Charge-Transfer Voltage Converter

In the prior art, one of the methods used to transform a high voltage to a lower voltage was the utilization of transformers. This method introduced weight limitations and decreased efficiency. It also resulted in greater space requirements. A further limitation was the higher cost. The present invention eliminates the need for transformers and provides a unique apparatus for voltage transformation without the prior art limitations. It may utilize a unipolar alternating current source or a direct current source. It is compact and light in weight while handling appreciable amounts of power. It provides excellent line and load regulation. Finally, it increases efficiency, saves weight and space, reduces voltage transients, and saves money when used in place of conventional transformers.

A charge-transfer voltage converter is provided whereby a high voltage is transformed to a lower value. There are utilized two capacitors connected together by a switch. The switch may be a mechanical one, but it is preferable that it be a semiconductor designed and manufactured for the purpose of switching electrical currents (i.e., powertransistor, power thyristor, gate-turn-off silicon-controlled rectifier, etc.). The two capacitors are then connected together to form an electrical circuit. The circuit is broken in one place and the switch is inserted again to form a continuous circuit (when the switch is in its closed position). Next, one of the two capacitors is charged to a high voltage. Then the switch may be turned rapidly on and off and this process transfers the electronic charge from the charged capacitor to the one which was initially uncharged. By precisely controlling the duty cycle and/or repetition rate of the series switch between the two capacitors, the output voltage of the capacitor which was initially uncharged can be maintained between the limits of zero volts and the value to which the supplying capacitor was initially charged. Thus, voltage transformation has been achieved without the use of a conventional transformer.

In the single FIGURE of the preferred embodiment there is shown in schematic diagram form the charge-transfer voltage converter of the present invention.

Now referring in detail to the single FIGURE, the prime power source for this example is ordinary 117 VAC, 60 hertz, line current at input 1. Switch 2 is the on/off switch for the circuit; when it is closed, rectifier diode 3 conducts current on the alternate positive half-cycles of the line voltage and charges the capacitor 4 to voltage (Vin). Resistor 5 in series with Zener diode 6 and shunt capacitor form an auxiliary regulated power supply to operate voltage comparator amplifier 8 and reference voltage source consisting of resistor 9 and Zener diode 10. Transistor 11 acts as a solid state "switch". It is turned on (saturated) or off (cut off) by transistor 12 which acts as its driver. Resistor 14 serves to keep transistor 11 in a nonconducting state when transistor 12 is nonconducting. Resistor 15 limits the conduction current of transistor 12 to a safe level. Amplifier 8 is a voltage comparator operating with positive feedback and hysteresis established by resistors 17, 18, and 20. Capacitor 21 stores the energy which will be supplied to the load resistor 22 at the desired output potential (Vout).

In operation, the energy stored in a capacitor is equivalent to the product of one-half of its capacitance times the square of the voltage to which it has been charged (i.e., E = 1/2 CV.sup.2). If Vout is less than Vin, and the capacitance of capacitors 4 and 21 are equal, the energy stored in capacitor 21 will be much less than that stored in capacitor 4 because of the effect the voltage-squared term has in the energy storage equation. The charge-transfer-voltage converter uses this principle. Capacitor 4 when charged to Vin contains much more energy than capacitor 21 charged to voltage Vout. Thus, energy may be transferred in "packets" from capacitor 4 to 21 via transistor switch 11 to establish and maintain the voltage Vout, with negligible effect on the value on Vin. In practice, capacitor 21 may have a considerably greater value than capacitor 4 without adversely affecting operation of the circuit. Comparator amplifier 8 compares the value of Vref with the value of Vout. If Vref is greater than Vout, the amplifier switches and turns transistor 12 on which in turn turns transistor 11 on and capacitor 21 is charged until the value of Vout exceeds the value of Vref. When this occurs, amplifier 8 again switches and turns transistors 12 and 11 off. As load resistor 22 discharges capacitor 21, Vout again falls below the value of Vref and the cycle repeats. The resistors 17, 18 and 20 may be sized to provide hysteresis about the value of Vout, thereby decreasing the frequency of switching action and increasing circuit efficiency.