JPH0720368B2 - Switching power supply - Google Patents

Description

The present invention relates to a switching power supply device which obtains an output DC voltage from a step-down chopper type switching power supply circuit from a single input DC voltage, and a simple drive circuit for a switch element. The present invention relates to a switching power supply device that realizes the above.

(B) Conventional technology The number of portable OA devices with a battery input represented by laptop computers is increasing. The power supply for these OA equipment is a battery with an input of 8 to 16V, and an output of 5V, ± 12V.
4 to 6 kinds of DC voltage such as V, -5V, 35V are obtained, and the condition is that the conversion efficiency is good. Therefore, a switching power supply circuit is used for these power supplies in order to make them compact and highly efficient.

As such a switching power supply circuit, a chopper type switching regulator is used for a 5V power supply that consumes a large amount of current to drive a microcomputer and memory, and a DC voltage (35V, ± 12V, -5V) higher than that of a battery that consumes less current is used. A flyback switching regulator is used for the power supply. A specific switching power supply circuit will be described with reference to FIG.

The one shown on the upper side of FIG. 3 is a chopper type switching regulator. The diode D1 and the capacitor C1 connected in series charge the DC voltage from the battery and supply it to the control circuit, and the control circuit IC1 (formed by an integrated circuit)
Outputs a control pulse whose pulse width is modulated corresponding to the output voltage + 5V, and is a complementary transistor Tr1, Tr2.
Is a driver circuit that connects and disconnects the switching element Tr3 composed of a MOS transistor by a control pulse, and the diode D2, the choke coil L1 and the capacitor C2 form a smoothing circuit to smooth the intermittent voltage that is the output of the switching element Tr3. Outputs + 5V power.

The lower part of FIG. 3 is a flyback type switching regulator. The control pulse that is pulse width modulated corresponding to the output voltage (for example, + 12V) output from the control circuit IC2 is a complementary transistor Tr4, Tr5.
MO that is input to the driver circuit formed by and is connected in series to the primary winding of the transformer (flyback transformer) T.
Switching element Tr6 consisting of S-transistor is intermittently connected, and AC voltage obtained from the secondary winding of transformer T is cleaned and smoothed by diodes D3, D4, D5, D6 and capacitors C3, C4, C5, C6. The DC output voltage of 35V, ± 12V, −5V is obtained.

As a chopper type switching regulator, Japanese Patent Laid-Open No. 62-48260 (H02M 3/155) and as a flyback type switching regulator Japanese Patent Laid-Open No. 62-64262 (H02M 3/28) are known.

(C) Problems to be Solved by the Invention However, in the chopper type switching regulator,
When an inexpensive N-channel MOS transistor is used as the switching element Tr3, it is necessary to bias the gate at a voltage higher than the source by at least 4V or more to turn it on. For this reason, there arises a problem that an auxiliary power supply circuit must be provided separately or a charge-up circuit must be provided in order to generate this voltage when operating efficiently.

In order to solve such a problem, the applicant of the present invention, as shown in FIG. 4, has a switching power supply for generating a voltage for operating efficiently by providing another winding on the primary side of a transformer of a flyback type switching regulator. Proposed a device.

(C) Problems to be Solved by the Invention Although the conventional example shown in FIG. 4 can certainly perform efficient switching operation, in this case, the step-down chopper type switching regulator and the flyback type switching regulator are combined. A combination is needed,
As described above, there is a problem that an auxiliary power supply circuit or a charge-up circuit must be separately provided in order to perform the switching operation efficiently with only the step-down chopper type switching regulator.

(D) Means for Solving the Problems The present invention has been made in view of the above problems, and a constant voltage circuit is provided between the input DC voltage line and the drive circuit, and the output voltage from the constant voltage circuit is charged. Set up a capacitor to solve the problem.

(E) Action As described above, according to the present invention, a constant voltage circuit and a charge-up circuit are provided by a single input DC voltage to create a constant voltage higher than the input DC voltage, and to prevent fluctuations in the input DC voltage. However, the switching element can be driven in a stable and efficient state.

(F) Embodiment A switching power supply device according to the present invention will be described in detail with reference to FIGS. 1 and 2.

As shown in FIG. 1, the switching power supply device of the present invention includes an input terminal to which a DC voltage is applied, a switching element Tr3 for turning on / off the DC voltage applied from the input terminal,
A drive circuit that drives the switching element Tr3, a control circuit that applies a predetermined pulse signal to the drive circuit,
It is composed of a constant voltage circuit connected between the DC voltage line and the drive circuit, and a capacitor C1 connected between one end of the drive circuit and the switching element Tr3.

