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Is 10mA enough to switch an opto?
Is 10mA enough to switch an opto on completely?
When looking at the datasheet of the SG3524, I noticed that the max. duty cycle when in flip flop mode is 45%. So we can say that the cigar box TS switch never ran at full 50% duty cycle.
The specs on the output section gives an Emitter output voltage of 18v when Vcc is 20V. That is about 90% of the supply voltage
So if we supply it with 12v, the pulse amplitudes must be about 10.8v.
The pickaxe chip probably only gives out 5v
I message Blackchisel on Skype the morning and we discussed the amount of current that we have to supply the opto to make sure it switch the transistors on fully
From the H11D1 the datasheet we see on the Normalized Output Current vs. LED Input Current graph that at a led current of 10mA, we already get a output collector current of 1A
At 60mA it is 2Amp!
That means to me that 10mA should be enough to switch the transistor on full, but I can be wrong.
The absolute max rating of Forward DC Current, IF as 80mA. I hope it is for the led part as they also talk about the emitter there
The LED Power Dissipation is 159mW. So I think 80mA should be fine.
From the LED Forward Voltage vs. Forward Current graph we see that at 80mA the forward voltage (voltage drop over the led part) is 1.25V
A Sg chip supplied with 12V gives an output of 10.8V
10.8v – 1.25v = 9.55V that must drop over the limiting resistor if we only drive the one opto
For 80mA we need a 9.55/60mA =160 ohm resistor
For 10mA we need a 955 ohm resistor
From 5V output of pic : 5V – 1.25V= 3.75V that must drop over the limiting resistor if we only drive the one opto
For 80mA we need a 3.75/60mA= 62 ohm resistor
For 10mA we need a 375 ohm resistor.
Now if you want to put more optos in series you need to deduct 1.25v for every opto from the supply volts to get the voltage drop over the limiting resistor
If you want to install a led in line to see the pulsing you must remember that a led should only get about 20mA. I don’t think it will like 60mA. You will have to put a series and parallel resistor with the led to pass the extra current.
Then of coarse if 10mA is enough this whole dicussion was in vain!!
Is 10mA enough to switch an opto on completely?
When looking at the datasheet of the SG3524, I noticed that the max. duty cycle when in flip flop mode is 45%. So we can say that the cigar box TS switch never ran at full 50% duty cycle.
The specs on the output section gives an Emitter output voltage of 18v when Vcc is 20V. That is about 90% of the supply voltage
So if we supply it with 12v, the pulse amplitudes must be about 10.8v.
The pickaxe chip probably only gives out 5v
I message Blackchisel on Skype the morning and we discussed the amount of current that we have to supply the opto to make sure it switch the transistors on fully
From the H11D1 the datasheet we see on the Normalized Output Current vs. LED Input Current graph that at a led current of 10mA, we already get a output collector current of 1A
At 60mA it is 2Amp!
That means to me that 10mA should be enough to switch the transistor on full, but I can be wrong.
The absolute max rating of Forward DC Current, IF as 80mA. I hope it is for the led part as they also talk about the emitter there
The LED Power Dissipation is 159mW. So I think 80mA should be fine.
From the LED Forward Voltage vs. Forward Current graph we see that at 80mA the forward voltage (voltage drop over the led part) is 1.25V
A Sg chip supplied with 12V gives an output of 10.8V
10.8v – 1.25v = 9.55V that must drop over the limiting resistor if we only drive the one opto
For 80mA we need a 9.55/60mA =160 ohm resistor
For 10mA we need a 955 ohm resistor
From 5V output of pic : 5V – 1.25V= 3.75V that must drop over the limiting resistor if we only drive the one opto
For 80mA we need a 3.75/60mA= 62 ohm resistor
For 10mA we need a 375 ohm resistor.
Now if you want to put more optos in series you need to deduct 1.25v for every opto from the supply volts to get the voltage drop over the limiting resistor
If you want to install a led in line to see the pulsing you must remember that a led should only get about 20mA. I don’t think it will like 60mA. You will have to put a series and parallel resistor with the led to pass the extra current.
Then of coarse if 10mA is enough this whole dicussion was in vain!!
Hopefully the optos and the diodes will arive tomorrow, please Mr. Postman! 
Hopefully tomorrow - then I can play with the digital big boys 
) neither with SC or TS. I just built another SS and will rotate them several times. Maybe this will help.
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