Specifications

CONSTRUCTION
shown in the circuit. Drains of
MOSEFTs of one bank are con-
nected to one extreme taping
of 9-volt primary of the in-
verter transformer X1, and
that of the MOSEFTs of the
second bank are connected to
the other extreme 9-volt tap-
ing of the same transformer.
Centre tap of the primary is
directly connected to the posi-
tive terminal of 12V, 7Ah bat-
tery. Capacitor C2 is connected
across the secondary of the in-
verter transformer, either di-
rectly or via inductor L1
(wound on the same core as ex-
tension of secondary winding),
using sine/square slide switch
SW2.
When mains power fails,
relay gets de-energised and
12V battery supply is fed to the
control circuit through top con-
tacts of the relay to produce
squarewave outputs at pin
Nos. 8 and 9 of IC 7473 with a
frequency of 50 Hz. At any in-
stant, if voltage at pin 8 of IC2
is +5V, the voltage at pin 9 of
IC2 is 0V, and vice versa.
Therefore, when transistor T1
conducts, transistor T2 is cut
off, and vice versa. When tran-
sistor T1 conducts, the voltage
at collector of transistor T1
drops to 0.7 V, and therefore
MOSFETs of bank 1 remain
cut off while collector of tran-
sistor T2 is at 5V. Thus,
MOSFETs of bank 2 conduct
and the current flows through
one-half of inverter trans-
former X1 primary. During the
next half cycle, the voltage at
pin 8 of IC2 is 0V and that at
pin 9 is +5V. As a result, the
voltage at the collector of tran-
sistor T1 is +5V and that at
the collector of transistor T2 is 0.7V.
Hence, MOSFETs of bank 2 are cut-
off while those of bank 1 conduct. This
results in a large DC current swing
through the other half of the inverter
transformer X1 primary. In this way,
two banks of the MOSFETs conduct
alternately to produce 230V AC, 50
Hz across the secondary of the in-
verter transformer X1. Inductance L1
Fig. 5: Actual-size component-side track layout for the PCB
Fig. 3: Battery current vs load (squarewave O/P)
Fig. 4: Battery current vs load (sinewave O/P)
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