JPH05137336A - Switching power source - Google Patents

Abstract

PURPOSE:To omit a drive transformer, and dissolve the delay of a drive signal so as to output a large current from a slave output circuit by providing a winding on the iron core of the choke coil of a slave output circuit, and converting the induced voltage into DC voltage so as to drive a FET directly. CONSTITUTION:In a slave output circuit 10, winding W6 is wound on a choke coil L1. A wave generating circuit 11 introduces the induced voyage VB of this winding W6, and outputs synchronous waves Vs. An error amplifier 14 outputs the comparison signal Vk between the slave output voltage V2 and the set voltage Vs. An sub power source 12 rectifies the induced voltage Vo of the winding W2 of an output transformer T via a diode D5 and a resistor R2, and further introduces the induced voltage VB of the winding W6, too, and when the slave output voltage V2 rises, it outputs DC voltage Vcc 2 being made by changing it over to the power from the winding W6. A PWM circuit 13, introduces synchronous waves Vc and comparison signals Vk, with the DC voltage Vcc as a power source, and drives a FET Q2 by the PWM signal Ve.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention In a multi-output switching power supply having a main output circuit and a slave output circuit, the present invention mainly relates to a structure of a slave output circuit section. More specifically, the secondary output circuit is of a system that obtains a DC output voltage of a desired value by appropriately cutting out the pulse width of the pulsed voltage applied to the circuit.

[0002]

2. Description of the Related Art FIG. 5 is a diagram showing a conventional multi-output switching power supply having a main output circuit and a slave output circuit, and FIG.
[Fig. 6] is a diagram showing waveforms of respective parts of Fig. 5. The main output circuit is a signal that controls the main switch Q1 on the primary side of the transformer T.
The output circuit that provides the voltage V1 that is the basis of S1.
Here, the control circuit 3 outputs the pulse width signal S1 such that the output voltage V1 of the main output circuit 1 matches the set voltage (not shown), and controls the duty of the switch Q1. As a result, the duty of the voltage V0 induced in the secondary winding W3 changes, which is rectified and smoothed, and the main output voltage V1 of the circuit becomes the set voltage. The main output circuit 1 is a secondary winding W3, a diode D1 that rectifies this induced voltage, a smoothing circuit composed of a choke coil L1 and a capacitor C1, and a choke coil.
It is composed of a diode D2 that releases the energy stored in L1. The output voltage V1 of the main output circuit 1 is insulated by the photocoupler 2 and fed back to the primary side of the transformer T.

The secondary output circuit is a circuit which is connected to the secondary winding W2 wound separately from the winding W3 of the main output circuit and obtains a DC voltage from the induced voltage of the winding W2. Duty of the voltage V0 induced in winding W2 of the secondary output circuit, since the changes by the load current I _OUT of the input voltage V _in and the main output circuit, unless countermeasures are taken, the DC output voltage of the secondary output circuit 10 V2
Will fluctuate. Therefore, the sub output circuit 10 is generally provided with means for stabilizing the sub output voltage V2. In FIG. 5, a waveform generating circuit 6, a control circuit 5, and a drive circuit 4 which will be described later are means for stabilizing the secondary output voltage V2. In FIG. 5, the induced voltage V0 of the winding W2 (see FIG. 6 (1)) is rectified by the diode D3 and is the switching element FET Q2.
Added to. On / off of the FET Q2 is controlled by the drive circuit 4. The voltage that has passed through the switch element Q2 is smoothed by the choke coil L2 and the capacitor C2 and becomes the secondary output voltage V2 with small ripple. The diode D4 transfers the energy stored in the choke coil L2 to the switching element Q2.
Is emitted during the off period.

To stabilize the secondary output voltage V2, the pulse width Tp (see FIG. 6 (1)) of the induced voltage Vo of the winding W2 is set to the switching element Q2.
Is cut out appropriately and is added to the smoothing circuit (choke coil L2 and capacitor C2) in the next stage. The control operation of the switch element Q2 will be described with reference to FIG. This secondary output voltage V2 is obtained by introducing the voltage Vo of the winding W2 as shown in FIG.
Waveform generation circuit 6 that outputs a synchronous waveform as shown in (3)
Then, the sub output voltage V2 and the output Vc of the waveform generating circuit 6 are introduced to stabilize the drive circuit 4 by the control circuit 5 for controlling the drive circuit 4 as shown in FIG. 6 (2). The FET Q2 operates as a switch, and the transformer T2 is a drive transformer that level-converts the output of the control circuit 5.

