# pic internal shunt voltage regulator

#### Svizoman

Joined Oct 23, 2016
9
I am using PIC16F616 in my design and I looking at the page 107: SHUNT VOLTAGE REGULATOR

It says that you can use unregulated power supply directly to the Vdd pin. It eliminates the need for linear voltage regulator, you only need capacitor and a resistor which value should be calculated as follows.

Since I am using car power supply (let's assume it's 14V) and controling two NPNs over 10k resistor my Iload is just 1mA.
So Rmax=171 4 ohm and Rmin=189 ohm.

Then I am also reading chapter: electrical specification where it says that voltage on Vdd with respect to Vss can be -0.3v to +6.5V.
What does that mean? Can I power my pic using car voltage and only internal voltage regulator or not?

#### AlbertHall

Joined Jun 4, 2014
10,056
First it is only the 16HV616 that has the internal regulator (not 16F)

Second your resistor values are wrong

VUmin = 11V (min car battery voltage)
VUmax = 15V (max car batter voltage)
Iload = 1mA (we'll go with our figure)
Rmax = (VUmin - 5V) / (1.05 * (4mA + Iload) = (11V - 5V) / (1.05 * (4mA +1mA) = 1.14kΩ
Rmin = (VUmax -5V) / (0.95 * 50mA) = (15V - 5V) / (0.95 * 50mA) = 210Ω

#### Picbuster

Joined Dec 2, 2013
1,009
I do not understand what you try to do but:
Vdd max =6.5V a car will carry relays hence V system could carry spikes of 60-100V but also negative going spikes.
a shunt will work however the voltage over the shunt is radiometric. A load at pic's output pins will show up at the input and will force the voltage over the shunt down.
An input filter is mandatory when dealing with dynamo's relays and other nasty spike producing things.

Advice: use a Mic2940A or similar with an input filter to the car battery ( cap's, coil, resistor and TVS will do the job)

Picbuster