GE DS3800HRDA Sequence control module
If a clamp is required, a power zener diode can be used as shown in the figure. The maximum zener clamp voltage must not exceed 75 volts. Caution If a clamp is required, the transformer secondary voltage must be re-checked to insure that the minimum clamp voltage is not exceeded under high line and low load conditions when there is no regeneration. Otherwise, the zener might overheat and fail.
To determine the required diode power rating
start with a 5W device and monitor the zener current with a current probe. Power (in watts) is the average current (in amps) times the zener voltage. Estimate the average current from the oscilloscope trace and compute the power. Select a zener rated slightly higher than the measured power. If the average power is too high to be conveniently dissipated in a zener diode, the active voltage clamp circuit shown below can be used instead. Power is dissipated in the 25W, 30W resistor if the Motor Power Supply voltage exceeds 75 volts.
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