Theory Of Operation; Functional Description - Lambda LJS-10-V Series Instruction Manual

THEORY OF OPERATION |
GENERAL
The Lambda power supply consists of an input circuit; internal power supply and starter circuit; clock
circuit; dead-time circuit; trigger circuit; pulse width modulator; soft-start circuit; steering circuit; voltage error |
amplifier; current limiter circuit; remote ON/OFF control circuit; inverter; output rectifier and overvoltage
protection circuit.
The circuit arrangement is shown in block diagram form in figure 8. The circuitry is discussed with
reference to the block diagram and the schematic diagram.
FUNCTIONAL DESCRIPTION
Input Circuit |
Single phase AC input power is applied to the input rectifier CR1-CR4, C5, C6 via EMI suppression net-
work L1, L2, C3, L3, C4. Fuse F1 protects against internal power supply circuit failure.
Internal Power Supply Circuit
The starter circuit CR5, CR6, R2, C6 and Q1 applies input power to the internal power supply consisting
of Q6, Q7, Q8, CR15, CR16, C8, C9, C10, R19, R20 and R21, whenever input power is initially applied or
when a no-load condition exists at the output after initial turn-on Feedback bias supply "A" CR11-CR14 and
R15 applies power to the internal power supply from the 20 KHz inverter. The internal power supply, a
linear power supply, provides 28.8 VDC at the emitter of Q6.
Clock Circuit
The clock circuit consisting of Q9-Q12, CR17-CR24, R24-R34, C11-C16, and T2 functions as the
master oscillator and the source of DC power to the control circuitry. The waveform at the collector of Q10
and Q12 is square, with a 5096 duty cycle in periods of 50 microseconds.
Control Circuitry
The pulse width modulator consisting of A3, R40, R41, CR35, C25-C27, is supplied triggered pulses by
trigger circuit CR29-CR34, R35-R37, A1 and A2. Bias supply "B" CR25-CR28 and C19 provides 5 VDC to
A1, A2 and A3 and to driver circuit transistors Q14 and Q15. The steering circuit, which consists of A1 and
A2 converts single-phase pulses from the pulse width modulator to two phase pulses which are fed to driver
circuit Q14, Q15, R58, C29 and ТЗ, which, in turn, applies the pulses to switching transistors Q2-Q5 in the
inverter. Dead-time circuit R35, R36 and C18 creates non-conducting dead-time for inverter switching
transistors Q2-Q5. Soft start circuit transistor Q13 prevents voltage overshoot when the unit is remotely
turned on via a remote turn-on signal applied to terminals RV1 and RV2.
Voltage Error Amplifier
The voltage error amplifier consists of A4, C33, R73, R74, CR41, CR42 and R75, reference voltage
diode CR45 and C35, R76, R78, R77 and output voltage sensing network R79, VR4, R82, R83, R81 and
C44. The programming current, 1 mA, used in the sensing network, is determined by R83.
Current Limiter Circuitry
The current limit circuitry consists of: buffer amplifier A5, CR36, CR37, R60, R61, C30; current
sampling circuit SHO, R68; reference voltage network R64-R66, VR3, CR38, CR44 and amplifier A4, CR39,
CR40, C31.
The buffer amplifier acts to change the polarity of the line-drop voltage between the load and the
output side of SHO with unity gain. R68 serves to sum the voltage drop across SHO and the line and between
the load and the input side of SHO to A-4. The reference voltage is set by adjustment of VR3 through
summing resistor R67 and serves to limit overcurrent conditions in the output of the supply.
The amplifier compares the reference voltage with the current sampling voltages and is combined with
the voltage error amplifier signal through the action of Q17. |
4 IM-LJS-10-V