hybridfree/eevblog-posts huggingface dataset:
24V 300mA to ~12V 600mA is it possible? - Page 1
Forum section: electronics / beginners

author: koziskey
author_rank: Newbie
timestamp: April 13, 2015, 11:51:46 am
content: I am helping my sister with school project. I need a power supply for led strip ~5W needed. I also have 24v power supply laying around. Is there a way to use it?

author: Zero999
author_rank: Super Contributor
timestamp: April 13, 2015, 12:12:22 pm
content: The short answer is no. You can't convert 24V at 300mA to 12V at 600mA because there will always be some power loss.Fortunately you're talking about 7.2W, which is more than enough to power a 5W LED strip from.You could use a DC-DC converter but it's probably cheaper to just buy the correct voltage power supply.

author: macboy
author_rank: Super Contributor
timestamp: April 13, 2015, 02:06:26 pm
content: Look for a "LM2596 buck" power supply on ebay or alibaba or wherever you prefer. These are small down-converting DC-DC power supplies that can do what you need. You should be able to get a module for $1 shipped. No joke. The only issue is the wait time for shipping from China/etc.

author: Rick Law
author_rank: Super Contributor
timestamp: April 14, 2015, 08:07:59 pm
content: To get 12V 600mA from 24V300mA, you need exactly 100% efficiency.It doesn't matter what buck converter you use, 100% efficiency is simply not possible. One can always try to break the annoying Laws of Thermodynamics, but one would most likely fail.If you do a good job, 12V 540mA (90%) is feasible. More likely, you will be at 80-85% range done well, and much lower if not done well.You have to pay the piper, in this case, the piper is Entropy.
24V battery charger red/green blinking is it dead ? - Page 1
Forum section: electronics / beginners

author: tigrou
author_rank: Regular Contributor
timestamp: July 10, 2025, 09:27:50 am
content: I have a 24V charger for a electric wheelbarrow.The led on charger blinks red/green constantly, and battery won't charge.I measured the voltage output of charger : is 0.6V DC at best (unplugged). It's a regular DC male connector (as found on most chargers).The manual just says : led is RED while charging and turn GREEN once it's charged. No mention of the red/green blinking.The battery also has a led that is RED when charging. It goes RED for 30 seconds then just go off.I'm wondering if the charger is dead or if it's the battery ?Maybe they use some protocol and charger will start working go on once battery is OK (that would explain why I measure only 0.6 VDC ?).I'm wondering how those chargers works in general for knowing when battery is charged : do they just monitor the DC voltage at the output and once it' around 24DC, battery is considered as charged ?

author: mikerj
author_rank: Super Contributor
timestamp: July 10, 2025, 09:37:32 am
content: Can you measure the battery voltage? It's possible the charger wont start charging unless it sees sufficient battery voltage present, many lithium ion chargers for power tools are like this.

author: tigrou
author_rank: Regular Contributor
timestamp: July 10, 2025, 03:17:14 pm
content: I measured 10.3VI think it's to be expected for a discharged but not completely dead battery.EDIT : battery is probably damaged as it shouldn't go that low, still charger should try to charge it up and be RED.

author: BeBuLamar
author_rank: Super Contributor
timestamp: July 11, 2025, 11:57:33 pm
content: Perhaps the charger indicates that the battery is bad and it won't charge the battery. I tried to charge for a few seconds then gave up.

author: darkspr1te
author_rank: Frequent Contributor
timestamp: July 12, 2025, 08:18:12 am
content: I recently had this issue on a hedge trimmer, the two light would just alternate , i opened it and found one cell dead, replaced it and battery works fine now (it was a 18650 pack)darkspr1te

author: tigrou
author_rank: Regular Contributor
timestamp: July 15, 2025, 06:18:01 pm
content: I just got new charger (generic one for small 24V electric cars and such) and battery is charging again. Maybe one of the cells is damaged as 10.3V is quite low for a lead/acid battery.

author: henryuan
author_rank: Newbie
timestamp: September 04, 2025, 02:05:05 am
content: The charger must be broken.10.3V voltage for a 12V lead-acid battery is ok.Generally speaking, the minimum charging voltage of a 12V lead-acid rechargeable battery is around 9V.You can look at the working mode of Henryuan portable 24V lead-acid battery charger：https://www.henryuan.com/e_products/24V-Lead-acid-Battery-Charger-8-26.html
circuit time controller  - Page 1
Forum section: electronics / beginners

author: silviasol
author_rank: Regular Contributor
timestamp: May 08, 2020, 04:10:05 am
content: any way to control on time of a powered circuit.

author: anvoice
author_rank: Frequent Contributor
timestamp: May 08, 2020, 04:17:37 am
content: Does the on/off time need to be controlled via a microcontroller, or via potentiometers?

author: anvoice
author_rank: Frequent Contributor
timestamp: May 08, 2020, 04:27:40 am
content: Ok, then what sort of light are you switching? A simple small LED or a more powerful light that needs a lot of current? Depending on that you may or may not need additional circuitry.You can go several routes. One way would involve using a very cheap Arduino pro nano and write a simple sketch that will blink your light. Advantage is that you simply input the seconds on/off, and it will adhere to it. Another is to use something like the 555 timer (probably the simplest thing you can use, but you will need to reduce the voltage to the 555 to below 18V) and adjust resistor/capacitor values to give you the desired on/off times. If you need to drive power-hungry loads, you may need to add something like a transistor to the scheme.

