28X1 maximum safe voltage on Vdd

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Andres Rodriguez

New Member
I am powering a 28X1 through a radio control receiver. The receiver power is from an electronic speed control the outputs a nominal 6V. See attachment.
According to the PIC16F886-I/SP datasheet the max voltage is 6.5V.
All the Picaxe documentation talks about 5V. My question is am I safe using 6V supply?
 

Attachments

A

Andrew Cowan

Senior Member
You should be OK. All of the ESCs I have that include a BEC output 5V. If in doubt, you could use a very low dropout 5V regulator. Maxim have a 300mV dropout range.

Hope this helps,

Andrew
 
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Andrew Cowan

Senior Member
Good idea shack - diodes have a forward voltage - a voltage drop as electricity is passed through them.

A standard 1N4001 diode has a voltage drop of 1.1V (at 1A draw). The 1N4001 to 1N4007 range is good for up to 1A.

Make sure you put the diode in the correct way or the circuit will not work - the side of the diode with the stripe should be nearest 0V - the side without the stripe should be nearest the 6V.

Andrew
 
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ylp88

Senior Member
It's probably best to use two diodes in series to drop the supply voltage as the Vf of a silicon diode is usually closer to 0.6-0.7V (rather than 1.1V).

ylp88
 
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westaust55

Moderator
Maxx safe voltage for PICAXE

The Absolute Maximum Voltage for Vdd is 6.5 V
But this is the Absolute Maximum Voltage – there is great prospect of rapid failure if ever operated above this voltage.

For normal continuous operation the datasheet states the maximum voltage for Standard Operating Conditions for Vdd as 5.5V and the typical value as 5.0V.

For the recommended 1N4001, the stated forward voltdrop of 1.1V is applicable with the max current of 1 Amp but can typically be around 0.95V at 1 Amp. For lower currents, like 50mA, the forward voltdrop is more like 0.7V.
Thus if using series diodes for volt drop, I agree with ylp88 that you should use 2 diodes in series.

IMHO, the better approach would be the low voltage drop-out (LDO) type voltage regulators for a consistent output voltage irrespective of the current drawn.
 
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westaust55

Moderator
The LP2950 LDO voltage regulator by National Semiconductor and other manufacturers is available in a 5V version. Rating is 100mA.
Available in a T0-92 case with three legs (akin to hole mounting transistor).
This can be purchased from Futurlec.
 
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