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Understanding the MS4/MS16 Stimulus Isolator Power Issues ...
The Stimulus Isolator is an integral part of TDT’s Multichannel MicroStimulator System. Designed to work with the RX7 Stimulator Base Station, it is capable of delivering a 100 μA current to up to 16 channels of high impedance electrodes (1 MΩ). The device acts as a constant current source (not a constant voltage source), therefore ensuring proper current under different impedance conditions. The stimulator uses built-in, rechargeable Lithium-ion batteries for general device operation (such as driving the D/A’s, powering the fiber optic interface, and controlling the digital I/O lines) and relies on an external battery pack for stimulation.
General Device Operation
The onboard Lithium-ion batteries charge in four hours. A 6-9 volt, 500 mA battery charger is included with the stimulator and can be connected via the Charger connector on the stimulator's back panel. The charger tip is center negative. If it is necessary to replace the charger, ensure that the replacement power supply has the correct polarity (or contact TDT for assistance).
High Voltage Input for Stimulation
TDT supplies the HV250 Battery Pack to power stimulation. The pack incorporates four Carbon Zinc batteries, each delivering 67 volts and a total of 140 milliamp hours (mAh) of power. The peak-to-peak voltage is 250 volts with a range of +/- 125 volts. In addition to supplying current for stimulation, the HV250 delivers current to enable the stimulation circuitry.
Within the MS4/16, stimulation channels are configured in banks of four channels. Each of the stimulator’s channels can be switched between three states: Open, Reference and Stimulate. Channels that are Open can be used for acquisition, channels set as Reference are used as the return path to a common ground and channels in Stimulate mode can be used to drive a stimulus current through an electrode. Channels in the Open or Reference state do not inherently draw any current from the external power supply. However, when a channel is switched to Stimulate, the bank that it is in will draw current to power the transistors used to drive the current through the electrodes. In Stimulate mode, each bank draws 1.5 mA before stimulation and will draw up to 1.9 mA in addition to current drawn for stimulation.
Because the HV250 Battery Back is a finite power source, it must be replaced periodically. To extend the life of the battery, we recommend limiting the duration of the enabled period i.e. switching between OPEN and STIMULATE—keeping it in Open mode only slightly longer than in Stimulate mode. Unfortunately, in many cases, this will not be possible or practical. We recommend keeping a spare HV250 on hand for these and similar situations. Replacement battery packs can be ordered through our sales department. Also, users can set up their own isolated power supplies (If you plan to use lower impedance electrodes (10-50 kΩ) a different power supply might be more suitable), but PLEASE CONTACT TDT for further information BEFORE attempting this.
CAUTION!: The HV250 is a high voltage power source, capable of delivering up to 250 Volts DC at high amperages. Shorting the device can cause damage to the device and injury to the user. Always use caution when handling or connecting the devices. The battery pack should be connected via the Battery connection on the back panel, as shown in the diagram below.
Copyright 2006 Tucker-Davis Technologies, Inc. All Rights Reserved.