author: Domagoj T
author_rank: Frequent Contributor
timestamp: May 08, 2020, 06:10:06 pm
content: Something like this?https://www.ebay.com/itm/DC-12V-Infinite-Cycle-Delay-Timing-Timer-Relay-ON-OFF-Switch-Loop-Module-Time/112308185789?hash=item1a2616eabd:g:wsUAAOSwgY9XdQwe
24v power supply basic question on 50% duty cycle. Voltage drop question. - Page 1
Forum section: electronics / beginners

author: lots o tots
author_rank: Contributor
timestamp: May 18, 2018, 01:34:08 pm
content: I have 2 sperate 24v loads that will required to be turned on separately. i am expecting the duty cycle to be about 50%.I plan on buying a good power suplly such as a genuine mean well.Since the duty cycle will be 50%, there will be some moments where 2 supplies are are on, but sometimes 1 will be on.Will the supply voltage be the same in both conditions? if they are slightly different, what can i expect a voltage drop to be? ie. 1 load is 24.05V, 2 loads is 24.00 V.I am trying to determine if the difference is negligable as the example i provided.thanks-LOT

author: sokoloff
author_rank: Super Contributor
timestamp: May 18, 2018, 01:47:25 pm
content: Power supplies with internal feedback are generally good at maintaining output voltage on their output terminals. (Meaning: yes, it will be negligible, assuming you're staying within the spec of the power supply.)After that, any common wiring will have voltage drops that vary with current. (If you go PS->common wire->relays/SSRs->individual loads, the common wire will have a higher voltage drop when both loads are on than when not. This is estimable, with voltage drop calculators on the web.)In general, you are overwhelmingly likely to be fine, unless your loads are extremely picky about input voltages (and most are not, because the real world is imperfect so things are designed around that).
24V PWM 400hz to 0-10V Analog - Page 1
Forum section: electronics / beginners

author: witty
author_rank: Newbie
timestamp: January 05, 2016, 06:46:29 am
content: Hi,I have a 400hz PWM 24VDC I would like to read on an analog input of 0-10V (high sample rate, high input impedance).I first thoughts were to make a voltage divider of 1K4 and 1K in series to ground to drop the voltage to 10V from 24V then use a 1uF in parallel with the 1K resistor.I would take the output across the 1K/1uF. I have a feeling this won't work and I don't have the hardware to test yet (should arrive in a few days).I saw some diagrams like this going the other way to amplify the 5V output signal,https://www.eevblog.com/forum/projects/0-10v-led-driver-control-with-microcontroller/What is the most appropriate solution for this problem?Thanks.

author: Seekonk
author_rank: Super Contributor
timestamp: January 05, 2016, 07:48:03 am
content: The last solution is the most correct. To be linear the source impedance should be at least ten times less than the resistor feeding the filter capacitor. So feeding the capacitor with 47K would likely work if the input voltage is stable. Then use a voltage divider to get the 1-V with a divider where toe two divider resistances total at least to get the 10V accounting for some loss and buffer with unity op amp.

author: pmbrunelle
author_rank: Regular Contributor
timestamp: January 05, 2016, 05:30:03 pm
content: With a 1k / 1.4k voltage divider you actually have less DC output resistance (583R) that that 680R resistor...I would do the divider and parallel capacitor if possible... seems much simpler (less parts).However, the cutoff frequency for the values you calculated is 273 Hz; much too high. Maybe use 100 uF instead.Also seems a little borderline for 1/4 W resistors... might be good to bump them up to 1/2 W parts.

author: Seekonk
author_rank: Super Contributor
timestamp: January 05, 2016, 06:29:33 pm
content: Just remember that the charge resistance has to be the same as the discharge resistance to the capacitor. Something many in that other thread ignored.

author: witty
author_rank: Newbie
timestamp: January 05, 2016, 11:08:16 pm
content: Hi guys, thanks for your replies; much appreciated.If you think the divider will work with higher rated resistors and a larger cap then that is simpler; the "push-pull" output PWM is good for 450mA according to the datasheet.I'm not quite sure what you mean by the charge resistance has to be the same as the discharge resistance to the capacitor; my intention is attached.
24v to +- 24v - Page 1
Forum section: electronics / beginners

author: thedarkrs
author_rank: Newbie
timestamp: February 15, 2015, 09:12:35 pm
content: Hey there guys.I am very new to electronics, so please excuse me if I might sound like an idiot.I need a little help with a project that I have started.I made an audio amplifier, and tested it, and it seems to work.Now I need to make a power supply for it.It asks for +-20-48V.I would be very happy if I can supply it with 40+ volts, because this way it will output the most power (I believe so).I tested it with a transformer that has 3 wires coming out of it, and a rectifier.But the thing is that I want to be able to use it in my truck, and it has 24v system.So I cant use a transformer without a power inverter.Is there a more simple way?I did try to use 2 boost converters, 1 generating 26V and the other 52V so this way I have 0, 26, 52. Use the 26 as ground. and I got something that looks like +-26V.It DID work, but the voltage would not stay stable on one of the boost converters, for some reason it would go up when I turn the volume up.I did try to google for a solution for DAYS, and I didn't find anything that helped mePLEASE HELP !!