The device shown in FIG. 5 operates as follows. The both ends of the capacitor C3, the DC voltage V _in is added. The switch element Q1 is turned on by the control circuit 3.
Controlled off. Therefore, since a voltage is intermittently applied to the primary winding W1, an induced voltage is generated in the secondary windings W2 and W3. Here, the main output voltage V1 obtained by the main output circuit 1
Is fed back to the primary side of the transformer T via the photocoupler 2. This main output voltage V1 is the set voltage (not shown)
The pulse width modulation signal S1 is generated by the control circuit 3 so as to satisfy the above condition, and the ON / OFF duty of the main switch element Q1 is controlled based on this.

Here, the voltage induced in the secondary winding W2
Duty of Vo varies due to the load current I _out of the input voltage V _in and the main output circuit side. The reason is as follows. When the input voltage V _in is lowered, the duty of the main switch Q1 to keep the primary output voltage V1 constant increases. When the load current I _out of the main output circuit increases, the main output voltage
To keep V1 constant, the duty of the main switch Q1 increases. Therefore, the winding W2 wound around the same core as the winding W3
The duty of the induced voltage Vo is also increased. Thus, even if the duty of the induced voltage Vo of the winding W2 fluctuates, the device of FIG. 5 performs control operation so that the secondary output voltage V2 becomes constant.

The control operation will be described. As described above, the input voltage Vo applied to the slave output circuit has a waveform as shown in FIG. 6 (1). The waveform generation circuit 6 introduces this input voltage Vo, and a synchronous waveform that increases in a ramp wave shape (sawtooth wave shape) only during the period Tp when the input voltage Vo is HIGH (see FIG. 6) (see FIG. 6 (3)).
Is output. This synchronization waveform is a signal synchronized with the switching waveform on the primary side of the transformer T, and the waveform generation circuit 6
Detects the on-side (HIGH) of the induced voltage Vo of the secondary winding W2 and creates this synchronization waveform. The control circuit 5
The comparison voltage VK is created by introducing the 6 (3) synchronization waveform Vc and the secondary output voltage V2.

This comparison voltage VK generated by the control circuit 5 (see FIG.
(Refer to (3)) is the sub output voltage V2 of the sub output circuit
If higher than (not shown), it will rise. The control circuit 5 compares the comparison voltage VK created by itself with the synchronization waveform Vc of FIG. 6, and the switch element Q2 is turned on during the period of the comparison voltage VK <synchronization waveform value (see FIG. 6 (2)). Apply signal to drive circuit 4. Specifically, when the secondary output voltage V2 is higher than the set voltage, the comparison voltage VK in FIG. 6 (3) rises. Therefore, the period in which the comparison voltage VK <the synchronous waveform value, that is, the period in which the switch element Q2 is turned on is reduced. As a result, the amount of electricity supplied to the smoothing circuit composed of the choke coil L2 and the capacitor C2 decreases, so that the value of the secondary output voltage V2 decreases and approaches the set voltage. On the contrary, when the secondary output voltage V2 is lower than the set voltage, the comparison voltage VK decreases, which is the reverse of the above operation. That is, the period during which the switch element Q2 is turned on is extended and the amount of electricity supplied to the choke coil L2 and the capacitor C2 is increased, so that the secondary output voltage V2 is increased. That is, the secondary output voltage V2 is
Approach the set voltage.

[0009]

[Problems to be Solved by the Invention] Here, the switching element Q2
In general, a MOS-FET is used, but the MOS-FET cannot be turned on unless the gate voltage is higher than the source voltage by at least 4 v (note that a general junction type FE
Even at T, the gate potential must be higher than the source potential). That is, it is necessary to apply a voltage signal higher than the point A in FIG. However, the point A is the positive side potential point of the slave output circuit 10, and an insulating means is required to obtain a higher potential. Therefore, in the conventional device, the drive transformer T2 is provided, and the output Va of the control circuit 5 is added to this to generate a voltage higher than the point A by 4 V or more and add it to the gate of the FET Q2.

