| ??? 07/21/10 14:24 Read: times Msg Score: +1 +1 Good Answer/Helpful |
#177404 - Always too short initial posts Responding to: ???'s previous message |
How come it took you so long to mention that you where aiming to power the device from USB?
Always supply ample information in your first post. Then it would have been obvious that you are trying to draw too much power. You have 100mA (0.5W) available to you, if doing it by the book. You may have 500mA (2.5W) if ignoring everything. Only by negotiation will you know if the port does allow 500mA or not. And as noted, 90mA at 33V is more than a normal USB 2.0 socket is designed to give you. You could do it with a USB3 socket, but then again, few computers etc have USB3. And even then, you should negotiate. And even then, you also have to take into account the efficiency of the circuit. And you will have to buffer the power so the USB connector sees the average current, and not the peak current from the switching transistor. Please - always give a full description even of the tiny details you think are irrelevant. |
