how to design programmble slew rate control circuit for electronic load

Newark has it in stock, as does Farnell UK. So it's easily available worldwide from all the InOne company sites, single pieces for £0.48 from the UK site, $1.51 from the US Newark.

The problem with this approach is the diodes, of course, and their lack of a sharp cutoff. Whereas the transconductance amplifier circuit could be programmed accurately over nearly a four-decade range, the diodes would restrict one to about two decades, or even less depending on the accuracy spec. This issue can be solved by adding more parts, in this case a set of nearly-perfect active rectifiers.

. R1 R2 R3 R4 . Vin o-/\\/\\-+-/\\/\\--------+--/\\/\\--+--/\\/\\---+--> Vout . | | __ | | . | | / -|-' | . | '--< | | . | \\_+|-- 0v | . | __ | . '--|- \\ R5 R6 C1 | . | >--/\\/\\-+--/\\/\\-+---||----+ . 0v --|+_/ | | __ | . | '--|- \\ | . Vclamp __ | | >--' . o-+-------|+ \\ D1 | 0v -|+_/ . | | >--+--|--, Vnode . | +---|--+--|>|--' | . | | ,--|-_/ | | . | | | D4 | | . | | +---|>|---' R8 | . | | '--------/\\/\\------------------' . | '----------------, . | R9 R10 | . '---/\\/\\--+--/\\/\\---+ . | __ | . '--|- \\ | . | >--' -Vclamp . 0v --|+_/

I warned notstop it was a lot more complex this way.

I recognize that, a nice touch, but the problem is accurately creating 100mV clamp voltages to get a simple 2-decade range, let alone 10mV or 1mV clamp voltages, hence active rectifiers. But if the OP only needs a 20:1 or perhaps 50:1 range ...

A programmed hard-clamp of the voltage into the integrator resistor is an alternative way. Not so elegant as the OTA, but possibly good enough for your application. Requires four opamps. R1 R2 R3 R4 Vin +-/\\/\\-+-/\\/\\--------+--/\\/\\--+--/\\/\\---+-->Vout | | _ | | | | / -|-+ | | +----/\\/\\-+-/\\/\\--+---||----+ 0v+--|+_/ _|_ | _ | D2/_\\ +--|- \\ | | |OP3>--+ (-Vc+Vd) 0v+-|+_/

(+Vc-Vd)/|\\ /|\\(-Vc+Vd) | | R7 | | R8 -15v -/\\/\\--+ +--/\\/\\- +15v | | Vc +----|>|---+-/\\/\\--+---/\\/\\---+--|>|--+ D3 R9 | R10 D4 | | _ | +--|- \\ | |OP4>-----------+ -Vc 0v+--|+_/

Vc= slewing rate control voltage, 0-10v.

Vout slewing rate = Vc/R6*C1, Volts/Sec.

R1=R2, R3=R4, R9=R10, say 10k each.

R5=R7=R8, value not less than 15v/5mA.

Haven't decided on the ratio of R5:R6 yet.

The saving grace Win is that OPA2 runs wide open and switches up/down like a comparator rather than an opamp.

Ah, ok. I see what you are getting at. I had assumed a relatively crude range of adjustment, (and got stuck in the 'getting it into 1 quad opamp' mode).

"Tony Williams" a écrit dans le message de news: snipped-for-privacy@ledelec.demon.co.uk...

You can delete OP1, swap OP2 inputs, change R1/R2 ratio, connect R1 to ground and then make OP2 minus input the input.

I guess there's also something clever to do around the follower and the 2 negative clamp opamps to reduce the count by one more, but I've not found something satisfactory.

Still it'll remain 5 opamps.

In article , Fred Bartoli wrote: [....]

How about this as a slew rate limiter:

Vcc 1/3 4053 ! +Va -------- ---!!--- \\ o--!X1 ! ! ! / ! Y0!---/\\/\\--+-!-\\ ! \\ o--!X0 ! ! >---+ Vin ----!-\\ ! -Vb ! ! GND---!+/ ! ! >--+---------!A ! ! --!+/ -------- op-amp ! ! Comp ! --------------------------------------------

When the circuit is in the resting state, there is a very small saw-tooth on the output. You trade this for the softness of the circuit with diodes.

It should work over a couple of decades.

"Ken Smith" a écrit dans le message de news:dlfhu6$5od$ snipped-for-privacy@blue.rahul.net...

wrote:

Nice idea. Adding a bit of signal to the feedback (say 10-20mV/100kHz-1MHz) will help reduce output ripple. The HF ripple will be easily filtered out if necessary.