If a drive transformer T2 is provided between the control circuit 5 and the drive circuit 4, the pulse width signal Va is delayed when passing through the drive transformer T2. When this delay time is Td, Td = 200 ns or so in general. Therefore, even if the comparison voltage VK becomes smaller than the synchronous waveform value at a certain time TA, it takes time Td until the control circuit 5 detects this and actually turns on the switch element Q2 (see FIG. 6).
(See (2)). Therefore, with respect to the input pulse width Tp (which is also the output pulse width of the transformer T) applied to the sub output circuit 10, only the maximum (Tp-Td) pulse width is applied to the smoothing circuit (L2 and C2 via the switch element Q2. Cannot be supplied to the configured circuit). Here, if the switching frequency of the power supply of FIG. 5 is a low frequency of about 100 KHz (the input pulse width Tp is about 3 μs), Td = 200 ns << Tp = 3 μs, so that FIG. 6 (3) The delay time Td shown in is negligible. However, since a low-frequency switching power supply has a large transformer shape and a large circuit element, a switching frequency has been designed to be a high frequency for downsizing.

However, in a high-frequency switching power supply, the input pulse width Tp is small, so that the proportion of the delay time Td is large and the delay time Td cannot be ignored. More specifically, when the input pulse width Tp is relatively larger than the delay time Tp and the switching frequency is 300 KHz or higher (Tp <1 μs), the delay time Td occupies a large proportion. Therefore, when a large current is to be output from the secondary output circuit, the amount of electricity supplied to the smoothing circuit is small, so that there is a problem in that the output cannot be secured.

Further, both the main output circuit and the slave output circuit appropriately control the pulse width of the quantity of electricity passing in a pulse form to control the obtained DC voltage values (V1, V2). Therefore, it is impossible to make the constituent circuits common. That is, the configuration of voltage stabilization control in the main output circuit is different from the configuration of voltage stabilization control in the slave output circuit. If it is possible to standardize the constituent circuits, it is possible to reduce the design man-hours of the switching power supply,
Also, since the variety of electronic parts can be reduced,
It is also effective in reducing costs.

An object of the present invention is to eliminate the delay of the drive signal Va due to the drive transformer T2 so that the output can be secured even at the time of outputting a large current, and at the same time, the stabilization control circuit of the main output circuit and that of the slave output circuit. It is to provide a switching power supply in which the number of types of constituent electronic components can be reduced by achieving commonality.

[0014]

The present invention is a transformer (T)
Switch the main switch (Q1) provided on the primary side of
Smooth the rectified waveform of the voltage induced in the first winding (W3) on the next side, and control the switching duty so that the obtained main output voltage (V1) becomes equal to the first set voltage (Vt). In the switching power supply, a second winding (W2) provided on the secondary side of the transformer, a smoothing circuit for smoothing a rectified waveform of a voltage induced in the second winding by using a choke coil (L2), and a second winding. And a smoothing circuit that controls the amount of electricity passing through by turning on and off.
2) and a third winding wire (W6) wound around the iron core of the choke coil (L2) and having one end connected to the source side of the FET,
By introducing the voltage (Vo) induced in the second winding (W2) and the voltage (VB) induced in the third winding, it has a function of producing a DC voltage from each of them, and is created from the voltage (Vo). When the DC voltage generated from the voltage (VB) becomes higher than the DC voltage, the auxiliary power supply that generates the DC voltage only from the voltage (VB) and the DC voltage obtained by this auxiliary power supply are used as the power supply,
A PWM circuit for applying a pulse signal (Ve) having a duty such that the second set voltage (Vs) and the slave output voltage (V2) of the smoothing circuit become equal to the FET to drive the FET on and off. It was done.

[0015]

In order to drive the FET, it is necessary to apply a signal having a potential higher than the source potential to the gate. The third winding wire of the present invention is wound around the iron core of the choke coil provided in the secondary output circuit, and one end thereof is connected to the source side of the FET. The auxiliary power supply obtains the DC voltage Vcc by regulating the induced voltage of this choke coil. Since the induced voltage of the third winding can be selected according to the number of turns,
The DC voltage Vcc can be set to a voltage sufficient to drive the FET by appropriately determining the number of turns of the third winding. Therefore, the PWM circuit can directly drive the FET with its output Ve, and is thus freed from the delay of the signal in the drive transformer T2 (which the conventional means has).

