Relay Circuit - FSP Technology EP450 series Specifications

9 Relay Circuit

Figure S-7 is the relay circuit.
The RY01 (main relay) is used to switch between line and battery modes. When the UPS is
changing from battery to line mode, CPU pin6 is set to HI to turn on Q1AP (2SC1815) and
activates RY01. Alternatively, if the UPS is changing from line mode to battery mode, CPU pin6
is set to LOW and turn off Q03. This causes RY01 to be OFF and return to its normal state.
R3AP, D1AP, C1AP and Q2AP are used to speed up the relay transfer action, so the power
failure time can be shorten to minimum. When UPS transfers to battery mode, C1AP is charged
by the + 12 Volts. After the main relay makes contact, C1AP provides instantaneous power to
the relay coils. This will increase the magnetic force and shorten the transfer time from battery
mode to line mode by switching the relay. See Figure W-6 for voltage changes on C1AP, during
transfer time from line to battery mode.
CPU pin29 is used to the drive signal for RY02 (boost relay). When the mains input voltage is
low as within boost activated point, pin29 sends a high signal to turn on Q05 (2SC1815). This
will activate the RY02, and UPS will transfer to the Boost mode. When the mains input voltage
increases back to reach inactivated boost point, the UPS will return to normal mode by sending
a LOW signal from pin29. This forces RY02 to switch to its normal position (OFF). At battery
mode, pin29 is always set to LOW and RY02 is disabled.
Buck situation is the similar process. CPU pin28 is used to drive signal for RY03 (buck
relay). When the mains input voltage rises beyond buck activated point, CPU pin28 sends
a high signal to turn on RY03. When the mains input voltage decreases below the inactivated
buck point, the UPS returns back to normal mode by sending a LOW signal from pin28.
Figure S-7 Relay Circuit
Page 18 of 26 Rev. A