Vibrator Power Supply Design - Vibrator Power Supply Circuits - II

Finally, Figure 63 illustrates a system developed originally for military equipment, but available for other uses. This device provides for securing two output voltages, ordinarily of different values, and common at one point in the circuit (normally at ground potential). A self-rectifying vibrator of the usual type is used. The vibrator acts as a full-wave interrupter into the usual transformer primary. However, instead of serving as a full-wave rectifier as is usual, the rectifier portion acts as two half-wave rectifiers. One portion rectifies on one-half of the cycle, while the other rectifies on the other half. This permits the two outputs to be either both negative with respect to ground, both positive, or one of each, as is desired. The circuit shown has one output positive to supply a B + plate and screen circuit, and the other negative to supply a C — bias circuit. Each is filtered in a smoothing action by respective filters, as shown in the form of reactors L2 and capacitors C3 and C5.
This system might be desirable in securing large values of positive and negative voltages at low currents, referred to ground as a reference point. If the watts drawn from one half of the cycle are decidedly different from those on the other half of the cycle, the magnetization of the core of the transformer will be unbalanced to a rather large degree, and unbalanced vibrator operation will result. This can be balanced by deliberately unbalancing the transformer primary by setting the "center-tap" off-center by the required number of turns to equalize the magnetizing action. The timing capacitor may be located on either of the windings of the secondary, or both. If one is to be used, the higher voltage one will provide for the smallest value of capacitance. The one to which the capacitor is attached should be closely coupled to the primary.
An additional secondary, S3 is shown, together with a suitable dry-disc rectifier and smoothing filter, as an illustration of how an isolated low DC voltage output may be supplied. The load should be small compared to the other output requirements or should be comparatively low compared to the vibrator's capacity, if suitable performance is to be maintained. Such a load in this instance consists of a series of Fila merit type electronic tubes, requiring very low current and voltage. Of course, if such a load were the only load supplied, the vibrator could supply such a rectified load, into the tank capacitor of the smoothing filter, up to the input rating of the vibrator.
Many other circuits could be illustrated, but these will give examples of the field to which vibrator power supplies may be expanded. This text is intended to convey to engineers, students, service engineers, etc., a working knowledge of the design and operation of vibrator power supplies. The services of the P. R. Mallory Company's Engineering Departments are available for consultation on any special circuit designs. Complete information about the application, including load ratings, transformer design data, buffer capacitor selected, ventilation, etc., should be submitted.