9. Modular AC Front-end System (ENMod) Design Guide & Applications Manual For Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies The ENMod component power front-end system for EN compliance provides an effective solution for an AC front end of a power supply enabled with Vicor DC-DC converters. The ENMod system’s basic building blocks are the MiniHAM passive harmonic attenuation module, the FARM3 autoranging AC-DC front-end module (Figure 9–3) and a discrete EMI filter. The ENMod system provides transient / surge immunity, harmonic current attenuation (Figure 9–2) and EMI filtering, in addition to all of the power switching and control circuitry necessary for autoranging rectification, inrush current limiting, and overvoltage protection. Converter enable and status functions for orderly power up / down control or sequencing are also provided. To complete the AC front-end configuration, the user only needs to add hold-up capacitors, EMI filter (Figure 9–1b), and a few discrete components. V5 C3 N N Filter AC line Input EMI GND PE (Fig.9–1b) L + N N V3 FARM3 (Fig.1b) SR L L L R1 BOK C7 V1 NC V2 NC ST EN C8 – +IN N/+ N/+ MINI HAM L/– Holdup Box (HUB) 410 μF HUB820-S 1100 μF HUB2200-S 600 μF HUB1200-S 1350 μF HUB2700-S 900 μF HUB1800-S 1650 μF HUB3300-S F1 C1 D3 NC PC Vicor 300 Vin DC-DC Converter NC C9 NC PR L/– –IN R2 C2 PE R3 V6 C4 D1 C5 F2 +IN Sizing PCB traces: All traces shown in bold carry significant current and should be sized accordingly. R4 D4 PC Vicor 300 Vin DC-DC Converter D2 C10 PR –IN Part C1,2 C3 – 6 C7,8 C9,C10 R1,2 R3, R4 V1,2 V3 V5,V6 F1,2 D1,2 D3,D4 C6 Vicor Description Part Number Holdup capacitors 4,700 pF (Y2 type) 01000 Film Cap., 0.61 µF 34610 0.001 µF 150 kΩ, 0.5 W 250 Ω, 0.125 W MOV 220 V 30234-220 270 V MOV 30076 Bidirectional TVS Diode 1.5KE51CA Use recommended fusing for specific converters Diode (1N4006) 00670 1N5817 26108 To additional converters Figure 9–1a — Offline power supply configuration R1 Part Input Output C2 N L2/N L3 L1 V1 R3 C1 L1 R4 CM F1 PE R2 C3 C4 PE C1 1.0 02573 4,700 pF (Y2 type) 01000 C4 0.33 µF 00927 F1 10 A Wickman 194 Series or Bussman ABC-10 L1, L2 27 µH 32012 L3 1.3 mH 32006 R1, R2 10Ω R3 150 kΩ, 0.5 W R4 2.2 Ω, 2 W V1 MOV Figure 9–1b — Input EMI filter for EN55022, Class B compliance Maxi, Mini, Micro Design Guide Page 41 of 88 Rev 4.9 Apps. Eng. 800 927.9474 Vicor Part Number C2, C3 L L2 Description vicorpower.com 800 735.6200 30076 9. Modular AC Front-end System (ENMod) Design Guide & Applications Manual For Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies Harmonic Current 10.00 Current (A) 1.00 Odd Harmonic Limits * Even Harmonic Limits Measured Values 0.10 0.01 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 Harmonic Number Figure 9–2 — Measured harmonic current at 230 Vac, 575 W vs. EN spec limits (*Measured values of even harmonics are below 0.01 A) Power Up +OUT PTC Thermistor 90–132 V AC Line Strap L 400 300 200 100 0 Strap Output Bus (Vdc) EMI Filter –OUT N Power Down 1.1 2.1 Strap PTC Thermistor Bypass SR EN Converter Enable Bus OK Microcontroller BOK 3.1 ~150 ms ~150 ms 4.1 5.1 2.2 1.2 EMI GND Figure 9–3 — Functional block diagram: FARM3 module Figure 9–4 — Timing diagram: Power-up / down sequence Vdc output ⇒ Vdc output Timing Diagram, Power Up/Down Sequence Strap Engaged Enable Enable Bus OK Bus OK Figure 9–5 — Start up at 120 Vac input Maxi, Mini, Micro Design Guide Page 42 of 88 Figure 9–6 — Start up at 240 Vac input Rev 4.9 Apps. Eng. 800 927.9474 vicorpower.com 800 735.6200 9. Modular AC Front-end System (ENMod) Design Guide & Applications Manual For Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies POWER-UP SEQUENCE (Figure 9–4) 1.1 Upon application of input power, the hold-up capacitors begin to charge. The thermistor limits the charge current, and the exponential time constant is determined by the hold-up capacitor value and the thermistor cold resistance. The slope (dV/dt) of the capacitor voltage versus time approaches zero as the capacitors become charged to the peak of the AC line voltage. The switch that bypasses the inrush limiting PTC (positive-temperature coefficient) thermistor is open when power is applied, as is the switch that engages