PS-40A-1 AC Bench Power Supply

Transcription

1 PS0A Bench power supply capable of direct line or 2 to 0 VAC variable output. Fused output at 0 A for line and 5 A for variable output. Includes voltage and current displays and external monitor outputs. Disclaimer: This document, associated technical descriptions and design information comprise a W5BWC Electronics project done exclusively for John L. Keith W5BWC. This is an original work of W5BWC Electronics intended to function properly and be accurately presented as described herein; however, no part of this project is offered for sale, presented to be free of patent infringements, or represented to be fit for any particular use. Any public use of this information is offered for educational purposes only, as a description of a personal project. Any and all liability of its' use is the sole responsibility of the user. Copyright 2009 by W5BWC Electronics PS0A90 Rev 0

2 Applications Intended for bench testing AC powered equipment. Variable transformer allows voltage to equipment under test to be brought up slowly. Excellent for testing input voltage range over which equipment operates correctly. True RMS current meter dedicated to measuring output current. With external BNC monitors, the shape of nonrms current can be measured. External monitors are phased correlated for power factor calculations. Features Selection of straight line voltage or variable 2 to 0 VAC output. Voltage monitored with precision rectifier and averaged for RMS display. External BNC monitors for voltage and current. All modes fused with front panel fuses. Front panel NEMA 55R receptacle Current monitored with true RMS converter for up to 5: crest factor. Characteristics Parameter Conditions Value Notes Input Voltage 60 Hz 20 VAC Input Current 20 VAC line voltage 0 A maximum 2 Output Voltage 0 to 5 A load current 2 to 0 VAC 0 to 0 A load current Input line voltage Output Current Variable Voltage Selected 0 to 5 A, Line Voltage Selected 0 to 0 A Output Voltage Display ½ Digits Type Precision Rectifier averaged for RMS Accuracy ± 2% Monitor Point, 50 ± 2%, M Output Current Display ½ Digits Type Accuracy Monitor Point, 50 True RMS Detector ± 2% (.5 to 0 Amps) ± 0 ma (0 to.5 Amps) ± 2% (.5 to 0 Amps) ± 0 ma (0 to.5 Amps) 2

3 Calibration Caution: At least two hours should be allowed for warmup prior to calibration. T, the voltage monitoring isolation transformer has a slight but significant internal heating which produces a couple of percent error, if not accounted for. First, calibrate the Voltage Display. Set the output voltage to 20.0 VAC using an accurate external meter and adjust the calibrate potentiometer on U. Use Caution while performing this step as the adjustment is near T2 s slider ring that exposes the output voltage. Second, calibrate the Voltage Monitor Point using an accurate meter connected to BNC connector J2. Adjust R8 on the PS0A0 printed circuit board assembly for 2.00 VAC with the Output voltage adjusted to 20.0 VAC. Third, calibrate the Current Display. Ensure the Output Voltage switch, S2 is in the Variable position and the Output Voltage is adjusted to 2 VAC. Connect a load to the output that consumes 600 to 200 Watts at nominal line voltage. Use either an accurate clampon or series connected Ampmeter capable of 0 Amps. Adjust the Output voltage to obtain 2.00 Amp load current. Adjust the calibrate potentiometer on U2 for a display of Connect an accurate AC Voltmeter to BNC J and adjust R7 on the PS0A0 assembly for Volts AC. Operation Warning: This line operated AC power supply has internal connections that expose Voltages capable of severe or lethal shock. In this age of low voltage miniature electronics, do not forget to use Caution while working inside this unit. Normal operation, with the unit enclosed, should pose no risk to the user, other than the fact its output can be lethal if exposed by external connections. The Power Switch, S, applies and removes power to the entire unit including the output connector, J. The Output Voltage selector switch, S2, selects either straight line Voltage or variable Voltage. The Output Voltage adjustment is accomplished by the variac, T2, which has approximate Voltage settings on the front panel. The Output is connected to the equipment under test by way of J, a NEMA 55R panel mounted receptacle. Poweron indicator, I, will light when S is on. If F is blown or removed it will not light. I is not effected by F2, the Variable Output fuse. Output Voltage and current are independently monitored by U and U2. The Voltage display is an averaged precision rectifier while the current display is a true RMS reading for peak to RMS ratios under 5. This feature is included to improve the current measurement accuracy for poor power factor loads such as rectifier or SCR equipment. Phase correlated Monitor Points are included for both Voltage and current. Using an oscilloscope, peak amplitudes and phase alignment can be determined. Theory of operation The primary use for the PS0A is to provide either line or variable AC power to equipment under test. Incoming power is protected by F, a 0A AG panel mounted fuse and controlled by on/off switch, S. Output selection is done by S2 for fixed line or variable AC output. Variac, T2, provides an adjustable Voltage from 0 to 20 VAC (or nominal line Voltage), which is boosted by T to 2 to 0 VAC. Note, for low line Voltage the full 0 VAC may not be available under full load conditions. The variable output is protected by F2. Output Voltage is displayed on U. U0 is a precision rectifier, feeding an averaging filter, C07 and R through R5. As well, this resistive divider scales the nominal.20 VDC rectifier output to VDC for U, resulting in a displayed reading of The rectifier s input is from T, which provides isolation from the AC output for both the rectifier and the monitor at J2. R8 is used to calibrate the Monitor Point output and U s calibrate potentiometer is used to calibrate the display. Output current is displayed on U2. U02 is an RMS to DC converter which along with C05 and C06 provides

