Technical Information
62
Precision Induction Heating
MBRELL
®
-
-
5.1.1 Primary regulation techniques not used in EASYHEAT products:
Adjustable DC power supply feed into the RF power stage - This method requires two
power sections: one to adjust the DC level and the other to deliver RF. Examples of this
can be found in the older Ameritherm Nova Star line, and in some competitor units. The
method requires many additional components and whole circuit boards for this type of
regulation. It is the most costly to produce.
Frequency Offset - This approach is only appropriate in a series resonant power supply.
Power regulation is obtained by adjusting the RF frequency away from resonance which
reduces the output. This technique is limited with respect to wide band tuning and can be
problematic for those applications where controlled frequency is required. EASYHEAT
uses this as a secondary regulation technique, requiring only small frequency variations
when lower percentage outputs are called for.
Pulse Width Modulation - This technique is used on the EKOHEAT product line, and is
commonly used in the industry.
EASYHEAT products borrow from a technique used for precision audio equipment called
“Modified Delta Sigma Modulation” for most of its dynamic range. This technique switches
between “run” and “coast” modes at high speeds, measuring and regulating true RMS current.
The current waveform can be seen to “ring up” during run intervals, and “ring down” during
coast. The intervals of each adapt to variations in load (including Q), line and frequency and can
be as fast as a single RF cycle. The method results in accurate regulation while using fewer
components.
EASYHEATs behave in a way similar to a current source. That is, they maintain regulation of
their controlled parameter - RF current. An ideal current source would work with any load; from
short circuit to open circuit (an ideal current source would also arc across an open circuit to
maintain its current). Like any real current source, EASYHEAT has a finite compliance range. It
protects itself when working into a shorted coil by having a very short run interval.
To Next Page
Loading...
