Hi all,
I have attached my circuit design below.
I have a load in which I am switching on a constant current through it. The switching signal is a very low duty cycle pulse (Ton = 100us, Tperiod = 33.33ms) that is coming from a microcontroller. The current pulse that I wish to pass for the attached example is 0.25V/47R ~= 5 mA. The load itself modelled as a resistor in series with a parallel RC, and requires a higher voltage than my 5V source provides, so I have a DC-DC converter to necessitate that.
The PNP connected to the Vcc high voltage rail is essentially the switch that gets the conduction going through the load and I needed to be able to control it via an I/O port on my microcontroller. I am using a 4N33 NPN optocoupler to isolate the 5V switch signal in order to bias it appropriately so that I can turn on the PNP switch.
I figure that both the NPN and PNP in series with the load need to be saturated and will have roughly Vce = +/- 0.3 V (2N3904/906).
Wondering if this bias setup is a reasonable way to get the job done. The high voltage source is going to be upwards of 70V and I wanted to be careful not to damage the optocoupler.
Thank you in advance,
JP
I have attached my circuit design below.
I have a load in which I am switching on a constant current through it. The switching signal is a very low duty cycle pulse (Ton = 100us, Tperiod = 33.33ms) that is coming from a microcontroller. The current pulse that I wish to pass for the attached example is 0.25V/47R ~= 5 mA. The load itself modelled as a resistor in series with a parallel RC, and requires a higher voltage than my 5V source provides, so I have a DC-DC converter to necessitate that.
The PNP connected to the Vcc high voltage rail is essentially the switch that gets the conduction going through the load and I needed to be able to control it via an I/O port on my microcontroller. I am using a 4N33 NPN optocoupler to isolate the 5V switch signal in order to bias it appropriately so that I can turn on the PNP switch.
I figure that both the NPN and PNP in series with the load need to be saturated and will have roughly Vce = +/- 0.3 V (2N3904/906).
Wondering if this bias setup is a reasonable way to get the job done. The high voltage source is going to be upwards of 70V and I wanted to be careful not to damage the optocoupler.
Thank you in advance,
JP
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