BLDC TOOL TERMINAL BATTERY VOLTAGE SERIES

The input filter itself presents a certain output impedance to the input of the boost.

BLDC TOOL TERMINAL BATTERY VOLTAGE SERIES

As a result, for most designs at a given duty cycle, the DCM boost design will give a higher Vin to Vout transfer function, allowing lower input voltages to be reached.ДЄs previously mentioned, any series losses of the input filter and reverse polarity protection diode reduce the input voltage level to the boost stage. In continuous conduction mode (CCM) this transfer function has less of a load dependency than in discontinuous conduction mode (DCM). This is commonly referred to as latch-up and most boost designs will have a Vout limitation of somewhere between three and five times the input voltage (Vin), depending upon the efficiency of the design, for high duty cycles. Any boost has a natural duty cycle limitation caused by increasing losses at high duty cycles, causing the output voltage (Vout) to collapse at a given duty-cycle. However, in designing to this requirement there are numerous considerations, some of which may discount a conventional boost. 1 вЂ“ Conventional Boost Topology using NCV8871 A conventional boost topology could do this so long as it can sustain the higher voltage transients it may encounter such as double-battery and load dump.ДЇig. Subject to such a condition the system designer looks to increase or boost that 2.0 V input voltage to a level that prevents the system power supply from entering drop-out or UVLO. So we have a power supply that doesnвЂ™t function at cold-crank! Irrespective of whether that system power supply is a linear voltage regulator or a buck switched mode power supply (SMPS), 2.0 V on its input will either put it into drop-out or incur under voltage lock-out (UVLO) before the internal voltage rail collapses.

Most system power supplies down convert normal battery input voltage to 5.0 V or 3.3 V. The input voltage to the system power supply could in fact be as low as 2.0 V. So, we now have down to 3.0 V at the system input, but of course this is not the input voltage that the vehicle power supply will see this will in fact be lower due to the series resistance of the reverse polarity protection and input filter circuits. The battery internal resistance is not a constant but a function of temperature, and as the temperature falls, the loaded battery terminal voltage falls further. Current is drawn from the battery, and a voltage is dropped across its internal resistance, which increases with current. So what happens at cold-crank that causes the voltage to be so low? The battery terminal voltage is a function of its off-load voltage and the voltage drop across its internal resistance. The conventional vehicle power supply architecture can be adapted to guarantee vehicle system operation through such conditions. However, subject to extreme cold temperatures, the battery voltage level when the starter is engaged can be as low as 3.0 V, a condition that might last for as long as 19 mS. The normal voltage level of what is designated as a 12 V vehicle lead acid battery may vary between 9 V and 16 V.

Bldc tool terminal battery voltage