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: February 15, 2015, 09:37:23 pm
content: i think you can use the 52V boost only and create a dual 24V from it

author: PeterFW
author_rank: Frequent Contributor
timestamp: February 15, 2015, 10:22:51 pm
content: Quote from: thedarkrs on February 15, 2015, 09:12:35 pmThe only thing i can think of the top of my hat are two isolated 24v to 48v DC-DC converters, wired in series with a "center tap".But they are rather pricey.The other way around is cheaper, 24v to 12v DC-DC converter in the same configuration.QuoteThe simple way would have been to take the available power supply into consideration and to design a amplifier that works of a single 24V power supply with low loadsA Class-D amp with a full h-bridge output stage.

author: Stephen37
author_rank: Contributor
timestamp: February 18, 2015, 12:46:28 pm
content: +- 24V = 48V DC with a stable center tap (that means you are in a big problem), you'd better switch to an automobile amp that takes only 24/12V or lower, it is way cheaper.The only rational solution is to get a 1:2 transformer (110V->220V or inverse for example) with an inverter (a simple 555 circuit) that doubles 24V with a center tap and rectify it, any other solution gets way over 50$.A single 50V boost converter can be split with a virtual ground circuit but you better avoid such a solution as much as possible especially if you want more than a few milliamps.

author: peter.mitchell
author_rank: Super Contributor
timestamp: February 18, 2015, 12:55:17 pm
content: something like this would also work;http://www.ebay.com.au/itm/DC12V-To-dual-32V-Boost-Power-Supply-Board-For-HiFi-Amplifier-Car-Amp-350W-/201270963543?pt=LH_DefaultDomain_0&hash=item2edcaf2d57
24V Transformer - Page 1
Forum section: electronics / beginners

author: metrologist
author_rank: Super Contributor
timestamp: January 14, 2019, 09:31:37 pm
content: I found this leftover from grampa's stock. It has the E laminating plates and the winding in a plastic housing. There is no "end" to the E laminating plates. (El).Were transformers ever made this way or was this one taken apart? Also, the laminates are not stuck together but are a little loose. Think I can use this?

author: Yolk
author_rank: Newbie
timestamp: January 15, 2019, 03:00:07 am
content: If you mean that the laminations are all missing the I piece,that's a problem,but if it's only the last lamination as in the end of the transformer,probably doesn't matter too much because it doesn't need it.If the laminations are loose,the core will wobble and that's a problem (It will also wobble when it's firm and set,but it will do it ever so slightly. Serious wobbling will lead to losses and damage to the transformer.)Maybe a picture?
24v VS 48v UPS inverter efficiency? - Page 1
Forum section: electronics / beginners

author: HKPolice
author_rank: Newbie
timestamp: October 03, 2013, 07:17:08 am
content: Sorry if this is too basic of a question, but I was trying to calculate runtime on my APC SUA2200 UPS and couldn't find any info on how efficient typical sinewave inverters in UPSes are. The only actual measurement I found is from a youtube user that converted his APC Smart-UPS 1500 into a full time inverter and measured an efficiency of 84% @ ~840w but that UPS uses 24v battery packs.The SUA2200 model accepts 48v input and I've added an extra bank of external batteries so the APC runtime chart no longer applies. Would a higher DC input voltage be more efficient? Standard 120v 60Hz North american output. My logic tells me that it should be easier to convert 48v DC than 24v DC to 120Hz AC but I'm not sure and googling yielded no efficiency charts.Thanks in advance for any help!

author: Rerouter
author_rank: Super Contributor
timestamp: October 03, 2013, 12:07:56 pm
content: there are a large number of parameters that govern it, if the unit was mainly designed for 24V it is slightly more likely to run more efficiently at that voltage, as they would have picked the peak efficiency off of that base model design,

author: Psi
author_rank: Super Contributor
timestamp: October 03, 2013, 12:21:56 pm
content: Why not just time it until it stops with a known load current.Trying to calculate the run-time will likely produce a wildly inaccurate result.As others have said, there are so many variables to take into consideration for the theory to produce something close to reality.All things being equal yes, a 48V inverter will be more efficient than a 24V inverter because the current is less at 48V.Less current = less wasted heat in the switching transistors and conductors.UPS efficiency is usually in the range of 75-87%.Being a reputable brand (APC) and given that the 24V version is 84% i would expect 48V to be around 86%. But its really just an educated guess.

author: dfmischler
author_rank: Frequent Contributor
timestamp: October 03, 2013, 12:34:19 pm
content: If you really need to know then you will have to measure it.Be careful adding batteries. Are you sure the charging circuit can handle the increased load if all the batteries were discharged to whatever level shuts down the inverter? Also beware of the possible increase in charging time from the discharged state to being ready to operate at full run time again. The most effective, proven uses for a UPS are to bridge the gap between utility power loss and generator startup, or to allow a clean shutdown.

author: Zero999
author_rank: Super Contributor
timestamp: October 04, 2013, 09:08:37 am
content: Quote from: Psi on October 03, 2013, 12:21:56 pmYes, I agree, a higher input voltage would give a greater efficiency and is why higher voltages are often used for UPS's.
25 degree C Junction Temperature - Page 1
Forum section: electronics / beginners

author: quaternion00
author_rank: Contributor
timestamp: March 19, 2019, 11:59:22 am
content: Datasheet specifies the electrical characteristics of some IC's under the condition of 25 degree C of junction temperature. The ambient temperature is commonly 25 degree C. I'm confused why the junction temp is equal to ambient temp. How come is the junction temp didn't changed temperature while it's operating?Thanks in advance.

author: newbrain
author_rank: Super Contributor
timestamp: March 19, 2019, 01:29:39 pm
content: Oh, but it will, according to the junction-to-ambient (including a possible heatsink) thermal resistance and the dissipated power.The 25°C is just a handy reference point for ideal conditions.For low power stuff, it may be close to the actual operating temperature.For high power semiconductors, it's important to check the data sheet for derating information, and the absolute maximum rating are sometimes given for Tc rather than Tj.e.g.IRF 520, Vishay:The maximum dissipated power is 60 W, for Tc = 25 °C and RthJC= 2.5 K/W this gives us a maximum Tj = 25 + 60 x 2.5 = 175 °C as stated in the same max rating table.

author: Gyro
author_rank: Super Contributor
timestamp: March 19, 2019, 01:41:23 pm
content: The reason that they do a 25'C Junction spec is that this is the condition the dies/devices are in when they go through manufacturing parametric test. The test is so quick that the die doesn't have time to warm up.Higher temperature limit specs are normally done on a sample basis.

