Figure 8-9. Basic Diode Circuits.
8-37. Diode Regulator. A diode regulator uses either
characteristic of a breakdown diode or the constant
forward-bias voltage drop characteristic of a silicon
diode. Power supply reference voltages are generally
prov ided by breakdown diodes which maintain a
constant voltage when supplied with a reverse-bias
voltage greater than their specified breakdown voltage.
Regulated voltages can also be prov ided by a forward-
biased silicon diode which maintains a constant 0.6 to
0.8 volt drop.
connections for both types of diodes.
8-38. SPECIAL TYPES OF SEMICONDUCTORS
8-34. STANDARD DIODE CIRCUITS
8-39. Silicon Controlled Rectifier . An SCR is the
semiconductor equivalent of a gas thyratron. A voltage
8-35. Diode Limiter or Clipper . The limiter or clipper
applied to a control element switches the controlled
is a circuit which removes positive or negative peaks
rectifier to a conducting state when a positive voltage is
from a waveform. It can be used either as a waveform
simultaneously applied to the anode. The controlled
shaping circuit or as a protective device to prevent
rectifier continues conducting until the anode voltage is
reduced to zero. Once triggered, the control element
Schematic A, shows a limiter which prevents the
has no control of the rectifier until it is turned off by
negative peak of the pulse from exceeding about X.6
volt. Note that for a conducting silicon diode the
illustrates the function of an SCR when used as a
cathode voltage is about 0.6 to 0.8 volt more negative
"crowbar" in a voltage regulation circuit.
than the anode.
8-40. If, when
a series regulator transistor fails,
8-36. Diode Clamp. The clamper is a circuit which
becomes a short circuit, rather than an open circuit, the
establishes either the positive or negative peak of a
waveform at a particular dc reference voltage; in other
output. Under these conditions the regulator circuits are
words, it prov ides a definite baseline voltage for the
no longer operative, and the load current is limited
mainly by the load resistance. In Figure 8-10 the circuit
which prov ides a baseline of about +20 volts for a