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How to control this circuit using a micro?

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megamicro

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I'd like to use this circuit in my new project to get different voltages from
+5V (for example from +5 to +24V). I know that this can work but I
cannot control it.

All comments and suggestions are wellcome!
 

aNdreiBuuu

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...

my advice is to use a clasic switching upconverter...
MAX1771 work great!
best,
//a

PS: make a search on www.m@xim-ic.com
 

bunalmis

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Apply the Pwm signal for the GVP input

You can produce different voltages
 

zorro

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Hi megamicro,

this is a two stage power supply: the first is step-up switching, the second is linear.
The linear regulator can provide accuracy and fast response. The switching source, acting as a preregulator, gives the necessary voltage to the linear regulator for working fine without bad efficiency.
You can control the duty cycle of the PWM signal injected at GVP taking the sample of output voltage of the first stage at A.
The linear regulator must be controlled taking the output voltage (VPP), comparing against a reference and controlling VPPE.
Regards

Z
 

bunalmis

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Ok, But i think VPPE. on off control pin. (VPPenable)
 

nebisman

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i'ts too complex to control the PMW signal and the VPPE signal. I agree with the use of simple STEP UP converter. The common lm3524 from National serves for this purpose and has built in automatic control of the output. only you shoul provide the reference input that can be one analog output of microcontroller (or the same , a filtered pwm output)

if you want to control the output voltaje with a micro only you need to implement the transistor, diode, and inductance in the STEP UP converter mode, feedback the output and realize a simple PI controller into the micro.

Nebisman
 

DBPhillips

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You can use the MAX1771 for variable output designs. One way to do it is to connect the feedback resistors to an external comparator and then apply a variable reference voltage to the comparator. But there are two tricks to doing this successfully with the MAX1771...
1. Comparator needs to be fast, with a propagation delay of around 200ns or less. A TLC372 works fine.
2. Keep the FB pin from going below 0.1V, otherwise the dual-mode feature will activate. One way is to connect a resistor from REF to FB and another from FB to the comparator output.
Don't forget that many comparators have open-drain outputs and also need a resistor to the positive supply.

In your case, the variable reference would be from a DAC in the micro or from an external DAC.
 

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