Multi-output switching power source circuit

A multi-output switching power supply circuit, comprising:

• a dc power source for generating a dc input voltage;
• a detecting circuit for detecting a voltage value of a second ac voltage generated by a first subordinate winding, the first subordinate winding constituting a voltage transformer including a primary side, a primary winding, a core, a secondary side, and a secondary winding;
• a switching circuit for turning on or off the dc input voltage according to a control signal generated by detecting variation in the voltage value of the second ac voltage and thereby producing a first ac voltage having a predetermined frequency and a pulse width corresponding to the second ac voltage;
• a control circuit for generating the control signal according to variation in the voltage value of the second ac voltage detected by said detecting circuit and a level of a detection signal detected by a voltage variation detecting circuit;
• an active clamp circuit for passing an exciting current through the primary winding of said voltage transformer during an off period of said switching circuit and for thereby resetting the core of said voltage transformer,
• said dc power source, said detecting circuit, said switching circuit, said control circuit, and said active clamp circuit being arranged on the primary side of said voltage transformer;
• a main output section disposed on the secondary side of said voltage transformer, comprising:
• a first rectifying circuit for rectifying a seventh ac voltage generated on a first secondary winding through voltage conversion of the first ac voltage by said voltage transformer and for thereby generating a first pulsating voltage;
• a first smoothing circuit for smoothing the first pulsating voltage into a first dc output voltage and for applying the first dc output voltage to a load;
• and
• the voltage variation detecting circuit for detecting variation in the first dc output voltage into a detection signal and for supplying the detection signal to said control circuit;
• and
• a plurality of output sections disposed on the secondary side of said voltage transformer, each of said output sections comprising:
• a magnetic amplifier for controlling, according to a reset current, on or off of an eighth ac voltage generated on the secondary winding through voltage conversion of the first ac voltage by said voltage transformer and for thereby generating a ninth ac voltage having a pulse width corresponding to the reset current;
• a second rectifying circuit for rectifying the ninth ac voltage into a second pulsating voltage;
• a second smoothing circuit for smoothing the second pulsating voltage into a second dc output voltage and for applying the second dc output voltage to a load;
• and
• a voltage control circuit for detecting variation in the second dc output voltage and for generating the reset current to conduct negative feedback control for the ninth ac voltage, wherein:
• said first rectifying circuit comprises a first NMOS transistor which turns the seventh ac voltage on or off at timing synchronized with switching timing of said switching circuit and which thereby generates the first pulsating voltage;
• said smoothing circuit comprises:
• a first smoothing capacitor for smoothing the first pulsating voltage into the first dc output voltage and for applying the first dc output voltage to a load;
• a first choke coil for accumulating electromagnetic energy associated with the first pulsating voltage;
• and
• a second NMOS transistor which turns on when said first NMOS transistor is off, and which thereby supplies the electro-magnetic energy from the choke coil to the smoothing capacitor;
• said second rectifying circuit comprises a third NMOS transistor which is turned on or off according to a voltage value of a tenth ac voltage generated on the second subordinate winding disposed on the secondary side of said voltage transformer;
• said second smoothing circuit comprises:
• a second smoothing capacitor for smoothing the second pulsating voltage into the second dc output voltage and for applying the second dc output voltage to a load;
• a second choke coil for accumulating electro-magnetic energy associated with the second pulsating voltage;
• and
• a fourth NMOS transistor which turns on, when said third NMOS transistor is off, according to a voltage value of an 11th ac voltage generated on a third subordinate winding disposed on the secondary side of said voltage transformer and which thereby supplies the electromagnetic energy from the second choke coil to the second smoothing capacitor;
• and
• said magnetic amplifier is arranged between the secondary winding and said third NMOS transistor.

A multi-output switching power supply circuit, comprising:

• a dc power source for generating a dc input voltage;
• a detecting circuit for detecting a voltage value of a second ac voltage generated by a first subordinate winding, the first subordinate winding constituting a voltage transformer including a primary side, a primary winding, a core, a secondary side, and a secondary winding;
• a switching circuit for turning on or off the dc input voltage according to a control signal generated by detecting variation in the voltage value of the second ac voltage and thereby producing a first ac voltage having a predetermined frequency and a pulse width corresponding to the second ac voltage;
• a control circuit for generating the control signal according to variation in the voltage value of the second ac voltage detected by said detecting circuit and a level of a detection signal detected by a voltage variation detecting circuit;
• an active clamp circuit for passing an exciting current through the primary winding of said voltage transformer during an off period of said switching circuit and for thereby resetting the core of said voltage transformer,
• said dc power source, said detecting circuit, said switching circuit, said control circuit, and said active clamp circuit being arranged on the primary side of said voltage transformer;
• and
• an output section disposed on the secondary side of said voltage transformer, comprising:
• a magnetic amplifier for controlling, according to a reset current, on or off of a third ac voltage generated on the secondary winding through voltage conversion of the first ac voltage by said voltage transformer and for thereby generating a fourth ac voltage having a pulse width corresponding to the reset current;
• a rectifying circuit for rectifying the fourth ac voltage into a pulsating voltage;
• a smoothing circuit for smoothing the pulsating voltage into a dc output voltage and for applying the dc output voltage to a load;
• and
• a voltage control circuit for detecting variation in the dc output voltage and for generating the reset current to conduct negative feedback control for the fourth ac voltage, wherein:
• said rectifying circuit comprises a first NMOS transistor which turns the third ac voltage on or off at timing synchronized with switching timing of said switching circuit and which thereby generates the pulsating voltage;
• said smoothing circuit comprises:
• a smoothing capacitor for smoothing the pulsating voltage into the dc output voltage and for applying the dc output voltage to a load;
• a choke coil for accumulating electromagnetic energy associated with the pulsating voltage;
• and
• a second NMOS transistor which turns on when said first NMOS transistor is off, and which thereby supplies the electro-magnetic energy from the choke coil to the smoothing capacitor;
• said first NMOS transistor includes a gate electrode, a source electrode, and a drain electrode, said gate electrode being connected to a winding end side of the secondary winding, said source electrode being linked with a ground side, said drain electrode being coupled with a winding start side of the secondary winding;
• said second NMOS transistor includes a gate electrode, a source electrode, and a drain electrode, said gate electrode being connected to the winding start side of the secondary winding, said source electrode being linked with a ground side, said drain electrode being coupled with an output port of said magnetic amplifier;
• said magnetic amplifier is arranged between the gate electrode of said first NMOS transistor and the drain electrode of said second NMOS transistor;
• and
• the reset current is supplied to a winding start side of said reset winding and is outputted to the ground side.