Wayne Kerr AP10030, Руководство пользователя и обслуживания

Страница: 34 / 70

34 Wayne Kerr AP 1kW Power Supplies • Issue 2
pin 2 of IC15 goes more positive than pin 3, the output of IC15 goes negative and takes
command of the voltage controlling the ramp comparator. This results from the action of
the OR gate formed by D30 and D31 which selects the lower of the output voltages from
the voltage and the current comparators. The system is then controlled by the current into
the load. IC14 and associated components provide an overriding upper current limiting
circuit. This operates if the normal current limit is programmed above a safe value when
in external operation.
Low Mains
IC17 (control board diagram) operates if the main voltage drops below the level required
to maintain correct operation of the auxiliary supplies. IC2-B (control board diagram)
operates if the mains ‘drops out’ for a small number of cycles. Under these conditions the
circuits switch off the drive to the switching FETs.
Indicators
Mode state indication is controlled by IC1 (control board diagram). In the constant
voltage mode, the current control amplifier, IC15 pin 6 is high and IC1-A output is low.
TR4 will be off. The opposite is true of IC1-B, controlled by the voltage amplifier.
Therefore TR5 will be on and constant voltage indicated. In the unregulated mode, both
voltage and current amplifier outputs will be high and the anodes of D5, D6 and D7 will
be low. The output of IC1-D will go high and switch on transistor TR2 which controls
the unregulated indicator. If a trip, overvoltage, overtemperature, etc. is initiated, TR15 is
turned on which turns off TR3 and TR1. TR1 turns off the power to the CV, CI and
unregulated indicators. The overtemperature legend is driven by TR19 and the
overvoltage limit legend by TR29.
Trip Circuits
Two over voltage trips are provided. The first, IC22 (control board diagram), is variable
and is only controlled from the front panel. It can be inhibited by TR25 when the units
are controlled by the IEEE488 bus. The second, IC27, is an absolute overvoltage trip and
will operate whenever the output voltage exceeds approximately full scale by 10%. IC27
protects the power supply if the sense leads are disconnected or if on external operation
excessive voltage is demanded. The temperature trips also operate the trip latching
system, IC28 and IC29, directly by controlling pin 12 of IC29-D.