I want to make a precision 40mA low side current sink that can work with 5V to 300 Volts maximum, for use in a pro audio amplifier. Any voltage up to 100V is also available to power the solution circuit.
Has to work -40 C to + 85 C
Analog Devices doesn't make any amplifiers that work up to 300V on the power side, so I don't think we can help you.
I have this circuit that uses a silicon carbide JFET to stand off up to
1200V and sink a constant 40mA with varying temperature.
silicon carbide JFET could be replaced with a transistor.
I need a suggested op-amp and voltage reference, ideally in through hole
On 13 October 2017 at 16:46, Brandon <
The biggest question here is what voltage is the Amplifier and Reference going to be subjected to across the device?
I have a rough design, see attachment, I was after a better design from
analogue electronic experts.
As mentioned in previous post, from my own limited research Sic JFET is not
practical for cost and availability reasons yet, so I will have to go with
a NPN transistor or MOSFET.
I am working on a class G amplifier that has -100V -50V +50V +100 Volt
The op amp and reference need to get power from 50V potential difference so
a voltage regulator or zener diode will be needed.
op amp needs short circuit protection and be designed for this application.
On 13 October 2017 at 18:40, Brandon <
Another option would be to use two MJE340's in a darlington pair configuration. This would increase HFE and decrease bias current errors. Alternatively, a high voltage MOSFET would also work. The amplifier you have looks fine. I'd go with an LT1027 or LT6657 for the reference.
I was simulating the circuit with both DC and then a severe 100KHZ test
waveform, using a MOSFET i could not get good simulation results with the
high frequency. MOSFET has about 1nf gate capacitance.
I don't understand the darlington pair proposal and how it reduces accuracy
error by transistor bias current.
On 13 October 2017 at 22:34, TimW <firstname.lastname@example.org>
Is the application for DC or 100kHz (or both)? How exactly were you testing at 100kHz? The Darlington would give you high HFE which would lower the base current requirements for transistor. Less bias current would lower the error from the base currents adding to the collector current.
What kind of performance issue were you having when using the MOSFET?
Testing from DC to 100KHZ, with a signal generator that goes 10V from
common ground to +200V.
I want to regulate to target the low side transistor collector current, not
the same transistor emitter current that also includes base current.
Please send a schematic of your proposed solution to the problem
On 17 October 2017 at 21:23, TimW <email@example.com>
I'm just curious as to what's wrong with the circuit you attached earlier? Is there an issue with it's performance?
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