How much capacity for these regulators ? - Page 1
Forum section: electronics / projects

author: JanJansen
author_rank: Frequent Contributor
timestamp: August 14, 2018, 02:41:50 pm
content: Hi, my project have a 9 volt wall adapter input, then a 5 volt regulator ( 7805 ), then a LDO 3,3v regulator ( LD33V ),the 3,3v section takes 100mA, on the 5 volt and 9 volt there is almost no difference, most power goes to the 3,3v regulator.What capacitance would you use for the 9 volt wall adapter in, and then for the 5 volt out, and for the 3,3v out ?, does it all need the same value ?Ofcourse i have extra 100n & 330n ceramics as needed.thank you

author: nctnico
author_rank: Super Contributor
timestamp: August 14, 2018, 06:10:35 pm
content: Regarding the LDO it would be careful. Some need capacitors with a minimal ESR value and ceramics may have an ESR which is too low so the LDO will start to oscillate. An easy fix is to use a small resistor like 0.47 Ohm in series with a several uF ceramic capacitor.

author: JanJansen
author_rank: Frequent Contributor
timestamp: August 15, 2018, 01:48:58 pm
content: That is a half ohm ?, i do have 1 ohm resistors.So from the 5v to the LDO a 1 ohm resistor and a big ceramic, not the regular 100n as in the datasheet ?

author: capt bullshot
author_rank: Super Contributor
timestamp: August 15, 2018, 02:07:11 pm
content: Look up the datasheet for the LD33 which output capacitor to use. Sometimes these are critical, I guess a 10uF tantalum will work fine.For the 7805's output capacitor, nearly anything will do the job. I'd suppose a 10uF electrolytic, or if space is at a premium a 100n ceramic. This also acts as the input cap for the LD33, but in general the input capacitor isn't critical.For the 9V input, I'd use an electrolytic in the 10uF ... 100uF range.

author: chemelec
author_rank: Contributor
timestamp: August 15, 2018, 02:44:38 pm
content: Why use a LDR Regulator from the 5 volts?If you need both voltages, Just use a 5 Volt and 3V3 one, Both connected to the 9 Volt battery.

author: JanJansen
author_rank: Frequent Contributor
timestamp: August 15, 2018, 03:34:59 pm
content: Quote from: chemelec on August 15, 2018, 02:44:38 pmThen the 3,3v regulator will be hotter then the 5v regulator is now.What is the problem then with LDO ?, it seems to work, only the 7805 gets very hot somehow.

author: JanJansen
author_rank: Frequent Contributor
timestamp: August 15, 2018, 03:41:26 pm
content: Quote from: capt bullshot on August 15, 2018, 02:07:11 pmThanks, i like to avoid tantalum.The datasheet says : Only a very common10 μF minimum capacitor is needed for stability.Suppose the load on the 3,3v was 1 ampere ?, is a 10uF still enough ?

author: capt bullshot
author_rank: Super Contributor
timestamp: August 15, 2018, 04:22:01 pm
content: Quote from: JanJansen on August 15, 2018, 03:41:26 pmYes, that's still enough. It's the regulators job to deliver the current and keep the voltage stable, the output capacitor is just an aid. For example, the capacitor can deliver (or absorb) very short pulses (in the us to 100us range) of current when the load current changes instantly. That's about the same thing the blocking capacitors do that you typically add to your digital logic circuitry. Any longer lasting change in load current will be delivered by the regulator from either its input capacitor or the external 9V supply. So a bigger input capacitor (at the 9V side) helps if you e.g. have problems with longer wires or a weak supply.

author: lapm
author_rank: Frequent Contributor
timestamp: August 15, 2018, 05:26:29 pm
content: Quote from: JanJansen on August 15, 2018, 03:34:59 pmThats sign that lots of power flows throw 7805. Maybe you should measure it current throw it?