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing a configuration example of a switching power supply according to the present invention, FIG. 2 is a time chart explaining the overall operation of FIG. 1, and FIG. 3 is a time chart of signals of respective parts of FIG.
FIG. 4 is a diagram showing another configuration example of the slave output unit.

In FIG. 1, the main switch Q1 on the primary side of the transformer T is a pulse width signal S1 applied from the PWM circuit 23.
Is switched by. This switching frequency is determined by the oscillator circuit 21. The pulsed voltage induced in the winding W3 on the secondary side is the diode D1 of the main output circuit 1.
And the main output voltage V1 due to the action of choke coil L1 and capacitor C1. This voltage V1 is then applied to the error amplifier 24, where it is compared with the set voltage Vt. Error amplifier
24 returns the comparison signal Vk ′ to the PWM circuit 23. Comparison signal V
The value of k'increases if the set voltage Vt <main output voltage V1, and decreases if the set voltage Vt is opposite. Then, if Vt = V1, it becomes a certain voltage level.
Since the PWM circuit 23 controls the duty of the pulse signal S1 to be output based on the introduced comparison signal Vk ′, the main output voltage V1 has a value equal to the set voltage Vt. Auxiliary power supply
The reference numeral 22 produces a direct current voltage from the induced voltage of the winding W4 wound around the iron core of the transformer T and supplies the power supply voltage of the PWM circuit 23.

The secondary output circuit will be described below. In FIG. 1, diodes D3 and D4, FET Q2, choke coil L2,
The capacitor C2 has the same action and effect as those described with reference to FIG. That is, the diode D3 has a function of rectifying the voltage induced in the winding W2, and the choke coil L2
And the capacitor C2 form a smoothing circuit. Also, F
The ETQ2 is provided between the winding W2 and the smoothing circuit, and controls ON / OFF operation to control the amount of electricity passing therethrough.

The present invention is characterized by the configuration thereafter. The winding W6 is wound around the iron core of the choke coil L2 forming the secondary output circuit 10, and one end thereof is connected to the point A on the source side of the FET Q2. The waveform generation circuit 11 detects the induced voltage of the winding W6.
By introducing VB, a sawtooth synchronization waveform Vc that repeatedly changes with a constant slope is output from the time when the main switch Q1 is turned off to the time when it is turned off next time. The waveform generating circuit 11 of the present application is a winding wire in which a timing signal, which is a basis for generating the synchronization signal Vc, is wound around the choke coil L2 of the secondary output circuit 10.
It is created from the induced voltage VB of W6, and the shape of the synchronization signal Vc is a sawtooth shape that repeats a constant slope from the time when the main switch Q1 is turned off to the time when it is turned off next time. , Which is different from the conventional waveform generating circuit.

The error amplifier 14 is a smoothing circuit (slave output circuit 1
0) The secondary output voltage V2 and the set voltage Vs of
Is output. The error amplifier 14 operates in the same manner as the error amplifier 24 described above, and the same configuration can be used. That is, the secondary output voltage V2 is applied to the error amplifier 14, where the set voltage is
Compared to Vs. The error amplifier 14 then outputs the comparison signal Vk
Output to the PWM circuit 13. The value of the comparison signal Vk increases if the setting voltage Vs <the secondary output voltage V2, and decreases if the setting voltage Vs is opposite. Then, if Vs = V2, it becomes a certain voltage level.

The auxiliary power supply 12 rectifies and introduces the voltage Vo induced in the winding W2 of the main transformer T through the diode D5 and the resistor R2. Further, the voltage VB induced in the winding W6 provided to the choke coil L2 is also introduced. And introduced 2
It has the function of producing a DC voltage from each of the three voltages Vo and VB. This function can be realized with a common configuration.
When the DC voltage generated from the voltage VB of the choke coil L2 becomes higher than the DC voltage generated from the voltage Vo of the main transformer T, the DC voltage Vcc2 is generated only from the voltage VB of the choke coil L2.