author: dmills
author_rank: Super Contributor
timestamp: March 19, 2019, 09:08:08 pm
content: There is also a 'trap for young players' here in that the parameters change with temperature, in particular for switching mosfets Rds(on) rises with increasing temperature and almost a factor of 2 between 25c and Tj(max) is not at all uncommon.This matters when doing the thermal sums.The good stuff has a proper datasheet with curves for all this stuff (But they tend to be 'typical' values, so stay well on the conservative side of the curve).Regards, Dan.
25 MHz spi routing - Page 1
Forum section: electronics / beginners

author: Unknown
author_rank: Unknown
timestamp: November 16, 2014, 03:19:26 pm
content: I need to route a 25 MHz spi interface on a two layer board between three device 100 mm apart.I never routed a spi with this frequency and distance so i would like some advice on what to avoid.Should i put resistors in series with the signal and design termination resistors?I will try to route all the signal on the top layer with a solid ground plane under them but to connect three device i have to use vias, what should i avoid?Thanks for the help

author: Scrts
author_rank: Frequent Contributor
timestamp: November 16, 2014, 07:34:12 pm
content: 25MHz is SLOW. You can put series resistors, however you should route SCK wire at least 2x the track width away from the data lines in order to avoid cross-talk. Even 125Mhz is no issue, unless you're targeting DDR designs.

author: markb82
author_rank: Regular Contributor
timestamp: November 17, 2014, 08:35:48 pm
content: Ditto. Check out the Saturn PCB Design Toolkit for cross-talk calculations. Or:http://www.eeweb.com/toolbox/microstrip-crosstalk. And keep the cross-talk between the clock line and any datalines to < -15dB. Series resistors would help slow down the rise time so I would add them (right at the driver, ie mcu for sck, mosi, and at your devices for miso), even a 25 MHz design can have problems if you have a 1ns driver.Edit:Since this is likely a 2-layer board?, I think you may need more than 2x the trace width. Or you could put a ground trace (or copper pour) between the clock line and the data lines?
#279 and UK wiring. - Page 1
Forum section: electronics / beginners

author: nx084f001
author_rank: Newbie
timestamp: June 26, 2018, 09:40:31 pm
content: Hi AllWhat is the implication of the topic that Dave discusses in #279 for me, being in the UK, where all electrical appliances are Earthed via a third connection in the mains plug?Also - did Dave permanently damage the Tek 2225 in his demonstration?Thanks.

author: james_s
author_rank: Super Contributor
timestamp: June 26, 2018, 09:55:51 pm
content: Even if the appliance is earthed, the power supply will *usually* provide the required isolation. It doesn't really make any difference where you live, even if there is no earth, the neutral is still bonded to earth so the same rules apply. Stay away from the primary side of the power supply, the DC outputs should be safe. If in doubt, either use a multimeter to verify or don't mess with it.
27C010 ROM question - Page 1
Forum section: electronics / beginners

author: Crambone
author_rank: Frequent Contributor
timestamp: January 11, 2023, 04:40:33 pm
content: Guys I’m not familiar with ROM and types but the HP 8591E I have requires 4ea ROMs 1 megabits each, reprogrammable just in case I screw up the programming.I believe the 27C010 1 Megabit 128k x 8 PDIP type are the correct ones.My question, any difference between a 27C010 or say a 27C010-200DC or 90DC…. ?Thanks Andrew

author: DavidAlfa
author_rank: Super Contributor
timestamp: January 11, 2023, 04:50:30 pm
content: The latter number is the access time, the lower the faster.Can be lower than original spec, but not higher.

author: edavid
author_rank: Super Contributor
timestamp: January 11, 2023, 05:02:24 pm
content: 27C010 is an EPROM, so if it's in PDIP it can only be programmed once. You can get erasable parts in ceramic window packages, but you will need a UV eraser lamp.It would probably be better to look for compatible EEPROM/flash parts like the AT29C010A.
27C64 EPROM file data - Page 1
Forum section: electronics / beginners

author: Roscoe1017
author_rank: Newbie
timestamp: February 01, 2024, 03:45:59 pm
content: I received a file to program a 27C64 EPROM.(see attached) The file has extraneous data at the beginning of the file and after further investigation it looks like a project file from a TOP type programmer. The TOP programmer and software do not have good reviews and any attempt to download TOPwin software gives virus warnings.Any ideas ?Thanks, Ross

author: HwAoRrDk
author_rank: Super Contributor
timestamp: February 01, 2024, 03:55:59 pm
content: Just spitballing here, but I would guess that the actual ROM data is the lines starting with "144", in signed 8-bit decimal format, one line per byte. So, 144 = 0x90, -1 = 0xFF, etc.

author: colorburst
author_rank: Regular Contributor
timestamp: February 02, 2024, 05:25:52 am
content: I'd suggest installing the software inside a virtual machine and converting it to a standard format there. Disable its network access in case it does get infected.

author: Ian.M
author_rank: Super Contributor
timestamp: February 02, 2024, 06:01:51 am
content: Quote from: HwAoRrDk on February 01, 2024, 03:55:59 pmThere's not enough data there for it to be that simple.A 27C64 EPROM is an 8K x 8 device so 8192 bytes.Notepad ++ reports 203 lines, and we can see a five line header so there cant be more than 198 lines of data. Similarly it reports a length of 12288 characters and that it uses UNIX (single LF) line endings. I counted 59 header characters, so the 'payload' can only take 12229 characters. The data appears to be right justified at four characters per line (what you'd expect for min. width to accommodate -128) so five with the LF, so there cant be more than 2446 data bytes (assuming the final LF is missing). That's under 30% of the capacity of a 27C64.The data is unlikely to be compressed due to the presence of a large run of -1, which we believe to be 0xFF, the erased state for an EPROM location.Unless you know for a fact that the EPROM is blank from address 0x098E upwards, the odds are that this project file does *NOT* contain the EPROM data.

