JPS5925580A - Switching regulator - Google Patents

Abstract

PURPOSE:To reduce the switching loss and the noise of the titled device by a method wherein the currents of switching transistors are made to a sine wave form utilizing resonance action of a coil and a capacitor. CONSTITUTION:When the switching transistor 3 is made to ON, an input voltage is applied to a winding 12, and a voltage is induced in a winding 13. As a result, a resonance curent flows into the capacitor 15 according to resonance action of the coil 14 and the capacitor 15. When the transistor 3 is made to OFF, and the transistor 18 is made to ON next, electric charge of the capacitor 15 is discharged to the capacitor 8 according to resonance action with the coil 17. Because the currents to flow in the respective transistors 3, 18 become to the sine wave type, noise to be generated is limited to a fundamental wave. Moreover the currents of the transistors 3, 18 are zero at turn-ON time and turn-OFF time, no switching loss is generated, and no surge current is generated also.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in switching regulators.

Conventionally, a forward converter as shown in FIG. 1 has been widely known as this type of switching regulator. After the voltage is converted by 4, it is applied to a smoothing circuit consisting of a coil 7 and a capacitor 8, and the average DC voltage output is taken out. Vi (v) for the input voltage, output voltage, switching period, transistor on-width, and number of primary and secondary windings of the transformer.

Vo (V), T (sec), ToN (see),
Assuming Nl (turn) and N2 (turn), there is a relationship between them as shown in Equation 11 below.

v O:=: T oN・-' V+ (V)...
...... Field T N.

In equation (1), the output voltage (2)0 is normally stabilized by fixing the period T and varying the on-width ToN.

However, in the case of a conventional forward converter, the load of the switching transistor is an inductive load, and a large current is suddenly switched at turn-on and turn-off, so not only does the switching loss of the transistor and diode become large (it also causes large radiation and noise). However, these drawbacks include the fact that the level is high over a fairly high frequency range.Furthermore, these drawbacks become more noticeable as the frequency of the switching operation increases, so they are a fundamental factor that hinders the miniaturization of power supplies due to the increase in frequency. Ta.

The present invention solves the above-mentioned problems by switching a sine wave current using LC resonance effect.In a switching regulator using a switching transistor and a voltage conversion transformer w, the first diode, the first coil and A series circuit of a first capacitor is connected to both ends of the output winding of the voltage conversion transformer, and a series circuit of a switching transistor, a second coil, and a second capacitor having an on-off phase opposite to that of the switching transistor. and a second diode are connected in parallel to the capacitor 1, and a load resistor is connected in parallel to the second capacitor.

□Hereinafter, one embodiment of the present invention will be described with reference to FIG.

In FIG. 2, voltage conversion trough 240 primary main winding 1
2 and the switch puffer transistor B, and the series circuit of the primary side auxiliary winding 11 of the transformer 4\, and the diode 2 are connected to the input power supply 1, and the first diode 5,
Series port W of first coil 14 and first capacitor 15
(Connected to both ends of the secondary winding 1 of the lance 4, and connected the series circuit of the second coil 17, switching transistor 18, and second capacitor 8, and the second diode 16 to the first capacitor 15. Furthermore, nine load resistors are connected in parallel to the second capacitor 8, with the voltage across the capacitor 80 being the output voltage of the switching regulator.The transistor 6 is driven by the control circuit 10 to stabilize the output detection voltage. The oscillation frequency is adjusted as shown in FIG.

That is, the transistor 18 is connected so that when the transistor 6 is turned on and the input voltage is applied to the winding 12, the induced voltage in the winding 19 turns off the transistor 18. It is turned on by the fly/zet voltage generated.

Here, assuming that the period in which the transistor 3 is on and the transistor 18 is off (1/2 cycle) is a cycle I, and the reverse period (1/2 cycle) is a cycle ■, the switching operation period of this circuit is cycle 1. , II also form one period with two cycles.

In the above circuit configuration, the voltage across the capacitor 150 immediately before the transistor is turned on is Ov, as will be described later. Therefore, when the transistor 1 turns on in cycle I, an input voltage is applied to the winding 12, and a voltage corresponding to the ratio of the number of turns, 12.13, is induced in the winding 13. As a result, a resonance current IL+4 (A) flows into the capacitor 15 due to the resonance effect between the coil 14 and the capacitor 15. When this charging current finishes flowing, capacitor 1
The voltage VC+4 (V) across the antenna 5 takes the maximum value of the resonant waveform as shown in FIG. 6 (3).

Here, the interftance of coil 14, con answer 15
The capacity, input power supply voltage, and number of turns of winding 12.13 are respectively L14 (Hl, Cl5(F), E(V), Nl
(TURN), N2(TtJI(N), and the time when the start of cycle l is the origin is t, then the following formula (
The relationships 2) to (4) hold true.

