Switching power supply unit and voltage detection circuit

A voltage detection circuit detecting a DC voltage, comprising:

• a voltage detection section;
• a voltage detection transformer;
• one or more switching elements;
• and
• detection signal lines,
• wherein the voltage detection transformer includes
• a first transformer coil as a primary winding being intermittently applied with the DC voltage in response to on/off of the switching element, and
• a second transformer coil as a secondary winding being connected to the detection signal lines,
• wherein the voltage detection section has two switching elements each disposed in each of both ends of the first transformer coil and a regeneration circuit which regenerates energy stored in the voltage detection transformer for a first power supply, and
• the first transformer coil and the two switching elements are connected in series with each other between a couple of output terminals of the first power supply.

A switching power supply unit, comprising:

• a power supply main section switching a DC input voltage inputted from a first power supply to convert the DC input voltage into an AC voltage, and outputting a DC output voltage into a second power supply, the DC output voltage being obtained by transforming and rectifying the AC voltage;
• a voltage detection section having a voltage detection transformer, a switching element, and detection signal lines;
• wherein the voltage detection transformer includes
• a first transformer coil as a primary winding being connected to the first power supply,
• a second transformer coil as a secondary winding being connected to the detection signal lines, and
• a third transformer coil magnetically coupled with the first transformer coil as a primary winding and intermittently applied with a DC voltage in response to on/off of the switching element, and
• wherein the first transformer coil, second transformer coil, and third transformer coil are magnetically coupled with one another such that polarity of the first and second transformer coils is opposite to polarity of the third transformer coil, and
• the voltage detection section has
• a first rectifier element disposed to allow current to flow through the first transformer coil only when the switching element is off, and
• a second rectifier element disposed to allow current to flow through the second transformer coil only when the switching element is off.

A voltage detection circuit detecting a DC voltage, comprising:

• a voltage detection section;
• a voltage detection transformer;
• a switching element;
• and
• detection signal lines,
• wherein the voltage detection transformer includes
• a first transformer coil as a primary winding being connected to a supply side of the DC voltage,
• a second transformer coil as a secondary winding being connected to the detection signal lines, and
• a third transformer coil magnetically coupled with the first transformer coil as a primary winding, and intermittently applied with a DC voltage in response to on/off of the switching element, and
• wherein the first transformer coil, second transformer coil, and third transformer coil are magnetically coupled with one another such that polarity of the first and second transformer coils is opposite to polarity of the third transformer coil, and
• the voltage detection section has
• a first rectifier element disposed to allow current to flow through the first transformer coil only when the switching element is off, and
• a second rectifier element disposed to allow current to flow through the second transformer coil only when the switching element is off.