JP3233266B2 - Switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply used for electronic equipment such as a computer, and more particularly to a reduction in the number of primary parts when an auxiliary power supply is provided.

[0002]

2. Description of the Related Art In a conventional switching power supply, as disclosed in Japanese Utility Model Laid-Open Publication No. 2-37592 proposed by the present applicant, a main converter having an output voltage stabilizing circuit, a ringing choke, and the like are disclosed. There is known a circuit in which an auxiliary converter having a simple circuit configuration such as a converter (RCC power supply) is combined. The capacity of the main converter is about several hundred watts, while the capacity of the auxiliary converter is about several watts.

[0003]

However, the auxiliary converter is still an independent converter even if it is an auxiliary converter, and requires a switching element and its control circuit. Even if it is several watts, it is inferior to the main converter. It requires an unprecedented number of parts. Therefore, there has been a problem that the ratio of the price of the primary circuit of the auxiliary converter and the mounting area on the printed circuit board to the entire power supply device is considerably large. In addition, since the switching element for the auxiliary converter needs to have a high withstand voltage, there has been a problem that a large-package FET or transistor having a current rating higher than the necessity is adopted and the cost must be reconsidered from the demand for cost reduction.

The present invention solves the above-mentioned problems, and reduces the number of components of the primary circuit of the auxiliary converter to minimize the mounting area on a printed circuit board.
An object is to provide a highly reliable switching power supply.

[0005]

In order to achieve the above object, the present invention provides a main switching element for turning on and off a DC current applied to a primary winding n1 of a main transformer and a secondary winding n2 of the main transformer. A secondary-side rectifying / smoothing circuit for rectifying / smoothing the induced on / off signal; an error amplifier for generating an error voltage signal between a main output voltage output from the secondary-side rectifying / smoothing circuit and a reference voltage; A main converter section having a main converter control circuit for sending an on / off control signal to the main switching element in a direction to reduce an error voltage signal sent from the main switching element, and an auxiliary switching section for turning on / off a DC current applied to a primary winding n3 of an auxiliary transformer. A secondary-side rectifying / smoothing circuit for rectifying and smoothing the on / off signal induced in the secondary winding n4 of the auxiliary transformer; A primary side rectifying / smoothing circuit for rectifying and smoothing the on / off signal induced in the ass winding n5, and an on / off control signal to an auxiliary switching element so as to stabilize a voltage detected by the primary side rectifying / smoothing circuit to a predetermined reference voltage. A switching power supply device having an auxiliary converter section having an auxiliary converter control circuit for transmitting the main converter control circuit, wherein an IC circuit in which the main converter control circuit, the auxiliary converter control circuit, and the auxiliary switching element are formed on one chip is used. .

According to the structure of the present invention, the main converter control circuit, the auxiliary converter control circuit, and the auxiliary switching element are placed on the primary side of the power supply. And the auxiliary converter has a smaller capacity than the main converter, so that there is no heat radiation problem even if it is integrated into one chip including the auxiliary switching element. Conventionally, an auxiliary converter control circuit that used a large number of discrete components is also available.
Since it is configured on a chip, the occupied area when mounted on a printed circuit board can be reduced, which contributes to cost reduction.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing one embodiment of the present invention. In the figure, a rectifying / smoothing unit 10 rectifies an AC current supplied from a commercial power supply by a diode bridge DB, smoothes the AC current by an input capacitor Cin, and converts a DC current into a main converter unit 2.
0 and is supplied to the auxiliary converter section 40.

The main converter section 20 has a main switching element Q1 for turning on and off a DC current applied to a primary winding n1 of a main transformer. For example, the main switching element Q1 is a MOSFET, the drain terminal is connected to the primary winding n1, and the source terminal is grounded to the primary side ground via the resistor R1. The resistor R1 generates a signal proportional to the load current, and is connected to the current detection terminal Is of the main converter control circuit 52. The secondary winding n2 of the main transformer is connected to a secondary-side rectifying / smoothing circuit having diodes D1 and D2, a choke coil L, and an output capacitor Cout. And the secondary winding n2
Since an on / off signal is induced, the secondary side rectification and smoothing is performed by the secondary side rectification and smoothing circuit, and the main output voltage Vout is supplied to the load side.

