Month: May 2015

Load Cancellation Circuit

Amplifier output loading can be reduced or even eliminated by use of a load cancellation circuit such as that of U2. Without load cancellation, the inverting unity- gain op amp U1 output current is a function of its input voltage Vin and its 1k load resistance RL. At Vin = 1V, both AM1 (U1 output) and AMload (load current) = -1mA.

With compensation adjusted for 100%, the load current is furnished entirely by the compensation circuit. Thus the output of U1 essentially sees an “open circuit”. Rc controls the degree of load current compensation. Bypass capacitors are not shown. (Circuit is created by Neil P. Albaugh,  TI-Tucson)

Load Cancellation Circuit:

Online Simulation of a Load Cancellation Circuit:

The great feature of the TINA circuit simulator that you can analyze this circuit immediately with TINACloud the online version of TINA. Of course you can also run this circuit in the off-line version of TINA.

Click here to invoke TINACloud  and analyze the circuit yourself or watch our tutorial video!

You can send this link to any TINACloud customers and they can immediatelly load it by a single click and then run using TINACloud.

Michael Koltai
www.tina.com

Two OPA569 Current Sources in Parallel

This circuit provides voltage- controlled constant- current biasing of a grounded- cathode laser diode. As shown, the OPA569 op amp provides an output current of 500mA per volt input. The OPA569’s output is current- limited to 2A by R3 & R4. Bypass capacitors are not shown. This circuit takes advantage of the unique topology of the OPA569; it does not require a shunt resistor to measure its output current. This amplifier provides an output monitor current from pin 19  that is 1/475 th of its output current. The voltage developed across R1 & R2 are used as negative feedback to the amplifier’s inverting input (pin 5).

A constant- current output is derived by this feedback.

Since no shunt resistor is required to measure output current, there is no reduction in output  voltage compliance due to shunt resistor voltage drop, this circuit can swing its output voltage very close to its supply rail. This increases efficiency and reduces heat sinking requirements. In fact, supply voltage can be reduced to only a few hundred mV above the load voltage.
The OPA569 features both a Current Limit (pin 4) and a Thermal Overtemp (pin 7) flag. These flags can be used to protect the amplifier and the Enable (pin 8) can be used to digitally control its status. (Circuit is created by  Neil P. Albaugh,  TI-Tucson)

Two OPA569 Current Sources in Parallel Circuit:

Online Simulation of the “Two OPA569 Current Sources in Parallel” Circuit:

The great feature of the TINA circuit simulator that you can analyze this circuit immediately with TINACloud the online version of TINA. Of course you can also run this circuit in the off-line version of TINA.

Click here to invoke TINACloud and analyze the circuit yourself or watch our tutorial video!

You can send this link to any TINACloud customers and they can immediatelly load it by a single click and then run using TINACloud.

Michael Koltai
www.tina.com

Shunt Amplifier with Offset Output

By reducing the +12V common- mode voltage, an INA122 can sense the voltage drop across a shunt resistor while being powered by the same +12V power supply.  Rg controls the voltage gain of U1. This circuit is scaled for a 2.5V output range centered around +1.25V; thus this amplifier can measure bidirectional shunt current. An INA122 does not feature a R-R output so the sinking current is limited to about -0.3A. This can be useful where battery current must be monitored while it is being charged or discharged. Bypass capacitors are not shown. (Circuit is created by Tucson)

Shunt Amplifier with Offset Output circuit:

Online Simulation of a Shunt Amplifier with Offset Output Circuit:

The great feature of the TINA circuit simulator that you can analyze this circuit immediately with TINACloud the online version of TINA. Of course you can also run this circuit in the off-line version of TINA.

Click here to invoke TINACloud and analyze the circuit yourself or watch our tutorial video!

You can send this link to any TINACloud customers and they can immediatelly load it by a single click and then run using TINACloud.

Michael Koltai
www.tina.com