Resistors, current sense

Current sense resistor (R15) and voltage sensing resistor divider (Rll and R13)... 

All current-carrying traces should be as wide and as short as possible. One-point grounding practices between the input, output, and low-level grounds should be done at the ground side of the current sense resistor. 

Figure 2. Schematic of a TOF apparatus. R is the current-sensing resistor. C is the total shunt capacitance.

For such reasons, low-side current sensing is becoming increasingly popular. Sometimes, a current sense resistor may be placed in the freewheeling path for the purpose. However, since low-resistance resistors are expensive, the forward drop across the low-side mosfet is often used for the purpose. 

Note that in general, a transfer function need not be Volts/Volts (dimensionless). In fact, neither the input nor the output of a two-port network need necessarily be voltage, or even similar quantities. For example, a two-port network can be as simple as a current sense resistor. Its input is the current flowing into it, and its output is the sensed voltage across it. So, its transfer function has the units of voltage divided by current, that is, resistance. Later, when we analyze a power supply in more detail, we will see that its pulse width modulator ( PWM ) section for example, has an input that is called the control voltage , but its output is the dimensionless quantity — duty cycle (of the converter). So the transfer function in this case has the units of Volts-1. 

Yet even they couldn t ultimately avoid this rather stubborn gate-source zener. Note that this is actually a gate to ground zener, because there usually is a current sense resistor between source and ground. 

The resulting high current ripped through the current sense resistor in the source, causing this MOF (Metal Oxide Film) resistor to fail open. 

Current limiting A technique used to provide short-circuit protection. Typically a current sensing resistor is used to turn a transistor on and off that in turn is used to provide negative feedback to hold the output current at a high but safe value. 

Figure 10.33 System diagram for a hybrid fuel cell/battery system. The bold arrows indicate energy flows. The resistor in series with the rechargeable battery is a current sense resistor used to measure the charge in and out.

For the cost down the air pressure in cuff is measured indirectly without using expensive air pressure sensor in this development. A current-sensing resistor is connected in series with the air pump/motor assembly drive circuit. The voltage dropout across this resistor is proportional to the driving current flow of the air pump/motor assembly. 

The voltage across the current sensing resistor is converted to digital by the 10-bit ADC built in MSP430F2012 microcontroller, where internal 1.5V reference voltage was used for the conversion. At the same time the air pressure in cuff was measured by an analog air pressure gauge (Welch Allyn CEO 123) to get the absolute air pressure in cuff. With... 

Fig. 3 Partial circuit of the system used to drive air pump-motor assembly and measure voltage at current sense resistor...

The voltage across the current sensing resistor is converted to digital by the 10-bit ADC built in MSP430F2012... 

Fig. 4 Voltage across the current sensing resistor for the same air pressure varies depending on the supply voltage...

Fig. 5 Upper waveform shows voltage measured at the current sensing resistor. Lower waveform shows magnified for the A in upper wave form...

The linear regulated supplies with power transformer, rectifiers, capacitor filtering, pass transistor, current sense resistor for current limitation either for constant current or with foldback characteristics and the error amplifier including the voltage reference source. 

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