Piezo Elements; Electric Motors - Stanford Research Systems SIM954 Operation And Service Manual

3.10 Miscellaneous Loads

3.10.4 Piezo Elements

3.10.5 Electric Motors

SIM954 300 MHz Dual Inverting Driver Amplifier
will form a resonant LC-circuit with the MOSFET's input capaci-
tance. It might be necessary to dampen these resonances with added
series resistors and or RLC snubbers.
For example, a foot (30 cm) of RG-58 will resonante with a 100 pF gate
capacitance at around 50 MHz and would require a 20
resistor, while three feet of RG-58 with a 1000 pF gate capacitance part
will resonate at around 9 MHz and behave reasonably with 5–10
of additional damping.
The user who wishes to drive power MOSFETs is advised to ex-
periment with di erent driver configurations to find the optimum
combination of cable, damping and device.
The SIM954 output voltage limit of 10 V is too low to drive high
voltage DC piezo elements. However, the module can drive piezo
resonators very well. Because it has a limited output voltage, the
piezo element has to be driven either by a series LC circuit, a trans-
former, or a combination of both. The unlimited stability will ease
the impedance matching of the device to the amplifier considerably
in comparison to RF amplifiers without isolation.
The SIM954 can be used to drive small electric motors. Stepper
motors and low voltage asynchronous or synchronous AC motors
usually present well behaved loads and can be driven by a SIM954
as long as the average and peak current do not exceed the amplifier's
specifications. Because of the fast amplifier risetimes, it is important
to filter the SIM954 output with beads and small ceramic capacitors
before connecting it to unshielded wires. These filters have to act on
the common mode as well as the di erential mode to make sure that
possible high frequency components generated by the SIM954 are
properly attenuated. Limiting the rise time of the driving voltages
will greatly reduce possible EMI problems.
Unlike their uncommutated counterparts, DC motors which have
mechanical or electronic commutators can produce voltage spikes
and sudden surge currents which can degarade or damage the am-
plifier. They should not be connected to a SIM954 without a detailed
investigation into the nature of their electric behavior and proper
filtering overvoltage protection.
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damping