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Bridge Excitation

Dogan Culum
Prodigy 40 points
Other Parts Discussed in Thread: LM337, REF102, INA105, OPA547

Hi,

 

I need a bridge excitation circuit for my project. Currently I am using REF102A with a boosted current using transistor for +10V and LM337 for -10V.

1-) I need slightly higher current than 100mA. I am using Figure 7b on data sheet of REF102. Is is possible to modify this circuit to be able to supply 200mA current without any heat sink.

What is the importance of the value R1 and transistor Q1.

2-) I want to replace LM337 with lower noise regulator. But it is hard to find such a fixed value negative regulator. Again is it possible to make it using REF102 and INA105. Figure9 of the data sheet, with higher current rating.

  • 0
    Guru 21975 points

    Dogan,

    The basic circuit diagram shown is probably capable of 200mA output current. The transistor Q1 should have a beta (hFE) of 50 or greater at 200mA for good operation. Value of R1 is set so that Q1 begins conducting output current when the load current exceeds approximately 3mA. If the value of R1 is set too high, Q1 will always be "on" due to quiescent current of the REF102.

    Q1 must dissipate 1W with a 200mA load (maybe a bit less since some load current comes from the REF102). You must provide enough heat sinking for Q1 to prevent it from overheating.

    It is possible to create a similar circuit with booster transistor on the negative side using the INA105. It might be easier to use a power op amp such as the OPA547 connected as a unity gain inverter. The OPA547 could be powered from 0V and -15V.

    Regards, Bruce.