This is a multi-part message in MIME format. ------=_NextPart_000_02E6_01C13024.9F1FC5A0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit OK - here are some actual test results from the divinely inspired super low cost switching regulator. I have included results below in an approximately unreadable table plus attached an Excel spreadsheet. This is in Excel Version 2.1 format which keeps the size small and should be readable by most other spreadsheet programs. Pasting the table below into a document with fixed width (eg Courier) font makes it reasonably readable. (I used notepad in Windoze 95 as a trial and it worked fine.) Tests were carried out from about 8 volts to 30 volts in with loads of open circuit, 1000 ohms and 100 ohms. Vout was about 11.3 volts nominal giving output currents of about 11 mA and 110 mA for 1k and 100 r respectively.. These test were made on a circuit intended to operate at 600 mA out working, 1 amp max at 11 volts with 10 < Vin < 200 volts. NO changes were made to the circuit for low power or lower voltage operation. The main switch is a P channel FET with RDSon = 1 ohm !!! There is also additional current limiting circuitry present which does not affect performance at all but may add slightly to current drain The FET is driven by a high side driver (BC327) - removing the FET and using this transistor as the main switch should produce superior results but I haven't tried this yet - another night. The Inductor is relatively immense as it is designed to allow reasonably low switching times at Vin = 200 volts. This uses over 200 turns on a Micrometal I-really-can't-remember-and-its-downstairs-and-its-late-and-nobody-will-care toroid. I'll dig up the size and spec if anyone is interested. (Just wind some turns on a toroid that will fit over a pencil and try it. Buck converters can be pretty tolerant :-) .) The only "plus" for this circuit over one purpose designed for low power levels is that this uses a BYV28 flyback diode which is liable to give less losses than a diode liable to be used at the lower power levels. For very low current applications a super cheap diode that would work OK would be a 1N9148.(!)(Probably the world's most common and cheapest semiconductor). Results: ********** NO LOAD ++++++++ Input current ranged from 0.22 mA at Vin = 8 volts to 0.65 mA at Vin = 30v. Note the slight drip in Iin at Vin = 11.5 volts as the regulator switches from linear to buck modes. This idle current is a significant part of the efficiency losses when 100r load is used and optimisation for low current levels should produce superior results. 1000 r LOAD +++++++++ Efficiency ranged from over 90% at Vin <= 13 volts with about 3% of losses being due to idle current to 55% at Vin = 30 volts with idle current contributing about 8% of losses. A linear regulator at Vin = 30 volts would be about 38% efficient giving losses higher by a factor of (100-38)/(100-55) = 1.38 times. The regulator is more efficient than a linear regulator for all Vin >= 13v with best ratio at Vin = 25 volts. 100r LOAD ++++++++++ Efficiency ranged from over 90% at Vin <= 13 volts to about 76% at Vin = 30 volts Idle current is an insignificant part of losses at this load. A linear regulator at Vin = 30 volts would be about 38% efficient giving losses higher by a factor of (100-38)/(100-55) = 1.38 times. The regulator is more efficient than a linear regulator for all Vin >= 13v with best ratio at Vin = 25 volts. Efficiency compared to a linear regulator increased with increasing Vin and hadn't topped out by Vin = 30 volts. Ratio of Eff-buck/Eff-linear at 30 volts = ~~ 2:1 at 76% versus 38% Relative dissipations would be (100-38)/(100-76) = 2.6 times as high in the linear regulator. COMMENTS *************** Improvements will be obtained by - Optimising the design for the target load range - ditto target Vin range - Changing nasty FET to a small bipolar. (The FET is used because of its suitability at high voltages and higher power levels - this is not relevant here). - Changing inductor I'll try to get to testing a more low power optimise design shortly. regards Russell McMahon _____________________________________ *** VIEW WITH FIXED WIDTH FONT (eg COURIER) *** Low cost buck converter Non optimised design No Load 1 K load 100 r load Vin Vout Iin mA Vout Iin mA Pout mW Effic % Vout Iin Pout mW Effic % = Iout mA = Iout/10 8 8 0.22 mA 9 9 0.25 10 10 0.28 11 11 0.32 11.5 11.31 0.28 12 11.31 0.28 11.30 11.5 128 92.9% 11.10 111 1232 92.5% 13 11.31 0.3 11.31 10.8 128 91.1% 11.29 110 1275 89.1% 14 11.31 0.32 15 11.32 0.34 11.31 10.1 128 84.3% 16 11.32 0.36 11.31 9.8 128 81.7% 11.22 99 1259 79.5% 18 11.32 0.4 11.32 9.3 128 77.0% 20 11.32 0.44 11.32 8.8 128 73.1% 11.29 79.5 1275 80.2% 25 11.33 0.54 11.34 7.1 129 72.1% 11.30 66.3 1277 77.0% 30 11.34 0.65 11.33 7.8 128 54.6% 11.31 56.3 1279 75.7% These test were made on a circuit intended to operate at 600 mA out working, 1 amp max at 11 volts with 10 < Vin < 200 volts The main switch is a P channel FET with RDSon = 1 ohm !!! No changes were made to any components. 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