Static Inverter Circuit Description

TM 11-6125-259-30

alternately shorted to ground by a switching circuit

overcurrent sense logic circuit for detection of an

(Q206, Q207, Q208, Q306, Q307, Q308). The cycle is:

overcurrent condition. After the five-second

(1) first choke shorted to ground for heavy current

duration, the inverter output is cycled off and on

flow. (2) first choke removed from ground and stored

until the overcurrent condition is corrected.

energy of choke released to heavy duty capacitors,

i. Major and Minor Drive. The major and minor

(3) second choke shorted to ground for heavy current

drive circuits receive the waveform from the drive

flow, (4) second choke removed from ground and

logic circuit and provides an amplification and

stored energy of choke released to heavy duty

buffering of these waveforms for the major and

capacitors, (5) cycle repeated. All during periods (2),

minor bridge converter circuits.

j. Major and Minor Bridge Converters. The major

(3), and (4), first choke is not shorted to ground and

and minor bridge converters receive amplified and

is free to release energy to heavy duty capacitors;

buffered waveform signals from the major and

each choke then has one period of high current flow

minor drive circuits. The waveform signals are

where it builds up energy and three periods of

converted into quasi sine waveshapes (chopped dc

releasing the energy to capacitors C401A and

waveforms); one uniquely phased quasi waveshape

C401B. Also, note that every other cycle, (2) and (3),

for the major and another for the minor converter.

no choke is being shorted to ground. In detail

These quasi sine wave forms are fed into the major

during heavy current flow period, energy will be

(T1) and minor (T2) transformers where they are

stored in the choke equal to one-half the inductance

superimposed upon each other to produce the 3,

times the current squared. The stored energy is

115 vac, 400 Hz, sine wave output voltage.

alternately released for each choke and discharges

k. Output EMI (Electromagnetic Interference)

through diode CR307 and CR207 to charge

Filter. The output EMI filter reduces conducted and

capacitors C401A and C401B which creates the 37

radiated energy.

vdc supply. Diodes CR307 and CR207 block current

k. Output Filter. The filter is tuned to the 12th

flow during energy build up when the voltage across

harmonic; the undesired 11th and 13th harmonics

each choke is the opposite of what it will be during

are suppressed from the inverter output voltage.

choke discharge of energy. Diodes CR306 and

CR206 prevent excessive voltage spikes when the

2-2. Static Inverter Circuit Description

chokes are switched from energy charge to

The following circuit description refers to figure FO

discharge. The energy charge (choke center tap

2-2, sheets 1, 2 and 3. Circuit paths from one sheet

effectively shorted to ground) cycle of the chokes is

to another are referred to in this discussion as

accomplished by utilizing power switch transsistors

etc.).

schematic points (

Q206, Q207, Q208, Q306, Q307 and Q308. These

a. High Level Boost. Input voltage from the EMI

transistors recieve base drive power from current

filter is fed to input chokes L201 and L301 (see fig.

drive transformers T201 and T301.

FO 2-2, sheet 1) and the center tap of each choke is

2-2