Warner Power Supply (As From Serial No. 3864); Description Of Warner Power Supply Operation - Storz XENON NOVA 175 Service Manual

3.2.4. Warner power supply (as from serial no. 3864)

3.2.4.1. Description of Warner power supply operation

The Warner power supply consists of input filtering, AC rectifier, dual buck regulators, auxiliary 12 V sup-
ply, a timing circuit, and a differential lamp igniter.
Warner power supply input
The input power entry starts with two 6.3 A, 250 V fuses (F1 and F2), one on the neutral ("N") line and
the other on the live ("L") line. Power switch, SW1, a single-throw double-pole switch, is connected
in series with the AC lines. The inrush current is limited by R14, a 10 h NTC thermistor. The input EMI
filtering consists of two X-capacitors, C9 and C10, four Y-capacitors, C17, C18, C43, and C44, and a
common-mode inductor, T4.
The power supply is protected from high input voltages by a 390 V varistor, RV1. The AC line is rectified
through an 8 A, 800 V bridge rectifier BR1. The rectified voltage is filtered through C1, C20, and L4 to
eliminate the 50/60 Hz ripple. This is supply voltage Vbulk1.
Vbulk1 is supplied to the first of two stages of buck regulators and also to the circuitry that is used to
make the maintenance and the auxiliary supplies.
Warner power supply maintenance / auxiliary supplies
Using the Vbulk1 as its supply, U1, a three-terminal pulse-width modulated IC, and T5, a flyback trans-
former, work together with other external circuitry to maintain the supply used as the 12 V auxiliary for
the fan, and for the control circuitry for the ballast.
Vbulk1 connected to pin 1 of T5 and the solid state switch TOP224 connected to pin 3 delivers the
excitation required to induce the power on pins 5 and 8 of T5. This power is rectified through D17 and
filtered by C12. The auxiliary voltage for the fan can be picked up at J4. The control circuitry power input
is connected after TS1, a thermal switch that provides the thermal protection for the ballast. When the
ballast is thermally overloaded, this switch will open, cutting power from the control circuitry and shut-
ting down the ballast. The voltage for the supply is determined by feedback to the TOP224 switch at pin
4. A third winding on T5, pins 5 and 6, provides pin 4 with the voltage information. This feedback wind-
ing is rectified by D14 and filtered by C11 and C7. D13, a zener diode allows further manipulation of the
feedback should it be necessary to change the supply voltage. D16 and D3 on the primary side of T5
provide a discharge path for the energy stored in the transformer.
Warner power supply control circuitry regulator
The regulation of this power supply uses a two-stage buck converter configuration found on the power
board. The first stage of the buck converter drops the Vbulk1 voltage down to the Vbulk2 voltage. Q1,
an IRFP450, working with L1, a 1.8 mH inductor, is capable of dropping Vbulk1 down to approximately
165 V. Q2, an IRFP260, working with L2, a 300 mH inductor, regulates the output power.
The control circuitry for both stages is located on the control board. The control circuitry for the first
stage uses UC3525, a pulse-width modulating integrated circuit, U1. The components C9, a 0.01 µF
cap, and R2, a 2.94 kh resistor determine the frequency of the regulator. The frequency of this buck
stage is approximately 50 kHz. C1, C2, C5, C6, and C7 prevent noise. D1 and D2, added to the output
of U1, prevent high voltages from damaging the IC. R3 and R4 are a voltage divider used as reference
voltage for the error amplifier. This error amplifier works with the feedback from the regulated supply
at Vbulk2 to determine changes in the output of the regulator. It will adjust the duty cycle of Q1 on the
power board to keep the level of Vbulk2 within the specified range. R5, R7A, and R13, on the power
board, establish the feedback from Vbulk2 to the error amplifier in U1. R1, in the error amplifier circuit,
determines the gain of the error amplifier. C29, a 0.1 µF capacitor, is used in the soft-start feature of the
IC.
The signal from the regulator circuitry to the buck FET, Q1, has to be transformed to a different voltage
reference, since the regulator circuit is referenced to RETURN and the buck FET, Q1, is referenced to
Vbulk2. A coupling transformer T1, and D9, D10, and R19 function together to change the reference of
the signal from the regulation circuit to the regulating buck FET, Q1. D5, a 15 V zener diode, protect the
gate of Q1 from over-voltage damage. Q3, D7, and R15 assist in the turning on and off Q1 to decrease
the losses during switching. At the higher power end of this first stage is Q1, D1, a 15 A commutat-
ing diode, and C15 and R20, the first stage snubber. The storage of Vbulk2 is accomplished with C4, a
390 µF, 200 V capacitor.
09.13 / V2.0
XENON NOVA 175
®
MODEL 20 1315 20
3-13