Abstract: Apparatus including a DC-DC converter that applies a variable voltage to an inductive load, such as a fan motor. The converter has a low-frequency high dynamic output impedance and applies a variable voltage from its output to the inductive load. A transient limiter, such as a capacitor, is connected in parallel with the inductive load to minimize the amplitude of transients generated by the load during the reception of the variable voltage from the converter. The converter has a low frequency of operation to inhibit the generated transients from being extended to a DC power source connected to the input of the converter. This prevents the transients from being applied to other circuits served by the DC power source. The fan may be used to provide cooling for the apparatus of which the DC-DC converter is a part.

Abstract: An electronic lock system having a data encryption key physically and electronically protected from identification for protecting electronic equipment from use by unauthorized personnel. The lock system includes two keys circuits that implement a data encryption key and algorithm for encrypting random data. The data encryption key and algorithm are physically protected from physical identification by encapsulating the implementation in an integrated circuit. The second key circuit identical to the first is included in a lock circuit for generating two output signals. One output signal represents an unlocked condition of the system, whereas the other represents the lock condition. A random data signal is applied to the two key circuits for encryption under the data encryption key and algorithm. The lock circuit further includes a match circuit which generates the unlocked condition output signal when the encrypted data from the two key circuits matches for a predetermined period of time.