Presented here is an isolated 6-W dc-dc converter optimized to provide low-cost and efficient isolated power across a 2500-V ac potential barrier. The converter, which incorporates inexpensive, readily available components, can provide either two isolated 3-W outputs (Fig. 1a) or one isolated 6-W output (Fig. 1b).

The CD4001, a CMOS quad NOR gate, is configured as an RC relaxation oscillator. The frequency is set at approximately:

F_OSC = 0.6/(R2 × C1)
      = 0.6/(10 kΩ × 220 pF)
      = 273 kHz

Actual measurement of the circuit came out to 250 kHz. Resistor R3 has a value that may vary and might need to be terminated to V_DD or ground. R3 is inserted to adjust the oscillator trip point so that a 50% duty-cycle waveform is available at the output of U1a and its complement is available at U1b.

This square wave and its complement are connected to the INA and INB inputs of the IXDD404SI, a 4-A dual-gate driver. The outputs, OUTA and OUTB of U2, are then applied to the primary of T1, a VAC #T60403-F4025-X142 transformer that has a single primary and 2500-V ac isolated, dual-secondary windings.

The converter is designed to function over a 13.5- to 25-V V_CC power range. C5, which blocks dc from T1's primary, and C6 and C7, which filter the floating dc outputs, are all low-voltage, low equivalent-series resistance and equivalent-series inductance, multilayer ceramic capacitors. D1 and D2, which are DDS10-40BA 1-A Schottky diodes, half-wave rectify the resulting square-wave output from T1.

D1 and D2 are connected in an anti-parallel configuration, minimizing T1 saturation at high currents. For a single isolated output, the portion of the converter after T1's secondary is modified as shown in Figure 1b, where D1 and D2 form a push-pull output. Because of the wide V_CC supply-voltage variation, a 15-V zener diode (Z1) is used to limit the voltage supplied for U1 to +15 V or less.

Total manufacturing volume costs for the isolated dc-dc converters are less than $3, or about $0.50/W. The total volume of the solution is about 0.25-in.³

Figure 2 shows both V_OUT1 and V_OUT2 loaded equally with R_L1 = R_L2. Figure 3 plots converter efficiency, (P_OUT/P_IN) × 100%, for various power outputs and V_CC voltages where:

P_OUT = (V_Float1)²/R_L1 + (V_Float2)²/R_L2,

and P_IN = V_CC × I_CC

Note that efficiency is over 80% for total V_OUT1 and V_OUT2 power levels of 6 W, or 200 mA each for V_OUT1 and V_OUT2 set at 15 V.

Reprints

Printer-Friendly

Email this Article

RSS

Submit PlanetEE del.icio.us Digg Reddit Newsvine StumbleUpon Netscape Yahoo MyWeb Live Bookmarks Fark  Submit

Font Size

What's This?

Ground-Fault Relay Avoids Nuisance Trips Low-Cost Common-Mode Chokes Deliver High Performance Front-End Supplies Take Digital Control Up A Notch Power-Entry Modules Now Offer Vertical Flange Mounting Bluetooth Modules Scrub For Medical Apps Laser Diode Performs At 1,400 nm To 2,000 nm

Engineers Rely On Internet For Product Info Rochester Electronics Establishes New Design and Technology Group Custom Sources Light Way To 22-nm IC Lithography In EDA, A Year Of Mergers, Failed And Otherwise Software Turns Scopes Into Vector RF Signal Analyzers Couple’s $15 Million Gift Advances Rice Engineering Education November 7, 2008 Startup Sets Sail For Speedier Spice Simulation

1) Ten Top Design Skills For Tough Times (3285 views today) 2) Build A Smart Battery Charger Using A Single-Transistor Circuit (332 views today) 3) Energy Harvester Perpetually Powers WIreless Sensors (322 views today) 4) Ultracapacitors Branch Out Into Wider Markets (300 views today) 5) Technology Has Been Very Good To Obama, And He Plans To Reciprocate (184 views today) ALL TOP 20

Reader Comments Excellent design. Contact me if you wanna sell these. SHYAM SUNDER TIWARI -May 02, 2007   (Article Rating: ) Thanks for the article. I have a suggestion to the authors to put it in your books because i've read many famous books where i've searched a lot for these articles. books : Chuttayile sheelam chudela vare Matthi vitta papachan Sheela's Apples with electronics. Sashi's Miracles with Protons. Invent your circuit by Mahindra Kill me and burn my bike by Sharath. Enikangana sambhavamakam by sambhvami yuge yuge How to get beatings by Akshay Raghavan -September 16, 2005   (Article Rating: ) This is a well designed site which was more informative. Actually my life partner kumarraja informed me about this and it is really fantastic. I think the information will add more value in our married life. - shyingly Nirubitha Nirubitha -September 15, 2005   (Article Rating: ) I WAS VERY MUCH AMAZIING WITH THIS SITE! VERY EXCELLENT FOR DESIGNERS KUMARARAJA -September 14, 2005 i got the equations form this notes which i searched lots of books from authors like panter,velayudhan's electrons,keshavan with kalam etc. athul -September 14, 2005   (Article Rating: ) The article has been very informative. I need help on the source for the 1A schottky diodes Thanks Dinesh Dinesh BR -August 08, 2005   (Article Rating: ) schematic regulator buck fajar sidik supradi -August 03, 2005   (Article Rating: ) Thanks for the article. I found the VAC website, but I am having trouble finding data on the transformer, could you please help. Thanks, Chuck Charles Lidstone -November 19, 2004
POST YOUR COMMENTS HERE Name: Email:
Your Comments: Enter the text from the image below Please refresh the page if you have trouble reading this text.