| Electronics > Beginners |
| Operational Amplifier driving MOSFET |
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| mike_mike:
Thanks for the reply. The circuit is OK now ? And sorry for bothering you with my beginner questions. |
| Ian.M:
If it works the way you want, its O.K. We eliminated all the major problems earlier. |
| mike_mike:
Thanks for the reply @Ian.M. The 1.5K ohms (R4) gate resistor is having a sufficient value to avoid ringing and oscillations ? |
| Ian.M:
Plenty. Even 100R would stop it oscillating as long as its close to the gate pin. The advantage of 1.5K is it limits the maximum gate current (even if the MOSFET fails shorted) to under 10mA, which the OPAMP can easily handle. If you put a 100R one there, if you short the load and blow the MOSFET, there's a significant risk of it taking out the OPAMP as well. Series gate resistors always need to be as close to the MOSFET as possible - if you put them too far away, you risk the track between them and the gate acting as an antennae coupled to the load circuit, possibly turning the MOSFET into a power oscillator. |
| mike_mike:
Thanks for the reply. You said about distance between the resistor (R4) and mosfet. On my layout, that distance is about 200 mils and the trace is about 2mm wide. It is sufficiently short ? |
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