The secondary-side control circuit 30 has a main output voltage Vout
Is divided by the voltage dividing resistors R2 and R3, input to the plus terminal of the error amplifier U1, compared with the first reference voltage Vref1 connected to the minus terminal, and outputs the error signal E / AOUT from the output terminal. I have. The error amplifier U1 performs amplification by providing a capacitor C1 for feedback and a resistor R4 between a minus terminal and an output terminal. The on / off circuit unit inputs a signal from a remote on / off circuit provided on the secondary side to a plus terminal of the comparator U2, compares the signal with a second reference voltage Vref2 connected to a minus terminal, and compares the power on / off signal P-ON. / OFF is sent to the transistor Q2. The transistor Q2 has a collector terminal connected to the output terminal of the error amplifier U1, an emitter terminal grounded, and a power on / off signal applied to a base terminal. Photo coupler PC
Applies an error signal E / AOUT to the light emitting diode to insulate the secondary side and the primary side, and inputs the transmitted signal to the feedback terminal F / B of the main converter control circuit 52 on the light receiving transistor side. .

The auxiliary converter section 40 has an auxiliary switching element Q3 for turning on and off the DC current applied to the primary winding n3 of the auxiliary transformer. The secondary-side rectifying / smoothing circuit rectifies and smoothes the on / off signal induced in the secondary winding n4 of the auxiliary transformer and supplies the auxiliary power supply voltage Vcc2, and includes a diode D3 and a capacitor C3. The auxiliary power supply voltage Vcc2 is used as a power supply for operating the secondary side control circuit 30, and is sent to the remote on / off circuit as an output voltage _VSB . The primary side rectifying and smoothing circuit rectifies and smoothes the on / off signal induced in the bias winding n5 of the auxiliary transformer and supplies the auxiliary power supply voltage Vcc, and has a diode D4 and a capacitor C4.

The PWM control IC 50 includes a main converter control circuit 52, an auxiliary converter control circuit 54, and an auxiliary switching element Q3 on one chip. With the progress of semiconductor manufacturing technology in recent years, a MOSFET used as a switching element and its control circuit can be manufactured as a semiconductor integrated circuit on the same chip. The auxiliary converter control circuit 54 sends an on / off control signal to the auxiliary switching element Q3 so as to stabilize the auxiliary power supply voltage Vcc detected by the primary side rectifying / smoothing circuit to a predetermined reference voltage. Auxiliary switching element Q3
Means that the source terminal is grounded and the drain terminal is
3 is connected. Preferably, when a frequency oscillator is commonly used for main converter control circuit 52 and auxiliary converter control circuit 54, main converter section 20 and auxiliary converter section 40
As a result, the divergence of the switching frequency is eliminated and noise countermeasures and the like can be easily performed.

The operation of the thus constructed apparatus will now be described.
I will tell. FIG. 2 is a waveform diagram for explaining the operation of the apparatus of FIG.
(A) shows the output DC voltage Vidc of the rectifying and smoothing unit 10,
(B) is the auxiliary power supply voltage Vcc of the bias winding n5, (C)
Is the output voltage V of the auxiliary converter _SB, (D) is the auxiliary switch
Gate voltage of switching element Q3, (E) is main converter
The feedback terminal F / B voltage of the control circuit 52, (F) is the main converter
(G) is the main output voltage.
The voltage Vout, (H) is a signal of the remote on / off circuit.
You.

In FIG. 1, a commercial power supply is input at time t1, and the output DC voltage Vidc of the rectifying / smoothing unit 10 rises.
Then, the auxiliary converter control circuit 54 and the auxiliary switching element Q3 of the PWM control IC 50 start operating, and the output of the bias winding n5 is connected to the diode D4 and the capacitor C4.
, The auxiliary power supply voltage Vcc which has been rectified and smoothed rises. The auxiliary power supply voltage Vcc is maintained at a constant voltage by the auxiliary converter control circuit 54 controlling the pulse width of the auxiliary switching element Q3. The output voltage V _SB of the auxiliary converter 40 also rises at the same time, and is controlled to a voltage value of the auxiliary transformer voltage Vcc of the turns ratio n4: n5 of the auxiliary transformer. The auxiliary converter section 40 operates at all times until the commercial power supply stops at time t4.

