A Solid-state Potentiostat J. E. Harrar, F. B. Stephens, and R. E. Pechacek, Lawrence Radiation Laboratory, University o f California, Livermore, Calif. sions of DeFord (3) and Kelley, Jones, and Fisher (4).
HE DESIGN of instrumentation for rcontrolled-potential electrolysis in this laboratory has led to the development of a potentiostat in which only solid-state circuit components are used, thus accruing certain advantages in operation. The instrument uses an operational amplifier as the principal control element, and the circuit arrangement is patterned after that first described by Booman (1) and the estenr
CIRCUIT DESCRIPTION AND OPERATION
The operational amplifier ( A V P . , Figure 1) is a Philbrick (6) Type P2 solid-state differential amplifier. It has an open-loop d.c. gain of about 20,000, and its lorn input current of 10-'0 amp. ensures negligible loading of the reference electrode. The P2 amplifier is used to drive a power amplifier com-
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posed of transistors &1 to Q6 to obtain up to 1 amp. current output. The output stage of the transistor power amplifier consists of an KPN and P X P complementary pair, &3 and QS, connected as a push-pull amplifier. These are driven by parallel NPN and PNP transistors, so that the over-all p o r e r amplifier is essentially a class B amplifier, one side of which is always cut off. Class B operation was chosen for its efficiency; although this type of transistor amplifier has crossover
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Philbrick Type P2 amplifier Binding posts 10 0 - p f fo 1-mfd. in steps 5-mfd., 200-v. d.c., M y l a r 500-mfd., 50-v. d.c., electrolytic 1 mfd., 200-v. d.c., Mylar 1N 2 4 8 4 1N 7 1 EA Zener 1 N 4 6 5 Zener '/*-amp., slow-blow 1 -amp., standard Banana jack 0.075-henry, 2-amp. NE-51 f 180,000-ohm assy. Microammeter, zero-center ANALYTICAL CHEMISTRY
Wiring schematic for solid-state potentiostat Power receptacle, 3-wire 2N333A HA7534 2N158A 2 N 1 3 2 5 or 2 N 1 3 3 2 10-ohm, 5-w., 1-turn, wire 1 0-ohm, 5-w. 5-ohm, 10-w. 5 1 0-ohm, 2-w. 1 00-ohm, 1 -w. as required for shunt 1 80-ohm, 1 -w. 300-ohm, 5-w. 2200-ohm, l / ~ - w .
50-ohm, l/?-w., trim for f 2 . 0 0 0 - v . control potential span 1 000-ohm, 5-w., 10-turn, 0.2% linearity, with dial 1 -megohm, l/4-w. Rotary switch, 2-pole, 3-position, shorting Rotary switch, 1-pole, 12-position, shorting Rotory switch, 1-pole, 4-position, shorting Toggle switch, SPDT Toggle switch, DPST Power transformers, 1 17-v. primary 25.2-v., 2-amp. secondary
Table 1.
Potentiostat Electrical Characteristics A 1 amp.
Output current, mas. Output voltage (aux. elec. t o gnd.), max. Control potential span: Stahility, constant ambient temp. 50-95' F. ambient temp. Regulation
f16 and - 2 v. f 5 mv. long-term =k 10 mv. long-term 1 mv. per line voltage change of 1 v. 2 mv. peak-to-peak
