Nice job explaining it. About the yellow meter, just send it to me and get it over! I have 2 kids and I'll tell them that you took care of the Father's Day for them! ha ha ha
Great video - I had to watch this a couple of times Eddie to get it but I understood what was happening; not sure I understood why it was happening? Let me see: is this negative resistance a function of the SMPS having to charge its input, internal (and output?) capacitors to get going? I don't think so otherwise it would stabilise back to a 'natural' resistance, but the resistance is dropping with the voltage and the current is rising to meet the physics and stabilises at that point. I got the bit about UVLO being used to control this and prevent what might end up being a runaway high-power startup. So resistance of the boost converter is following the input voltage and current is pulled to allow that to happen. Why does it do this? EDIT: I think I get it - because there is a power requirement at the output and it's trying to meet that as a function of voltage and current (obviously), and thus resistance has to change to match the laws of the universe. As input voltage starts low, current has to start high, these variables moving in relation to each other in terms of Ohms law. Why does this only impact SMPS?
I think you just about have it;) It is because of the load being a constant power supply. I happens whenever you have a regulated output with a load that wants constant power - like another power supply. With a linear, as the voltage comes up, the linear can not supply the correct output voltage until the input is high enough, so the output power is not there yet. Then when the input is high enough to account for the voltage drop across the linear, then the output voltage will be regulated. As the input voltage increases, the linear has an unused voltage across the input. Make sense? thanks for the great question!
Kiss Analog yes I think so. I forget you don’t have the SMPS feeding into a regulation stage before the load. With a linear supply, it’s regulation is kicking in and ‘starving’ the load until the voltage levels are high enough. Assuming you set a current limit before startup, it must go into CC immediately and then, if able/necessary, flips to CV. Thanks Eddie
You like meters, so do I, but I'm looking to get a meter that measure 0-12.5 or 20 KV AC and DC - what would be the most inexpensive meter for me to get? If anyopne out there reads this, I'm all ears. The reason I need it is to measure Tesla Coil output and few Jacob Latter gizmos I demo on our annual show. Anyway, thatnks for any suggestions!
I have a lot of different SMPS from very little power (Plug-in PSUs) up to 6 kW (heavy Server SMPS) - but i never heard of "negative resistance" in that case :-). I think i got the point you wanted to make - but i won't call it negative resistance. I tend to prefer buck-converters over boost-converters as the last are normally less efficient. I just have a few smaller boost converters and when i tested them i recognized for the cheaper ones that they have a severe problem when the input voltage decreases under a certain point. Then it can happen that the output voltage suddenly rises to unexpected levels - can happen that you end up with 50V output when you adjusted the output to only 10 or 5 V. The better boost converters sometimes have that UVLO to protect it - the chinese cheapies don't. This can be a problem when you power your boost-converter with a li-ion battery that in some point faints to below 3.5 V - and then shit may happen! You normally dont have these effects with buck converters.
I’m working towards a more complex subject, so I’m paving the road;) it will seem simple when I explain it, now that I have the concept of negative resistance taken care of. We’re all going to have expertise in power supplies as I move along. The buzz words need to be covered too, so when someone hears or reads about input impedance - they’ll smile and say I know what that is;) That high voltage spiking scares me - I’m afraid a capacitor is going to explode;) a load, even a small one can take care of that.
Hey thanks for the video Eddie! I hadn't heard the term negative resistance before but I've experienced this behavior from say a constant current supply to LEDs. I always thought of this as "proportional", which isn't a technical term just the way I think about it.
It is an important concept - and I’m paving the road so that another more complex subject will go over more easily with the understanding of the negative resistance concept. Keep it simple right? The complex can seem simple if broken down the right way:)
You touched on and hit me in a sore point. Many Chines PSU's claim say 10A. On this side of the pond one would assume that is what the PSU would be capable of producing. NO. They are referencing what can be put into the PSU. When in fact the said PSU may only be able to produce 5A at a given voltage. They in fact Fuse some PSU on the INPUT.
That is only true, when the voltage needs to be boosted, which is not usually the case for PSU types that are supplied with mains voltage and are therefore based around buck converters, which almost always output higher currents than what their input is. In fact they do not usually tell if they refer to input or output amps. If there is no information then you have to consider the worst scenario and calculate the input or output manually and also factor in some losses (usually between 10% and 20%).
Another great demonstration.. Thank you!!🙏
Thank you - much appreciated!
Nice job explaining it. About the yellow meter, just send it to me and get it over! I have 2 kids and I'll tell them that you took care of the Father's Day for them! ha ha ha
LOL, I’d love to Tony!
Soft starts could probably use a video of their own.
Would be cool to go through the process of designing one into an amplifier or power supply.
Thanks for this Chris! I'll do this and explain why a soft-start is desired.
Love your videos as always, the link to the Boost Converter just goes to Amazon's main page...
