I read atleast 3 or 4 topics about diodes but in none of them actually I found something useful.
I just want to have a diode. Common diode
I will be using it sometimes for rectification (max 24V), as a flywheel (for reverse motor shitty things) and for similar things that just require something to prevent for wrong placed "+" and "-" wires. I read about 1N and did a google search plus I viewed its datasheet, but it says that there are "stronger" diodes - 1N to 1N... And I got confused...
So would you please suggest me a proper diode? Thanks in advance.
If you are looking for more details, kindly visit Hornby Electronic.
The two most important specs are forward current and reverse voltage. I usually buy a higher voltage version (1N) since they don't cost much more and I'm usually buying more than I need so I don't know what I'll be using them for.
As a flyback (or flywheel) application the (peak) current through the diode will be the same as the current through the motor/coil, and the reverse voltage will be the applied voltage.* (So, in most low-voltage applications, voltage isn't an issue and you just have to check the current.)
I will be using it sometimes for rectification (max 24V)
When I'm building a power supply I usually use a [u]bridge rectifier[/u] which is 4 diodes in one package. I may have made a bridge from 4 1N's, but I don't remember. With a single diode, the power is "off" for half of the AC cycle which means you get more ripple (or you have to use a bigger capacitor) and you can only get half the current.
Contact us to discuss your requirements of small signal schottky diode. Our experienced sales team can help you identify the options that best suit your needs.
Or, if you have a center-tapped transformer you can get full-wave rectification with two diodes.
The forward voltage across a standard silicon diode is about 0.7V (depending on current) and in some applications where you want a smaller voltage drop, you can use a Schottky diode. Schottky diodes also switch faster than standard silicon diodes so they are sometimes used in high-frequency circuits.
- When you disconnect an inductor/coil you get a high-voltage kick (back EMF). But, since the diode is "backwards", that back EMF becomes the forward voltage across the diode. That "kills" the high-voltage kickback, and your diode never sees high voltage.
It depends what you want to do. Most of the time it is probably not so important. If you have supply voltage 20V or more it is not so important if the diode drops 0.7 or 0.3V. If motor needs 1A you don't care if diode leakage is 1mA or 10uA. If you want something more delicate such as reverse voltage protection difference between normal and Schottky diode may be more important if the battery voltage is close to your intended operating voltage. OTOH if you build some analog circuit "large" leakage current of Schottky may cause problems.
Another important spec - diodes rated for large current are also large - they have thick leads and they are difficult to stick into solderless breadboard. I even got diodes too thick to fit into hole in protoboard.
Are you interested in learning more about high voltage diode? Contact us today to secure an expert consultation!
Hello All,
I have made small mistake for SPI Communications.
i have used ADC and Isolator which is ISO as shown in below architecture
When i tried to connect both ADC as 1 master and 2 slave configurations.. i dont get MISO signal,
Independent ADC SPI Communication is working fine..
I observed in datasheet:ISO
Output pin is in Push-pull configurations, due to which Miso response of any digital isolator is pulled by another Digital isolator, so Communication is not working.
I thought to place Diode to Digital isolator output pin so that other oscillator will not pull down MISO Signal, Can someone explain how to select diode? My SPI CLK Frequency is 13.5 MHZ
or
Can someone help how we can drive both Slaves?
Hi,
you are looking for solution as workaround for one board?
Or for redesign?
***
The problem in your circuit is:
AS long as CS of an SPI slave is inactive: the slave has to three state MISO.
While the ADCs most probably will three state it´s MISO, the isolator does not three state it´s output.
for the diode solution to work properly you need at least three pull up resistors and two diodes.
* pullup at MISO of ADC1
* pullup at MISO of ADC2
* pullup at MISO input directly at the STM
* diode in series from isolator1_MISO (C) to STM_MISO (A)
* diode in series from isolator2_MISO (C) to STM_MISO (A)
***
diode is relatively uncritical. Most important:
* reverse voltage must be >= your SPI signal HIGH level
* forward current must be >= pull up current
but the diodes (forward drop voltage) increases the LOW level seen by the STM.
So if the diode drop is 0.6V then the STM sees a LOW level of 0.6V (in best case)
Thus the lower the voltage drop the better your (noise) margin.
--> chose a diode with low voltage drop. Thus Brian recommended a schottky diode. BAT54 is good.
BAT54A is a double diode in one SOT-23 package.
***
Instead of the double diode:
* a HC(T)1G08 gives better LOW level and better timing
***
I personally avoid the use of two seperate CS by using standard IO. I´d rather use the dedicated CS form the STM_SPI module and use an external 74HC138 as DEMUX.
The benefits:
* only one SLAVE can be activated
* automatic CS of the STM SPI periferal (faster, less software overhead)
* up to 8 slaves possible
* same or less pin count of STM32
Drawback:
* external device
****
If you use more than 2 slaves, or if you use high speed SPI, then I don´t recommend the diode circuit.
Go for dedicated Three state drivers, like 74HC1G126.
Klaus
Try adding a resistor between the MCU side of the diodes and ground to pull the line down faster. The problem with using diodes for isolation is they can only actively pull the signal in one direction and they isolate it in the other so some assistance may be needed to restore the logic levels when they are not conducting. You may have to experiment with the value but I would suggest 1K as a starting point, lower values will speed up the signal but at the expense of more load on the isolators.
Brian.
Hi Klaus and Betwix
Please find attached image
I have done experiment with only Diode, reduced SPI Frequency to 1MHZ where i could see Communication working proper.. I pulled down MCU pin of MISO.
I agree that BAT54 should work, try small simulation in LTSpice (No problem).
What do you thing of Internal Capacitance of Diode which is 10pF, will it cause problem for data reduction?
--- Updated Nov 3, ---
Hi,
For next iteration of PCB.. i am planning to put Mosfet in open drain configuration.
Waveform from optoisolator output as as per below image.
Can you suggest Transistor which will translate this levels
Beware of another potential problem: when the CS signal is passed to the ADC it can put the MISO into a high impedance state and 'float' the input to the isolator. If it doesn't have a default state or pull down it could result in a false signal leaving the isolator. The diode can't protect against that !
If you use an open drain MOSFET, don't forget it will invert the logic levels. The BS138 would be a suitable cheap device.
Brian.
in that case 2N would also work here, I have few stock of this in my inventory.
--- Updated Nov 3, ---
Hi,
That's O.K.
But could you do an internet search "RC cutoff frequency"
Klaus
Got it.