tutorials:learn:powersupply:transformeracdc.html
Differences
This shows you the differences between two versions of the page.
| Both sides previous revision Previous revision Next revision | Previous revision | ||
|
tutorials:learn:powersupply:transformeracdc.html [2010/10/26 16:07] ladyada |
tutorials:learn:powersupply:transformeracdc.html [2016/01/28 18:05] (current) |
||
|---|---|---|---|
| Line 37: | Line 37: | ||
| {{http://www.ladyada.net/images/parts/1n4001.jpg?350}} | {{http://www.ladyada.net/images/parts/1n4001.jpg?350}} | ||
| - | You'll want to use a [[http://www.ladyada.net/wiki/partfinder/diodes#power_blocking|power diode such as a 1N4001]], they're extremely common and can put up with a lot of abuse. The side with the silver stripe matches the schematic symbol side that the 'arrow' in the diode symbol is pointing to. Thats the only direction that current can flow. The output is then chopped in half so that the voltage only goes positive | + | You'll want to use a [[http://www.ladyada.net/wiki/partfinder/diodes#power_blocking|power diode such as a 1N4001]], they're extremely common and can put up with a lot of abuse. The side with the silver stripe matches the schematic symbol side that the 'arrow' in the diode symbol is pointing to. That's the only direction that current can flow. The output is then chopped in half so that the voltage only goes positive |
| {{:tutorials:learn:powersupply:halfsch.png?500|}} | {{:tutorials:learn:powersupply:halfsch.png?500|}} | ||
| Line 49: | Line 49: | ||
| {{:tutorials:learn:powersupply:halfwave.png?500|}} | {{:tutorials:learn:powersupply:halfwave.png?500|}} | ||
| - | What we have now isnt really AC and isnt really DC, its this lumpy wave. The good news is that it's only positive voltage'd now, which means its safe to put a capacitor on it. | + | What we have now isnt really AC and isn't really DC, its this lumpy wave. The good news is that it's only positive voltage'd now, which means its safe to put a capacitor on it. |
| This is a 2200 microFarad (0.0022 Farad) capacitor, one leg has (-) signs next to it, this is the negative side. The other side is positive, and there should never be a voltage across is so that the negative pin is 'higher' than the positive pin or it'll go POOF | This is a 2200 microFarad (0.0022 Farad) capacitor, one leg has (-) signs next to it, this is the negative side. The other side is positive, and there should never be a voltage across is so that the negative pin is 'higher' than the positive pin or it'll go POOF | ||
| Line 55: | Line 55: | ||
| {{http://www.ladyada.net/images/parts/2200uf.jpg?300}} | {{http://www.ladyada.net/images/parts/2200uf.jpg?300}} | ||
| - | A capacitor **smoothes** the voltage out, taking out the lumps, sort of how spring shocks in car or mountain bike reduce the bumpiness of the road. Capacitors are great at this, but the big capacitors that are good at this (electrolytic) can't stand negative voltages - they'll explode! | + | A capacitor **smooths** the voltage out, taking out the lumps, sort of how spring shocks in car or mountain bike reduce the bumpiness of the road. Capacitors are great at this, but the big capacitors that are good at this (electrolytic) can't stand negative voltages - they'll explode! |
| {{:tutorials:learn:powersupply:halfwavecapsch.png?500|}} | {{:tutorials:learn:powersupply:halfwavecapsch.png?500|}} | ||
| Line 63: | Line 63: | ||
| Because the voltage is very uneven (big ripples), we need a really big electrolytic-type capacitor. How big? Well, [[http://en.wikipedia.org/wiki/Ripple_%28electrical%29|there's a lot of math behind it which you can read about]] but the rough formula you'll want to keep in mind is: | Because the voltage is very uneven (big ripples), we need a really big electrolytic-type capacitor. How big? Well, [[http://en.wikipedia.org/wiki/Ripple_%28electrical%29|there's a lot of math behind it which you can read about]] but the rough formula you'll want to keep in mind is: | ||
| - | Ripple voltage = Current draw / (Ripple frequency) * (Capacitor size) | + | Ripple voltage = Current draw / ( (Ripple frequency) * (Capacitor size) ) |
| or written another way | or written another way | ||
| - | Capacitor size = Current draw / (Ripple frequency) * (Ripple Voltage) | + | Capacitor size = Current draw / ( (Ripple frequency) * (Ripple Voltage) ) |
| For a half wave rectifier (single diode) the frequency is 60 Hz (or 50 Hz in europe). The current draw is how much current your project is going to need, maximum. The ripple voltage is how much rippling there will be in the output which you are willing to live with and the capacitor size is in Farads. | For a half wave rectifier (single diode) the frequency is 60 Hz (or 50 Hz in europe). The current draw is how much current your project is going to need, maximum. The ripple voltage is how much rippling there will be in the output which you are willing to live with and the capacitor size is in Farads. | ||
| - | So lets say we have a current draw of 50 mA and a maximum ripple voltage of 10mV we are willing to live with. For a half wave rectifier, the capacitor should be **at least** = 0.05 / (60 * 0.01) = 0.085 Farads = **85,000 uF**! This is a **massive** and expensive capacitor. For that reason, its rare to see ripple voltages as low as 10mV. Its more common to see maybe 100mV or ripple and then some other technique to reduce the ripple, such as a linear regulator chip. | + | So lets say we have a current draw of 50 mA and a maximum ripple voltage of 10mV we are willing to live with. For a half wave rectifier, the capacitor should be **at least** = 0.05 / (60 * 0.01) = 0.085 Farads = **85,000 uF**! This is a **massive** and expensive capacitor. For that reason, its rare to see ripple voltages as low as 10mV. Its more common to see maybe 100mV of ripple and then some other technique to reduce the ripple, such as a linear regulator chip. |
| - | You don't have to measure that formula, but you should keep the following in mind: When the current goes **up** and the capacitor stays the same, the ripple goes **up**. If the current goes **up** and you want the ripple the same, the capacitor must also **increase** | + | You don't have to measure that formula, but you should keep the following in mind: When the current goes **up** and the capacitor stays the same, the ripple goes **up**. If the current goes **up** and you want the ripple the same, the capacitor must also **increase**. |
| ===== Full wave rectifiers ===== | ===== Full wave rectifiers ===== | ||
/home/ladyada/public_html/wiki/data/pages/tutorials/learn/powersupply/transformeracdc.html.txt · Last modified: 2016/01/28 18:05 (external edit)
Page Tools
Except where otherwise noted, content on this wiki is licensed under the following license: CC Attribution-Share Alike 4.0 International
