Circuit Enables Single NiMH Cell to Simulate a Lithium Battery


Posted on Feb 6, 2014

Lithium-based (Li+) batteries are becoming common in portable equipment. They have desirable characteristics, but they are often in short supply. Lead times can be long unless you have a preferred-customer status with the battery manufacturer. A backup alternative to Li+ is therefore desirable, especially for smaller companies. This note describes


Circuit Enables Single NiMH Cell to Simulate a Lithium Battery
Click here to download the full size of the above Circuit.

a circuit that allows a nickel-metal hydride (NiMH) cell to be used in a circuit designed for a Li+ battery. It provides the same performance, size, and cost as a Li+ battery. A circuit that interfaces a NiMH battery with a lithium-optimized circuit should mimic the battery`s terminal voltage, which declines as the battery discharges. The nominal terminal voltage for Li+ batteries (3. 6V) is about three times that of NiMH batteries (1. 2V). As a simple approach, therefore, you can force the output of an efficent step-up converter to equal battery voltage times 3: 6V/1. 2V = 3. Allowing the circuit to run constantly during shutdown, however, consumes unnecessary power. The NiMH circuit`s equivalent leakage (its quiescent current) can be as a high as 200 µA during shutdown, which is unacceptable. In fact, only a power-control capability is needed during shutdown. Instead of maintaining 3x the NiMH voltage while in shutdown, you can run the proposed circuit in burst mode, which activates the step-up converter only when the circuit output drops below a defined threshold. When the output reaches the upper threshold, the step-up shuts down, allowing the output capacitor to discharge through the output load plus the NiMH circuit. Thus, the output voltage forms a sawtooth wave. If battery voltage falls below a lower limit, however, the circuit remains deactivated to protect the battery from depletion. The circuit of Figure 1...




Leave Comment

characters left:

New Circuits

.

 


Popular Circuits

Instrument preamp
One-IC two-tones Siren
jk electrical lighting sound systems
running lights brake light to work but not the turn signal harness
The 146.460 MHz Repeater
Hard Disk Switch
Railway Points Sequencer
OTL tube amp amplifier production
Digital Cameras -DV machine power supply circuit



Top