At time t2, when the remote on / off circuit is turned on, the comparator U2 becomes L, and the transistor Q2, which has shorted the output of the error amplifier U1 to the ground GND, is turned off. The error amplifier U1 performs error amplification by comparing the divided value of the main output voltage Vout with the first reference voltage Vref1. Then, this error amplification signal is transmitted to the feedback terminal F / B of the main converter control circuit 52 of the PWM control IC 50 via the photocoupler PC, and the main converter control circuit 52 turns on and off the main switching element Q1, thereby The output voltage Vout is stabilized.

At time t3, when the remote on / off circuit is turned off, the output of the error amplifier U1 is short-circuited to 0V, so that the error amplified signal is not fed back to the feedback terminal F / B of the main converter control circuit 52, and Stops.
When the supply of the commercial power is stopped at time t4, the operation of the auxiliary converter unit 40 is also stopped.

In the above embodiment, the PWM control I
Only the minimum necessary terminals are described in C50.
In addition, a terminal for outputting a reference voltage, a terminal for variably setting an oscillation frequency, and the like may be provided to provide a more versatile high withstand voltage PWM control IC.

[0017]

As described above, according to the present invention, P
In the WM control IC 50, since the main converter control circuit 52, the auxiliary converter control circuit 54, and the auxiliary switching element Q3 are formed on one chip, the cost of the primary circuit of the auxiliary converter and the mounting area on the printed circuit board are reduced. It has the effect of being done. In addition, since the auxiliary switching element Q3 can incorporate an element having a rating suitable for auxiliary switching, there is an effect that the element price can be reduced as compared with the case where a conventional standard product is adopted.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a waveform chart for explaining the operation of the device of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Rectification smoothing part 20 Main converter part 30 Secondary side control circuit 40 Auxiliary converter part 50 PWM control IC 52 Main converter control circuit 54 Auxiliary converter control circuit Q3 Auxiliary switching element

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-95765 (JP, A) JP-A-61-240771 (JP, A) JP-A-5-227746 (JP, A) 37592 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) H02M 3/28

Claims (3)

(57) [Claims] 1. A main switching element for turning on / off a DC current applied to a primary winding (n1) of a main transformer, and rectifying and smoothing an on / off signal induced in a secondary winding (n2) of the main transformer. A secondary-side rectifying / smoothing circuit, an error amplifier for generating an error voltage signal between a main output voltage output from the secondary-side rectifying / smoothing circuit and a reference voltage, and a direction for reducing the error voltage signal sent from the error amplifier A main converter section having a main converter control circuit for sending an on / off control signal to the main switching element; an auxiliary switching element for turning on / off a DC current applied to a primary winding (n3) of the auxiliary transformer; A secondary-side rectifying / smoothing circuit for rectifying and smoothing the on / off signal induced in the secondary winding (n4), and a bias winding (n5) induced in the auxiliary transformer. It has a primary side rectifying and smoothing circuit for rectifying and smoothing the on / off signal, and an auxiliary converter control circuit for sending an on / off control signal to an auxiliary switching element so as to stabilize a voltage detected by the primary side rectifying and smoothing circuit to a predetermined reference voltage. An auxiliary converter unit, comprising: a main converter control circuit; an auxiliary converter control circuit;
And an auxiliary switching element formed on one chip.
A switching power supply device comprising a C circuit. 2. The switching power supply device according to claim 1, wherein the IC circuit formed on the one chip uses a common switching frequency for the main converter control circuit and the auxiliary converter control circuit. 3. The switching device according to claim 1, wherein the current rating of the auxiliary switching element of the IC circuit formed on the one chip is a value satisfying the rating required for the auxiliary converter unit. Power supply.