author: Shonky
author_rank: Frequent Contributor
timestamp: February 02, 2024, 07:02:15 am
content: Run tool in VM or post actual file here. Showing the first 40 lines is not really helpful. Is every line after the header a single 8 bit signed looking number (i.e. -128 to 127)? That's an unlikely way to store an image for programming an EPROM.I wouldn't trust the 12288 bytes notepad++ reports necessarily but that's exactly 12kB (3 x 4kB blocks size on disk common in Windows). Seems odd from the text based nature of the snippet shown that it's exactly 12kB
27C64 Memory - Page 1
Forum section: electronics / beginners

author: IvoS
author_rank: Frequent Contributor
timestamp: August 11, 2013, 11:27:50 am
content: I have 27C64A memory, I think it's made by National Semiconductors. I need to make a clone of it. Can I use a memory from different manufacturer? Like ST? Are these memory pin and voltage compatible? Thanks.

author: amyk
author_rank: Super Contributor
timestamp: August 11, 2013, 12:08:27 pm
content: Pinouts are JEDEC-standard, programming algorithm and speed may vary depending on the part.

author: madires
author_rank: Super Contributor
timestamp: August 11, 2013, 12:21:54 pm
content: Yes, but make sure that the new EPROM has the same or a lower access time then the old one. The naming is 27C64A-<time>, e.g. 27C64A-15 for 150ns. And as amyk already wrote, select the correct type in your programmer software.

author: amyk
author_rank: Super Contributor
timestamp: August 11, 2013, 12:59:00 pm
content: You may consider a flash EEPROM instead, a 28C64 will behave the same for read applications and is cheaper than a windowed EPROM.

author: IvoS
author_rank: Frequent Contributor
timestamp: August 11, 2013, 02:18:47 pm
content: Quote from: amyk on August 11, 2013, 12:59:00 pmIs that 28C64 pin and voltage compatible? The same?

author: digsys
author_rank: Unknown
timestamp: August 11, 2013, 02:42:28 pm
content: Quote from: IvoSBasically - for readin -You can use just about anything that has the same pinout and voltage. There are many OTPs (even cheaper) or FlashEEs etc that would work and are available in 5V. As been noted - as long as they are at least as fast. You will need tocheck the specs though, just in case you've picked a slightly "odd" one.Erasing / writing is a whole different thing, but if you're ONLY doing that manually, then who cares.

author: ignator
author_rank: Regular Contributor
timestamp: August 11, 2013, 05:29:15 pm
content: If procuring this small of EPROM is difficult, you can go up to 27C256, just make sure the unused address pins are grounded on your PWB. Maybe 27C512 if you your programmer supports the Pin1 change from Vpp to A15. Also check, maybe other address pins were connected, and you can use the larger eprom space if needed.

author: fluxcapacitor
author_rank: Frequent Contributor
timestamp: August 14, 2013, 02:42:42 am
content: Heres a project where a 27C64A and a 27C256 is used on the same board,jumpers are used to switch between them.Also the later version was stacked.http://www.dos4ever.com/8031board/8031board.html#appendixF
28VAC plug/socket? - Page 1
Forum section: electronics / beginners

author: pwnell
author_rank: Regular Contributor
timestamp: July 18, 2024, 04:29:07 pm
content: The 2.5mm DC plug is ubiquitous. AFAIK they can be rated for 24V DC and up to about 8A.What connector can I use - panel mount type - for 24V AC? I want to connect a 115 - 24V AC transformer's secondary to a small project box, but need a connector that can be panel mounted and will accept 24V AC and at most 100mA.I tried searching but can only find line voltage AC plugs.

author: calzap
author_rank: Frequent Contributor
timestamp: July 18, 2024, 05:32:50 pm
content: Are you looking for a plug or socket or both? If you go to the Digikey or Mouser website, you’ll find a huge number of styles that can handle 24 VAC and 0.1 A. Not sure what you mean by ubiquitous 2.5 mm connector. 2.5 mm JST? … not exactly ubiquitous. 2.1 x 5.5 mm connectors are ubiquitous though. Unless it’s critical or going commercial, I wouldn’t be too concerned about 24 VAC at 0.1 A into connector rated 24 VDC at 8 A. Most connectors have an AC as well as DC rating … just have to find it. Line voltage plugs can easily handle 24 VAC, but for safety reasons, do not use standard line voltage plugs for low voltage connections.Mike

author: pwnell
author_rank: Regular Contributor
timestamp: July 18, 2024, 05:45:40 pm
content: Thanks - I did try to search on digikey and mouser and newark but I get like 1 or 2 socket/plug pairs when I filter on low voltage AC - and they cost $500 or something crazy.https://www.mouser.ca/c/connectors/power-connectors/ac-power-plugs-receptacles/?mounting%20style=Panel~~Panel%20Mount&voltage%20rating=30%20VAC%2C%20125%20VAC%2C%20250%20VAC%2C%2032%20VDC%2C%2042.4%20VDC~~48%20VAC%2FDC&rp=connectors%2Fpower-connectors%2Fac-power-plugs-receptacles%7C~Voltage%20Rating%7C~Mounting%20StyleNot sure what I am doing wrong.