author: mariush
author_rank: Super Contributor
timestamp: August 15, 2018, 06:02:47 pm
content: If you care about battery life, then you should not use linear regulators.Linear regulators throw the voltage difference as heat which means you'll get very low power efficiency.So let's say you have this:[ 9v battery ] --------> [ 5v regulator ] -----------> [ 3.3v regulator]Your device will use around 100mA from 3.3v so that means the 5v regulator needs to provide 100 mA to the 3.3v regulator.This means you're using at least 5v x 100mA = 500mW to deliver 330 mW to your device. The difference (170mW) is wasted as heat, so that's 35% loss.In order for the 5v regulator to produce 100mA for the 3.3v regulator it needs to take 100mA from the 9v battery, so that's 9v x 0.1 = 900mW going in, 500mW going out ... so basically almost half of your energy is getting lost as heat on the regulators.LD33V seems to be a "nickname" for a a regulator from the *1117 series of linear regulators. These regulators require a capacitor on the output with a ESR value between 0.1 ohm and 1 ohm and something like at least 10uF of capacitors.Higher capacitance than the minimum recommended won't hurt (in any significant way), but you have to be careful with capacitor type. Ceramic capacitors have very low ESR so if you want to use such capacitor (let's say to save space) sometimes it makes sense to add a small resistor in series with the capacitor to fake out a higher ESR ... for example add a 0.27 ohm resistor in series.Tantalum capacitors will often have a higher than 0.1 ohm esr and they're relatively stable and small size, but they're expensive.Electrolytic capacitors ... if you go with something like let's say 10uF 6.3v, the ESR of such capacitor could be higher than 1 ohm.But you don't have to go with the minimum capacitance and the minimum voltage rating higher than the one you need.For example, you could easily go with something like 33uF or 47uF rated for 16v or 25v maximum voltage from a low ESR modern series, and you can use one of these for both the 5v regulator and the 3.3v regulator.The diameter and height of such capacitor won't be much bigger than the ones of lower voltage rating (6.3v, 10v) but it's enough to get the ESR within 0.1 - 1ohm.See for examplePanasonic FC series- 47uF 25v is 5mmx11mm and has an ESR value of ~0.8 ohm , orRubycon ZL series- 47uF 25v is 5mmx11mm and 0.3 ohm esr ,,, these would be considered entry level / base low esr capacitors, there's much higher performance/ultra low esr capacitors nowadays but linear regulators don't need such high end capacitors.You should redesign your project to use 5v from a power adapter, this way you can reuse cheap 5v phone chargers.Some of those will output slightly more, like 5.5v so you may still want to use a very low drop linear regulator to stabilize the voltage to 5vSee for exampleLP3985orNCP603.

author: JanJansen
author_rank: Frequent Contributor
timestamp: August 16, 2018, 02:48:04 pm
content: Quote from: lapm on August 15, 2018, 05:26:29 pm100 milli ampere it takes.The optocoupler is on the 5v.I soldered a new prototype board, this time with a 6N137 optocoupler with a 10K pullup resistor.This time i did not use the 6N138 with the 330 ohm pullup resistor,the heatsink is now long time touchable with pressure,with my old board you could not touch that to long,maybe here is a difference ?, or am i to suspicous, was it more a capacitor problem ?It still gets hot, i need something to measure that sooner or later.Quote from: mariush on August 15, 2018, 06:02:47 pmI use a 5532 opamp for audio, they need at least 10v, 9v will work also, not 5.I,m not sure if a rail to rail opamp will be good as output stage for a synthesizer.

author: mariush
author_rank: Super Contributor
timestamp: August 16, 2018, 03:20:24 pm
content: Quote from: JanJansen on August 16, 2018, 02:48:04 pmYou could use a charge pump/voltage doubler IC to get 9-10v from 5..5.5v :example chipsDon't know how much current that opamp needs... if it's something like 20-50mA then you have plenty of cheap options.For example MAX1720 is less than 1$ in small quantities... see page 9 and 10 for voltage doubler and tripler (minus voltage drop on 1-2 diodes) in datasheet:http://www.onsemi.com/pub/Collateral/MAX1720-D.PDFI don't know if this type of voltage booster would affect sound quality but I doubt it, it's low frequency enough, and you can add some low pass/high pass filter with some ceramic resistors and capacitors if you wish.

