Maryli
- 9th August 2018, 13:10
Good day,all
In a lot of power supplies the main transformer has several outputs, which are switched via a relay when the supply output exceeds a certain voltage.
Below is a Mastech HY1803 psu schematic - the SK1 relay switches the transformer outputs, while the schematic around the U2A opamp handles the switching after the output voltage exceeds 5V.
The question is - why is that switch needed? Am I understanding it right that it is just to lower the transformer output voltage when the voltage on the psu output is lower than 5V and lower the 2N3055 (https://wintronic.hqew.net/MOSFET/product-detail/21219) dropout voltage and, therefore, the power dissipation? Are there any other reasons to do that?
In a lot of power supplies the main transformer has several outputs, which are switched via a relay when the supply output exceeds a certain voltage.
Below is a Mastech HY1803 psu schematic - the SK1 relay switches the transformer outputs, while the schematic around the U2A opamp handles the switching after the output voltage exceeds 5V.
The question is - why is that switch needed? Am I understanding it right that it is just to lower the transformer output voltage when the voltage on the psu output is lower than 5V and lower the 2N3055 (https://wintronic.hqew.net/MOSFET/product-detail/21219) dropout voltage and, therefore, the power dissipation? Are there any other reasons to do that?