Amplifier with switchmode power supply
View Patent ↗An amplifier is driven by DC voltage from a switchmode power supply, whereby the switchmode power supply includes on the primary side a primary winding and bias supply winding. The bias supply winding supplies a reflected voltage from a secondary winding to a bias supply capacitor. The bias supply capacitor drives the control circuit and provides a sensing to the control circuit. The power supply further includes an active clamp circuit for controlling the voltage stress on a main switch. In another embodiment, boost inductors and a balancing transformer are added on the primary side of the transformer to prevent overvoltage conditions at light loads.
1. An amplifier with a switchmode power supply comprising:
an amplification means;
a power supply for said amplification means;
the power supply utilizing a current fed topology;
the current fed topology comprising:
a source of rectified direct current voltage;
at least one inductor with one end connected to the voltage source;
at least one main switch connected in series with the inductor and voltage source;
an isolation transformer having a primary and at least one secondary winding;
said transformer primary being connected to the junction of said main switch and inductor, whereby the main switch closing allows current to increase through the inductor and voltage source, the main switch opening diverting the inductor current into the transformer, allowing the inductor to supply energy to the secondary winding;
at least one rectifier and energy storage capacitor connected to a transformer secondary, as the current is limited by the inductor, no inductors are used between the rectifier and energy storage capacitor;
said power supply utilizing an active clamp snubber;
said active clamp snubber comprising:
an auxiliary switch in parallel with a diode;
a clamp capacitor;
the auxiliary switch and diode anode being connected to the junction of the primary winding and the main switch;
the clamp capacitor being connected to the auxiliary switch and diode cathode, the other end of the capacitor being connected to the source of rectified direct current voltage;
the main switch being turned on a short time after the auxiliary switch is turned off;
the main switch being turned off a short time before the auxiliary switch is turned on, such that the main switch and auxiliary switch are turned on when there is little voltage across them;
the power supply utilizing a control means; and
the control means operating and connected in such a way as to maintain a constant voltage across the energy storage capacitor, and to force the input current to be proportional to the input voltage.
2. The invention of claim 1 wherein a bias supply winding is wound on the transformer;
wherein the bias supply winding is connected to a rectifier and bias capacitor;
the bias capacitor supplying power to the control means;
the control means detecting and controlling the voltage on the bias capacitor; and
the control means turning off all switches when the bias capacitor voltage drops below a certain value.