Vibrator Power Supply Design - Vibrator Power Supply Circuits - I

The following circuit diagrams are presented to illustrate a few used in various vibrator power supply applications.
Figure 60 illustrates the usual construction of a power unit utilizing a self-rectifying vibrator. The vibrator illustrated is of the "reversing" type where the contact materials used are non-polarized. The base is so constructed and wired that it can be inserted into its matching socket in two positions 180 degrees apart. By wiring the socket in a manner similar to a reversing switch, the polarity of the connections to the secondary of the transformer can be reversed with this rotation of the base, and thus the output polarity can be reversed. This provision permits the maintenance of a correct output polarity when the input polarity can not be predetermined, such as would occur in automobile receivers made for universal application. The new 250-cycle vibrator uses polarized contacts and since the reed always must be connected to minus A, the mechanism is connected to the "reversing" base and the wires to the socket in a different manner. However, the same end results are obtained.
The usual amount of "hash" filtering is provided in resistors Ri and R2, capacitors Ci, C2 and d, and inductances CHi and CH2. The smoothing filter consists of electrolytic capacitor C3, of the common cathode type, and reactor CH3. Resistor R4 acts as a bleeder to discharge the high-voltage capacitors, and to act as a minimum load when the unit is operated on no-load. Capacitor C6 and resistor RA form the timing capacitor circuit.

Figure 61 illustrates an arrangement which may be utilized in some special instances such as military equipment. The circuit suggests one arrangement for operating a vibrator power unit from two or more different input voltages. In this case, provision has been made for three voltages, although the general rule would be for two; an example would be for 6, 12 or 24 volt equipped mobile vehicles, such as "jeeps," trucks, and tanks.
The transformer may be designed, as shown, with a series primary arrangement, taps being made at the appropriate number of turns for the different voltages, and with graduated sizes of wire for the different currents encountered at the various inputs. This arrangement permits greater flexibility in adjusting the primary to secure identical output with different input voltages, and permits a simpler form of switching for manual control, but it requires more winding space for the primary as various sizes of wire are required with this method. An alternate method used for two input voltages of multiple value, such as 6 and 12, or 12 and 24 volts, is for a series and parallel arrangement of primaries. Here all four primaries are constructed of the same number of turns and wire sizes; they are then connected in parallel groups of two, or in a series group of four, with appropriate center-taps. This system permits better utilization of the winding space, but requires a more difficult switching arrangement and does not permit adjustment of the outputs by primary turn juggling.
The single vibrator is used on all voltages by bringing out the driving-coil lead, and switching an appropriate value of resistor in series with this lead as the transformer primary connections are changed. These switches are ganged for convenience. The capacitor C» is usually required with the shunt-coil type of unit when a high value of resistance is placed in series with the coil, such as when a 6-volt unit is operated on 24 or 32 volts. The value varies, but often runs from 0.2 to 0.5 mfds. The value of RI and R2 will depend upon the driving-coil resistance and impedance; usually a resistance value slightly higher than the resistance of the coil is required to double the operating input voltage.
The only other unusual feature of the circuit lies in the connection of the primary timing capacitor across the entire primary winding. This keeps the effect of the capacitor constant insofar as its addition to the secondary timing capacitor is concerned, and a fairly constant waveform is maintained on all input voltages. It will also serve its purpose of preventing starting arcs.

Figure 62 illustrates another type of circuit, in which the power supply is to function equally well when operating from a standard AC line and from a battery. This is made possible by the addition of an AC primary winding and an additional tap upon the vibrator prima) y so that this winding can be used for filament power when operating on AC. Because of the different form factors of the sine and the square wave-forms, if the AC primary is adjusted to provide the same DC high voltage output as is secured with the vibrator, the voltage across one-half of the vibrator primary (on AC) will be less than 5 volts, for instance, instead of 6.3 volts RMS. The actual voltage value will depend largely upon the time efficiency of the vibrator, and upon the design center for input voltage for vibrator operation. The use of the AC primary requires a much larger amination to be used in order to accommodate this added winding
The output circuit is of the conventional type, except a heater circuit filter choke has been added, since the receiver tubes must be supplied through this common lead The input switching has two positions, one for DC, or battery, as shown in solid arrows, and one for AC as shown in dashed lines. When the connection is to the battery, the AC snap-switch is open on both sides of the line to avoid conduction of interference picked up on the transformer to the outside leads. These leads are also by-passed to ground by capacitors Ct. When operating on DC, the primary connections to the vibrator are conventional, with the "off-center" tap open. When switched to AC, the battery is disconnected, the lower end-tap of the primary is switched to ground, and the tube heater connection, which was formerly connected to the battery and primary center-tap, is connected to the "off-center" tap so that additional voltage is provided for the circuit.
When winding this type of transformer, the secondary and vibrator primary should be adjacent, so as to obtain the closest coupling and lowest leakage reactance.
Another means of operating vibrator power supplies on AC power lines consists of removing the vibrator and replacing it with a plug of the same basing, to which is connected an AC cord. This is attached to the interrupter contact pins of the plug, so that a suitable AC voltage may be applied to the vibrator primary. For a 6-volt power unit, the required voltage would be approximately 10.0 volts RMS across the entire primary. This can be supplied by an ordinary step-down transformer of sufficient volt-amperes capacity. This arrangement permits the design of the vibrator power supply to be made for minimum size and maximum efficiency, with reasonable cost. When there is a demand for AC operation, the additional equipment can be added.