the strap for voltage doubling. In addition, the converter modules are disabled via the Enable (EN) line, and Bus OK (BOK) is high. Vdc output Iac input @2A / mV Enable Bus OK Figure 9–7 — Power down from 120 Vac 2.1 If the bus voltage is less than 200 V as the slope nears zero, the voltage doubler is activated, and the bus voltage climbs exponentially to twice the peak line voltage. If the bus voltage is greater than 200 V, the doubler is not activated. Vdc output Iac input @2A / mV 3.1 If the bus voltage is greater than 235 V as the slope approaches zero, the inrush limiting thermistor is bypassed. Below 235 V, it is not bypassed. Enable 4.1 The converters are enabled ~150 ms after the thermistor bypass switch is closed. Bus OK 5.1 Bus OK is asserted after an additional ~150 ms delay to allow the converter outputs to settle within specification. Figure 9–8 — Power down from 240 Vac POWER-DOWN SEQUENCE (Figure 9–4) When input power is turned off or fails, the following sequence occurs as the bus voltage decays: 1.2 Bus OK is de-asserted when the bus voltage falls below 210 Vdc. 2.2 The converters are disabled when the bus voltage falls below 190 Vdc. If power is reapplied after the converters are disabled, the entire power-up sequence is repeated. If a momentary power interruption occurs and power is reestablished before the bus reaches the disable threshold, the power-up sequence is not repeated, i.e., the power conversion system “rides through” the momentary interruption. Maxi, Mini, Micro Design Guide Page 43 of 88 Vdc output Enable Bus OK Figure 9–9 — Output overvoltage protection 240 Vac range Rev 4.9 Apps. Eng. 800 927.9474 vicorpower.com 800 735.6200 9. Modular AC Front-end System (ENMod) Design Guide & Applications Manual For Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies FILTERING AND TRANSIENT PROTECTION The ENMod system maintains the DC output bus voltage between 250 and 370 Vdc over the entire input-voltage range, which is compatible with all Vicor 300 V input converters. Autoranging automatically switches to the proper bridge or doubler mode at startup depending on the input voltage, eliminating the possibility of damage due to improper line connection. The ENMod system is rated at 575 W output power. These modules can serve as the AC front end for any number and combination of compatible converters as long as the maximum power rating is not exceeded. CAUTION: There is no input to output isolation in the ENMods, hence the –Out of the ENMods and thus the –In of the downstream DC-DC converter(s) are at a high potential. If it is necessary to provide an external enable / disable function by controlling the DC-DC converter’s PC pin (referenced to the –In) of the converter an opto-isolator or isolated relay should be employed. FARM3 MODULE PIN DESCRIPTIONS Strap (ST) Pin. In addition to input and output power pin connections, it is necessary to connect the Strap pin to the center junction of the series hold-up capacitors (C1, C2) for proper (autoranging) operation. Varistors V1 and V2 provide capacitor protection. The bleeder resistors (R1, R2) discharge the hold-up capacitors when power is switched off. Capacitors C7 and C8 are recommended if the hold-up capacitors are located more than 3 inches (75 mm) from the output pins. Figure 9–10a — Peak detection Enable (EN) Pin. The Enable pin must be connected to the PC pin of all converter modules to disable the converters during power up. Otherwise, the converters would attempt to start while the hold-up capacitors are being charged through the current limiting thermistor, preventing the bus voltage from reaching the thermistor bypass threshold, thus disabling the power supply. The Enable output (the drain of an N channel MOSFET) is internally pulled up to 15 V through a 150 kΩ resistor. (Figure 9–11) A signal diode should be placed close to and in series with the PC pin of each converter to eliminate the possibility of control interference between converters. The Enable pin switches to the high state (15 V) with respect to the SR pin to turn on the converters after the power-up inrush is over. The Enable function also provides input overvoltage protection for the converters by turning