C
There is a relationship between and allowable voltage (2) such that the product CV is constant, and the energy stored in a capacitor with a constant volume is proportional to the voltage value.

Therefore, in equations (2) and (3) above, assuming that the volume of the capacitor C2 used is constant, the device shown in Figure 1 can store N 2 / N 1 times the energy, and the voltage will increase accordingly. Holding time can be increased.

Furthermore, since the capacitance of the input capacitor C1 can be reduced, the duration of the rush current can be shortened, and the time required to turn on the power can be shortened.

FIG. 2 shows the constituent countries of a specific example of the DC/DC converter of the present invention.

In the figure, parts similar to those in FIG. 1 are designated by the same reference numerals.

Q is a switching transistor, D1 to D3 are diodes, and R is a resistor.

The transformer T has a center tap on its primary winding, and has two primary windings N1 that share a part. A switching transistor Q is connected to one end of the transistor N2.

The switching transistor Q is the switching circuit SW shown in FIG.

It also functions as SW2.

Capacitor C1 is connected to primary winding N1 via diode D1 for backflow prevention, and capacitor C2 is connected to primary winding N2 via diodes D2, D3 and current limiting resistor R, which are connected in opposite directions. It is connected to the.

When the switching transistor Q is driven by the signal Sd, power is supplied from the DC power supply Ein to the load via the transformer T.

At the same time, the capacitor C2 has a primary winding N2. Diode D3. Charging takes place via a current limiting resistor R.

Here, since the capacitor C2 is gradually charged via the current limiting resistor R, there is no adverse effect on the secondary winding Ns.

Furthermore, since the discharge from the capacitor c2 is performed via the diode D2, the output voltage does not drop.

In addition, in the above explanation, the primary winding N2 of the transformer T
The case where only capacitor C2 is connected to the side is shown as an example, but
There is no problem even if another backup power source is connected to this capacitor C2.

For example, if a power supply with a voltage slightly lower than the DC power supply Ein is connected to the capacitor C2, normally the DC power supply Ein
Power is supplied to the load only by Ein, and when the voltage on the DC power supply Ein side drops due to a power outage or the like, power is supplied from the capacitor C2 side.

As explained above, in the DC/DC converter of the present invention, a transformer having two primary windings with different windings is used, and a DC power source is connected to the primary winding side with a smaller number of turns via a switching circuit. Since the holding capacitor is connected to the primary winding side with a large number of turns via a switch circuit, it is possible to extend the voltage holding time without increasing the volume of the capacitor, and it is also possible to increase the voltage holding time when the power is turned on. A DC/DC converter that does not adversely affect characteristics can be realized with a simple configuration.

[Brief explanation of the drawing]

FIGS. 1 and 2 are configuration diagrams showing an embodiment of the DC/DC converter of the present invention. SWl, SW2...Switching circuit, CON
... Drive circuit, RFC ... Rectification and smoothing circuit, L ... Load.

Claims (1)

[Scope of utility model registration request] In a DC/DC converter in which an input capacitor charged by a DC power supply is connected to a primary winding of a transformer via a switching circuit, the input capacitor is connected to a primary winding provided in the transformer and connected to the input capacitor. a second primary winding having a number of turns; and a second capacitor connected to the second primary winding via the switching circuit or a second switching circuit driven in synchronization with the switching circuit. A DC/DC converter comprising: