Switching power supply device

Patent metadata

Field	Value
Publication number	US-2020280264-A1
Application number	US-202016794428-A
Country	US
Kind code	A1
Filing date	Feb 19, 2020
Priority date	Mar 1, 2019
Publication date	Sep 3, 2020
Grant date	—

Abstract

Disclosed is a switching power supply device including: a transformer for voltage conversion; a main switching element connected in series to a primary coil; a primary side control circuit that performs on/off control of the main switching element; a synchronous rectification MOS transistor connected in series to a secondary coil; and a secondary side control circuit that performs on/off control of the MOS transistor, wherein the secondary side control circuit includes: an off-timing detection circuit that compares a drain voltage of the MOS transistor with a predetermined threshold voltage, and detects a timing to turn off the MOS transistor; and a threshold voltage setting circuit that sets the threshold voltage, and the threshold voltage setting circuit sets the threshold voltage based on a conduction period of the secondary coil or a period obtained by adding the conduction period to a conduction period of the primary coil.

First claim

What is claimed is:

1 . A switching power supply device comprising:
a transformer for voltage conversion; a main switching element that is connected in series to a primary coil of the transformer; a primary side control circuit that performs on/off control of the main switching element; a synchronous rectification MOS transistor that is connected in series to a secondary coil of the transformer; and a secondary side control circuit that performs on/off control of the synchronous rectification MOS transistor, wherein the secondary side control circuit includes:
an off-timing detection circuit that compares a drain voltage of the synchronous rectification MOS transistor with a predetermined threshold voltage, and detects a timing to turn off the synchronous rectification MOS transistor; and
a threshold voltage setting circuit that sets the threshold voltage, and
the threshold voltage setting circuit sets the threshold voltage based on a conduction period of the secondary coil or a period obtained by adding the conduction period of the secondary coil to a conduction period of the primary coil.

2 . The switching power supply device according to claim 1 , wherein the threshold voltage setting circuit includes:
a judgement timing detection circuit that generates a predetermined judgement timing signal at a judgement timing which is set immediately before rise of the drain voltage; a timing judgement circuit that compares the judgement timing signal with an off-timing detection signal which is output from the off-timing detection circuit, and judges a signal at an earlier timing of the judgement timing signal and the off-timing detection signal; and a voltage adjustment circuit that adjusts the threshold voltage to be set according to a judgement result of the timing judgement circuit.

3 . The switching power supply device according to claim 2 , wherein the threshold voltage setting circuit adjusts the threshold voltage with the voltage adjustment circuit so that an off timing is advanced, in response to a judgement by the timing judgement circuit that the judgement timing signal is earlier than the off-timing detection signal.

4 . The switching power supply device according to claim 2 , wherein the threshold voltage setting circuit adjusts the threshold voltage with the voltage adjustment circuit so that an off timing is delayed, in response to a judgement by the timing judgement circuit that the judgement timing signal is later than the off-timing detection signal.

5 . The switching power supply device according to claim 2 , further comprising:
a first drain detection circuit that compares the drain voltage with a predetermined first voltage and detects a first timing when the drain voltage rises after the synchronous rectification MOS transistor is turned off; a second drain detection circuit that compares the drain voltage with a second voltage lower than the first voltage and detects a second timing when the drain voltage rises; and a mode judgement circuit which judges that an operation mode is a discontinuous current mode in response to exceeding over a predetermined value which is set in advance of a time difference between a detection signal of the first drain detection circuit and a detection signal of the second drain detection circuit, wherein the mode judgement circuit outputs a signal indicating that the operation mode is the discontinuous current mode to the voltage adjustment circuit.

6 . The switching power supply device according to claim 5 , wherein the signal indicating that the operation mode is the discontinuous current mode is not input to the voltage adjustment circuit, and the voltage adjustment circuit does not perform an adjustment of the threshold voltage, the adjustment delaying an off timing.

7 . The switching power supply device according to claim 2 , wherein the secondary side control circuit turns off the synchronous rectification MOS transistor at the judgement timing in response to a judgement that the judgement timing signal is earlier than the off-timing detection signal.

Assignees

• Kado Minoru
• Hyugaji Takumi
• Sato Takeshi
• Mitsumi Electric Co Ltd

Inventors

• Kado Minoru
• Hyugaji Takumi
• Sato Takeshi

Classifications

• Y02B70/10

  Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes · CPC title

• H02M3/33561 Primary

  having more than one ouput with independent control · CPC title

• H02H7/1213

  for DC-DC converters · CPC title

• H02M3/33592 Primary

  having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer · CPC title

• H02M3/33523

  with galvanic isolation between input and output of both the power stage and the feedback loop · CPC title