off the converters if the DC bus voltage exceeds 400 Vdc. The thermistor bypass switch opens if this condition occurs, placing the thermistor in series with the input voltage, reducing the bus voltage to a safe level while limiting input current in case the varistors conduct. The thermistor bypass switch also opens if a fault or overload reduces the bus voltage to less than 180 Vdc. (Figure 9–3) Figure 9–10b — Quasi-peak detection Figure 9–10c — Average detection Maxi, Mini, Micro Design Guide Page 44 of 88 Rev 4.9 Apps. Eng. 800 927.9474 vicorpower.com 800 735.6200 9. Modular AC Front-end System (ENMod) Design Guide & Applications Manual For Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies Bus OK (BOK) Pin. (Figure 9–12) The Bus OK pin is intended to provide early-warning power fail information and is also referenced to the SR pin. Energy is given up by the capacitors as they are discharged by the converters. The energy expended (the power-time product) is: CAUTION: There is no input-to-output isolation in the ENMods. It is necessary to monitor Bus OK via an optoisolator if it is to be used on the secondary (output) side of the converters. A line-isolation transformer should be used when performing scope measurements. Scope probes should never be applied simultaneously to the input and output as this will damage the module. L, N Pins. Line and neutral input. ε = P∆t = C(V 12 where: P = operating power ∆t = discharge interval V1 = capacitor voltage at the beginning of ∆t V2 = capacitor voltage at the end of ∆t C = 2P∆t / (V12 – V22) SR Pin. Signal return for BOK and EN outputs. FOR MINIHAM MODULE PIN CONNECTIONS (Figure 9–1a) Filter. (Figure 9–1b) The input EMI filter consists of differential and common-mode chokes,Y-capacitors (lineground), and X-capacitors (line-line). This filter configuration provides sufficient common-mode and differential-mode insertion loss in the frequency range between 100 kHz and 30 MHz to comply with the Class B conducted emissions limit, as illustrated in Figures 9–10a thru 9–10c. Hold-up Capacitors. Hold-up capacitor values should be determined according to output bus voltage ripple, power fail hold-up time, and ride-through time. (Figure 9–13) Many applications require the power supply to maintain output regulation during a momentary power failure of specified duration, i.e., the converters must hold-up or ride-through such an event while maintaining undisturbed output voltage regulation. Similarly, many of these same systems require notification of an impending power failure in order to allow time to perform an orderly shutdown. The energy stored on a capacitor which has been charged to voltage V is: 2 where: (1) C = 2P∆t / (2052 – 1902) C = 2P∆t / (5,925) It should be noted that the series combination (C1, C2, Figure 9–1a) requires each capacitor to be twice the calculated value, but the required voltage rating of each capacitor is reduced to 200 V. Allowable ripple voltage on the bus (or ripple current in the capacitors) may define the capacitance requirement. Consideration should be given to converter ripple rejection and resulting output ripple voltage. Equation 3 is again used to determine the required capacitance. In this case, V1 and V2 are the instantaneous values of bus voltage at the peaks and valleys (Figure 9–13) of the ripple, respectively. The capacitors must hold up the bus voltage for the time interval (∆t) between peaks of the rectified line as given by: ∆t = (π – θ) / 2πf where: f = line frequency V = voltage across the capacitor Page 45 of 88 (3) The power fail warning time (∆t) is defined as the interval between Bus OK and converter shutdown (EN) as illustrated in Figure 9–13. The Bus OK and Enable thresholds are 205 V and 190 V, respectively. A simplified relationship between power fail warning time, operating power, and bus capacitance is obtained by inserting these constants in Equation (3): C = capacitance Maxi, Mini, Micro Design Guide (2) Rearranging Equation 2 to solve for the required capacitance: + / – Pins. Positive and negative outputs. ε = 1/2(CV ) ε = stored energy – V22) / 2 Rev 4.9 Apps. Eng. 800 927.9474 θ = rectifier conduction angle vicorpower.com 800 735.6200 (4) 