Activity for Chupacabras
| Type | On... | Excerpt | Status | Date |
|---|---|---|---|---|
| Edit | Post #292792 | Initial revision | — | 2 months ago |
| Answer | — |
A: Opto-coupler, slow turn off I changed value of resistor R318 from 10 kΩ to 1 kΩ, and that alone significantly improved off-time. From 200 μs to around 25 μs. That is much better. Improved off-time So I looked into datasheet again. I found the answer on page 5, figure 8: Switching time vs load resistance Test circ... (more) |
— | 2 months ago |
| Comment | Post #292791 |
Thanks for quick answer. I have added link to that opto. I mentioned target speed to be 9600 baud. Currently the on-time is about 5 μs, so I would be absolutely fine with such off-time. As I understand, you blame transistor Q301 is not switching-off fast enough. It's probably not the case. I mentione... (more) |
— | 2 months ago |
| Edit | Post #292787 |
Post edited: |
— | 2 months ago |
| Edit | Post #292787 | Initial revision | — | 2 months ago |
| Question | — |
Opto-coupler, slow turn off I have an opto-coupler circuit where is very slow turn off. I can't figure out what is the cause of this problem. It's for UART isolation, with speed 9600 baud. Datasheet: EL357NC Do I have some error in my schematic? Or is actually opto-coupler IC faulty? This is schematic: sc... (more) |
— | 2 months ago |
| Comment | Post #291003 |
I actually went through searching. BCM847 costs like 0.15€ and has hFE matching around 0.90 (so 10% tolerance).
But I found better part IMHO, DMMT3904W and DMMT3906W, they cost 0.04€, and have hFE matching 0.98 (so 2% tolerance). (more) |
— | 10 months ago |
| Edit | Post #291003 | Initial revision | — | 10 months ago |
| Question | — |
Matched transistors There are circuits that require matched transistors. Whether BJTs or FETs. Like current mirrors, logarithmic amplifiers, etc.. There are some examples: https://www.youtube.com/watch?v=DUlugLSroN8 https://www.youtube.com/watch?v=QY48IQXJIRI https://www.youtube.com/watch?v=RpKEq5WyoLg ... (more) |
— | 10 months ago |
| Comment | Post #289577 |
@#36396 The slope control actually doesn't start from 0V, but starts at 2 diode drops. Is it wise to remove R8 and change value of R7 to 10k? So the startup time is the same, but it starts at 1 diode drop, instead of 2 diode drops. (more) |
— | over 1 year ago |
| Comment | Post #289577 |
I have stimulated this circuit to figure out how it works, it works perfectly well. I extremely like it :) thanks for sharing it and your experience.
How long it took one to develop such circuit? (more) |
— | over 1 year ago |
| Comment | Post #282140 |
Thanks for answer. It's LMV431 (1.25V reference), not TL431 (2.5V reference), but that's probably not important in this case. About R21,D21,C21, now I found the same thing in another datasheet, for TPS23750 on page 31. It seems like TI's special recipe. (more) |
— | over 3 years ago |
| Comment | Post #282205 |
The switching frequency of that flyback is 98kHz. So it corresponds with the chart of the compensator response you posted. Do I understand it correctly that it (R22, C22, C23) basically filters out 100kHz ripple from feedback? (more) |
— | over 3 years ago |
| Edit | Post #282124 |
Post edited: |
— | over 3 years ago |
| Edit | Post #282124 | Initial revision | — | over 3 years ago |
| Question | — |
Meaning of some components around voltage reference in SMPS I have generated flyback convertor schematic by TI's Webench Power Designer. Parameters: - universal AC input (85-265V AC) - 5V, 2A output - isolated - UC3843A controller Basically I understand flyback topology, but I do not understand the function of some components around voltage referenc... (more) |
— | over 3 years ago |
| Comment | Post #280675 |
Thanks for XR46010ISBTR. It's not usable in this case, but I could use it somewhere else. (more) |
— | almost 4 years ago |
| Comment | Post #280672 |
@Lundin Well, my question was not focused on alternative schematics or options how to modify that circuit. My question was really specifically about that one device, because I can't find any such device. I could use it in different circuits as well, it could be handy. btw. I already changed LED for m... (more) |
— | almost 4 years ago |
| Comment | Post #280672 |
@Lundin There is no failing part. It is working correctly. My plan was to increase output power (so increase current). But there is a device that outputs constant current, which I would like to replace for part with higher constant current. Thus I would like to find such part (what is name of it gene... (more) |
— | almost 4 years ago |
| Edit | Post #280672 |
Post edited: |
— | almost 4 years ago |
| Comment | Post #280676 |
As I wrote, there is booster and after that is the schematic I posted here (no point to put here booster from 1.5V to 3.3V). Those 2 parts are basically independent. Booster just boosts voltage to stable 3.3V. From this point it's not important, so I omitted it.
