POWER SUPPLY FOR AN ELECTRONIC PABX

• US 3,743,887 A
• Filed: 03/24/1972
• Issued: 07/03/1973
• Est. Priority Date: 03/24/1972
• Status: Expired due to Term

• Current Assignee: Alcatel USA Corp (Nokia Corporation)
• Original Assignee: Charles James Kalensky, Timothy James Keough
• Inventors: Keough, Timothy James, Kalensky, Charles James
• Primary Examiner(s): Trammell, James D.
• Application Number:
  US05/237,973
• Time in Patent Office: 466 Days
• Field of Search: 321/14,18 323/24 317/33VR,33SC,31,16
• US Class Current: 361/86
• CPC Class Codes: H02H 7/127 having auxiliary control electrode to which blocking control voltages or currents are applied in case of emergency
• CPC Class Codes: H02M 7/1557 with automatic control of the output voltage or current

Abstract

A compact power supply characterized by low heat dissipation is provided. Phase control of main silicon controlled rectifiers is provided by cosine modified ramp and pedestal control. Overvoltage and overcurrent conditions are detected by SCRs and relay means which reduce the amplitude of control signals to the main SCRs thus turning off the output of the system to prevent damage.

Claims

1. A power supply for an electronic system comprising two main SCRs connected in adjacent arms of a first bridge circuit responsive to an AC power supply voltage and to control voltages to provide a desired DC output voltage, a second bridge circuit coupled to receive a voltage proportional to said AC power supply voltage and provide a pulsating DC voltage, means coupling said pulsating DC voltage to a capacitor to produce a cosine ramp voltage across said capacitor, a source of reference voltage, a differential amplifier coupled to compare the reference voltage with the DC output voltage of the system and to provide a difference voltage in accordance with the difference, means for receiving said difference voltage and providing a pedestal voltage proportional thereto, means for receiving said cosine ramp voltage and said pedestal voltage and forming an intermediate voltage proportional to the sum of said voltages, and two gate SCRs coupled to be energized alternately by the intermediate voltage, said two gate SCRs directly providing separate control voltages to energize respective main SCRs in adjacent arms of the second bridge circuit.

2. A power supply as claimed in claim 1, in which the second bridge circuit forms a full-wave rectifier for providing said pulsating DC voltages, and the reference voltage is provided by a zener diode placed across said pulsating DC voltage.

3. A power supply as claimed in claim 1, in which the second bridge circuit forms a full-wave rectifier for providing said pulsating DC voltages and the means for forming an intermediate voltage includes a unit junction transistor.

4. A power supply as claimed in claim 1, in which means are provided for protecting the power supply against excessive current levels, said means including a current sensitive relay responsive to current above a certain level to close contacts and energize a current overload SCR, said current overload SCR including connections to reduce the pedestal voltage, and thus lower the intermediate voltage and the control signals below levels necessary to turn on the two SCRs in the second bridge.

5. A power supply as claimed in claim 4, in which means are provided for protecting the system from an overvoltage, said means including a zener diode and a SCR connected across output terminals of the system, said zener diode responding to overvoltage to conduct, means coupling the zener diode to control the SCR across the output to produce a short circuit through the SCR when the zener conducts, said short circuit causing operation of said means for protecting against excessive current levels.