Pierrot: Bus Pirate v5

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Pierrot: Bus Pirate v5
Codename Pierrot
Status Idea
Development development forum
ID # {{{id}}}

Adjustable power supply idea

The idea is to replace the fixed voltage supply channels by adjustable ones.

Bpv5-adjustablepwr-va.png

At the bottom of the page is a simple charge pump, it produces a negative auxilliary voltage to power the opamp. It needs to be driven by a toggling GPIO pin. It needs no further software, we'll only need to setup a timer during startup to toggle a pin at a few 10s of kHz.

The circuitry around the opamp forms a differential amplifier, which allows us to use the MIC5205 voltage regulator for voltages close to 0 V (usually the minimum voltage would be 1.242 V). The two diodes in series form a basic voltage reference, giving approx. 1.2-1.3 V. I've omitted the companying filter capacitors for the MIC5205, these have to be added in the real world.

The voltage is set by the MCU using PWM, which is filtered to obtain an adjustable voltage. Please note, the voltage control is completely done by the MIC5205 voltage regulator, the PIC just commands the output voltage, so there is no need to implement a control loop in software.

With this circuit the voltage range is 0-5 V.

One half of the LMV358 is unused and could be used in the second power supply channel, the 2 diode-voltage reference and the charge pump are only needed once can be reused as well.

MCU ressources needed:

  • 1 PWM channel per power supply
  • 1 Enable pin for switching the power supply off/on
  • 1 Timer channel + IO pin for driving the charge pump

Logic level shifters/buffers

Add the ADG3308 octal bidirectional buffer/level shifter to the interface circuitry. It operates from 1.15 V to 5.5 V.