What You Need To Know Before Buying A Boost/Buck Converter

in this video we're going to go over some of the basics and also what to look for when purchasing a boost or a buck converter so let's start off with the basics what is a boost or buck converter or as they're sometimes referred to as a step up or step down converter well essentially what a boost or buck converter does is depending on the type of unit you buy it'll either increase or decrease voltage that is fed into the unit some of the boost or buck converters you'll find on the Internet will also have extra features such as current control now this can be useful when driving LEDs per se because we not only want to control the voltage but sometimes we want to control how much current is fed to the LED so it's important to figure out what application your boost or buck converter will be used for to buy the appropriate unit so here's a small sample of some of the boost and buck converters that I happen to have on hand at the moment and fundamentally they all do the same job however some have features which would be handy and some applications for example this one has a voltmeter on it which can measure the input and output voltage can also get boost buck converters that can also measure how much current is being passed through the end which can be very handy this buck converter is designed to charge lithium batteries though there's no reason it can't be used just purely as a buck converter so here's a trim pot for adjusting voltage and current and it has a bicolor LED on it to indicate when the battery is being charged and when it's fully charged for instance so we're going to get some of these out of the way as we mentioned we're going to look at three different types of converters which are these three units here we have a buck converter a boost converter and a boost buck converter first we're going to have a look at the boost converter so this is the first converter we're going to be looking at today and on one end we have a blue trim pot with a screw on the top this is used for we're adjusting the output voltage and on the other end we have our screw down terminal headers there's an LED down there to indicate when the unit is running and on the underside if you have a look we have our terminal headers in there marked input and output positive or negative respectively now when purchasing a boost or buck converter quite often you'll be purchasing these online and they'll be shipped from overseas and quite often sellers and retailers would like to stretch the truth of how much current one of these units can be fed so that the hoping that provided the rest of the competition actually lists the rated current this unit can handle if they put an extra amp or two on top of that hopefully you'll think their units special and buy it now the problem with that is obviously were being lied to it's not uncommon sadly but what can we do to protect ourselves from this well not a whole lot apart from what we can do is once we've received the unit we can have a look and the cameras not going to pick it up because it's very faint but we can have a look at the semiconductor ICS here and if we google the part numbers which will be printed on the face here where my pins pointed we should find data sheets on line for the ICS here and then we'll be able to work out how much current this unit can actually handle so here's an example of the datasheet you can find for those semiconductor ICS so this particular one is for one of the buck converters I've got and we can see here that it features 8 240 volt input range adjustable from 1.25 to 36 we get a dropout voltage 0.3 and it can handle a maximum of 8 amps constant current so what should you look for in a boost converter well obviously we need to take into consideration what voltage and current our load is going to be on the converter so hypothetically let's bring in this LED and let's say that this LED NEADS 34 volts at 4 amps to run at full brightness and our power supply is going to be this 12 volt battery so we've got 12 volts been fit into our boost converter now this boost conveyor has a mentioned is rated at 6 m/s and you'd be forgiven for thinking that we're only going to be drawing 4 amps that's how many amps our LED can handle everything should be good right and the setup absolutely not and here's why let's use a calculator now you could use an Ohm's law calculator for this purpose however we are only doing some basic calculations for how much power we're going to be consuming so a regular calculator will do just fine so let's calculate how many watts our LED or load on the boost converter is going to be now as I mentioned that's 34 volts and we're going to times that by the current in this case for MS and hit equals and our load our LED is going to draw 136 watts of power from our boost converter now for the sake of simplicity we're going to assume our boost converter is a hundred percent efficient obviously in reality it's not it's probably going to be between 90 and 95 percent if it's well designed however it let's just assume it's 100 percent efficient for argument's sake so our LED is going to draw one hundred and thirty six watts of power now we need to divide this number by the voltage our power supply feeding the boost converter is in this case it's a 12 volt battery it's going to divide 136 by 12 and hit equals and we get eleven point three so here is where the catch exists we need our battery to supply eleven point three amps to our boost converter to be able to output 34 volts at four amps now the current rating which I mentioned earlier on this unit is six MS there is not definitely not output current that is input current so we have almost doubled what this unit is rated for we're most pushing 12 amps through this to boost the current and voltage now how do we get around this well you could buy a bigger and beefier step-up or boost converter to handle this job however if we had a higher voltage power supply so that this unit is not having to increase the voltage from such a low voltage