author: JanJansen
author_rank: Frequent Contributor
timestamp: August 16, 2018, 03:50:50 pm
content: Nice one thank you,wont i have switching noise in my audio then ?

author: mariush
author_rank: Super Contributor
timestamp: August 16, 2018, 04:02:26 pm
content: Quote from: JanJansen on August 16, 2018, 03:50:50 pmYou'll have to figure that out for yourself.You'll have some switching noise from a 9v wallwart adapter, those are switching power supplies as well.A 5v wallwart adapter will also introduce some switching noise... I don't know off the top of my head if the noise from such a charge pump chip will be noticeable enough or matter over the noise from the adapter.If anything... usb adapters being so mass volume produced, they may be of higher quality compared to some no name brand 9v DC or adjustable 3-12v dc switching adaptersIf you want minimal noise, maybe consider buying a toroidal transformer and shove it inside the box with your device.

author: JanJansen
author_rank: Frequent Contributor
timestamp: August 16, 2018, 04:33:52 pm
content: I thought i have linear wall adapters, maybe new ones are switching only ?

author: mariush
author_rank: Super Contributor
timestamp: August 16, 2018, 05:14:02 pm
content: Most lightweight adapters are switching power supplies.Basically, i'd say if your adapter weighs less than around 200g, it's a high chance it's a switching power supply.

author: JanJansen
author_rank: Frequent Contributor
timestamp: August 17, 2018, 02:18:54 pm
content: Thanks for the info Marius.I got the really heavey ones, and big.

author: JanJansen
author_rank: Frequent Contributor
timestamp: August 26, 2018, 04:34:05 pm
content: Ok, i will buy a switching regulator, since that goes in the 3,3v LDO, so it will be good again for audio.Or a DC/DC converter, whats the difference ?

author: mariush
author_rank: Super Contributor
timestamp: August 26, 2018, 06:47:31 pm
content: Well, a DC-DC converter is any device or chip which converts one input voltage to another output voltage.A switching regulator is a particular type of DC-DC converters, which use a specific technique to convert a voltage into another voltage, resulting in higher efficiency .A linear regulator is a DC-DC converter, because you have one input voltage and another output voltage, and the chip contains a transistor or mosfet that takes care of limiting the output voltage.A LDO is just a fancy linear regulator, designed so that the dropout voltage (the minimum amount of voltage that must be above the output voltage in order for the regulator to produce a stable output voltage)A switching regulator produces the output voltage by (typically) producing pulses of energy and adjusting the number of these pulses produced within some period of time, depending on the amount of current your device produces. So instead of dissipating the excess voltage in a transistor like it happens in a linear regulator, a switching regulator has "brains" inside which constantly monitor the output voltage and adjusts the number of pulses of energy going through the chip, and their duration, in order to keep the output stable.There are different kinds of dc-dc converters and you can produce dc-dc converters by yourself ...For example.. a very inefficient dc-dc converter could be something like this: connect a bunch of leds to the input voltage and have a small calculator solar cell directly on top of the leds and then connect a tiny ldo to the voltage produced by the solar cell and you have a stable output voltage. It's a dc-dc converter because you have an input voltage and an output voltage that's different, but there's no "switching" involved, just conversion to light and then back to electrons in the solar cells.

author: JanJansen
author_rank: Frequent Contributor
timestamp: August 27, 2018, 01:54:57 pm
content: Thanks.I mean switching DC/DC converters, like RECOM brand.RECOM dont has parts at mouser under the catagory switching regulator, only under DC/DC converters.RECOM is a good brand.https://nl.mouser.com/ProductDetail/RECOM-Power/R-78E50-05?qs=sGAEpiMZZMt6Q9lZSPl3Re5VKOUP6OK3oKGplDCSDFs%3dhttps://nl.mouser.com/ProductDetail/RECOM-Power/R-78E50-10?qs=sGAEpiMZZMt6Q9lZSPl3RX83uO1i4l1iFggiu9VT7gqvFlrlqew%252bZw%3d%3dThe manual speaks about max capacitive load : you can not add more then 220UF.