author: calzap
author_rank: Frequent Contributor
timestamp: July 18, 2024, 06:23:02 pm
content: Not sure either what you are doing wrong. Likely going too low on voltage. If a connector can handle 120 or 240 V, it can handle a lower voltage. If you limit search to low voltage only, the selection will be limited. Also search for plugs and sockets separately, not for pairs.Mike

author: mariush
author_rank: Super Contributor
timestamp: July 18, 2024, 06:36:15 pm
content: Most barrel jacks will be fine with 24v ... lots of laptop adapters use barrel jacks and output 20v DC ... 24v AC is not a big difference.Also Digikey has a bunch of barrel jacks rated for 48v AC/DC , here's a link :https://www.digikey.com/short/5pj74hzdYou may want to use a 3 pin keyed connector or maybe a PowerDIN connector , just in case you'll get a transformer with center tap as that would make it easier to get positive and negative voltages.example :https://www.digikey.com/short/p57j30t3You could even go to more basics like plain RJ45 connectors ... they do power over ethernet up to 56v so they'll handle 24v AC easily ... Just use a couple pairs for the ac- and ac+

author: pwnell
author_rank: Regular Contributor
timestamp: July 18, 2024, 07:03:15 pm
content: Thanks!
2n2222 is not working - Page 1
Forum section: electronics / beginners

author: nikoso40@yahoo.com
author_rank: Newbie
timestamp: July 23, 2025, 10:20:35 pm
content: Hello all. I have connected on a pic 16f18346 a sensor BH1750 and trying to control it with a 2n2222 transistor(as a switch) but i fail. I get calculations from some tutorials but i am not sure where i am wrong. The output from the IO pin is measured 4.97vdc. The BH1750 Operating current: 120uA (typ) 190uA (max). Is possible someone to help here with the calculations of the resistors as shown on the schematic please.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 23, 2025, 10:44:41 pm
content: First of all, are you sure you have a 2N2222 and not a PN2222?They're not the same thing, and in fact have different pin assignments.I didn't know that, thought they were the same and wondered why my damn circuit didn't work.

author: TimFox
author_rank: Super Contributor
timestamp: July 23, 2025, 10:48:12 pm
content: Easy to check: a real 2N2222 is in a TO-18 metal case, with a triangular pin array.There are plastic variants, with different prefixes, most of which use in-line pins, and not all are CBE ordered.

author: IanB
author_rank: Super Contributor
timestamp: July 23, 2025, 11:02:52 pm
content: Maybe it is more relevant to discuss the important factors when using an NPN bipolar transistor as a switch:1. When turned on, it needs to receive enough base current to fully saturate it2. The source of the base current needs to be able to supply that required currentNot saying anything is wrong with the schematic and resistor values presented, but it helps to know how to choose the values.Usually an NPN will be off unless it is on, so the base pull down resistor may not be required, and may be counter-productive.Also, a 10 kΩ current limiting resistor may, or may not, allow enough current to pass.

author: MLXXXp
author_rank: Frequent Contributor
timestamp: July 23, 2025, 11:05:29 pm
content: Is the BH1750 a standalone chip or is it mounted on a PCB as a module? The pinout you've shown doesn't match the chip, so I suspect it's a module.The BH1750 has a specified operating voltage of 2.4V to 3.6V, so you shouldn't be running it at 5V. If it's a module, I hope it has a voltage regulator and signal level shifters to allow 5V operation.That said, why use a transistor at all? The BH1750 draws only 190μA maximum. Even with a voltage regulator and level shifters added, the output pin of the PIC16F18346 should easily be able to provide enough current to power the BH1750 (module?) directly.
2N3904 datasheet small signal specs are for common emitter, or common base? - Page 1
Forum section: electronics / beginners

author: RoGeorge
author_rank: Super Contributor
timestamp: September 22, 2024, 12:34:18 pm
content: In page 2 of the datasheethttps://www.onsemi.com/pdf/datasheet/2n3904-d.pdf, at the table for "SMALL− SIGNAL CHARACTERISTICS", what does theCoboandCibo(input and output capacitance) refers to?

author: Roehrenonkel
author_rank: Frequent Contributor
timestamp: September 22, 2024, 12:40:19 pm
content: Hi RoGeorge,...since it's for Ic/Ie=0 i'd say it's neither of them.Best regards

author: G0HZU
author_rank: Super Contributor
timestamp: September 22, 2024, 12:51:31 pm
content: Pretty sure it’s for common base. That’s what the b refers to for Cibo.The i is input and the final o means output open.Cobo is for output with the input open. Both are common base.

author: RoGeorge
author_rank: Super Contributor
timestamp: September 28, 2024, 07:31:10 am
content: Just for the docs, accidentally found today this 2 pages AN from Infineon, which defines the notations:Application Note No. 024 - Parasitic Capacitance in Bipolar Junction Transistorshttps://eva.fing.edu.uy/pluginfile.php/68403/mod_resource/content/1/Parasitic_Capacitances_Bipolar_Transistors_AN024_Infineon.pdf
2N4401 C-E 2.2V - Page 1
Forum section: electronics / beginners

author: stafil
author_rank: Regular Contributor
timestamp: March 08, 2020, 11:32:00 pm
content: I have a circuit like the one in the image (plus a few more caps)P1 on the MCU is a PWM pin, 270Hz frequency and 60% duty.What I am trying to achieve is convert the PWM output from the MCU to a 12Volt open drain output.According to my oscilloscope the voltage on the collector is about 2.2V (when it's ON). I would expect it to be closer to 0V. Any idea what am I doing wrong?

author: fcb
author_rank: Super Contributor
timestamp: March 08, 2020, 11:47:47 pm
content: https://www.mouser.co.uk/datasheet/2/68/2n4400-31590.pdfI would have thought you'd get aa little lower than that, you might have to tip more current through the base (lower the base drive resistor).Also, if you want to achieve much closer to zero, probably use a small MOSFET (2N7000/2N7002), or something like an FDN337 to be sure.

