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Using this AC pulsating power technique, the output signals are tightly coupled to the reference input, and the only power dissipated is the current times the small voltage difference between the pulsating power stage and the synchro signal outputs.
Because both the power stage and the signal outputs are sinusoidal, and the power stages headroom is very small, the power required to drive the load is minimal. Thus, the Reference Powered Synchro Amplifiers provide the highest efficiency attainable, low loss, and minimum heat dissipation.
Because there is no internal high frequency PWM or charge-pump switching; there is no RF switching noise emitted from the unit, of discontinuities in the outputs, to compromise other user circuits, and the outputs are inherently compatible with all and any existing synchro converters.
Using this type of “dynamic power transfer technique,” the efficiency is nominally better than 80%, and loss (power dissipation & heat generation) for reactive loads is less than half that of conventional DC powered amplifiers.
Care should be take to minimize the phase shift between the reference and signal inputs. Since the power supplies are only a few vols higher that the signal, the output could be affected by phase shift. Phase shift effect, compensation, and management techniques are detailed in
CCC ap.note#G-SA1 “Driving Synchro Loads.”
Packaging/Conductive Cooling
These models are all self-contained in an easy to install “Bolt-On” bulkhead mount chassis. The chassis is a light weight, single piece aluminum 1/8” thick solid base plate, that provides excellent thermal transfer for conductive cooling of the unit.
Mounting and Thermal Considerations:
Since the unit is primarily conduction cooled, make sure that it is tightly mounted to an appropriately large, thermally conductive (unpainted) surface. Thermal grease can also be applied to the mounting surface.
Kick Circuit
For Torque Receiver applications a kick circuit is provided to free stalled rotors, simply wire a jumper between the “CO” (current overload) output, and the “Kick” input.
More common an occurrence with large digital or switched step inputs, or after power up; a synchro torque receiver may get hung up at a false null, and just sit there and vibrate while draining large circulating currents. The amplifier will sense the overload that occurs if the rotor is persistently drawing too much current trying (unsuccessfully) to move the shaft load, and (with the kick/CO jumper installed) the amp will automatically shift the output by 120 degrees for a nominal 1/2 second duration to free the rotor from the false null.
Once the rotor is put in motion it has greater control of its output. Use this feature only if at least one Torque Receiver is being driven from the outputs.
Disable Input
The disable input is a TTL compatible Opto-Isolated input used to provide a circuit-safe means of disabling (turning off & on) the amplifier outputs for various applications. When disabled the outputs appear as an open circuit to the load.
The disable can be used to sequentially power up the synchro amps if several are used in a power sensitive application, or when used where the synchro signal outputs are going through switching relays for auxiliary, back-up, or test systems.
The disabling the outputs prior to switching either the reference/power inputs or the stator outputs, or both, and then driving the synchro amp inputs to match the angle dictated on the destination source prior enabling the outputs. The relays can very safely switch these points without any appreciable power demand during the actual switching. This will provide a very smooth transition that will reduce surges, and inductive content, allowing the user to minimize the required size of the relays, and dramatically increase the life of any relays used for switching these (high power) terminations. A logic 1 is used to disable the power outputs, a logic 0 will will enable the outputs providing the unit is powered and is not in a thermal overload sensed condition.
BIT Output
The Built-in-test output is a TTL compatible Opto-Isolated output that uses a logic level 1 to indicate that the amplifier has sensed either a thermal overload condition forcing it to shut down its outputs until the internal temperature cools down, or a current overload that is straining and thereby distorting the outputs, until the load is recovered (or kicked to free a stalled rotor), or if in thermal overload (when the internal temperatures sense shuts down the outputs).
Current-Load Sense
The output current on 25VA units is limited to 1.0 amp peak, and approximately 1 amp/25VA on larger units, after a 4 second nominal delay; an over current indication is sensed, setting the BIT output to a logic 1 (see Built-in-test, above).
When Driving Torque Receivers, the current limiting is typically experience whenever the rotor is off null (any significant difference in angle, from where it is being commanded to go), typically activating the kick circuit to rapidly set the driven synchro in motion (to free the rotor from hang-up), allowing the rotor to move towards its commanded angle (=null).
Thermal Sense
These synchro amplifiers are thermally protected, the amplifier outputs will shut down when the internal temperature reaches 125oC, also setting the BIT output to a logic 1. Thermal overload recovers when the internal temperature recovers.
Specifications:
DC Power Input for Logic Output Supply:
+5VDC. +10% @ 10ma MAX. (Not Required on -P units, add a p to the end of part number).
Digital Inputs/Outputs: (All Units)
*Disable...Input (DIS): Logic “0” = L=OVDC Enable Power Amplifier Output, TTL Compatible, requires 2.5ma. at logic 0
Isolation: OptoIsolated - 1000V Peak min. Breakdown voltage to Ground.
Built-in-test:
Output, Overload Indicator (BIT): logic level 1=H, drives 2 TTL loads, indicates amplifier sensed over load condition forcing it to shut down its outputs until conditions are satisfied (see txt).
Isolation: OptoIsolated - 1000V Peak min. Breakdown voltage to Ground.
Kick Circuit: Kick & CO
(Kick input & current over load); are normally connected for Torque Receiver Loads (not for Passive CT of CDX loads); If Output is hung-up due to excessive current output; Shifts output 120o for .5 sec. to unjam rotor hang-up. (see txt).
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