Such an operation can be realized by ordinary means. For example, the cathodes of two diodes are connected to each other, the DC voltage generated from the voltage Vo of the main transformer T is applied to the anode of one diode, and the anode of the other diode is generated from the voltage VB of the choke coil L2. Apply DC voltage. In this way only the high voltage is extracted from the cathode of the diode. In addition,
The auxiliary power supply 12 incorporates a regulator having a known structure in order to stabilize the voltage introduced from the main transformer T and the choke coil L2. The DC voltage output from the auxiliary power supply 12 is Vc
c2. The induced voltage VB of the winding W6 of the choke coil L2 is
Since the DC voltage Vcc2 of the auxiliary power supply 12 can be selected according to the number of turns, the FE can be obtained by appropriately determining the number of turns of the winding W6.
It can be a sufficient voltage to drive TQ2. PWM
The circuit 13 uses the DC voltage Vcc2 obtained from the auxiliary power supply 12 as the power supply voltage, and outputs the synchronization waveform Vc from the waveform generation circuit 11 and the error amplifier.
A comparison signal Vk is introduced from 14, and a signal Ve obtained by comparing the magnitude of this signal is directly added to the gate of the FET Q2 to drive it on / off.

The operation of the apparatus of FIG. 1 configured as above will be described with reference to FIG. The first feature of the present invention is that a winding is newly added to the choke coil L2 of the secondary output circuit 10.
W6 is provided, and from this winding W6, DC voltage Vcc2 higher than point A
This is the point where The second characteristic is that the timing signal that is the basis for generating the synchronization signal Vc is the secondary output circuit 10
The point is that it is created from the induced voltage VB of the winding W6 wound around the choke coil L2. With this configuration,
Many effects can be obtained.

The winding W6 of the choke coil L2 is shown in FIG.
A waveform of voltage VB as shown in is induced. Where the time
From t1 to t2 and t3 to t4, the main switch Q1 is on, and at times t2 to t3, the main switch Q1 is off.
Since one end of the winding W6 is connected to the point A shown in FIG. 1, the auxiliary power supply 12 can supply the PWM circuit 13 with a voltage Vcc higher than the point A as Vcc. Therefore, the PWM circuit 13 outputs a voltage about Vcc2 higher than the point A to the FET Q2.
FET Q2 can be directly driven without using a driving transformer (see FIG. 5).

Next, the operations of the waveform generating circuit 11 and the PWM circuit 13 will be described. The pulse waveform VB shown in FIG. 3A is applied to the waveform generation circuit 11. This pulse waveform VB is the main switch Q1
Since the on / off of is expressed, the waveform generation circuit 11
By recognizing the falling edge of the waveform VB, the time from when the main switch Q1 is turned off to when the main switch Q1 is turned off next can be grasped. Then, as shown in FIG. 3 (2),
A sawtooth shape that repeatedly changes with a constant inclination is output during this period.

The PWM circuit 13 compares the comparison voltage Vk, which changes as described above, with the magnitude of the synchronization waveform Vc, and as a result, outputs the signal Ve whose pulse width is controlled as shown in FIG. 3C. FE
In addition to TQ2, it drives this on and off. As described above, according to the present invention, the original timing signal (a signal indicating ON / OFF of the main switch Q1) for producing the synchronization waveform Vc is not taken in from the transformer T but is introduced from the choke coil L2 of the slave output circuit 10. As a result, it is possible to obtain an effect that a high withstand voltage component is not required as an electronic component forming the waveform generating circuit 11.

Next, the overall operation of the apparatus shown in FIG. 1 will be described with reference to FIG. First, the control operation on the primary side will be described. When the DC voltage V _in rises as shown in FIG. 2 (1),
A DC voltage is supplied to the auxiliary power supply 22 through the resistor R1. The auxiliary power supply 22 has the same configuration and operation as the auxiliary power supply 12 described above, and is controlled by the voltage supplied via the resistor R1 as shown in FIG.
The output voltage Vcc1 is increased as in (2). Here, the correspondence relationship between the signals applied to the auxiliary power supply 12 and the auxiliary power supply 22 will be described. Voltage Vo from the main transformer T applied to the auxiliary power supply 12, the auxiliary power supply 22, which corresponds to a voltage V _in applied via the resistor R1. Further, the voltage VB of the winding W6 of the choke coil L2 applied to the auxiliary power supply 12 corresponds to the voltage from the winding W4 wound around the main transformer T in the auxiliary power supply 22.

