Author Topic: What is a "Switching Power Supply"  (Read 109 times)

veggie

  • Keep Calm and Start the Lister !
  • Sr. Member
  • ****
  • Posts: 454
    • View Profile
What is a "Switching Power Supply"
« on: August 22, 2019, 09:02:02 PM »
Excuse my ignorance but...

What is a "Switching" power supply vs other power supplies?
And when does one need a switching power supply.?
- 6/1 GM90 Listeroid - Delco 33si Alternator
- Changfa R175 - Lease/Neville Alternator
- Kubota Z482 - 4kw
- JiangDong R165 Air cooled - 2 kw

mike90045

  • Mendocino Metro
  • Hero Member
  • *****
  • Posts: 1379
  • Mmmm BBQ
    • View Profile
    • Mikes Solar PV page
Re: What is a "Switching Power Supply"
« Reply #1 on: August 22, 2019, 09:38:37 PM »
A Linear Supply has a step down transformer and diode bridge, and an IC that controls a PASS Transistor to regulate the output  50-60% efficient.  No Power Factor correction easily possible.

A Switcher rectifies the line voltage to DC, powers a high frequency oscillator and uses a tiny thimble sized transformer to convert the voltage.  The regulator IC controls the frequency to regulate the voltage, which is then rectified to usable DC at the desired voltage.   95% efficient and can often have Power Factor correction implemented.

BruceM

  • Hero Member
  • *****
  • Posts: 2751
    • View Profile
Re: What is a "Switching Power Supply"
« Reply #2 on: August 22, 2019, 10:38:52 PM »
Here's a good summary:
https://en.wikipedia.org/wiki/Switched-mode_power_supply

The potential efficiency and PF of linear supplies is misrepresented by Mike. If the linear supply uses a higher efficiency toroidal transformer (93 to 96%), efficiency can be quite good.  Likewise, if a toroidal inductor is used as the primary filter, instead of capacitor, the PF can be 1. Using output voltage close to the desired regulated voltage with a low dropout regulator also improves performance, which can then 85-90%.  What he says is true for the cheapest, most poorly designed linear supplies, but he has not used this same criteria for switching supplies.  All linear supplies generate very low levels of EMI, as the only significant source is diode on/off noise at 120Hz. 

Mike has also misrepresented the typical efficiency of switching supplies and their PF.  Most are around 80-85% and for low power ones, as low as 60%. Most wall warts sold with products made in China will have both piss poor PF and efficiency.  The 95% efficiency he states is pure fantasy, virtually unheard of for switching, transformer isolated power supplies. Even most buck converters, the simplest and most efficient of all DC to DC (down only) converters can rarely achieve 95% except in the hands of marketing bullshit artists.

One characteristic of all switching supplies stated in every textbook on EMI mitigation and the field of Electro- Magentic Compatibility or EMC is substantial conducted and directly radiated EMI. It is a serious design challenge to reduce/suppress this EMI as it is inherent to high speed switching.

One characteristic noted by researcher MD Milham and other independent researchers is that the presence of high levels of EMI on home/workplace wiring such as schools is related to  accelerated cancer growth rates.  Those with unfiltered off grid inverter systems often have very high levels of EMI.  Inline commercial 2 or 3 stage passive filters on the inverter AC output and PV cables seem a wise and inexpensive health insurance.  Due to severe cost pressures, the inverter designers, such as the good ones I've talked to at Magnum, just aren't allowed to do the EMC improvements they'd like to and are well aware of.  Since the public is unaware of the situation, and HUGE potential liabilities prevent disclosure, the problem is ignored.

I notice that people often develop serious new or severely aggravated old health problems within a relatively small number of years of moving off grid, and what I've seen lately in on-grid homes, with the spread of poorly designed switching supplies in electric ranges, washers, dryers and refrigerators (on 24/7 even when the appliance is "off"), this would also help account for the increasing rate of chronic illnesses and cancers in on-grid homes, where home power EMI is now nearly as bad as off grid has been for the last 40 years.

In the past, some of the worst cases of grid power EMI  in the home are from inside the home due to micro arcing on thermal fuses or corroded contacts in appliances or small transformers, or are delivered via power company, from induced arcing on loose and corroded metal insulator support structures on power poles within 2 miles of the home.  This power line EMI, well covered by the US ham radio community and Marv Loftness's book on Power Line Interference can completely obliterate all AM radio reception in and near the home.

While the power co.s  once policed their own lines to find and fix these sources, many now do not unless there are many complaints about radio/TV reception.

Conventional public health "wisdom"/experts (mouthpieces for teleom industry)  says all radio waves and EMI is harmless unless strong enough to heat you like a hot dog, despite hundreds of peer reviewed, published papers by independent researcher's findings showing otherwise.  It's a profitable problem to ignore, except for the people who are struggling with "excess cancer rates" and serious chronic illnesses.









veggie

  • Keep Calm and Start the Lister !
  • Sr. Member
  • ****
  • Posts: 454
    • View Profile
Re: What is a "Switching Power Supply"
« Reply #3 on: August 23, 2019, 01:13:03 AM »

Very good explanations.

Thanks guys.
- 6/1 GM90 Listeroid - Delco 33si Alternator
- Changfa R175 - Lease/Neville Alternator
- Kubota Z482 - 4kw
- JiangDong R165 Air cooled - 2 kw