Hello,
I'm trying to figure out a way to use 4-20mA to control 0-40V.... basically, I have a current output module that I can control with my computer... but I need to use these 4-20mA to supply 0-40V across a resistive load (it's a heater), so the heater is around 80Ω and will draw around 0.75A....
I'm googling around the internet for a transistor circuit that may accomplish this... but I was also thinking of maybe using an op amp...
Right now I'm thinking about a BJT with the load between Vcc and the Collector, and sending my 4-20mA to the Base... which would basically be using 4-20mA to control a larger current.... ic = βib ....
i was wondering if someone could tell me if I'm on the right path with this solution or if there's a better way
much thanks!
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I just found the TI OPA548, which is an op amp that can do up to around 60V and 5A.... plenty for what I'm trying to do, so I tried to spice my circuit (with the OPA547 which is limited to 0.5A) but my simulation isn't giving me the results I expected... there was an E/S pin that I needed to pull high according to the datasheet, to make this work... but I was shooting for 40V out and I'm only getting around 7.75V.... I calculated my values for the gain according to Av = 1 + R3/R2... but it's not giving me that gain... can anyone tell me if I hooked up something wrong here, thanks!
![opa547.JPG opa547.JPG](https://www.electro-tech-online.com/data/attachments/25/25096-3421dbee963a3b7be71e6b1190c9937a.jpg)
I'm trying to figure out a way to use 4-20mA to control 0-40V.... basically, I have a current output module that I can control with my computer... but I need to use these 4-20mA to supply 0-40V across a resistive load (it's a heater), so the heater is around 80Ω and will draw around 0.75A....
I'm googling around the internet for a transistor circuit that may accomplish this... but I was also thinking of maybe using an op amp...
Right now I'm thinking about a BJT with the load between Vcc and the Collector, and sending my 4-20mA to the Base... which would basically be using 4-20mA to control a larger current.... ic = βib ....
i was wondering if someone could tell me if I'm on the right path with this solution or if there's a better way
much thanks!
-------------------------------------------------------------------------
I just found the TI OPA548, which is an op amp that can do up to around 60V and 5A.... plenty for what I'm trying to do, so I tried to spice my circuit (with the OPA547 which is limited to 0.5A) but my simulation isn't giving me the results I expected... there was an E/S pin that I needed to pull high according to the datasheet, to make this work... but I was shooting for 40V out and I'm only getting around 7.75V.... I calculated my values for the gain according to Av = 1 + R3/R2... but it's not giving me that gain... can anyone tell me if I hooked up something wrong here, thanks!
![opa547.JPG opa547.JPG](https://www.electro-tech-online.com/data/attachments/25/25096-3421dbee963a3b7be71e6b1190c9937a.jpg)
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