The output voltage Vcc1 of the auxiliary power supply 22 is PWM
When the start voltage V _TH1 of the circuit 23 is exceeded, the oscillation circuit 21
Since the PWM circuit 23 operates, the main switch Q1 starts turning on and off. Therefore, since the main output circuit 1 starts to operate, the main output voltage V1 rises as shown in FIG. 2 (3). The error amplifier 24 introduces the main output voltage V1 and the set voltage Vt, and feeds back the above-mentioned comparison voltage Vk ′ to the PWM circuit 23. PWM
The circuit 23 performs the above-described operation and becomes stable when the main output voltage V1 becomes equal to the set voltage Vt. The main output voltage
When V1 rises, the auxiliary power supply 22 is supplied with electric power from the winding W4, and the auxiliary power supply 22 produces an output voltage Vcc1 by the electric power from the winding W4 instead of the DC voltage V _in (the auxiliary power is still supplied from the DC voltage V _in). The power flow to the power supply 22 is shut off).

When the main output circuit 1 rises, the induced voltage Vo of the secondary winding W2 of the main transformer T also rises as shown in FIG. 2 (4). The induced voltage Vo is supplied to the auxiliary power supply 12 of the slave output circuit 10 through the diode D5 and the resistor R2. Therefore,
The output voltage Vcc2 of the auxiliary power supply 12 increases as shown in FIG. Then, the value of the output voltage Vcc2 of the auxiliary power supply 12 is PW
When the start voltage V _TH2 of the M circuit 13 is exceeded, the PWM circuit 13
Starts to operate, and FETQ2 is switched. Therefore, the pulse power of the induced voltage Vo of the winding W2 is FE
It is supplied to the smoothing circuit via TQ2, and the secondary output circuit 10 starts up. That is, the secondary output voltage V2 increases as shown in FIG.

When the secondary output voltage V2 rises, the auxiliary power supply 12 is supplied with floating power from the winding W6 of the choke coil L2, and the auxiliary power supply 12 replaces the induced voltage Vo by the power from this winding W6. The output voltage Vcc2 is generated (the inflow of power from the induced voltage Vo to the auxiliary power supply 12 is cut off). For example, the auxiliary power supply 12 is the choke coil L2.
DC voltage Vcc2 is created by rectifying and smoothing the voltage VB from the forward direction. The secondary output voltage V2 is compared with the set voltage Vs by the error amplifier 14, and the comparison voltage Vk is PW.
The secondary output voltage V2 is stabilized by being fed back to the M circuit 13.

As described above, the auxiliary power supplies 12 and 22, which are the respective constituent circuits of the main output circuit 1 and the sub output circuit 10, and the PW.
The M circuits 13 and 23 and the error amplifiers 14 and 24 can use the same type of electronic components. Further, the output of the PWM circuit 13 can directly drive the FET Q2, and insulation is unnecessary.

FIG. 4 shows a choke coil L2, a capacitor C2 and a diode D3 in the slave output circuit 10 of the device of the present invention.
FIG. 11 is a diagram showing another configuration example of the FET Q2. In the present invention, since the drive circuit of the FET Q2 is configured to be floating, the choke coil L2, the capacitor C2, the diode D3, and the FET Q2 may be arranged at any positions. For example, a configuration as shown in FIG. Good. Also, in the above, PW
Although the M circuit 23 is arranged on the primary side of the transformer T, the so-called primary side control system has been described.
The present invention is also applicable to a so-called secondary side control system arranged on the secondary side. In this case, the output S1 of the PWM circuit 23 is isolated by, for example, a transformer and added to the main switch Q1.

