ITT - Index of

APPLICATION NOTES
FOUR-LAYER DIODE
A
Figure 21
REGULAR
POWER
SUPPLY
EMERGENCY
POWER
SUPPLY
Figure 19
Emergency Power Transfer
In the normal state, the 4-loyer diode in
Figure 19 is OFF and the regular power supply
is the source of power for the load RL. If the
supply voltage should fall off for any reason,
the voltage at point A will drop. If this change
in voltage is sufficient to cause the potential
from 8 to A to exceed the diad .. V" it will turn
ON and the emergency power supply will
provide power to the load until the condition
is corrected.
In Figure 21, succeeding half cycles can
have different firing angles since there are two
control diodes, One for each leg of the rectifier
circuit.
A.C.
C'
Figure 20
1J
Rectifier Control Circuits
Figure 20 illustrates a method for controlling
the power output of a rectifier by varying the
point at which a 4-layer diode is triggered.
Pulses may be applied at any phase angle
from the start of the input waveform (100%
power! to 180° (zero power!.
AC Control Circuits
The circuit in Figure 22 is useful for the control
of AC power in such applications as light
dimmers and motor controls. The trigger portion
is composed of two back-to-back relaxation
oscillators with an adjustable resistor COntrolling
the time at which they fore the control
diodes and thus the amount of current through
the load.
The load resistor of the oscillator and C set
up the time constant to fore the trigger diodes
at approximately 90° in each half cycle. When
a positive input cycle occurs the diode A will
break down at approximately 90°. The charged
capacitor C will discharg e through diad e A
with the result that a negative pulse will appear
at point CI.
This pulse will turn ON control diad e AI which
will allow current to flow until the half cycle is
completed. 80th diodes will then turn OFF
since the current through them will drop below
their holding current. This cycle is repeated
during the negative portion of the input waveform.
15-12