Replace the voltage conversion circuit of 1.35V zinc-mercury battery

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The zinc-mercury battery (mercury battery) has a stable discharge and an open circuit voltage, but these batteries have been banned due to environmental pollution.

The circuit below simulates a single-cell zinc-mercury battery (1.35 volts) that drives a low-current load circuit and is powered by a pair of ordinary dry cells. When the load is removed, the circuit will automatically turn off the power, no power switch is OK.



The reference portion of operational amplifier LM10 provides the desired output voltage that can be adjusted by varying the 4.7 megahertz and 180K resistors on the collector of 2N4401. The output current flows through the emitter-base junction of the 2N4403 and turns the 2N4401 on, activating the regulator. 22 ohm resistors, 0.01 UF capacitors and 4.7K resistors are used to stabilize the circuit when connecting large capacitive loads. A 22 ohm resistor can be reduced to account for high current loads, but if the load includes a large shunt capacitor, a resistance value below about 10 ohms stability can be a problem. Increasing the input voltage will increase the available current, but the LM10 will limit the final current to around 20mA, so the circuit will not drive the motor!

Constructed below is a shunt regulator that requires a power switch. Note that the output of the op amp is directly connected to the power supply pin. When the voltage of the entire operational amplifier exceeds 1.35 volts, the output stage sinks current and lowers the voltage. A 100 ohm resistor determines the current consumption. Determine how much current the load requires and then select this value to provide the required current. The circuit is designed to drive a load of 500uA. When the new battery voltage is about 1.6 volts, the voltage across the 100 ohm resistor is 1.6 - 1.35 = 0.25 volts and the current is 2.5 mA, which is easily handled by alkaline AA batteries. The voltage drops to 1.4 volts and can still be used. Reducing the resistance of 100 ohms provides higher load current or lower voltage drop. A 57.5 kΩ resistor was selected to achieve an accurate 1.35 volts, including two parallel resistors.



This circuit can only provide low current, and because the LM10 must shunt the current that is not used by the load, it can only absorb about 20 mA. Therefore, the load current can only change up to 20 mA. This is for most gadgets, but some devices may have a need to exceed this current (especially the motor).

For higher voltages, consider a simple regulator:



Use a Zener diode to get the desired 8.4 volt output. The J108 can deliver a few milliamps with almost no voltage drop, so the circuit will work in many zinc-mercury battery applications until the 9 volt battery drops below 8.4 volts. It is a waste of 9 volts to use only 8.4 volts. You can put it on the radio or multimeter and continue to use it to make the most of the battery. Or use a 1.5 volt AAA battery in series with a 9 volt battery to extend battery life.