4 a DC voltage that is equivalent to the AC Voltage at it s input. Transformers T and T are orthogonally mounted to minimize magnetic coupling. C08 removes a residual MHz from the relatively low level at J s output. This provides a cleaner appearance for scope monitoring. The MHz artifact is from the DC to DC conversion process in U0 and U0. These microcurrent power supplies are required to provide isolated operating power to U and U2 which are LCD DPM that cannot monitor their own supply Voltage source. Power to operate U0 and U0 as well as the remaining circuitry is provided by T0 and the 5.6 and 5.6 VDC zener regulated power supply. T T2 T T0 T ASSY PS0A0 F2 T S2 VOLTS DISPLAY CAL U MON CURRENT CAL T T U2 MON VOLTS CAL CURRENT DISPLAY CAL Figure. Top view, looking down into steel enclosure. Front panel is at the bottom and the variac, T2, is in the center and assembly PS0A0 is to the right. Figure 2. Top view of chassis removed from the steel enclosure. Note locations of key components and calibration points. R6 U0 T0 D0 R0 C0 C0 R02 C02 D0 C0 U0 R0 R R06 U02 R0 R08 R07 U0 R R2 C06 C05 R7 R8 J CAL E08 E5 E E0 E06 E07 ASSY PS0A0 PWB PS0A20 Figure. Component locator for assembly PS0A0.

5 5.6V 7 VAC 60 HZ 5.6V E2 VOLTAGE (A.C. VOLTS) 20.0 IN U0 OUT R6 PWR U PS90A 20K DPM 2 (NOTE 7) E (NOTE 6) DP IN E0 E R5 00K R 887K T 2 5 A R K C07.0 POLY.2 20 VAC RMS D07 N5 5.6V 8 U0 LF5 2 R 6.9K VAC RMS R2 K NOTES: UNLESS OTHERWISE SPECIFIED, ALL VALUES IN OHMS, uf AND uh. COMPONENT DESIGNATORS BELOW 00 ARE CHASSIS MOUNTED. COMPONENT DESIGNATORS ABOVE 00 ARE MOUNTED ON ASSY PS0A0 (PWB PS0A20). R7 ADJUSTED TO CAL CURRENT AT J. P F LINE 0A S POWER ON T2 VOLTAGE I V POWER VARIABLE F2 5A LINE (0A) VARIABLE (5A) S2 W J T 7.77: E O VAC RMS R09 2.7K CW R8 K (NOTE 5) E09 R0 0K R8 ADJUSTED TO CAL VOLTAGE AT J2. VOLTAGE CONTAINS A 0.02%/AMP ERROR. DPM CAL IS USED FOR FINAL DISPLAY CAL. U0 AND U0 PROVIDE DC ISOLATION FOR DPM POWER. T AND T ORTHOGONALLY MOUNTED J2 VOLTAGE X 0. (INTO M OHM) C0 22 6V C0 22 6V 5.6V 2 D05 N 522B D06 N 522B R0 80 R02 80 U0 IN PS90A OUT (NOTE 7) C0 00 6V C V D0 N00 D02 N00 D0 N00 D0 N00 E0 R0 20K E02 PWR T0 VAC 0.A CURRENT A.C. AMPS (RMS) (NOTE 6) 0.00 U2 DPM DP IN E0 E0 R0 K R05 0K R W R06 02 C05 22 C OUT CF (NOTE 8) 5.6V 7 VS U02 AD76 T :2.26 IN CAV IN VS COM 8 2 E05 R07 72 RMS TO DC CONVERTER CW (NOTE ) mv AC PER AMP R7 K E5 R08 0K E07 E06 E C J CURRENT 0. V/AMP (INTO M OHM) PS0A AC BENCH POWER SUPPLY 2 TO 0 0 TO 5 A RMS LINE 0 A RMS JL KEITH W5BWC ELECTRONICS Figure. Complete schematic for PS0A. 5