author: stafil
author_rank: Regular Contributor
timestamp: March 08, 2020, 11:56:04 pm
content: Quote from: fcb on March 08, 2020, 11:47:47 pmThanks I just tried with a 2N7000 MOSFET and the output on the oscilloscope is the same.. Could it be that I am measuring things wrong?If I change the scale on the oscilloscope to 5V my signal looks fine. When I reduce it to 1V, I see the wrong base.(PS: Also tried reducing the resistor at the base down to 100Ohm, but the signal is the same, minus some more under/overshoot)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 09, 2020, 12:06:25 am
content: Probably exceeding the input range of the scope. Try moving the trace to the bottom of the screen, or another measurement method.Tim

author: stafil
author_rank: Regular Contributor
timestamp: March 09, 2020, 12:39:41 am
content: I think you are right. The EspoTek Labrador oscilloscope shows the ON voltage to be around 0V, which is the expected.
2n5818 transistor replacement - Page 1
Forum section: electronics / beginners

author: cowboy303
author_rank: Regular Contributor
timestamp: July 03, 2012, 12:20:58 am
content: OK I have a BK Precision 1730 that has a little 2n5818 transistor that is bad. And I need a replacement for it but the cheepest I can find it is $1 each and that's on eBay which I don't want to do. So I was wondering if there is a replacement for it that's a bit cheaper.

author: rsjsouza
author_rank: Super Contributor
timestamp: July 03, 2012, 01:22:59 am
content: Hi,When searching at Jameco, the result is a very common BC337 (its characteristics seem very similar)http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_254810_-1Some repair sites also list this (and others) as equivalents:http://www.lcdtvrepair.us/transistor/2N5818_Driver_de_audio_--13440However, always keep in mind that, if the equipment requires precision or depends on a very specific characteristic of the device, an equivalent is not identical...

author: vk6zgo
author_rank: Super Contributor
timestamp: July 03, 2012, 05:15:35 am
content: One trick if the transistor characteristics are very critical to the circuit,is to examine the schematic to see if they also use the same type in a non-critical application,such as turning on an LED,or whatever.Very carefully remove that transistor,use it to replace the critical one,& fit a substitute part in the non-critical position.Manufacturers frequently use one type of transistor both in circuits that need its special characteristics,& in other positions that don't,as a method of reducing inventory.Of course,If the original transistor is in a non-critical position,just replace it with a substitute.

author: Codemonkey
author_rank: Regular Contributor
timestamp: July 03, 2012, 07:53:47 am
content: FWIW, towers international transistor selector book also lists the BC337 as an equivalent.

author: cowboy303
author_rank: Regular Contributor
timestamp: July 03, 2012, 01:14:19 pm
content: Quote from: vk6zgo on July 03, 2012, 05:15:35 amGood idea I will switch it out with the transistor that runs the constant current led.
2N5912 replacement - Page 1
Forum section: electronics / beginners

author: txescientist
author_rank: Regular Contributor
timestamp: September 15, 2013, 12:45:08 pm
content: I have to repair some old equipment and need replacement for 2N5912 Dual N JFET. Found that replacement chip is LS5912, but I can't buy it i my country. Can I use two identical JFETs instead and which one? Any recommendations will be greatly appreciated !
2nd. order Butterworth as attenuator - Page 1
Forum section: electronics / beginners

author: IvoS
author_rank: Frequent Contributor
timestamp: September 21, 2014, 07:51:28 pm
content: I need to generate clean 1kHz 1mV sinusiodal signal. I am using Arta soft on my notebook using headphone output. I can adjust generator in Arta soft to somewhere -21dB and lower the volume on the notebook and that gets me to 1mV out. The problem is the noise floor and therefore to take accurate measurement of 1mVAC. I have couple of multimeters they have 1uV resolution but the noise floor is a killer.So I was thinking to get 100mV out from my notebook, which produces reasonably clean signal and then use LM49710 in inverting configuration with G=-100 to get me to 1mV.I was trying to use FilterLab soft to make a 2nd order(or higher order) Butterworth low pass filter to reject unwanted noise but the problem is that options are only for gain 1+. Does it mean there is no chance to have low pass Butterworth as attenuator?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 21, 2014, 09:20:39 pm
content: 1mV / 100mV = 0.01 gain, not -100. Use a resistor divider.If you still need a cleaner signal, you can filter it, but mind you will still be left with the noise in the passband.Also, try the laptop on battery power, AC adapter disconnected. The adapter often adds a lot of noise for some reason.Tim

author: macboy
author_rank: Super Contributor
timestamp: September 24, 2014, 02:16:07 pm
content: I would construct a precision 100:1 divider. You can verify the divider by either measuring it with DC or by measuring the resistor ratios directly (99:1). Then send a 100 mV signal into it, and trust that you have 1 mV coming out. Equipment that can accurately measure 1 mV is out of reach of most people. You can measure the 100 mV much more easily. Buffer the output of the divider to prevent voltage sag due to the load.

author: David Hess
author_rank: Super Contributor
timestamp: September 24, 2014, 08:05:22 pm
content: Quote from: macboy on September 24, 2014, 02:16:07 pmA simple divider is also easy to capacitively compensate if necessary for a flat frequency response.I have done this exact thing to generate precisely known low voltage waveforms but I used a precision switched RF attenuator which neatly avoids any compensation issues. I calibrated the attenuation at high signal levels were I could accurately measure the input and output and then relied on the now calibrated attenuation to know the miniscule output signal level based on the measured input signal level.
2PSU, Same problem-same fix-different results: Odd Power supply output "flicker" - Page 1
Forum section: electronics / beginners