[0033]

As described above, according to the present invention, the drive transformer T2 (see FIG. 5) is no longer necessary.
The delay of the signal Ve driving ETQ2 has been eliminated. Therefore, even if the switching power supply is composed of a high frequency circuit, a large current can be taken out from the secondary output circuit. Also drive
Since the transformer T2 is no longer required, high frequency noise does not flow out to the primary side of the transformer T. In addition, the signal that is the basis of the sync signal Vc is generated by the transformer T.
Since it is taken from circuits (choke coil L1) other than,
The waveform generating circuit 11 can be composed of low-voltage electronic components, and as a result, the switching power supply can be downsized. The same types of electronic components can be used for the auxiliary power supplies 12 and 22, the PWM circuits 13 and 23, and the error amplifiers 14 and 24, which are the constituent circuits of the main output circuit 1 and the slave output circuit 10, respectively. Therefore, the number of types of electronic components used is reduced, so that the cost can be gradually reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a switching power supply according to the present invention.

FIG. 2 is a time chart explaining the overall operation of FIG.

FIG. 3 is a time chart of signals at various parts in FIG.

FIG. 4 is a diagram showing another configuration example of a slave output unit.

FIG. 5 is a diagram showing a conventional example.

FIG. 6 is a time chart showing the operation of FIG.

[Explanation of symbols]

 11 Waveform generation circuit 12, 22 Auxiliary power supply 13, 23 PWM circuit 14, 24 Error amplifier L1, L2 Choke coil Q2 FET

Claims (2)

[Claims] 1. A main switch provided on the primary side of a transformer (T).
Main output voltage (V1) obtained by switching (Q1) and smoothing the rectified waveform of the voltage induced in the first winding (W3) on the secondary side.
In the switching power supply that controls the duty of the switching so that the voltage becomes equal to the first set voltage (Vt), the second winding (W2) provided on the secondary side of the transformer and the voltage induced in the second winding are A smoothing circuit that smoothes the rectified waveform using a choke coil (L2), and a FET (Q2) that is provided between the second winding and this smoothing circuit to control the amount of electricity that passes by turning it on and off.
A third winding (W6) wound around the iron core of the choke coil (L2) and having one end connected to the source side of the FET, and a voltage (Vo) induced in the second winding (W2) The voltage induced by three windings (VB) has the function of creating a DC voltage from each, and the DC voltage created from the voltage (VB) is better than the DC voltage created from the voltage (Vo). When it becomes higher, an auxiliary power supply that produces a DC voltage only from the voltage (VB) and the DC voltage obtained by this auxiliary power supply are used as the power supply, and the second set voltage (Vs) and the secondary output voltage (V2) of the smoothing circuit are equal. A switching power supply comprising: a PWM circuit that applies a pulse signal (Ve) with such a duty to an FET to drive it on / off. 2. A main switch provided on the primary side of the transformer (T).
Main output voltage (V1) obtained by switching (Q1) and smoothing the rectified waveform of the voltage induced in the first winding (W3) on the secondary side.
In the switching power supply that controls the switching duty so that the voltage becomes equal to the first set voltage (Vt), the second winding (W2) provided on the secondary side of the transformer and the rectification of the voltage induced in the second winding A smoothing circuit that smoothes the waveform using a choke coil (L2), and a FET (Q2) that is provided between the second winding and this smoothing circuit to control the amount of electricity that passes by turning on and off.
And a third winding (W6) wound around the iron core of the choke coil (L2) and having one end connected to the source side of the FET, and the induced voltage of the third winding is introduced to the main switch (Q1). )
A waveform generator that outputs a sawtooth synchronous waveform that repeatedly repeats with a constant slope from the time when is turned off to the time when the next is turned off; and a secondary output voltage (V2) output from the smoothing circuit and a second Set voltage
(Vs) is introduced and an error amplifier that outputs a comparison signal, a voltage (Vo) induced in the second winding (W2) and a voltage (VB) induced in the third winding are introduced, and DC is supplied from each of them. When the voltage generated from the voltage (VB) is higher than the DC voltage generated from the voltage (Vo) and has the function of generating voltage, an auxiliary power supply that generates DC voltage from only the voltage (VB), and this auxiliary A direct current voltage obtained by a power source is used as a power source, the synchronizing waveform and a comparison signal are introduced, and a signal (Ve) obtained by comparing the magnitude of this signal is added to the gate of the FET to drive it on / off. A switching power supply characterized by including a PWM circuit.