Patent ID: 8331111
Filing Date: 2012-12-11
Classification: H02M

Abstract:
1. A switching power supply device which is disposed in an electronic equipment and supplies a direct current voltage based on a first direct current voltage having a previously set first voltage value to a device that is disposed in the electronic equipment, the switching power supply device is characterized by comprising: a direct current voltage generating portion which has a switching element and a transformer and generates a direct current voltage having at least one voltage value from power that is supplied from a power source through the switching element and the transformer; a control voltage detecting portion which detects a control voltage which is proportional to voltage of a secondary side of the transformer; a constant voltage output portion which receives the first direct current voltage and outputs a second direct current voltage having a second voltage value different from the first voltage value; a feedback current detecting portion which detects a feedback current which is approximately proportional to the first voltage value of the first direct current voltage; a feedback current decreasing portion which, when the second voltage value is equal to or less than a previously set first voltage threshold value, outputs part of a current output from the direct current voltage generating portion to the constant voltage output portion to the output side of the constant voltage output portion and thereby makes an electric current value of the feedback current less than an electric current value approximately proportional to the first voltage value of the first direct current voltage; a control portion which controls the direct current voltage which is generated by the direct current voltage generating portion based on the voltage value of the control voltage and the electric current value of the feedback current input from the feedback current detecting portion; an over current generating portion which, when the first voltage value is equal to or more than a previously set second voltage threshold value, makes an over current having an electric current value equal to or more than a previously set current threshold value flow through the secondary side of the transformer; and an over current protection circuit which, when the over current flows through the secondary side of the transformer, makes the direct current voltage generating portion stop generating the direct current voltage.