R1 could be as failsafe option. In ca... (more) |
— | almost 4 years ago |
| Comment | Post #280675 |
I have seen NCR402 during my searching. That is current source, not sink. And it has much larger dropout voltage. In my case source is 3.3V, LED is at 3.1V, so there is just 0.2V difference. (more) |
— | almost 4 years ago |
| Comment | Post #280676 |
I'm absolutely sure about that schematic. I have just verified it. The current keeps constant despite I have changed the value of that resistor (from 1 ohm to 0.5 ohm) (more) |
— | almost 4 years ago |
| Comment | Post #280672 |
Yes, it is 1 ohm. Before I reverse engineered the circuit I thought it is current sense. But it is not. I changed it to 0.5 ohm and current did not change. Then I reverse engineered schematic. I assume it is there to limit the current in case that driver failed. (more) |
— | almost 4 years ago |
| Edit | Post #280672 | Initial revision | — | almost 4 years ago |
| Question | — |
Name of this current limiting device I'm trying to modify a LED torch, and there is a DC-DC booster (1.5 V to 3.3 V) and after that some SOT-23 device which (I assume) keeps constant 90 mA current through LED. I know I could remove that device and replace it with a resistor, but that has disadvantage that current won't be as stable with... (more) |
— | almost 4 years ago |
| Comment | Post #280395 |
I was just hoping the device is better than it is :) Thanks for you answer. I'm going to read datasheets from a little bit different perspective. (more) |
— | almost 4 years ago |
| Comment | Post #280395 |
Well, I always considered charts and graphs to be more relevant. I expected real data there and I could see data for the exact range I care about. I have added response from NXP support. (more) |
— | almost 4 years ago |
| Edit | Post #280392 |
Post edited: added response from NXP |
— | almost 4 years ago |
| Edit | Post #280392 | Initial revision | — | almost 4 years ago |
| Question | — |
PCT2075 temperature sensor accuracy I read datasheet for PCT2075 temperature sensor and there are some contradicting data about accuracy for me. Page 21: accuracy ±1°C (Tamb = -25°C to +100°C) accuracy ±2°C (Tamb = -55°C to +125°C) Page 23: figure 24 looks much better than those numbers. The accuracy looks like ±0.3°C ov... (more) |
— | almost 4 years ago |
| Edit | Post #276329 |
Post edited: |
— | over 4 years ago |
| Edit | Post #276329 |
Post edited: |
— | over 4 years ago |
| Edit | Post #276329 | Initial revision | — | over 4 years ago |
| Question | — |
Switch-off time of relay with flyback diode When switching a relay there should be a flyback diode. It could be just a diode or diode with resistor in series. I understand there is a difference in the speed of relay switch-off. But what is the difference really, how to calculate it? Example in this answer: https://electrical.codi... (more) |
— | over 4 years ago |
| Comment | Post #276117 |
Interesting. How much faster will relay switch off with resistor compared to alone diode? (more) |
— | over 4 years ago |