On Saturday, April 15, 2023 at 1:21:01 PM UTC+10, boB wrote:> On Fri, 14 Apr 2023 08:41:38 -0700 (PDT), Ricky > <gnuarm.del...@gmail.com> wrote: > > >On Friday, April 14, 2023 at 10:07:39?AM UTC-4, Lamont Cranston wrote: > >> On Friday, April 14, 2023 at 9:04:12?AM UTC-5, Fred Bloggs wrote: > >> > On Friday, April 14, 2023 at 9:59:07?AM UTC-4, Lamont Cranston wrote: > >> > > I have a Toshiba 3.4A, 19V laptop power supply that I want to reduce to 12V. > >> > > Is it as simple as finding a 19V zener and changing it to a 12v zener? > >> > > Thanks, Mikek > >> > No. That question is beyond unbelievable. > >> Well not really unbelievable. > >> Is there reference against which the output voltage is compared to in a switching power supply? > > > >The whole of the power supply is designed for providing 19V. If you try to change that to 12V, you would need to go through the design process again, to assure it will work correctly. > > > >To answer your question, there is typically a resistor divider that feeds a portion of the output voltage to the controller chip. This is compared to an internal reference (or it could be a separate reference, but that's not important). To change the output voltage, you change one or both of those resistors. If the circuit has capacitors in parallel with the resistors, make sure you get the data sheet for the controller part and adjust the capacitors if required. > > > >Why not just buy a 12V supply (there's plenty of them around)? If you buy off eBay or Alibaba, be sure to derate the power output by 2 or 3 or 4x. > > I highly doubt that a 19V laptop is going to run at 12V.That's because you are an ignorant idiot.> You MIGHT get lucky ?> I would bet it won't work.Not a good bet. The off-the-shelf 12V supply I posted a link to runs from 90V AC to 264V AC, and Toshiba lap-top supply is probably going to be equally flexible. Pushing out 12V rather than 19V just means running at a different mark-to-space ratio. It shouldn't be a problem. -- Bill Sloman, Sydney
Reducing voltage of laptop power supply
Started by ●April 14, 2023
Reply by ●April 15, 20232023-04-15
Reply by ●April 15, 20232023-04-15
On Friday, April 14, 2023 at 11:21:01 PM UTC-4, boB wrote:> On Fri, 14 Apr 2023 08:41:38 -0700 (PDT), Ricky > <gnuarm.del...@gmail.com> wrote: > > >On Friday, April 14, 2023 at 10:07:39?AM UTC-4, Lamont Cranston wrote: > >> On Friday, April 14, 2023 at 9:04:12?AM UTC-5, Fred Bloggs wrote: > >> > On Friday, April 14, 2023 at 9:59:07?AM UTC-4, Lamont Cranston wrote: > >> > > I have a Toshiba 3.4A, 19V laptop power supply that I want to reduce to 12V. > >> > > Is it as simple as finding a 19V zener and changing it to a 12v zener? > >> > > Thanks, Mikek > >> > No. That question is beyond unbelievable. > >> Well not really unbelievable. > >> Is there reference against which the output voltage is compared to in a switching power supply? > > > >The whole of the power supply is designed for providing 19V. If you try to change that to 12V, you would need to go through the design process again, to assure it will work correctly. > > > >To answer your question, there is typically a resistor divider that feeds a portion of the output voltage to the controller chip. This is compared to an internal reference (or it could be a separate reference, but that's not important). To change the output voltage, you change one or both of those resistors. If the circuit has capacitors in parallel with the resistors, make sure you get the data sheet for the controller part and adjust the capacitors if required. > > > >Why not just buy a 12V supply (there's plenty of them around)? If you buy off eBay or Alibaba, be sure to derate the power output by 2 or 3 or 4x. > I highly doubt that a 19V laptop is going to run at 12V. > > You MIGHT get lucky ? > > I would bet it won't work.Some of us do engineering by using design principles and reading data sheets. A lot of people here just like to hack. I think I know which camp you are in. -- Rick C. + Get 1,000 miles of free Supercharging + Tesla referral code - https://ts.la/richard11209
Reply by ●April 15, 20232023-04-15
On 14/04/2023 15:07, Lamont Cranston wrote:> On Friday, April 14, 2023 at 9:04:12 AM UTC-5, Fred Bloggs wrote: >> On Friday, April 14, 2023 at 9:59:07 AM UTC-4, Lamont Cranston wrote: >>> I have a Toshiba 3.4A, 19V laptop power supply that I want to reduce to 12V. >>> Is it as simple as finding a 19V zener and changing it to a 12v zener? >>> Thanks, Mikek >> No. That question is beyond unbelievable. > > Well not really unbelievable. > Is there reference against which the output voltage is compared to in a switching power supply? > > MikekThe simplest solution might be to find someone else with a scrap 12v laptop PSU that wants to swap it for a 19v one! A bit like the lateral thinking solution to height of a tall building using a barometer. Offer to give the barometer to the janitor if he can tell you how tall the building is! How near to 12v does it need to be and at what current? You could daisy chain an external regulator onto it. -- Martin Brown
Reply by ●April 15, 20232023-04-15
