Inductive Loads - Stanford Research Systems SIM954 Operation And Service Manual

300 mhz dual inverting driver amplifier

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3.3 Inductive Loads

SIM954 300 MHz Dual Inverting Driver Ampliﬁer

Similar to the case of capacitive loads, inductive loads and the am-

pliﬁer's ﬁnite output impedance form series RL circuits. Such a

circuit behaves like a high pass ﬁlter with a 3 dB corner frequency of

R 2 L.

A 1 H inductor will form a 525 kHz highpass ﬁlter with the 3.3

output resistor. Often, the ampliﬁer will be used to drive inductors

above this corner frequenciy, but this is not always the case.

In Figure 3.4 the ampliﬁer was driving a 1 H inductor with a 1 MHz

square wave with 750 mA

easily seen. While the voltage on the inductor goes to almost 0 V, the

ampliﬁer is still driving the full current. The highest output voltage

in this case was chosen such that the ampliﬁer does not reach its 1 A

current limit, and stays in its linear regime. Had a larger driving

voltage been applied, the nonlinearity due to the saturation of the

output current would have been visible.

Most importantly, since in this case the internal power dissipation

is proportional to the output current times the ampliﬁer's power

supply voltage, even a 500 mA average current will lead to no less

than 7.5 W of additional power dissipation. If such RL highpass

ﬁlter behavior is observed at high signal levels, a signiﬁcant amount

of heat will be generated in the ampliﬁer. Users need to carefully

evaluate the thermal load and the resulting heating of the SIM954 and

mainframe when driving inductive loads below their RL-highpass

corner frequency.

TDS 3034 24 Jul 2008 16:31:16

Figure 3.4: The SIM954 driving a 1 MHz square wave with 750 mA

peak current into a 1 H inductor

. The clean RL-highpass response can be

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