Murata Manufacturing Co., Ltd.

Eito Moromizato

Tadahiko Matsumoto

Jun Nagai

Takayoshi Nishiyama

Hitoshi Tsuji

Seiichi Takahashi

An isolated switching power supply device includes a main transformer having a primary coil on a primary circuit side and a secondary coil on a secondary circuit side. On the primary circuit side are disposed an input smoothing capacitor, a switching control circuit, a high-side driver, a low-side power switch, a high-side power switch, capacitors, and edge signal-generating circuits. A symmetrical control half bridge converter is thus provided. The secondary circuit side has a voltage clamping circuit including a clamp capacitor, a clamp switch and a diode.

Isolated switching power supply device

A rectification switch control switch element (Q) is provided between a gate and a source of a rectification switch element (Q). The rectification switch control switch element (Q) is turned ON in response to a signal on a secondary side of a pulse transformer (T) at a turn OFF timing of a main switch element (Q) to forcedly turn OFF the rectification switch element (Q). As a result, the rectification switch element (Q) can be turned OFF in synchronism with an OFF of the main switch element at a time of a backflow. With use of a free resonance between a capacitance between a gate and a source of the rectification switch element (Q) and a commutation switch element (Q) and a choke coil (L), an excitation state of the choke coil (L) can be reset. Then, it is possible to stabilize a detection voltage of a tertiary rectification smoothing circuit () which uses a tertiary winding (N) of a transformer (T), thus stabilizing control of the circuit functions.

Synchronous rectification forward converter

A first drive control signal regenerating circuit outputs an ON timing drive signal at turn-ON of a main switch element, and a second drive control signal regenerating circuit generates an OFF timing drive signal at turn-OFF of the main switch element. A rectifying switch controlling switch element connected between the gate and source of a rectifying switch element is driven by an output of the second drive control signal regenerating circuit. An output of the first drive control signal regenerating circuit connects to the gate of a commutating switch controlling switch element, which connects to one end of an auxiliary winding, the other end thereof being connected to the gate of a commutating switch element. Accordingly, the rectifying switch element is directly controlled from the primary side.

Synchronous rectifying forward converter

A commutation switch turning-on control switching element is controlled with a voltage generated at a fourth coil (auxiliary coil) of a main transformer and controls application of a control voltage to a control terminal of a commutation switching element. A commutation switch turning-off control switching element is provided which is connected to the control terminal of the commutation switching element and, when the commutation switch turning-off control switching element is turned on, controls a voltage at the control terminal of the commutation switching element to turn off the commutation switching element. A control switching element drive circuit turns on the commutation switch turning-off control switching element at a time when a primary switching element is turned on.

Forward converter with synchronous rectification

A switching power supply circuit reduces the time from start-up driving to normal operation while a soft-start is carried out with an output voltage Vout. A soft-start capacitor is charged during the start-up time. After a soft-start voltage Vz has reached a predetermined signal-output starting voltage Vlow, soft start of the output voltage Vout is carried out by controlling the operation based on the soft-start voltage Vz. A time constant for charging the soft-start capacitor is set as a time constant that causes the charge voltage of the soft-start capacitor to sharply increase at least until the soft-start voltage Vz reaches the signal-output starting voltage Vlow after the circuit has started driving, and is switched to a time constant that causes a rising trend of the charge voltage of the soft-start capacitor to become gentle with a predetermined time-constant switching timing. The start-up time is reduced by an amount equivalent to a reduction in the delay time from the start of driving to the start of voltage output.

Switching power supply circuit with a soft-start function

A switching power supply apparatus has a transformer having a primary winding, a secondary winding and a tertiary winding; a primary switching element connected to the primary winding of the transformer for providing the primary winding with an input voltage in accordance with an on-off operation of the main switching element; an output circuit connected to the secondary winding of the transformer for receiving a voltage based on the input voltage from the secondary winding, rectifying the voltage and outputting an output voltage; a detection circuit in which the output voltage output from the output circuit is indirectly detected using the tertiary winding, and the detected voltage is output; a compensating-voltage-superposition circuit which generates a compensating voltage, in accordance with the detection voltage, for compensating a deviation of the detection voltage of the detection circuit to the output voltage of the output circuit in accordance with a change of the input voltage and which superposes the compensating voltage on the detection voltage output from the detection circuit; and a control circuit which controls the on-off operation of the primary switching element so that the output voltage of the output circuit is stabilized based on the detection voltage having the compensating voltage superposed thereon.

Switching power supply apparatus and method

A DC-DC converter has improved electrical characteristics, including a voltage-reduction detection circuit and a zero-voltage switching control circuit. In the voltage-reduction detection circuit, in a period when a switching device is OFF, when a drain voltage of the switching device is reduced to an input voltage level, a voltage of a connection section of registers is allowed to reach a threshold voltage level to reverse a signal outputted from a NOR gate from a higher level to a lower level. In the zero-voltage switching control circuit, the signal reduced as above is received and a signal outputted from a NOR gate is reversed to a higher level, according to which a pulse-control signal outputted from a NOR gate to the switching device is reversed to a higher level to turn on the switching device. Since the output pulse-control signal from the NOR gate controls switching operations performed by the switching device, no switching loss occurs and zero-voltage switching can be performed; accordingly, short-circuit loss also does not occur.

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Nagaokakyo, Japan

Eito Moromizato