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Modeling Inductor Voltage-Controlled Switching Regulators

IP.com Disclosure Number: IPCOM000100011D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 4 page(s) / 128K

Publishing Venue

IBM

Related People

Kelkar, S: AUTHOR

Abstract

Current-injected control is a popular technique used in switching converter power processors; inductor voltage control differs from current-injected control in that the inductor voltage is sensed instead of the transistor current (1). The design of inductor voltage controlled (also called SCM control) regulators is greatly facilitated by easy-to-use models; such models form the subject of this disclosure.

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This is the abbreviated version, containing approximately 52% of the total text.

Modeling Inductor Voltage-Controlled Switching Regulators

       Current-injected control is a popular technique used in
switching converter power processors; inductor voltage control
differs from current-injected control in that the inductor voltage is
sensed instead of the transistor current (1).  The design of inductor
voltage controlled (also called SCM control) regulators is greatly
facilitated by easy-to-use models; such models form the subject of
this disclosure.

      Fig. 1 shows a full-bridge topology power processor with
SCM-Type control.  The inductor L voltage is sensed and used along
with the actual output voltage Vo to modulate the on-time Ton of the
four transistor switches in the power stage.  The key difference
between the current-injected form of control and the SCM type is that
in the former the power stage transistor current is sensed and used
in place of the inductor voltage.  Fig. 2 shows the key-operating
waveforms of the circuit.  The control voltage V1 ramps down during
the on-time Ton, and when it equals a set reference Vt, the power
switches are turned off.  The slope of the ramp during Ton is set by
the voltage Vac at the inductor sense winding, as shown in Fig. 2.

      The output of the control loop is thus a digital signal with a
variable width and constant frequency, while the inputs are analog
signals.  Simulating such a circuit, is hampered by the mixed analog
and digital nature of the circuit and a technique that removes these
problems was disclosed earlier [2].  By replacing the digital
portions of the circuit with equivalent analog models, a very
efficient simulation technique is possible.  Disclosed are analog
models for the SCM type of control; these models can be used along
with earlier disclosed power stage models to design and analyze
SCM-controlled switching converters. The key equation is one relating
the voltage V1 to the two analog input voltages

                            (Image Omitted)

 where Ve is the error
voltage produced at the output of the error processor by comparing Vo
to the reference voltage Vr. Thus, V1 equals Ve if Vo were the only
input to the error processor circuit.  The inductor voltage is sensed
with a winding of n turns and Vl' = (Vl x N), with N being
the power transformer turns ratio.  The on-time Ton can then be
derived as The reference voltage Vt is set during the control loop
design to produce a usable range for the duty cycle.

      Equation 2 describes the action of the digital signal processor
(DSP) and can be used to model...