author: EEVPiobee
author_rank: Contributor
timestamp: June 14, 2014, 07:19:30 pm
content: Hello there!Today I fixed two small power supplies, same model, same design, same batch on manufacture production run... (SMPS, 12v, 4a, rated, classic Chinese design) that broke down two years ago (don't say I'm slacker, I just reallly busy and those were not a priority at the moment)The problems on these two turned out to be the PMIC that went bad for some reason and the output diodes (2x 3amps in parallel argh!) were heating up, even without load on them...So here is what I've done...I changed:PMIC for new ones, same model (and added a socket for serviceability) (CR6853T)output diodes (cheap generic) for a Schottky TO220 pack 10 amps (B10150CTG)andChanged the opto-couplers used for feedback for new ones if ever this was the reason PMIC didn't work properly. (PC817C)This trick WORKED on both, (at least nothing blows up, and now passes the finger test) but...One of the two power supplies gives me a "flicker" on the output voltage... I'd say it's some sort of a sawtooth every 0.3-0.5 seconds or so...for that purpose, let's call them PSU1 and PSU2...As PSU1 outputs a perfect steady 11.89volts (good enough to me for a 12v supply and what is powers)PSU2 Reads from 11.86 and drops down to 11.6 within a .3-.5 period delay and then instantly raises back to 11.86v (the led on the board flickers as well)Any ideas??p.s. I haven't tested them with load on them yet, also, I tried swapping the new PMICs between the two but same result... Flicker stayed on PSU2
2SC5200 fake or original? - Page 1
Forum section: electronics / beginners

author: kingofthevua
author_rank: Newbie
timestamp: October 14, 2018, 01:43:53 pm
content: Hi all!I'm a new member, please help me.I have some kind of transistor 2SC5200. I don't know it is fake or original (I think left is original and right is fake)? I had took some pictures about it. Please help me!

author: Audioguru
author_rank: Super Contributor
timestamp: October 14, 2018, 01:57:07 pm
content: ebay might sell fake Toshiba ones. Why guess if it is fake? Simply buy genuine ON Semi ones at Digikey.
2SD870 Question - Page 1
Forum section: electronics / beginners

author: OpenCircuit
author_rank: Regular Contributor
timestamp: February 09, 2020, 01:59:00 am
content: Faulty?

author: floobydust
author_rank: Super Contributor
timestamp: February 09, 2020, 02:14:31 am
content: It doesn't look promising.Why aren't you using diode-test? I have no idea of ohms test current and voltage on UT-61E.There are six possible readings to look at when testing a tranny.2SD870 has a built-in EB resistor, and CE damper diode, so those readings would be unexpected.

author: OpenCircuit
author_rank: Regular Contributor
timestamp: February 09, 2020, 02:21:59 am
content: Sorry I updated the images. With ohm test I was diagnosing a blown fuse.

author: floobydust
author_rank: Super Contributor
timestamp: February 09, 2020, 05:53:29 pm
content: That's pretty much dead shorted, all the readings way too low. 2SD871 also works.

author: OpenCircuit
author_rank: Regular Contributor
timestamp: February 09, 2020, 09:50:03 pm
content: I sent the seller images on ohms settings showing dead short while removed from circuit and they stated it was functioning normally.I am no EE, but I know a place....

author: floobydust
author_rank: Super Contributor
timestamp: February 10, 2020, 01:40:01 am
content: I would hacksaw off the top and peek inside. Might be good for a laugh. Where was the seller, so we can avoid them.

author: ArthurDent
author_rank: Super Contributor
timestamp: February 10, 2020, 02:25:43 am
content: When I click on the images above I get a 'malicious link' warning from Kaspersky Internet Security.

author: OpenCircuit
author_rank: Regular Contributor
timestamp: February 10, 2020, 06:06:13 am
content: Quote from: ArthurDent on February 10, 2020, 02:25:43 amBeen posting images there for years.Quote from: floobydust on February 10, 2020, 01:40:01 amChop it up...sounds like fun- if I do I will post what I find.Sorry, I'd rather not say. I don't think this person actually looked at the ohm reading images I sent and just assumed based on historical information. I'm curious as to how many of those are new defects.

author: OpenCircuit
author_rank: Regular Contributor
timestamp: February 11, 2020, 09:09:24 pm
content: Let down was all I found... not even a laugh inside.

author: wraper
author_rank: Unknown
timestamp: February 11, 2020, 09:26:25 pm
content: Blue glass seals are a dead giveaway of fake Chinese crap.
2SK118 transistor alternative, what are most important parameters to look for? - Page 1
Forum section: electronics / beginners

author: HMS
author_rank: Contributor
timestamp: January 19, 2024, 04:59:21 am
content: Hello,i have an old microphone and found a TOSHIBA 2SK118 transistor. so, i want to replace the PCB and buy new components but could not find an alternative to this 2SK118 FET transistorthere are many parameters in datasheet, I have strong feelings that the Gate to source voltage also the very low current drain both are unique, but which parameters or (main parameters) i should be careful about to achieve similar or better results. have no ideafor an electret microphone, what would be the best alternative for this one? or better.thanks.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 19, 2024, 08:12:51 am
content: Which fets work can depend on the circuit it is used in. A problem with JFETs is that the threshold voltage and thus Idss is quite scattering. Most circuits are made to work with a certain range - some care more about the current and others more about the threshold voltage. With Electret microphone the additional problem can be that the gate leakage can matter - they may use it to set the DC biasing.Most electret microphones are a closed system with essentially no way to exchange the 1st critical FET. If the JFETs is used in a later stage so with a separate capsule that alread contains a FET things are easier. Than its only a more normal amplifier stage and it really depends on the ciruit and target (low noise, low power or wide voltage range). For audio amplifiers one usually prefers low threshold types, so maybe SK209 or SK3557 for low noise but with higher current, mmbfJ201 or SK208R for not so high current. For a later stage there is not real need to go overkill with the noise, as the capsule itself has quite some noise.