Modern Voltage Inverter Alternative To MC34063? - Page 1
Forum section: electronics / projects

author: hal9001
author_rank: Regular Contributor
timestamp: November 04, 2021, 10:37:14 am
content: I want to make a -18 V supply 120 mA max from a 5 V input. The MC34063 looks like it can do the trick but is there a modern efficient alternate to this chip?Cheers!

author: PartialDischarge
author_rank: Super Contributor
timestamp: November 04, 2021, 11:38:44 am
content: Use a buck converter that can handle at least 25V and use it in the inverting configuration.... LMR54410...etc

author: Terry Bites
author_rank: Super Contributor
timestamp: November 04, 2021, 03:34:01 pm
content: The MC34063 is good to 40V. Its cheap and available. Have a look at the ADP2442 an check the truth of their claims!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 05, 2021, 12:04:09 am
content: NCP3063 and 4 are improved versions; no need for the bad old one.Any boost regulator can also do Cuk configuration, with the catch that an inverter is needed to read the output voltage. CS5171 family has this in the even-numbered models:https://www.onsemi.com/pdf/datasheet/cs5171-d.pdfThere are a few high-side regulators or controllers (suitable for buck-boost or zeta), but not a whole lot that's interesting.Tim

author: hal9001
author_rank: Regular Contributor
timestamp: November 05, 2021, 06:21:58 am
content: Quote from: MasterTech on November 04, 2021, 11:38:44 amCan any buck be configured to be inverting?Quote from: T3sl4co1l on November 05, 2021, 12:04:09 amThanks Tim. CS5171 is a good option.. Will read to find if it can output enough current for -18 V.Besides higher frequency does the NCP3063 have other improvements? I read MC34063 gets hot at higher currents, is NCP3063 more efficient?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 06, 2021, 12:11:25 am
content: The problem with 34063 is, it fakes it. It has a current sense pin but its effect is to skew the oscillator duty cycle and frequency, it only acts to limit current by coincidence; it works under certain assumptions (namely, that the output is around nominal V, I).3063/4 actually does a proper current limit and on/off latch, as you'd expect. It's a bit faster. It's still shitty hysteretic control, so don't expect great output ripple. And it's bipolar so don't expect miracles on efficiency (especially annoying for a 5V input application; might be worthwhile using it as a controller into a MOSFET).The CS5171 seems to have the quirks that its error amp has really, really wonky transconductance. I'm not sure if it's actually intentional, or some strange accident of available topology, it's weird. The characteristic is, gm is very dependent on input value, much higher in one direction than the other. I guess it could improve transient response, but the effect is, if it's not compensated stable, it goes batshit crazy, chaotic oscillation -- it's harder to figure out which way the compensation components need to go, because it's not singing at some resonant frequency. Seems alright once it's stable though.Tim

author: magic
author_rank: Super Contributor
timestamp: November 06, 2021, 07:01:17 am
content: Quote from: T3sl4co1l on November 06, 2021, 12:11:25 amThat alone could be a good reason for using the improved part.It also has thermal shutdown, unlike the 34063.All of those chips use darlington swiches so expect up to 1V drop when driving low (open collector, boost) and up to 2V when driving high (emitter follower, buck/inverting). This is documented in the datasheets, of course.

author: hal9001
author_rank: Regular Contributor
timestamp: November 09, 2021, 10:56:19 am
content: Quote from: T3sl4co1l on November 06, 2021, 12:11:25 amThanks! Because there are changes in the NCP3063, are the calculations for circuit components the same as for MC34063? Lots of online calculators are available for MC34063 but not so for NCP3063.