A number of low voltage vacuum tube circuits include using supply voltages well below the manufacturer's recommended voltages applied to the plate or screen grid. Some of the tube circuits operate at near zero plate and or screen grid voltages. Other low voltage circuits have forward biasing on one or more grids that are normally biased at a non positive voltage or a grid that is normally connected a cathode. Substantially lower supply voltages allow for example, the filament supply to also supply voltage to the plate and or grid for providing an output signal at a grid and or a plate.

A number of low voltage vacuum tube circuits include using supply voltages well below the manufacturer's recommended voltages applied to the plate or screen grid. Some of the tube circuits operate at near zero plate and or screen grid voltages. Other low voltage circuits have forward biasing on one or more grids that are normally biased at a non positive voltage or a grid that is normally connected a cathode. Substantially lower supply voltages allow for example, the filament supply to also supply voltage to the plate and or grid for providing an output signal at a grid and or a plate.

A power supply apparatus includes: an inductor to which an input voltage is applied; a switching element that switches a current flowing to the inductor on and off so as to cause an induced voltage to be generated; an electrolytic capacitor that smoothes the induced voltage and outputs the voltage to a load; and a control circuit that controls the switching element, wherein the control circuit outputs a second switching control signal obtained by superimposing a degradation detection-purpose signal for detecting degradation of the electrolytic capacitor on a first control signal, detects an output voltage output by switching performed by the switching element controlled by the second control signal, and estimates the degradation of the electrolytic capacitor by using the output voltage detected, a duty cycle of the first control signal, and a frequency component of the degradation detection-purpose signal contained in the output voltage detected.

A power supply apparatus includes: an inductor to which an input voltage is applied; a switching element that switches a current flowing to the inductor on and off so as to cause an induced voltage to be generated; an electrolytic capacitor that smoothes the induced voltage and outputs the voltage to a load; and a control circuit that controls the switching element, wherein the control circuit outputs a second switching control signal obtained by superimposing a degradation detection-purpose signal for detecting degradation of the electrolytic capacitor on a first control signal, detects an output voltage output by switching performed by the switching element controlled by the second control signal, and estimates the degradation of the electrolytic capacitor by using the output voltage detected, a duty cycle of the first control signal, and a frequency component of the degradation detection-purpose signal contained in the output voltage detected.

High-resolution switched digital regulators are disclosed having fast cross corner and variable temperature response, with constrained ripple. The strength of the power transistors utilized by the regulator are adjusted to control the current delivered to the load. The regulators utilize a slow control loop in parallel with a primary fast switching loop. The slow loop uses the switching signal of the primary loop to estimate the load current and set the power transistor size accordingly.

A voltage regulator is provided comprising: a pass transistor that includes a first node coupled to receive an input voltage and a second node coupled to provide a regulated voltage and a control node; an amplifier circuit coupled to produce a control voltage on a control line that is coupled to control a voltage at the control node of the pass transistor, based at least in part upon a reference voltage and the regulated voltage; a switch configured to transition between a first switch state in which the switch couples the control line to a turn-off voltage having a value to turn off the pass transistor and a second switch state in which the switch decouples the control line from the turn-off voltage; and a switch control circuit configured to maintain the switch in the first switch state during a first time interval while the input voltage ramps up and to transition the switch to the second switch state after the first time interval.

A voltage regulator is provided comprising: a pass transistor that includes a first node coupled to receive an input voltage and a second node coupled to provide a regulated voltage and a control node; an amplifier circuit coupled to produce a control voltage on a control line that is coupled to control a voltage at the control node of the pass transistor, based at least in part upon a reference voltage and the regulated voltage; a switch configured to transition between a first switch state in which the switch couples the control line to a turn-off voltage having a value to turn off the pass transistor and a second switch state in which the switch decouples the control line from the turn-off voltage; and a switch control circuit configured to maintain the switch in the first switch state during a first time interval while the input voltage ramps up and to transition the switch to the second switch state after the first time interval.