A feature of the present invention is that a constant voltage circuit is connected between the drive circuit and the DC voltage line, and a capacitor C1 that charges a predetermined voltage applied from the constant voltage circuit between one end of the drive circuit and the switching element Tr3. Is to connect.

In such a configuration, the DC output voltage applied from the constant voltage circuit is charged in the capacitor C1 via the diode D1, superimposed on the intermittent voltage which is the output of the switching element Tr3, and supplied to the drive circuit. That is, the constant voltage output from the constant voltage circuit is charged to the capacitor C1 via the diode D1 and the intermittent voltage (equal to the input DC voltage) when the switching element Tr3 is turned on and the constant voltage charged to the capacitor C1. A DC voltage higher than the input DC voltage is superimposed and applied to the collector of the NPN transistor Tr1 of the drive circuit, and is applied to the gate of the switching element Tr3 when the NPN transistor Tr1 of the drive circuit is turned on.

In the invention proposed by the applicant (Japanese Patent Application No. 63-264557), the switching element cannot be operated efficiently (using the winding of the transformer) unless it is combined with a flyback type switching regulator. The step-down chopper type regulator alone can efficiently operate the switching element Tr3 with a single input DC voltage without requiring an auxiliary voltage from the winding.

FIG. 2 is a diagram showing the waveform of each part of FIG.

(A) shows the output waveform of the switching element Tr3.

The peak value is equal to the input value current voltage, and the switching element Tr3
An intermittent waveform is formed by the on / off operation of.

(B) shows the output waveform of the constant voltage circuit, which outputs a constant voltage that is not affected by fluctuations in the input DC voltage.

(C) shows a voltage waveform applied to the collector of the NPN transistor Tr1 of the drive circuit.

Now, when the switching element Tr3 is turned off,
The output potential of the switching element Tr3 at the point (a) becomes the GND level, and at this time, the voltage shown at the point (b) is charged in the capacitor C1 via the diode D1. Switching element Tr
Switching element T at point (a) when 3 is turned on
The output potential of r3 becomes equal to the input DC voltage, the potential charged in the capacitor C1 is superimposed, the waveform at point (c) appears, and the shaded area is the voltage obtained by the constant voltage charge-up circuit. By being superimposed on the input DC voltage, a potential that efficiently drives the gate of the switching element Tr3 is formed. The diode D1 prevents the superimposed voltage from flowing backward.

In this embodiment, N channel M is used as the switching element Tr3.
Although the OS transistor is used, even if the NPN transistor is used, it is necessary to raise the potential of the base to the emitter by at least 0.6 to 1 V or more, and the same effect can be obtained by using the present invention. The transistors Tr4 and Tr5 are pre-driver circuits connected to compensate the withstand voltage of the control circuit.

(G) Effect of the Invention According to the present invention, a constant voltage circuit, a diode D1 and a capacitor
The constant voltage charge-up circuit composed of C1 obtains a voltage higher than the input DC voltage and applies it to the gate of the switching element Tr3 of the step-down chopper type switching regulator. Since a MOS field effect transistor can be used as the switching element Tr3, extremely high efficiency can be realized by a single step-down chopper type regulator alone without a separate power source for the switching element gate drive.

Further, according to the present invention, since a high efficiency circuit can be achieved with a single input voltage, a rectifying / smoothing circuit for another power supply can be omitted and the input system can be simplified, so that an OA device that is required to be downsized. The optimal switching power supply can be realized.

[Brief description of drawings]

FIG. 1 is a circuit diagram for explaining a switching power supply device according to the present invention, FIG. 2 is a waveform diagram for explaining the operation of the present invention, and FIG.
FIG. 4 and FIG. 4 are circuit diagrams for explaining a conventional switching power supply device. Tr1, Tr2 are drive circuits, Tr3 is a switching element, Tr4,
Tr5 is a pre-driver circuit.

Claims (2)

[Claims] 1. An input terminal to which a DC voltage is applied, a switching element for turning on / off the DC voltage applied from the input terminal, a drive circuit for driving the switching element, and a predetermined pulse for the drive circuit. In a step-down chopper type switching power supply device comprising a control circuit for applying a signal, and a smoothing circuit for smoothing a DC voltage intermittently obtained by the switching element, a constant voltage between the input terminal and the drive circuit. A circuit is provided, and a capacitor for charging a voltage applied from the constant voltage circuit is provided between the drive circuit end on the constant voltage circuit side and the switching element end on the smoothing circuit side. Switching power supply. 2. An N channel as the switching element
2. The switching power supply device according to claim 1, wherein a MOS transistor is used.