On the Control of Electroluminescent Cells by Unipolar Transistors†

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Abstract
This paper describes an attempt to use a unipolar transistor to control an electroluminescent cell. The unipolar transistor, like photoconductors, provides the control through a resistance change instead of a reactance change. By varying the channel conductance, the supply voltage can be shifted from the unipolar transistor to the EL cell and vice versa. An approach to the design of a control element is given with an example. The unipolar transistor is used here as a constant-current limiter. For higher transconductance and sensitivity in control, low pinch-off voltage is required. The control voltage in most cases is about one-half of the pinch-off voltage. The optical response of a silicon photo-diode was measured as a function of wavelength between 400 to 1000 millimicrons. These results are used in estimating the optical sensitivity of a photo-unipolar transistor. In the case of optical control a power gain beyond one hundred may be obtainable at a control frequency of kilocycles per second. Preliminary test results on the control and storage are also given. With a proper bias resistor, the time constant in the gate circuit can be adjusted to reach a storage time of 1/60 sec.

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