On 14-04-2023 15:59, Lamont Cranston wrote:> I have a Toshiba 3.4A, 19V laptop power supply that I want to reduce to 12V. > Is it as simple as finding a 19V zener and changing it to a 12v zener? > Thanks, MikekIt's almost 100% certain to be controlled with a shunt feedback regulator like the TL431. So you can change a single resistor and it will provide 12V instead. Provided that the power supply designer did his job and made sure there is enough phase margin at lower output voltage. Change RFB1 in linked schematics: https://i.stack.imgur.com/s8rg4.png Do not change RFB2 since that is directly used for the feedback loop stability. Cheers Klaus
Reply by ●April 16, 20232023-04-16
On 14/04/2023 14:59, Lamont Cranston wrote:> I have a Toshiba 3.4A, 19V laptop power supply that I want to reduce to 12V. > Is it as simple as finding a 19V zener and changing it to a 12v zener? > Thanks, MikekGiven that 19V is a *very* common laptop supply voltage, I wouldn't be surprised if they used a fixed 19V supply chip. -- Cheers Clive
Reply by ●April 16, 20232023-04-16
On 2023-04-14, Lamont Cranston <amdx62@gmail.com> wrote:> I have a Toshiba 3.4A, 19V laptop power supply that I want to reduce to 12V. > Is it as simple as finding a 19V zener and changing it to a 12v zener? > Thanks, Mikekno. If you're lucky the aux winding on the main flyback transformer Produces enough output to keep the controller running when the output is reduced by 35% Then all you need to do is find the feedback path (usually through an opto-isolator) and modify whatever circuit is driving that to trigger at 12V instead of 19V - it might be a zener diode. or it could be using a TL431 etc... If you're unlucky the auxillary winding isn't going to provide enough power and then it's not going to work unless you can modify the transformer. -- Jasen. 🇺🇦 Слава Україні
Reply by ●April 16, 20232023-04-16
On Sunday, April 16, 2023 at 10:01:47 PM UTC+10, Clive Arthur wrote:> On 14/04/2023 14:59, Lamont Cranston wrote: > > I have a Toshiba 3.4A, 19V laptop power supply that I want to reduce to 12V. > > Is it as simple as finding a 19V zener and changing it to a 12v zener? > > Thanks, Mikek > Given that 19V is a *very* common laptop supply voltage, I wouldn't be > surprised if they used a fixed 19V supply chip.I would. On-chip voltage references aren't all that tightly specified, so you have to have a twiddle mechanism to get exactly 19V out. Once you have that twiddle mechanism you can use the same chip for a range of supply voltages. I do exclude the National Bureau of Standard voltage reference chip - it does have a very tightly specified output, but it is a stack of Josephson junctions running in liquid helium. https://www.nist.gov/news-events/news/2013/04/primary-voltage-standard-whole-world -- Bill Sloman, Sydney
Reply by ●April 18, 20232023-04-18
On 2023-04-16, Clive Arthur <clive@nowaytoday.co.uk> wrote:> On 14/04/2023 14:59, Lamont Cranston wrote: >> I have a Toshiba 3.4A, 19V laptop power supply that I want to reduce to 12V. >> Is it as simple as finding a 19V zener and changing it to a 12v zener? >> Thanks, Mikek > > Given that 19V is a *very* common laptop supply voltage, I wouldn't be > surprised if they used a fixed 19V supply chip.with a built in opto-isolator? -- Jasen. 🇺🇦 Слава Україні
Reply by ●April 18, 20232023-04-18
I'm just going to use the 19V to run the heaters, and add a 12V regulator to power the Arduino and the 12V relays I have.
I have tested with all 5 heaters in series on 19V (6 Watts) it is not enough heat, so I'll probably go with the 30 Watt configuration using four heat strips.
Although if I parallel two and parallel 3, then put those in series, it is 31 watts and I can have a little better heat distribution. ( I have 5 heat strips)
Mikek
Reply by ●April 18, 20232023-04-18
On Tuesday, April 18, 2023 at 11:25:43 AM UTC-4, Lamont Cranston wrote:> I'm just going to use the 19V to run the heaters, and add a 12V regulator to power the Arduino and the 12V relays I have. > I have tested with all 5 heaters in series on 19V (6 Watts) it is not enough heat, so I'll probably go with the 30 Watt configuration using four heat strips. > Although if I parallel two and parallel 3, then put those in series, it is 31 watts and I can have a little better heat distribution. ( I have 5 heat strips) > MikekYou will do well to provide better insulation around the bits you are heating. I believe you are heating the space between the buckets, which would be your insulation, but if you are heating it, it ain't insulating. Maybe you need a third bucket, or can wrap the entire thing with corrugated cardboard. That includes a bit of air gap that would be better than nothing. In fact, if the buckets will nest enough, the cardboard could be the insulation between them, with the heating strips between the cardboard and the inner bucket. You don't need to worry so much about distributing the heat. The heat will flow, from the heaters, to the outside. The inner part will not have so much temperature variation, unless that heat flow is through the part you are trying to heat. If the top and/or bottom are not insulated, then the heat will flow through the core to the top and/or bottom, creating a temperature gradient. So insulate all sides. Not trying to criticize, but I think I would have started with a box. The heaters could be near the bottom, and all sides insulated, with a door on a hinge. Line with even a thin layer of styrofoam and you can keep it warm with a 7W night light. Do they still sell 7W, incandescent night lights? lol -- Rick C. -- Get 1,000 miles of free Supercharging -- Tesla referral code - https://ts.la/richard11209
