Abstract: A keep-alive circuit for a regulated switched-type power supply for forcing the power supply to generate power pulses under conditions where the apparent output voltage level is such as to cause the regulator circuit normally to reduce the power pulses effectively to zero. The keep-alive circuitry responds to the absence of the power pulses over a predetermined time interval to modify the regulating circuit so that the regulating circuit responds to a different output voltage level to force the power supply to generate a power pulse under the aforesaid conditions. The action is made cyclic and the power supply is thereby caused to generate a series of low frequency power pulses indicating that it is still alive.

Abstract: A transformer isolated switched power supply of the forward converter type in which a small bias winding is provided on the transformer so that both sides of the operating area of the B/H curve of the transformer core may be used for increased efficiency.

Abstract: A battery back-up system providing a short term hold-up for a converter type switched power supply. The back-up system includes a regulated charger circuit for maintaining the battery in a charged condition and a direct current fan which cools the power supply in both the normal and battery back-up modes. Over-voltage protection for the system is provided during the battery back-up mode, and protection for the battery is provided against excessive battery charging voltages. The fan and regulator are automatically turned off when the battery reaches a deep discharge condition to protect the battery.

Abstract: A high power factor, regulated synchronous converter for converting 110-volt, rectified, 50-60 Hz alternating current into a direct current output, which has enhanced hold up (energy storage). The circuit includes a half-bridge inverter for converting the half-wave rectified voltage into high frequency alternating current in the range of 20-30 KHz. The high frequency alternating current is coupled through an inductance coil to a half-bridge synchronous regulator/rectifier which produces a direct current output. The energy delivered to the half-bridge synchronous regulator/rectifier is stored in a capacitor, and the voltage across the capacitor may be regulated making energy storage independent of the line voltage. Additional synchronous regulator/rectifiers may be coupled to the circuit to produce additional direct current outputs.

Abstract: A switched power supply of the self-balancing push-pull square-wave converter type which includes a pair of switching transistors connected to the primary of a transformer and which are driven by a square-wave oscillator, and which also includes a pre-regulator chopper connected to the transistors. A ripple voltage appears on the output of the pre-regulator which is a function of the current flow through the individual transistors, and this voltage is coupled through a capacitor and a series resistor to the square-wave oscillator to terminate the drive current through each transistor for each cycle in which the current flow through the transistor exceeds a predetermined maximum.

Abstract: An isolation circuit for preventing the current surges drawn by a direct current cooling fan from appearing in the output of the power supply. The fan has one terminal connected to one terminal of the power supply, and a regulator circuit connects the other terminal of the fan to the other terminal of the power supply. The regulator circuit includes a capacitor connected across the fan to provide a low impedance circulating path for the current surges, and it also includes a network which provides a constant current to the parallel combination of the fan and capacitor.

Abstract: An over-current sensing circuit for use with a switching-type power supply for achieving fold-back, which senses not only the load current drawn from the power supply, but also the voltage at the load and the voltage across the power supply potentiometer which is used to set the output voltage. The sensing circuit thereby serves to maintain the current limit point at which fold-back occurs virtually constant in the presence of adjustments of the output voltage of the power supply and regardless of the resistance of the bus which connects the power supply to the load.

Abstract: A system is provided for aligning the read/write magnetic heads in a multi-head disc drive which includes a four quadrant balanced circuit and which responds to the peak amplitudes of dibits recorded in servo tracks on the discs of a prerecorded servo disc pack as read by the various heads to produce, without offset errors, digital signals representative of individual head misalignments; the system being insensitive to distortions of waveform. The system can also be used to provide an analog position signal to a feedback servo mechanism for positioning the head, or heads, which is insensitive to waveform distortions and to baseline shift due to write recovery.

Abstract: An overlap control system is provided in a push-pull switching mode inverter power supply which prevents a second switching transistor from being turned on after a first switching transistor has been turned off until the end of the storage time of the transistor being turned off so as to prevent the conduction of through currents from one transistor to the other which would otherwise occur if the switch-over took place during the storage time, and which would cause high stress and failure of the switching transistors because there is no inherent limit to the magnitude of the through currents, and because the through currents do not pass through the load circuit of the power supply. The overlap control circuit of the invention permits operation of the power supply with up to 100% duty cycle without any possibility of damaging cross-conduction of the switching transistors to occur.

Abstract: A system is provided for driving the switching transistors in a push-pull switching mode inverter-type power supply. The system of the invention provides drive current adjusted to the actual power supply load throughout the entire switching cycle from turn-on to the completion of turn-off for each of the switching transistors. There is essentially zero power dissipation in the various elements which make up the system. Moreover, the system obtains substantially all of its drive power from the outputs of the switching transistors themselves, and it provides transformer isolation for the switching transistors.