to such a high voltage then we're going to draw a less current so now let's change things up as before where our load as the LED which is going to consume 136 watts of power and before we divided that figure by 12 volts which was our 12 volt battery but let's say our power source supplying the boost converter was now 26 volts it equals and we get 5.2 amps of current being consumed by our boost converter so just by changing the power supply voltage to our boost converter to 26 volts now means that we're not going to exceed the 6 amp maximum input rating on our boost converter and that we can drive our LED at full brightness from exactly the same boost converter as before except the differences from a 26 volt power supply this is going to live a happy life and from a 12 volt power supply it's going to absolutely die driving this LED and here is the second converter we're going to be looking at today this is a buck converter now this unit features two trimpots one is used to adjust the output voltage and the other is used to adjust the output current this can be particularly useful for things like LEDs or it can also be implemented as a safety measure so that if something goes wrong on a electronic project you can restrict how much current can be fed to the circuit we have a bicolor LED mounted down there between the capacitors this is used to indicate if the unit is in voltage or current limiting mode and as before we have our 10 headers for input and output voltage and as before they are mapped underneath as well see is the set up we've got a veritable voltage power supply and this is that display it's going to show us the volts and current the buck converter is consuming over here so the lab power supply is feeding the buck converter and then our load on the buck converter is a set of wire around resistors this meter is going to measure the output voltage from our buck converter and this meter is going to measure the current from our buck converter so let's turn on the lab power supply and we can see our dummy load the wire round resistors are being fed with 12 volts and they're consuming about 0.7 m/s now if you ever look on our lab power supply which is feeding power to our buck converter you can see we're supplying 27 volts and our buck converter is consuming about 370 melenz now note what happens when I start decreasing the voltage watch what happens to the current draw from our buck converter is the volts decrease the current needed to supply the difference to our buck converter over here yes to start going up and if you'll notice our voltage and current draw from the buck converter with our dummy load hasn't changed so I'll push the voltage back up here you can see the current draw goes back down now you might be thinking to yourself well that's all fine and dandy what does this demonstration prove that's a good question well what we're proving here is what we explained earlier with the boost converters how the supply voltage makes a huge difference to how many amps and volts we can feed the load doesn't actually apply the same way to a buck converter and that's because even if I push the voltage down all the way to let's see 12 volts twelve point eight volts you can see El load is still around the point seven amps we're still feeding at 12 volts but the power needed to supply the buck converter is more or less what the buck converter is outputting this is because we don't need any extra current because we're not stepping up the voltage so what I'm saying in a nutshell is that with a 10 amp buck converter we could have more or less a 10 amp load a respect of the voltage which makes choosing a buck converter a lot easier than choosing a boost converter so by now we've taken a look at a buck converter and we've taken a look at a boost converter and I'm sure a lot of you are aware but I will clarify anyway that although these are both converters they don't do each other's jobs a buck converter can only ever drop voltage compared to it's supplied voltage so for instance if we feed the buck converter here 20 volts we can't get 21 volts out of it we can only get say 20 volts to 1 volt now with the boost converter it's the opposite we can't get below the supplied voltage we can only raise compared to the supplied voltage now one thing which we can look at though is a boost buck converter analysis arguably a more Universal converter because it can do both jobs so I'm going to demonstrate that now with my lab power supply and my multimeter is hooked up to the output of the boost buck converter so at the moment my lab power supply is feeding the boost buck converter here 10 R sorry 20 volts and it's outputting 10 volts so at the moment it's an buck mode but I'm going to raise the keep raising the voltage until it changes to boost mode and now we're starting to boost past the supplied voltage so these are arguably a more Universal type of converter can be handy to have one lying around because it fills both jobs the same principles I explained about both boost and buck converters previously do apply to us depending whether it's and boost or buck mode so that covers pretty much all the basic things you should know before purchasing a boost or a buck converter and perhaps the last thing which is also rather obvious to a lot of people is don't exceed the voltage rating of your boost or buck converter or things will go pop fizz bang and a bit of smoke potentially fire can come out so that's a good one to avoid so I hope you found this video very informative if you have give it a like and be much appreciated and if you like this video just check out some others because you'll probably find something good in there too thank you very much for watching I'll see you next video bye for now

Channel: Schematix

Views: 392,101

Rating: 4.8930693 out of 5

Keywords: how, to, electronics, step, up, down, converter, converters, boost, buck, buyers, guide, schematix, volt, voltage, amps, increase, decrease, volts, dc, direct, current

Id: 9--_jaxiXhE

Length: 14min 11sec (851 seconds)

Published: Sun Nov 20 2016