However, 0 < 1 < πF-7 little (s generation)...
...(4).

During the remaining period of cycle I πm<t< (T is the switching period), charging of the capacitor 5 is completed, but the transistor 18 is in an off state, and the diode 5
Since the direction of conduction is opposite, the capacitor 5 is not discharged to the input side or the output side, and the capacitor 5 maintains the maximum voltage Vc15 (MAX) = 2E during charging.

Next, in cycle 2 (-ffl-<t<T), when the trapstor 6 is turned off and the transistor 18 is turned on, the charge on the capacitor 5 is transferred to the capacitor 8 due to resonance with the coil 17, as shown in FIG. 6(2). Be discharged to. At this time, a flying voltage is generated in the winding 13, but this has the opposite polarity to the voltage across the capacitor 5, and since the diode 5 is in the non-conducting direction, a charge flows from the capacitor 5 to the winding 13. is never discharged.

Here, if the inductance of the coil 17 and the voltage across the capacitor 8 are respectively L1
;If QV is 1×4 time τDC (sec), then
The current I L12 (A) of the coil 17 and the voltage VC+5 (V) across the capacitor 5 are calculated by the following equations (5) to (9).

As can be seen from the diagram, the voltage across the capacitor 15 is o
When the voltage drops to V, the excitation current of the coil 17 reaches its maximum.

The maximum excitation current IL17m of the coil 17 is calculated by the following formula (11
).

...Ql] Thereafter, the excitation current of the coil 17 is reset via the third diode 16.

If this reset period is τR8 (sec), then the current I of the coil 17 during this period is LH and rR8.
It is represented by Q31.

Vo T I L17-I L17 m b,, (t-1
7DC) included) ・--aa147 IL,,m τR8= (sec)
......0th floor ■0 After the demagnetization of the coil 17 is completed, the circuit operation remains stationary until the next cycle 1 is started.

Furthermore, in deriving the above-mentioned (4) to zero-order equations, the voltage across the capacitor 8, that is, the output voltage Vo, is based on the assumption that the time constant of the discharge circuit of the capacitor 8 and the resistor 9 is much larger than the period T. It is assumed that the voltage value remains unchanged throughout cycles I and If.

As can be seen from the above explanation, since the current flowing through each transistor has a sine wave shape, the noise generated is only one fundamental wave and there is no harmonic component.

Also, the transistor at turn-off and turn-off, 1
The current of No. 8 is O, and there is no switching loss and no surge current. Therefore, even if the operating frequency is increased,
There is no increase in noise or surge current, or a decrease in the power conversion efficiency of the power supply.

The power excited in the transformer 4 when the transistor 6 is on is fed back to the input power source 1 via the winding 11 and the diode 2 when the transistor 6 is off.

Here, the operating frequency and the resistance value of the load resistor 9 are f
(Hz) and -(Ω), the output power Po (W) can be expressed as ++5). In other words, it becomes.

From the above equation, the output voltage Vo is a function of the operating frequency f (Hz), the resistance value R9 (Ω) of the load resistor 9, and the input voltage E (V), and conversely, the output voltage Vo is a function of the input voltage B (V) or the load resistor 9 The frequency f(llz)'(
It can be seen that the output voltage is stabilized by adjusting ff.

As explained above, the present invention utilizes the resonance effect of the coil and capacitor to make the current of the switching transistor/resistor into a sine wave shape.Therefore, the switching loss is small and even when the frequency is increased, the loss is low and the noise is kept at the resonant frequency. It has excellent features such as only the fundamental wave and low noise in principle.

[Brief explanation of drawings]

Fig. 1 is a block diagram for explaining the operation of the conventional forward method, Fig. 2 is a circuit diagram showing an embodiment of the present invention, and Fig. 6 is a waveform diagram showing the operation of Fig. 2. be. 1 ゛... Input power supply 3... Switching transistor 4... Voltage conversion transformer 5.
-First diode 8...Second capacitor 9...
-Load resistor 14...first coil 15...first
Capacitor 162...Second diode 17...
Second coil 18 ・Switching transistor Patent attorney Naka Kanno, patent attorney for NEC Co., Ltd.
−□2 voices

Claims (1)

[Claims] +ll In a switching regulator using a switching transistor and a voltage conversion transformer, the first
A switching transistor connected to both ends of the output winding of the voltage conversion transformer and having an on-off phase opposite to that of the switching transistor, A switching regulator characterized in that a series circuit of a second coil and a second capacitor and a second turn-off time are connected in parallel to the first capacitor, and a load resistor is connected in parallel to the second capacitor.