9. Modular AC Front-end System (ENMod)s Design Guide & Applications Manual For Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies The approximate conduction angle is given by: θ = cos-1(V2 / V1) (5) Another consideration in hold-up capacitor selection is their ripple current rating. The capacitors’ rating must be higher than the maximum operating ripple current. The approximate operating ripple current (rms) is given by: Irms = 2P / Vac (6) where: P = total output power Determining the Ripple on the Output of the DC-DC Converter. Figure 9–17 is used to determine the ripple rejection of the DC-DC converter and indicates a ripple rejection of approximately 60 dB for a 12 V output. Since the ripple on the bus voltage is 12 Vac and the ripple rejection of the converter is 60 dB, the output ripple of the converter due to ripple on its input (primarily 120 Hz) will be 12 m Vp-p. A variety of hold-up capacitor options are available. Please visit our website at http://asp.vicorpower.com/calculators/calculators.asp?ca lc=4. Vac = operating line voltage Calculated values of bus capacitance for various hold-up time, ride-through time, and ripple voltage requirements are given as a function of operating power level in Figures 9–14, 9–15, and 9–16, respectively. Not used with VI-260/VI-J60 N +IN + 15 Vdc PC (GATE IN) BOK EMI GND 150 k FARM3 EXAMPLE SR In this example, the output required from the DC-DC converter at the point of load is 12 Vdc at 320 W. Therefore the output power from the ENMods would be 375 W (assuming a converter efficiency of 85%). The desired hold-up time is 9 ms over an input range of 90 to 264 Vac. L Vicor DC-DC Converter ST EN PR – –IN Microcontroller Figure 9–11 — Enable (EN) function Determining Required Capacitance for Power Fail Warning. Figure 9–14 is used to determine capacitance for a given power fail warning time and power level, and shows that the total bus capacitance should be at least 820 µF. Since two capacitors are configured in series, each capacitor should be at least 1,640 µF. Note that warning time is not dependent on line voltage. A hold-up capacitor calculator is available on the Vicor website, at http://asp.vicorpower.com/calculators/calculators.asp?calc=4. Determining Ride-through Time. Figure 9–15 illustrates ride-through time as a function of line voltage and output power, and shows that at a nominal line of 90 Vac, ride-through would be 68 ms. Ride-through time is a function of line voltage. N + 15 Vdc EMI GND 27 kΩ SR Page 46 of 88 BOK ST Secondary referenced EN Microcontroller – L FARM3 Figure 9–12 — Bus OK (BOK) isolated power status indicator Determining Ripple Voltage on the Hold-up Capacitors. Figure 9–16 is used to determine ripple voltage as a function of operating power and bus capacitance, and shows that the ripple voltage across the hold-up capacitors will be 12 Vp-p. Maxi, Mini, Micro Design Guide +5 Vdc Rev 4.9 Apps. Eng. 800 927.9474 vicorpower.com 800 735.6200 9. Modular AC Front-end System (ENMod) Design Guide & Applications Manual For Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies Hold-up Time Ripple (V p-p) π–θ Power Fail Warning θ 254 V 205 V 190 V Ride-Through Time Bus OK Power Fail Converter Shut down Figure 9–13 — General timing diagram of bus voltage following interruption of the AC mains 100 1,300 µF 1,600 µF 1,100 µF 820 µF 35 30 2,200 µF * 90 680 µF Ride-through Time (ms) Power Fail Warning Time (ms) 40 25 20 15 10 * 5 0 250 Operating Power (W) 80 70 60 50 40 90 Vac 20 10 0 250 500 Figure 9–14 — Power fail warning time vs. operating power and total bus capacitance, series combination of C1, C1 (Figure 9–1a) 115 Vac 30 Operating Power (W) 500 Figure 9–15 — Ride-through time vs. operating power 80 25 1,100 µF 820 µF 1,300 µF 1,600 µF 75 µF * 680 2,200 µF 20 Ripple Rejection (dB) P-P Ripple Voltage (Vac) 30 * 15 10 70 65 60 55 50 45 5 40 0 250 2 Operating Power (W) Figure 9–16 — Ripple voltage vs. operating power and bus capacitance, series combination of C1, C1 (Figure 9–1a) Maxi, Mini, Micro Design Guide Page 47 of 88 5 15 500 30 50 Output Voltage Figure 9–17 — Converter ripple rejection vs. output voltage (Typical) Rev 4.9 Apps. Eng. 800 927.9474 vicorpower.com 800 735.6200