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Inverter Start Circuit

IP.com Disclosure Number: IPCOM000075458D
Original Publication Date: 1971-Sep-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Duspiva, WS: AUTHOR [+2]

Abstract

Many inverters obtain their internal biasing from their own outputs. In order to begin operation, however, the internal circuitry usually requires a low-voltage level "start pulse" (5 to 20 volts DC, depending on the application) obtained from the high-level input (115 to 230 volt AC rectified). This voltage pulse starts the multivibrators or other choppers running and an output voltage results, which is fed back to sustain the operation.

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Inverter Start Circuit

Many inverters obtain their internal biasing from their own outputs. In order to begin operation, however, the internal circuitry usually requires a low-voltage level "start pulse" (5 to 20 volts DC, depending on the application) obtained from the high-level input (115 to 230 volt AC rectified). This voltage pulse starts the multivibrators or other choppers running and an output voltage results, which is fed back to sustain the operation.

In this circuit, capacitor C1 is charged slowly thru R1 to about 25 volts. This may take about 10 to 20 seconds. Resistors R2 and R3, transistor T1, and V REF form a threshold network and when the potential across C1 reaches about 25 volts T1 conducts, turning on T2 and T3. V REF may be obtained from a six volt zener elsewhere in the system.

Transistors T2 and T3 and resistors R5 and R6 form a

"second-collector-to-first-emitter" feedback network. The output voltage (neglecting V(be)'s, which somewhat cancel) is approximately V out = V ref >(R5 + R6)/R6|. Thus, a regulated output is provided to R LOAD until C1 discharges so much as to saturate pass transistor T3. Capacitor C1 should be chosen so that the inverter starts before this occurs. Once the inverter starts, the sustaining voltage derived from the inverter and applied to the anode of diode D should be such that the internal circuitry of the inverter controls (R LOAD) is biased-up and the R5-R6 divider back biases the base-emitter of T2, turning off...