DC to DC Power Supply Design - Page 1
Forum section: electronics / projects

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 23, 2020, 04:13:32 pm
content: HI. I am wondering if anyone can shed some light on this DC to DC power supply design? (see attached image).I am not sure exactly what is going on here as I have never dealt with this type of power supply before.I can see that it outputs +5V (VCC)and ground is AGso I am assuming VEE is -5V? But it is not labelled.I may be missing something obvious but can anyone explain what is going on with this circuit and how it is generating a negative voltage from the +5VDC?I am working on a little project which requires both a +5V and -5V supply, and I am looking at powering it from USB, which of course is only +5V.Any alternative designs or suggestions are welcome.Thank you.

author: Mark
author_rank: Frequent Contributor
timestamp: October 23, 2020, 05:14:27 pm
content: Depending on your current requirements, what about the LTC1044? 5Vin, -5Vout.The LTC®1044 is a monolithic CMOS switched capacitorvoltage converter which is manufactured using AnalogDevices’ enhanced LTCMOS™ silicon gate process. TheLTC1044 provides several voltage conversion functions:the input voltage can be inverted (VOUT = –VIN), doubled(VOUT = 2VIN), divided (VOUT = VIN/2) or multiplied (VOUT= ± nVIN).

author: Mark
author_rank: Frequent Contributor
timestamp: October 23, 2020, 05:17:45 pm
content: Another option for a possibly cleaner supply: LTC3265, so this part takes 5V from USB, boosts the voltage and uses LDO for lower noise +/- outputs.Boost Charge Pump Generates 2 • VIN_P(VIN_P Range: 4.5V to 16V)Inverting Charge Pump Generates –VIN_N(VIN_N Range: 4.5V to 32V)Low Noise Positive LDO Post Regulator Up to 50mALow Noise Negative LDO Post Regulator Up to 50mA

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 23, 2020, 06:00:00 pm
content: It's a blocking oscillator, though not a great one I think. Would be okay for low to modest currents, where efficiency and ripple don't matter. The transformer could be a small pulse transformer, coupled inductor, or even some common mode chokes.Tim

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 24, 2020, 03:53:23 pm
content: Thanks everyone! Using the information you all have provided I think the simplest solution for me is to use an ICL7660 (because they are cheap and easy to get). I found that it is a compatible IC for the aforementioned LTC1044.Additionally, the output current of the 7660 far exceeds what my circuit needs on the -5V rail.After reading the data-sheet for the ICL7660 and looking up some example circuits, I have come up with the attached schematic. Anyone have any opinions on this design or suggestions for improvement?

author: tooki
author_rank: Super Contributor
timestamp: October 24, 2020, 04:37:41 pm
content: For what it's worth, in a project I'm working on, we are using the TI TPS65133 to get ±5V rails from a single Li-Ion battery (3.7V). I simply duplicated the layout and component choices from the datasheet and it works perfectly, being clean enough for audio.

author: eplpwr
author_rank: Regular Contributor
timestamp: October 24, 2020, 07:47:28 pm
content: Quote from: paul_g_787 on October 24, 2020, 03:53:23 pmC2 has the polarity wrong.

author: LaryPant
author_rank: Contributor
timestamp: October 26, 2020, 10:32:46 am
content: Quote from: eplpwr on October 24, 2020, 07:47:28 pmEdit: I was looking at the wrong schematic. Disregard everything down below.No it does not.C2 is connected between Vee and ground. Vee is at -5 V and ground is zero. So the positive terminal should be connected to ground, as is shown in the circuit diagram. Ground is at a higher potential than Vee.By your logic C3 would have no polarity wrong as well, but it is correct AFAIK.The positive terminal of a capacitor goes to the highest potential, and in this case it is ground and not Vee.Lary

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 26, 2020, 01:26:33 pm
content: Are you looking at the wrong one?C2 positive goes to "-5V", pretty obvious typo, just flip it around.Tim

author: LaryPant
author_rank: Contributor
timestamp: October 26, 2020, 01:35:24 pm
content: Quote from: T3sl4co1l on October 26, 2020, 01:26:33 pmOh dammit, I looked at the original schematic.Sorry!I will update my other post.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: November 12, 2020, 11:14:21 pm
content: Quote from: eplpwr on October 24, 2020, 07:47:28 pmYes indeed!. I did notice that too and have corrected it but thanks for pointing it out