Thanks Robert - I appreciate you! And thanks for giving me the heads up on the link;)
Great video - I had to watch this a couple of times Eddie to get it but I understood what was happening; not sure I understood why it was happening? Let me see: is this negative resistance a function of the SMPS having to charge its input, internal (and output?) capacitors to get going? I don't think so otherwise it would stabilise back to a 'natural' resistance, but the resistance is dropping with the voltage and the current is rising to meet the physics and stabilises at that point. I got the bit about UVLO being used to control this and prevent what might end up being a runaway high-power startup. So resistance of the boost converter is following the input voltage and current is pulled to allow that to happen. Why does it do this? EDIT: I think I get it - because there is a power requirement at the output and it's trying to meet that as a function of voltage and current (obviously), and thus resistance has to change to match the laws of the universe. As input voltage starts low, current has to start high, these variables moving in relation to each other in terms of Ohms law. Why does this only impact SMPS?
I think you just about have it;) It is because of the load being a constant power supply. I happens whenever you have a regulated output with a load that wants constant power - like another power supply.
With a linear, as the voltage comes up, the linear can not supply the correct output voltage until the input is high enough, so the output power is not there yet. Then when the input is high enough to account for the voltage drop across the linear, then the output voltage will be regulated. As the input voltage increases, the linear has an unused voltage across the input. Make sense? thanks for the great question!
Kiss Analog yes I think so. I forget you don’t have the SMPS feeding into a regulation stage before the load. With a linear supply, it’s regulation is kicking in and ‘starving’ the load until the voltage levels are high enough. Assuming you set a current limit before startup, it must go into CC immediately and then, if able/necessary, flips to CV. Thanks Eddie
You like meters, so do I, but I'm looking to get a meter that measure 0-12.5 or 20 KV AC and DC - what would be the most inexpensive meter for me to get? If anyopne out there reads this, I'm all ears. The reason I need it is to measure Tesla Coil output and few Jacob Latter gizmos I demo on our annual show. Anyway, thatnks for any suggestions!
Tony, what if you got some high voltage resistors - say to divide by 100 then you could use your meter and multiply by 100?
Hi Eddie thanks for the video, It was great.
Thanks - I appreciate you!
I have a lot of different SMPS from very little power (Plug-in PSUs) up to 6 kW (heavy Server SMPS) - but i never heard of "negative resistance" in that case :-). I think i got the point you wanted to make - but i won't call it negative resistance. I tend to prefer buck-converters over boost-converters as the last are normally less efficient. I just have a few smaller boost converters and when i tested them i recognized for the cheaper ones that they have a severe problem when the input voltage decreases under a certain point. Then it can happen that the output voltage suddenly rises to unexpected levels - can happen that you end up with 50V output when you adjusted the output to only 10 or 5 V. The better boost converters sometimes have that UVLO to protect it - the chinese cheapies don't. This can be a problem when you power your boost-converter with a li-ion battery that in some point faints to below 3.5 V - and then shit may happen! You normally dont have these effects with buck converters.
I’m working towards a more complex subject, so I’m paving the road;) it will seem simple when I explain it, now that I have the concept of negative resistance taken care of. We’re all going to have expertise in power supplies as I move along. The buzz words need to be covered too, so when someone hears or reads about input impedance - they’ll smile and say I know what that is;) That high voltage spiking scares me - I’m afraid a capacitor is going to explode;) a load, even a small one can take care of that.
THE FIRST THING THAT COMES TO MY MIND WHEN YOU TALK ABOUT NEGATIVE RESTANCE IS HOW A TUNNEL DIODE OR UJT WORKS.
Hi David - great to hear from you;) Yes that’s interesting that you thought of those examples - thanks!
Love that!
Thanks!
Hey thanks for the video Eddie! I hadn't heard the term negative resistance before but I've experienced this behavior from say a constant current supply to LEDs. I always thought of this as "proportional", which isn't a technical term just the way I think about it.
It is an important concept - and I’m paving the road so that another more complex subject will go over more easily with the understanding of the negative resistance concept. Keep it simple right? The complex can seem simple if broken down the right way:)
You touched on and hit me in a sore point. Many Chines PSU's claim say 10A. On this side of the pond one would assume that is what the PSU would be capable of producing. NO. They are referencing what can be put into the PSU. When in fact the said PSU may only be able to produce 5A at a given voltage.
They in fact Fuse some PSU on the INPUT.
Great feedback! I’ve heard a little about this practice! Too easy to play with numbers.
That is only true, when the voltage needs to be boosted, which is not usually the case for PSU types that are supplied with mains voltage and are therefore based around buck converters, which almost always output higher currents than what their input is.
In fact they do not usually tell if they refer to input or output amps. If there is no information then you have to consider the worst scenario and calculate the input or output manually and also factor in some losses (usually between 10% and 20%).