6Tutorial
180 E364xA User’s and Service Guide
Overview of the Power Supply Operation
The basic design technique, consists of placing a control element in series with
the rectifier and load device. Figure 6-1 shows a simplified schematic of a series
regulated supply with the phase-controlled pre-regulator described as a power
switch and the series element depicted as a variable resistor. The
phase-controlled pre-regulator minimizes the power dissipated at the series
element by maintaining the voltage drop across the series element at a low and
constant. Feedback control circuits continuously monitor the output and adjust
the series resistance to maintain a constant output voltage. Because the variable
resistance of Figure 6-1 is actually one or more power transistor operating in the
linear (class A) mode, supplies with this type of regulator are often called linear
power supplies. Linear power supplies have many advantages and usually provide
the simplest most effective means of satisfying high performance and low power
requirements.
Figure 6-1 Diagram of a simple series power supply
This power supply has two ranges, allowing more voltage at a lower current or
more current at a lower voltage. Single range supplies can only output maximum
power at full-scale voltages and full-scale current. This supply can provide output
power that is close to maximum at full-scale for both ranges. The pre-regulator in
this power supply uses solid state transformer tap switches on the secondary
winding of the power transformer. This technique is very effective in reducing the
power dissipated in the series element.
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