JPH0550229B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Field of Industrial Application The present invention relates to a switching power supply device that obtains a plurality of different DC output voltages from a common input DC voltage from a switching power supply circuit having a chopper type switching power supply circuit and a transformer. In particular, the present invention relates to a switching power supply device that realizes a simple starting circuit for switching elements of a chopper-type switching power supply circuit.

(b) Conventional technology The number of portable OA devices with battery input, such as laptop computers, is increasing. The power supply for these OA devices is a battery with an input of 8 to 16 V, and the output is 4 to 6 types of DC voltage such as 5 V, ±12 V, -5 V, 35 V, etc., and the condition is that the conversion efficiency is good. It's summery. Therefore, switching power supply circuits are used in these power supplies in order to make them smaller and more efficient.

For such a switching power supply circuit, a chopper-type switching regulator is used for a 5V power supply that consumes a lot of current to drive a microcomputer or memory, and a DC voltage (35V, ±12V, - A flyback switching regulator is used for the 5V) power supply. A specific switching power supply circuit will be explained with reference to FIG.

What is shown in the upper part of FIG. 3 is a chopper type switching regulator. The diode D1 and capacitor C1 connected in series charge the DC voltage from the battery and supply it to the control circuit.
IC1 (formed by an integrated circuit) outputs a pulse width modulated control pulse in response to the output voltage +5V, and the complementary transistor Tr
1. Tr2 is a driver circuit that connects and connects the switching element Tr3, which is made up of a MOS transistor, using a control pulse. The diode D2, the choke coil L1, and the capacitor C2 form a smoothing circuit that smooths the intermittent voltage that is the output of the switching element Tr3. outputs +5V power.

What is shown at the bottom of FIG. 3 is a flyback switching regulator. A control pulse whose pulse width is modulated in accordance with the output voltage (for example, +12V) output from the control circuit IC2 is input to a driver circuit formed by complementary transistors Tr4 and Tr5, and is connected to a transformer (flyback transformer). A switching element consisting of a MOS transistor connected in series to the primary winding of T.
By intermittent Tr6, the AC voltage obtained from the secondary winding of transformer T is passed through diodes D3, D4, D5, D.
6 and capacitors C3, C4, C5, and C6 to rectify and smooth multiple DC output voltages of 35V, ±12V,
-5V is obtained.

Note that as a Chiyotupa type switching regulator, Japanese Patent Application Laid-Open No. 62-48260 (H02M 3/155),
As a flyback type switching regulator, Japanese Patent Application Laid-Open No. 62-64262 (H02M 3/28) is known.

(c) Problems to be Solved by the Invention However, in a chopper type switching regulator, if an inexpensive N-channel MOS transistor is used as the switching element tr3, the gate must be at least as large as the source in order to turn on.
It is necessary to bias at a voltage higher than 4V. Therefore, in order to operate efficiently, a problem arises in that a separate auxiliary power supply circuit or a charge up circuit must be provided in order to generate this voltage.

(d) Means for Solving the Problems The present invention has been made in view of the above points, and a separate winding is provided on the primary side of the transformer of a flyback switching regulator to generate a voltage for efficient operation. By doing so, a switching power supply device that solves the problems of the conventional device is realized.

(E) Function According to the present invention, when the flyback switching regulator starts and output is generated in the secondary winding, voltage is generated in the separate winding provided on the primary side of the transformer T. Create a voltage that is approximately 5V or more higher than the input DC voltage,
Switching element Tr3 can be efficiently driven.

(F) Embodiment A switching power supply device according to the present invention will be described in detail with reference to FIGS. 1 and 2. The switching power supply according to the present invention is composed of a chopper-type switching regulator and a flyback-type switching regulator like the conventional one, and the same components are common between FIGS. 1 and 3. A symbol is attached.

The feature of the present invention is that a separate winding 1 is provided on the primary side of the transformer T, and the voltage of the separate winding 1 is supplied to the driver circuit of the chopper type switching regulator via the diode D7. That is, the voltage generated from the separate winding 1 added to the transformer T is connected to the input voltage (+) from the battery via the diode D7.
A DC voltage approximately 5 V higher than the current voltage (8 to 16 V) is applied to the collector of the NPN transistor Tr1 of the driver circuit, and is applied to the gate of the switching element Tr3 when the driver circuit is turned on.

According to the above configuration, when the battery input is applied, the +5V chopper type switching regulator charges the input DC voltage through the diode D1 to the capacitor C1, and charges the N channel.
Switching element Tr3 composed of MOSFET is activated. However, in this state, as shown in Figure 2a, only the input DC voltage Vin (DC) is applied to the gate of switching element Tr3, and the gate is not high enough relative to the source, so switching element Tr3 is turned on. The saturation voltage is approximately 4V,
Switching operation is performed in a very inefficient state.

Next, when the flyback switching regulator starts up and starts supplying the output voltage to the secondary side of the transformer T, the separate winding 1 installed on the primary side receives approximately 5V.
A voltage higher than 5V is generated, and a DC voltage approximately 5V higher than the input DC voltage Vin (DC) is applied to the driver circuit via the diode D7 as shown in Figure 2b.
The gate of switching element Tr3 is approximately lower than the source.
It becomes higher than 5V and performs switching operation efficiently. Note that the diodes D1 and D7 each prevent current from flowing backward.

In this embodiment, N is used as the switching element Tr3.
Although a channel MOSFET was used, even if an NPN transistor is used, it is necessary to raise the base potential to the emitter by at least 0.6 to 1 V or more, and if a voltage of about 0.6 to 1 V or more is generated in the separate winding 1, the efficiency will be reduced. A good Chiyotupa type switching regulator can be realized.

The same effect can also be achieved by using a forward switching regulator instead of a flyback switching regulator.

(g) Effect of the invention According to the invention, a separate winding 1 is provided on the primary side of the transformer T.
is provided, and when the flyback switching regulator starts, a voltage of about 5V is obtained from a separate winding 1 and applied to the gate of switching element Tr3 of the chopper switching regulator.
Switching element Tr is N-channel MOSFET, which is cheaper than P-channel MOSFET and has lower on-resistance.
3, and has the advantage of achieving extremely high efficiency without providing a separate power source.

Further, in the present invention, since this can be achieved using only the separate winding 1 and the diode D7, there is no increase in space, and a switching power supply device that is ideal for portable OC equipment that is required to be small and thin can be realized.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram explaining the switching power supply device according to the present invention, FIG. 2 is a waveform diagram explaining the operation of the present invention, which corresponds to points a and b in FIG. 1, and FIG. FIG. 2 is a circuit diagram illustrating a conventional switching power supply device. Tr1, Tr2, Tr4, and Tr5 are transistors forming a driver circuit, Tr3 and Tr6 are switching elements, IC1 and IC2 are integrated circuits containing a control circuit, D1 to D7 are diodes, and C1 to C6.
is a capacitor, T is a transformer, L1 is a chiyoke, 1
is a separate winding.

Claims (1)

[Scope of Claims] 1. A chopper-type switching power supply circuit that smooths the intermittent DC voltage obtained by intermittent input DC voltage with a switching element, and 1.
A switching power supply circuit which is connected to a switching element via a secondary winding and which rectifies and smoothes an AC voltage obtained from a secondary winding of the transformer by intermittent switching of the switching element to obtain a DC output voltage. A switching power supply device characterized in that a separate winding is provided on the primary side of the transformer, and the voltage generated in the separate winding when activated is used to drive the switching element of the chopper type switching power supply circuit. 2 N channel as the switching element
2. The switching power supply device according to claim 1, wherein a MOS transistor is used.