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oxxyfx

Voltage regulator question

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Hello,

My AWM633 transmitter has 2 voltage regulators. One is from whatever to 5V and the other one is from 5 to 3.3V to power the transmitter. I need both of these on board the transmitter circuit.

However - because of the total power consumption = 850mA = both these heat up quite nicely - also the 633 isn't the cooldest either while under power.

I measured the temperature of the circuit - without cooling it runs about 90-100 Celsius which corresponds to 194-212 F.

Is this in the acceptable range? Beside adding heat sinks to the voltage regulatros is there any other option? Like going with a 1.5A regulator instead a 1A? Would that make any difference?

The system is powered from an 8.4-9V battery.

Thanks, Ox.

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Or, pick a lower battery voltage. BTW, it is odd that your AWM633 design draws 850mA. Max should be around 600mA. If you are sharing the VRegs with a CCD camera, then you can reduce the thermal issues by powering the camera from its own VReg board.

Lastly, the AWM633 will run cooler if it is soldered directly to a well designed PCB, which will act as a heatsink. All it takes is adequate copper groundplane connections to all the ground pins. Be sure to use a impedance controlled stripline trace on the RF output.

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LM2675-05 would be worth a try, the noise problem is the only worry of course. What voltage are you dropping from ?

Terry

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The circuit powers the Kx131. The 633 is drawing within the allowed limits - around 600mA.

The circuit is fed by an 8.4V-9V battery which goes into the 5V LDO (LM2940) and from there it splits - one way goes to the camera, the other goes to the second LDO - 3.3V (LM3940). I measured the power consumtion on the switch which is on the positive line of the battery.

The AWM633 it is soldered to the circuitboard properly - however so are the LDO's. So I think these guys are heating up each other... :) The original LDO's I was using were TO263's (to conserve space) and are properly soldered to the board. I can see the heat exchange is great, because almost everything heats up at the same time... :)

Now I am thinking of redesigning this board, and pulling the two v-reg up on the top beside the sma connector with added heat sinks. Only I wanted to check with you first to see if any other v-reg - like a 1.5A - or a switching one would run much cooler than these...

The RF line is impedance controlled.

The minimum battery I can pick is still a 2 cell lipo - 7.4V I tried that as well, it heats up slower but to the same temperature.

Also let's not forget that since this is a transmitter unit it has to be as small and light as possible.

Thank you.

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Only I wanted to check with you first to see if any other v-reg - like a 1.5A - or a switching one would run much cooler than these...

A bigger linear Vreg will reduce the heat only from the added mass of its body. It would be just as easy to add an external heatsink or a hunk of aluminum plate.

Thomas S. has announced that he designed a FPV qualified DC-DC switcher supply that has zero EMI/RFI. If it is as good as claimed, it would solve your problem with the heat and not add noise to your installation.

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