Instructions

This amplifier converts an analog voltage signal to a current. The input signal is referenced against ground. The dual amplifier configuration allows the amplifier to operate across the full supply voltage.

Schematic

The voltage difference between V- and V+ must be at least 15 volts.
The J1 and J2 connector are mislabeled on the schematic

Ripple suppression

The output displays a 100 mV pk-pk sine wave at 60 kHz. In order to remove this oscillation, a 0.1 uF capacitor is placed across resistor R2.

Trim Pot Tuning

Consider the combined resistance of resistor R3 and the trim pot as . The trim pot must be adjusted such that:

Current Gain

The gain equation is which gives approx. 1 amp/volt ratio for this amplifier.

Derivation

R8 is the current sensing resistor. Designate the output of the first op-amp as and the amplifier output at such that the voltage drop across R8 is

Also, designate the input signal as . Thus, for the op-amp inputs, we find that


Using op-amp analysis, we assume and get

We can re-arrange this as

At this point choose such that

(This is how we adjust the trim pot, this equation can be simplified to the trim pot equation)
Which simplifies the above equation to

Using ohm's law across resistor R8

Which can be re-arranged to find the gain equation.

-- SalomonTrujillo - 28 May 2008