6 Material List PS0A00 Chassis Assembly Qty Designator Value/Type Description Part Number* Supplier C 0.0 µf, 50V Disc Ceramic F 0A, 250V AG 0.25 X.25 Fuse F2 5A, 250V AG 0.25 X.25 Fuse I V, 0.A Bayonet Type CM85 MOU J Receptacle, prong NEMA 55R 2 J2, J BNC Female, 50 Bulkhead P SJT Pwr Cord AWG, NEMA 55P R 0.05, 5%, 5W Lo Ind Curr Sense, IRC OAR 66OAR5R050JLF MOU S SPST 5A, 250V Toggle Switch S2 SPDT 5A, 250V Toggle Switch T 2 5A 7 VAC Transformer T2 5A Variac 7 VAC Variable T 7.77: Ratio 60 Hz Isolation Transformer T :2.26 Ratio 60 Hz Isolation Transformer 2 U, U2 ½ Digit Panel Meter 99.9 mv LCD PM28 2 XF, XF2 ¼ X ¼ Fuse Holder Panel Mount XI T ¼ Min. Bayonet Panel Mount Cable Clamp 0.0 I.D. Nylon Panel Bushing 0.0 I. D. Snap Nylon.9 Knob 0.75 Shaft Black w/ White Pointer Rubber Foot Heavy Duty 572 MOU Main Chassis Shop Built Pwr Cord Bracket Shop Built T2 Bracket 0.25 Al Rt Angle Front Panel Al Shop Built 0.25 X 0.75 # Screw Hex Standoff Enclosure Steel 8X8X2 * Items without a part number came from Shop stock. Most items are available from Mouser Electronics. 6

7 Material List PS0A0 PWB Assembly Qty Designator Value/Type Description Part Number* Supplier** 2 C0, C02 00 µf, 6 VDC Radial Aluminum 67UVZC0MDD C0, C0, C05 22 µf, 6 VDC Radial Aluminum 67UVRC220MDD C06 7 µf, 6 VDC Radial Aluminum 67UVRC70MDD C07.0 µf, 6 V Polyester Film 80R82DC00DQ60J 2 D0 D0 N00 A, 50 V Si Rectifier 2 D05, D06 N522B 5.6 V, 0.5 W Zener 78N522B D07 N5 Si Switching Diode 52N5 2 R0, R02 80 Carbon Film 2980RC 2 R0, R6 20 K, 0.25W, 5% Carbon Film 2920KRC 2 R0, R2 K, 0.25W, % Metal Film 27KRC R05, R08, R0 0 K, 0.25W, % Metal Film 270KRC R06, 0.25W, % Metal Film 2702RC R07, 0.25W, % Metal Film 2772RC R K, 0.25W, % Metal Film 272.7KRC R 6.9 K, 0.25W, % Metal Film 276.9KRC R K, 0.25W, % Metal Film 27KRC R 887 K, 0.25W, % Metal Film 27887KRC R5 00 K, 0.25W, % Metal Film 2700KRC 2 R7, R8 K Cermet Trimmer 62586F02LF T0 VAC 0. A 7 VAC PRI 2 U0, U0 DC Isolation Micro Current Supply PS90A W5BWC U02 AD76 Analog Devices RMS to DC Converter U0 LF5 Dual JFET Op Amp PWB PS0A20 W5BWC * Items without a part number came from Shop stock. Most items are available from Mouser Electronics. ** Part numbers are Mouser Electronics unless otherwise noted in Supplier column. 7

8 Prototype tests and notes Output Voltage Display and Monitor Accuracy Display Monitor Range Output (Amps) Range ± 0. % (tracking) ± 2 % (Composite) ± % (tracking) ± 2 % (Composite) Current Display and Monitor Accuracy Display Monitor ± 2 % (.50 Amps) ± 0 ma (0.5.5Amps) ± 2 % (.50Amps) ± 0 ma (0.5.5 Amps) Voltage and Current monitor points are phase aligned to 0.2 ms out of 6.67 ms for.2% which appears to hold within ±.5% (± 5 Degrees). Output Voltage Display Accuracy During warmup Display Elapsed Time (Hrs:Mins) : : : : : : : : : : : : : : : Note: T and T have a voltage nonlinearity that contributes to the error at the monitor points. T actually improves a slight nonlinearity in the precision rectifier, but imposes an error on the Voltage Monitor point. Notice the Current Monitor point tracks the Current display within a fraction of a percent, but the error contribution of T can be seen when the Current Monitor reading is compared to the actual output current. T also has a considerable warmup time that effects the Voltage Display and Monitor Point as can be seen from the above data. After one hour warmup the contribution of T stablizes and supports ± 2 % when the initial calibration is done at hours operation. T and T provide isolation for voltage and current measurements, but at the expense of accuracy. The transformers contribute significant inaccuracies in the PS0A. A Triad CSE current transformer might improve T, but the data sheet is too vague to be sure. T may need to be : 5 VAC 2.5 VA type with a 0: resistive divider on its primary side. Or 600 Ohm transformers could be used with the line Voltage divided by 00. Also, an RMS converter in place of the precision rectifier would improve harmonic induced errors in Voltage display. 8

9 Notes: For Characteristics (page 2).. Input voltage below 20 VAC may not provide 0 VAC output under 5 Amp load. 2. Input current for the PS0A control circuitry is a fraction of an Amp.. Fuses are 5 Amp and 0 Amp. Extended periods at maximum current may cause one or the other to open. Also, R is at full rated dissipation at 0 amp.. Output Voltage display accuracy based on initial calibration after hours operation. 9