Adjustable power supplies for BPv4

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Adjustable power supplies for BPv4

January 18, 2011, 03:32:11 pm

Hi,

how about adjustable power supplies for the target section in BPv4?

It's quite easy to accomplish, all we need is a dual rail-to-rail opamp, some resistors and capacitors and two GPIOs with PWM output. When using the MIC5205 in its adjustable version, the minimum output voltage would be 1,24xx V, by adding two diodes, two capacitors and one additional GPIO pin toggling at a few 10 kHz to build a charge pump based voltage inverter we could even have adjustable power supplies starting from 0 V.

Regards,

Jan

Re: Adjustable power supplies for BPv4

Reply #1 – January 18, 2011, 05:05:48 pm

Hi Jan,

Welcome to the forum

V4 is almost ready for manufacturing now. Maybe we can look forward to v5? I'm thinking about a CPLD for real @voltage interfacing.

Re: Adjustable power supplies for BPv4

Reply #2 – January 18, 2011, 06:44:29 pm

look at the various clones of the pickit2, there are many ways to vary voltage, using pwm from micro for a buck/boost converter has a few drawbacks

Re: Adjustable power supplies for BPv4

Reply #3 – January 18, 2011, 07:44:29 pm

My circuit is not based on a switch mode converter, it will use the MIC5205 by feeding a control voltage into the ADJ input. The control voltage is produced using PWM and a low pass filter.

OK, when hardware design is nearly ready for production it's not a good moment to add this and start all over again. I will draw up some schematics and post them here.

Jan

Re: Adjustable power supplies for BPv4

Reply #4 – January 18, 2011, 07:49:24 pm

i have not looked at the mic5205, is there a built in fail safe, or will that have to be implemented by separate hardware?

Re: Adjustable power supplies for BPv4

Reply #5 – January 18, 2011, 11:45:58 pm

http://www.analog.com/library/analogDia ... nable.html

I came across this recently, not the Antennas/Filters bit, but the 4 voltage controllable pins and the booster, sounded ideal for high voltage programming and other things, would a breakout board be possible with those parts you think ? or some type of addon board for the bus pirate

Re: Adjustable power supplies for BPv4

Reply #6 – January 19, 2011, 08:37:33 am

The voltage feedback on pin 2 is similar to any adjustable regulator, it could be controlled with pulse-width modulation in a feedback loop.

Re: Adjustable power supplies for BPv4

Reply #7 – January 19, 2011, 11:48:25 am

http://dangerousprototypes.com/docs/Pie ... _Pirate_v5

This is the schematic.

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.

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.

Regards,

Jan

Re: Adjustable power supplies for BPv4

Reply #8 – January 19, 2011, 11:56:09 am

Thanks Jan,

I attached the schematic so it doesn't break the forum. I also created a new Bus Pirate v5 page on the wiki we can use to track things like this:
http://dangerousprototypes.com/docs/Pie ... _Pirate_v5