Current clamp output

Fig. 5. (A) Simplified diagram of the experimcnlal procedure. Upper part a simplified diagram of the system used to switch on the membrane potential control system. Lower part the recorded membrane potential and membrane current. On the left side of Fig. 5A the membrane is in open loop current clamp condition because the switch at the output of the control amplifier is connected to the auxiliary feed-back loop. The action potential is excited by a short pulse of voltage through a very high resistor connected to the axial wire. On the right side of Fig. 5A the switch connects the output of the control amplifier to the axial wire and the membrane is under voltage-clamp control. The free course of the action potential is interrupted and the recorded potential is equal to the command potential. Simultaneously membrane currents are recorded as shown in the bottom of the Fig. 5A. (B) The superimposed traces shown in the upper part were obtained with set at 60 mV. For the records in the middle was set at —80 mV. (Used with permission from F. Bezanilla et al. [19].)...

The Constant Amplitude Current Output (Current Clamp)... 

U sing OAs allows construction of potential and current control circuitry that operates more ideally than the simple voltage and current sources of Fig. 1 [2]. In voltage control appKcations, the use of an OA buffer between a voltage source and the cell replaces the internal resistance of the voltage source with the low-output impedance of the OA. However, a simple extension of the OA buffer permits elimination of a large fraction of the solution resistance of the electrochemical cell. This OA circuit is called a potentiostat or voltage clamp. 

The power switch Q1 then turns off and the secondary of the switching transformer flies back above the output voltage and is clamped by diode D1 at the output voltage. The energy stored within the transformer is then transferred to the secondary circuit. The secondary current then begins to linearly ramp downward until the energy within the transformer core is completely depleted. This is shown as t > in Fig. 10.46 (see also Fig. 10.47) and is described as... 

A commonly used neuro-stimulation scheme is to inject charge with a constant-current pulse, then recover the charge by clamping the circuit output back to ground voltage. In the passive recharge phase, the circuit operates similarly to the recharge... 

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