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| 9 volt low current power supply circuit wanted. |
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| Jim0000:
I am looking for a circuit for a 240v mains supplied power supply that will deliver around 9 volts at 50ma max. The requirements are that this device be a small as possible. What it comes down to, is the question of finding a very small 240/12 volt transformer. I am able to design a full bridge rectifier, zender diode, cap and resistor regulated system. If someone can direct me to a source I would appreciate it. Jim. |
| MarkF:
I saw these for some else yesterday. I do not know how noisy these might. They seem simple enough with a 12V Wall Wart. They say they accept either AC or DC inputs. https://www.ebay.com/itm/AC-DC-Power-Supply-Buck-Converter-Step-Down-Module-3-3V-5V-9V-12V-15V-24V-36V-US/122832954547?hash=item1c996a24b3:m:mNop_RHwBUxr99MJ7MTU6Cg |
| Jim0000:
That would most likely do the job nicely. Is that a LM7809 regulator? I assume that it is. Thanks! |
| Jwillis:
Both examples from MarkF and blueskull are buck convertors .They are in a class of switch mode power supply (SMPS). The LM7809 is a linear regulator that would require a much larger package to facilitate a transformer and rectifier. But I'm sure either would be fine for your purposes. |
| mariush:
if you want to fully avoid switching power supplies, tme.eu sells some tiny pcb mounted transformers Here's a link with 7.5v..12v ac , 0.5va.. 2.5va : long link In theory a 7.5v transformer could be used if you don't need a stable 9v, like for ex. you just want a 9v battery replacement. you use a bridge rectifier which converts 7.5v ac to dc with peak of 7.5v x 1.414 - 2 diode drops ... so ~10.5v - 2 x 04..0.6v (low drop at 50mA) so around 8.v..9.5v You'd only need a capacitor to smooth the output .. let's say a 1000uF 16v cap would be enough ... c= i/[2 x Fac x (Vpeak-Vmin)] = 0.05/2x50x(9.5v-9v) =0.05/100x0.5 = 0.001 Farads Problem is when your circuit only consumes 5-10mA instead of 50mA.. at such low voltage and current transformers output much higher voltage at low load.. ex at 5mA a 7.5v ac transf. may output up to 25% more, let's say 9v ac.. which rectified could mean 10..11v dc So it may be better to go with 9v AC, rectify with bridge rectifier to ~11v, use a smaller electrolytic to guarantee a minimum of let's say 9.5v and then use a LDO to get 9v A 7809 or 1117 will need ~0.7v even at 50mA but there are ldos with 100..300mV drop at low currents. ex. 1.69$ each : 12v 1.9VA (158mA) 32.5 x 27.5 x 23.8mm 81g : https://www.tme.eu/en/details/bvei3032032/pcb-transformers/hahn/bv-ei-303-2032/ 1.95$ 12v 1.5va (125mA) more sqare-ish and taller 70g : https://www.tme.eu/en/details/tez1.5_d_12v/pcb-transformers/breve-tufvassons/tez1-5-d230-12v/ 1.95$ 9v 1.5va (166ma) same size/weight : https://www.tme.eu/en/details/tez1.5_d_9v/pcb-transformers/breve-tufvassons/tez1-5-d230-9v/ 2.00$ : 9v 1.8va (200mA) : https://www.tme.eu/en/details/bvei3022001/pcb-transformers/hahn/bv-ei-302-2001/ for ldo theres plenty mic5225 : https://www.digikey.com/product-detail/en/microchip-technology/MIC5225YM5-TR/576-2998-1-ND/1834780 ap2204k : https://www.digikey.com/product-detail/en/diodes-incorporated/AP2204K-ADJTRG1/AP2204K-ADJTRG1DICT-ND/4505290 lp2951 (100mA max) : https://www.digikey.com/product-detail/en/on-semiconductor/LP2951CDR2G/LP2951CDR2GOSCT-ND/2120680 etc... |
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